Interferometric interrogation of in-fiber Bragg grating sensors without mechanical path length scanning

We report the interrogation of a fiber Bragg grating (FBG) using an interferometer with a tilted mirror such that the optical path difference is a function of position on an array detector. Absolute measurements of mean resonant wavelength from the phase of the analytic signal of the spatial interferogram are determined, and a technique based on using a reference laser to compensate for performance degrading effects otherwise associated with spatially scanned interferometers is introduced. These measurements are not critically dependent on the accurate location of zero phase position. We have applied the technique to the absolute measurement of temperature-induced shifts in the grating resonant wavelength. A resolution of 0.025 nm for a spatially scanned optical path delay of only 200 µm was achieved. The technique has the potential for higher resolutions and for multiplexing.