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Multiplexed long-length fiber Bragg grating distributed sensors based on synthesis of optical coherence function

Recently, we have reported a scheme for measuring Bragg-wavelength distribution inside a long-length fiber Bragg grating using synthesis of optical coherence function, which is one of the reflectometry techniques based on interferometer and heterodyne detection with an optical frequency-shifter and an electronic band-pass filter. However, the system did not have enough measurement range since it measured the distribution with only one grating. For extending the range, long-length FBG sensors are multiplexed and distribution in each grating is measured. In the process of multiplexing FBGs, a scheme for compensating the beat frequency shift due to the high speed sweep of the optical center frequency of the light source is introduced in the system.