Spectral Demodulation System Based on Two Transmission Volume Bragg Gratings

Abstract

In this paper, a fiber grating demodulation system based on two transmission volume Bragg gratings (VBGs) was proposed. In order to resolve the problem that the spectral resolution of the present fiber grating demodulation system is not high enough, the two transmission VBGs were applied to improve the spectral resolution and reduce the volume of the spectrometer. The diffraction characteristics of the transmission VBGs were analyzed, and the optical path of the two transmission VBGs demodulation system was designed based on the diffraction characteristics. The grating constant, lens parameters, and aberration correction of the system were analyzed and calculated. The calculation showed that the theoretical wavelength range of the demodulation system was from 1525 nm to 1565 nm and the theoretical optical resolution was 60 pm when the grating constant was 0.9168, the angle between two transmission VBGs was 89°, the focal length of the collimator was 60 mm, and the focal length of the imaging lens was 131.5 mm. The aberration of the system was well corrected by using a lens as the collimator and a reflector as the imaging lens. The system principle prototype was assembled and calibrated, and its performances were experimentally investigated. The results showed that the spectrometer worked stably, with a wavelength range from 1525 nm to 1565 nm, an optical wavelength resolution of 65.3 pm, and a high demodulation speed of 10 kHz.

Keywords

Spectrometer / diffraction / transmission volume Bragg grating / fiber grating

References

[1] Liu T G, Wang S, Jiang J F, Liu K, Yin J D. Research progress of optical fiber sensing technology in aerospace. Chinese Journal of Scientific Instrument, 2014, 35(8): 1681-1692.

[2] Deng H Y, Rao Y J, Ran Z L, Liao X, Liu W J. Photonic crystal fiber based Fabry-Perot sensor fabricated by using 157nm laser micromachining. Acta Optica Sinica, 2008, 28(2): 255-258.

[3] Favero F C, Araujo L, Bouwmans G, Finazzi V, Villatoro J, Pruneri V. Spheroidal Fabry-Perot microcavities in optical fibers for high-sensitivity sensing. Optics Express, 2012, 20(7): 7112-7118.

[4] S. Liu, Y. P. Wang, C. R. Liao, Z. Y. Li, and K. M. Yang, et al. “High-sensitivity strain sensors based on in-fiber reshaped air bubbles,” in Fifth Asia Pacific Optical Sensors Conference, Korea, May 20–22, 2015, pp. 96550A-1–96550A-4.

[5] Li Y H, Yang M W, Liao C R, Wang D N, Lu J, Lu P X. Prestressed fiber Bragg grating with high temperature stability. Journal of Lightwave Technology, 2011, 29(10): 1555-1559.

[6] Niu W Q, Ma Y Y, Wu Y, Yuan Z L, Gong Y, Rao Y J. Non-gel encapsulation process of a high temperature strain fiber Bragg grating sensor and its sensing properties. Chinese Journal of Sensors and Actuators, 2013, 26(7): 927-931.

[7] Dong X R, Xie Z, Song Y X, Yin K, Chu D K, Duan J A. High temperature-sensitivity sensor based on long period fiber grating inscribed with femtosecond laser transversal-scanning method. Chinese Optics Letters, 2017, 15(9): 51-55.

[8] Zhang H, Jiang J Z, Liu S, Chen H X, Zheng X Q, Qiu Y S. Overlap spectrum fiber Bragg grating sensor based on light power demodulation. Sensors, 2018, 18(5): 1597-1-1597-11.

[9] Grobnic D, Mihailov S J, Smelser C W, Ding H M. Sapphire fiber Bragg grating sensor made using femtosecond laser radiation for ultrahigh temperature applications. IEEE Photonics Technology Letters, 2004, 16(11): 2505-2507.

[10] Ferreira L A, Santos J L, Farahi F. Pseudoheterodyne demodulation technique for fiber Bragg grating sensors using two matched gratings. IEEE Photonics Technology Letters, 1997, 9(4): 487-489.

[11] Jiang B Q, Zhao J L, Qin C, Huang Z, Fan F. An optimized strain demodulation method based on dynamic double matched fiber Bragg grating filtering. Optics and Lasers in Engineering, 2011, 49(3): 415-418.

[12] Jia Z A, Liu J, Qiao X G, Wei T, Gao H, Feng H F. A demodulation technology based on digital tunable F-P filter for fiber Bragg grating sensing signals. Journal of Optoelectronics. Laser, 2011, 5(5): 649-651.

[13] Q. Y. Li, Y. L. Xiong, Y. Xia, M. Z. Wu, J. Y. Zou, and Z. Y. Ma, “The simulation of FBG demodulation system based on the tunable F-P filter,” in Proceedings of 2013 2nd International Conference on Measurement, Information and Control, China, Aug. 16–18, 2013, pp. 337–340.

[14] Davis M A, Kersey A D. All-fibre Bragg grating strain-sensor demodulation technique using a wavelength division coupler. Electronics Letters, 1994, 30(1): 75-77.

[15] Yu Y L, Tam H Y, Chung W H. A fiber Bragg grating sensor system with interferometric demodulation technique. Acta Optica Sinca, 2001, 21(8): 987-989.

[16] Pang D D, Sui Q M, Jiang M S. New fiber Bragg grating high temperature sensing network based on diffraction demodulation. Chinese Journal of Lasers, 2011, 38(11): 174-179.

[17] Z. W. Feng and L. Zhang, “Demodulation technique based on diffraction optical elements for fiber Bragg grating sensing system,” in Photonics Asia 2010, China, Oct. 17–20, 2010, pp: 78530I-1–78530I-9.

[18] I. V. Ciapurin, L. B. Glebov, and V. I. Smirnov, “Spectral combining of high-power fiber laser beams using Bragg grating in PTR glass,” in Lasers and Applications in Science and Engineering, United States, Jan. 25–29, 2004, pp. 116–124.