Wide absorption spectrum measuring methods by DFB-LDs in water vapor detection system

Abstract

Two measuring methods of the wide absorption spectrum by distributed feedback laser diodes (DFB-LDs) are presented in detecting the water vapor absorption line. One is the subsection scanning method, and it takes advantage of the wide spectrum tuning range by the temperature modulation and fast spectrum tuning speed by current modulation. Specifically, this method is realized by dividing a target spectral region into several sections which correspond to the specific temperature of DFB-LD, scanning every section by current modulation for hundreds times, and averaging the data to raise the signal to noise ratio (SNR), then combining all sections to get the whole spectrum. An accuracy of 10 ppmv had been obtained in the measurement of water vapor with a 10-cm path length by this method. Another is data fitting method, based on the absorption line-shape function; the absorption line can be described by fitting with partial measured data. The fitting absorption line was fitted well with the measured data, and the square of correlation coefficient (R-square) was no less than 0.99.

Keywords

DFB-LD / wide spectrum / subsection scanning / data fitting / water vapor detection

References

[1] Zhang S C, Wang Q, Zhang Y, Song F J, Chen K, Chou G Q, . Water vapor detection system based on scanning spectra. Photonic Sensors, 2012, 2(1): 71-76.

[2] Y. Zhang, J. Chang, Q. Wang, S. C. Zhang, and F. J. Song, “The theoretical and experimental exploration of a novel water-vapor concentration measurement scheme based on scanning spectrometry,” 2011 International Conference on Electronics and Optoelectronics, China, Jul. 29–31, 2011.

[3] Wang L M, Zhang Y J, Li H B, Zhou Y, He Y, Liu W Q. Study on long distance transmission technique of weak photocurrent signal in laser gas sensor. Chinese Optics Letters, 2012, 10(4): 042802.

[4] Werle P. A review of recent advances in semiconductor laser-based gas monitors. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 1998, 54(2): 197-236.

[5] Weldon V, McInerney D, Phelan R, Lynch M, Donegan J. Characteristics of several NIR tuneable diode lasers for spectroscopic based gas sensing: a comparison. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2006, 63(5): 1013-1020.

[6] Liu X, Jeffries J B, Hanson R K. Measurements of spectral parameters of water-vapour transitions near 1388 and 1345 nm for accurate simulation of high-pressure absorption spectra. Measurement Science and Technology, 2007, 18(5): 1158-1194.

[7] Chen W G, Yun Y X, Pan C, Sun C X. Analysis of infrared absorption properties of dissolved gases in transformer oil. Proceeding of the Chinese Society for Electrical Eegineering, 2008, 28(16): 148-153.

[8] J. Chang, G. P. Lv, G. Q. Zhou, K. Chen, Y. Zhang, Z. L. Wang, et. al., “Application of wavelength scanning for measuring water vapour concentration by distributed laser diode,” Procceeding of 5th Photonic Fiber and Crystal Devices: Advances in Materials and Innovations in Device Applications, USA, Aug. 21, 2011.

[9] Wang Q, Chang J, Zhu C G, Li C, Song F J, Liu Y N, . Detection of water vapor concentration based on differential value of two adjacent absorption peaks. Laser Physics Letters, 2012, 9(6): 421-425.

[10] J. Chang, Q. J. Huang, X. Z. Liu, K. Chen, H. T. Chang, G. P. Lv, et al., “Noise investigation and signal process in fiber optic gas sensor with wavelength modulation of the DFB laser diode,” Proceeding of 6th Photonic Fiber and Crystal Devices: Advances in Materials and Innovations in Device Applications, USA, Aug. 12, 2012.