Photonic integrated circuits for the extended short and mid-wave infrared (eS-MWIR) wavelength regime are crucial for potential applications including on-chip chemical and biological sensing and non-invasive medical diagnosis. The lack of high-performance lasers on an SOI wafer and material limitations in InP necessitate an alternative material system. A monolithic platform based on GaSb addresses these concerns through the tight integration of both passive and active components since it is an optimal material system for realizing long-wavelength lasers and photodetectors. In this work, we modeled and optimized various fabrication-compatible passive components including 1×2 power splitters/combiners based on directional coupler (DC), multimode interferometer (MMI), and Y-branch as well as a grating coupler on GaSb substrates at 2.56 μm.

Surface ridge waveguides designed on GaSb-based epitaxial layers are schematically shown in Figure 1(a). Figure 1(b) shows the effective refractive indices n_eff, of a few lowest-order guided modes as a function of the ridge width W, and the inset shows the mode profile of TE₀ at W = 4 μm. Figure 1(c) shows the transmission through the two output ports of DC-, MMI-, and Y-branch- splitters with 1-dB bandwidth, Δλ ~ 1 μm at a center wavelength of 2.56 μm. For all the splitters, we achieve 50:50 power splitting with an excess loss lower than 0.12 dB. For the grating coupler, a coupling efficiency of -5.4 dB and a 3-dB bandwidth of 80 nm are achieved at 2.56 μm. Details of the design and simulation results of all these passive photonic devices will be presented at the conference.