Frequency Locking Technology of Mid-Infrared Quantum Cascade Laser Based on Molecule Absorption
WANG Chun-hui1, 2, YANG Na-na2, 3, FANG Bo2, WEI Na-na2, ZHAO Wei-xiong2*, ZHANG Wei-jun1, 2
1. School of Environmental Science and Optoelectronics Technology, University of Science and Technology of China, Hefei 230026, China
2. Anhui Institute of Optics and Fine Mechanics, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, China
3. Science Island Branch of Graduate School, University of Science and Technology of China, Hefei 230026, China
Abstract：Quantum cascade laser (QCL) plays an important role in mid-infrared detection because of the high output power and wide coverage range. However, due to the fluctuation of laser wavelength caused by the sensitivity of the laser to changes in the external environment, the peak-to-peak frequency drift is as high as 180 MHz within the observed time of 400 s, which affects the performance of the QCL to some extent and reduces the accuracy of molecular spectral detection. Frequency locking has been widely applied to the mid-infrared areas. In this paper, a QCL frequency locking system based on gas absorption was developed. Taking 5.3 μm QCL as an example, the laser frequency is locked to the absorption peak of nitric oxide (NO) molecule at 1 875.812 8 cm-1 by modulating laser wavelength. The principle of error signal generation was introduced, and the advantages of using the third harmonics as an error signal for frequency locking were analyzed. The NO absorption signal with a high signal-to-noise ratio (SNR) was obtained using a NO absorption cell with a length of 30 cm. The conversion coefficient between the third harmonic voltage and the laser frequency was calibrated. The locking process was introduced in detail and explored the significance of proportional, integral, differential parameters of the feedback loop during the locking process, and the locking parameters had been given in detail. Disturbing the locking system, with the recovery time better than 40 ms demonstrate that the locking system can respond quickly and remain stable against external disturbances. In addition, the stability of the frequency locking system was also verified by the fluctuation of the error signal with the voltage-frequency conversion coefficient. A frequency drift better than 673 kHz (1σ, 10 ms integration time) was achieved. The Allan variance analysis results show that when the integrated time is extended to 100 s, the frequency drift is lower than 4.5 kHz (corresponding to stability of 8×10-11), effectively improving the laser frequency's long-term stability. This method of directly modulating laser frequency without an external modulator simplified the system and improved the stability of the optical detection system.
Key words：Quantum cascade laser; Mid-infrared; Frequency locking; Proportional integral derivative control; Wavelength modulation
[1] Jerome Faist, Federico Capasso, Deborah L Sivco, et al. Science 1994, 264(5158): 553.
[2] Gordon I E, Rothman L S, Hargreaves R J, et al. Journal of Quantitative Spectroscopy & Radiative Transfer, 2022, 277: 107949.
[3] Pierre Jouy, Markus Mangold, Béla Tuzson, et al. Analyst, 2014, 139(9): 2039.
[4] Irène Ventrillard, Paula Gorrotxategi-Carbajo, Daniele Romanini. Applied Physics B, 2017, 123(6): 180.
[5] Zhou Sheng, Han Yanling, Li Bincheng. Applied Physics B, 2018, 124(2): 27.
[6] MA Yu-fei, HE Ying, YU Xin, et al（马欲飞，何 应，于 欣，等）. Acta Physica Sinica（物理学报）, 2016, 65(6): 060701.
[7] Ulf Bressel, Ingo Ernsting, Stephan Schiller. Optics Letters. 2012, 37(5): 918.
[8] Borri S, Galli I, Cappelli F，et al. Optics Letters，2012, 37(6): 1011.
[9] Bartalini S, Cancio P, Giusfredi G，et al. Optics Letters，2007, 32(8): 988.
[10] LI Chuan-liang, DENG Lun-hua, YANG Xiao-hua, et al（李传亮，邓伦华，杨晓华，等）. Acta Optica Sinica（光学学报）, 2009, 29(10): 2822.
[11] KANG Peng, SUN Yu, WANG Jin, et al（康 鹏，孙 羽，王 进，等）. Acta Physica Sinica（物理学报）, 2018, 67(10): 104206.
[12] MENG Teng-fei, WU Yue-long, JI Zhong-hua, et al（孟腾飞，武跃龙，姬中华，等）. Chinese Journal of Lasers（中国激光）, 2010, 37(5): 1182.
[13] Cappelli F, Galli I, Borri S, et al. Optics Letters 2012, 37(23): 4811.
[14] Alan A Madej, A John Alcock, Andrzej Czajkowski, et al. Journal of the Optical Society of America B, 2006, 23(10): 2200.
[15] Hemanth Dinesan, Eugenio Fasci, Antonio Castrillo. Optics Letters, 2014, 39(7): 2198.
[16] Shailendhar Saraf, Paul Berceau, Alberto Stochino, Optics Letters, 2016, 41(10): 2189.
[17] Sow P L T, Mejri S, Tokunaga S K, et al. Applied Physics Letters, 2014, 104(26): 264101.
[18] Michael G Hansen, Evangelos Magoulakis, Chen Qunfeng，et al. Optics Letters, 2015, 40(10): 2289.
[19] Bérengère Argence, Bruno Chanteau, Olivier Lopez, et al. Nature Photonics, 2015, 9(7): 456.
[20] Yin Wang, Michal Nikodem, Eric Zhang, et al. Scientific Reports, 2015, 5: 9096.
[21] Luo Han, Hua Xia, Tao Pang, et al. Infrared Physics & Technology, 2018, 91: 37.
[22] Chu C Teng, Chao Yan, Aric Rousso，et al. Optics Express, 2021, 29(2): 2769.
[23] William L, Luyben. Industrial & Engineering Chemistry Research, 1996, 35(10): 3480.
[24] Zhao Gang, Thomas Hausmaninger, Ma Weiguang, et al. Optics Letters, 2017, 42(16): 3109.
[25] Allan D W. Proceedings of the IEEE, 1966, 54(2): 221.
