High power narrow-linewidth fiber lasers have been highly desired for various applications. In this paper, we presented new considerations of high power narrow-linewidth fiber amplifiers operating within 1030~1060 nm by using newgeometry active fiber, and the power-breakthrough operating at 1050 nm was achieved. We also reported our recent achievements on power scaling of high-power narrow-linewidth fiber lasers which operates within 1060~1080 nm based on system-optimized step-index and confined-doped active fibers, including linear-polarized and stochastic-polarized ones. Meanwhile, our new progress on special designed active fibers assisted high power fiber amplifiers with sub-GHz to within 1.5 GHz were demonstrated. Besides, the basic considerations of end-reflection on the SBS and SRS effects will be discussed, which provide a new insight for the suppression of SBS and SRS effects.
High power, narrow linewidth all-fiber amplifiers are under intensive investigation in recent years. In this paper, the research status of high power, narrow linewidth all-fiber amplifiers (including those operate at single frequency regime) is briefly summarized. Then the recent progress in our research group is introduced, including more than 500 Watt level single frequency fiber amplifier, more than 4 kW linearly-polarized narrow linewidth all-fiber amplifier and more than 6 kW narrow linewidth all-fiber amplifier. Performance exploring of the operating spectrum property is also discussed.
A novel phase modulation technique, calling multi-phase coded signal (MPCS) modulation, is demonstrated for stimulated Brillouin scattering (SBS) effect managing in high power narrow-linewidth polarization-maintained all-fiber amplifier. Combining with laser gain competition where two signal lasers operating at 1045 nm and 1064 nm are applied, the output power of 1064 nm laser could be boosted to 1023 W with FWHM linewidth of 4.6 GHz. The polarization extinction ratio (PER) is 13.3 dB and the output beam quality is measured to be M2=1.11. This work could provide a feasible method for linewidth controlling in high power narrow linewidth fiber amplifier.
In this report, by comparing the RIN and beam pointing error of the signal laser at different output powers, the impact of the modal degeneration on both the spacial and temporal noise properties of high-power single-frequency fiber amplifiers will be demonstrated. The new finding reveal that obvious mode-related enhancement of the RIN could occur well below the conventional transverse mode instability (TMI) threshold of the fiber amplifier while the mode-related enhancement of the beam pointing error occurs near the TMI threshold. This work could provide a new insight for obtaining high-power, high spacial stability and low-noise single-frequency fiber lasers.
The mechanism of high power intra-channel crosstalk attack is analyzed theoretically and the conclusion that power of attack signal and crosstalk coefficient of optical switch are the main factors for which high power intra-channel have destructive effect on quality of legitimate signals is drawn. Effects of high power intra-channel crosstalk attack on quality of legitimate signals and its capability of attack propagation are investigated quantitatively by building the simulation system in VPI software. The results show that legitimate signals through the first and the second stage optical switch are affected by attack and legitimate signal through the third stage optical switch is almost unaffected by attack when power of original attack signal (OAS) is above 20dB more than that of legitimate signals and crosstalk coefficient of optical switch is -20dB at optical cross connect 1 (OXC1). High power intra-channel crosstalk attack has a certain capability of attack propagation. Attack capability of OAS can be propagated to OXC3 when power of OAS is 27dB more than that of legitimate signals and crosstalk coefficient of optical switch is -20dB. We also find that the secondary attack signal (SAS) does not have capability of attack propagation.
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