Biochemical spectroscopy based on germanium-on-insulator platform for mid-infrared optical sensor

We experimentally demonstrated the germanium (Ge)-on-insulator (Ge-OI) gas sensor at the mid-infrared (MIR) range for biochemical sensing. Based on the numerical simulation to optimize the dimension of the slot waveguide (SlW), we fabricated the waveguides as sensing elements using the wafer bonding. The Ge-OI SlW sensor had a low loss (1.88 dB/cm) and a high optical confinement factor (44.3%) in the sensing region. To accomplish a high performance with our Ge-OI SlW on an integrated chip within the compact footprint, the spiral Ge-OI SlW with a length of 20 mm on 3.5-mm
²
of the area was successfully fabricated. From the spectral response of the spiral waveguide, we verified a stronger lightmatter interaction between the SlW and CO
2
beyond 4.18 μm wavelength λ. Sensitivity and limit-of-detection (LoD) for the SlW were estimated to be 0.0885%/ppm and 8.5 ppm. Furthermore, we delivered the optimized dimensions of the Ge-OI waveguides for sensing other several gases. Finally, we benchmarked the performances of the biochemical sensors.