Investigation On All-Fiber Microstructure Devices And Their Applications

Optical fiber sensing network owes unique merits of fast transmission speed, long transmission distance, high reliability and strong interference immunity, and thus can meet the requirements of modern IOT industry. Considering that the optical fiber sensing network is built on basis of all-fiber devices such as optical sources, sensors, modulators, developing all-fiber devices is obviously important and urgent. Until now, most of the all-fiber devices are based on standard singlemode fiber whose simplex material property and optical property, however, would obstruct researchers to improve the diversity, size and performance of the all-fiber devices. Consequenly, designing and investigating all-fiber devices with miniature size and high performance are crucical for the further developments of optical fiber sensing network.Facing the urgent demands of optical fiber sensing network, we design and systematically investigate several all-fiber miniature devices by taking advantages of microfiber, photonic crystal fiber and compound fiber. The main contents of this thesis are as follows:Firstly, a cascaded microfiber knot resonator (CMKR) with Vernier effect is proposed and experimentally demonstrated. The CMKR is the first combination of microfiber resonator and Vernier effect, which offers many unique advantanges. Based on the transmission matix method, we thoroughly analyze the working principle and optical characteristics of the CMKR. Then, we experimentally prove its ability to measure refractive index (RI) with ultra-high sensitivity of 6523 nm/RIU and ultra-low resonlution of 1.52×10-7 RIU. Moreover, the CMKR working as a filter in a single longitudial mode fiber ring laser is also investigated. Stable singlemode laser with extinction ratio of 57 dB is achieved, demonstrating the single frequency filtering ability of the CMKR.Secondly, a multifunctional ?-shaped micfiber resonator is originally designed, systematically analyzed and experimentally demonstated. The theoretical analyzing results reveal that due to the specifically physical structure, clockwise and counter-clockwise resonant modes can co-exist in the ?-shaped microfiber resonator, inducing analogous electromagnetically induced transparency in transmission and reflection spectra. By adjusting coupling efficiency, coupling loss and cavity length, the ?-shaped microfiber resonator can exhibit multifuctional filtering characteristics, as well as tunable group delay. Meanwhile, the experimental results show that the ?-shaped microfiber resonator can be used as a comb filter in under-coupling state while exhibits bandpss/bandstop filtering ability in over-coupling state. Beisides, group delay tuning from fast light -60 ps to slow light 160 ps is experimentally achived. Moreover, the ?-shaped microfiber resonator is intentionally cascaded with a fiber Fabry-Perot interferometer to generate Vernier effect. The compound structure is demonstrated the ability to detect RI with sensitivity widely tuning from 131.77 nm/RIU to 2460.07 nm/RIU, as well as the ability of single-frequency filtering to realize a temperature-switchable single longitudial mode fiber laser.Thirdly, we investigate the influences of distance between the silica core and the glycerin core of a selectively glycerin-infiltrated photonic crystal fiber (PCF) on the mode characteristics, as well as the temperature sensitivity. Both simulation and experimental results reveal that the smaller distance between the silica core and the glycerin core does not affect the modes indices, but enhances the temperature sensitivity.Finally, two miniature devices based on modal interferometers in compound fibers for sensing applications are also proposed and experimentally demonstrated. By wrapping a multimode-singlemode-multimode compound fiber onto a polyurethane hollow column, an all-fiber volumestrain sensor for earthquake prediction is formed. Sensitivity higher than 3.93 pm/?? within the volume strain ranging from 0 to 1300 ??, and hysteresis less than 2.1% are experimentally demonstrated. Besides, a curvature sensor based on single mode-dual core-single mode compound fiber structure with curvature sensitivity of -4.31 nm/m-1 is experimentally achieved.According to the research process of basis theories—simulation—experimental demonstration, we achieve innovative results in aspects of structure design, theoretical study and experimental results. The achievements are expected to provide insights into the related future investigations, and play important roles in the optical fiber sensing network.