Recently, narrow linewidth fiber lasers are widely applied in coherent detection and wavelength beam combining. In high-power linearly polarized narrow linewidth fiber lasers, the effect of mode instability (TMI) is one of the main factors limiting its power increase. In this paper, the influence of TMI effect on the output power of high-power linearly polarized narrow-linewidth fiber laser is analyzed, and the suppression method of TMI effect is proposed. Long-wave pumping technologies are used in this article. A single frequency laser with an output power of 100mW is used as the seed source. And the phase modulator broadens the linewidth of the seed source to 23GHz. After three stage amplification, the linewidth of 23GHz, power of 2.2kW, and center wavelength of 1064nm are finally realized. Linearly polarized narrow linewidth fiber laser output with extinction ratio of 98% is achieved. Beam quality is M2x=1.2 and M2y=1.21. The influence of the pump wavelength on the TMI effect is analyzed. Due to the small core diameter of the fiber (20μm), a high absorption coefficient of the gain fiber for the pump light (1.8dB/m@976nm), the core temperature is high. And the heat introduced by the pump photo quantum defect, causes the refractive index of the fiber core to change. Finally, the TMI effect occurs at lower power. When the pump wavelength is shifted to the long wavelength, the quantum defect of the pump light and the pump absorption coefficient are both reduced. The heat distribution on the entire length of the fiber or on the unit length is reduced. The TMI threshold is increased. And the output power of the linearly polarized narrow linewidth fiber laser is improved.
Recently, narrow linewidth fiber lasers are wide applied in coherent detection and wavelength beam combining. In high power narrow linewidth fiber laser, Stimulated Brillouin Scattering (SBS) is the major power limitation factor. Through increasing the frequency number and frequency spacing, SBS threshold power multiplied. In this paper, tow stage white noise phase modulation technology is used to control the frequency number and frequency spacing. Under tow stage white noise phase modulation and three stage fiber amplified technology, the laser linewidth of 13GHz,power of 2.7kW and central wavelength of 1064.4nm, are achieved respectively. And the beam quality is M2x = 1.31 and M2y = 1.3.
Recently, narrow linewidth fiber lasers are wide applied in coherent detection and wavelength beam combining. The influence of fiber grating oscillating longitudinal mode distribution and the amplifier gain fiber characteristics on the output laser spectrum width are explored. The influence of the optical field distribution and the spatial hole burning effect on oscillating longitudinal modes number is analyzed. And the influence of four-wave mixing effect (FWM) in the amplified laser on the spectral width of the output laser is analyzed. The main oscillation power amplification technology of one-stage oscillation and one-stage amplification is used. Finally, the influence of the reflection bandwidth of the resonant cavity, the longitudinal mode number of the main oscillation stage and the length and core diameter of the gain fiber of the amplifier stage on the output laser spectrum width is studied. Spectral width of 0.29nm, power of 2kW and center wavelength of 1064.4nm is realized. The beam quality is Mx2=1.2,My2=1.3.
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