Gas Sensing Based On Fiber Microstructure And Fast Frequency-Modulated Laser Spectroscopy

In recent years, we have witnessed huge boosts of industrial production and improvement of living qualities, however, the accompanying environmental pollution caused by human activities has also become more serious, therefore, preventing pollution, protecting the environment and implementing sustainable development has become an urging issue of the society. As one of the most critical kinds of pollution, air pollution is affecting people’s health and living condition in many serious ways, therefore an effective, rapid way to measure air quality has great significance as a practical research subject.As a traditional way of gas sensing, TDLAS is suffering from shortage of interaction length, unportable due to the huge size of the volume of gas cell, and a limited frequency sweep speed. This article has provided a new method for gas sensing by combing fiber microstructure sensor and rapid frequency modulation with TDLAS, the details include:(1) We elaborated on the working principles of the gas sensing based on absorption spectrum, analyzing the trends of absorption spectrum under different conditions; introduced on the HITRAN The online simulation database and how it is used, provided the theoretical foundation of how to implement air quality measurement with the improved TDLAS(2) Designed and set up the fiber microstructure machining system, by attempting to machining Ordinary single-mode optical fiber and quartz capillary tube, we measured the machining results and optimized the system, analyzed the effect of different machining methods.Designed and manufactured a fiber microstructure sensor with a 1.4 meter photonic bandgap fiber as a micro gas cell to contain the air sample to be measured. We Set up and tested the performance of the optical system, the testing result have shown consistency with the HITRAN simulation result, proving that this sensor is able to detect ultra-low gas particle density.(3) Based on the traditional techniques for TDLAS, we used external radio frequency modulation module to perform rapid frequency sweep, and first time to our knowledge, detected Rapid Passage of the transmission spectrum of acetylene in the communication wavelength. By changing the experiment condition, we summarized the relationship between the gas particle density and when rapid passage occurs.By conducting multiple measurements on the the transmission spectrum of acetylene under different air pressure, we observed the relationship between the particle density and the refractive index of the gas sample. We simulated a dynamic procedure of the rapid changes of the gas environment with the electromagnetic valve, and measured the changes of the refractive index during the inflation process, the results could be explained by the Lambert-Beer law.