Spectrally and temporally isolated Raman soliton features in microstructure fibers visualized by cross-correlation frequency-resolved optical gating

We study soliton phenomena accompanying the propagation of femtosecond Cr: forsterite-laser pulses through a microstructure fiber in the regime of efficient anti-Stokes frequency conversion. The dispersion of the fiber is designed in such a way as to minimize the group delay of the 1.25-m pump and the Stokes pulse within the length of soliton pulse compression in the regime of anomalous dispersion. Spectrally and temporally isolated solitonic features, resulting from soliton self-frequency shift, are detected at the output of such a microstructure fiber by means of cross-correlation frequency-resolved optical gating. PACS 42.65.Wi; 42.81.Qb     

Enhanced soliton self-frequency shift of ultrashort light pulses

Photonic-crystal fibers are used to study scenarios of soliton self-frequency shift for laser pulses with initial pulse lengths much less than the Raman-mode period of the fiber material. A typical frequency shift of subnanojoule Ti: sapphire-laser pulses with an initial duration of about 30 fs transmitted through a fiber with a core diameter of about 1.6 μm and a length of about 7 cm exceeds 100 THz. The rate of soliton self-frequency shift is radically increased by reducing the initial pulse width.     

Soliton self-frequency shift in a short tapered air-silica microstructure fiber

We report a soliton self-frequency shift of more than 20% of the optical frequency in a tapered air-silica microstructure fiber that exhibits a widely flattened large anomalous dispersion in the near infrared. Remarkably, the large frequency shift was realized in a fiber of length as short as 15 cm, 2 orders of magnitude shorter than those reported previously with similar input pulse duration and pulse energies, owing to the small mode size and the large and uniform dispersion in the tapered fiber. By varying the power of the input pulses, we generated compressed sub-100-fs soliton pulses of ~1-nJ pulse energy tunable from 1.3 to 1.65 mum with greater than 60% conversion efficiency.     

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.     

在光纤零群速色散区传输的光孤子波

通过对超短光脉冲在单模光纤中传输方程的分析研究,给出了在零群速色散传输方程的亮,反波解。结果表明,超短光脉中在光纤的零群群速色散仍能以亮,暗孤波的形式传输,且不存在孤子自频移现象。     

高阶效应对光纤系统中孤子和艾里脉冲传输特性影响的数值研究

以变系数耦合高阶非线性薛定谔方程为理论模型,采用分步傅里叶方法,讨论了孤子和艾里脉冲在光纤中的传输特性。研究表明三阶色散、自频移和自陡峭效应导致孤子和艾里脉冲所分离出的俘获孤子的中心位置发生偏移,且三阶色散会影响俘获孤子的强度,并讨论了两脉冲的中心位置及强度对艾里脉冲截断系数的依赖关系。     

Pulse trapping by ultrashort soliton pulses in optical fibers across zero-dispersion wavelength

A new phenomenon of pulse trapping by the ultrashort soliton pulse of an optical fiber has been experimentally observed. The trapped pulse in the normal-dispersion region copropagates with the soliton pulse in the anomalous-dispersion region along the fiber, and the wavelength of the trapped pulse is shifted to satisfy the condition of group-velocity matching. The wavelengths of the soliton pulse and the trapped pulse change almost continuously as the power of the soliton pulse is varied. Almost perfect conversion efficiencies are observed for soliton self-frequency shift and pulse trapping.     

Soliton self-frequency shift in highly nonlinear fiber with extension by external Raman pumping

A completely fiber-integrated, wavelength-tunable subpicosecond pulse source is demonstrated using the soliton self-frequency shift in highly nonlinear dispersion-shifted fiber from a 1.56-microm 10-GHz 400-fs signal. Solitons as short as 100 fs are obtained at tunable wavelengths as high as 1.72 microm. Raman gain from an external pump is used to extend the soliton self-frequency shift to longer wavelengths.     

Wavelength-tunable high-energy soliton pulse generation from a large-mode-area fiber pumped by a time-lens source

We demonstrate high-energy soliton generation from 1560?nm to 1700?nm using soliton self-frequency shift in a large-mode-area fiber. A 1.5?ps time-lens source at 1544?nm is used as the input source. The combination of a time-lens source and soliton self-frequency shift in a large-mode-area fiber enables a turn-key, high pulse quality, wavelength-tunable, energetic femtosecond source with arbitrary pulse repetition rate.     

基于级联型光纤的孤子自频移增强特性

设计了一种10m掺铥光纤级联于3m大模场光子晶体光纤末端的结构,利用400fs、1 550nm脉冲光产生孤子自频移,在入射光功率相同的情况下,掺铥光纤末端的孤子频移量比大模场光纤末端多100~150nm,平均多30%左右.孤子与泵浦光在掺铥光纤末端的输出光谱表明,残留泵浦光作用于Tm3+,在1.8~2.1μm范围产生受激辐射,从而增强了拉曼效应,导致孤子自频移增强.实验结果揭示了一种增强孤子自频移效应的方法,对于了解孤子在光纤中频移特性和提高基于孤子自频移的可调谐光源的调谐范围等具有参考意义.     

Soliton self-frequency shift decelerated by self-steepening

Self-steepening of ultrashort light pulses is shown to reduce the soliton self-frequency shift (SSFS) induced by the Raman effect in an optical fiber. We derive an analytical expression for the SSFS that conserves the number of photons and allows the SSFS to be calculated for arbitrary frequency profiles of fiber dispersion and Raman gain without a numerical solution of the pulse evolution equation. The accuracy of this analytical approach to SSFS calculation is tested by numerical simulations based on the generalized nonlinear Schr?dinger equation.     

孤子激光器及其发展

激光和孤子研究的进展,导致一种新型的、输出脉宽及形状可控的超短光脉冲激光器——孤子激光器的诞生。孤子激光器在光通讯、光计算、超高速现象的研究、超高速光电子器件的研制等方面有其独特的应用。它也使我们有可能对孤子效应本身进行深入研究。本文将叙述在单模光纤中形成孤子的机制,孤子激光及喇曼孤子激光原理,孤子及孤子激光研究的进展,包括孤子激光的稳定性、孤子自频移以及孤子间的相互作用力等。最后介绍一些已经出现的或将来可能出现的应用,并指出这是一个正在迅速发展的研究领域。     

120 nm Bandwidth noise-like pulse generation in an erbium-doped fiber laser

We report on the generation of noise-like pulses with up to 120 nm bandwidth in a passively mode-locked erbium-doped fiber ring laser. By inserting a segment of slightly normal dispersion fiber in a mode-locked fiber laser cavity, we found that the spectrum of the noise-like pulse emission of the laser can be significantly broadened as a result of the four-wave-mixing and the soliton self-frequency shift effects in the inserted fiber.     

Generation of mid-infrared supercontinuum by designing circular photonic crystal fiber

A circular photonic crystal fiber (C-PCF) based on As₂Se₃ is designed, which has three zero dispersion wavelengths and flat dispersion. Using this fiber, a wide mid-infrared supercontinuum (MIR-SC) can be generated by launching a femtosecond pulse in the first anomalous dispersion region. The simulation results show that the MIR-SC is formed by soliton self-frequency shift and direct soliton spectrum tunneling on the long wavelength side and self-phase modulation, soliton fission on the short wavelength side. Further, optical shocking and four-wave mixing (FWM) are not conducive to the long-wavelength extension of MIR-SC, while the number and intensity of fundamental solitons have a greater effect on the short-wavelength extension of MIR-SC. The generation of optical shocking waves, FWM waves and fundamental solitons can be obviously affected by changing the fiber length and input pulse parameters, so that the spectrum range and flatness can be adjusted with great freedom. Finally, under the conditions of 4000 W pulse peak power, 30 fs pulse width, 47 mm fiber length, and 0 initial chirp, a wide MIR-SC with a coverage range of 2.535 μm-16.6 μm is obtained. These numerical results are encouraging because they demonstrate that the spread of MIR-SC towards the red and blue ends can be manipulated by choosing the appropriate incident pulse and designing optimized fiber parameters, which contributes to applications in such diverse areas as spectroscopy, metrology and tomography.     

色散平坦渐减光纤中超连续谱的产生

对双正交偏振光脉冲在色散平坦渐减光纤中传输时超连续谱的产生进行了计算和分析。结果表明，由于交叉相位调制效应的作用，双光脉冲可以产生比单光脉冲明显展宽且更为平坦的超连续谱。对于双基孤子脉冲，可以得到-20dB谱宽达388nm的平坦宽带超连续谱，比单基孤子脉冲产生的超连续谱谱宽增加72nm，交叉相位调制效应对超连续谱的产生起到增强的效果。当输入脉冲的抽运功率较低时，交叉相位调制效应对超连续谱的产生的增强效果更为显著，它极大地提高了超连续谱的产生的效率。数值计算的结果还表明，与其他高阶非线性效应相比，拉曼自频率移效应对超连续谱产生的影响更为明显。     

高码率光孤子传输系统中用光相位共轭补偿高阶扰动

在由分布式掺铒光纤级联的高码率传输系统中存在不可忽略的高阶扰动,它们引起孤子自频率漂移和孤子变形。本文用光相位共轭补偿高阶扰动,结果表明:由分布式掺铒光纤级联的高码率传输系统中,适当选取光相位共轭周期长度,可以完全消除高阶扰动引起的孤子自频率漂移和孤子变形。     

Demonstration of soliton self-frequency shift below 1300 nm in higher-order mode, solid silica-based fiber

We demonstrate soliton self-frequency shift of more than 12% of the optical frequency in a higher-order mode solid, silica-based fiber below 1300nm. This new class of fiber shows great promise for supporting Raman-shifted solitons below 1300nm in intermediate energy regimes of 1 to 10nJ that cannot be reached by index-guided photonic crystal fibers or air-core photonic bandgap fibers. By changing the input pulse energy of 200fs pulses from 1.36 to 1.63nJ we observe Raman-shifted solitons between 1064 and 1200nm with up to 57% power conversion efficiency and compressed output pulse widths less than 50fs. Furthermore, due to the dispersion characteristics of the HOM fiber, we observe redshifted Cerenkov radiation in the normal dispersion regime for appropriately energetic input pulses.     

Suppression of soliton self-frequency shift by upshifted filtering

We consider the effects of stimulated Raman scattering on ultrashort light pulses propagating in long-haul fiber transmission lines. We propose an efficient method for suppressing the soliton self-frequency shift by use of upshifted filters without any compromise in signal-to-noise ratio and with the pulse stability preserved.     

Soliton generation via stimulated Brillouin self-scattering under slow light conditions

Acousto-optic soliton generation via stimulated Brillouin self-scattering is predicted for light propagating at the speed of sound under electromagnetically induced transparency conditions. As in stimulated Raman self-scattering, the frequency of the electromagnetic component is gradually Stokes shifted as its intensity increases; the acoustic component has no carrier frequency. This phenomenon is explained by the possibility of forward stimulated Brillouin scattering, which is forbidden in nondispersive media. In contrast to stimulated Raman self-scattering, the Stokes shift of the electromagnetic component approaches a constant limit after the pulse has propagated to a certain distance. It is shown that the predicted soliton generation does not involve any threshold condition and can occur at extremely low input pulse intensities.     

Soliton Propagation in Birefringent Fibers

In this article, the propagation of solitons in a single mode fiber with polarization mode dispersion (PMD) is analyzed. In optical fibers, the randomly varying birefringence degrades soliton transmission system in two aspects. First, the dispersive waves cause pulse broadening. Second, the dispersive waves interact with other soliton pulses. Here we studied the effects of PMD on a single pulse and the variation of pulse broadening, energy decay, and degree of polarization on a single soliton pulse propagating over a very long distance.