Parametrically amplified ultrashort pulses from a shaped photonic crystal fiber supercontinuum

By seeding a noncollinear optical parametric amplifier with a photonic crystal fiber supercontinuum, temporally well-defined amplified output pulses have been generated with durations down to 13 fs. The phase of the supercontinuum seed has been characterized by the ZAP-SPIDER technique and can be tailored with a femtosecond pulse shaper. Thus, a very flexible source for arbitrarily shaped, amplified ultrashort laser pulses has been realized.     

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.     

飞秒激光在光子晶体光纤中产生超连续光谱机制的实验研究

报道了利用零色散在780nm处的光子晶体光纤与纳焦耳量级的飞秒激光脉冲相互作用的实验结果.实验使用35fs，中心波长810—840nm，单脉冲能量可达14nJ的飞秒激光光源获得了超过一个倍频程的平坦超连续光谱（500—1100nm）.在不同功率、不同中心波长、不同啁啾和有无直流成分的多种飞秒脉冲激光的条件下，研究了超连续光谱的产生情况.并对一系列现象进行了对比，分析了超连续光谱产生的机制. 关键词： 光子晶体光纤 飞秒脉冲激光 超连续光谱     

Self-Q-switched Er-Brillouin fiber source with extra-cavity generation of a Raman supercontinuum in a dispersion-shifted fiber

Brillouin mirrors based on a single-mode optical fiber provide the simplest, completely passive, and most universal way to produce nanosecond pulses with extensive wavelength tunability. We propose an all-fiber solution, where a passively Q-switched Er-doped Briilouin fiber laser pumped by a low-power laser diode produces pulses with a peak/average power contrast of 500 W/25 mW and, in association with a conventional dispersion-shifted fiber employed as an extracavity nonlinear medium, causes the generation of a nanosecond supercontinuum extending from 900 to over 1800 nm. Expanding evolution of the spectrum kicked off by the multicascade Brillouin process is reported.     

利用锁模光纤激光器在色散位移光纤中产生超连续谱的研究

采用主动锁模光纤激光器输出的重复频率10GHz、脉宽7．97ps的脉冲作为抽运光源,无需压缩后直接抽运4．2km的普通色散位移光纤(DSF)．利用色散位移光纤中自相位调制、交叉相位调制等非线性效应的联合作用,获得了20dB带宽达125nm、覆盖整个C波段、L波段和部分S波段的超连续(SC)谱。实验研究了抽运光脉冲峰值功率和抽运波长对超连续谱宽度的影响,结果表明抽运光脉冲峰值功率越高,得到的超连续谱的带宽越宽;通过对抽运波长的优化,可以实现最大程度的超连续展宽;分析了滤波器带宽对脉冲质量的影响;利用0．4nm带宽的可调谐滤波器对从超连续谱中滤出脉冲的特性进行了研究,在超连续谱的不同波长处获得了脉宽为8．90～9．80ps、时间一带宽积为0．44～0．49的稳定的窄光脉冲。     

Continuous-wave supercontinuum laser based on an erbium-doped fiber ring cavity incorporating a highly nonlinear optical fiber

We experimentally demonstrate a novel erbium-doped fiber based continuous-wave (cw) supercontinuum laser. The laser has a simple ring-cavity structure incorporating an erbium-doped fiber and a highly nonlinear dispersion-shifted fiber (HNL-DSF). Differently from previously demonstrated cw supercontinuum sources based on single propagation of a strong Raman pump laser beam through a highly nonlinear fiber, erbium gain inside the cavity generates a seed light oscillation, and the oscillated light subsequently evolves into a supercontinuum by nonlinear effects such as modulation instability and stimulated Raman scattering in the HNL-DSF. High quality of the depolarized supercontinuum laser output with a spectral bandwidth larger than 250 nm is readily achieved.     

光子晶体光纤超连续谱产生过程中色散波的孤子俘获研究

基于光子晶体光纤中脉冲演化遵循的非线性薛定谔方程, 用数值模拟的方法分别研究了飞秒脉冲在单零色散点和双零色散点光子晶体光纤中超连续谱的产生和色散波的孤子俘获现象. 结果表明: 与单零色散点光子晶体光纤相比, 双零色散点光子晶体光纤产生的超连续谱既包含了蓝移色散波, 又包含了红移色散波, 且当满足群速度匹配时, 孤子通过四波混频不仅能俘获蓝移色散波, 而且能俘获红移色散波, 从而产生新的俘获波频谱成分. 为了清楚地观察脉冲传输的时频特性, 通过模拟交叉相关频率分辨光学开关技术, 得到了孤子俘获色散波的演化过程. 关键词： 超连续谱 色散波 孤子俘获 光子晶体光纤     

Pulse collapse and blue-shifted enhanced supercontinuumin photonic crystal fiber

The blue-shifted supercontinuum generation in a photonic crystal fiber pumped by high peak power femtosecond pulses with wavelength located in the anomalous dispersion region is investigated experimentally and numerically. The formation of a blue-shifted enhanced supercontinuum due to the pulse collapse is demonstrated. The process of the pulse collapse is measured by using the grating-eliminated no-nonsense observation of ultrafast incident laser light e-fields technique (GRENOUILLE). Numerical simulations in spectral and temporal domains are conducted. The data from numerical simulations are in good agreement with the experimental results. Our experimental results and numerical simulations show that the pulse collapse is the determining factor in the generation of blue-shifted supercontinuum.     

Fundamental amplitude noise limitations to supercontinuum spectra generated in a microstructured fiber

Broadband supercontinuum spectra are generated in a microstructured fiber using femtosecond laser pulses. Noise properties of these spectra are studied through experiments and numerical simulations based on a generalized stochastic nonlinear Schrödinger equation. In particular, the relative intensity noise as a function of wavelength across the supercontinuum is measured over a wide range of input pulse parameters, and experimental results and simulations are shown to be in good quantitative agreement. For certain input pulse parameters, amplitude fluctuations as large as 50% are observed. The simulations clarify that the intensity noise on the supercontinuum arises from the amplification of two noise inputs during propagation – quantum-limited shot noise on the input pulse, and spontaneous Raman scattering in the fiber. The amplification factor is a sensitive function of the input pulse parameters. Short input pulses are critical for the generation of very broad supercontinua with low noise. PACS 42.50.Lc; 42.65.Re; 42.81.Dp; 02.60.CbAn Erratum to this article can be found at     

All fiber supercontinuum light source using photonic crystal fibers pumped by nanosecond fiber laser pulses

A novel compact supercontinuum (SC) source using the single mode photonic crystal fibers (PCF) pumped with an all fiber MOPA fiber laser is demonstrated experimentally. A bandwidth of 700 nm is achieved by operating the pumping fiber laser at a wavelength of 1064 nm, pulse duration of 10 ns, repetition rate of 50 kHz and peak power of 1 kW. The SC generation is initiated through modulation instability (MI) which breakups the nanosecond pump pulses into picosecond or femtosecond pulses, and further broadened through nonlinear effects of PCF.     

Spectral-temporal properties and nonlinear-optical transformation of supercontinuum radiation with an energy over 1 μJ generated by a large-mode-area photonic-crystal fiber

Nonlinear-optical transformation of chirped femtosecond Cr:forsterite-laser pulses in a large-mode-area photonic-crystal fiber gives rise to the generation of a supercontinuum in the near infrared spectral range with an energy exceeding 1 μJ. A broadband light source with a wavelength tunability range from 550 to 1800 nm is implemented through second-harmonic-and sum-frequency-generation transformation of the supercontinuum photonic-crystal fiber output.     

Pulse collapse and blue-shifted enhanced supercontinuum in a photonic crystal fiber

The blue-shifted supercontinuum generation in a photonic crystal fiber pumped by high peak power femtosecond pulses with a wavelength located in the anomalous dispersion region is investigated experimentally and numerically.The formation of a blue-shifted enhanced supercontinuum due to the pulse collapse is demonstrated.The process of the pulse collapse is measured by using the grating-eliminated no-nonsense observation of ultrafast incident laser light e-fields technique(GRENOUILLE).Numerical simulations in spectral and temporal domains are conducted.The data from the numerical simulations are in good agreement with the experimental results.Our experimental results and numerical simulations show that pulse collapse is the determining factor in the generation of a blue-shifted supercontinuum.     

A novel ultra-broadband transient spectrometer with microsecond measurement range based on a supercontinuum fiber laser

We show that the combination of a free-running 24 kHz supercontinuum fiber laser with a kHz femtosecond laser renders a sensitive and easy to implement transient spectrometer. It can directly extend the observation range of a standard broadband femtosecond spectrometer from the usual limit of a few nanoseconds to 1 millisecond and with the additional use of a chopper to seconds. The transmission signal from all supercontinuum pulses is recorded and assigned to the proper delay time by data post-processing. To demonstrate the performance of the device, the relaxation dynamics of Nd:YAG is measured.     

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     

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.     

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.     

Chirped pulse amplification in single mode Tm:fiber using a chirped Bragg grating

We report femtosecond pulse generation and chirped pulse amplification in Tm:fiber. A mode-locked oscillator operating in the soliton regime produced 800 fs pulses with 5 nm spectral bandwidth, at 40 pJ pulse energy. This oscillator seeded a pre-amplifier that utilizes a Raman soliton self-frequency shift to produce wavelength tunable pulses with 3 nJ energy, reduced pulse duration of 150 fs, and increased bandwidth of 30 nm. For further amplification, the pulses were stretched up to 160 ps using a chirped Bragg grating (CBG). Stretched pulses were amplified to 85 nJ after compression in single-mode Tm:fiber and recompressed with the CBG as short as 400 fs. Compressed pulses were coupled into a highly nonlinear tellurite fiber to investigate the potential of this ultrashort pulse 2-μm fiber source as a pump for mid-IR supercontinuum generation.     

基于光子晶体光纤和拉锥式单模光纤的超连续光谱产生的实验研究

本文使用重复频率为250 MHz、脉冲宽度为135 fs、最大功率为2.2 W的锁模掺镱光纤激光作为种子源,利用光子晶体光纤和自制的拉锥式单模光纤两种高非线性光纤研究了超连续光谱的产生特性,通过对比两种光纤的结构、色散等特性,分析了拉曼孤子、色散波及其他非线性效应对产生的超连续谱形状的影响,并均得到了大于一个倍频程的超连续光谱,特别是拉锥式单模光纤产生的超连续光谱,耦合效率达到60%,这为众多研究领域,尤其是光学频率梳的建立提供了实用的超连续光源.     

孤子光脉冲的产生及其应用研究

利用非线性偏振旋转技术实现自起振被动锁模.在掺铒光纤环形腔激光器中产生了中心波长为1563.3 nm、重复频率为12.5 MHz、脉冲宽度为352.0 fs、3 dB光谱宽度为7.8 nm的孤子光脉冲.采用该孤子光脉冲作为抽运光源，经掺铒光纤放大器放大后，输入到101 m长的高非线性光子晶体光纤中，获得了20 dB带宽约为240 nm的超连续激光光谱.实验详细观测了光脉冲随抽运功率的变化及超连续激光光谱的形成过程，分析了其形成机理.研究表明：当抽运功率较低时，光谱加宽主要由高阶孤子的分裂引起；随着抽运功率的增加，高阶孤子分裂成基本孤子的数目逐渐增大，光谱进一步加宽；当抽运功率增加到受激拉曼散射的阈值时，受激拉曼散射成为光谱展宽的主要原因；抽运功率进一步增加时，受激拉曼散射、参量四波混频等非线性的共同作用将使光谱进一步加宽且变得光滑. 关键词： 孤子光纤激光器 超连续 光子晶体光纤     

Supercontinuum generation in an anisotropic microstructure fiber with periodic modulation of hole ellipticity

The supercontinuum generation in an anisotropic microstructure fiber with periodic modulation of hole ellipticity has been numerically simulated. The structure proposed makes it possible to alternate fiber segments with positive and negative differences in group velocities, thus affecting the interaction of pulses with orthogonal polarizations. This configuration makes it possible to effectively control supercontinuum generation. The dynamics of polarized solitons in a microstructure fiber with high nonlinearity is simulated using the modified Schrödinger equation, including the stimulated Raman scattering and higher order dispersion.