Effects of different serial fiber arrangements on microbending losses

Abstract

This study investigated a fiber optic microbending sensing system. An optical time domain reflectometer (OTDR) and a mode scrambler were used to construct a serially configured fiber optic microbending system. The main objective of the study was to analyse the response (sensitivity) of different types of optical fibers to microbends induced by linear displacements of the mode scrambler plate. Simultaneous measurements of loss at two points were investigated. The types of fiber tested were single-mode (SMF 8/125) and multimode (MMF 62.5/125, MMF 50/125) optical fiber. The fibers were spliced to form serial connection. Power losses at the two points measurement were noted with different linear displacement applied. Based on the result, SMF 8/125 shows a wider range of detectable pressure induced by the linear displacement from 12.6 to 20.3 µm, whereas for MMF 62.5/125 the range observed was from as low as 9.8 µm up to 14.7 µm. It was observed that SMF 8/125 showed two sensitivities which are 0.016 dB/µm for the initial linear displacement and 1.281 dB/µm at higher displacement. It shows that there is a threshold value of linear displacement before a high sensitivity can be achieved. The sensitivity of MMF 62.5/125 is divided into three different parts, namely 0.092 dB/µm for the first part, 0.646 dB/µm for the second part and 0.281 dB/µm for the third part. As for simultaneous measurements at the two points microbends induced, the second point reading loss in the serial configuration was affected by the increasing pressure at the first point. The second part is further away from the OTDR. Similar results were obtained for every fiber tested except for the response from the single-mode-multimode configuration. The loss at the second point (with constant linear displacement) did not show any noticeable decrease but the signal appeared to have relatively higher noise