High-power supercontinuum generation in highly nonlinear, dispersion-shifted fibers by use of a continuous-wave Raman fiber laser

High-power supercontinua are demonstrated in highly nonlinear, dispersion-shifted fibers with a continuous-wave Raman fiber laser. Supercontinuum growth is experimentally studied under different combinations of fiber length and launch power to show output powers as high as 3.2 W and bandwidths greater than 544 nm. Modulation instability (MI) is observed to seed spectral broadening at low launch powers, and the interplay between MI and stimulated Raman scattering plays an important role in the growth of the continuum at high launch powers. The effect on continuum generation of parametric four-wave mixing coupled with the higher-order dispersion properties of the fiber is investigated.     

Temperature effects on supercontinuum generation using a continuous-wave Raman fiber laser

We describe the effect of temperature variations on supercontinuum (SC) generation in optical fibers using a continuous-wave (CW) Raman fiber laser as a pump. We achieve supercontinuum generation by pumping only ∼2 W of power into a 7 km-long nonzero dispersion-shifted fiber (NZDSF) in the region of small anomalous dispersion. In these conditions, the supercontinuum builds up basically on modulational instability and Raman. At room temperature, the supercontinuum covers effectively the S, C and L transmission bands defined by the International Telecommunication Union (ITU). Temperature tuning of the fiber environment provides a means of tuning the fiber dispersion, and thus a means of changing the width and shape of the supercontinuum spectrum. We demonstrate a 27% increase in the 10-dB SC width. We believe that the application of this new tuning mechanism to other experimental configurations using pulsed sources might be used to produce extremely broad supercontinuums.     

Experimental investigation of supercontinuum generation in highly nonlinear dispersion-shifted fiber pumped by spectrum-sliced amplified spontaneous emission

Spectral broadening of spectrum-sliced amplified spontaneous emission (SS-ASE) in highly nonlinear, dispersion-shifted fiber in different dispersion regimes is investigated experimentally. We find that, the spectral noise of the amplified SS-ASE pump from Er³⁺-doped fiber amplifier seeds the spectral broadening via four-wave mixing or modulation instability. Stimulated Raman scattering, red-shifted Raman solitons, and blue-shifted dispersion waves all enhance the broadening of the spectrum. The effect of the polarization state of pump on supercontinuum generation is also investigated, and it is found that, linear polarization is more efficient than random polarization for pumping supercontinuum. Supercontinuum with −10 dB bandwidth of 200 nm is generated by launching linearly polarized pump with 33.5 dB m power into anomalous dispersion regime near to zero dispersion wavelength of fiber.     

120-nm,10-GHz supercontinuum generation in a dispersion-shifted fiber pumped by a three-stage compressed gain-switched DFB laser

The supercontinuum (SC) generation in conventional dispersion-shifted fiber (DSF) at the repetition rate of 10 GHz with a three-stage compressed gain-switched distributed feedback (DFB) laser as pump source was demonstrated. A novel SC pulse source with a bandwidth up to 120 nm was obtained. At the same time, the stable, narrow pulses with pulsewidth of 9.2 ps and time-bandwidth product of 0.46 were filtered out across the whole SC bandwidth.     

Pulsed and continuous-wave supercontinuum generation in highly nonlinear, dispersion-shifted fibers

Supercontinuum generation in a highly nonlinear, dispersion-shifted fiber at 1550 nm is discussed. Spectrum generation under both pulsed and continuous-wave conditions is considered. With a few meters of highly nonlinear, dispersion-shifted fiber and a femtosecond erbium fiber laser, an octave-spanning supercontinuum is demonstrated. Kilometer lengths of nonlinear fiber pumped by a continuous-wave Raman fiber laser are shown to generate a continuum with a bandwidth greater than 247 nm. A nonlinear Schrödinger-equation model is used to investigate the effect of varying the dispersion on the pulsed continuum and noise effects in the continuous-wave continuum. PACS 42.81.Dp; 42.65.Wi; 42.55.Wd     

Supercontinuum generation in short dispersion-shifted fiber by a femtosecond fiber laser

The supercontinuum generation has been obtained in short conventional dispersion-shifted fiber using the femtosecond pulses from a passively mode-locked erbium-doped fiber laser. In the experiment, the supercontinuum spectrum of >300 nm has been observed by injecting 70-fs pulses into a several-meter dispersion-shifted fiber. The simulation of the evolution in the fiber shows that spectral broadening arises from soliton dynamics when pumping using femtosecond pulses in the anomalous group velocity dispersion regime of the fiber.     

中红外超连续谱在氟化物光纤中的产生

为获得高功率全光纤中红外超连续谱,采用自制的掺Er锁模光纤激光器作为种子源,激光经过两级放大至1.67 W,泵浦氟化物光纤,获得光谱覆盖1000~2400 nm的超连续光谱;光谱宽度随着泵浦功率的增加而展宽,当输出功率达到1.21 W时,转换效率为72%,并且产生的超连续谱被强烈的调制,在多个波长点处谱功率密度调制到0 mW/nm,但调制波长与泵浦功率无关。     

High-efficiency generation of a supercontinuum in an optical fiber

The results of experimental studies of high-efficiency generation of a supercontinuum in different types of single-mode optical fibers by pulses with a width of ～20 ps and with a wavelength widely tunable within the regions of normal and anomalous dispersion of the fibers are reported. A high efficiency of transformation of initially monochromatic radiation into a wide-spectrum supercontinuum with intense wings (in the range of 1000–2100 nm at a transformation efficiency of 95%) is demonstrated.     

Extended continuous-wave supercontinuum generation in a low-water-loss holey fiber

We report on the development of a 2.5 microm core photonic crystal fiber with a substantially reduced water-peak loss around 1.38 microm, which allows extended Raman-soliton supercontinuum generation up to 1.55 microm with a cw ytterbium fiber laser pump source. The resulting broadband, high-spectral-power-density, low-coherence light source can be employed for advanced, submicrometer resolution optical coherence tomography.     

Generation of a broadband single-mode supercontinuum in a conventional dispersion-shifted fiber by use of a subnanosecond microchip laser

We report the experimental generation, simply by use of a subnanosecond microchip laser at 532 nm and a conventional dispersion-shifted fiber, of a supercontinuum that spans more than 1100 nm. We show by detailed spectral analysis that this supercontinuum originates from a preliminary four-wave mixing process with multimode phase matching and subsequent double-cascade stimulated Raman scattering and is transversely single mode as a result of Raman-induced mode competition. This technique is believed to be the simplest configuration that allows one to generate a stable supercontinuum.     

双零色散光子晶体光纤中可见光超连续谱的产生

在掺镱锁模光纤激光器发出的皮秒脉冲的抽运下,本文报道了双零色散的多芯光子晶体光纤中可见光超连续谱的产生.这种光子晶体光纤的类似同轴双芯结构提供了相隔很近的双零色散点.第二个零色散波长的存在阻止了反常色散区内的由脉冲内拉曼散射引起的孤子的频移,形成了稳态孤子,在短波长和长波长方向上的正常色散区均产生了可观的色散波.在2 W的平均功率下得到了550 nm到1700 nm的超连续谱.此外,光纤的同轴双芯特性也导致了入射脉冲的模式转换.实验结果和数值计算十分符合.     

Demonstration of supercontinuum generation in a long-cavity fiber ring laser

We demonstrate generation of supercontinuum pulses directly from a passively mode-locked long-cavity fiber ring laser. The laser output exhibited a blueshifted spectrum extending from 1350 to 1550 nm with an average output power greater than 60 mW.     

High power supercontinuum generation in a nonlinear ytterbium-doped fiber amplifier

High power supercontinuum generation with 70 W average output power in a nonlinear ytterbium-doped fiber amplifier is demonstrated using all-normal dispersion, all-fiber master oscillator power amplifier configuration. The supercontinuum covers from 1064 nm to beyond 1700 nm with spectral flatness better than 12 dB and 67.3% optical to optical conversion efficiency. The almost uniform spectral power density across the whole continuum is more than 70 mW/nm and the nanosecond bursts output have an effective peak power of 82.7 kW.     

Multiwatt octave-spanning supercontinuum generation in multicore photonic-crystal fiber

High-power supercontinuum spanning over more than an octave was generated using a high power femtosecond fiber laser amplifier and a multicore nonlinear photonic crystal fiber (PCF). Long multicore PCFs (as long as 20 m in our experiments) are shown to enable supercontinuum generation in an isolated fundamental supermode, with the manifold of other PCF modes suppressed due to the strong evanescent fields coupling between the cores, providing a robust 5.4 W coherent supercontinuum output with a high spatial and spectral quality within the range of wavelengths from 500 to 1700 nm.     

七芯光子晶体光纤中百瓦量级超连续谱的产生

采用平均功率为141.6 W的皮秒光纤激光泵浦一段国产七芯光子晶体光纤,获得了平均功率为104.2 W、连续光谱覆盖范围从750至1700 nm以上的超连续谱输出.详细研究了超连续光谱随泵浦功率增加的演变过程,并对基于该七芯光子晶体光纤的超连续谱光源的光谱拓展和功率提升潜力进行相关的分析和讨论.该研究结果对高功率超连续谱光源的发展具有一定的参考价值.     

Noise amplification during supercontinuum generation in microstructure fiber

Supercontinua generated by femtosecond pulses launched in microstructure fiber can exhibit significant low-frequency (<1-MHz) amplitude noise on the output pulse train. We show that this low-frequency noise is an amplified version of the amplitude noise that is already present on the input laser pulse train. Through both experimental measurements and numerical simulations, we quantify the noise amplification factor and its dependence on the supercontinuum wavelength and on the energy and duration of the input pulse. Interestingly, the dependence differs significantly from that of the broadband white-noise component, which arises from amplification of the input laser shot noise.     

White-light supercontinuum generation with 60-ps pump pulses in a photonic crystal fiber

The generation of a spatially single-mode white-light supercontinuum has been observed in a photonic crystal fiber pumped with 60-ps pulses of subkilowatt peak power. The spectral broadening is identified as being due to the combined action of stimulated Raman scattering and parametric four-wave-mixing generation, with a negligible contribution from the self-phase modulation of the pump pulses. The experimental results are in good agreement with detailed numerical simulations. These findings demonstrate that ultrafast femtosecond pulses are not needed for efficient supercontinuum generation in photonic crystal fibers.     

基于光子晶体光纤的百瓦量级超连续谱光源研究

采用脉冲重复频率可调的高功率皮秒脉冲光纤激 光抽运光子晶体光纤产生了平均输出功率为101 W的全 光纤化超连续谱. 通过一系列的对比实验, 详细研究了抽运激光的脉冲重复频率以及光子晶体光纤的长度对超连续谱产生的影响. 最后, 对如何实现更高平均功率的超连续谱输出进行相关的分析和讨论. 相关研究结果可以为进一步发展基于光子晶体光纤的高功率超连续谱光源提供一定的参考. 关键词： 光子晶体光纤 非线性光纤光学 超连续谱产生     

Raman effects in the infrared supercontinuum generation in soft-glass PCFs

Measurements of the Raman gain spectra in the SF6 and SF57 highly nonlinear glasses demonstrated twice as high Raman shift in comparison with the fused silica. Numerical simulation predicted that a large Raman shift in combination with high nonlinearity can significantly reduce the required input pulse intensity for supercontinuum in these glasses, retaining the necessary degree of coherence. We found that the degradation of the SC coherence due to Raman soliton jitter can be effectively controlled by a correct choice of input intensity and fiber length. Also it was found that a high degree of coherence correlates with the spectrum shape in the vicinity of the Raman threshold, providing an convenient experimental observable. PACS 42.65.Tg; 42.81.Dp; 42.72.Ai     

光子晶体光纤超连续谱产生的实验研究

报道了利用掺钛蓝宝石飞秒激光器产生重复频率为80MHz,脉宽为10fs的超短激光脉冲在10cm长光子晶体光纤产生超连续谱的实验,获得展宽范围为450nm到1100nm的连续谱。实验中观察到孤子自频移和高阶孤子分裂现象,非孤子辐射与随后光谱向短波方向的拓展有密切关系。