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  Arrayed waveguide grating deviceUSPTO Application #: 20080089646Title: Arrayed waveguide grating device Abstract: A grating device has a waveguide array cyclically arranged. A horned waveguide is used in a star coupler of the grating device. An optical signal is divided into streams. The streams are slanted from original central axes. Or, a waveguide having an asymmetrical structure is used. Thus, a flat-top pass-band of the optical signal is obtained. The present invention can be used in any optical device. (end of abstract) Agent: Troxell Law Office PLLC - Falls Church, VA, US Inventor: Hung-Chih Lu USPTO Applicaton #: 20080089646 - Class: 385037000 (USPTO) Related Patent Categories: Optical Waveguides, With Optical Coupler, Input/output Coupler, Grating The Patent Description & Claims data below is from USPTO Patent Application 20080089646. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] The present invention relates to an arrayed waveguide grating device; more particularly, relates to using compensating central axes or a waveguide having an asymmetrical structure coordinated with a horned waveguide to obtain a flat-top pass-band of an optical signal. DESCRIPTION OF THE RELATED ARTS [0002] A traditional arrayed waveguide grating device has its waveguide array and waveguide outputs set along central axes. But, for a traditional cyclic arrayed waveguide grating device, such an arrangement produces a non-flat-top pass-band. [0003] As shown in FIG. 7A and FIG. 7B, a traditional cyclic arrayed waveguide grating device comprises a first star coupler 61, a waveguide array 62 and a second star coupler 63. An optical signal is inputted from a waveguide input 611. After passing through a first slab waveguide 612, a light field of the inputted optical signal is scattered and is coupled into the waveguide array 62. Then the optical signal is passed through a second slab waveguide 631 with multi-slit interferences and is coupled to waveguide outputs 632 in the end. Because the inputted optical signal comprises various wavelengths, optical path differences are different and streams of the optical signal are focused and coupled to different positions of waveguide outputs 632 after the optical signals pass through the waveguide array. Thus, streams of the optical signal having different wavelengths are divided. Owing to free spectral range (FSR), the cyclic arrayed waveguide grating device is characterized in a cyclic pass-band with a 3 dB unevenness in the pass-band distributed as a Gaussian function curve, as shown in FIG. 8. To deal with this 3 dB unevenness in the pass-band for a system, optical attenuators are linked after the waveguide outputs to obtain even optical powers. Yet, in actual practices, a laser light source having high accurate wavelengths is demanded; and thus, a cost for fabricating such a system becomes high. [0004] In the other hand, there are still some other prior arts for obtaining a flat-top pass-band, which are grouped into two categories: one is to put a horned waveguide 7 between the waveguide input 611 and the first slab waveguide 612, as shown in FIG. 9A and FIG. 9B; and, the other is to put the horned waveguide 7 between the second slab waveguide 631 and the waveguide outputs 632, as shown in FIG. 10A and FIG. 10B. And the waveguide array 62 and the waveguide outputs 632 are put along a central axis 8 to obtain the same coupling efficiency between the waveguide outputs 632 and the second slab waveguide 631. However, owing to the 3 dB unevenness in the pass-band, the pass-band in the outer channel of the waveguide outputs 632 is deformed, as shown in FIG. 11; thus, all prior arts for obtaining a flat-top pass-band become useless to the cyclic arrayed waveguide grating device. [0005] A prior art to deal with the 3 dB unevenness is revealed, where an optical coupling loss is generated to uniform the pass-band through slanting from original central axes 8. Because the channels closer to the center of the cyclic arrayed waveguide grating device have a stronger optical power, a bigger optical coupling loss is required and hence an angle required for slanting from the original central axis 8 is bigger. On the contrary, an outer channel have a weaker optical power and hence a smaller angle is required for slanting from the original central axis 8. In this way, the pass-band may become even. However, the 3 dB unevenness in the pass-band can be also made even through using optical attenuators. The core issue is not to even the pass-band but to make it flat-top. Furthermore, the prior art can only even the pass-band, but the deformation of the flat-top pass-band cannot be modified by this prior art. [0006] Another prior art is to deal with pass-band deformation through general horned waveguides as compensating waveguides by replacing outer waveguides. It is because pass-band at the outer side of a cyclic arrayed waveguide grating has a more serious deformation. So, the outer pass-band is deformed to solve the problem. Yet, this method solves the problem with the outer pass-band only, but not the inner pass-band, which is a partial compensation. On the contrary, the present invention uses horned waveguides having an asymmetrical structure, coordinated with a central compensating axis, to compensate the whole pass-band. Thus, the present invention is a complete compensation, totally different from the prior arts. Hence, the prior arts do not fulfill all users' requests on actual use. SUMMARY OF THE INVENTION [0007] The main purpose of the present invention is to provide a cyclic arrayed waveguide grating device having a flat-top pass-band. [0008] To achieve the above purpose, the present invention is a cyclic arrayed waveguide grating device using a horned waveguide, comprising a first star coupler, a waveguide array, a second star coupler and a horned waveguide, where an optical signal inputted from a waveguide input of the first star coupler is directed to a first slab waveguide of the first star coupler for obtaining streams of the optical signal; the waveguide array comprises a plurality of single-mode waveguides to obtain a fixed phase difference of streams of the optical signal between each two neighboring single-mode waveguides; the second star coupler is connected at a rear end of the waveguide array to obtain interferential focuses of the streams at a front end of a second slab waveguide of the second star coupler to be coupled into waveguide outputs of the second star coupler for dividing streams of the optical signal having different wavelengths; the horned waveguide is located between the waveguide input and the first slab waveguide or between the second slab waveguide and the waveguide outputs; and, thus, a flat-top pass-band of the optical signal is obtained through compensating central axes or a waveguide having an asymmetrical structure coordinated with a horned waveguide. Accordingly, a novel cyclic arrayed waveguide grating device using a horned waveguide is obtained. BRIEF DESCRIPTION OF THE DRAWINGS [0009] The present invention will be better understood from the following detailed descriptions of the preferred embodiments according to the present invention, taken in conjunction with the accompanying drawings, in which [0010] FIG. 1 is the view showing the present invention; [0011] FIG. 2A and FIG. 2B are the views showing the first preferred embodiment of the first star coupler and the second star coupler; [0012] FIG. 3A and FIG. 3B are the views showing the second preferred embodiment of the first star coupler and the second star coupler; [0013] FIG. 4A and FIG. 4B are the views showing the third preferred embodiment of the first star coupler and the second star coupler; [0014] FIG. 5 is the view showing the spectrum of the optical signal outputted; [0015] FIG. 6A to FIG. 6Y are the views showing the preferred shapes of the horned waveguides; [0016] FIG. 7A and FIG. 7B are the views of the first star coupler and the second star coupler of the first prior art; [0017] FIG. 8 is the spectrum view of the first prior art; [0018] FIG. 9A and FIG. 9B are the views of the first star coupler and the second star coupler of the second prior art; [0019] FIG. 10A and FIG. 10B are the views of the first star coupler and the second star coupler of the third prior art; [0020] FIG. 11 is the spectrum view of the second and the third prior arts. 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