Resolution Improvement in a Multi-Point Fiber Refractometer Based on Coherent-OFDR

In this letter, we propose a signal processing method for improving the resolution of a multi-point fiber refractometer from 10
^-4
to 10
^-6
. The fiber refractometer uses the Fresnel reflection at the fiber tip to measure the refractive index (RI), based on the coherent optical frequency domain reflectometry (C-OFDR) technique; using a standard four-pin coaxial pigtailed DFB diode laser as the optical source. The proposed method is divided into two steps; first the raw signal is processed to reduce the nonlinearity generated by the optical frequency sweeping laser, and then a pattern that repeats itself in the sensing signal is identified, extracted and replicated several times to improve the sensing signal used to calculate the RI. In the experimental results, using 30 ms of effective acquisition time, and the proposed method, an improvement of two orders of magnitude in the resolution of the system was obtained.