Mid-infrared SOI waveguide thermo-optic Fourier-transform spectrometer

The mid-infrared (mid-IR) is an important wavelength range for vibrational absorption spectroscopy (e.g. for gas sensing, medical diagnostics, environmental monitoring), and thus there is a strong need for small and stable on-chip spectrometers. It is also desirable for it to be inexpensive to fabricate and for it to be able to perform high-resolution measurements over a wide bandwidth. To this end, we demonstrate two kinds of mid-IR thermo-optic type Fourier Transform spectrometers (FTS). Both variations of the device are designed to target a central wavelength of 3.8 μm and are based on the silicon-on-insulator platform. These two devices are verified by using them to retrieve the spectrum of a quantum cascade laser when it is tuned to different wavelengths. They have the potential to achieve higher resolution and bandwidth through subsequent design optimization, and could in future be integrated with mid-infrared photodetectors.