Formation of a D-shaped optical fiber by in-cavity online polishing for high resolution sensing in a chaotic correlation fiber loop ring down system

Online monitoring of the polishing process of a D-shaped optical fiber sensor is performed in this paper by means of a chaotic correlation fiber loop ring down (CCFLRD) system. The ring down time of the autocorrelation coefficient decreases with the increase in polishing loss caused by different mesh sizes. A comparison of the sensitivity and resolution of the CCFLRD system with different polishing losses in the length of a fiber loop cavity are carried out. Online polishing in the fiber loop cavity with a very short length is proposed and demonstrated using different polishing mesh numbers to increase the sensitivity and resolution of the system. A high sensitivity of 31.871ns-1RIU-1 and resolution of 10-4RIU for refractive index sensing in the range of 1.3347-1.3721 correspond to different concentrations of sodium chloride.