Fiber-Optic Sensors Based On Metal Nano-Wire Grid And Photonic Crystal Fiber

In recent decades, fiber-optic sensing technology has been rapidly improved. Owing to the numerous advantages of fiber-optic sensing such as immunity to electromagnetic interference, electrical insulation, corrosion-resistant, light weight, compact size, shape variable, multiplexing capability, being compatible with modern fiber-optic network and so on, the fiber-optic sensors have been replacing traditional measuring methods in many fields. In this thesis, we focus on the study of fiber-optic sensors which mainly include fiber current sensor and fiber hydrogen sensor.Our results are listed as follows:(1) Taking advantage of metal nano-wire-grid’s (NWG’s) polarization selectivity, we fabricate a fiber tip polarizer by magnetron sputtering and Focused Ion Beam technology. The NWG has a thickness of80nm, a period of200nm, and a duty ratio of0.5. As for the incident light of different polarization, the NWG acts as both reflective and transmissive polarizers at the same time, and the specific performance of the NWG is that the input TE mode light is reflected while the TM mode light may transmit through it. The test result shows the NWG has a16.3dB reflection contrast and a4.8dB transmission contrast. Based on the NWG, we demonstrate a heterodyne all-fiber optical current sensor, which has a sensitivity of0.528degree/A. We introduce a Faraday Rotating Mirror (FRM) to the sensing unit. On one hand, the FRM constitutes a reflective system which increases the effective optical path in the magnetic field. On the other hand, the FRM eliminates the disadvantages of existing birefringence of the optical fiber. The NWG’s polarization selectivity allows the sensor become an in-line optical heterodyne system without any bulky optical elements. Compared with the sensors using Wollaston prism, our system has more advantages.(2) Based on the special structure of index-guiding Photonic crystal fiber (PCF), we demonstrate a PCF in-line interferometer. In our hydrogen sensor, the PCF in-line interferometer is used as the sensing unit. The optical path of the system is all-fiber without any discrete elements. So the sensor not only has a relatively high sensitivity but also has a high level of integration. In our experiment, when hydrogen concentration ranges from0%～5%, the sensor gives a sensitivity about0.25nm for one percent of hydrogen. Under the explosion limit of hydrogen, the resonant wavelength shifts over1nm toward the short wavelength. As for most hydrogen sensors based on fiber Bragg grating, the wavelength-shift is only pm magnitude under the same condition.In conclusion, in the design and fabrication of optical fiber sensors, we have done some useful exploration. But in order to put them into real life, there still need more effort to improve their performance, stability and repeatability.