Silicon photonic sensors, photodetectors, and spectrometers for the mid-infrared

Mid-infrared (MIR) silicon photonics has seen rapid development in recent years amidst interest in developing integrated photonic systems that could be used for applications in sensing and communications. In particular there is a focus on MIR absorption spectroscopy, since many gases, chemicals, and biological molecules exhibit strong and unique absorption features in this part of the electromagnetic spectrum (approximately 2-16 μm). Silicon photonics is offering an opportunity to create fully integrated MIR sensing systems on silicon chips, which can benefit from existing silicon manufacturing infrastructure so that sensor chips can be fabricated at low cost in high volumes. To achieve this low loss waveguide platforms must be developed that span the MIR, and passive components, light sources, modulators, photodetectors, and spectrometers must be developed.

This talk will give an overview of our group’s recent work in pursuit of that goal. Firstly, we show a SOI waveguide Fourier transform spectrometer based on a single thermally tunable Mach-Zehnder interferometer (MZI), working in the range 3.7-3.9 μm, whose mid-IR bandwidth is only fundamentally limited by the bandwidths of the individual components used to build the MZI. To broaden the operating range of such devices, we have also experimentally demonstrated for the first time planar “endlessly” single-mode waveguides in SOI, which are shown to have low propagation loss and to be single-mode between 1.95 µm and 3.8 µm, i.e. an octave of frequency. For on-chip mid-IR spectrometers to become fully integrated, waveguide integrated detectors will also be required. Performance results on two types of group-IV material detectors will be presented: i) c-Si and a-Si waveguide integrated bolometers working at 3.8 µm, and ii) high performance Ge-on-SOI detectors working at 2 µm and 3.8 µm. Finally, chemical sensors integrated with SOI waveguides will be shown.