U-shaped micro-groove fiber based on femtosecond laser processing for humidity sensing

A novel optical fiber sensor with a U-shaped micro-groove structure ablated by femtosecond laser on single-mode fiber for measuring air relative humidity(RH)is reported in this paper.In order to improve the accuracy of sensor,a graphene oxide(GO)/polyvinyl alcohol(PVA)composite film is coated on the surface of micro-groove structure.In the U-shaped micro-groove structure,the remaining core and micro-cavity in the micro-groove make up two major optical propagation paths,forming a Mach-Zehnder interferometer(MZI).The sensor has a good linear response within the RH range of 30%—85%,and the maximum sensitivity can reach 0.638 1 nm/%RH.The effect of temperature on the overall performance of the humidity sensor is also investigated.As a new type of all-fiber device,the sensor shows excellent sensitivity and stability.