Six-bit all-optical quantization using photonic crystal fiber with soliton self-frequency shift and pre-chirp spectral compression techniques

In this paper, we propose an optical quantization scheme for all-optical analog-to-digital conversion that facilitates photonics integration. A segment of 10-m photonic crystal fiber with a high nonlinear coefficient of 62.8 W-1/kin is utilized to realize large scale soliton self-frequency shift relevant to the power of the sampled optical signal. Furthermore, a 100-m dispersion-increasing fiber is used as the spectral compression module for further resolution enhancement. Simulation results show that 317-nm maximum wavelength shift is realized with 1550-nm initial wavelength and 6-bit quantization resolution is obtained with a subsequent spectral compression process.

Optimizational 6-bit all-optical quantization with soliton self-frequency shift and pre-chirp spectral compression techniques based on photonic crystal fiber

In this paper, we optimize a proposed all-optical quantization scheme based on soliton self-frequency shift(SSFS)and pre-chirp spectral compression techniques. A 10m-long high-nonlinear photonic crystal fiber(PCF) is used as an SSFS medium relevant to the power of the sampled optical pulses. Furthermore, a 10m-long dispersion flattened hybrid cladding hexagonal-octagonal PCF(6/8-PCF) is utilized as a spectral compression medium to further enhance the resolution. Simulation results show that 6-bit quantization resolution is still obtained when a 100m-long dispersion-increasing fiber(DIF)is replaced by a 6/8-PCF in spectral compression module.

Broadband tunable Raman soliton self-frequency shift to mid-infrared band in a highly birefringent microstructure fiber

Raman soliton self-frequency shifted to mid-infrared band（λ 〉 2 μm） has been achieved in an air-silica microstructure fiber（MF）. The MF used in our experiment has an elliptical core with diameters of 1.08 and 2.48 μm for fast and slow axis. Numerical simulation shows that each fundamental orthogonal polarization mode has two wide-spaced λZDW and theλZDW pairs located at 701/2110 nm and 755/2498 nm along the fast and slow axis, respectively. Using 810-nm Ti：sapphire femtosecond laser as pump, when the output power varies from 0.3 to 0.5 W, the furthest red-shift Raman solitons in both fast and slow axis shift from near-infrared band to mid-infrared band, reaching as far as 2030 and 2261 nm. Also, midinfrared Raman solitons can always be generated for pump wavelength longer than 790 nm if output pump power reaches0.5 W. Specifically, with pump power at 0.5 W, the mid-infrared soliton in slow axis shifts from 2001 to 2261 nm when the pump changes from 790 nm to 810 nm. This means only a 20 nm change of pump results in 260 nm tunability of a mid-infrared soliton.

Polarisation-sensitive four-wave mixing and soliton self-frequency shift effect in the highly birefringent photonic crystal fibre

By adjusting the polarisation state of the pump at 805 nm parallel to slow （x） and fast （y） axes of the highly birefringent photonic crystal fibre with zero dispersion wavelengths 790 nm and 750 nm, this paper demonstrates the efficient polarisation-sensitive four wave mixing involved in pump, anti-Stokes and Stokes signals and soliton self- frequency shift effects induced by the phase-matching between red-shifted solitons and blue-shifted dispersive waves. If the reduction of coupling efficiency to the circular pump laser mode or other circular fibres due to asymmetry of the core is neglected, more than 98% of the total input power is kept in a single linear polarisation. Controlled dispersion characteristic of the doublet of fundamental guided-modes results in achieving light field strongly confined in principal axes of photonic crystal fibre, and enhancing the corresponding nonlinear-optical process through the remarkable nonlinear birefringence.

Ultraviolet and mid-infrared continuum generation by cross-phase modulation between red-shifted solitons and blue-shifted dispersive waves in a photonic crystal fiber

Using a photonic crystal fiber with a zero dispersion wavelength of the fundamelItal mode at 780 nm designed and fabricated in our lab, the ultraviolet and mid-infrared continua are generated by cross-phase modulation between red-shift solitons and blue-shift dispersive waves. The dependences of continuum on the pump power and wavelength are investigated. With the pump working at 820 nm, when the pump power increases froul 300 to 500 mW, the bandwidths of ultraviolet and mid-infrared continua change from 80 to 140 nm and 100 to 200 nm, respectively. The wavelength of ultraviolet continuum is below 246 nm, and the wavelength of mid-infrared continuum exceeds 2500 nm. Moreover, the influences of pump power on wavelength and conversion efficiency of different parts of continua are also demonstrated.

Large phase shift of spatial soliton in lead glass by cross-phase modulation in pump-signal geometry

We investigate the co-propagation of a strong pump beam and a weak signal beam in lead glass, and find that the large phase shift of the strongly nonlocal spatial optical soliton （SNSOS） can be realized via cross-phase modulation. The theoretical study suggests a synchronous propagation of the pump SNSOS and the signal SNSOS under the required initial condition. A π-phase shift of the signal SNSOS is experimentally obtained by changing the power of the pump SNSOS by about 13 mW around the soliton critical power, which agrees qualitatively with our theoretical prediction. The ratio of the phase shift rate of the signal SNSOS to that of the pump SNSOS shows a close match to the reciprocal of the ratio between their wavelengths.

Third-order nonlinear wavelength conversion in chalcogenide glass waveguides towards mid-infrared photonics

The increasing demand in spectroscopy and sensing calls for infrared(mid-IR)light sources.Here,we theoretically investigate nonlinear wavelength conversion of Ge_(28)Sb_(12)Se_(60)chalcogenide glass waveguide in the mid-IR spectral regime.With waveguide dispersion engineering,we predict generation of over an octave wavelength(2.8μm-5.9μm)tuning range Raman soliton self-frequency shift,over 2.5 octaves wavelength cover range supercontinuum(1.2μm-8.0μm),as well as single soliton Kerr comb generated in suspended Ge_(28)Sb_(12)Se_(60)waveguide.Our findings evidenced that Ge_(28)Sb_(12)Se_(60)chalcogenide glass waveguides can simultaneously satisfy the generation of Raman soliton self-frequency shift,supercontinuum spectrum,and Kerr frequency comb generation through dispersion engineering towards mid-IR on chip.

重频可调谐U波段被动谐波锁模光纤激光器

U波段(1 625~1 675 nm)高重频锁模光纤激光器在甲烷气体检测、扩展通信波段、光子显微镜、眼部手术等领域有广泛的应用前景。基于被动谐波锁模(Harmonic Mode-Locking, HML)的孤子自频移(Soliton Self-Frequency Shift, SSFS)技术是一种实现高重频U波段激光输出的有效方式。首先搭建了基于非线性偏振旋转(Nonlinear Polarization Rotation, NPR)的被动HML光纤激光器,并以此为种子源,通过级联的放大系统将输出功率最高放大至1.7 W。而后将放大的脉冲输入到一段反常色散的色散位移光纤(Dispersion-Shifted Fiber, DSF)中,利用SSFS效应将其中心波长频移至U波段。研究了其中三个重复频率(722.0、941.7、1 224.2 MHz)状态,系统地探究了脉冲重复频率对SSFS的影响。首次使用NPR被动HML光纤激光器作为SSFS效应种子源,实现了波长可覆盖整个U波段范围的GHz脉冲输出。

Soliton molecules and dynamics of the smooth positon for the Gerdjikov–Ivanov equation

Soliton molecules are firstly obtained by velocity resonance for the Gerdjikov–Ivanov equation, and n-order smooth positon solutions for the Gerdjikov–Ivanov equation are generated by means of the general determinant expression of n-soliton solution. The dynamics of the smooth positons of the Gerdjikov–Ivanov equation are discussed using the decomposition of the modulus square, the trajectories and time-dependent "phase shifts" of positons after the collision can be described approximately. Additionally, some novel hybrid solutions consisting solitons and positons are presented and their rather complicated dynamics are revealed.

基于孤子自频移效应的超短脉冲波长连续调谐

作为光纤非线性效应中的一种,孤子自频移效应由于其特殊的脉冲自持性而成为光纤中超短脉冲波长调谐的有效方式。从理论计算和实验验证角度对光纤中的孤子自频移效应进行研究,基于广义非线性薛定谔方程对光纤中的孤子自频移效应进行仿真计算,通过测量超短脉冲在保偏光子晶体光纤输出端的光谱对其进行实验分析,理论和实验结果相符合,均表明基于孤子自频移效应的超短脉冲波长可以实现大于300 nm的光纤反常色散区连续调谐。

飞秒脉冲作用下光子晶体光纤超连续谱的产生

采用钛宝石超快fs激光器泵浦 2m长光子晶体光纤产生超连续谱 ,重点研究了不同输入功率下 35 0～ 95 9nm波长范围内光谱的演变过程 ,实验中产生的超连续光谱宽度超过 5 5 0nm 分析表明 ,内脉冲喇曼散射和孤子自频移在开始阶段对光谱长波方向上的展宽起主要作用 。

一种改进的基于部分信息喷泉码度分布设计

与传统的喷泉码相比,基于反馈信息的喷泉码可以有效降低译码开销,其编码所采用度分布则是喷泉码设计的关键,本文提出一种适用于反馈喷泉码的基于部分信息度分布构造方法.该方法首先提出具有较小译码开销的最佳单项式度分布函数,并将其与传统的SRSD度分布相结合,然后通过参数调整可以获得修正后的ISRSD度分布函数.仿真结果表明在已知部分信息的喷泉码中,与传统的SRSD度分布函数相比,采用ISRSD度分布函数进行编码使其性能得到明显的提高.

飞秒脉冲在光子晶体光纤中的传输特性

基于广义非线性薛定谔方程,利用分步傅里叶法数值模拟了超高斯时间分布的飞秒脉冲在光子晶体光纤中的传输特性。结果表明:超高斯脉冲比高斯脉冲在更短距离内形成孤子衰变,而且出现比强孤子功率稍低的次峰,孤子自频移更显著;另外,三阶色散会导致脉冲波形及频谱不对称,出现精细结构,并且有形成孤子的趋势;脉冲内拉曼散射对脉冲有平滑作用;自陡改变了主峰与次峰之间的能量分配。

高阶非线性效应影响下二阶孤子的衰变

数值求解了标准化高阶修正非线性薛定谔方程.对二阶孤子在自陡峭(Self Steepening,简称SS)和自频移(Self FreguencyShift,简称SFS)两种高阶非线性效应影响下的传输特征及原理分别进行了研究,讨论了二阶孤子衰变产生的两个基孤子的峰值强度比与自陡峭参量、自频移参量之间的关系.结果表明,在高阶非线性效应影响下,二阶孤子在单模光纤中传输时会发生衰变,衰变后小振幅基孤子在前,大振幅基孤子在后;在自陡峭效应影响下,衰变后两个基孤子都发生时间轴上的延迟;在自频移效应影响下,衰变后小振幅基孤子发生时间轴上的超前,大振幅基孤子发生时间轴上的延迟;随着高阶非线性效应的增强,衰变产生的小振幅基孤子与大振幅基孤子的峰值强度比逐渐减小,在相同传输距离处,它们的分离程度逐渐增大.

Kerr系数随机扰动下孤子间相互作用的研究

从描述光纤中皮秒孤子传输的修正非线性薛定谔方程出发,应用对称分步傅立叶变换对色散位移光纤中Kerr系数随机扰动影响下的孤子间相互作用进行了数值研究。结果表明,Kerr系数随机扰动下孤子间的作用比Kerr系数不变时更为严重,前者增强了孤子间的相互作用,恶化了孤子的传输特性。研究结果还表明,传统的不等振幅传输法在一定程度上仍然可以有效地抑制Kerr系数扰动影响下的孤子间作用。

PSA平均光孤子系统传输性能的研究

本文采用计算机系统仿真的方法,研究了应用相敏光放大器(PSA)作为在线放大器的采用平均孤子传输方案的光孤子通信系统中,泵浦光与信号光之间的相位漂移、光纤色散对光孤子通信系统传输性能的影响。仿真的结果表明:泵浦光与信号光之间的相位漂移将导致孤子幅度的下降;由于PSA增益的相敏特性,光纤色散导致孤子脉冲主瓣幅度下降,脉宽展宽,出现旁瓣。

色散管理光纤中超短光脉冲压缩效应研究

本文研究了色散管理光纤中超短光脉冲的压缩效应 .对于两种不同的色散管理光纤 ,分析了脉冲压缩机制和效果 .发现总色散为零和总色散不为零的色散管理光纤对超短光脉冲压缩都有较大的压缩比 ,而后者比前者所需最佳纤长缩短一半 .当考虑高阶色散和高阶非线性项效应时 ,发现脉冲压缩质量有所下降 。

DPSK色散管理线性和类孤子系统传输的简约解

采用简化法分别研究了差分相移键控(DPSK)色散管理线性和类孤子系统的传输特性,得出较为简洁明了的脉宽以及脉冲啁啾随距离演化的方程组.研究的结果发现,线性的DPSK系统只有在色散完全补偿的情形下是一种临界的稳定,而类孤子的DPSK系统即使在欠补偿情形下,系统也是完全的稳定,啁啾的演化是独特的闭合曲线.其完全稳定性的物理实质来自于非线性效应引入的自束缚势.从而说明DPSK色散管理类孤子系统良好的传输性能.

Highly efficient Cherenkov radiation generation in the irregular point of hollow-core photonic crystal fiber

Highly efficient Cherenkov radiation （CR） is generated by the soliton self-frequency shift （SSFS） in the irregular point of a hollow-core photonic crystal fiber （HC-PCF） in our laboratory. The impacts of pump power and wavelength on the CR are investigated, and the corresponding nonlinear processes are discussed. When the average power of the 120 fs pump pulse increases from 500 mW to 700 mW, the Raman soliton shifts from 2210 nm to 2360 nm, the output power of the CR increases by 2.3 times, the maximum output power ratio of the CR at 539 nm to that of the residual pump is calculated to be 24.32：1, the width of the output optical spectrum at the visible wavelength broadens from 35 nm to 62 nm, and the conversion efficiency η of the CR in the experiment can be above 32%.

色散管理孤子中 Raman效应引起的时移及定时抖动(英文)

给出了色散管理孤子中 Raman效应所引起的脉冲中心位置时移的解析表达式并讨论了孤子脉宽的波动所引起的 Raman定时抖动 .结果表明 :时移的演化和不同的色散配置有关 ,并且色散管理孤子 Raman时移和常规孤子一样与传输距离及平均色散的平方成正比 。