Measurement of milli-Newton axial force and temperature using a hybrid microsilica sphere Fabry–Perot sensor

An optical fiber sensor based on the Hybrid Fabry-Perot for simultaneous measurement of milli-Newton axial force and temperature is proposed. This structure is composed of a single-mode optical fiber (SMF) integrated to a silica capillary tube (SCT) with polydimethylsiloxane (PDMS). A microsilica sphere cavity (MSSC) is fabricated at the tip of a capillary tube. Consequently, an air gap followed by a microsilica sphere forms two cascade cavities. To explain the transferring load from the SMF to the SCT through PDMS, a shearing mechanism is employed. The experimental results show that axial force and temperature sensitivities of the air gap cavity in the range of 0-3.43 mN and 30-65°C are 170 pm/mN and 24 pm/°C, respectively, while the MSSC did not show any force sensitivity due to its rigidity. However, its temperature sensitivity is 34 pm/°C. The different sensitivities enable us to implement simultaneous sensing of force and temperature.