Tunable Twin-core Fiber And Its Application In Fiber Grating Sensors And Filter

Twin-core fiber is a special type of optical fiber which contains two close cores. The power can exchange between the two cores during its transition in the fiber. Due to this speciality twin-core fiber can act some functions of coupler. But rather than the coupler it is more flexible because of its spectral characteristics. The spectrum can be tuned through changing the length, pulling and twisting. By using these traits we can design many fiber devices according to the engineering needs.Nowdays fiber Bragg grating (FBG) is the focus of optical sensor field. It is widely used owing to its characteristics such as wavelength coding, structureal ingenious and convenient fabrication. If we can integrate the advantages from twin-core fiber and FBG to design noval sensors, it would be very meanful in both theory and practice.In this dissertation, the development and current applications of twin-core fiber and FBG have been reviewed and the principles of them were narrated firstly. Secondly, as the focus of this dissertation, properties of twin-core fiber have been analyzed detailedly and the effects of altering fiber length, pulling, twisting, bending and temperature change have been studied systematically. The relations between these methods and effects have been obtained and testified experimentally. Thirdly, a noval demodulation method of linear edge filter based on a piece of tunable twin-core fiber in FBG temperature sensor has been put forward. It extends the application of twin-core fiber. The displacement sensor which used the springs and FBG as sensor head and twin-core fiber as demodulation has also been proposed and implemented in experiment. The results exhibit that this sensor can be a good scheme in crack detection for its above 10mm measurement range and 0.05mm resolution. Finally, the gain flattening filter is realized by using a WDM coupler and a piece of twin-core fiber, and output spectrum is 30nm bandwidth and±0.5dB ripples. The pieces of twin-core fiber with different length are also been cascaded to achieve the band-pass filter. This is another extension of application areas of twin-core fiber. And we believed that with the deeper research there are many characteristics of twin-core fiber can be exploited and promote the development of optical communication and optical sensor.