Research On Novel Multi-wavelength Ytterbium-doped Fiber Lasers Based On Sagnac Fiber Filters

Fiber lasers have broad applications and practical values in the field of optical communication,optical sensing,measurement and material processing with the advantages of good beam quality,efficient laser output,small size,no water cooling and all-fiber structure.In this thesis,for the ytterbium-doped fiber lasers?YDFLs?which have been widely used,researches about the theoretical and experimental researches are carried out by developing novel fiber filters with high performance.Researches are about Sagnac interferometer based on polarization maintaining fiber?PMF?and polarization maintaining photonic crystal fiber?PMPCF?respectively,and the corresponding multi-wavelength YDFLs.The main research achievements obtained are as follows:?1?Based on the high concentration YDF,the switchable seven-wavelength YDFL is proposed without filters.The line width of lasing is only 22 pm,the maximum wavelength shift and peak power fluctuation are less than 0.05 nm and 1 d B respectively,and side-mode suppression ratio?SMSR?is up to 34.734 d B.Through a simple structure,multi-wavelength laser outputs are realized with high SMSR,narrow line width and high stability.?2?The Sagnac interferometer based on PMF is proposed and fabricated.The theoretical spectrum curves of the Sagnac interferometer can be achieved using Jones matrix theory and Matlab naumerical simulation.It is found that the comb spectrum curves are consistent basically by compared with the experimental results.The Sagnac interferometer can obtain excellent filtering,stability,transmissivity when the PMF length is 13 cm,and the free spectral range?FSR?is 10.67 nm.?3?Based on the Sagnac interferometer which is based on PMF,the switchable,tunable and stable dual-wavelength ring YDFL is proposed and demonstrated.The maximum SMSR of single-wavelength lasing is 44 d B,and the tuning range is 17.9 nm.Besides,tunable dual-wavelength lasing output is obtained with three different wavelength intervals,respectively.The causes of different intervals are explained through theoretical analysis.The peak power difference is only 0.98 d B and the maximum tuning range is up to 12 nm.The wavelength shift and peak power fluctuation are less than 0.06 nm and 0.94 d B,respectively.The YDFL with wide tuning range,high SMSR,good power balance and high stability is achieved.?4?The Sagnac interferometer based on PMPCF is proposed and fabricated.Comsol is used to simulate and model for the calculated spectuum curves.Through comparative analysis of Comsol theoretical analysis,Matlab numerical simulation and experimental verification,the comb spectra are obtained,and the wavelength intervals are within the order of 10^-2 nm.The 70 cm length of PMPCF is chose for outstanding performance.And the corresponding FSR is 4.8 nm.?5?Based on the Sagnac interferometer which is based on PMPCF,the switchable and tunable triple-wavelength YDFL is proposed and demonstrated with high SMSR,high temperature stability and high power balance.Switchable and tunable single-wavelength,dual-wavelength with different intervals and triple-wavelength is proposed.The maximum tuning range of single-wavelength is 4 nm,and SMSR is up to50 d B.The maximum peak power difference of dual-wavelength is only 0.48 d B.At room temperature,the maximum wavelength shift is 0.018 nm and the maximum peak power fluctuation is 0.64 d B.When the temperature varies from 10?to 90?,the temperature sensitivity is 0.014 nm/?.The developed YDFL achieves tuning triple-wavelength and high temperature stability,and the SMSR,power balance and room temperature stability are all improved.