Ultrahigh-resolution wavelength scanning system with FBG Fabry-Perot interferometer for displacement sensing

A wavelength scanning system with ultrahigh-resolution is proposed and demonstrated for displacement sensing. Light from a linewidth-narrowed and frequency-stabilized laser is put into an electro-optic modulator (EOM) which is connected to a microwave source (MS), and the frequency of the radio frequency (RF) signal output from the MS is set to scan from 2.3 GHz to 6.5 GHz with a high resolution covering the free spectrum range (FSR) of a fiber Bragg grating Fabry-Perot interferometer (FBG-FPI), thus the laser output from EOM scans with the same resolution to RF signal within certain wavelength range. The laser is injected into the FBG-FPI yielding extremely narrow transmission peaks within the FBG reflection wavelength range. Experimental results show that the longitudinal modes caused in the FPI cavity which is invisible to normal commercial optical spectrum analyzer (OSA) can be measured accurately and displacement measuring with nanometer resolution can be expected by using this system.