Polarization-dependent Properties Of Microfiber And Its Applications

The microfibers are fabricated through pulling of common optical fibers in the melting state.Microfibers have been widely used in optical sensing,optical communication,non-linear optics and active light emitting devices in recent years due to their small size,strong optical field constraints,low loss,strong evanescent field transmission ability,high mechanics and high flexibility.In this thesis,microfiber baded polarization beam splitter has been proposed and demonstrated.The theoretical analysis,simulation and device fabrication of polarization beam splitter based on microfiber evanescent field coupling have been given.Then,it is successfully applied to passive mode-locked fiber lasers and the generation of ultrashort pulses has been achieved successfully.The main works of this thesis include:(1)Mode distribution of polarization beam splitter based on evanescent field coupling is analyzed by coupled mode theory.The theory shows that TE/TM polarization beam splitting can be realized based on the microfiber coupling structure.(2)The polarization splitting characteristics of two parallelly placed microfibers in both 1.55 ?m and 1.06 ?m bands are discussed by the full vector finite element method in Comsol Multiphysics software and the finite difference beam propagation method of Beam PROP module in Rsoft software.The relationship between the coupling length and the diameter of the microfiber polarization beam splitter that satisfies the polarization splitting effect has been studied.(3)Three microfiber polarization beam splitter samples were successfully fabricated at 1550 nm band.The polarization contrast of the three devices at around 1550 nm can reach more than 10 d B,and the maximum can reach 25.23 d B.(4)The prepared microfiber polarization beam splitter is applied to a passive mode-locked fiber laser to realize the generation of mode-locked pulses.The center wavelength of the mode-locked pulses is about 1559 nm and the 3 d B bandwidth is 3.83 nm,the output pulse period is 13.5 ns with corresponding repetition frequency of 7.3928 MHz,the emission spectrum has a signal-to-noise ratio of 43.82 d B,the pulse width is 0.92 ps,and the time-bandwidth product(TBWP)is 0.44.