Research On Mode-locked Laser Based On All-fiber Polarizing Beam Splitter

As an important optical component in the optical fiber system,the all-fiber polarization beam splitter can separate or combine the polarized lights of two orthogonal polarization states.It has a wide range of applications in optical fiber sensing,optical fiber laser,optical communication,optical storage,biomedicine and other fields.This thesis proposes an all-fiber polarization beam splitter composed of two parallel micro-nano optical fibers,which has the characteristics of small size,low cost,and variable working wavelength.This thesis focuses on the all-fiber polarization beam splitter and its application in mode-locked lasers as the research content.The main contents are as follows:Based on the coupling mode theory,the numerical simulation of the all-fiber polarization beam splitter is carried out,and it is clarified from the theoretical point of view that the all-fiber polarization beam splitter can realize the polarization splitting of the TE mode and the TM mode.The all-fiber polarization beam splitter is calculated and simulated using Comsol and Rsoft software in the 1550nm band and 2000nm band.An all-fiber polarization beam splitter was fabricated using the fused tapered technology,and the manufacturing and packaging methods of the fused-cone all-fiber polarization beam splitter were introduced in detail.Experimental samples of three all-fiber polarization beam splitters in the 1550nm band are given.The polarization contrast ratios of these three samples near 1550nm are all greater than 10dB,and the highest can reach 25.827dB.Similarly,an all-fiber polarization beam splitter in the 2000nm band was fabricated,and the polarization contrast of the two samples near 2000nm was greater than 15dB.Based on the nonlinear polarization rotation effect,the fabricated all-fiber polarization beam splitters in the 1550nm and 2000nm bands were applied to the ring fiber laser mode-locking respectively.In the all-fiber laser in the 1550nm band,a stable mode-locked pulse with a central wavelength of 1557.024nm is realized;in the 2000nm band,a stable mode-locked pulse is obtained near the central wavelength of 2001.74nm.The all-fiber polarization beam splitter in the 1550nm band is applied to the all-fiber 8-cavity fiber laser,and a stable mode-locked pulse is realized.In a figure-of-eight cavity composed of an all-fiber polarization beam splitter,under the condition that the cavity length is 30m,adjusting the polarization controller in the cavity can realize the wavelength switching mode locking of the short wavelength 1529.996nm and the long wavelength 1557.32nm.And the equivalent model of PBS-PC-SMF-PC-PBS is given,and the effect of single-mode fiber length on the filtering performance of the model is analyzed through numerical simulation.