Single-platform Si photonic components for mid-infrared sensing and chemical imaging

摘要

Basic challenges for mid-infrared (MIR) Si photonics are developing of appropriate sources and detectors, detection sensitivity, size minimization and downscaling to a single-platform, spectral tunability. We address such challenges via proper design, modeling and material choice for a series of photonic structures. Our research is done in three steps: modeling, fabrication, characterization. The modeling starts with ellipsometry investigation of Si, Si_3N_4 and SiOx, to estimate the materials' complex dielectric function ε = ε_r +i·ε_i in MIR. The technique showed Si and SiN optical transparency in the range λ=4.5-6.5 μm, and negligible absorption for SiOx, which makes it appropriate for MIR photonics (Figure 1). Figure 2 demonstrates the device concept: MIR source emits electromagnetic field, which is coupled to/from a Si-waveguide (WG) via grating couplers. The WG performs as interaction medium between the propagating field and fluid atop the WG. It results in field attenuation, measured at the output, due to partial absorption by the fluid. To achieve efficient device performance, size, spectral tuning and evaluation of the attenuation, the structures were investigated by means of 3D photonic simulations.The structures were fabricated via the 200-mm-wafer-CMOS technology in Infineon involving deep-UV lithography and Bosch etching. PhC structures were fabricated as holes in a Si-slab with SiOx-filling to avoid residuals from the fluid into the holes, which modifies the photonic band gap and device sensitivity. Figure 3 shows SEM images of the structures. Our paper discusses the design, material characterization, single-platform integration of the source, WG and detector and first experiments with recently fabricated prototypes.