Optical recording medium having auxiliary information and reference clock   

Abstract: An information recording medium is composed of a substrate having a microscopic pattern constituted by a continuous substrate of grooves formed with a groove portion and a land portion alternately, a recording layer, and a light transmitting layer. The microscopic pattern is formed with satisfying a relation of P≦λ/NA, wherein P is a pitch of the land portion or the groove portion, λ is a wavelength of reproducing light, and NA is a numerical aperture of an objective lens. The land portion is formed with wobbling so as to be parallel with each other for both sidewalls of the land portion. Auxiliary information and a reference clock is recorded alternately. Information is recorded in the recording layer corresponding to a land portion by either one change of reflectivity difference and refractive index difference in the recording layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of co-pending application Ser. No. 12/652,809, filed on Jan. 1, 2010 (allowed), which is a Continuation of application Ser. No. 11/969,503, filed on Jan. 4, 2008 (now U.S. Pat. No. 7,668,072), which is a Continuation of application Ser. No. 11/620,150, filed on Jan. 5, 2007 (now U.S. Pat. No. 7,336,595), which is a Continuation of application Ser. No. 10/419,149, filed on Apr. 21, 2003 (now U.S. Pat. No. 7,177,162), and for which priority is claimed under 35 U.S.C. §120; and this application claims priority of Application No. 2002-117555 filed in Japan on Apr. 19, 2002 under 35 U.S.C. §119; this application also claims priority of Application No. 2002-141286 filed in Japan on May 16, 2002 under 35 U.S.C. §119; this application also claims priority of Application No. 2002-160129 filed in Japan on May 31, 2002 under 35 U.S.C. §119; this application also claims priority of Application No. 2002-123612 filed in Japan on Apr. 25, 2002 under 35 U.S.C. §119; and this application claims priority of Application No. 2002-148781 filed in Japan on May 23, 2002 under 35 U.S.C. §119; the entire contents of all are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an information recording medium that is particularly used for recording information and a reproducing apparatus for reading out information recorded in the information recording medium with making the information recording medium move relatively, particularly, relates to an information recording medium for recording and/or reproducing information optically and a reproducing apparatus thereof.

2. Description of the Related Art

Until now, there existed a system used for reading out information from an information recording medium while the information recording medium is made relatively move. In order to reproduce the system, such a method as optical, magnetic or capacitance is utilized. A system for recording and/or reproducing information by the optical method has been most popular in daily life. In the case of a read-only type information recording medium in disciform, which is reproduced by a light beam having a wavelength of 650 nm, for example, such a medium in disciform as a DVD video disc pre-recorded with picture image information, a DVD-ROM disc that is pre-recorded with a program or like, a DVD audio disc, or an SACD (Super Audio CD) disc that is pre-recorded with musical information is popularly known.

In the case of a recording and reproducing type information recording medium, there existed a DVD RAM disc utilizing a phase change effect, an ASMO (Advanced Storage Magneto-Optical) disc and an iD (intelligent image disc) utilizing a magneto-optical effect.

On the other hand, in order to increase recording density, such a study as shortening a wavelength of laser beam so as to realize emission of violaceous light has been continued. A second harmonic oscillating element or a semiconductor light emitting element of gallium nitride system compound, which was invented recently, emits light having a wavelength λ in the neighborhood of 350 nm to 450 nm. Consequently, they are possible to be an important light emitting element, which increases recording density drastically.

Further, a design of objective lens complying with such a wavelength has been advanced. Particularly, an objective lens having an NA (numerical aperture) utilized for a DVD disc, that is, an NA of exceeding 0.6 and more than 0.7 is being developed.

As mentioned above, a reproducing apparatus for information recording medium that is equipped with a light emitting element of which wavelength λ is reduced down to 350 nm to 450 nm and equipped with an objective lens of which an NA is more than 0.7 is being developed. By using these technologies, it can be expected that an optical disc system, which surpasses recording capacity of current DVD disc further more, will be developed.

Further, it is also desired that an information recording medium having higher recording density, which is designed on the basis of a violaceous laser beam and a higher NA, is developed.

On the other hand, a recent recording and reproducing type disc adopts a microscopic configuration, namely the land-groove system. With referring to FIGS. 41 and 42, an information recording medium designed for a higher NA recording and reproducing system is explained.

FIG. 41 is a cross sectional view of a conventional information recording medium adopting the microscopic configuration that is called the land-groove system according to the prior art.

FIG. 42 is an enlarged plan view of the information recording medium shown in FIG. 41 showing the horizontal configuration of the information recording medium according to the prior art.

As shown in FIG. 41, an information recording medium 100 is composed of a recording layer 120 and a light transmitting layer 110 that are sequentially laminated on a substrate 130. A microscopic pattern 131 is formed on the substrate 130. The recording layer 120 is formed directly on the surface of the microscopic pattern 131. The microscopic pattern 131 is composed of a plural of land portions “La” and “Lb” (hereinafter generically referred to as land portion “L”) and a plural of groove portions “Ga” to “Gc” (hereinafter generically referred to as groove portion “G”). Macroscopically, the configuration corresponds to that the microscopic pattern 131 is constituted by a continuous groove composed of the land portion “L” and another continuous groove composed of the groove portion “G”.

Further, as shown in FIG. 42, a record mark “M” is formed in both the grooves composed of the land portion “L” and the groove portion “G” respectively when recording.

With paying attention to the dimensions of the microscopic pattern 131, while a shortest distance between the groove portions “Ga” and “Gb” is assumed to be a pitch “P0” (another shortest distance between the land portions “La” and “Lb” is also the pitch “P0”), the microscopic pattern 131 is formed so as to satisfy a relation of P0>S0, wherein “S0” is a spot diameter of reproducing light beam.

Hereupon, the spot diameter “S0” is calculated by a wavelength λ of laser beam for reproducing and an NA of objective lens such as S0=λ/NA. In other words, the pitch “P0” is designed so as to satisfy a relation of P0>λ/NA.

In the case of the information recording medium 100, a light beam for recording (recording light) is irradiated on the light transmitting layer 110 and a record mark “M” is formed on both the land portion “L” and the groove portion “G” of the recording layer 120.

Further, a light beam for reproducing (reproducing light) is irradiated on the substrate 130 or the light transmitting layer 110 and reflected by the recording layer 120, and then the reflected reproducing light is picked up for reproducing.

Inventors of the present invention have actually manufactured an information recording medium 100 as an experiment, and experimentally recorded and reproduced the information recording medium 100. The inventors founded a problem such that a cross erase phenomenon was extremely noticeable. The cross erase phenomenon is a phenomenon such that information is recorded with being superimposed on a signal previously recorded in a groove portion “G”, for example, when recording the information in a land portion “L”. In other words, it is such a phenomenon that information previously recorded in a groove portion “G” is erased by recording another information in a land portion “L”.

Further, this phenomenon can also be noticeable in a reverse case, that is, the cross erase phenomenon is also recognized if previously recorded information in a land portion “L” is observed when recording information in a groove portion “G”. If such a cross erase phenomenon occurs, as mentioned above, information recorded in an adjacent groove is damaged. In case of an information system having larger capacity, an amount of lost information becomes excessively large. Consequently, affection to a user is enormous.

Consequently, it is considered for such an information recording medium 100 that information shall be recorded only in either land portion “L” or groove portion “G”. However, there is existed a problem such that recording capacity of an information recording medium will decrease and a merit of the information recording medium having a potential of recording in higher density will decline if such an information recording method is conducted.

SUMMARY

Accordingly, in consideration of the above-mentioned problems of the prior art, an object of the present invention is to provide an information recording medium that is reduced in cross erase and can be recorded in higher density, and an reproducing apparatus for reproducing information recorded in the information recording medium with making the information recording medium move relatively.

In order to achieve the above object, the present invention provides, according to an aspect thereof, an information recording medium at least comprising: a substrate having a microscopic pattern constituted by a continuous substrate of grooves formed with a groove portion and a land portion alternately; a recording layer formed on the microscopic pattern for recording information; and a light transmitting layer formed on the recording layer, the information recording medium is further characterized in that the microscopic pattern is formed with satisfying a relation of P≦λ/NA, wherein P is a pitch of the land portion or the groove portion, λ is a wavelength of reproducing light for reproducing the recording layer, and NA is a numerical aperture of an objective lens, and that the land portion is formed with wobbling so as to be parallel with each other for both sidewalls of the land portion, and that an auxiliary information based on data used supplementally when recording the information and a reference clock based on a clock used for controlling a recording speed when recording the information is recorded alternately and continuously.

According to another aspect of the present invention, there provide a reproducing apparatus for reproducing a recording layer of an information recording medium comprising: a substrate having a microscopic pattern constituted by a continuous substrate of grooves formed with a groove portion and a land portion alternately; the recording layer formed on the microscopic pattern for recording information; and a light transmitting layer formed on the recording layer, the information recording medium is further characterized in that the microscopic pattern is formed with satisfying a relation of P≦λ/NA, wherein P is a pitch of the land portion or the groove portion, λ is a wavelength of reproducing light for reproducing the recording layer, and NA is a numerical aperture of an objective lens, and that the land portion is formed with wobbling so as to be parallel with each other for both sidewalls of the land portion, and that an auxiliary information based on data used supplementally when recording the information and a reference clock based on a clock used for controlling a recording speed when recording the information is recorded alternately and continuously, the reproducing apparatus comprising: a light emitting element for emitting reproducing light having a wavelength λ of 350 nm to 450 nm and a noise of less than RIN (Relative Intensity Noise) −125 dB/Hz; a reproducing means equipped with an objective lens having a numerical aperture NA of 0.75 to 0.9; and a control means for controlling the reproducing means to irradiate the reproducing light only on the land portion for reproducing.

Other object and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.

FIG. 1 is a cross sectional view of an information recording medium according to a first embodiment of the present invention.

FIG. 2 is an enlarged plan view of a microscopic pattern of the information recording medium shown in FIG. 1.

FIG. 3 is another enlarged plan view of a microscopic pattern of the information recording medium shown in FIG. 1 exhibiting a state of being recorded.

FIG. 4 is a cross sectional view of the information recording medium shown in FIG. 1 exhibiting a state of reproducing or recording a recording layer of the information recording medium.

FIG. 5 is an enlarged plan view showing an auxiliary information area and a reference clock area in the information recording medium according to the first embodiment, of the present invention.

FIG. 6 is an enlarged plan view of the information recording medium according to the first embodiment of the present invention when information is recorded in the information recording medium through the CLV (Constant Linear Velocity) recording method.

FIG. 7 is an enlarged plan view of the information recording medium according to the first embodiment of the present invention when information is recorded on the information recording medium through the CAV (Constant Angular Velocity) recording method.

FIG. 8 is an enlarged plan view of the information recording medium in disciform according to the first embodiment of the present invention when information is recorded in the information recording medium through the CLV recording method.

FIG. 9 is an enlarged plan view of the information recording medium in disciform according to the first embodiment of the present invention when information is recorded on the information recording medium through the CLV recording method and further the information is recorded on a land portion.

FIG. 10 is an enlarged plan view of a photo-detector mounted on an apparatus for reproducing an information recording medium according to the present invention showing a state of dividing the photo-detector into four.

FIG. 11 is a first example showing a distributed recording of auxiliary information.

FIG. 12 is a second example showing a distributed recording of auxiliary information.

FIG. 13 is a third example showing a distributed recording of auxiliary information.

FIG. 14 is a fourth example showing a distributed recording of auxiliary information.

FIG. 15 is a table exhibiting data change before and after modulating a base-band.

FIG. 16 is a table exhibiting an example of actual data change before and after modulating a base-band.

FIG. 17 shows a first example of an amplitude-shift keying modulation waveform according to the present invention.

FIG. 18 shows a second example of an amplitude-shift keying modulation waveform according to the present invention.

FIG. 19 shows a third example of an amplitude-shift keying modulation waveform according to the present invention.

FIG. 20 shows a first example of a frequency-shift keying modulation waveform according to the present invention.

FIG. 21 shows a second example of a frequency-shift keying modulation waveform according to the present invention.

FIG. 22 shows a third example of a frequency-shift keying modulation waveform according to the present invention.

FIG. 23 shows a first example of a phase-shift keying modulation waveform according to the present invention.

FIG. 24 shows a second example of a phase-shift keying modulation waveform according to the present invention.

FIG. 25 shows a third example of a phase-shift keying modulation waveform according to the present invention.

FIG. 26 shows a first example of a shape of the information recording medium according to the present invention.

FIG. 27 shows a second example of a shape of the information recording medium according to the present invention.

FIG. 28 shows a third example of a shape of the information recording medium according to the present invention.

FIG. 29 is a cross sectional view of an information recording medium according to a second embodiment of the present invention.

FIG. 30 is a cross sectional view of an information recording medium according to a third embodiment of the present invention.

FIG. 31 is a cross sectional view of an information recording medium according to a fourth embodiment four of the present invention.

FIG. 32 is a cross sectional view of an information recording medium according to a fifth embodiment of the present invention.

FIG. 33 is a block diagram of a first reproducing apparatus of an information recording medium according to an embodiment of the present invention.

FIG. 34 is a block diagram of a second reproducing apparatus of an information recording medium according to an embodiment of the present invention.

FIG. 35 is a flow chart showing a reproducing method of an information recording medium according to an embodiment of the present invention.

FIG. 36 is a block diagram of a recording apparatus of an information recording medium according to an embodiment of the present invention.

FIG. 37 is a flow chart showing a recording method of an information recording medium according to an embodiment of the present invention

FIG. 38 is a graph exhibiting a relation between reflectivity and error rate.

FIG. 39 is a chart exhibiting reflectivity and reproduction characteristics of embodiments 1 through 7 and comparative examples 1 and 2.

FIG. 40 is a graph exhibiting a relation between modulated amplitude and error rate.

FIG. 41 is a cross sectional view of a conventional information recording medium according to the prior art.

FIG. 42 is an enlarged plan view of the information recording medium shown in FIG. 41.

DETAILED DESCRIPTION

With referring to FIG. 1, a basic configuration of an information recording medium according to the present invention will be explained. An information recording medium according to a first embodiment of the present invention is such an information recording medium that at least one of recording and reproducing is conducted through an optical method. Actually, it is such an information recording medium as a phase change recording type information recording medium, a dye type information recording medium, a magneto-optical type information recording medium or a light assist magnetic type information recording medium.

FIG. 1 is a cross sectional view of an information recording medium according to a first embodiment of the present invention. In FIG. 1, an information recording medium 1 according to the present invention is at least composed of a light transmitting layer 11, a recording layer 12, and a substrate 13 formed with a microscopic pattern 20. They are formed sequentially on the substrate 13. Unevenness of the microscopic pattern 20 forms a shape of continuous substance of approximately parallel grooves, wherein a symbol sign 21 is a microscopic pattern that is recorded with a record mark “M” as shown in FIG. 3.

Further, a shape of the information recording medium 1 can be applicable in any shape such as disciform, card and tape even in circular, rectangular or oval shape. The information recording medium 1 can also be acceptable although it is perforated.

Furthermore, a light beam for reproducing (reproducing light) or recording (recording light) is irradiated on the light transmitting layer 11.

The substrate 13, the recording layer 12, and the light transmitting layer 11 are detailed first. The substrate 13 is a base substance having a function of sustaining mechanically the recording layer 12 and the light transmitting layer 11 sequentially laminated thereon. With respect to a material for the substrate 13, any of synthetic resin, ceramic and metal is used. A typical example of synthetic resin is various kinds of thermoplastic resins and thermosetting resins such as polycarbonate, polymethyle methacrylate, polystyrene, copolymer of polycarbonate and polystyrene, polyvinyl chloride, alicyclic polyolefin and polymethyle pentene, and various kinds of energy ray curable resins such as UV ray curable resins, visible radiation curable resins and electron beam curable resins. They can be preferably used.

Further, it is also acceptable that these synthetic resins are mixed with metal powder or ceramic powder.

With respect to a typical example of the ceramic, soda lime glass, soda aluminosilicate glass, borosilicate glass or silica glass can be used. With respect to a typical example of the metal, a metal plate such as aluminum having no transparency can be used. A thickness of the substrate 13 is suitable to be within a range of 0.3 mm to 3 mm, desirably 0.5 mm to 2 mm due to necessity of supporting mechanically the information recording medium 1 totally. In case that the information recording medium 1 is in disciform, the thickness of the substrate 13 is desirable to be designed such that the total thickness of the information recording medium 1 including the substrate 13, the recording layer 12, and the light transmitting layer 11 becomes 1.2 mm, for the purpose of interchangeability with a conventional optical disc.

The recording layer 12 is a thin film layer that has a function of reading out information, recording or rewriting information. The recording layer 12 is formed with the microscopic pattern 20 that is constituted by a plurality of land portions “L1” through “L4” (hereinafter generically referred to as land portion “L”) and a plurality of groove portions “G1” through “G5” (hereinafter generically referred to as groove portion “G”) respectively. Information is recorded on either one of a land portion “L” and a groove portion “G” as a record mark “M”. With respect to a material for the recording layer 12, a material that is represented by a phase-change material of which reflectivity or refractive index changes in a process of before and after recording or both of reflectivity and refractive index change in a process of before and after recording, a dye material of which refractive index or a depth changes in a process of before and after recording or both of refractive index and depth change in a process of before and after recording, or a material represented by a magneto-optical material, which produces a change of Kerr rotation angle in a process of before and after recording, can be used.

With respect to an actual example of phase change material, alloys composed of an element such as indium (In), antimony (Sb), tellurium (Te), selenium (Se), germanium (Ge), bismuth (Bi), vanadium (V), gallium (Ga), platinum (Pt), gold (Au), silver (Ag), copper (Cu), aluminum (Al), silicon (Si), palladium (Pd), tin (Sn) and arsenic (As) are used, wherein an alloy includes a compound such as oxide, nitride, carbide, sulfide and fluoride. Particularly, alloys composed of a system such as Ge—Sb—Te system, Ag—In—Te—Sb system, Cu—Al—Sb—Te system and Ag—Al—Sb—Te system are suitable for the recording layers 12. These alloys can contain one or more elements as a micro additive element within a range of more than 0.01 atomic % to less than 10 atomic % in total. Such a micro additive element is selected out of Cu, Ba, Co, Cr, Ni, Pt, Si, Sr, Au, Cd, Li, Mo, Mn, Zn, Fe, Pb, Na, Cs, Ga, Pd, Bi, Sn, Ti, V, Ge, Se, S, As, Tl and In.

With respect to compositions of each element, for example, there is existed Ge2Sb2Te5, Ge1Sb2Te4, Ge8Sb69Te23, Ge8Sb74Te18, Ge5Sb71Te24, Ge5Sb76Te19, Ge10Sb68Te22 and Ge10Sb72Te18 as for the Ge—Sb—Te system and a system adding a metal such as Sn and In to the Ge—Sb—Te system as for the Ge—Sb—Te system.

Further, as for the Ag—In—Sb—Te system, there is existed Ag4In4Sb66Te26, Ag4In4Sb64Te28, Ag2In6Sb64Te28, Ag3In6Sb66Te28, Ag2In6Sb66Te26, and a system adding a metal or semiconductor such as Cu, Fe and Ge to the Ag—In—Sb—Te system.

With respect to an actual example of magneto-optical material, alloys composed of an element such as terbium, cobalt, iron, gadolinium, chromium, neodymium, dysprosium, bismuth, palladium, samarium, holmium, praseodymium, manganese, titanium, erbium, ytterbium, lutetium and tin can be used, wherein an alloy includes a compound such as oxide, nitride, carbide, sulfide and fluoride. Particularly, constituting an alloy of a transition metal, which is represented by TbFeCo, GdFeCo and DyFeCo, with rare earth element is preferable. Further, the recording layer 12 can be constituted by using an alternate lamination layer of cobalt and platinum.

With respect to an actual example of dye material, cyanine dye, phthalocyanine dye, naphthalocyanine dye, azo dye, naphthoquinone dye, fulgide dye, polymethine dye, acridine dye, and porphyrin dye can be used.

With respect to a method of forming the recording layers 12, a film forming method such as a vapor phase film forming method and a liquid phase film forming method can be used. As a typical example of the vapor phase film forming method, such methods as vacuum deposition of resister heating type or electron beam type, direct current sputtering, high frequency sputtering, reactive sputtering, ion beam sputtering, ion plating and chemical vapor deposition (CVD) can be used.

Further, with respect to a typical example of the liquid phase film forming method, there is existed a spin coating method and a dipping and drawing up method.

The light transmitting layer 10 is composed of a material having function of conducting converged reproducing light to the recording layer 12 while keeping the converged reproducing light in less optical distortion. A material having transmittance of more than 70%, for example, at a reproduction wavelength λ, desirably more than 80% can be suitably used for the light transmitting layer 11.

It is essential for the light transmitting layer 11 to be less optical anisotropy. In order to suppress reduction of reproducing light, actually, a material having birefringence of less than ±100 nm, preferably ±50 nm by 90-degree (vertical) incident double paths is used for the light transmitting layer 11.

With respect to a material having such a birefringence characteristic, a synthetic resin such as polycarbonate, polymethyle methacrylate, cellulose triacetate, cellulose diacetate, polystyrene, copolymer of polycarbonate and polystyrene, polyvinyl chloride, alicyclic polyolefin and polymethyle pentene can be used for the light transmitting layer 11.

The light transmitting layer 11 can be provided with a function of protecting the recording layer 12 mechanically and chemically. With respect to a material having such a function, a material having higher stiffness can be used for the light transmitting layer 11. For example, transparent ceramics (such as soda lime glass, soda aluminosilicate glass, borosilicate glass, and silica glass), thermosetting resin, energy ray curable resin (such as ultraviolet rays curable resin, visible radiation curable resin and electron beam curable resin), moisture curable resin and two-part liquid mixture curable resin are preferably used for the light transmitting layer 11 having higher stiffness.

Further, a thickness of the light transmitting layer 11 is desirable to be less than 0.4 mm in view of suppressing aberration when the information recording medium 1 is inclined.

Furthermore, in view of preventing the recording layer 12 from being scratched, the thickness of the light transmitting layer 11 is desirable to be more than 0.05 mm. In other words, the desirable thickness of the light transmitting layer 11 is within a range of 0.05 mm to 0.4 mm. More desirably, the thickness is within a range of 0.06 mm to 0.12 mm.

More, scattering of thickness in a single plain is desirable to be ±0.003 mm maximum in view of spherical aberration, because an NA of objective lens is relatively large. Particularly, in case that an NA of the objective lens is more than 0.85, the scattering of thickness in a single plain is desirable to be less than ±0.002 mm.

Moreover, in case that an NA of the objective lens is 0.9, the scattering of thickness in a single plain is desirable to be less than ±0.001 mm.

With referring to FIG. 2, the microscopic pattern 20 that is one of major features of the present invention is explained next. As mentioned above, microscopically, the microscopic pattern 20 is composed of a continuous substance of approximately parallel grooves. However, macroscopically, the continuous substance can be in a shape of not only linear but also coaxial or spiral.

FIG. 2 is an enlarged plan view of a microscopic pattern of the information recording medium shown in FIG. 1. In FIG. 2, symbol signs “P” and “S” are a pitch between adjoining two groove portions “G2” and “G3” and a spot diameter of reproducing light beam respectively. As shown in FIG. 2, a land portion “L” of the microscopic pattern 20 corresponds to the land (raised) portion “L” shown in FIG. 1 and a groove portion “G” of the microscopic pattern 20 corresponds to the groove (recessed) portion “G” shown in FIG. 1.

Further, the land portion “L” and the groove portion “G” can be wobbled, will be mentioned later. However, centerlines of the land portion “L” and the groove portion “G” are formed in parallel to each other.

In case that a user records data in the information recording medium 1, the data are recorded only on either one of the land portion “L” and the groove portion “G”. Accurately, the data are recorded on a portion corresponding to either one of the land portion “L” and the groove portion “G” in the recording layer 12. Selecting either the land portion “L” or the groove portion “G” is arbitrary. However, it is desirable for selecting the land portion “L” or the groove portion “G” to maintain at least a same selection result of either the land portion “L” or the groove portion “G” even in any place in the recording layer 12. In case of recording on different portions by a place, it is hard to reproduce continuously and resulted in degrading a recording capacity substantially.

In FIG. 2 and succeeding drawings FIGS. 3 to 9, a width of the land portion “L” and a width of the groove portion “G” is illustrated in different width in each drawing. However, it is understood that the width is not limited to one specific width.

FIG. 3 is a plan view of a microscopic pattern of the information recording medium 1 shown in FIG. 1 exhibiting an example of recording that is conducted only on land portions “L” of the recording layer 12. As shown in FIG. 3, a record mark “M” is recorded only on the land portions “L1” through “L4” not on the groove portions “G1” through “G5”, which constitute the microscopic pattern 21. The record mark “M” is recorded by a mark position recording method or a mark edge recording method.

A signal, which is used for recording, is a modulation signal that is a so-called (d, k) code, which is defined as that a minimum mark length is “d+1” and a maximum mark length is “k+1”, wherein either a fixed length code or a variable length code can be applied for a (d, k) modulation signal. Actually, with defining that a minimum mark length is 2T, a (d, k) modulation such as (1, 7) modulation, 17PP modulation, DRL modulation, (1, 8) modulation and (1, 9) modulation can be used.

A typical example representing the (1, 7) modulation of the fixed length code is the “D1, 7” modulation (that is disclosed in the Japanese Patent Application No. 2001-80205 in the name of Victor company of Japan, Limited). The “D1, 7” modulation can be replaced by the (1, 7) modulation or the (1, 9) modulation, which is based on the “D4, 6” modulation of the fixed length code (that is disclosed in the Japanese Patent Application Laid-open Publication No. 2000-332613). The 17PP modulation is one of the (1, 7) modulation of the variable length code and disclosed in the Japanese Patent Application Laid-open Publication No. 11-346154/1999.

Further, the (2, 7) modulation and the (2, 8) modulation, which are the variable length code with defining the minimum mark length as 3T, the EFM modulation, the EFM plus modulation, and the “D8-15” modulation (that is disclosed in the Japanese Patent Application Laid-open Publication No. 2000-286709) as the (2, 10) modulation of the fixed length code can be used.

Furthermore, a modulation system, which defines the minimum mark length as 4T such as the (3, 17) modulation, and another modulation system, which defines the minimum mark length as 5T such as the (4, 21) modulation, can be used.

A groove portion “G” hereupon follows the definition shown in the Table 4.4-1 described in the publication “Understanding Optical Disc Properly” (edited by the Japan Patent Office and published by the Japan Institute of Invention and Innovation in 2000). In other words, a groove portion “G” is defined as a recessed groove previously provided spirally or coaxially on a surface of base substance in order to form a recording track.

Further, a land portion “L” also follows the definition described in the publication. In other words, a land portion “L” is defined as a land portion previously provided spirally or coaxially on a surface of base substance in order to form a recording track.

Furthermore, the base substance hereupon is a name equivalent to the substrate 11 of the present invention.

In FIGS. 2 and 3, with defining that a distance between adjoining two groove portions “G2” and “G3” is a pitch “P” (in the same way, a distance between adjoining two land portions “L1” and “L2” is also defined as the pitch “P”), the pitch “P” is designated so as to satisfy a relation of P≦S, wherein “S” is a spot diameter of reproducing light. The spot diameter “S” is calculated by a wavelength λ of laser beam for reproducing and an NA of objective lens such as S=λ/NA. In other words, the pitch “P” satisfies a relation of P≦λ/NA.

In case of using a violaceous laser beam, its wavelength λ is within a range of 350 nm to 450 nm, and in case of using a high NA lens, its NA is 0.75 to 0.9. Consequently, a pitch “P” is set to be within a range of 250 nm to 600 nm.

Further, in case of considering that a digital picture image of HDTV (High Definition Television) program is recorded for approximately two hours, more than 20 GB is necessary for a recording capacity. Consequently, the pitch “P” is desirable to be within a range of 250 nm to 450 nm. Particularly, in case that an NA is 0.85 to 0.9, the pitch “P” is more desirable to be 250 nm to 400 nm.

Furthermore, in case that a wavelength λ is 350 nm to 410 nm and also an NA is 0.85 to 0.9, the pitch “P” is most desirable to be 250 nm to 360 nm.

A depth of groove portion “G” is preferable to be within a range of λ/8n to λ/20n, wherein “n” is a refractive index at a wavelength λ of the light transmitting layer 11. Since a reflectivity of the recording layer 12 is reduced a little due to existence of the microscopic pattern 20, a depth of groove portion “G” is desirable to be shallower. Less than λ/10n is suitable for the depth of groove portion “G” as a limit for jitter of a reproduced signal not to be deteriorated.

Further, an output of push-pull signal increases in accordance with a depth of groove portion “G” when, tracking down a land portion “L” or a groove portion “G”. Consequently, more than λ/18n is suitable for a limiting value for enabling to track. In other words, a range of λ/10n to λ/18n is suitable for a depth of groove portion “G”, and a most suitable range for the depth of groove portion “G” is λ/10n to λ/18n.

As mentioned above, the information recording medium 1 according to the first embodiment of the present invention is such an information recording medium that is recorded on either a groove portion “G” or a land portion “L” of the recording layer 12. Therefore, recording is conducted with keeping a distance of pitch “P” and resulted in decreasing the cross erase phenomenon.

Further, it is designed for the relation between the pitch “P” and the spot diameter “S” to be P≦S, so that recording density is prevented from decreasing.

A result of evaluation with respect to the cross erase phenomenon in comparison with a conventional information recording medium 100 is depicted hereinafter. With respect to an information recording medium of which recording layer 12 is formed by a phase change material, a second track is recorded and reproduced, and the reproduced output is measured. Then, a first track and a third track is recorded ten times each with a signal having a frequency different from that recorded on the second track, and an output from the second track is measured once again. With defining that an output difference between the outputs originally measured and secondary measured is a cross erase amount, a cross erase amount cause by the conventional information recording medium 100 is −5 dB. On the contrary, by the information recording medium 1 according to the first embodiment of the present invention, a cross erase amount is reduced to the order of −2 dB. In other words, by using the information recording medium 1 according to the first embodiment of the present invention, a cross erase phenomenon can be improved by 3 dB in comparison with the conventional information recording medium 100.

Further, a similar evaluation is conducted to an information recording medium of which recording layer 12 is formed by a magneto-optical material. By the conventional information recording medium 100, an output decreases by 4 dB. On the contrary, by the information recording medium 1 according to the first embodiment of the present invention, an output decreases by just 1 dB. In other words, by using the information recording medium 1, a cross erase phenomenon is improved by up to 3 dB in comparison with the conventional information recording medium 100 although a magneto-optical material is used for the information recording medium 1.

Furthermore, a similar evaluation is conducted to an information recording medium of which recording layer 12 is formed by a dye material. By the conventional information recording medium 100, an output decreases drastically by 12 dB. On the contrary, by the information recording medium 1, an output decreases by as low as 2 dB. In other words, by using the information recording medium 1, a cross erase phenomenon is improved by up to 10 dB in comparison with the conventional information recording medium 100 although a dye material is used for the information recording medium 1.

The information recording medium 1 according to the first embodiment of the present invention is such an information recording medium that is recorded with information on either a groove portion “G” or a land portion “L” of the recording layer 12. It is studied that either portion is suitable for recording information in view of reproduction, and it is founded that recording on a land portion “L” of the recording layer 12 decreases an error rate and is excellent in a rewriting characteristic. In view of that a land portion “L” is disposed in a side closer to the light transmitting layer 11 than a groove portion “G”, and reproducing light and recording light is irradiated on the light transmitting layer 11, it is considered that thermal flow of a material constituting the recording layers 12 is suppressed to some degree in an area of land portion “L”.

FIG. 4 is a cross sectional view of the information recording medium 1 according to the first embodiment of the present invention exhibiting a state of recording and reproducing the recording layer 12. In FIG. 4, a recording apparatus and a reproducing apparatus is illustrated by an objective lens 50b as a representative of them. A laser beam 89 is emitted through the objective lens 50b of the recording apparatus when recording. The laser beam 89 is converged selectively on a land portion “L” of the microscopic pattern 20 in the information recording medium 1 with respect to the horizontal direction. As for the vertical direction, the laser beam 89 is converged selectively on the recording layer 12 through the light transmitting layer 11.

Further, a record mark “M” is recorded on a portion where the laser beam 89 is converged on. In other words, recording is selectively conducted to the recording layer 12 corresponding to a land portion “L”.

As mentioned above, in the case that the recording layer 12 is formed by a phase change material, the recording hereupon is conducted by change of reflectivity, change of refractive index, or change of both of them. In the case of being formed by a magneto-optical material, the recording is conducted by change of Kerr rotation angle.

Further, in the case of a dye material, the recording is conducted by change of refractive index, change of depth, or change of both of them.

On the other hand, when reproducing, a laser beam 99 is emitted through the objective lens 50b of the reproducing apparatus. The laser beam 99 is converged selectively on a land portion “L” of the microscopic pattern 21 in the information recording medium 1 with respect to the horizontal direction.

Further, with respect to the vertical direction, the laser beam 99 is converged selectively on the recording layer 12 through the light transmitting layer 11. A record mark “M” is recorded selectively on the recording layer 12 corresponding to a land portion “L”. Consequently, a record mark “M” can be read out from a portion where the laser beam 99 is converged on.

According to the first embodiment of the present invention, as mentioned above, the microscopic pattern 20 of the information recording medium 1 is formed to be P≦λ/NA, wherein “P” is the pitch between adjoining two groove portions “G” or land portions “L”, “λ” is a wavelength of a laser beam for recording or reproducing, and “NA” is a numerical aperture of an objective lens.

Further, recording is conducted to either, one of a land portion “L” and a groove portion “B”. Consequently, an information recording medium recorded in high density can be obtained as well as reducing a cross erase phenomenon.

In addition thereto, according to the first embodiment of the present invention, an information recording medium that is low in error rate and excellent in rewriting characteristic can be obtained by recording selectively on a land portion “L”.

A method of embedding an auxiliary information such as address and a reference clock, which is a second object of the information recording medium 1 according to the first embodiment of the present invention, is explained hereafter. The present invention is explained by specifying an embodiment in which recording is conducted on a land portion “L” hereupon.

In case of a recording type information recording medium, it is required that recording is accurately conducted in an arbitrary position, which is requested by a user. If the recording type information recording medium is constituted by arranging a groove portion “G” and a land portion “L” alternatively as shown in FIG. 2, positioning based on a relative distance between a recording apparatus or reproducing apparatus and the information recording medium can only be conducted. Therefore, recording in a required position can not be conducted accurately.

Accordingly, an address information is essential to be embedded in somewhere on the microscopic pattern 20. It is considered that an alternating configuration of groove portion “G” and land portion “L” as the same configuration as a commonly known optical disc such as a CD, for example, is transported to a free plane at each certain macroscopic interval (each interval of the order of milli) and pits having a plurality of lengths are arranged into the free plane. An address information is defined by a combination of the pit length. Reading out a pit in such a free plane can be conducted by reading out a depth as phase change that is the same manner as a CD, so that the reading out a pit is an easy method. However, providing such a free plane as an address area makes losses of recording capacity expands. In view of reliability of reading out, the loss is approximately 10% and hard to be allowed.

Furthermore, in the case of the recording type information recording medium, a relative speed between an information recording medium and a recording apparatus, that is, a recording speed affects a recording density and besides, signal quality. Therefore, a reference clock for designating a recording speed correctly is essential. In case that a reference clock is provided in a recording apparatus, a relative speed can hardly be adjusted even though the relative speed is shifted by various conditions. Consequently, it is desirable for the reference clock to be provided inside an information recording medium. Particularly, the information recording medium 1 is in disciform and a linear velocity changes every moment in case of a recording mode by the CLV (Constant Linear Velocity) recording method. Therefore, it is essential for the reference clock to be provided inside the information recording medium 1.

In order to solve the problems and satisfy the requirements mentioned above, there provided a method for embedding an auxiliary information and a reference clock in the information recording medium 1. An auxiliary information hereupon is a data array that is used subsidiarily when recording in the recording layer 12 of the information recording medium 1 by a user.

Actually, an auxiliary information is composed of at least an address information. An address information exhibits an address that changes continuously by a position of the information recording medium 1 and is data selected out from information such as absolute address allocated to the whole area of the information recording medium 1, relative address allocated to a partial area, track number, sector number, frame number, field number, and time information.

These address data sequentially change in the order of increment or decrement in accordance with progress of a recording track such as a land portion “L”, for example.

It is acceptable that an address information can be accompanied by a specific information, which is composed of a small amount of data. A specific information is common data in the plain of the recording layer 12. Such a specific information is at least selected out from, for example, type of an information recording medium, size of the information recording medium, estimated recording capacity of the information recording medium, estimated recording linear density of the information recording medium, estimated recording linear velocity of the information recording medium, track pitch of the information recording medium, recording strategic information such as peak power, bottom power, erase power, and pulse period, reproduction laser power information, manufacturer\'s information, production number, lot number or batch number, control number, copyright related information, key for ciphering, key for deciphering, ciphered data, recording permission code, recording refusal code, reproducing permission code, and reproducing refusal code.

Further, an auxiliary information is such information that, for example, is described by the decimal number system or the hexadecimal notation and converted into the binary number system such as a BCD (Binary-Coded Decimal) code and a gray code.

Furthermore, the auxiliary information can accompany an error correcting code in order to prevent a data error.

In addition, a reference clock is provided for representing a pause of a certain period of time on a signal. Actually, a reference clock is composed of a single frequency that will be mentioned later.

FIG. 5 is a plan view showing a structure of the microscopic pattern 20, which is embedded with an auxiliary information and a reference clock, of the information recording medium 1 according to the first embodiment of the present invention. That is, the microscopic pattern 20 is composed of a land portion “L” and a groove portion “G”.

Further, the land portion “L” or the groove portion “G” is formed by being wobbled. In other words, both an auxiliary information and a reference clock are recorded by a wobbling groove. In FIG. 5, the drawing is illustrated such that an auxiliary information and a reference clock are recorded by wobbling a land portion “L”.

Furthermore, the microscopic pattern 20 is divided into at least two areas macroscopically, and at least composed of an auxiliary information area 200 and a reference clock area 300. As mentioned above, each of the auxiliary information area 200 and the reference clock area 300 is wobbled respectively. By a wobbling groove, an auxiliary information is recorded in the auxiliary information area 200 and a reference clock is recorded in the reference clock area 300. These areas are continuously formed without being interrupted, so that continuous reproduction is enabled. FIG. 5 is illustrated such that only two areas of the auxiliary information area 200 and the reference clock area 300 are allocated. However, this alternative allocation of the auxiliary information area 200 and the reference clock area 300 is repeated and constitutes whole area of the microscopic pattern 20 of the information recording medium 1.

Moreover, in FIG. 5, both of the auxiliary information area 200 and the reference clock area 300 are formed on the land portion “L” as a most preferable example. How ever, it is essential that one of the auxiliary information area 200 and the reference clock area 300 is formed on a groove portion “G” if the other one of the auxiliary information area 200 and the reference clock area 300 is formed on a groove portion “G”.

As mentioned above, by forming the auxiliary information area 200 and the reference clock area 300 on the same shaped portion, that is, a land portion “L” or a groove portion “G”, an auxiliary information and a reference clock can be reproduced continuously.

The auxiliary information 200 is composed of a waveform that is modulated digital data hereupon. Actually, the waveform is composed of any one of an amplitude-shift keying modulation wave 250 (250, 251, and 252), a frequency-shift keying modulation wave 260 (260, 261, and 262) and a phase-shift keying modulation wave 270 (270, 271, and 272) or any one of them that are transformed. FIG. 5 exemplifies particularly that the auxiliary information 200 is the frequency-shift keying modulation waveform 260 (260, 261, and 262).

Although these modulation methods will be detailed later, in the amplitude-shift keying modulation method, digital data of an auxiliary information are expressed such as “1” or “0” by a fundamental wave whether or not the fundamental wave is existed. In the case of the frequency-shift keying modulation method, digital data of an auxiliary information are expressed such as “1” or “0” by a frequency of a fundamental wave whether the frequency is higher or lower. In the case of the phase-shift keying modulation method, digital data of an auxiliary information are expressed such as “1” or “0” by a difference of phase angular of a fundamental wave. It is possible to record an auxiliary information such as an address more efficiently and to allocate the reference clock area 200 relatively longer by adopting these modulation methods. Being able to allocate the reference clock area 200 longer enables to detect a reference clock for a long period of time when recording the information recording medium 1, so that stable recording can be conducted.

A fundamental wave of these modulation methods hereupon can be selected out from a sinusoidal wave (or cosine wave), a triangular wave, and a rectangular wave. In case that a sinusoidal wave (cosine wave) is selected out from them, a harmonic component can be minimized when reproducing, and resulted in improving power efficiency and suppressing a jitter. Consequently, a sinusoidal wave (cosine wave) is suitable for a fundamental wave.

In addition thereto, a signal waveform formed by any of these modulation methods is recorded geometrically as a wobbling sidewall of land portion “L”.

On the other hand, the reference clock area 300 is composed of a single-frequency wave 350 that is continuously repeated. Since the frequency is single, it is possible to generate a frequency in response to a number of revolutions by making the information recording medium 1 move relatively while reproducing. Consequently, a reference clock can be produced. The reference clock can be used for revolution control when recording.

Further, a fundamental wave having a single frequency is composed of any one of a sinusoidal wave (cosine wave), a triangular wave, and a rectangular wave. In case that a sinusoidal wave (cosine wave) is selected out from them, a harmonic component can be minimized when reproducing, and resulted in improving power efficiency and suppressing a jitter. Consequently, a sinusoidal wave (cosine wave) is suitable for a fundamental wave.

In addition thereto, a signal waveform formed by any of these modulation methods is recorded geometrically as a wobbling sidewall of land portion “L”.

As mentioned above, the microscopic pattern 20 according to the present invention is at least composed of the auxiliary information area 200 and the reference clock area 300. An auxiliary information and a reference clock are recorded continuously by a wobbling groove without interruption. These auxiliary information and reference clock recorded on a sidewall of the land portion “L” in a shape of wobbling are read out from a push-pull signal by using a well-known 2-division or 4-division detector. Revolution control can be conducted by the read-out reference clock while recording, and further an information can be written in or erased from a predetermined address by extracting an address information from an auxiliary signal.

It is desirable for reproduction that the auxiliary information area 200 and the reference clock area 300 are in uniform length with each other and allocated alternately. In case that a length is not uniform with each other, it is not predicted that an auxiliary information such as an address or a reference clock can be detected at which timing while reproducing. Consequently, confusions may occur. On the contrary, in case that each length is uniform and they are allocated alternately, arrival of a succeeding signal can be easily predicted once reproduction is enabled. Accordingly, a timing of obtaining an auxiliary information and a reference clock is predicted by a logic circuit and the auxiliary information and the reference clock can be reproduced in less error.

Further, the reference clock area 300 is an important signal for controlling a number of revolutions when reproducing the information recording medium 1, so that the reference clock area 300 is desirable to be formed as long as possible. Actually, it is necessary for a ratio of a length of the reference clock area 300 to a total length of the auxiliary information area 200 and the reference clock area 300 to be more than 50%, desirably more than 60%. If the ratio is less than the value mentioned above, a reference clock can only be obtained for a short period of time. Consequently, revolution control is conducted intermittently and a reproduction operation becomes unstable. In a worst case, mismatching occurs in a logic circuit for reproducing and the operation is resulted in interrupting the reproduction.

It is acceptable that a shape of fundamental waveform and an amount of amplitude of these two areas are different from each other. However, they are desirable to be the same in view of simplification and stabilization of a recording circuit and a reproducing circuit.

With respect to a frequency, in case that the auxiliary information area 200 is formed with the amplitude-shift keying modulation wave 250 or the phase-shift keying modulation wave 270, it is acceptable that a frequency of the amplitude-shift keying modulation wave 250 or the phase-shift keying modulation wave 270 is different from a frequency of the single-frequency wave 350 of the reference clock area 300. However, in case of the same frequency, the recording circuit and the reproducing circuit can be simplified drastically. Consequently, the same frequency is desirable. Their frequencies are desirable to be at least related to “integral multiples” or “one over an integer”.

Further, in case that an auxiliary information of the auxiliary information area 200 is formed by the frequency-shift keying modulation wave 260, it is acceptable that two frequencies constituting the frequency-shift keying modulation wave 260 are different from a frequency of the single-frequency wave 350 in the reference clock area 300. However, in case that one of the two frequencies constituting the frequency-shift keying modulation wave 260 is the same as the frequency of the single-frequency wave 350, a physical length utilized for extracting a clock can be extended slightly. Consequently, the same frequency is desirable. These three frequencies are desirable to be related to “integral multiples” or “one over an integer” respectively in view of simplifying a recording circuit and a reproducing circuit.

Furthermore, it is also acceptable that a start-bit signal, a stop-bit signal and a sync signal is recorded as a wobbling groove at the boundary between the auxiliary information area 200 and the reference clock area 300 in order to clarify the division of them. With respect to such a signal, a single-frequency wave having a predetermined period and a predetermined frequency can be used. However, the predetermined frequency is essential to be at least different from the frequency of the single-frequency wave 350 that constitutes the reference clock area 300. It is most desirable that the predetermined frequency is different from any frequency constituting the single-frequency wave 350, the amplitude-shift keying modulation wave 250, the frequency-shift keying modulation wave 260, or the phase-shift keying modulation wave 270.

As mentioned above, the information recording medium 1 according to the first embodiment of the present invention can be in any shape such as disciform, card and tape. Consequently, the microscopic pattern 20 that is composed of approximately parallel grooves can also be in any shape such as spiral, coaxial and line. In case that the information recording medium 1 is in disciform and the microscopic pattern 20 is recorded spirally, the land portion “L” and the groove portion “G” is recorded by a recording method such as the constant angular velocity (CAV), the constant linear velocity (CLV), the zone constant angular velocity (ZCAV) and the zone constant linear velocity (ZCLV) recording methods, wherein the ZCAV and the ZCLV recording methods are a method that forms zones, which vary by radius, and conducts a different controlling system independent of each zone. In case that the information recording medium 1 is recorded by the CLV recording method, for example, a same linear velocity is maintained in the whole area of the information recording medium 1.

Further, in case of recording by the ZCAV recording method, the CLV recording method is conducted in one zone and a controlling system similar to the CAV recording method is conducted in the information recording medium 1 totally.

Furthermore, in case of recording by the ZCLV recording method, the CAV recording method is conducted in one zone and a controlling system similar to the CAV recording method is conducted in the information recording medium 1 totally.

FIG. 6 is an enlarged plan view of the reference clock area 300 in the information recording medium 1 on the basis of recording on a land portion “L” through the CLV recording method. In case that recording is conducted on a portion corresponding to a land portion “L” of the recording layer 12, an auxiliary information or a reference clock is essential to be extracted from the land portion “L”. Consequently, a single-frequency wave 350 to be a reference clock must be recorded on the land portion “L”. In view of that recording light scan along a centerline not shown of the land portion “L”, both sidewalls of the land portion “L” are essential to be parallel to each other. In other words, three land portions “L1” through “L3” (hereinafter generically referred to as land portion “L”) and two groove portions “G1” and “G2” (hereinafter generically referred to as groove portion “G”) are illustrated in FIG. 6.

Further, in FIG. 6, a sidewall of the inner circumferential side of the land portion “L2” or “L3” is shown as “L2i” or “L3i” (hereinafter generically referred to as inner sidewall “Li”) and another sidewall of the outer circumferential side of the land portion “L1” or “L2” is shown as “L1o” or “L2o” (hereinafter generically referred to as outer sidewall “Lo”).

Further, a side wall of the outer circumferential side of the groove portion “G1” or “G2” is shown as “G1i” or “G2i” (hereinafter generically referred to as inner sidewall “G1”) and another sidewall of the outer circumferential side of the groove portion “G1” and “G2” is shown as “G1o” or “G2o” (hereinafter generically referred to as outer sidewall “Go”). The inner sidewall “Li” of the land portion “L” and the outer sidewall “Go” of the groove portion “G” represents the same wall, and the outer sidewall “Lo” of the land portion “L” and the inner sidewall “G1” of the groove portion “G” represents the same wall hereupon.

Furthermore, a reference clock is recorded on the land portion “L” as a sinusoidal-wave signal through the CLV recording method. Therefore, as shown in FIG. 6, three land portions “L1” through “L3” are not parallel to each other in almost all cases. However, in order to extract a sinusoidal-wave signal accurately with avoiding interference from both sidewalls caused by a phase shift of each sidewall, the inner sidewall “Li” and the outer sidewall “Lo” of the land portion “L” are essential to be always formed in parallel to each other. From a point of view contrary to this, it is represented such that the inner sidewall “G1” and the outer sidewall “G0” constituting the groove portion “G”, which is the other portion than the land portion “L”, are never in parallel to each other.

FIG. 7 is an enlarged plan view of the reference clock area 300 in the information recording medium 1 on the basis of recording on a land portion “ ” through the CAV recording method. In case that the information recording medium 1 is recorded by the CAV recording method, a same angular velocity is maintained in a whole area of the information recording medium 1. By this CAV recording method, the wobbling land portion “L” and the groove portion “G” can always be in parallel to each other completely, so that a crosstalk amount between adjoining grooves becomes constant at all times. Consequently, ideal reproduction that can suppress output fluctuation of wobbling frequency and fluctuation in a time axis direction can be conducted. In other words, as shown in FIG. 7, each land portion “L” becomes in parallel to each other and at the same time each groove portion “G” also becomes in parallel to each other due to the characteristic of angular velocity. Three land portions “L1” through “L3” (hereinafter generically referred to as land portion “L”) and two groove portions “G1” and “G2” (hereinafter generically referred to as groove portion “G”) are illustrated in FIG. 7. In FIG. 7, a sidewall of the inner circumferential side of the land portion “L2” or “L3” is shown as “L2i” or “L3i” (hereinafter generically referred to as inner sidewall “Li”) and another sidewall of the outer circumferential side of the land portion “L1” or “L2” is shown as “L1o” or “L2o” (hereinafter generically referred to as outer sidewall “Lo”).

Further, a side wall of the outer circumferential side of the groove portion “G1” or “G2” is shown as “G1i” or “G2i” (hereinafter generically referred to as inner sidewall “G1”) and another sidewall of the outer circumferential side of the groove portion “G1” or “G2” is shown as “G1o” or “G2o” (hereinafter generically referred to as outer sidewall “Go”). The inner sidewall “Ai” of the land portion “L” and the outer sidewall “Go” of the groove portion “G” represents the same wall, and the outer sidewall “Lo” of the land portion “L” and the inner sidewall “G1” of the groove portion “B” represents the same wall hereupon.

As mentioned above, in case of recording on a land portion “L” of the recording layer 12, for example, a clock is essential to be extracted from the land portion “L”. Therefore, the single-frequency wave 350 to be a reference clock is recorded on the land portion “L”. The clock is recorded by the CAV recording method, so that the three land portions “L1” through “L3” are completely in parallel to each other as shown in FIG. 7. At the same time, the groove portion “G” that is the rest portion other than the land portion “L” is also in parallel to each other perfectly. In other words, in order to extract a sinusoidal-wave signal accurately, the inner sidewall “Li” and the outer sidewall “Lo” of the land portion “L” are essential to be always formed in parallel to each other. However, in the case of recording by the CAV recording method, the inner sidewall “Gi” and the outer sidewall “Go” of the groove portion “G” is also formed to be in parallel to each other.

In either recording method of the CLV and the CAV, both the sidewalls constituting the land portion “L”, that is, the inner sidewall “Li” and the outer sidewall “Lo” of the land portion “L” are essential to be in parallel to each other.

Further, particularly in the case of recording by the CAV recording method, not only the land portion “L” but also both the sidewalls “Gi” and “Go” constituting the groove portion “G” are in parallel to each other. In other words, the inner sidewall “Li” and the outer sidewall “Lo” of the land portion “L” and the inner sidewall “Gi” and the outer sidewall “Go” of the groove portion “G” are all in parallel to each other.

The shape of the sidewall of the reference clock area 300 in the microscopic pattern 20 recorded spirally in the information recording medium 1 in disciform is mentioned above. This situation is exactly the same as for the auxiliary information area 200 due to a similar reason for the reference clock area 300. In other words, in either recording method of the CLV and the CAV, both the sidewalls constituting the land portion “L”, that is, both the inner sidewall “Li” and the outer sidewall “Lo” of the land portion “L” are essential to be in parallel to each other.

In the information recording medium 1 according to the present invention, the auxiliary information area 200 and the reference clock area 300 is continuously formed without interruption, so that both sidewalls constituting the land portion “L”, that is, the inner sidewall “Li” and the outer sidewall “Lo” of the land portion “L” are formed in parallel to each other in any area on the information recording medium 1.

With referring to FIG. 8, a wobbling amount Δ of a wobbling groove that is formed in the information recording medium 1 according to the first embodiment of the present invention is explained next.

FIG. 8 is an enlarged plan view of the microscopic pattern 20 formed by the CLV recording method in the information recording medium 1 according to the first embodiment of the present invention. The microscopic pattern 20 is composed of the auxiliary information area 200 and the reference clock area 300, which are formed with a fundamental wave based on the sinusoidal wave or the cosine wave and continue without interruption. In FIG. 8, a centerline of wobbling groove is shown by a chain line. A distance between two chain lines, which are adjacent to each other, is defined as a pitch “P”.

Further, the information recording medium 1 shown in FIG. 8 is assumed to be recorded on a land portion “L” and a spot of reproducing light beam or a recording light beam that focuses on the land portion “L” is shown by a circle in doted line. The spot diameter is exhibited by “S”, that is equal to “λ/NA”, as mentioned above.

Furthermore, the land portion “L” wobbles and its wobbling width Δ in peak to peak value is shown by two doted lines.

Moreover, in case that the information recording medium 1 is in disciform, a wobbling direction corresponds to a radial direction of the disc-shaped information recording medium 1.

A reproducing apparatus of the information recording medium 1 can extract a wobbling amplitude of the auxiliary information area 200 and the reference clock area 300 as a signal through a reproducing light spot without interruption. In other words, by producing a push-pull signal from reflected light of the reproducing light spot, a single-frequency wave 350, a amplitude-shift keying modulation wave 250, a frequency-shift keying modulation wave 260, or a phase-shift keying modulation wave 270, which is based on a sinusoidal wave, can be directly extracted as a signal of similar figure. More accurately, a track direction of wobbling groove is transformed into a time axis direction, and further a radial direction of the wobbling groove is transformed into an amplitude direction of a reproduced signal, and then the single-frequency wave 350, the amplitude-shift keying modulation wave 250, the frequency-shift keying modulation wave 260, or the phase-shift keying modulation wave 270 is reproduced as the signal of similar figure.

According to another aspect of the present invention, the information recording medium 1 of the first embodiment is formed with a wobbling groove of which wobbling width Δ is within a range of Δ<P. In case that the information recording medium 1 is manufactured as mentioned above, adjacent tracks, that is, adjacent land portions “L”, for example, do not contact with each other physically, so that crosstalk caused by recording can be avoided.

Further, the inventors of the present invention make an experiment on a case that a phase change material is used for the recording layer 12 and recording is conducted by difference of reflectivity, phase difference, or both of them. In other words, the inventors try to reproduce an auxiliary information through a push-pull signal detecting method from the information recording medium 1 that is recorded with random data by conducting a phase change recording method. As a result of the experiment, a limit of enabling to detect an auxiliary information is 0.01 S≦Δ. In case of a groove of which wobbling width Δ is formed to be less than 0.01 S, random data caused by the phase change recording method are superimposed extremely on an auxiliary information as a noise and an error rate of the auxiliary information drastically increases.

On the contrary, the wobbling width Δ is set to the limitation of 0.01 S≦Δ, an auxiliary information can be reproduced sufficiently even in a low reflectivity condition such as an amorphous state due to the phase change recording method. However, in case of 0.15 S<Δ, a jitter in time axis direction occurs in an auxiliary information signal and a reference clock signal due to an affection of reproduction crosstalk caused by an adjacent groove, particularly, stability of the reference clock signal is deteriorated.

Accordingly, a relation between the wobbling width Δ and the pitch P shall be Δ<P, particularly, conditions satisfying relations Δ<P and 0.01 S≦Δ≦0.15 S are most suitable for forming a wobbling groove.

FIG. 9 is an enlarged plan view of the microscopic pattern 20 of the information recording medium 1, wherein recording is conducted on the recording layer 12 of the information recording medium 1 shown in FIG. 8. In FIG. 9, a record mark M is recorded on the land portions “L” that are wobbled. The record mark M represents whether a modulated signal is ON or OFF. There provided various lengths of record mark M as it will be explained later. As mentioned above, the record mark M is formed on the recording layer 12. In case that the recording layer 12 is formed by a phase change material, a record mark M is recorded by reflectivity and phase difference, difference of reflectivity, or phase difference.

A structure of how a shape of wobbling groove is reflected to a differential signal is complemented hereupon.

FIG. 10 is an enlarged plan view of a photo-detector 9 that collects reproducing light, which is irradiated on the information recording medium 1 and reflected. In case that the photo-detector 9 is a 4-division detector, as shown in FIG. 10, the detector 9 is divided into four elements in accordance with the radial direction and the tangential direction of the information recording medium 1. A push-pull signal can be produced by subtracting each sum signal in the tangential direction. More accurately, with defining that the four elements are A, B, C, and D respectively, and further defining that electric currents, which are obtained from each of the elements A, B, C, and D when they receive light, are Ia, Ib, Ic and Id respectively, the push-pull signal can be represented by an equation “(Ia+Ib)−(Ic+Id)”. In other words, a signal to be obtained is a differential signal in the radial direction. When a reproducing apparatus of the information recording medium 1 traces a center of groove, that is, the center of the chain line shown in FIGS. 8 and 9, the push-pull signal is in a form of obtaining an output difference in the radial direction with respect to the centerline. Consequently, a wobbling shape can be reproduced as a signal that reflects the wobbling shape.

The total constitution of the information recording medium 1 according to the first embodiment of the present invention is detailed above.

Further, it is acceptable that the auxiliary information area 200 is conducted with not only recording on a sidewall by selecting one modulation wave out of the amplitude-shift keying modulation wave 250, the frequency-shift keying modulation wave 260, and the phase-shift keying modulation wave 270 but also time-division recording on each sidewall in different areas by selecting two or three modulation methods.

A single-frequency wave can be superimposed on the amplitude-shift keying modulation wave 250, the frequency-shift keying modulation wave 260, or the phase-shift keying modulation wave 270. In other words, with respect to the amplitude-shift keying modulation wave 250 and the frequency-shift keying modulation wave 260, a wave having a same frequency as a frequency that constitutes those modulation waves or a different frequency from frequencies of those modulation waves can be superimposed and recorded.

Particularly, with respect to the frequency-shift keying modulation wave 260, a wave having either a higher frequency or a lower frequency of the frequency-shift keying modulation wave 260 can be superimposed on the frequency-shift keying modulation wave 260. Similarly, a wave having a frequency of “an integer multiple” or “one over an integer” of either a higher frequency or a lower frequency of the frequency-shift keying modulation wave 260 can be superimposed on the frequency-shift keying modulation wave 260.

Further, with respect to the phase-shift keying modulation wave 270, a wave having a frequency of “an integer multiple” or “one over an integer” of the frequency constituting the phase-shift keying modulation wave 270 can be superimposed on the phase-shift keying modulation wave 270.

In any case, by using a well-known band pass filter or phase detector, it is possible to separate a single-frequency wave and any of the amplitude-shift keying modulation wave 250, the frequency-shift keying modulation wave 260, and the phase-shift keying modulation wave 270 from the superimposed wave. For example, an experience is conducted with respect to the phase-shift keying modulation wave 270. It is confirmed that a single-frequency wave and a phase-shift keying modulation wave can be separated as far as an amplitude ratio of the phase-shift keying modulation wave to the single-frequency wave is within a predetermined range of 1:5 to 5:1 while superimposing the single-frequency wave on the phase-shift keying modulation wave. In other words, in case that an information recording medium is manufactured as a trial by setting the amplitude ratio for out of the predetermined range, one wave having larger amplitude can be reproduced. However, the other wave having smaller amplitude can not be reproduced due to an excessively low signal to noise ratio (S/N).

In case of such a constitution that a single-frequency wave to be superimposed and the single-frequency wave 350 of the reference clock area 300 is the same frequency, a reference clock can also be extracted form the auxiliary information area 200. Consequently, such a constitution is more suitable for recording by superimposing. That is to say, since a reference clock continues substantially although the auxiliary information area 200 is formed over a long distance, extremely stable recording can be conducted.

It is acceptable that an auxiliary information to be formed on a sidewall of a land portion “L” is highly discomposed and recorded with distributed. By combining with dummy data “101”, for example, distributed recording is one recording method such that an auxiliary information is recorded as a data array such as “101X”, wherein X is either “0” or “1”, and the data array is allocated in each predetermined interval.

FIG. 11 is a first example showing a distributed recording of an auxiliary information. As shown in FIG. 11, the dummy data “101” as a data trigger “Tr” is allocated in the predetermined interval, at every 11 bits herein, and an “X” is allocated in succession to the data trigger “Tr”. In other words, by extracting only the “X” allocated immediately after the data trigger “Tr”, an auxiliary information can be restored. In this case, with defining that the “1” is data, the auxiliary information shown in FIG. 11 can be restored as a series of data that are composed of existing data (Data), none data (None) and existing data (Data) in sequence, so that “101” can be reproduced as the auxiliary information. This recording method is effective for a format that is allowed to read a data array to be processed with spending a longer period of time. It is defined hereupon that one-bit data to be extracted at each predetermined interval is a “word” and an auxiliary information is constituted by integrating a plurality of “words”.

Further, a variation of the recording method shown in FIG. 11 is exhibited in FIG. 12.

FIG. 12 is a second example showing a distributed recording of an auxiliary information. As shown in FIG. 12, a data trigger “Tr” and data “X” can be allocated with separating them in a predetermined bit of interval. In FIG. 12, the data trigger “Tr” is “11” and allocated at every 11 bits. Data are recorded by “101” whether the “101” is existed or not in a predetermined interval. In other words, by extracting data existing in the fourth bit to the sixth bit, one-bit data can be restored. In this second example, data can be restored as a series of data composed of existing data (Data), none data (None) and existing data (Data) in sequence, so that “101” is reproduced as the auxiliary information. This recording method is effective for reducing erratic readout because the data “X” is separated from the data trigger “Tr”.

Furthermore, with respect to a third example of the highly distributed recording method, a first specific data pattern such as “11” is allocated or recorded at every predetermined interval. Then, a second specific data pattern such as “101” is allocated between the first specific patterns. A position at where the second specific pattern is allocated is advanced by a predetermined bit, distance or period with respect to the first specific data pattern. Particularly, two positions are allocated previously.

FIG. 13 is a third example of the highly distributed recording method showing a distributed recording of an auxiliary information. As shown in FIG. 13, a data trigger “Tr” or “11”, is allocated at every predetermined interval, actually every 11 bits hereupon, as the first specific data pattern, and a second specific data pattern “101” is allocated between the data triggers “Tr” or “11”. A position at where the second specific data pattern is allocated is provided with two positions; one is within a range of the third bit to the fifth bit from the data trigger “Tr” or “11” and the other is within a range of the fifth bit to the seventh bit. Decoding is conducted by judging that the second specific data pattern is allocated in either position. In the case of FIG. 13, the second specific data pattern “101” is sequentially allocated in the positions starting with the third bit, fifth bit and third bit respectively, so that data or words “101” can be reproduced as an auxiliary information. This recording method is effective for ensuring higher reliability to an auxiliary information because the recording method can add a parameter whether or not the data “101” can be read out to one of standards for judging reliability.

In other words, data to be recorded in an auxiliary information area are at least composed of a data trigger that is allocated at every predetermined interval and data allocated at a predetermined position between the data triggers. The information recording medium 1 according to the present invention is recorded with an auxiliary information by a relative distance between the data trigger and the data or the second specific data pattern.

In the description of the third example of the highly distributed recording method mentioned above, the method of distributed recording that is conducted by using a position difference between the first specific data pattern and the second specific data pattern is explained. However, in case that a pattern, which is extremely high in readout accuracy, can be provided, it is acceptable for both the first specific data pattern and the second specific data pattern that their patterns are the same pattern. In other words, decoding can be conducted by extracting a specific pattern having a shorter time interval from a specific data pattern recorded at a predetermined time interval and by measuring a distance interval or the time interval between the specific data pattern and the specific pattern. With referring to FIG. 14, further details are explained next.

FIG. 14 is a fourth example showing a distributed recording of an auxiliary information. As shown in FIG. 14, a data trigger “Tr” or “11” is allocated at a predetermined interval, at every 11 bits hereupon, as a first specific data pattern, and a second specific data pattern “11” having the same pattern as the data trigger “Tr” is allocated between the data triggers “Tr”. A position at where the second specific data pattern is allocated is provided with two positions; one is within a range of the third bit to the fifth bit from the data trigger “Tr” or “11” and the other is within a range of the fifth bit to the seventh bit. Decoding is conducted by judging that the second specific data pattern is allocated in either position. In the case of FIG. 14, the second specific data pattern “11” is sequentially allocated in the positions starting with the third bit, fifth bit and third bit respectively, so that data or words “101” can be reproduced as an auxiliary information. This recording method is advantageous to a reproducing circuit to be simplified because the recording method requires only one specific data pattern.

The highly distributed recording method is explained above in four types. According to these highly distributed recording methods, an auxiliary information is recorded as data that are decomposed into every one bit. Actually, some bits of dummy data are prepared for a data trigger “Tr” first, and a data array composed of continuing single data such as continuing zeros, for example, is prepared next. The data trigger “Tr” is connected with the single data array so as to be allocated at every predetermined interval for the data trigger “Tr”. Then, the auxiliary information that is decomposed into every one bit is recorded so as to convert a part of the single data array by a predetermined rule. In other words, an auxiliary information is recorded by converting data allocated in a bit, which is advanced by a predetermined distance from the data trigger “Tr”, by the predetermined rule.

On the other hand, when reproducing the auxiliary information, all data are once read out from a sidewall of land portion “L” as a data array and a data trigger “Tr” that is allocated at every predetermined interval is detected from the data array. Then, one bit of data that is equivalent to a “Word” shown in FIGS. 11 to 14 is extracted from the data array excluding the data trigger “Tr” with referring to the predetermined rule. The auxiliary information is restored by integrating the detected one-bit data.

The methods for recording in highly distributed and for reproducing an information recording medium according to the present invention are explained above. In case of an auxiliary information, particularly, an address information, a plurality of zeros or ones may continue, so that there is existed a possibility of generating a DC component in a data array being read out. In order to eliminate such a possibility, it is acceptable that the data array is previously modulated by the base-band modulation method and recorded. In other words, there existed a method such that a data array to be recorded on a sidewall of land portion “L” by wobbling modulation is previously replaced with another codes so as to reduce a sequence of zeros and ones to a certain number or less. With respect to such a method, the method such as Manchester code, PE (phase encoding) modulation, MFM (modified frequency modulation), M2 (Miller squared) modulation, NRZI (non return to zero inverted) modulation, NRZ (non return to zero) modulation, RZ (return to zero) modulation and differential modulation can be used independently or by combining some of them together.

FIG. 15 is a table exhibiting data change before and after modulating a base-band.

With respect to a base-band modulation method, which is most suitable for the information recording medium 1 of the present invention, there is provided the Manchester code (biphase modulation) method. The Manchester code method is a method of applying two bits to each one bit of an original data to be recorded as shown in FIG. 15. That is, “00” or “11” is assigned to a data “0” to be recorded, and “01” or “10” to a data “1”.

Further, an inverted code of inverting a last code of preceding data is essentially applied to a head code of succeeding data when arranging the succeeding data after the preceding data.

FIG. 16 is a table exhibiting an example of actual data change before and after modulating a base-band. As shown in FIG. 16, an original data “100001” is assigned to be a code array of “010011001101”. The original data contains a sequence of four “0”s and is an asymmetrical data in which an appearing probability of “0” is twice that of “1”. If such an asymmetrical data is modulated by the Manchester code method, a sequence of “0” or “1” is only two maximally and the original data is converted into a symmetrical data having equal appearing probability of “0” and “1”. As mentioned above, the base-band modulation, which restricts a sequence of same bits within a certain quantity, is effective to increase stability of reading out data. Consequently, the base-band modulation method is suitable for pre-treatment for a long array of auxiliary information.

An amplitude-shift keying modulation wave 250 (250, 251 and 252), a frequency-shift keying modulation wave 260 (260, 261 and 262) and a phase-shift keying modulation wave 270 (270, 271 and 272), which are used for the information recording medium 1 according to the embodiment one of the present invention as a wobbling groove modulation wave, are explained next.

With referring to FIGS. 17 through 19, the amplitude-shift keying modulation waves 250, 251 and 252 are depicted.

FIG. 17 shows a first example of an amplitude-shift keying modulation waveform according to the present invention. FIG. 18 shows a second example of an amplitude-shift keying modulation waveform according to the present invention. FIG. 19 shows a third example of an amplitude-shift keying modulation waveform according to the present invention.

As shown in FIG. 17, the amplitude-shift keying modulation wave 250 according to the present invention is geometrically recorded by modulating data through the amplitude-shift keying modulation method and actually, constituted by an amplitude section 2501 and a non-amplitude section 2500, wherein the amplitude section 2501 is formed by wobbling a groove in a predetermined period. In other words, the amplitude section 2501 is a wobbling part of groove and the non-amplitude section 2500 is a non-wobbling part of groove.

Further, the amplitude section 2501 and the non-amplitude section 2500 is corresponding to “1” and “0” of a data bit respectively. The amplitude section 2501 is composed of a plurality of waves that continue more than one cycle hereupon. A number of waves is not limited to a specific cycle. However, if it is too many, length of the non-amplitude section 2500 consequently becomes longer and resulting in that a fundamental wave, which produces a gate when reproducing, is hardly detected. Therefore, two to one hundred cycles, preferably three to thirty cycles are suitable for the number of waves of the amplitude section 2501. As mentioned above, digital data (in case of FIG. 17, it is “10110”) is recorded by whether or not amplitude is existed. The push-pull signal detecting method mentioned above can be used for reading out the recorded data.

Furthermore, it should be understood that the amplitude-shift keying modulation wave 250 according to the present invention does not limit each length or each amplitude size of the amplitude section 2501 and the non-amplitude section 2500 to specific figure. In the case of the amplitude-shift keying modulation wave 250 shown in FIG. 17, the length of the amplitude section 2501 is set to be longer than that of the non-amplitude section 2500.

In FIG. 18, an amplitude-shift keying modulation wave 251 is constituted by amplitude sections 2511a through 2511c and non-amplitude sections 2511. Each amplitude of the amplitude sections 2511a through 2511c is unequal to each other. However, unequal amplitude is acceptable for the amplitude-shift keying modulation method.

Further, it is also acceptable that assigning each amplitude in multiple levels intentionally realizes recording in multi-values more than three values.

Furthermore, in case of an amplitude-shift keying modulation wave 252 shown in FIG. 19, each amplitude of amplitude sections 2521 is equal to each other and each length of the amplitude sections 2521 is equal to that of non-amplitude sections 2520. This configuration is also acceptable for the amplitude-shift keying modulation method. Particularly, in case that data are recorded in digital by the binary value of “0” and “1”, an isotropic layout as shown in FIG. 19 is desirable for the digital recording by the binary value. In other words, if each height of the amplitude sections 2521 is made equal to each other and each length of the amplitude sections 2521 is made equal to that of the non-amplitude sections 2520, judging “0” or “1” when reproducing can be realized by sufficient threshold value of amplitude.

Moreover, data arranged in series can be read out by one threshold value of time, so that a reproducing circuit can be simplified.

In addition thereto, even in case that jitter exists in reproduced data, there is existed a merit that influence of the jitter can be minimized.

Further, with assuming that a code to be recorded is ideally symmetrical, total length of the amplitude sections 2521 is made equal to that of the non-amplitude sections 2520 and resulted in that no DC component is existed in a reproduced signal. It is advantageous to digital recording that no DC component releases a burden on data decoding and servo.

As mentioned above, by using any of the amplitude-shift keying modulation waves 250, 251 and 252, an auxiliary information is recorded in an information recording medium 1 according to the first embodiment of the present invention. Either “0” or “1” is recorded in response to whether a wobble is existed on a sidewall of groove or not, so that ability of judging “0” or “1” is excellent. In other words, a low error rate can be obtained although an auxiliary information is in relatively low C/N (carrier to noise ratio).

Further, although recording on the recording layer 12 is conducted by a user, influence of random noise caused by the recording can be reduced and a low error rate can be maintained. With referring to FIGS. 20 through 22, frequency-shift keying modulation waves 260 through 262 are explained next.

FIG. 20 shows a first example of a frequency-shift keying modulation waveform according to the present invention. FIG. 21 shows a second example of a frequency-shift keying modulation waveform according to the present invention. FIG. 22 shows a third example of a frequency-shift keying modulation waveform according to the present invention.

A frequency-shift keying modulation wave is for recording data geometrically by the frequency-shift keying modulation method and is composed of a plurality of sections that are formed by wobbling grooves by different frequencies. Actually, in the case of binary data, the frequency-shift keying modulation wave is geometrically recorded by using a higher frequency section and a lower frequency section. In case of multi-valued data such as “n” values, a frequency-shift keying modulation wave is geometrically recorded by the frequency-shift keying modulation method that uses “n” kinds of frequency sections. Hereinafter the examples are explained with assuming that data to be recorded are in binary. FIG. 20 is one example of recording data “10110” geometrically. In FIG. 20, the frequency-shift keying modulation wave 260 is composed of three higher frequency sections 2601 and two lower frequency sections 2600. The higher frequency section 2601 and the lower frequency section 2600 are equivalent to “1” and “0” of a data bit respectively and they are recorded in digital by changing the frequency at each one channel bit. A number of waves that constitute each frequency section is not limited to one specific number. Each frequency section is composed of a wave that continues more than one cycle. However, in consideration of that data are not redundant too much in a reproducing apparatus so as to detect a frequency accurately and to obtain a certain degree of data transfer rate, each frequency section, which is corresponding to each data bit mentioned above, is desirable to be constituted by a number of waves within a range of one cycle to one hundred cycles, preferably one cycle to thirty cycles.

Further, it is acceptable that each amplitude of the higher frequency section 2601 and the lower frequency section 2600 is equal to each other. However, an amplitude ratio is not limited to one specific figure. Amplitude of the higher frequency section 2601 can be formed larger than that of the lower frequency section 2600 in consideration of a frequency response of reproducing apparatus.

Furthermore, the push-pull signal detecting method mentioned above can be used for reading out the recorded data.

It should be understood that the information recording medium 1 according to the first embodiment of the present invention does not place a restraint on physical length or amplitude size of a channel bit, which is composed of the higher frequency section 2601 and the lower frequency section 2600. For example, in FIG. 20, the physical length of lower frequency section 2600 is designated to be longer than that of the higher frequency section 2601.

As shown in FIG. 21, in case of a frequency-shift keying modulation wave 261, it is acceptable that amplitude of a higher frequency section 2611 and a lower frequency section 2610 are equal to each other and length of the higher frequency section 2611 is equal to that of the lower frequency section 2610. By equalizing each amplitude and length as mentioned above, judging “0” or “1” can be conducted by sufficient threshold value of amplitude when reproducing.

Further, data arranged in series can be read out by one threshold value of time, so that a reproducing circuit can be simplified.

Furthermore, in case that jitter exists in reproduced data, there is existed a merit that influence of the jitter can be minimized.

Moreover, with assuming that a code to be recorded is ideally symmetrical, total length of the higher frequency sections 2611 is equal to that of the lower frequency sections 2610 and resulted in that no DC component is existed in a reproduced signal. It is advantageous to digital recording that no DC component releases a burden on data decoding and servo.

In FIGS. 20 and 21, the higher frequency section 2601 or 2611 and the lower frequency section 2600 or 2610 is connected to each other respectively, wherein each waveform rises at a point where a channel bit changes. However, phase jump happens in probability of 50% at the moment when a channel bit changes. Consequently, a high frequency component is generated and resulted in deterioration of power efficiency per each frequency.

In order to eliminate such phase jump, a frequency-shift keying modulation wave 262 is provided. In FIG. 22, the frequency-shift keying modulation wave 262 is composed of a higher frequency section 2621r or 2621f (hereinafter referred generically to as higher frequency section 2621) and a lower frequency section 2620. The higher frequency section 2621 and the lower frequency section 2620 is arranged so as to maintain phase continuity at a point where each channel bit of the frequency-shift keying modulation wave 262 changes over. Actually, a starting phase of the lower frequency section 2620 is selected so as to be that a phase direction of the end of the higher frequency section 2621 and a phase direction of the start of the lower frequency section 2620 are the same direction.

Further, the reverse connection is the same as such that a starting phase of the higher frequency section 2621 is selected so as to be that a phase direction of the end of the lower frequency section 2620 and a phase direction of the start of the higher frequency section 2621 are the same direction. If the starting phase is selected as mentioned above, continuity of phase is maintained and power efficiency is improved.

Furthermore, a reproduction envelope becomes constant, so that a data error rate of auxiliary information, which is recorded in the information recording medium 1, is improved. Such a method of maintaining continuity of phase at a point where a channel bit changes can be applied to the auxiliary information area 200 and the reference clock area 300 shown in FIG. 5. A data error rate of auxiliary information is further improved if waveforms of the auxiliary information area 200 and the reference clock area 300 are arranged as mentioned above.

A frequency of the higher frequency section 2621 (2601, 2611 or 2621) and the lower frequency section 2620 (2600, 2610 or 2620) is arbitrary selected. However, in order to eliminate interference with a frequency range that is provided for recording data on the information recording medium 1 by a user, it is strictly required for the higher frequency section 2621 not to be extremely high frequency in comparison with a frequency of the lower frequency section 2620.

On the other hand, in order to improve a reproduction error rate of address data, a frequency difference between the higher frequency section 2621 and the lower frequency section 2620 shall be kept in certain degree so as to maintain excellent separativeness. From these viewpoints, a frequency ratio of the higher frequency section 2621 to the lower frequency section 2620 is desirable to be within a range of 1.05 to 5.0, particularly, desirable to be within a range of 1.09 to 1.67. In other words, phase relation between two frequencies is desirable to be within a range of 2π±(π/20.5) to 2π±(π/0.75), particularly, desirable to be within a range of 2π±(π/12) to 2π±(π/2), that is, 360±15 degrees to 360±90 degrees, wherein the reference phase is defined as 2π.