Compound Phase-Shifted Fiber Bragg Structures as Intrinsic Magnetic Field Sensors

We report on the simulation and characterisation of compound phase-shifted fiber Bragg structures for use as novel in-fiber magneto-optical point sensors. Through simulation we show that the Faraday rotation spectra of phase-shifted gratings can be tailored by tuning the ratio of substructure lengths. A design process for tailoring the magneto-optical spectrum is illustrated, and it is shown that a general optimum structure exists for producing a region of total reflection incorporating magneto-optical Faraday rotation that is enhanced both in strength and spectral width. A practical optical fiber system that exploits the proposed distributed feedback (DFB) structures to enable novel all-fiber sensors for the dual measurement of magnetic field strength and temperature is described in detail, and the sensor response is simulated. The study is supported by laboratory fabrication of the proposed fiber DFB structures which demonstrates the principle of enhancement in terms of tailored group delay spectra and highlights practical issues for sensor packaging.