Ultracompact Transverse Load and Temperature Fiber Sensor Probe Based on Cascaded Polymer Microspheres With Vernier Effect

An ultracompact fiber sensor probe based on cascaded polymer microspheres with high sensitivity is proposed for simultaneously measuring the transverse load and the temperature. The cascaded polymer microspheres are integrated on the endface of the single-mode fiber (SMF) by using a simple ultraviolet (UV) curing technique, and a dual Fabry-Perot (FP) cavities fiber probe with Vernier effect is obtained. The total cavity length and the transverse size of the proposed fiber sensing probe are about 110 and $140~\mu $ m, respectively. The transverse dimensions of the cascaded polymer microspheres are slightly larger than that of the SMF. The Vernier lower envelope is obtained by connecting the minimum point of the interference peak in the reflected interference spectrum. The envelope valley near 1370 nm and the high-frequency peak near 1510 nm are used to monitor the changes in transverse load and temperature. The transverse load sensitivities are 28 and 38 nm/N, and the temperature sensitivities of the envelope valley and high-frequency peak are 0.31201 and −0.20238 nm/°C, respectively. The simultaneous measurement of the transverse load and the temperature can be achieved by using the sensing matrix method. The temperature crosstalk during the transverse load measurement can be effectively avoided. It may find widespread application in civil engineering, structural safety monitoring, and cars industry due to its easy preparation process, compactness, and high sensitivity.