Microwave spectroscopy of the fiber Bragg grating

In this paper the modulation methods for poly-harmonic microwave signals on optical carrier forming and detecting are demonstrated, especially for applications in fiber-optic sensor systems. The methods of the single-frequency optical signal conversion into the poly-harmonic ones with the difference frequency between the components of SHF, UHF and partly EHF bands has been proposed. In order to form the poly-harmonic signals we used the amplitude Mach-Zehnder modulator (JDSU) or the polarization modulator (Versawave Technologies). The resulting probing radiations were used for microwave spectroscopy of separate or combined into groups fiber Bragg gratings, as sensors of measuring systems. Application of microwave probing signals with detection in the frequency domain or by the envelope allowed simplifying methods for the spectral characterization of gratings and improvement of technical and economic performance of fiber-optic sensor systems.