Multiplexing of temperature-compensated fiber-Bragg-grating magnetostrictive sensors with a dual-wavelength pulse laser

We present a simple technique for the multiplexing of fiber-Bragg-grating (FBG) magnetostrictive sensors using a recently demonstrated principle for the generation of dual-wavelength laser pulses. Each sensor consists of an FBG bonded on two joined pieces of metal alloys, which have almost identical thermal expansion coefficients and significantly different magnetostriction coefficients. When a magnetic field is applied along the sensor, the reflection spectrum of the FBG is split into two close peaks, whose separation is insensitive to the temperature of the sensor. By using the FBG as a wavelength-selective element for a gain-switched self-seeded Fabry-Perot laser diode, stable short pulses at the two reflected wavelengths of the FBG are generated simultaneously from one of the modes of the laser diode, when the radio frequency (RF) of the laser diode is set properly. By transmitting the pulses through a dispersive fiber, the wavelength separation of the pulses at the two wavelengths is converted into a time difference, which provides a measure of the wavelength separation and, hence, the applied magnetic field (or electric current). Interrogation of a series of sensors is achieved by changing the driving RF of the laser diode.