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.     

Influence of the Raman effect on dispersion-managed solitons and their interchannel collisions

We calculate the self-frequency shift experienced by a soliton in a dispersion-managed fiber that is due to the Raman effect, as well as the energy and frequency shifts that result from a collision of such solitons with different wavelengths. We find that dispersion management suppresses both types of frequency shift but does not significantly affect the energy shift that is accumulated over a large propagation distance. The latter shift may represent a potential problem for wavelength-division-multiplexed systems with several gigabits per second in a single channel.     

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.     

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.     

飞秒孤子传输演化的数值研究

利用分步傅里叶法数值模拟了飞秒孤子在光纤中的传输演化过程。对光纤中单个孤子的传输及二阶孤子的自陡峭效应和自频移效应进行了分析,指出在一定的参数取值范围内,自频移效应对二阶fs孤子传输的影响要比自陡峭效应大,占主导地位,且对自陡峭效应有一定的抑制作用。     

孤子光纤中拉曼自频移效应的研究

首次报道孤子光纤中拉曼自频移效庆的研究结果。对满足孤子光纤色散关系条件时含损耗，拉曼延迟效应的广义非线性薛定谔方程进行了微扰分析。求得了拉曼自频移关系表达式。发现改变光纤几何参数可以有效地控制孤子拉曼自频移。     

Long-range interaction of picosecond solitons through excitation of acoustic waves in optical fibers

We present the theory of electrostrictional interaction of soliton pulses in optical fibers. Solitons excite acoustic waves propagating in the direction transverse to the fiber axis. Scattering of optical radiation on these waves leads to a timing jitter of the optical pulses arrival time. We consider this effect as nonlinear self-scattering of light on acoustic waves. Because of the fact that a value of acoustic lifetime can reach a value of about 100 ns self-scattering on acoustic waves can be observed for a single optical pulse as well as for an optical pulse sequence as a whole. The value of single soliton self-frequency shift due to excitation of acoustic waves as a function of soliton duration have been obtained. For soliton duration _sol > 14 ps an acoustic wave soliton self-frequency shift is larger than the Raman soliton self-frequency shift.The obtained theoretical results describe well the long-range interaction of soliton pulse trains in an optical fiber. The value of bit error rate due to electrostrictional interaction of optical pulses in high bit rate, ultra long soliton communication systems have been obtained.     

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.     

Polarization-dependent efficient Cherenkov radiation at visible wavelengths in hollow-core photonic crystal fiber cladding

Efficient Cherenkov radiation (CR) is experimentally generated by a soliton self-frequency shift (SSFS) in a knot of hollow-core photonic crystal fiber (HC-PCF). When the angle of the half-wave plate is rotated from 0° to 45° , the Raman soliton shifts from 2227 to 2300 nm, the output power of the CR increases 8.15 times, and the maximum output power ratio of the CR at 556 nm to the residual pump is estimated to be 20:1. The width of the output optical spectrum at visible wavelengths broadens from 25 to 45 nm, and the conversion efficiency of the CR can be above 28%. Moreover, the influences of the pump polarization and wavelength on the CR are studied, and the corresponding nonlinear processes are discussed.     

Supercontinuum Gneneration and Modes Analysis in Secondary Cores of a Hollow-Core Photonic Crystal Fiber

We demonstrate the generation of supercontinuum spectra in three secondary cores of a hollow-core photonic crystal fiber pumped by femtosecond laser pulses, respectively. The supercontinuum spectra are mainly a result of the soliton self-frequency shift and an amplification of dispersive wave at visible wavelengths. Detailed mode simulations show that with the increasing core length, the modes transfer from ＂double-points＂ to ＂single-point＂ since the pump laser is more easily coupled into the two side cores of a secondary core when the core length is small. The simulation results also explain why the experimental observed far-field beam patterns of first two secondary cores are different.     

Widely tunable femtosecond soliton pulse generation at a 10-GHz repetition rate by use of the soliton self-frequency shift in photonic crystal fiber

We demonstrate a soliton self-frequency shift of approximately 120 nm in a fiber with 1.56-microm pulses generated at a 10-GHz repetition rate by an actively mode-locked laser. A highly nonlinear photonic crystal fiber with a length of only 12.6 m and a nonlinear coefficient of 62 W(-1) km(-1) is used to achieve such broadband operation. The wavelengths of the resulting sub-300-fs solitons can be tuned effectively by adjusting the input power. The maximum output power of the solitons exceeds 200 mW.     

Broadly wavelength- and pulse width-tunable high-repetition rate light pulses from soliton self-frequency shifting photonic crystal fiber integrated with a frequency doubling crystal

Soliton self-frequency shift (SSFS) in a photonic crystal fiber (PCF) pumped by a long-cavity mode-locked Cr:forsterite laser is integrated with second harmonic generation (SHG) in a nonlinear crystal to generate ultrashort light pulses tunable within the range of wavelengths from 680 to 1800?nm at a repetition rate of 20?MHz. The pulse width of the second harmonic output is tuned from 70 to 600?fs by varying the thickness of the nonlinear crystal, beam-focusing geometry, and the wavelength of the soliton PCF output. Wavelength-tunable pulses generated through a combination of SSFS and SHG are ideally suited for coherent Raman microspectroscopy at high repetition rates, as verified by experiments on synthetic diamond and polystyrene films.     

Dispersion and diffraction mechanisms suppressing soliton self-frequency shift in a medium with retarded optical nonlinearity

The frequency dependence of group-velocity dispersion and diffraction-induced increase in the effective mode area in the long-wavelength range suppress the soliton self-frequency shift in a medium with retarded nonlinearity. This effect reduces unwanted variations in the central wavelength, as well as fluctuations of the delay time of the frequency-shifted soliton with respect to the input pulse.     

Log-normal distribution of pulse amplitudes due to Raman cross talk in wavelength division multiplexing soliton transmission

The effect of delayed Raman response on soliton collisions in wavelength division multiplexing (WDM) transmission systems is investigated. Taking into account the stochastic nature of pulse sequences in different frequency channels and the Raman-induced cross talk, it is shown that the soliton amplitude is a random variable with a log-normal distribution. Moreover, the Raman-induced self-frequency shift and cross-frequency shift are also random variables with log-normal-like distributions. These results imply that fluctuations in soliton amplitude and frequency induced by soliton collisions in the presence of delayed Raman response play an important role in massive WDM transmission.     

Tunable Supercontinuum Generated in a Yb~(3+)-Doped Microstructure Fiber Pumped by Ti:Sapphire Femtosecond Laser

We experimentally demonstrate that a tunable supercontinuum(SC) can be generated in a Yb3+-doped microstructure fiber by the concept of wavelength conversion with a Ti:sapphire femtosecond(fs) laser as the pump.Experimental results show that an emission light around 1040 nm in an anomalous dispersion region is first generated and amplified by fs pulses in the normal dispersion region. Then, SC spectra from 1100 to 1380 nm and 630 to 840 nm can be achieved by combined effects of higher-order soliton fission and Raman soliton self-frequency shift in the anomalous dispersion region and self-phase modulation, dispersive wave, and four-wave mixing in the normal dispersion region. It is also demonstrated that the 20 nm change of pump results in a 280 nm broadband shift of soliton and the further red-shift of soliton is limited by OH-absorption at 1380 nm.     

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。     

Dissipative Kerr solitons in optical microresonators with Raman effect and third-order dispersion

Using the mean-field normalized Lugiato–Lefever equation, we theoretically investigate the dynamics of cavity soliton and comb generation in the presence of Raman effect and the third-order dispersion. Both of them can induce the temporal drift and frequency shift. Based on the moment analysis method, we analytically obtain the temporal and frequency shift,and the results agree with the direct numerical simulation. Finally, the compensation and enhancement of the soliton spectral between the Raman-induced self-frequency shift and soliton recoil are predicted. Our results pave the way for further understanding the soliton dynamics and spectral characteristics, and providing an effective route to manipulate frequency comb.     

光孤子放大过程中的动态增益

分别用逆散射微扰方法和傅里叶变换求系综平均观点详细分析了在光孤子放大过程中，如果设法使放大器增益随孤子频率变化而变化，在一定条件下，既可大大减弱光孤子脉冲的喇曼自泵效应引起的自频移现象，又可有效地控制放大过程中产生的自发辐射噪声（ＡＳＥ）．结果表明，在两种特性的动态增益中，可有效地控制ＡＳＥ噪声从而突破Ｇｏｒｄｏｎ－Ｈａｕｓ限制，也可使自频移明显减弱，并与计算机数值研究结果作了比较。 关键词：     

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。     

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.