Efficient 5 . 2 μ m wavelength fiber-to-chip grating couplers for the Geon-Si and Geon-SOI mid-infrared waveguide platform

We present the design, fabrication and characterization of efficient fiber-to-chip grating couplers on a Germanium-on-Silicon (Ge-on-Si) and Germanium-on-silicon-on-insulator (Ge-on-SOI) platform in the 5 μm wavelength range. The best grating couplers on Ge-on-Si and Ge-on-SOI have simulated coupling efficiencies of -4 dB (40%) with a 3 dB bandwidth of 180 nm and -1.5 dB (70%) with a 3 dB bandwidth of 200 nm, respectively. Experimentally, we show a maximum efficiency of -5 dB (32%) and a 3 dB bandwidth of 100 nm for Ge-on-Si grating couplers, and a -4 dB (40%) efficiency with a 3 dB bandwidth of 180 nm for Ge-on-SOI couplers. © 2017 Optical Society of America OCIS codes: (050.2770) Gratings; (130.3120) Integrated optics devices. References and links 1. P. A. Werle, “Review of recent advances in semiconductor laser based gas monitors,” Spectrochim. Acta Mol. Biomol. Spectrosc. 54(2), 197–236 (1998). 2. J. Hodgkinson and R. P. Tatam, “Optical gas sensing : a review,” Meas. Sci. 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