Apodized fully-etched surface grating coupler using subwavelength structure for standard silicon-on-insulator waveguide
We design and demonstrate the fully-etched apodized grating couplers based on the silicon-on-insulator (SOI) platform using subwavelength structure for both transverse electric (TE) and transverse magnetic (TM) modes operation. The subwavelength grating (SWG) is used to engineer the refractive index using second-order effective medium theory (EMT). The whole designing procedure is given in details, especially a feasible and programmable method is developed to precisely manipulate the coupling strength of each grating cycle. A perfect Gaussian output beam can be synthesized for the TE mode operation, achieving a field overlap up to 98.3% with the Gaussian fiber mode. The simulated peak coupling losses are −4.63 and −2.99 dB for the TE mode and the TM mode, respectively, which are comparable with conventional shallowly etched grating couplers, realizing a fabrication simplification without performance penalty. The measured peak coupling loss is −7.6 dB for the TE mode coupler with a 1 dB bandwidth of 45 nm, and −6.1 dB for the TM mode coupler with a 1 dB bandwidth of 34 nm.
KeywordsGrating couplers Silicon-on-insulator Sub-wavelength grating Apodized Fully-etched Second-order EMT
This work was supported by the National Hi-Tech Research and Development Program of China (Grant No. 2008AA1Z207), Natural Science foundation of Hubei Province, China (Grant No. 2010CDB01606), Fundamental Research Funds for the Central Universities (HUST: 2016YXMS027), Huawei innovation Research Program (YJCB2010032NW, YB2012120133, YB2014010026, and YB2016040002) and Scientific Research Foundation for the Retuned Overseas Chinese Scholars.
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