High-Sensitivity Sensing for Relative Humidity and Temperature Based on an Optoelectronic Oscillator Using a Polyvinyl Alcohol-Fiber Bragg Grating-Fabry Perot Filter

In this paper, a relative humidity (RH) and temperature sensing scheme with high sensitivity based on an optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. A polyvinyl alcohol-Fiber Bragg grating-Fabry Perot (PVA-FBG-FP) filter, in which the PVA film acts as an RH-strain transducer, is employed in the OEO to implement a single passband microwave photonic filter (MPF). In the OEO loop, the oscillating frequency is determined by the center frequency of the PVA-FBG-FP filter and the laser source. When the external RH or temperature changes, the central wavelength of PVA-FBG-FP filter is shifted, leading to the change in the center frequency of the MPF. By simply monitoring the variation of oscillating frequency using an electrical spectrum analyzer or a digital signal processor, the measurements for the RH and temperature can be achieved. In the experiment, the sensitivities of the RH and temperature are measured to be as high as 508.3 MHz/%RH and 1.8118 GHz/degrees C, respectively.