A high efficiency silicon nitride waveguide grating coupler with a multilayer bottom reflector

Jianxun Hong,Andrew M Spring,Shiyoshi Yokoyama,Feng Qiu

doi:10.1038/s41598-019-49324-5

Jianxun Hong, Andrew M Spring + Show 2 more

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We propose a high efficiency apodized grating coupler with a bottom reflector for silicon nitride photonic integrated circuits. The reflector consists of a stack of alternate silicon nitride and silicon dioxide quarter-wave films. The design, fabrication and optical characterization of the couplers has been presented. The measured fiber to detector insertion loss was −3.5 dB which corresponds to a peak coupling efficiency of −1.75 dB. A 3 dB wavelength bandwidth of 76.34 nm was demonstrated for the grating coupler with a 20-layer reflector. The fabrication process is CMOS-compatible and requires only a single etching step.

Highlights

Silicon nitride (SiNx) has recently attracted increasing attention and has emerged as an alternative material for photonic integrated circuits (PICs)[1]
Linear silicon grating reflectors have been adopted to achieve a higher directionality[2,16]. This involves several pattern steps and multiple waveguide layers. Another problem is that the field distribution of the coupled out beam from a uniform SiNx grating coupler does not match the field distribution of a single mode fiber (SMF)[2,11]
We have introduced a bottom multilayer reflector and period apodization to improve the coupling efficiency of the SiNx grating couplers

Summary

Introduction

Silicon nitride (SiNx) has recently attracted increasing attention and has emerged as an alternative material for photonic integrated circuits (PICs)[1]. One of the problems is that a majority of the optical power is reflected downward into the substrate and dissipates Bottom reflectors such as a metal mirror[12,14] and distributed Bragg reflector[3,9,15] have been utilized to improve the coupling efficiency of silicon and silicon nitride grating couplers. Linear silicon grating reflectors have been adopted to achieve a higher directionality[2,16] This involves several pattern steps and multiple waveguide layers. Another problem is that the field distribution of the coupled out beam from a uniform SiNx grating coupler does not match the field distribution of a single mode fiber (SMF)[2,11]. The main advantages of the proposed waveguide grating coupler are a high coupling efficiency, versatile design, simple fabrication and complementary metal-oxide semiconductor (CMOS) compatibility

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