色散缓变光纤中Raman孤子自频移效应的研究

利用绝热扰动法研究了色散缓变光纤中Ｒａｍａｎ孤子自频移效应，得到了色散缓变光纤中Ｒａｍａｎ孤子自频移的表达式。结果表明：光纤色散变化率存在一个可以有效抑制孤子自频移的阈值，当光纤色散变化率大于这个阈值时，色散缓变光纤可以抑制孤子自频移，而当光纤色散变化率小于这个阈值时，色散缓变光纤不仅不能抑制孤子自频移，反而加剧孤子自频移。     

Bandwidth limits due to polarisation multiplexed soliton interactions

The authors reveal the bandwidth limits that result from the interactions between orthogonally polarised solitons in an optical fibre transmission link with time and polarisation division multiplexing.<>     

Experimental investigation of soliton optical phase jitter

The soliton optical phase stability versus amplified spontaneous noise is investigated in a recirculation loop experiment in the presence of in-line filters. The behavior of phase fluctuations is shown to be in good agreement with numerical simulations. The phase standard deviation is kept below 0.15×π for distances up to 8000 km. We, therefore, demonstrate the feasibility of phase-shift keying on solitons for long-haul transmission systems     

线双折射光纤与正交极化孤子碰撞的研究

从描述线双折射光纤中ｐｓ量级孤子脉冲的归一化ＮＬＳ方程出发,利用对称分步傅里叶变换计算方法,分析和归纳了正交极化孤子在双折射光纤中的碰撞数值特性,并对相关结论作了粗略探讨。     

High-order Nonlinearity Influence on Performances of High Rate Soliton Communication System and its Suppression Method

The propagation equation is established to investigate the feasibility and the validity of the suppression of the soliton self-frequency shift(SSFS) in the picosecond and femtosecond soliton communication system employing a compound control method of time domain and frequency domain . By the use of the variational approach, the evolution of the chirping Gaussian quasi-soliton pulse is analyzed in the presence of intrapulse Raman scattering. The self-frequency shift(SFS) is eliminated by an up frequency-guiding filter control method. The soliton perturbation method is employed to study the steady-state solutions in the presence of intrapulse Raman scattering. The relation between the transmission performances of the soliton and the system construction parameters such as 3dB-temporal width of the modulator, center frequency and bandwidth of the filter is deduced and a stable transmission condition is revealed. The long-haul soliton transmission system without SSFS at the rate of 160 Gb/s is designed and its performance is numerically simulated. The simulation results are in well within accordance with our theoretical analysis. This work is supported by the National Natural Science Foundation of China (Grant No.60072046).     

HNL-PCF中的SSFS及其在光纤通信中的应用

分析了高非线性光子晶体光纤(HNL-PCF)中拉曼孤子自频移(SSFS)的原理.讨论了HNL-PCF中SSFS效应在波长变换、飞秒孤子脉冲、超快数模转换和改善通信的稳定性等方面的应用.随着PCF技术的发展和对SSFS研究的深入,基于PCF中SSFS的各种器件将在未来的光纤通信系统中发挥重要的作用.     

All-optical phase-independent logic elements based on phase shiftinduced by coherent soliton collisions

We demonstrate, for the first time to our knowledge, that a fast coherent collision between two Kerr spatial solitons can give rise to a significant phase shift for both interacting beams. The maximal collision-induced phase shift ≈π rad takes place when the amplitudes of the solitons are equal (η₁=η₂) and the length of the interaction zone is comparable with a soliton phase period. Depending on the ratio η₂/η₁, and the collision angle between the solitons, the magnitude of the phase shift can be varied within a reasonable range, for example from 180° to 40°. The analysis of the effect performed by the finite-difference beam-propagation method has shown that it is insensitive to the initial phase difference between the incident beams (δ_i), even in the case when η ₁≠η₂. It has been demonstrated that the phenomenon can be used for all-optical three-soliton logic elements, which are capable of providing more than 3-dB signal amplification and possess bi -independent output characteristics     

Scattering of Spatial Optical Solitons by Subwavelength Air Holes

Using the finite-difference time-domain method, we model the propagation of spatial optical solitons having two orthogonal electric field vector components, and the scattering of such solitons by compact subwavelength air holes (i.e., abrupt dielectric discontinuities in the direct paths of the solitons). Our propagation and scattering studies assume a realistic glass characterized by a three-pole Sellmeier linear dispersion, an instantaneous Kerr nonlinearity, and a dispersive Raman nonlinearity. An unexpected spatial soliton scattering phenomenon is observed: the coalescence of the scattered electromagnetic field into a propagating lower-energy spatial soliton at a point many tens of wavelengths beyond the scattering air hole. Overall, our computational technique is general, and should permit future investigations and design of devices exploiting spatial soliton interactions in background media having submicrometer air holes and dielectric and metal inclusions.     

e—偏振非相干均匀背景光照射下光伏光折变晶体中的开路空间亮孤子

本文推导了在外加e-偏振非相干均匀背景光照下开路光伏光折变晶体中的亮空间孤子的演化方程,给出了方程的数值积分形式的解,并且得到了小振帐条件下亮孤子解析角以及孤子宽度的解析表达式,本文还讨论了外加e－偏振非相干均匀背景光对开路光伏孤子的影响,结果表明,若外加e－偏振非相干均匀背景光的强度远远大于晶体的暗辐照强度,则不利于开路光伏孤子的形成。ee     

Highly Functional All-Optical Control Using Ultrafast Nonlinear Effects in Optical Fibers

Using the optical fibers and ultrashort pulses, we can demonstrate highly functional optical control. We have succeeded in generation of low-noise, ultraflat, high-quality supercontinuum (SC). Recently, octave spanning high-quality SC is also generated. The carrier envelope offset frequency measurement and ultrahigh resolution optical coherence tomography are demonstrated using SC. We can also generate widely wavelength-tunable ultrashort soliton pulses using soliton self-frequency shift (SSFS). So far, several new techniques have been proposed and demonstrated using SSFS. The author has also discovered novel two-pulse trapping phenomena. The ultrafast all-optical switching is demonstrated using the pulse trapping techniques, and principles and characteristics are described.      

指数响应的强非局域介质中正交偏振双厄米高斯光束传输特性

运用变分法研究了具有e指数响应的强非局域介质中两束正交偏振、中心重合的厄米高斯光束的传输特性,得到了光束各参量的演化方程和一个临界功率Pc。当两光束以临界功率入射时,可以形成厄米高斯型空间光孤子;当两光束以总功率2Pc入射,但两光束入射功率不相等时,两光束可以形成厄米高斯型呼吸子。通过数值模拟研究发现,低阶光束时,可以得到近似孤子解;当光束阶数大于3阶时,则得不到孤子解。比较变分解与数值解,结果表明在光束阶数小于3阶时,变分解较好的反映了具有e指数响应的强非局域介质中两束正交偏振、中心重合的厄米高斯光束的传输特性。     

分布放大传输系统中暗孤子链的传输特性研究

研究了由低掺杂浓度的分布式掺铒光纤级联传输系统中,多个暗孤子组成的暗孤子链的传输特性,结果表明：在分布放大传输中,奇或偶数个暗孤子组成的暗孤子链的传输特性存在较大的差异,其中奇数个暗孤子组成的暗孤子链的传输稳定性较好,而偶数个暗孤子组成的暗孤子链在传输过程中存在明显的由暗孤子相互作用引起的孤子自频率漂移和孤子变形。     

自傅立叶光孤子的相互作用特性

用分步傅立叶变换方法数值求解非线性薛定谔方程,研究了一阶自傅立叶光孤子信号在光纤传输中的相互作用特性。证明了算法内部不存在理论误差。数值模拟结果表明：（1）一阶自傅立叶孤子对中的相互作用表现不同于一阶标准孤子对,它类似于二阶或准二阶孤子之间的相互作用特性。两孤子经历一段周期性的相互吸引后,出现强烈的相互排斥;（2）孤子相互作用特性不足以用孤子的阶去区分或分类,在同一阶的孤子中,不同的脉宽对孤子的相互作用有显著不同的影响;（3）微弱的三阶色散效应有利于抑制一阶自傅立叶孤子间的相互作用。     

Special erbium fiber amplifiers for short pulse switching, lasers,and propagation

We show that specially tailored erbium-doped fiber amplifiers (EDFA's) can be useful for short-pulse soliton lasers, switching, and propagation. EDFA properties include group-velocity dispersion, birefringence, doping level, and doping distribution; and changing each of these properties enables novel applications. Polarization-maintaining EDFA's can Re used in erbium-doped fiber lasers to avoid intensity-dependent or temperature-dependent state of polarization. We have demonstrated a passively mode-locked erbium-doped fiber laser that generates nearly transform-limited 320 fs pulses with 40 pJ energy using a polarization-maintaining EDFA near the zero dispersion wavelength and a bulk InGaAsP saturable absorber. Moderately birefringent EDFA's can be used to control the walkoff and interaction between orthogonally polarized solitons in all-optical switches. For example, through numerical simulations, we design an all-optical cascadable logic gate with a fanout of 2.7 and energy contrast of 5.5 based on interactions in a soliton period long EDFA. Furthermore, distributed EDFA's can be used for long-distance soliton propagation to shepherd the pulse using bandwidth-limited gain. For picosecond soliton pulses, we show that soliton self-frequency shift and Gordon-Hans effects limit propagation to below 100 km even for low-dispersion fibers. Bandwidth-limited amplification in EDFA may counteract frequency shift due to the soliton self-frequency shift, while frequency filters may suppress the Gordon-Hans effect. Also, because the gain spectral profile for the three-level EDFA changes with pump intensity, complications arise from pump attenuation, and the corresponding changes in the gain spectral profile along the length of the fiber     

横向非周期性调制Kerr介质中的空间光孤子

数值方法研究了横向非周期调制Kerr介质中所支持的空间光孤子。数值模拟结果显示研究模型存在三种类型空间光孤子：低功率下的双峰孤子、高功率下的基本孤子和稳定传输的双极孤子。应用线性稳定性分析方法研究了三种类型空间光孤子的稳定传输的稳定谱,总结出三种类型光孤子稳定传输的条件。     

有偏压光伏光折变晶体中低振幅非相干耦合孤子对

从理论上研究了有偏压的光伏光折变晶体中低振幅屏蔽光伏孤子对的特性，给出了明一明、暗一暗屏蔽光伏孤子对的单孤子解。它们起源于对外电场的非均匀空间屏蔽和光伏效应，不同于起源于对外电场非均匀空间屏蔽孤子和起源于光伏效应的光伏孤子，具有有趣的特性。当光伏效应可忽略时，它们的非线性波动方程就转化为低振幅屏蔽孤子对的非线性波动方程，它们就转化为低振幅屏蔽孤子对；当外偏压为零时，它们的非线性波动方程就转化为低振幅闭路和开路光伏孤子对的非线性波动方程，它们就转化为低振幅闭路和开路光伏孤子对。如果载体光束具有相同的偏振和波长以及互不相干时，这些孤子对就能得到，相关的例子在光伏光折变晶体铌酸锂(LiNbO3)中给出。     

Noise characteristics of femtosecond fiber Raman soliton laser withhigh-Q cavity

The amplitude noise characteristics of femtosecond optical pulses generated from a synchronously pumped all-fiber Raman soliton laser with high-Q cavity are investigated under different operation states of the laser. By suppressing the soliton self-frequency shift (SSFS) effect in the high-Q fiber cavity, real femtosecond soliton oscillation can be obtained in the laser. Low-noise 400 fs optical pulses with a white amplitude noise level of -120 dBc/Hz have been generated from the laser operating in such an SSFS-free state     

Dark spatial solitons sequence in the biased centrosymmetric photorefractive crystal

We theoretically investigate the evolution of dark screening spatial solitons originating from the quadratic electro-optic effect in biased centrosymmetric photorefractive (CP) crystal by using beam propagation method (BPM). The results indicate that the multiple dark solitons sequence can be obtained in the CP crystal with the odd or even initial conditions. If the initial width of the dark notch is smaller, only a fundamental soliton or a Y-junction soliton pair is generated. When the initial width of the dark notch and the bias electric field are increased, the multiple dark spatial solitons sequence is formed, which realized a progressive transition from a low-order soliton to a higher-order solitons sequence in both odd and even conditions. The solitons characteristic is similar to that of screening solitons in the non-centrosymmetric photorefractive (NCP) crystals.     

高阶飞秒孤子演化特性的数值研究

本文以高阶非线性薛定谔方程为数学模型,数值研究了高阶色散和高阶非线性效应影响下高阶飞秒孤子的演化特性,并与高阶皮秒孤子的演化特性进行了比较.结果发现二阶飞秒孤子的演化特性与二阶皮秒孤子的演化特性非常相似,都具有很好的周期性;而三阶和四阶飞秒孤子的演化特性与相应的皮秒孤子的演化特性有很大不同,高阶效应的存在不同程度上破坏了三阶和四阶孤子演化的周期性.     

光折变晶体中的光生伏打灰空间孤子

在自散焦介质中，平面波的传播对小的调制扰动是绝对稳定的，暗空间孤子正是作为平面波背景上的一种局域暗迹而存在的。基于这种调制稳定性，给出了由光生伏打自散焦非线性支持的一维灰空间孤子的演化方程，并在光生伏打光折变LiNbO3：Fe晶体中给出了它的静态解。数值研究了这种灰空间孤子的诸多性质：例如在不同的孤子灰度下的孤子轮廓和它的相位分布；光生伏打灰孤子的归一化横向传播速度和归一化半峰全宽随归一化的背景光强和孤子灰度的变化等。所有这些性质都可以通过调节孤子波两侧的相位差加以控制，并详细地比较了光生伏打灰孤子和屏蔽灰孤子之间的异同。