| Environmental humidity is vital important in numerous fields such as chemical engineering,biomedical device,food processing,agriculture.How to monitor the environment humidity quickly,in real time and in a distributed way is a hot topic in the research of humidity sensor at present.Compared with the traditional humidity sensor,the optical fiber humidity sensor has a wide attention in environmental humidity monitoring because of its inherent characteristics such as small size,corrosion resistance and strong electromagnetic interference.However,when monitoring the environmental humidity,the temperature will have a great impact on the measurement.However,in the monitoring of environmental humidity,temperature will have a greater impact on the measurement,so how to eliminate the temperature effects of humidity sensor design is a major problem in the design of humidity sensor.In some special applications such as high temperature,chemical corrosion and other harsh environment,and humidity-sensitive materials,the performance of fiber-optic humidity sensor will be affected by the nature of humidity-sensitive materials,resulting in large measurement errors.The optical fiber humidity sensor,which is combined with the humidity sensitive material,can be affected by the humidity sensitive material itself in some special application fields such as high temperature and strong chemical corrosion,resulting in large measurement error.In view of the above problems,based on the principle of interference,two optical fiber humidity sensors with no humidity sensitive material are designed and fabricated,and their humidity and temperature sensing characteristics are introduced in theory and experiment in detail.A fiber optic humidity sensor based on Mach-Zehnder interference principle is designed and fabricated by using a grapefruit-shaped photonic crystal fiber(G-PCF)cascaded with a short section of multimode fiber.To enhance sensitivity to humidity,femtosecond laser micromachining is performed to remove a portion of cladding of G-PCF to expose its core to the ambient medium.The results show that the proposed sensor is sensitive to humidity and its sensitivity is-0.077 d B/%RH in the range of 25%RH to 80%RH.In addition,temperature characteristics are investigated.Experimental results indicate that the intensity spectrum is insensitive to change in temperature.Nonetheless,the ambient temperature can be determined from the variation in the dip wavelength and the sensitivity is measured to~3.3pm/?C.The proposed fiber structure has great potential in the application of simultaneous humidity and temperature measurement.A kind of Fabry-Perot interference structure is fabricated by fusing the hollow-core fiber and photonic crystal fiber.Humidity in the environment through the photonic crystal fiber air hole into the hollow-core fiber in the cavity caused by the change in the refractive index,so as to achieve environmental humidity measurement.The results show that the proposed sensor is sensitive to humidity and its sensitivity is 0.06273 d B/%RH in the range of35%RH to71%RH.In addition,the temperature sensing characteristics of the sensor are studied experimentally,the temperature sensitivity of the transducer is 10.64pm/?C when the temperature range is 25?C-70?C,which shows that the wavelength of interference spectrum changes when the temperature changes,but its strength is not affected.The sensor can also be used in harsh environments for simultaneous monitoring of humidity and temperature. |
PDF Full Text Request