Study on fabrication and sensing characteristics of a D-shaped fiber long-period fiber grating

A long-period fiber grating (LPFG) structure based on D-shaped fiber is proposed, where a graphene oxide (GO) film layer is deposited on the fiber by the dipping method to jointly construct a new humidity sensor. The D-shaped fiber structure can provide a stronger evanescent field than conventional fibers, and therefore offer much higher sensitivity. The maximum average sensitivity achieved by the sensor in the range of ambient humidity of 20-80% RH (relative humidity) is -0.1908 nm/% RH, and the linearity is 0.998. The experimental results show that the humidity sensor has higher response sensitivity, and improved linear response characteristics. It provides a beneficial exploration for the development of low-cost, easy-to-manufacture, and highly sensitive fiber-optic humidity sensors.