Low Coherent Optical Frequency Domain Reflectometry Interrogates Fiber Bragg Grating Sensors

A novel fiber optical reflectometry is proposed for long distance measurements and sensing applications. The reflectrometric information is included in the phase difference of two interfering light beams reflected at the same scattering point on the fiber under test (FUT). The reflection position and local information can be determined by modulating the frequency difference and analyzing the reflecting signal in frequency domain. Theoretical analysis and experimental demonstration are presented. Two adjacent reflection points 50 km away from the reflectometry with a gap of 11 meters between each other is distinguished. It is estimated that the operating range could be over 500 km theoretically by employing a light source with 0.3 nm bandwidth. This novel reflectometry is applied as a fiber Bragg grating interrogation solution as an example.