Group IV mid-IR photonics

Silicon and germanium are transparent up to approximately 8 μm and 15 μm, respectively, thus offering a range of applications in biochemical and environmental sensing, medicine, astronomy and communications [1]. Silicon-on-insulator (SOI), can be used only up to 4 μm due to the high absorption loss of silicon dioxide, and therefore alternative material platforms have to be utilized for longer wavelengths. Also, to fully exploit the transparency range of SOI, 400 or 500 nm thick overlayers need to be used rather than the most popular 220 nm platform [2]. In this paper we report record low loss MIR SOI strip and slot waveguides, as well as Vernier racetrack configurations. If the buried oxide can be removed and replaced with air, such a platform would be transparent up to 8 μm. We report a robust design based on single etch suspended Si waveguides. Ge-on-Si waveguides have already been demonstrated with losses of 2.5–3.0 dB/cm at λ=5.8 μm by Chang et. al [3] and Shen et. al [4]. We report a record low loss in Ge-on-Si and a demonstration of all optical modulation in such waveguides. Although Si is transparent beyond 1.1 μm, it has been demonstrated that it can be used as a photodetector if mid-bandgap states are created by ion implantation. In this paper we show that detection in Si can be extended to up to 2.5 μm by implantation of SOI waveguides with boron. Finally, we also report theoretical analysis of electroabsorption and electrorefraction in Ge.