Thermal treatment impact on self-written waveguide Fabry-Perot sensors for temperature and humidity detection

Abstract

UV curable photopolymers enable rapid fabrication of micro-optical structures that support highly integrated compact platforms. Light-induced polymerization can realize the formation of self-written waveguides, offering a scalable in-situ fabrication of functional microstructures. The thermal curing process of photopolymerizable materials can, however, have a significant impact on the mechanical and structural properties of the material. In this work, several self-written waveguides based on a UV-curable polymer are fabricated on the tip of single mode fibers by applying different laser powers. In a reflection scheme, a Fabry-Perot cavity arises from this structure, which is monitored for temperature and relative humidity variations. A study of the influence of two types of thermal curing is conducted for the sensor’s stability as well as its response to the measurands concerning sensitivity, hysteresis, and resolution. Continuous high temperature curing allows for greater stability of the spectrum and lower hysteresis to temperature while slow curing – annealing – results in different temperature profiles of the sensors depending on the laser power during its fabrication. Conversely, a similar response for all curing laser powers is achieved to relative humidity after each curing treatment.