Schematic of the proposed IFM system.

(a) The system consists of a single-polarization dual-wavelength laser, two polarization controllers (PCs), a polarization modulator (PolM), a polarization-maintaining Bragg grating (PM-FBG), a single mode fiber (SMF), a wavelength division multiplexer (WDM), two photodetectors (PDs) and a processing unit. The modulator is driven by a voltage of radio frequency (VRF) and is adjusted by a DC bias voltage (Vbias). (b) Evolution happens from location I to II in optical spectra and polarization (x and y axes are the principal axes of PolM, xʹ and y′ axes are the fast and slow axes of PM-FBG).