A photonic microsystem for hydrocarbon gas analysis by mid-infrared absorption spectroscopy

This paper demonstrates the functional integration of a linear variable optical filter (LVOF) and a gas cell at the wafer level, i.e. a gas-filled LVOF, where the resonator cavity of the filter is also used for storing the gas sample. A mm-level effective optical absorption path length is achieved from a μm-level physical path length, by exploiting multiple reflections from highly reflective Bragg mirrors and the high-order operation of the filter. The wideband spectral response of the device is ensured by using a tapered cavity, where the cavity length changes linearly along the length of the filter. Therefore, combined with a detector array and a light source, the gas-filled LVOF enables wideband operation and long absorption path in a single MEMS device, thus ensuring a highly sensitive on-chip gas absorption microspectrometer.