Perpendicular Grating Coupler Based on a Blazed Antiback-Reflection Structure

Silicon photonic grating couplers are demonstrated featuring a perfect vertical coupling and predicted coupling efficiencies of 87% and 78% with an apodized and a standard periodic structure, respectively. Vertical coupling is usually difficult to be achieved with standard diffraction gratings, since both the forward and backward scattered light meet the Bragg condition alike. In this work a vertical grating coupler which satisfies both high directionality (> 97%) and low back-reflection (< 1%) simultaneously is realized using a blazed sub-wavelength structure. The measured maximum coupling efficiencies with a standard single-mfiber are −1.5 dB and −2.2 dB for apodized and periodic structures, respectively. The suggested structure offers an ultimate solution for compact coupling schemes in Si photonics, since it meets the most important needs of grating couplers, which are directionality, ease of fabrication, and a possibility to vertically couple. The vertical grating coupler are fabricated on a silicon-on-insulator wafer with a 220 nm-thick silicon layer, relying only on a 2-step etching technology.

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