光子晶体光纤拉曼激光器研究

利用100m非线性光子晶体光纤，以光纤光栅对作为谐振腔，研制成功了低阈值光子晶体光纤拉曼激光器．该光子晶体光纤拉曼激光器的闽值为2W，在抽运功率6．2W时，得到最大功率为1．8W．波长为1115．9nm的连续拉曼激光输出，拉曼半峰全宽为1．39nm，对应光-光转化效率29％，斜率效率41％．且在低功率连续光泵浦下观察到5级拉曼荧光．

Research on the Raman photonic crystal fiber laser

Photonic crystal fibers(PCFs) can be designed with a much larger nonlinear coefficient by reducing mode area through its air hole microstructure region,thus leading to orders of magnitude higher Raman gain.So PCF Raman laser(PCF-RL) can greatly reduce cavity length while maintaining a low-pump-threshold.A low-pump-threshold photonic crystal fiber Raman laser was demonstrated,with 100 m nonlinear photonic crystal(Crystal Fiber A/S,NL-1550) fiber as gain medium.Both ends of the PCF were spliced to standard single mode fiber using a piece of tapered fiber to provide matched mode field diameter.The cavity utilized a pair of fiber Bragg gratings(FBGs) at 1 115.7 nm as resonator.The FBG at the input end has a reflectivity larger than 99.9% and spectral width of ~0.26 nm,while the other at the output end is of 92% reflectivity and ~0.1 nm spectral width.A 20W,CW ytterbium fiber laser(IPG Model PYL-20M) with a single-mode randomly polarized 1 070 nm output was used as the pump.The collimated laser beam emerging from the pumping source was coupled into the input FBG with a coupling efficiency of 46%.The Stokes spectral evolution was studied.The luminescence spectrum of the fifth order Stokes was observed at a low continuous wave pump power of 0.046 W.The peak wavelength of each order stokes luminescence was(1 124.1) nm(S1),1 187.3 nm(S2),1 259.9 nm(S3),1 323.9 nm(S4),1 400.5 nm(S5),corresponding respctively to a frequency shift X1=444.6 cm~(-1),X2=473.3 cm~(-1),X3=485.8 cm~(-1),X4=383.2 cm~(-1),X5=413.4 cm~(-1).When reaching the threshold pump power of 2 W,the Raman luminescence disappeared and the laser of(1 115.9) nm was emitted.Increasing the pump power,the pump translated to Raman laser and the central wavelength of the laser was basically stable,with the spectrum width gradually broadening.The maximum output power was 1.8 W at the incident pump power of 6.2 W.Consequently,the optical conversion efficiency and the maximum slope efficiency were 29% and 41% respectively.The FWHM of lasing light was 1.39 nm.From ASE measurements,the peak Raman gain was found to be at 1 124.6 nm rather than 1 115.9nm.When the incident pump power was over 6.67 W,the 1 124.6nm Stokes at the peak Raman gain would be generated.Because the cavity gain at this wavelength is higher than the cavity loss beyond this pump power level,so the 1 124.6 nm lasing light would take part in the mode competition.We believe that,with a pair of specially designed FBG at the peak Raman gain region,lower threshold pump power and higher output power would be achieved.