Multiplexed strain sensing by synthesis of optical coherence function with time-division phase shift modulation

Abstract

Fiber Bragg grating (FBG) can be multiplexed to realize a quasi-distributed strain or temperature sensing system by use of FBGs of different Bragg wavelength. For a sensing system requiring large number of sensing points, however, this method has difficulties in cost and multiplexable number. On the other hand, we have successfully multiplexed FBGs of the same Bragg wavelength by applying the technique of synthesis of optical coherence function. The measurement range of the technique is limited to the period of the coherence function. Thereafter, we applied Vernier scheme to the system which actively makes use of the periodical coherence function to distinguish the FBGs. In this paper, we propose a new frequency modulation method, time-division phase shift modulation, which solves the FBG-positioning problem in our previous system applying Vernier scheme to the multiplexed FBG sensing with SOCF. Experimental results are reported.