Effect of transient susceptibility on femtosecond pulse propagation in semiconductor quantum well waveguide

Ultra fast pulse evolution in a semiconductor quantum well structure (QWS) is theoretically analyzed. The polarization induced in the medium due to an incident Gaussian electromagnetic beam has been obtained using the semiconductor Bloch equations. The non-linear Schrödinger equation is used to analyze the effect of the induced polarization on the pulse. An interesting manifestation of the intensity dependence of the refractive index in non-linear media occurs through self-phase modulation (SPM), a phenomenon that leads to spectral broadening of the optical pulses. In doing the miniaturization of the device, we use semiconductor nanostructures in which the non-linearity is very large as compared to their bulk counterparts. Consequently, the phenomenon of SPM becomes significant at lower length scale leading to the limitations of the device. Numerical analysis was performed for a 150 fs Ti:sapphire laser radiation propagating along the transverse plane of a GaAs/AlGaAs QWS with realistic material parameters reveals asymmetric spectral broadening of the pulse due to SPM. The results agree qualitatively well with those available in the literature.     

左手材料薄板波导中的传导模

推导了左手材料薄板波导中传导模的色散方程,分析了波导中存在传导模与波导材料和包敷材料参数取值范围之间的关系.数值算例证实了这些关系.     

Tailoring of group velocity dispersion in dual-core chiral nihility waveguide

The article focuses on an approach to overcome the dispersion present in optical communication systems. The group velocity dispersion (GVD) remains an important issue in this context. The approach presented in this paper is based on the use of chiral nihility mediums with different chirality parameters in dual-core planar optical waveguide. It is found that the two cores can be resonantly coupled in the guide, and also, the waveguide would yield high GVD by choosing suitable design parameters. For the analytical investigation, transfer matrix method is used and the dispersion relation is derived by implementing appropriate boundary conditions. Excitation of supermodes in the guide may be achieved through the coupling of two particular core modes, which would ultimately result in giant GVD. This essentially demonstrates that the structure may find applications in dispersion compensating systems.     

Pulse propagation and windowed wave functions

Abstract

We apply quasi-distribution methods developed for quantum mechanics to the propagation of pulses in dispersive media with attenuation. We show that a Schrödinger type equation follows for propagation of the pulse for each mode. One then transforms the equation to obtain an equation of evolution in the phase space of position and wavenumber. In this paper we emphasize windowed wave functions and their corresponding phase space quasi-distributions. We obtain the time evolution equation, discuss possible approximations, and compare to the Wigner distribution approximation previously derived by Loughlin and Cohen by different methods.     

Third-order dispersion in a pair of prisms

The general equation for third-order group velocity dispersion is derived in this paper, which contains all the terms of equation (11) in Arissian and Diels [1], as well as one extra term, which we have verified is not negligible. To verify our equation we have modeled the sum of Gaussian modulated frequencies. We show the electric field of bandwidth limited incident ultrashort pulses with a time duration of: 5 fs, 10 fs, 15 fs, 20 fs, 30 fs and 50 fs after propagating through a pair of identical isosceles prisms for a central frequency of 0.8 µm and 0.620 µm. The model is applied by using (a) the finite phase, (b) the phase approximated up to the second-order dispersion and (c) up to the third-order dispersion for each frequency component of the pulse. Graphs are presented for prisms made with fused silica and SF14.     

超光速问题与电磁波异常传播

讨论了超光速研究的历史背景和在狭义相对论框架内进行工作的可能性;指出已有的实验（用单光子、激光脉冲和微波）在量子隧穿过程中呈现出的超光速行为,是在特定物理条件下才有的。认为经典电报员方程与Klein-Gordon方程的相似,使得前可用于粒子隧穿和超光速现象的研究。讨论了不久前发表的王力军博士的超光速实验,展望了超光速研究的未来。     

广义Pochhammer频谱特性分析

本文分析了在无限长空心圆管与周围背景介质完好粘结系统纵向运动时,粘结体中的弹性波传播。导出了广义Ｐｏｃｈｈａｍｍｅｒ频率方程,研究了不同材料组合及尺度对其频谱特性的影响,并给出了相应的频谱曲线。     

Design and comparative performance analysis of different chirping profiles of tanh apodized fiber Bragg grating and comparison with the dispersion compensation fiber for long-haul transmission system

Various dispersion compensation units are presented and evaluated in this paper. These dispersion compensation units include dispersion compensation fiber (DCF), DCF merged with fiber Bragg grating (FBG) (joint technique), and linear, square root, and cube root chirped tanh apodized FBG. For the performance evaluation 10 Gb/s NRZ transmission system over 100-km-long single-mode fiber is used. The three chirped FBGs are optimized individually to yield pulse width reduction percentage (PWRP) of 86.66, 79.96, 62.42% for linear, square root, and cube root, respectively. The DCF and Joint technique both provide a remarkable PWRP of 94.45 and 96.96%, respectively. The performance of optimized linear chirped tanh apodized FBG and DCF is compared for long-haul transmission system on the basis of quality factor of received signal. For both the systems maximum transmission distance is calculated such that quality factor is ≥ 6 at the receiver and result shows that performance of FBG is comparable to that of DCF with advantages of very low cost, small size and reduced nonlinear effects.     

基于PWM占空比的印刷量子点图像信息识读

目的 针对目前PQP点阵数据的识读算法准确率较低速度较慢的问题,为了加快该信息隐藏与印刷防伪方法的推广应用,文中设计一种基于PWM占空比判据的PQP快速识读算法。方法 首先对采集到的PQP图像在非校正条件下,利用脉冲宽度调制(PWM)和最小占空比寻优方法,估算其点阵图像的栅格角度,然后根据所求得的栅格角度参照PQP点阵图像,分别计算横纵2个方向的极大值序列,之后对该序列进行二次差分和自适应阈值判决以绘制PQP点阵数据识读栅格,最后以方形螺旋线指向顺序索引网格内各位置特征值来识读PQP点阵数据信息。结果 通过仿真和实验测试得出,当打印分辨率为600 dpi时,PQP图像信息的识读时间和误码率分别控制在0.5 s和±5%以内。结论 在非校正、无参考和盲同步信息等不确定条件下,实现了对PQP点阵图像的信息提取。     

超光速研究的40年——回顾与展望

自美国物理学家O.M.Bilanuik和E.C.Sudarshan（1962年）以及G.Feinberg(1967年)的开创性工作以来,在美国、欧洲和中国都对超光速展开了研究。根据A.Einstein于1905年发表的原始论文,超光速没有存在的可能,但其1907年的论文对“信号传播不能超光速”却不很肯定。文章把速度问题分解为若干类、项,并提出“广义信息速度”定义以利于对众多速度概念的讨论。在反思了40年来（1962—2003年）的超光速研究以后,得出结论认为“超过真空中光速c”是一种可实现的科学陈述。     

Transmission characteristic of interaction between Airy pulses and solitons in silicon-on-insulator waveguides

In this paper, we numerically simulate the transmission characteristics of Airy pulses and solitons interacting in silicon-on-insulator waveguides by utilizing Split-step Fourier method implemented in MATLAB. During transmission, the energy of Airy pulse is focused, and a new Airy pulse is subsequently separated from frontal edge. The new Airy pulse and the initial pulse exhibit reversal characteristics in time domain. In process of interaction with soliton, partial energy of the main lobe is separated from Airy pulse and transmitted along soliton transmission trajectory. The soliton produce a series of end edge oscillations. When the soliton is affected by Airy pulse, the propagation distance decreases, in constrast to the trailing edge oscillation frequency. In addition, third-order dispersion, Kerr effect and two-photon absorption on Airy pulse and soliton are also mentioned. At the same time, the effect on transmission of Airy pulse and solition will be showed in different truncation coefficients, powers and pulse widths.     

Comparison of epoxy- and siloxane-based single-mode optical waveguides defined by direct-write lithography

This paper reports on the fabrication and characterization of single-mode polymer optical waveguides at telecom and SOI compatible wavelengths; by making a comparison between an epoxy and a siloxane polymer waveguide material system (both commercially-available). The proposed waveguides can be used in short-reach optical interconnects targeting chip-to-chip communication on the interposer level or providing a coupling interface between single-mode optical fibers and photonic integrated circuits (PICs). This technology enables the integration of optoelectronic chips for photonic packaging purposes. First, the single-mode dimensions (4 × 4 μm² and 5 × 5 μm²) for both materials at selected wavelengths (1.31 μm and 1.55 μm) were determined based on the refractive index measurements. Then, the waveguides were patterned by a direct-write lithography method. The fabricated waveguides show a high-quality surface with smooth sidewalls. The optical propagation losses were measured using the cut-back method. For the siloxane-based waveguides, the propagation losses were found to be 0.34 dB/cm and 1.36 dB/cm at 1.31 μm and 1.55 μm respectively while for the epoxy-based waveguides the losses were 0.49 dB/cm and 2.23 dB/cm at 1.31 μm and 1.55 μm respectively.     

分散介质中波群速度的物理现象(英文)

波的相速度与群速度是研究分散介质的物理过程与现象时最为频繁使用的概念.然而,理想的谐波相速度与真实的非单色波相速度之间存在差异,这一差异与其物理学解释不符,从而常常增加了理论研究和实际测量结果的误差.20世纪初提出的这两个概念尚未得到恰当的评估,当前应对其涵义进一步明确及修正.     

溶胶-凝胶法制备全反射型CO2激光空芯波导的可行性分析

通过对CO2激光空芯导研究现状的分析,指出了全拓射型空芯导目前所面临的问题,在此基础上结合溶胶－凝胶法的特点,提出了用溶胶－凝胶法制备全反射型CO2激光空芯波导反常色散膜的新思想,并分析了其在原理、工艺及光学上的可行性。     

Propagation properties and dispersion characteristics of the tapered gap plasmonic waveguides

Abstract

In this study, we numerically analyse the propagation properties and dispersion characteristics of the tapered gap plasmonic waveguides (TGPWs). Using the finite element method, the waveguide parameters such as modal field distribution and complex propagation constant are calculated for different geometrical parameters over a wide spectral range. Moreover, using a kind of active medium with appropriate gain, the required gains for lossless propagation are obtained. Results show that the propagation properties and dispersion characteristics of the waveguide along with the value of required gain for achieving lossless propagation can be well controlled by adjusting the geometrical parameters of the waveguide. The simulation results indicate that the calculated gain values are obtainable using the existing semiconductor technology such as InGaAsP–InGaAlAs multi-quantum well and InAs/GaAs quantum dot active medium at the wavelength of 1550 nm. The strong mode confinement of the TGPWs can be used for achieving strong nonlinear effects. Furthermore, due to optical energy confinement in nanoscale, optical nanofocusing devices based on TGPWs are attainable. TGPWs can be utilized in the field of nanotechnology to fulfil the photonic devices integration.