High Performance Optical Humidity Sensing on Chip Using Differential Refractive Index

Generally, in a fiber-based humidity sensor, increasing relative humidity (RH) causes the cladding refractive index (RI) to increase due to cladding water absorption. However, if reduced graphene oxide (rGO) is employed, a reverse effect is experienced. This interesting property is applied in order to develop a differential humidity sensor using the difference between RI of rGO and TiO2 in a chip. First, a methodology is proposed to prepare TiO2 nanoparticles in solution form, making the fabrication process simple and straightforward. Then, the resulting solutions (TiO2 and GO) are effortlessly drop casted, reduced on D-shape optical fibers and extensively examined against several humid conditions. The results show a great linearity in a dynamic range of RH (35 to 98%), response time of only similar to 0.7 sec and high sensitivity of (similar to 0.47 dB/% RH).