Optical Fiber Sensor Based On Sensitive Film

Due to good resistance to temperature, corrosion and electromagneticinterference, optic fiber sensors as detection device are widely used in scientificresearch and engineering application filed. Recently, sensitive films coated on fiberwhich are used to change the transmission properties of optical fiber have become aresearch hotpot. These fiber sensors have an attractive application prospect due to itsexcellent optical properties and adjust the flexible design. In the field of sensor,coated fibers are widely used in gas sensors, humidity sensors, temperature sensors,chemical sensors and biosensors according to different applications. This paperfocuses on research of optical fiber sensors based on sensitive film. Following arethe main contents:1. A simple multiplexing method for relative humidity (RH) sensors is realizedwith a multimode-fiber taper coated with a layer of polyvinyl alcohol (PVA). Bycascading an Arrayed-Waveguide Grating (AWG), multipoint RH measurement isachieved. The taper was coated with a layer of PVA along the taper waist. Therefractive index of the PVA coating change with the humidity changing, thustransmission loss of the light signal will change too. Humidity measurement istherefore realized. Experimental results show that the proposed multipoint RHsensor system works well. The output power for every sensor head is almost linearlyincreased with the RH, and the average sensitivity is about0.23nW/%RH within themeasurement range of35%RH~90%RH with the taper waist diameter of~22μm.2. A simple multipoint humidity measurement by PVA-coated Fresnelreflection-based optical fiber sensors with an Array-Waveguide Grating (AWG) isproposed and demonstrated. Every channel end of the AWG is split as a verticalplanar surface, and then is coated with a layer of a PVA whose refractive index (RI)is sensitive to moisture. The reflection intensity for each channel will change with itssurrounding humidity, since the optical fiber interface’s Fresnel reflection is affectedstrongly by the refractive index difference of the interface two sides. Experimentalresults show that the proposed Fresnel reflection-based optical fiber sensor formultipoint humidity measurement works well and the average sensitivity is0.135dB/%RH within the measurement range of30-80%RH.3. A simple chemical vapor sensor measuring isopropanol by MFI zeolite-coated Fresnel reflection-based optical fiber sensors with an Array-Waveguide Grating(AWG) is proposed and demonstrated. Isopropanol was chosen as a model chemicalbecause of its nontoxic nature. Every channel end of the AWG is split as a verticalplanar surface, and then is coated with a layer of all-Si MFI-type zeolite (also calledsilicalite) thin film. The reflection intensity for each channel will change with itssurrounding isopropanol concentration, since silicalite is a strong adsorbent fororganic molecules because of its high hydrophobicity. The experimental setup issimple and easy to handle. Experimental results show that the proposed Fresnelreflection-based optical fiber sensor for chemical vapor measurement works well andthe average isopropanol concentration sensitivity is~9E-4dB/ppm within themeasurement range of0ppm to4900ppm.