Mid-IR is an interesting wavelength range for highly-selective molecular sensing. Infrared spectroscopy is a widely used characterisation technique used to probe the chemical nature of matter. Infrared spectroscopy, in principle, relies on the molecular absorption. Since fundamental absorption of many molecules is in the mid-IR range, this region of wavelengths is also termed “fingerprint” region, where molecules have distinct absorption of particular energy of photon matching its vibrational energy. Though the technique is widely used, it requires bulky optic and impossible to use in the field; for example, agricultural field and storage. We are building photonic circuits that operate in the short-wave and long-wave IR wavelength range (>2000 nm) for gas sensing.

Short-to-Long- IR spectrum is interesting for many applications, in particular, for sensing hazardous gases in the environment, chemical and bio-sensing, telecommunication, and strategic security applications. So far, research in this wavelength range is primarily done on Silicon-on-Insulator (SOI) platform, which is not an ideal material platform. Silicon is transparent until 8 micrometres and Silicon dioxide that is used as bottom clad starts absorbing beyond 3 micrometres; so effectively the SOI technology can be only used until 3 micrometres.

Germanium, a CMOS compatible material, has wider transparency extending until 15 micrometre that makes it an ideal platform for mid-IR integrated photonics. We are exploring Ge as a waveguide platform for multiple applications, including, mid-IR. In addition to mid-IR, Ge offers other advantages such as active devices (photodetector, light-modulators, Ge-alloy laser) and nonlinear optical platform that is also investigated. Under this research, we develop deposition techniques and waveguide engineering for various requirements discussed above.