Abstract
A grating coupler is an essential building block for compact and flexible photonics integration. In order to meet the increasing demand of mid-infrared (MIR) integrated photonics for sensitive chemical/gas sensing, we report a silicon-on-insulator (SOI) based MIR subwavelength grating coupler (SWGC) operating in the 3.7 μm wavelength range. We provide the design guidelines of a uniform and apodized SWGC, followed by numerical simulations for design verification. We experimentally demonstrate both types of SWGC. The apodized SWGC enables high coupling efficiency of -6.477 dB/facet with 3 dB bandwidth of 199 nm, whereas the uniform SWGC shows larger 3dB bandwidth of 263.5 nm but slightly lower coupling efficiency of -7.371 dB/facet.
Highlights
Mid-infrared region is abundant of vibrational fingerprints of chemical bonds of many kinds, which are attractive to molecular identification and detection [1]
To make the photonics sensors compact even portable in the near future, efficiently converting the external light source into the in-plane waveguide is of much significance in terms of packaging flexibility, wafer level testing, etc
Applying Particle Swarm Optimization (PSO) [49] in the finite-difference time-domain (FDTD) simulation, taper length of 20 μm can be guaranteed with high transmission above 90% around 3.7 μm
Summary
Mid-infrared region is abundant of vibrational fingerprints of chemical bonds of many kinds, which are attractive to molecular identification and detection [1]. There are several near- and mid-infrared grating couplers reported recently [9,10,11,12,13,14,15,16,17,18,19], others such as applied in the integrated evanescent field sensor [20], or in the integrated ring resonator system [21]. The simulation designs such as exploiting the SiGe coupler on the suspended waveguide at 4.5 μm [15], employing silicon-on-sapphire (SOS) with bottom reflector at 2.7 μm [14] and the Ge-on-Si3N4 platform with high index prism to suppress the dependence of diffracted angle on wavelength at 3.8 μm [16], theoretically open up more opportunities for efficient near- and mid-infrared grating couplers
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