A novel hybrid diffraction method is proposed to simulate the demultiplexing of an etched diffraction grating (EDG). The scalar diffraction formula is adopted to simulate the propagation of the light field in the free propagation region (FPR), and a rigorous coupled-wave analysis (RCWA) is used to calculate the polarization-dependent diffraction near the grating. The hybrid diffraction method takes the advantages of both the conventional scalar diffraction method and the rigorous coupled-wave analysis and can simulate accurately the imaging property as well as the polarization-dependent efficiency of an EDG demultiplexer. Compared with the conventional scalar diffraction method, the proposed hybrid diffraction method reduces greatly the design error in, for example, the polarization-dependent insertion loss.
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