光纤中无波分裂脉冲的平坦超连续谱产生

Flat supercontinuum generation via wave-free breaking pulse in the optical fiber

基于无波分裂脉冲产生的平坦超连续谱被报道。笔者采用非线性偏振旋转(NPR)作为锁模方法来实现耗散孤子脉冲和无波分裂脉冲的切换输出。在0.3 W的泵浦功率下,获得了耗散孤子脉冲。脉冲宽度为5.8 ps,脉冲间隔为54 ns,与11.05 m的腔长一致,信噪比为55 dB,压缩后的脉冲宽度为0.61 ps。值功率可以被提升到1.18 kW。通过适当调整腔偏振态和增加泵浦功率,耗散孤子可以演化为无波分裂脉冲。随着泵浦功率的提高,脉冲宽度从11.7 ps增加到20.2 ps,几乎增加了两倍。经过计算,时间带宽积从23.9增加到53.43。较大的啁啾可以抵抗非线性相移的影响,从而避免脉冲分裂。无波分裂脉冲的脉冲能量可以提高到3.89 nJ,是耗散孤子脉冲能量的五倍。随后,使用耗散孤子和无波分裂脉冲作为种子源去获得超连续谱。结果表明,在锥形高非线性光纤中,无波分裂脉冲产生的超连续谱范围和平坦度均优于耗散孤子脉冲。基于耗散孤子脉冲和无波分裂脉冲产生的超连续谱范围为1400~2000 nm,覆盖了S波段、C波段、L波段三个主要通信波段,20 dB带宽分别为310.3 nm和426.4 nm。这项工作将有助于高能量脉冲光纤激光器的发展,并提高其在超连续谱产生和光通信领域的潜在应用。

Objective Supercontinuum light source has the advantages of wide spectral range and good spatial coherence.Thus,it is widely applied in optical communication,optical frequency comb,optical fiber sensing,spectrum detection,and other fields.With the development of new technology such as optical coherence tomography and fluorescence lifetime imaging,supercontinuum light source has become an interesting research field.Although the combination of 1.55μm mode-locked pulse and highly nonlinear fiber can realize all-fiber near-infrared supercontinuum light source.However,due to the low output energy of the mode-locked pulse,the energy of the supercontinuum light source is mainly concentrated in the spectral region of the pump wavelength.How to enhance the coverage and flatness of the near-infrared supercontinuum is a problem need to be solved.For this purpose,we designed a high-energy erbium-doped fiber laser.Methods The generation of flat supercontinuum via wave-free breaking pulse is proposed.Nonlinear polarization rotation(NPR)is employed as a mode-locking way to switch the output of dissipative soliton pulse and wave-free breaking pulse(Fig.1).Dissipative soliton pulse is obtained at 0.3 W pump power(Fig.3).The pulse width is 5.8 ps,and the pulse interval is 54 ns corresponding to the cavity length of 11.05 m.The signal-to-noise ratio is 55 dB,and the compressed pulse width is 0.61 ps(Fig.4).The pulse peak power can be increased to 1.18 kW.By properly adjusting the cavity polarization state and increasing the pump power,the dissipative soliton pulse can evolve into wave-free breaking pulse(Fig.5).With the increase of pump power,the pulse width increases almost twice from 11.7 ps to 20.2 ps.After calculation,the time bandwidth product increases from 23.9 to 53.43.The larger chirp can resist the influence of nonlinear phase shift,avoiding pulse splitting.The pulse energy of wavefree breaking pulse can be increased to 3.89 nJ,which is five times of the pulse energy of dissipative soliton(Fig.6).Results and Discussions we use dissipative soliton pulse and wave-free breaking pulse as seed sources to obtain supercontinuum in tapered highly nonlinear fiber.After the taper is pulled,the core diameter will change from 9μm to 6μm.Since the peak power of the wave-free breaking pulse has been maintained at about 197 W,which can effectively avoid the pulse splitting caused by higher-order dispersion and nonlinear disturbance of the tapered high nonlinear fiber,and the spectrum can be effectively broadened by self-phase modulation.In the experiment,the total length of the tapered highly nonlinear fiber is 4 m,the waist area is 3 m,and the taper region is 1 m(Fig.2).The results show that the supercontinuum range and flatness produced by wave-free breaking pulse is better than dissipative soliton pulse in tapered highly nonlinear fiber(Fig.7).The supercontinuum range based on dissipative soliton pulse and wave-free breaking pulse is 1400-2000 nm covered communication region of Sband,C-band,and L-band.And the 20 dB bandwidth is 310.3 nm and 426.4 nm respectively.Conclusion A passively mode-locked structure of nonlinear polarization rotation is used to realize ultra-fast pulse output.And the conversion of dissipative soliton pulse and wave-free breaking pulse is realized through dispersion management.Under the mode-locked state of dissipative soliton pulse,the maximum output pulse energy is 0.82 nJ,and the peak power is 124.4 W.By adjusting the cavity parameters and increasing the pump power,the mode-locked state of wave-free breaking pulse can be realized.The pulse energy of wave-free breaking pulse can be increased to 3.89 nJ,which is 5 times of the energy of dissipative soliton pulse.In tapered HNLF,the flatness of supercontinuum generated by employing wave-free splitting pulse as seed source is better than dissipative soliton pulse.At the same time,the supercontinuum range covers three main communication bands(S-band,C-band and L-band).This flat supercontinuum is not only of great significance for the research of multi-channel wavelength division multiplexing light source applications,but also can be applied in biomedical imaging and other fields.This work will contribute to the development of high-energy pulse fiber lasers and improve their potential applications in supercontinuum generation and optical communication.