Germanium based optical waveguides for sensing in the mid-infrared

This paper presents recent work on the design and characterization of germanium-on-silicon (Ge-on-Si) waveguides, multimode interferometers, and grating couplers in the 7.5-8.5 mm wavelength range. The development of photonic integrated circuits (PICs) that can operate in the mid-infrared wavelength rage (3-14 mm) is attracting great interest in the field because of the potential to address a broad range of applications related to the on-chip sensing of gases, chemicals, and biological molecules. Ge-on-Si is a very promising material platform for use in the mid-infrared because of the wide transparencies of Si (1.1 to ~8 mm) and Ge (2 to ~16 mm). This work extends its wavelength range of operation up to ~8 mm for the first time. Experimental techniques for characterizing PICs in this challenging range will be discussed, as will prospects for using Ge-on-Si at even longer wavelengths. Finally, the ongoing development of alternative Si and Ge based mid-infrared material platforms will also be discussed.