Grating couplers beyond silicon TPA wavelengths based on MPW

Abstract

Silicon photonic integrated circuits (PICs) at 2.2–2.5 μm wavelengths have great potential in applications of nonlinear optics, spectroscopy, and light detection and ranging, due to the merits of negligible two-photon absorption and moderate Rayleigh scattering from the waveguide sidewall roughness. As key components in silicon PICs, grating couplers at such wavelengths have been previously studied. However, previous devices were mainly developed based on the e-beam lithography (EBL) process, being challenging for high-volume and low-cost fabrication. Here, we demonstrated focusing subwavelength grating couplers at the spectral range of 2.2–2.5 μm based on a multi-project wafer (MPW) service. A mean coupling efficiency of −7.77 dB with a standard deviation of 0.5 dB at a center wavelength of 2.36 μm and a mean 3 dB bandwidth of 85 nm was experimentally achieved. Moreover, we studied the reproducibility of the fabricated grating couplers from die to die, as well as the grating design and fiber coupling tolerance. Our study is expected to provide a useful guideline for developing short-wavelength mid-IR devices based on MPW.