| Volume holographic grating couplers (VHGCs) are become increasingly attractive devices for the application of optical interconnects because of their higher preferential coupling, dry fabrication processing, and low cost. Moreover, for many practical cases for high-data rate interconnects, the needed gratings have limited spatial apertures and are usually illuminated by finite-width beams, such as Gaussian beams.; In order to design and characterize the performance of finite-size volume holographic gratings, a rigorous method of analysis is needed. In this work, the finite-difference frequency-domain (FDFD) method is applied to analyze rigorously both unslanted and slanted finite-number-of-periods gratings and is compared to the rigorous coupled-wave analysis (RCWA). Furthermore, the FDFD method is adapted for the analysis of VHGCs and is compared to the RCW A/leak-mode approach. Both output and input grating couplers, which are placed either in the waveguide film region or in the waveguide cover region, are investigated in this research. On the other hand, the DuPont OmniDex613 photopolymers are used to fabricate VHGCs in the experiment. In order to obtain a holographic grating with higher refractive-index modulation and thus higher diffraction efficiency, both the theoretical analysis of a nonlocal diffusion model solved rigorously by use of the finite-difference time-domain (FDTD) method and the experimental techniques of real-time diffraction-monitoring and angular-selectivity measurements are applied to study the optimization of holographic recording process. Finally, a VHGC in the waveguide cover region is designed, fabricated, and tested. |
