Research On The Side-pumping Combiner And Supercontinuum Generation Based On Fiber Tapering

Pump/signal fiber combiner is one of the most core components of high power laser and amplifier in all-fiber structure.Recently,side-pumping combiner has attracted researchers' great attention due to its un-interrupted signal fiber core and un-limited pump points.Among many types of side-pumping combiner which have been reported recently,a fused tapered method,seems to be a more potential method because of its high coupling efficiency and the capability of handling high pump power up to kW-class.The numerical and experimental investigation about the the side-pumping combiners based on fused tapered method is demonstrated.Besides,a novel method of extending the spectral range of Supercontinuum(SC)directly from an Ytterbium-doped fiber amplifier(YDFA)based on double-clad passive fiber tapers and the related experiment are presented.1.Using both the geometrical optics and wave optics,the pump light propagation in the tapered pump fiber,as well as the normalized pump light vignetting length with the respect to the pump light incident angel and taper ratio,is analyzed.Based on the basic optical theory of the fused taper side-pumping combiner and fabrication process of the fused tapered method,it is the first time to introduce fused ratio and fused depth between the pump fiber and the signal fiber into the numerical model of the combiner.The influence of these two parameters and other structure parameters on the performance of the combine is analyzed.The simulation results show that: the rise of fused depth leads to the coupling efficiency growth as well as the decrease of leakage power from the coating(LPC)of the signal fiber while backward pump isolation(BPI)becomes worse at the same time.2.(2+1)×1 side-pumping combiners with a 20/400 ?m signal fiber and two 220/242 ?m pump fibers are fabricated by using fused tapered technology.The coupling efficiency versus fusion time is measured,which shows good agreement with the numerical results.The total pump efficiency,the working temperature of the coating of signal fiber,the signal insertion loss and BPI of the combiner are measured.A total coupling efficiency of 97.2% is achieved when injecting 1223 W pump power.The highest signal insertion loss is about 0.11 dB.The combiner is also successfully applied in kW-class all fiber laser amplifiers.3.For the purpose of making up for the the shortcoming that SC generated directly in YDFA can only extend to longer wavelength rather than shorter wavelength,tt is the first time to develop a SC generation by using broadband spectrum light source from an YDFA to pump double-clad passive fiber tapers,which can experimentally result in the two times of spectral range to that directly from an YDFA.A seed pulse at 1060 nm is amplified to 15.9 W and spectrally broadened from 1000 nm to 1600 nm in an YDFA system.Using this broadband source to pump cascaded double-clad passive fiber tapers,a 14.1 W SC source is obtained,covering 630 nm to 2000 nm.It is found that the use of fiber tapers lead to a proper group velocity matching between the red-shift solitons and blue-shift dispersion wave as well as an enhanced nonlinear parameter.