High Sensitivity Fiber Bragg Grating Relative Humidity Sensors Fabricated with Polyimide Tubing

A relative humidity (RH) sensor (sensitivity of 1.57 pm/%RH at 60 °C) was fabricated by applying a polyimide (PI) tube (inner diameter of 114 μm and wall thickness of 12.7 μm) to an 80-μm diameter uncoated fiber Bragg grating (FBG). The sensitivity was increased to 3.31 pm/%RH when the PI tubing was applied to a FBG written through the 12 μm-thick PI coating of the fiber. This high sensitivity sensor is easily manufactured without a labor-intensive fiber coating process.