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Use of volume bragg gratings for the conditioning of laser emission characteristicsRelated Patent Categories: Coherent Light Generators, Particular Active Media, Semiconductor, Injection, Monolithic Integrated, Laser ArrayUse of volume bragg gratings for the conditioning of laser emission characteristics description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070047608, Use of volume bragg gratings for the conditioning of laser emission characteristics. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is a division of U.S. patent application Ser. No. 11/407,796, filed Apr. 19, 2006, which is a division of U.S. patent application Ser. No. 10/884,524, filed Jul. 2, 2004, which claims benefit under 35 U.S.C. .sctn.119(e) of provisional U.S. patent applications Nos. 60/484,857, filed Jul. 03, 2003, and 60/564,526, filed Apr. 22, 2004. The respective disclosures of each of the above-referenced patent applications are incorporated herein by reference. [0002] The subject matter disclosed and claimed herein is related to the subject matter disclosed and claimed in U.S. patent application Ser. No. 10/390,521, filed Mar. 17, 2003, the disclosure of which is hereby incorporated herein by reference. FIELD OF THE INVENTION [0003] The invention is related generally to light emitting devices, such as lasers, laser diodes, light-emitting diodes, super-luminescent laser diodes, etc. More specifically, the invention provides for using one or more volume Bragg grating (VBG) elements for modifying (or conditioning) one or more output characteristics of such devices. BACKGROUND OF THE INVENTION [0004] Laser cavities or resonators, however complex, typically include two or more mirrors or other reflecting devices that form a closed optical path for rays traveling in a certain direction. An optical element positioned in that closed optical path, which includes mirrors and/or other reflecting devices that form the path, may be referred to as "intra-cavity." An optical element positioned in the path of light that has departed from the resonator may be referred to as an "extra-cavity" element. [0005] Using extra-cavity partial reflectors as feedback elements with a solitary laser cavity has been attempted in the past with a purpose of achieving single longitudinal mode operation of the otherwise multi-mode laser. Such reflectors, however, were not wavelength-selective devices. Such designs may be referred to as the "coupled-cavity" approach. This approach suffered from instabilities stemming from the non-selective nature of the feedback. [0006] Another approach used was to employ a dispersive element, such as surface diffraction grating, as an extra- or intra-cavity wavelength-selective device in order to induce narrow-band or single longitudinal mode operation of a semiconductor laser. Although successful in a laboratory, this approach results in rather bulky devices, which are difficult to align and to maintain in the field. [0007] A somewhat more practical approach for inducing narrowband operation of a single-transverse mode semiconductor laser proved to be a fiber Bragg grating functioning typically as an extra-cavity element. This device is a narrow-band reflector that functions only in an optical fiber waveguide. It is, therefore, inapplicable to solid-state lasers, laser diode arrays, and, most likely, even to multi-mode (transverse) broad-area high-power single-emitter laser diodes, whether fiber-coupled or not. [0008] The use of a volume Bragg grating element has been suggested as an intra-cavity element to induce single-longitudinal mode (also called single-frequency) operation of a single-transverse mode laser diode. In this approach, the volume Bragg grating element forms the external Bragg mirror of an external-cavity single-spatial mode semiconductor laser diode. However, to the inventors' knowledge, neither the possibility of using a VBG element for extra-cavity narrow-band feedback nor a practical device for achieving narrow-band operation of a single-transverse mode semiconductor laser diodes have been disclosed previously. Furthermore, to the inventors' knowledge, not even the possibility of applying VBG elements to multiple-transverse mode, broad-area laser diodes, laser diode arrays or the possibility of conditioning other attributes of laser emission (such as its spatial mode and temporal profile) have been disclosed previously. [0009] To the inventors' knowledge, there are currently no devices in the market that employ volume Bragg grating elements for conditioning of laser characteristics, nor are there any successful practical devices in the market that use any of the above-mentioned approaches to improve the output characteristics of arrays of lasers. SUMMARY OF THE INVENTION [0010] The invention provides methods and apparatuses that can overcome the problems known in the prior art. The invention provides several practical embodiments of using VBG elements for conditioning any or all of the output characteristics of lasers and other light-emitting devices. [0011] The inventors have found that volume Bragg grating (VBG) elements recorded in photorefractive materials, particularly those recorded in inorganic photorefractive glasses (PRGs), have many properties that can improve one or more characteristics of light-emitting devices such as solid-state lasers, semiconductor laser diodes, gas and ion lasers, and the like. A volume Bragg grating ("VBG") element may be any structure that: a) has a periodically varying index of refraction in its bulk (the shape of the surface of the constant index of refraction can be any smooth figure, flat or curved); b) is generally transparent in the spectral region of its operation; and c) has a thickness in the direction of propagation of light of 0.05 mm or more. [0012] A photorefractive material may include any material that has the ability to change its index of refraction subsequent to illumination by light of certain wavelength region or regions. Such a change in refractive index may occur in the material either immediately upon illumination by light or as a result of secondary processing step or steps, whether chemical, thermal, etc. Such a material may also be generally transparent in the spectral region of its photosensitivity, i.e. the light at the recording wavelength may have the ability to penetrate sufficiently deep into the material (>0.1 mm) without suffering excessive absorption (>90%). Further, the material may be amorphous and generally isotropic. [0013] Though the embodiments described herein are directed to certain examples of laser devices, it should be understood that the principles of the invention apply to other light-emitting devices as well. For example, applications of this invention include but are not limited to: high-power, semiconductor, solid state, ion, and gas lasers; light-emitting diodes and super-luminescent laser diodes; medical diagnostics, treatment, and surgical instruments; environmental sensors; metrology instruments; industrial applications; and defense applications. [0014] Properties of VBG elements, and methods for manufacturing VBG elements, have been described previously (see, for example, U.S. patent application Ser. No. 10/390,521, filed Mar. 17, 2003). [0015] Generally, there are at least three distinct characteristics of the output of a laser device that may be improved using the techniques of the invention: 1) emission spectrum (e.g., peak wavelength of the laser emission and its spectral width); 2) spatial/angular beam characteristics (e.g., the angular divergence of the output laser beam and its spatial mode structure); and 3) temporal profile of the laser pulses (e.g., the duration of the laser pulse, its temporal phase variation or chirp etc.). As used herein, spectral, spatial, or temporal conditioning, refer to affecting any of the above characteristics, respectively. [0016] The inventors have found that VBG elements permanently recorded in a suitable material, particularly a PRG, have a number of properties that can be utilized for improving one or more of the above characteristics. These properties include, but are not limited to: 1) single spectral pass band without any extraneous pass bands; 2) ability to control the spectral width of the VBG filter pass band; 3) ability to control the amplitude and phase envelope of a VBG filter; 4) narrow acceptance angle range otherwise called field of view; 5) ability to control the acceptance angle and the field of view; 6) ability to multiplex more than one filter in the same volume of the material; 7) high damage threshold of the VBG elements manufactured in a suitable material, particularly PRG; 8) ability to be shaped into bulk optical elements with sufficiently large clear aperture; and 9) reflectivity distributed over the volume of the material. [0017] The invention provides apparatus and methods by which these properties of VBGs may be applied to the improvement of the above-mentioned laser characteristics. BRIEF DESCRIPTION OF THE DRAWINGS [0018] FIGS. 1A-1C depict a VBG as an extra-cavity element for wavelength locking by self-seeding; FIG. 1D provides plots of wavelength characteristics with and without laser conditioning. [0019] FIGS. 2A and 2B depict wavelength locking by use of a transmission VBG. Continue reading about Use of volume bragg gratings for the conditioning of laser emission characteristics... Full patent description for Use of volume bragg gratings for the conditioning of laser emission characteristics Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Use of volume bragg gratings for the conditioning of laser emission characteristics patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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