The Study On Technology Of High-power Linearly Polarized Fiber Laser

Linearly polarized fiber lasers have important applications in many fields,such as laser communication,high-resolution sensing,second harmonic generation,optical parameter oscillation,beam combination and so on.Generally,linearly polarized laser can be obtained by introducing in-line or free-space polarization selecting components in laser system.However,introducing polarization selecting components will be faced with problems in high insert loss,weak stability of system,high cost and limitation of output power.The linearly polarized fiber lasers without polarization selecting components can effectively overcome these defects and benefit extending linearly polarized fiber lasers to all-fiber structure.So far,the researches on all-fiber high-power linearly polarized fiber lasers are rarely reported interiorly.Based on current conditions in our laboratory,the dissertation experimentally and theoretically study the technology of high-power linearly polarized fiber lasers without polarization selecting components by employing single oscillator or master oscillator power amplifier(MOPA)configuration,aiming to obtain output of high-power,high-efficiency and high polarization-extinction-ratio(PER)linearly polarized fiber laser.Firstly,an investigation on current situation and progress of researches on linearly polarized fiber lasers at home and broad is conducted.Furthermore,the characteristics of four kinds of linearly polarized fiber lasers and corresponding advantages as well as disadvantages are analyzed,and the scheme of linearly polarized fiber laser which fits all-fiber structure and has potential to realize high-power output is confirmed.Secondly,the basic principle of polarization selection based on polarization maintaining fiber Bragg gratings(PM FBGs)is depicted and an all-fiber linearly polarized laser oscillator employing this principle is developed,which realizes an output power of 42.3 W,with PER beyond 14 dB.The thermal property of FBGs is measured and theoretically analyzed.Furthermore,the impact of temperature of FBGs and polarization cross talk(PCT)on output properties of this linearly polarized fiber laser is experimentally investigated and analyzed.Meanwhile,the features of this kind of linearly fiber laser are pointed out and corresponding effective approach is put forward to scale its output power and improve its output properties.At the same time,the basic principle of polarization selection based on bend loss is introduced.The bend loss of panda-type polarization maintaining fiber is numerically simulated.Furthermore,an all-fiber linearly polarized laser oscillator based on this principle is developed,obtaining an output power of 93.2 W with PER beyond 15.3 dB,which is the highest output power of linearly polarized fiber laser based on this principle interiorly at the present.The relationships between the output properties of this linearly fiber laser and bend loss,parameters of FBGs,temperature of FBGs and PCT are analyzed.The differences of this kind of linearly polarized fiber laser from the linearly polarized fiber laser employing principle of polarization selection based on PM FBGs and corresponding advantages as well as disadvantages are analyzed comparatively.Further,the approach to reform and improve output properties of all-fiber linearly polarized fiber laser without polarization selecting components is put forward,which is worth being refered and guiding us to realize linearly fiber laser with higher power,higher PER and higher stability.Further,with the linearly polarized laser oscillator employing principle of polarization selection based on bend loss as seed laser,a high-power,high-efficiency high-PER and approximately diffraction-limited linearly polarized fiber laser is realized successfully by one-stage MOPA structure,possessing maximal output power of 1491 W,slope efficiency of 82.6 %,PER better than 13.8 dB and M2 factor about 1.2,which is the highest output power of linearly polarized fiber laser reported in public to date.Moreover,a rate-equation model taking amplified spontaneous emission(ASE)and stimulated Raman scattering(SRS)into account is utilized to analyze the potential of this scheme for scaling power further.