Generally, in a waveguide-based humidity sensors, increasing the relative humidity (RH) causes the cladding refractive index (RI) to increase due to cladding water absorption. However, if graphene oxide (GO) is used, a reverse phenomenon is seen due to a gap increase in graphene layers. In this paper, this interesting property is applied in order to fabricate differential humidity sensor using the difference between RI of reduced GO (rGO) and nano-anatase TiO₂ in a chip. First, a new approach is proposed to prepare high quality nano-anatase TiO₂ in solution form making the fabrication process simple and straightforward. Then, the resulted solutions (TiO₂ and GO) are effortlessly drop casted and reduced on SU8 two channels waveguide and extensively examined against several humid conditions. Investigating the sensitivity and performance (response time) of the device, reveals a great linearity in a wide range of RH (35% to 98%) and a variation of more than 30 dB in transmitted optical power with a response time of only ~0.7 sec. The effect of coating concentration and UV treatment are studied on the performance and repeatability of the sensor and the attributed mechanisms explained. In addition, we report that using the current approach, devices with high sensitivity and very low response time of only 0.3 sec can be fabricated. Also, the proposed device was comprehensively compared with other state of the art proposed sensors in the literature and the results were promising. Since high sensitivity ~0.47dB/%RH and high dynamic performances were demonstrated, this sensor is a proper choice for biomedical applications.

An on-chip optical humidity sensor using Nano-anatase TiO₂ coating is presented here. The coating material was prepared so that the result is in solution form, making the fabrication process quick and simple. Then, the solution was effortlessly spin-coated on an SU8 straight channel waveguide. Investigating the sensitivity and performance (response time) of the device revealed a great linearity in the wide range (35% to 98%) of relative humidity (RH). In addition, a variation of more than 14 dB in transmitted optical power was observed, with a response time of only ~0.7 s. The effect of coating concentration and UV treatment was examined on the performance and repeatability of the sensor. Interesting observations were found, and the attributed mechanisms were described. In addition, the proposed sensor was extensively compared with other state-of-the-art proposed counterparts from the literature and remarkable advantages were found. Since a high sensitivity of ~0.21 dB/%RH and high dynamic performances were demonstrated, this sensor is proposed for use in biomedical applications.

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 ∼0.7 sec and high sensitivity of (∼0.47 dB/%RH).