Ultrashort pulse propagation in carbon nanotubes in a magnetic field

The problem of ultra-short optical pulse behavior in a system of carbon nanotubes with an applied magnetic field parallel to the nanotube axis was considered. The electromagnetic field was explored using the Maxwell equations. The electronic system of the carbon nanotubes was a quantum system and was mechanically investigated for the case of low temperatures. The distributional pattern of the ultra short pulses and their collision were established by means of numerical modeling.     

Frequency conversion in nonlinear photonic crystal of strontium tetraborate

Using a nonlinear photonic crystal (NPC) of strontium tetraborate, we obtained the second-harmonic generation of femtosecond pulses in the nonlinear diffraction regime with an efficiency of 1.9% that is tunable in the near-UV spectral range, as well as fourth-harmonic generation under the conditions of random quasi-phase-matching with maximum efficiency of 10⁻⁵ that is tunable in the far-UV spectral range. The efficiency of second-harmonic generation in strontium tetraborate NPC under the conditions of random quasi-phase-matching was significantly lower. The fourth-harmonic was tunable between 187.5 and 232.5 nm. The previously predicted red shift of spectral components in the generated radiation spectrum upon NPC rotation is demonstrated experimentally.     

光子晶体波导中的孤子传输及其延迟特性研究

研究了正方晶格和三角晶格空气背景硅介质柱光子晶体线缺陷波导导模左带隙边缘处的亮孤子脉冲传播特性及其慢光延迟特性. 采用平面波展开法仿真分析了波导相邻两行介质柱大小r₁和r₂以及波导宽度D对孤子脉冲传输所需峰值功率P₀和延迟时间T_s的影响,总结了其变化规律. 通过调整波导结构得到了正方晶格和三角晶格优化波导结构,优化后,正方晶格结构波导P₀减小了81.17%,T_s增加了66.32%;三角晶格结构波导P₀减小了73.7%,T_s增加了67.63%,实现了孤子传输性能的大幅度优化. 关键词： 光子晶体波导 光孤子 峰值功率 延迟时间     

高非线性光子晶体光纤中飞秒脉冲的传输特性和超连续谱产生机制的实验研究及模拟分析

用实验和数值模拟两种方法研究了高非线性光子晶体光纤中飞秒激光脉冲的传输特性和超连续谱的产生机理，给出了抽运脉冲在三种不同中心波长情况下输出光谱展宽并形成超连续谱的实际测量及理论模拟结果.研究表明：在零色散波长抽运时，光谱展宽以自相位调制为主，同时三阶色散的影响明显，传输脉冲在时域内出现振荡次峰.而在反常色散区抽运时，光谱展宽的初期以自相位调制为主，随后根据抽运功率的不同孤子自频移、高阶光孤子的裂变和四波混频效应会逐渐增强，进而成为光谱展宽的主要原因.与此相应，在时域中能明显看到孤子的形成和红移，飞秒传输脉 关键词： 光子晶体光纤 高非线性光子晶体光纤 飞秒脉冲激光 超连续谱     

Soliton-like propagation of light pulses in a nonlinear photonic crystal

On the basis of computer simulation, we analyze the dynamics of interaction of subpulses localized inside certain layers of a one-dimensional nonlinear photonic crystal. Localized subpulses are shown to move and interact like solitons. Possible scenarios of their interaction are described: a spatially periodic regime, the merging of several subpulses with similar characteristics into a single higher intensity and more slowly propagating subpulse, and the formation of an immovable pulse in a layer of the photonic crystal. To verify the results of the computer simulation and to elucidate the nature of spatially localized structures forming, a comparison with the analytical solution for a medium with cubic nonlinearity is performed.     

Ultrashort pulse compression and delivery in a hollow-core photonic crystal fiber at 540 nm wavelength

We have fabricated a bandgap-guiding hollow-core photonic crystal fiber (PCF) capable of transmitting and compressing ultrashort pulses in the green spectral region around 532 nm. When propagating subpicosecond pulses through 1 m of this fiber, we have observed soliton-effect temporal compression by up to a factor of 3 to around 100 fs. This reduces the wavelength at which soliton effects have been observed in hollow-core PCF by over 200 nm. We have used the pulses delivered at the output of the fiber to machine micrometer-scale features in copper.     

Optimal poling of nonlinear photonic crystals for frequency conversion

Nonlinear photonic crystals formed by two-dimensional periodic poling of the quadratic susceptibility chi(2) can support quasi-phase-matched harmonic generation. The frequency-conversion efficiency depends on the photonic crystal's poling pattern through certain Fourier coefficients of the poling function. A procedure is described for finding those poling patterns that are most efficient for any specific quasi-phase-matched frequency-conversion scheme.     

Supercontinuum generation and nonlinear pulse propagation in photonic crystal fiber: influence of the frequency-dependent effective mode area

Numerical simulations are used to study the effect of the frequency dependence of the effective mode area in photonic crystal fiber on supercontinuum generation. We quantify how the frequency dependence of the effective area influences the propagation characteristics through a modified optical shock term and identify the major consequence as a reduction in the extreme long-wavelength edge of the supercontinuum spectrum. Our results show that, for the parameter regimes used in many previous supercontinuum generation experiments using near-infrared femtosecond pump sources around 800 nm, this effect would be expected to be negligible. However, for pumps in the 1000–1500 nm range, the inclusion of this effect would be expected to be crucial for accurate comparison of simulations with experiment.     

Combined frequency conversion and pulse compression in nonlinear tapered waveguides

We suggest an application of pump-degenerate four-wave mixing process in tapered waveguides for generation of ultrashort pulses with central frequency tunable over the material transparency range. Our method can produce strongly compressed frequency-converted pulses in presence of group-velocity mismatch and group-velocity dispersion. Additionally, the proposed technique does not require pulse phase synchronization and effectively operates for strongly chirped pump pulses, thus enabling the use of longer nonlinear media for high conversion efficiency.     

Ultrashort pulse propagation in multiple-grating fiber structures

We propose a multiple-grating fiber structure that decomposes an ultrashort broadband optical pulse simultaneously in both wavelength and time. As an initial demonstration, we used a transform-limited 1-ps Gaussian pulse centered at 1.55 mu;m as the ultrashort broadband input into a three-grating fiber structure and generated three output pulses separated in wavelength and time with good correlation between experimental results and simulations. This device structure can be used to generate a multiwavelength train of pulses for use in wavelength-division-multiplexed systems or to implement frequency-domain encoding of coherent pulses for optical code-division multiple access.     

The two-dimensional superconducting photonic crystal

The band structure of a two-dimensional superconducting photonic crystal is studied. The temperature dependence of the photonic band structure in a wide temperature region below the superconducting transition is analyzed. It is found that the photonic crystal has two full band gaps and two incomplete band gaps, which are shifted to the high frequency region with decreasing temperature.     

飞秒光脉冲在光子晶体光纤中的非线性传输和超连续谱产生

采用分步傅里叶方法数值模拟了飞秒光脉冲在光子晶体光纤中非线性传输和超连续谱的产生. 计算和分析了高阶色散和非线性效应对超连续谱形状和带宽的影响. 结果表明在光子晶体光纤中产生了孤子自频移现象. 同时也发现脉冲内拉曼散射和自相位调制的联合作用导致了超连续谱中精细结构的出现. 另外，还发现高阶色散和初始光脉冲的峰值功率对超连续谱的带宽和平滑也有直接影响. 关键词： 光子晶体光纤 孤子自频移 超连续谱     

Ultrashort pulse propagation under manipulated resonance conditions

The propagation of a polarized ultrashort laser pulse is analyzed by the inverse scattering method under initial conditions including a spatial pulse profile, a state of the medium, and a “switched-on” resonant atom-field interaction. Magnetic degeneracy of atomic levels is taken into account. The Maxwell-Bloch equations are rewritten in Hamiltonian form without redefining the spatial and temporal variables. The inverse scattering method is based on an analysis of a new spectral problem. Gelfand-Levitan-Marchenko-type equations are derived, a soliton solution is obtained, and the changes in parameters of two solitons after their collision are calculated. A possible experimental setup for implementing the system under analysis is discussed.     

Ultrashort pulse measurements using a nonlinear mirror

The use of nonlinear optical phenomena at the boundary of a nonlinear medium for measuring the duration and the pulse shape of ultrashort light pulses are considered. Two different schemes are discussed.     

外磁场与温度对低温超导光子晶体低频禁带特性的影响

文中用传输矩阵法(TMM)分析了TM波垂直入时,超导光子晶体的低频禁带特性,并讨论了外磁场与温度对禁带的影响.分析结果表明:超导光子晶体存在频率从0开始的低频禁带;当没有外磁场作用时,由于超导中正常态电子的影响,低频禁带的截止频率与温度无关;有外磁场作用时,温度才对截止频率具有可调性.外加恒定磁场时,低频禁带的截止频率随温度升高而减小;而在正常态电子的作用下,温度对处在超导态超导光子晶体禁带截止频率的调节范围相对忽略正常态电子情况下减小.恒温下,通过调节外磁场来控制带隙时,正常态电子的贡献很小可忽略不计;外磁场强度增大禁带截止频率减小.当超导体完全处于正常态时,低频禁带消失.     

Light frequency conversion in photonic crystals

Light frequency conversion when light interacts with a shock wave propagating through a photonic crystal is investigated. Two new phenomena are found, the first is that frequency increases by integral multiple of a certain amount in the process of frequency conversion. The second phenomenon is frequency conversion that still occurs when the shock wave front is replaced by a vacuum area. Through FDTD simulations and analytical theory, photon-phonon interaction and surface decaying mode interpretations for the mechanism of frequency conversion are found.     

Localization of the femtosecond pulse train energy in a one-dimensional nonlinear photonic crystal

Computer simulation demonstrates the feasibility of pumping a one-dimensional nonlinear photonic crystal (layered one-dimensional periodic structure) by optical energy localizing in the crystal when it is irradiated by a femtosecond pulse train. Simulation is based of the recently suggested approach to similar problems. It is shown that the pumping effect can be employed in 3D optical storages.     

Adaptive split-step Fourier method for simulating ultrashort laser pulse propagation in photonic crystal fibres

In this paper, the generalized nonlinear Schr\"{o}dinger equation (GNLSE) is solved by an adaptive split-step Fourier method (ASSFM). It is found that ASSFM must be used to solve GNLSE to ensure precision when the soliton self-frequency shift is remarkable and the photonic crystal fibre (PCF) parameters vary with the frequency considerably. The precision of numerical simulation by using ASSFM is higher than that by using split-step Fourier method in the process of laser pulse propagation in PCFs due to the fact that the variation of fibre parameters with the peak frequency in the pulse spectrum can be taken into account fully.