| We introduces a new type of optical fiber humidity sensor,which is based on the significance of humidity sensor,and introduces the advantages of optical fiber humidity sensor compared with ordinary humidity sensor.The properties and preparation methods of several humidity sensitive materials were studied.The new fiber humidity sensing materials were coated with different humidity sensing materials.1.A fiber sensor based on the simultaneous measurement of temperature and refractive index of M-ZI is proposed and experimentally.It can excite a part of the light into the cladding by using the light in the core when it passed through the first fused spherical structure,because the difference of optical path between the light transmitted in the cladding and the optical path in the core is different.The light in the cladding interacts with the light transmitted in the core during the second fusion spherical structure.It was shown that the highest sensitivity of the structure is-248.677 dB/RIU in the range of 1.339?1.370RIU?Refractive Index Unit?refractive index,and the highest sensitivity of the structure is -0.0982 dB/? at 30 ? 95?.The resolution of temperature and refractive index are 0.2036? and 8 × 10-5RIU,respectively.When the ambient temperature changes,the center wavelength of the interference spectrum will drift along with it,but the change of its intensity is very small,and the highest sensitivity of temperature sensitivity is 0.0773nm/?.The fiber sensor is suitable for simultaneous measurement of temperature and refractive index in practical industrial production because of its low cost and small structure due to its small interference with external environment.2.We proposed a new Mach–Zehnder interferometer?M-ZI?structure.It is fabricated by sandwiching a PCF between two standard single mode fibers?SMFs?with the air holes of the PCF in the fusion splicing region being fully collapsed.A methylcellulose?MC?coated humidity sensor for humidity measurement.Experimental results show that this structure can not only carry on the intensity modulation,but also carry on the wavelength modulation,and the sensitivity in high humidity region is 0.57nm/%RH?relative humidity unit?,0.608 dB/%RH respectively.We can be seen that the sensor has high sensitivity in high humidity area.It also shows that the humidity sensitive film of the wet characteristics of good,good stability,so it can be applied to humidity measurement.3.A refractive index sensor,which is based on Michelson interferometer?MI?with a thin core fiber?TCF?coated by CNT?Carbon Nanotube?,is proposed and experimentally demonstrated.This sensor is fabricated by the splice of a sectioned single mode fiber?SMF?on one end of TCF,and the other end is turned into a circular arc by fusion discharge.Such an all-fiber MI incorporates an intermodal interference between the core mode and the cladding modes.CNT is coated on the surface of the TCF.With the variations inside the environmental refractive index?RI?,the shift of the wavelength and intensity of the interference pattern have been brought about.Experimentally,sensitivity of 178.88 dB/RIU?refractive index unit?,165.77nm/RIU,as well as a resolution of 5.59×10-4RIU and 1.21×10-4RIU,are achieved respectively within a field ranging from 1.334 to 1.371 RIU.Moreover,CNT is better than silicon materials in compatibility,and it will not be washed away after its being adsorbed to the surface of optical fibers.In addition,its application could be better implemented in actual measurements,due to its insensitivity to temperature.4.A humidity sensor based on a thin core fiber?TCF?coated with humidity sensitive material is proposed.It is fabricated by splicing a section of TCF into the single mode fiber?SMF?,and the other end of the TCF is made into a circular arc shape by discharging.It is sensitive to external refractive index?RI?,due to intermodal interference between the core mode and the cladding modes.Humidity varies corresponding wavelength shift or intensity change of the interference spectrum through RI of the humidity sensitive material coating.When the structure was coated with different humidity sensitive materials,the sensitivity of the sensor was also different.When coated with methyl cellulose,the sensitivity of the sensor can reach 0.224 dB/%RH and 0.133 nm/%RH within the range of 55?85%RH.When the carboxymethyl cellulose was coated on the sensor,the sensitivity is 0.041 dB/%RH and 0.155 nm/%RH.RH range is 60% to 85%RH.When coated with chitosan,the highest sensitivity can be up to 0.058 dB/%RH.It can be seen that different humidity sensitive materials have different effects on the sensor.The sensor has the advantages of small volume,simple fabrication,and has great potential in relative humidity monitoring. |
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