In-fiber humidity sensor based on Black Phosphorus-Polyvinyl alcohol

An in-fiber humidity sensor based on black phosphorus (BP)-polyvinyl alcohol (PVA) is proposed and experimentally demonstrated. The sensing head is fabricated by depositing BP-PVA film on single mode fiber–up taper–thin-core fiber–up taper–single mode fiber structure. Experimental results reveal that the maximum sensitivity is 0.6106 nm/%RH in the relative humidity (RH) range of 40–50 %RH, and a low instability of 3% is realized, which reveals the combination of BP and PVA can not only improve the sensor’s humidity sensitivity, but also enhance the stability of the BP in air. Meanwhile, the measurement error brings by temperature is 0.16 %RH/℃ and the response time is 0.8 s for human breathing measurement, which indicate its good application potential in humidity sensing.