Modeling and design of planar slanted volume holographic gratings for wavelength-division … D. M. Paiand K. A. Awada, “Analysis of dielectric gratings of arbitrary profiles and … Modeling and design of planar slanted volume holographic gratings for wavelength-division- multiplexing applications Modeling and design of planar slanted volume holographic gratings for wavelength-division-multiplexing applications Modeling and design of planar slanted volume holographic gratings for wavelength-division- multiplexing …

1. Introduction For previous substrate-guided-wave holograms for wavelength divisiondemultiplexing~WDDM! ,1,2 opti- calsignalsof various wavelengths were dispersed by an input holographic grating, propagated withina waveguidingplate with total internal reflection, and then coupled out of the substrate by output holographic gratings. The interchannel wavelength sep- arationofsuchaWDDM is totally dependent on the length between the input and the output couplers. To obtain a smaller channel wavelength spacing such as 0.8 nmrequiresuseofa long substrate. Meanwhile, a lens array is always needed to couple the output optical signals with different wavelengths into a fiber array. Recently, path-reversed substrate-guided- wave optical interconnects for dense WDDM were proposed,3 asshownin Fig. 1. In this approach, the beveled edge providesawayto overcome the limitation of the critical angle of thewaveguiding substrate and to enhance the dispersion of the holographic grating. The grating is a path-reversed structure because the optical signals are dispersed by the output waveguide hologram for which the input light comes from the waveguidingplate and the diffracted light goes into the air. Only one lens is needed to couple the dis- persedoptical signals into their designated fibers. Moreover, multiple fan-outs can be realized by inte- grationofa cascaded holographic grating array on the samewaveguiding plate.3 In the research reported in Ref. 3, two of the present authors investigated design issues of volume holographic gratings for WDDM in terms of dispersion and bandwidth and demonstrated experimental results near 800-nmwavelength; atheoretical interpretation of the experimental results of the diffraction efficiency was not given there. As the optical signals go from larger to lower refractive-index media, backward diffraction is encountered.3,4 Rigorous coupled-wave analysis~RCWA! has proved to be a powerful tool to simulate diffraction efficiency of gratings. In this paper we develop an efficient and practical method to solve the complicated linear equations and to overcome the instability problem for thick gratings.5,6 Experi- mentswerecarried out to verify the validity of our theoretical simulations at center wavelengths of 1555 nmand 800nm. When this research was performed, J. Liuand R. T. Chenwere

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