We verify its advantage for fiber coupling through experiments base on large clad fiber, and which core/clad diameter is 196.5/788 μm. The coupling fiber with core/clad diameter of 200/220 μm was fused behind the large clad fiber, and which diameter of the fiber core is bigger than or equal to the diameter of the fiber core of the large clad fiber. The output laser power is 528 W at the incident power 600 W, and the corresponding fiber coupling efficiency is 88%.
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.
The scheme of N×1 multi-beam combination with single gradient-index lens (GRIN) was proposed and the coupling model was simulated with ZEMAX software. One end of the GRIN was fabricated to polyhedral convex cone with N surfaces and taken as output port, and multiple beams of light converge after passing through this plane. The influences of length of GRIN lens, angle of inclined surface and distance between of fiber end and GRIN lens on coupling efficiency were analyzed. The results show that this kind of combiner has very high efficiency for multi-beam coupling, and the coupling efficiency of N×1 fiber pump combiner reaches 97.64%. When the length of GRIN lens was between 7.36mm and 7.96mm, the coupling efficiency of the beam combiner can be maintained above 95%. When the slope angle φ is 40.995︒ <φ< 43.095︒, the coupling efficiency of the combined beams were greater than 97%.
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