Multiplexed optical fiber sensors using a single Fabry-Perot resonator for phase modulation

Abstract

Abstruct-This paper describes the use of different optical return paths in a single Fabry-Perot phase modulator to perform coherence division multiplexing, and a combination of coherence and frequency division multiplexing of Fabry-Perot interferometric optical fiber sensors. A path-matched differential interferometry (PMDI) using low finesse Fabry-Perot sensors, one moderate finesse Fabry-Perot read-out resonator, and a broadband light source consisting of amplified spontaneous emission (ASE) from an erbium-doped fiber amplifier (EDFA) is used to illustrate the idea. The first, second and third order of multiple paths in a single Fabry-Perot read-out resonator are used to path-match three Fabry-Perot sensors. These three orders of path-matches provide a single, double and triple depth of modulation (phase-change) when the read-out is used as an optical phase modulator, and therefore provide a single, double and triple carrier frequency when serrodyne demodulation is used. The use of a single moderate finesse read-out Fabry-Perot resonator to simultaneously path-match coherence multiplexed sensors reduces the complexity of the optical system. Experiments and modeling are used to show the existence of the first, second, and third order of interference path-match conditions, and to determine the read-out configuration that enhances the visibility of the higher order path-match conditions. Using the multiple return paths in a single PZT-based Fabry-Perot read-out interferometer and serrodyne demodulation, several multiplexing schemes are investigated, and their relative merits discussed.

Phase-generated carrier demodulation scheme for fiber Fabry–Pérot interferometric sensor with high finesse

“…Though the finesses of the two PMDC-FRRs are not very high, they are larger than that of FFPI with R 1 < 0.1 in the literatures. [12][13][14][15][16][17] And, the experimental result can verify the theoretical analysis that this PGC scheme is feasible for the FFPI sensor with high finesse, because this demodulation method is not restricted by the finesse in theory.…”

“…In recent years, some phase demodulation methods for FFPI sensors have been reported. [12][13][14][15][16][17] The main principle is to assume a two-beam interferometric approximation for the Fabry-Pérot cavity used in reflection with a demodulation in path-matching differential interferometry. In these methods, the Fabry-Pérot interferometer is restricted at very low intensity reflectivity, typically less than 10%.…”