Spider silk-based tapered optical fiber for humidity sensing based on multimode interference

Abstract

We develop a novel humidity sensor by wrapping the spider dragline silk (SDS) on a tapered single-mode fiber (TSMF) to configure a multimode interference (MMI) structure and obtain the optical spectrum. The TSMF is fabricated by heating a single-mode fiber (SMF) while applying tension. SDS is employed as humidity-sensing material, thus the SDS wrapped on the TSMF enable TSMF structure to be sensitive to the changes of environmental relative humidity (RH). SDS refractive index changes with the change of environmental RH, which causes the shift of multimode (MMI) interference spectrum. Experimental results indicate that the average sensitivity of the proposed SDS-based sensor is 0.532 nm/%RH in the range of 30 %RH–89 %RH and the maximum sensitivity is 0.789 nm/ %RH in the range of 70 %RH-89 %RH. The humidity-sensing curve is approximately fitted by the linear method. The response time is 374.46 ms. We provide a new method for the fabrication of natural protein-based environmental friendly sensor.