光纤模式混合器在差分吸收光谱系统中的应用研究

Application of fiber mode mixer in differential optical absorption spectroscopy

差分吸收光谱技术(DOAS)已经发展为监测对流层痕量气体的重要技术,一般采用光电倍增管(PMT)作为探测器.由于光电二极管阵列(PDA)在多道探测及像元灵敏性方面的优势,采用PDA代替扫描探测装置将能改善系统剩余噪声,提高系统性能.但实际应用中由于使用收发一体Cassegrain望远镜造成灯谱与大气谱结构不统一,在消除PDA像元间差异的过程中给系统带来误差,从而导致剩余噪声的标准偏差达到1.4×10-3.根据光纤扰模原理在系统中加入自制光纤模式混合器很好的解决了上述难题,在实际应用中起到良好的作用,系统剩余噪声的标准偏差为3.4×10-4.

Differential optical spectroscopy （DOAS） has become an important method for determination of tropospheric trace gases, using the photomultiplier （PMT） as detector. The use of photodiode array （PDA） detectors enhances DOAS system considerably owing to PDA＇ s higher sensitivity and advantage in multi-channel application. When the PMT is simply replaced by PDA, a difference between lamp spectrum and atmosphere spectrum, as will as unwanted standard deviation of residual noise as much as 1.4× 10^-3 appears after corrected for the pixel response. A fiber mode mixer, based on fiber disturb mode principle was developed and tested. This new device reduces the standard deviation to 3.4 × 10^-4 in field experiments.