Study On Characteristics Of Interferometers Based On Solid-Core Photonic Crystal Fibers

As one kind of new photonic transmission medium, photonic-crystal fiber has many unique characteristics because of its special microstructures, such as endless single-mode characteristic, high nonlinearity, and large mode field area, etc. Those unique characteristics have attracted much interest as it provides a chance to solve difficult problems in communication and sensing fields. As we know, optical fiber sensor has many advantages, e.g. immunity to interference, simple manufacture, high accuracy, good reliability and capability for remote measurement. In this thesis, the solid-core photonic-crystal fiber is introduced into the Mach-Zehnder interferometer and Fabry-Perot interferometer, and their principles of operation are analyzed theoretically. Then three structures of such interferometers, based on solid-core endless single-mode photonic-crystal fiber and multimode solid-core photonic-crystal fiber, are fabricated by manual fusion, respectively. The optical and sensing characteristics of the three interferometers are investigated experimentally. The main work is summarized as follows:1. First, the optical characteristics of photonic-crystal fibers and coupling between single mode fiber and photonic-crystal fibers are introduced briefly. The manufacturing process for the Mach-Zehnder and Fabry-Perot interferometers based on solid-core photonic-crystal fibers are described in details. In addition, the coupling mechanism and transmission loss are analyzed, too.2. The optical characteristics of the Mach-Zehnder interferometer based on solid-core photonic-crystal fiber have been investigated both theoretically and experimentally.(1)The environmental responses, such as refractive index, temperature, strain, bend, etc, have been analyzed in theory;(2)The results of refractive index test show that, the device exhibits good linear response within a RI range from 1.34 to 1.384, and the sensitivity is 70.45 nm/RIU. After etched an interferometer arm, the sensitivity is enhanced to 198.77 nm/RIU. Besides, such a sensor can partially overcome the cross-sensitivity problem between temperature and strain. It can also be used as a bending sensor as the bend sensitivity is as high as 3.046 nm/RIU without hysteresis effect;(3)A new type of device by cascading a long-period fiber grating(LPFG)and a Mach-Zehnder interferometer based on solid-core photonic-crystal fiber with zero offset is proposed. The experimental results demonstrate that this device has a higher bending sensitivity and resolution than that of the Mach-Zehnder interferometer based on solid-core photonic-crystal fiber.3. The optical characteristics for in-line Fabry-Perot interferometer based on solid-core photonic-crystal fiber have been studied theoretically and experimentally. (1) The gas refractive index sensing mechanism for in-line Fabry-Perot interferometer based on solid-core photonic-crystal fiber is investigated both theoretically and experimentally. The experimental result shows that, the interferometer can be used to measure the gas refractive index under different pressure and the refractive index sensitivity is 805.1um/RIU without hysteresis effect. In addition, it also can used to measure the concentration of uncompressed gas;(2) The strain characteristic under high temperature for the Fabry-Perot interferometer based on the multimode solid-core photonic-crystal fiber is demonstrated. From the experimental results, we found that the device can endure temperature of up to 750℃with quite low temperature sensitivity, and its strain sensitivity is 2.3pm/με. It would find important applications in aeronautics or metallurgy areas.In conclusion, the characteristics of three types of interferometers based on solid-core photonic-crystal fibers are investigated. It has branched out the classes of all-fiber sensing devices, and provided several alternatives for the sensing filed. It has certain academic significance and application value.