Novel gas sensor combined active fiber loop ring-down and dual wavelengths differential absorption method

Abstract

A novel active fiber loop ring-down gas sensor combined with dual wavelengths differential absorption method is proposed. Two Distributed Feedback Laser Diodes (DFB LDs) with different wavelengths are employed. One LD whose wavelength covered with the absorption line of target gas is used for sensing. Another LD whose wavelength is centered outside the absorption line is used for reference. The gas absorption loss can be obtained by differencing the reference signal and sensing signal. Compared with traditional method of one wavelength employed, it can eliminate the influence of the cavity loss variety and photoelectric device drift in the system efficiently. An Erbium Doped Fiber Amplifier (EDFA) with Automatic Gain Control (AGC) is used to compensate the loss of the light in the ring-down cavity, which will increase the cavity round trips and improve the precision of gas detection. And two fiber Bragg gratings (FBGs) are employed to get rid of amplified spontaneous emission (ASE) spectrum noise as filters. The calibrating ethyne samples of different concentrations are measured with a 65 mm long gas cell in order to evaluate the effect of reference. The results show the relative deviation is found to be less than ± 0.4% of 0.1% ethyne when a certain additional loss from 0 to 1.2dB is introduced to the cavity and the relative deviation of measured concentration is less than ± 0.5% over 24 hours.

Continuous-Wave Frequency-Shifted Interferometry Cavity Ring-Down Gas Sensing With Differential Optical Absorption

“…Hence, we can obtain (8), which shows that the relationship between absorption loss and acetylene concentration is 7.8125%/dB. The results are in good agreement with Beer-Lambert's law and the latest database of HITRAN12 [26], which showed both the strength of the material for a monochromatic light absorption and its concentration have a linear relationship [17] whose slopes are closely related to the measurement system. The calculated minimum detectable [27] acetylene concentration is 105.25 ppm in our experimental system C ¼ 7:8125:…”

“…These amplifier methods resulted in the degradation of the inherent loss in cavity. In a recent paper, Zhao et al [17] combined FCRD and dual-wavelength differential absorption method for gas detection. Compared with the traditional method that employed only one wavelength, the dualwavelength method can efficiently eliminate the influence of the cavity loss variety as well as the photoelectric device drift in the system.…”

Optical technology for detecting the decomposition products of SF6: a review

“…70 However, the detection precision of FLRDS cannot currently meet the requirement of SF 6 decomposition products. 68,71,72 Thus, further detailed research is required.…”

Fiber loop ring-down cavity integrated U-bent single-mode-fiber for magnetic field sensing

“…Consequently, the result is immune to the intensity fluctuation of the light source as well as other external loss contributions, thus enhancing the stability of the sensing system [2]. Integrated with various sensing heads, FLRD can realize measurements of different parameters, including refractive index of liquids [3][4][5][6], pressure [7,8], curvature [9], macro-bend loss of single-mode fiber (SMF) [10], and the concentration of gas [11]. In particular, by coating a piece of etched SMF with magnetic fluid (MF), a kind of liquid nanomaterial with outstanding magneto-optical effects, magnetic field sensing based on the FLRD technique was recently demonstrated by Wang et al [12] and Shen et al [13].…”