Spatio-temporal dynamics of multicolor spatial Kerr solitons

We present numerical and experimental results showing the rich and complex spatio-temporal dynamics of multicolor spatial vector soliton generated by stimulated Raman scattering in a Kerr planar waveguide. By taking into account their temporal dimension, we found the precise domain of existence of multicolor soliton whose components are mutually guided and spatio-temporally superimposed. In addition, we observe the Raman Stokes component in the trailing edge of the pump pulse and show that it is associated with the slow-light process induced by the sharp resonance of the Raman gain medium.     

Slow-light solitons in three-level atomic systems modified by a microwave field

We study the modified effect of slow-light soliton in a resonant three-level atomic system via electromagnetically inducedtransparency (EIT) by utilizing a microwave field. We derive ahigh-order nonlinear Schrödinger equation by using a perturbation method of multiple-scales, and calculate the modification ofsoliton velocity and frequency shift. We find that in the presence of the microwave field an obvious decrease of propagating velocityof soliton can be realized, which provides an effective method to slow down optical solitons in EIT systems. We also find that thedown shift of oscillating frequency of soliton in such system can be largely suppressed by the microwave field.     

Propagation of a self-induced transparency pulse in a spatially dispersive medium

Propagation of a self-induced transparency pulse in spatially dispersive media is analyzed. A generalized model of two-level systems allowing for excitonic energy transfer is proposed. Periodic and soliton solutions to the governing equations are found. Estimates show that the spatial dispersion of a pulse propagating in a slow-light medium can be substantially enhanced and become important in the case of resonant transition and sufficiently long pulse duration.     

高功率2 μm波长可调谐超短脉冲光纤激光器

高功率2 μm波长可调谐的超短脉冲激光具有峰值功率高、脉冲宽度窄、波长可调谐等优势,在医疗手术、大气通信、光电对抗等领域具有广泛的应用。利用高峰值功率的掺铒光纤放大器泵浦高非线性光纤,在全光纤化结构中获得了1895～2165 nm可调谐的拉曼孤子输出。采用啁啾脉冲放大技术对拉曼孤子的脉冲能量进行提升,放大后拉曼孤子的单脉冲能量为1.56 μJ,平均功率达到50.6 W,脉冲宽度为83 ps。经过光栅对压缩后,脉冲宽度降低至1.23 ps,平均功率为22 W,峰值功率达到0.55 MW。放大后的脉冲仍具有波长调谐的能力,当输出功率为5 W和50.6 W时,脉冲的波长调谐范围分别为38 nm和8 nm。     

Enhanced stimulated Raman scattering in slow-light photonic crystal waveguides

We investigate for the first time, to our knowledge, the enhancement of the stimulated Raman scattering in slow-light silicon-on-insulator (SOI) photonic crystal line defect waveguides. By applying the Bloch-Floquet formalism to the guided modes in a planar photonic crystal, we develop a formalism that relates the intensity of the downshifted Stokes signal to the pump intensity and the modal group velocities. The formalism is then applied to two prospective schemes for enhanced stimulated Raman generation in slow-light photonic crystal waveguides. The results demonstrate a maximum factor of 104(66,000) enhancement with respect to SOI channel waveguides.     

偏振模色散影响下飞秒孤子的传输特性研究

以Maxwell电磁场理论为基础，在综合考虑了高阶色散、高阶非线性、自相位调制、交叉相位调制、自变陡、脉冲内喇曼散射及偏振模色散等因素的基础上，推导了飞秒孤子脉冲在双折射光纤中传输的耦合非线性薛定谔方程，并利用分步傅里叶方法对该方程进行了数值计算，研究分析了偏振模色散对飞秒孤子传输的影响。结果发现：当Dp≤0.1ps/km1/2时，偏振模色散对系统的影响很小，随着偏振模色散值的增大，系统的传输性能迅速恶化，当偏振模色散值达到0.3ps/km1/2时，系统的传输距离已经不到无偏振模色散时的1/3；若同时考虑光纤的高阶效应，以飞秒孤子作为载体的系统已经不能实现高速长距离的传输。     

Spectrally efficient slow light using multilevel phase-modulated formats

A phase-preserving and spectrally efficient slow-light scheme has been proposed and demonstrated by utilizing advanced multilevel phase-modulated formats. A 60 ps symbol delay with error-free demodulation of both I and Q channels for 10 Gbit/s return-to-zero differential-quadrature-phase-shift-keyed (DQPSK) signals via a broadband stimulated Brillouin scattering-based slow-light medium is achieved experimentally. Simulation results on 20 Gbit/s DQPSK and 30 Gbit/s D8PSK propose to transmit very high spectrally efficient multilevel formats through a bandwidth-limited slow-light element.     

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.     

高重复频率锁模光纤激光器及其超连续谱产生

设计并实验研究了一种结构简单的主动调制锁模高重复频率窄脉宽光纤激光器。采用窄线宽连续激光调制4 GHz高重频后,通过拉曼增益孤子压缩效应将脉宽由27 ps压窄至2.6 ps。该高重频锁模激光泵浦一段300 m长高非线性光纤,同时脉冲被展宽至7.4 ps。产生的超连续谱平坦度20 dB宽带可达250 nm,功率波动为±0.2 dB。     

拉曼增益对高双折射光纤中暗孤子俘获的影响

从高双折射光纤中含有拉曼增益的耦合非线性薛定谔方程出发, 利用拉格朗日方法, 推导出了暗孤子俘获的阈值, 并利用快速分步傅里叶变换, 模拟了孤子的两个正交偏振分量的演化, 对比了两种方法得到的阈值, 探究了暗孤子俘获受拉曼增益的影响. 研究发现解析解所得阈值比数值解偏小, 且群速度失配越小时, 二者符合得越好; 并且拉曼增益减小了暗孤子的俘获阈值, 当平行拉曼增益增大时, 俘获阈值减小加快.     

Generation of multicolor vector Kerr solitons by cross-phase modulation, four-wave mixing, and stimulated Raman scattering

We numerically and experimentally show the existence of multicolor vector spatial solitons in a Kerr planar waveguide through the combined effects of cross-phase modulation, four-wave mixing, and stimulated Raman scattering. Mutual spatial guiding of the Raman-Stokes, anti-Stokes, and pump waves is achieved in the high-conversion regime mainly by cross-phase modulation and phase-matched four-wave mixing induced by a power imbalance between Stokes and anti-Stokes components, leading to the generation of a clear-cut sech-shape three-frequency spatial soliton.     

Stabilization of the Soliton Transported Bio-energy in Protein Molecules in the Improved Model

We study the stabilization of the soliton transported bio-energy by the dynamic equations in the improved Davydov theory from four aspects containing the feature of free motion and states of the soliton at the long-time motion and at biological temperature 300 K and behaviors of collision of the solitons by Runge-Kutta method and physical parameter values appropriate to the $\alpha$-helix protein molecules. We prove that the new solitons can move without dispersion at a constant speed retaining its shape and energy in free and long-time motions and can go through each other without scattering. If considering further influence of the temperature effect of heat bath on the soliton, it is still thermally stable at biological temperature 300 K and in a time as long as 300 ps and amino acid spacings as large as 400, which shows that the lifetime of the new soliton is at least 300 ps, which is consistent with analytic result obtained by quantum perturbation theory. These results exhibit that the new soliton is a possible carrier of bio-energy transport and the improved model is possibly a candidate for the mechanism of this transport.     

Enhanced Compression of Fundamental Solitons in Dispersion Decreasing Fibers with Negative Third-order Dispersion Ⅱ. Effects of Fiber Characteristics and Initial Soliton Width

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中红外可调谐大能量飞秒脉冲激光产生

可调谐中红外飞秒光纤激光器具有非常普遍的应用,从而引起了人们的广泛关注。目前,非线性光纤中的拉曼孤子自频移效应是实现大范围可调谐飞秒脉冲激光的理想方法之一。然而,非线性光纤中其他高阶非线性效应的产生通常会限制拉曼孤子脉冲的能量提升。本文提出了利用有源掺杂光纤作为非线性介质和增益介质实现可调谐大能量中红外飞秒激光脉冲的方法。在理论上研究了有源掺杂非线性光纤中高阶孤子劈裂和孤子自频移效应的产生,以及线性增益对波长移动拉曼孤子能量、脉宽、光谱的影响。结果表明,通过为波长红移的低能量拉曼孤子提供线性增益,孤子脉冲的能量得到了显著提升且保持了其单脉冲特性,脉冲宽度为45 fs,且孤子脉冲的波长可通过所提供的增益进行大范围调谐。因此,利用有源掺杂光纤作为非线性介质是实现大能量可调谐中红外飞秒脉冲激光的一种有效方法。     

Enhanced Compression of Fundamental Solitons in Dispersion Decreasing Fibers with Negative Third-order Dispersion Ⅱ. Effects of Fiber Characteristics and Initial Soliton Width

Previous work have shown that the combined effects of negative third-order dispersion (TOD) and Raman self-scattering (RSS) can significantly enhance soliton compression in dispersion decreasing fibers (DDFs). In this paper, the effects of the negative TOD coefficient and the effective amplification of DDF′s on the performance of soliton compression are investigated. It is shown that for a given initial soliton width and a given effective amplification, there exists an optimum value of the negative TOD coefficient of the DDF at which the enhancement in soliton compression is maximum. It is also shown that the compression enhancement saturates when the effective amplification exceeds a certain value, which has been explained as a compromise between the higher-order effects induced increase of the ratio of input to output group-velocity dispersion coefficients of the DDF and the TOD induced non-adiabatic compression characteristics. The dependence of the compression enhancement on the initial soliton width have also be studied and the scheme is found works well for solitons with initial widths less than 3 ps.     

Third-harmonic generation in slow-light chalcogenide glass photonic crystal waveguides

We demonstrate third-harmonic generation (THG) in a dispersion-engineered slow-light photonic crystal waveguide fabricated in AMTIR-1 chalcogenide glass. Owing to the relatively low loss and low dispersion in the slow-light (c/30) regime, combined with the high nonlinear figure of merit of the material (～2), we obtain a relatively large conversion efficiency (1.4×10(-8)/W(2)), which is 30× higher than in comparable silicon waveguides, and observe a uniform visible light pattern along the waveguide. These results widen the number of applications underpinned by THG in slow-light platforms, such as the direct observation of the spatial evolution of the propagating mode.     

Femtosecond second-order solitons in optical fiber transmission

A propagation of the femtosecond second-order solitons in an optical fiber is studied. We show that a generalized nonlinear Schrödinger equation well describes the propagation of the second-order soliton even containing only a few optical cycles. The propagations of a 50 fs and a 10 fs second-order soliton in an optical fiber are numerically simulated. It is found that, for the case of 10 fs second-order soliton, the soliton decay is dominated by the third-order dispersion, in contrast to the case of 50 fs second-order solitons, where the soliton decay is dominated by the delayed Raman response. It is also found that the exact delayed Raman response form must be used for the propagation of the 50 fs or less than 50 fs second-order soliton.     

Generation and detection of acoustic solitons in crystalline slabs by laser ultrasonics

Acoustic solitons have been recently observed in different systems (Si, Sapphire, MgO, alpha-quartz). Such acoustic waves could lead to sub-picosecond acoustic pulses. In this paper, we report on the formation of acoustic solitons in a GaAs crystalline slab. A short picosecond acoustic pulse is generated by absorption of a femtosecond laser pulse in an aluminum thin film deposited on one side of the slab. This strain pulse travels through the sample up to the opposite side where it is detected by a time delayed laser pulse reflected by an aluminum transducer. We use interferometric detection to measure independently the real and imaginary parts of the relative change in optical reflectivity induced by the acoustic pulse. We find that, at low temperature and with a laser pump pulse energy of 10 nJ, an acoustic soliton clearly separates from the acoustic pulse in GaAs slab. The soliton shape is compared with numerical simulations for different excitation conditions. From the very unique properties of solitons, we infer a soliton pulse duration of about 2.3 ps which corresponds to a spatial extent of only 12 nm.     

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.     

色散渐减光纤的脉冲压缩研究

介绍了色散渐减光纤的绝热孤子压缩(ASC)过程，分析结果表明利用线性渐减的色散渐减光 纤(DDF)对飞秒基态孤子进行绝热压缩可以得到高质量的压缩脉冲，但用于压缩的DDF长度很 长，因此又提出DDF的高阶孤子(1＜N≤21)脉冲压缩技术，以在较短的DDF长度下获得 较大压缩比和高质量的压缩脉冲. 关键词： 色散渐减光纤 绝热孤子压缩 脉冲压缩 高阶孤子