Self-written waveguide Fabry-Perot sensor for temperature and humidity detection: a curing study

Abstract

Self-written waveguide structures based on a UV curable polymer (Norland Adhesive 68) are fabricated on a single mode fiber tip using different laser curing powers. The self-trapping effect ensures that when launching UV light through the fiber, the material cures in front of the fiber tip through the direction of the fiber core, resulting in a Fabry-Perot interferometer. The structures are characterized to temperature and humidity both before and after annealing. It is revealed that for low power laser fabricated SWWs, the temperature response changes from positive and linear to negative and non-linear, due to the densification of the structure post-annealing. While the high-power laser fabricated SWWs remain with a positive response to temperature, due to the lack of densification. For RH, the annealing treatment has little influence on the response of the sensors, where each sensor has a high positive sensitivity to this parameter with high resolution and good response time. Generally, annealing also helps to decrease hysteresis for both parameters, as well as the resolution of the sensors.