Germanium-on-Silicon (Ge-on-Si) platform has been demonstrated as an excellent candidate for mid-infrared photonics applications, including on-chip mid-infrared spectroscopy and biochemical sensing. However, this platform is often saddled by high propagation loss due to a combination of threading dislocation defects at the Ge/Si interface, absorption in the silicon for λ < 8 μm, and surface scattering due to sidewall roughness. This work investigates the effects on loss reduction through different annealing techniques on Ge-on-Si waveguides fabricated using CMOS-compatible processes. We explore the use of local laser annealing at waveguide sidewalls, whereby the fluence was varied. A non-local annealing technique in hydrogen ambient was also employed as comparison. The propagation losses for wavelengths, ranging from λ = 5 μm to λ = 11 μm, were systematically characterized by fabricating waveguide and grating coupler structures on the same chip. Cutback measurements were performed by varying the waveguide length (of the same width) from L = 1 mm to L = 4 mm. Both hydrogen and laser annealing experiments show marked reduction in the propagation loss, by up to 27% and 46% respectively. This finding paves the way for post-processing techniques to reduce propagation loss in Ge-on-Si platform, which will enable various on-chip mid-IR applications in the future.

Microelectromechanical system (MEMS)-based thermal emitter is a key component in an optical sensor to provide broadband emission at mid-infrared wavelengths, where a lot of molecules have their unique absorption profile. However, the thermal emission from a MEMS emitter is typically fixed at a specific spatial coordinate. In this work, a MEMS thermal emitter with piezoelectric actuation to realize active tuning is demonstrated. Thermal emission comes from a doped silicon layer acting as a resistive heater. Piezoelectric actuation is enabled by an aluminum nitride layer on a designed cantilever. The devices are fabricated on a complementary metal-oxide semiconductor (CMOS)-compatible process line. The fabricated thermal emitter at the tip of the cantilever generates broadband MIR thermal emission with spectrum peaked around 10 µm wavelength, and piezoelectric actuation with a displacement of more than 20 μm. The work paves the way towards self-adaptable MEMS directional emitter for various applications including chemical/gas sensing.