| Supercontinuum(SC)is the generation of intense ultrafast broadband pulses spanning the ultraviolet to the near infrared that arises from the nonlinear interaction.Because of the combination of high brightness and ultra-broad spectral coverage,SC sources are widely applied to a range of fields including spectroscopy,biomedical field and material chacraterization et.al..The traditional strategy of visible SC generation is using the 1.06 ?m ytterbium-doped pulsed lasers to pump the photonic crystal fiber(PCF).A series of deep-blue SC sources with short wavelength edge extending to 300-400 nm have been developed in PCFs with very small core diameter with <1 ?m zero dispersion wavelength(ZDW).However,the shifting of ZDW away from the pump wavelength of 1.06 ?m reduces the blue-shifted power.Besides,the power scaling of the PCF with small core diameter to higher levels could be challenging.Therefore,in the tradisional strategy of visible SC generation,there is a contradiction between the spectrum extension to deep-blue and the improvement of the output power and the blue-shifted power.We propose and demonstrate a new technique to generate high-power visible-enhanced SC.The SC is generated in a newly-designed seven-core PCF,with a high air-filling fraction,pumped by a high power 1016 nm pulsed fiber laser,whereby the short-wavelength extension,output power and blue-shifted power are all improved.The main contents are as follows:Firstly,we proposed a new technique of SC generation in a seven-core PCF pumped by a short-wavelength(near the ZDW of the multi-core PCF)pulsed fiber laser,to achieve a high-power visible-enhanced SC.The new technique was confirmed by the numerical simulation results.We studied the denpendence of the dispersion property of multi-core PCFs on the structural parameters,including the air hole diameter and the hole-to-hole center spacing in the fiber cladding.Then we designed a seven-core PCF and a three-core PCF with tailored dispersion characteristic for visible SC generaion.The numerical results comfirmed that the new technique of SC generation in the newly designed multi-core PCF pumped at short wavelength,is benefical for spectrum extension as well as the enhancement of blue-shifted light.Secondly,a 153 W 1016 nm pulsed all-fiber laser was experimentaly demonstrated.This is,to the best of our knowledge,the best result in pulsed fiber lasers at the special wavelength of <1020 nm.A semiconductor saturable absorber mirror(SESAM)passively mode-locked fiber laser at 1016 nm with pulse width of 120 ps was firstly demonstrated.Then by optimizing the length of yetterbium-doped fiber(YDF),filtering the residual ASE in signal and multiplying the repeatation rate of the pulses to suppress nonlinearity,the average power of the 1016 nm pulse train was boosted to 153 W by a four-stage YDF amplifier chain and the peak power was 11 kW.Thirdly,using the new technique of the visible SC generation in the newly-desighed seven-core PCF pumped by the high-power 1016 nm pulsed fiber laser,an 80 W 350-2400 nm monolithic visible-enhanced SC source was reported.To the best of our knowledge,the achieved output power and the high spectral power density across the visible region,are the best results reported for visible SC sources.The high-power 1016 nm pulsed laser was fusion spliced to the seven-core PCF with a low splicing loss of 0.2 dB.An end-cap was frabricated at the end of the seven-core PCF to avoid optical feedback and protect the PCF from humidity,dust and other contaminants.A 350-2400 nm SC with 80.8 W output power and a high spectral power density of up to 100 mW/nm(at 580 nm)and over 50 mW/nm across entire visible region was demonstrated. |
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