High-speed interrogation of multiplexed fiber Bragg grating sensors with similar Bragg wavelength by synthesis of optical coherence function

Zuyuan He; Tetsuya Hayashi; Kazuo Hotate

doi:10.1117/12.630324

10 November 2005 High-speed interrogation of multiplexed fiber Bragg grating sensors with similar Bragg wavelength by synthesis of optical coherence function

Zuyuan He, Tetsuya Hayashi, Kazuo Hotate

Author Affiliations +

Proceedings Volume 6004, Fiber Optic Sensor Technology and Applications IV; 600409 (2005) https://doi.org/10.1117/12.630324
Event: Optics East 2005, 2005, Boston, MA, United States

Abstract

We have reported recently a multiplexed fiber Bragg grating (FBG) strain sensor by using the technique of synthesis of optical coherence function. By modulating the optical frequency of the light source in a sinusoidal waveform, the coherence function is synthesized into a series of periodical peaks in the meaning of time- integration. Using one of the coherence peaks as a measurement window, and sweeping it along a string of FBGs by adjusting the repetitive frequency of the sinusoidal modulation waveform, we can selectively pick up the reflection as interference signal from any one FBG from the string. Therefore, the FBGs are resolved spatially; they are not necessarily different to each other in Bragg wavelength. By sweeping the center frequency of the light source in a sawtooth waveform, the shape of the FBG reflection spectrum can be obtained, and thus the amount of the strain applied to the FBG can be estimated. Up to date, 100-Hz interrogation speed was achieved with this method, and the measurement range is limited to within the coherence length of the light source. In this presentation, novel methods are proposed to enhance the interrogation speed and the measurement range further. The performance-limiting factors on the interrogation speed and the measurement range are evaluated. It is found that the detected interference signal appears at a certain frequency shifted from the heterodyne beat due to the sweeping of the center frequency. By observing at the shifted frequency, 1-kHz interrogation speed and measurement range beyond coherence length of the light source are achieved.

Citation Download Citation

Zuyuan He, Tetsuya Hayashi, and Kazuo Hotate "High-speed interrogation of multiplexed fiber Bragg grating sensors with similar Bragg wavelength by synthesis of optical coherence function", Proc. SPIE 6004, Fiber Optic Sensor Technology and Applications IV, 600409 (10 November 2005); https://doi.org/10.1117/12.630324

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