Multichannel Gas Absorption Spectrometer Based on On-Chip Frequency-Modulated Continuous-Wave Interference System

Absorption spectroscopy based on frequency-modulated continuous-wave (FMCW) technology is characterized by a wide measuring range, high detection sensitivity, and high sensing speed. These features enable sensing of multiple target points, and continuous real-time gas monitoring. In this article, an on-chip FMCW multichannel absorption spectrometer is designed for the simultaneous measurement of optical path and gas absorption spectra. The wide tuning range of FMCW facilitates the measurement of multiple absorption bands of gas molecules under test. Based on the characteristics of frequency division multiplexing, the gas absorption spectra corresponding to different points can be detected simultaneously. Frequency modulation nonlinearity is corrected by introducing an auxiliary interference optical path with a fixed delay of 4 m, and the dual-interference optical path of the system is integrated into a silicon chip. Three-way parallel sensing experiments are carried out to demonstrate the efficacy of the proposed spectrometer. The results show that the coherent average measurement accuracy of gas absorption peak wavelength is better than 0.002 nm, and the optical path measurement accuracy is better than 25 μm. The system offers several advantages such as excellent integrability, wide band operation, high precision and multichannel synchronous online measurement. Due to these features, this system has high practical value in the field of gas sensing.