Fiber Grating Wave, The Space Division Multiplexing Sensor Network Active Query Technology,

A simple method based on broadband source and optical spectrum analyzer to measure the optical path difference (OPD) of a fiber interferometer was described in this paper. Sticking one arm of an all fiber unbalanced Mach-Zehnder interferometer on a translation stage, when the arm was being stretched, and then the different OPD can be got. The method was proved to be effective and the resolution of the OPD was 20 μm, which was enough to meet the demands of making interferometer used in the demodulation of fiber Bragg grating (FBG).An all fiber unbalanced scanning Michelson interferometer with the OPD 3.19 mm was made. In the case of elimination of environmental interference, the interferometer was put in a metal obturator. In the case of elimination of the heat generated by the PZT when scanning, a temperature controller was used to control the temperature inside the obturator. The temperature fluctuation that less than 0.02℃ was got after the temperature controller had worked 40 minutes.A spatial/wavelength division multiplexed 4×10 FBG sensor array, acted as the reflector of a ring cavity fiber laser, was interrogated by employing a 1 X 4 optical switch and a tunable F-P filter. Demodulation was achieved by using the unbalanced Michelson scanning interferometer that transform the wavelength-shift signal induced by the measured strain into phrase-shift signal. The sensor sensitivity of the system was demonstrated to be 1.6749° /με, which agreed with the theoretical value of 1.6855° /με. A feedback subsystem was introduced to make the system track the measuring FBG automatically.