Experimental Electrically Reconfigurable Time-Domain Spectral Amplitude Encoding/Decoding in an Optical Code Division Multiple Access System

Abstract

An electrically reconfigurable time-domain spectral amplitude encoding/decoding scheme is proposed herein. The setup is based on the concept of temporally pulse shaping dual to spatial arrangements. The transmitter is based on a short pulse source and uses two conjugate dispersive fiber gratings and an electro-optic intensity modulator placed in between. Proof of concept results are shown for an optical pulse train operating at 1.25 Gbps using codes from the Hadamard family with a length of eight chips. The system is electrically reconfigurable, compatible with fiber systems, and permits scalability in the size of the codes by modifying only the modulator velocity.     

Photonic ultra-wideband monocycle pulses generation using semiconductor optical amplifier and electro-absorber in parallel

A scheme for photonic generation of ultra-wideband （UWB） pulses using a semiconductor optical amplifier （SOA） and an electro-absorber （EA） in parallel is proposed and numerically demonstrated. By adjusting the time delay between two pump signals incident into the SOA and the EA, we can obtain monocycle pulses with reversed polarities and different bandwidths. The proposed method is flexible in pulse shaping and easy in practical optimization.     

The improvement of Nyquist pulse shaping for all-optical OFDM system in multi-users network

The all-optical orthogonal frequency division multiplexing has a better spectral efficiency and a lower response requirement of modulators for high capacity transmission. In the system, the optical filter will degrade the performance of subcarriers which are far away from the center carrier. We proposed an improvement method of all-optical OFDM scheme using Nyquist pulse shape in the pulse source generator. Comparing a Nyquist shape pulse with a Gauss pulse in a 4 × 100 Gb/s DP-QPSK all-optical sampling OFDM system, the side lobe of transmitted spectrum can be effective suppressed, and the optical power will be more focused on the effective frequency band. By coherent receiver, the results show that the Nyquist pulse shaping can improve the OSNR and transmission performance of subcarriers which deviate mostly from the center frequency of optical filter. This improvement is of great benefit for multi-users system.     

Shaping of ultrashort pulses using bulk acousto-optic filter

Our paper deals with temporal shaping of ultrashort pulses by direct spectral filtering performed with bulk acousto-optic filters using noncollinear geometry. This geometry allows arbitrary optical pulse repetition rate and high diffraction efficiency at relatively large optical apertures. A theoretical model of the pulse shaper is presented, emphasizing the degrees of freedom in this shaping technique. Phase and angular dispersion effects are analyzed, and experimental results on generating controllable pulse trains are presented. PACS 42.65.Re; 42.79.J     

Highly sensitive single-beam heterodyne coherent anti-Stokes Raman scattering

Single-beam coherent anti-Stokes Raman-scattering (CARS) microspectroscopy achieves a complete CARS scheme with a femtosecond laser. Here, we introduce heterodyne detection in a simple experimental extension: the optical fields driving the CARS process and the local oscillator used for heterodyning are derived from a single beam of ultrashort laser pulses by pulse shaping. The heterodyne signal is amplified by more than 3 orders of magnitude and is linearly dependent on the concentration of Raman scatterers. This dramatically increases the sensitivity of chemically selective detection at microscopic resolution while maintaining the simplicity of the single-beam setup.     

Femtosecond pulse shaping using counter-propagating pulses in a semiconductor optical amplifier

An efficient pulse shaping method using counter-propagating pulses in the femtosecond regime is proposed and investigated. The effects of pump pulse power and pulsewidth on probe pulse are studied in counter-propagation scheme. It is shown that, with the proposed method, output probe pulse temporal and spectral peak shift due to femtosecond nonlinearities can be compensated, while the output pulse is amplified sufficiently. Furthermore, in relatively high power regime, the probe pulsewidth and time-bandwidth product are improved using counter-propagating pump pulse.     

基于单模光纤的交叉相位调制型频率分辨光学开关超短脉冲测量

利用单模光纤中的光弹效应和交叉相位调制(XPM)效应,提出了一种频率分辨光学开关法测量超短脉冲的新方案.在本方案中,单模光纤的前一部分产生可变延迟,后一部分作为非线性介质产生非线性效应.该方案只需一根单模光纤,无须复杂的光路校准,结构简单,损耗低;光纤中的XPM效应易发生,无须相位匹配.对提出的方案进行了数值模拟,采用基于矩阵的主元素广义投影算法,恢复出待测脉冲的幅度和相位信息,并研究了光纤长度和待测超短脉冲的脉冲宽度对测量结果的影响.结果表明:测量准确度随着光纤长度的增加而提高,选取长度为2 km的光纤,就可以实现对超短脉冲的准确测量;本文方案适用于脉冲宽度不小于80 fs的超短光脉冲的测量.     

混沌超宽带系统的广义负熵盲检测机理研究

本文提出了利用广义负熵盲检测机理对混沌超宽带系统的进行非相干盲检测的研究方法, 在传输信道状态未知的情况下即可检测出混沌脉冲信号. 该方法能够克服用于超宽带无线电通信的直接混沌通信方案存在的实际应用问题, 能够有效解决未知复杂多径信道问题. 通过仿真结果分析表明, 采用非相干盲检测方法的直接混沌通信超宽带方案, 不需要信道状态信息, 具有很好的分离检测效果. 为未知非理想信道下, 非相干盲检测的混沌超宽带系统提出了新思路.     

Generating a quasiellipsoidal electron beam by 3D laser-pulse shaping

A generic 3D laser-pulse-shaping scheme is proposed towards the generation of a uniform ellipsoidal particle distribution, an ideal distribution due to the linear dependence of the space-charge force on the particle position. The shaping is accomplished via spatiotemporal coupling of the laser dynamics via chromatic aberration in an optical lens. Particle tracking simulations show that the electron beam initiated by such a laser pulse in a high-gradient radio-frequency photoinjector delivers very low emittance, ideal for beam-based light sources such as the x-ray free-electron laser.     

时域多模飞秒压缩光场测量中的本地光脉冲整形研究

基于飞秒脉冲的同步泵浦参量过程产生的多模时域飞秒压缩光场,由于其独特的优势,特别是可以享有单模光纤网络兼容,是实现可扩展量子计算及大容量量子通讯的良好光源。由于无法实现多模时域飞秒压缩光场的空间分离,目前对于多模时域飞秒压缩光场的测量,采用最为有效的平衡零拍探测。因此如何构造与时域飞秒压缩光场时域函数分布相同的本地光,是其中的关键内容,并直接影响测量效果。本文主要理论研究了本地脉冲光的时域整形方案,分析了系统参数对整形后的多模本地光的保真度以及系统调制效率的影响,并结合实验参数提出可能的解决办法。     

基于各向异性晶体的光学微分运算

光学微分运算是边缘图像的光学检测核心原理,与传统的数字图像处理方法相比,具有效率高、结构简单且无需考虑算法和功耗等优点.本文提出一种基于各向异性晶体的光学微分运算装置,用定制的晶体片实现光的空间分化,从而实现多角谱分量下的全方位边缘成像.本文中的方案需要将光束的左右旋圆偏振分量横向分离,再对中间部分的线偏振光进行滤波处理.该方案主要是基于各向异性晶体的双折射效应,整个装置整合为一条笔直的光路,与自旋霍尔效应和超表面相比,具备原理简单、成本较低且成像稳定的优点,不过对晶体的厚度有较高的要求.实验结果也较为理想地验证了此方案,未来可望在量子观测、生物细胞和医学等领域实现一定潜在应用.     

啁啾匹配OPCPA方案用于消除超短激光脉冲的预脉冲

采用了一种利用啁啾匹配光参量啁啾脉冲放大（OPCPA）技术来消除泵浦脉冲时间窗口内的预脉冲的方法,并对该方法展开了数值模拟研究。分析了泵浦光脉冲形状、预脉冲提前时间等因素对预脉冲消除效果以及信噪比提升情况的影响。通过与传统的非共线OPCPA方案对比,发现啁啾匹配OPCPA方案可以消除掉离主脉冲更近的预脉冲,且它对预脉冲的消除效果受泵浦光脉冲形状的影响较小。     

Multitap microwave photonic filters with programmable phase response via optical frequency comb shaping

We present a programmable multitap microwave photonic filter with an arbitrary phase response operating over a broad bandwidth. Complex coefficient taps are achieved by optical line-by-line pulse shaping on a 10 GHz flat optical frequency comb using a novel interferometric scheme. Through high-speed real-time measurements, we demonstrate programmable chirp control of a waveform via phase filtering. This achievement enables us to compress broadband microwave signals to their corresponding bandwidth-limited pulse duration.     

Artificial collimation of fast-electron beams with two laser pulses

A scheme for artificially collimating fast-electron beams produced in high intensity (>10(19) W cm(-2)) laser-solid interactions is proposed. The scheme uses a laser pulse at the relativistic threshold (approximately 10(18) W cm(-2)) that precedes the high intensity pulse to pregenerate a collimating magnetic field. This concept is supported by analytical calculations and numerical calculations performed using a novel hybrid-Vlasov-Fokker-Planck code called LEDA. This scheme may be highly useful for fast ignition inertial confinement fusion.     

Coherent control multiphoton processes in semiconductor saturable Bragg reflector with freezing phase algorithm

A freezing phase concept has been proposed for adaptive coherent control with a femtosecond pulse shaper. We applied the scheme to investigate multiphoton processes in InAs quantum dot saturable Bragg reflector (SBR). The optical transition of InAs quantum dots can be revealed in the spectral phase sensitivity plot of second harmonic signal. We also achieved a three-time increase in image contrast on regions with photoluminescent wavelength differing only 18 nm by using coherent control nonlinear optical microscopy. Our results suggest the new freezing phase scheme to be useful for various investigations which require fast and reliable complete-field characterization and coherent control on one setup. PACS 42.65.Re; 42.50.Md; 78.67.Hc     

160-Gb/s polarization-multiplexing optical NRZ-DQPSK transmission using differential detection

Using differential detection,we perform polarization-multiplexing 160-Gb/s optical non-return-to-zero(NRZ) differential quadrature phase shift keying(DQPSK) signal transmission over 100-km standard single mode fiber at a bit error rate(BER) of less than 10-9.The enabling technology includes clock recovery,fine dispersion compensation,and polarization tracking for de-multiplexing.Furthermore,a hybrid clock recovery scheme is proposed.The scheme is realized with ordinary devices using an optoelectrical modula...     

Femtosecond shaping of transverse and longitudinal light polarization

Femtosecond laser pulse shaping techniques have been restricted to propagating transverse electromagnetic waves. We present a scheme for pulse shaping of optical near fields based on the excitation of longitudinal electromagnetic fields with polarization-shaped light pulses. By solving Maxwell's equations for a model nanostructure, i.e., a scanning tunneling microscope tip, with help from the boundary-element method, we demonstrate that the electric field vector oscillates in a complex yet controllable fashion in three dimensions. Many applications are envisioned because literally another dimension in the optimal control of light-matter interaction is accessible.     

Two alternative approaches to electro-optical detection of terahertz pulses

The electro-optical detection of terahertz radiation is analyzed theoretically. While a conventional detection scheme of this type is based on the measurement of the phase shift of an optical pulse arising from its interaction with the terahertz field in a nonlinear medium, it is shown that both the phase and amplitude of the optical pulse vary because of this interaction. The amplitude modulation carries information on the dynamics of the amplitude and phase of the terahertz field and can be used to measure these parameters. With this energy-sensitive detection scheme, avoiding all restrictions on the symmetry type of the nonlinear medium is much simpler than with the phase scheme. Variants of the electro-optical detection technique using periodically poled crystals with the lithium-niobate symmetry and crystals with the zincblende structure are considered. It is shown that spectral sensitivities of the methods based on measurements of the phase and amplitude modulations are related as the frequencies of the laser and terahertz fields.     

激光脉冲时域整形及其对发射度的改善效果

 利用脉冲堆积法对驱动激光脉冲进行了时域整形,并利用条纹相机测量到了理想的整形结果。在脉冲堆积法的基础上,给出了近似椭球体整形的方案。模拟结果表明：利用脉冲堆积法整形后得到激光脉冲驱动光阴极可以获得更小的发射度;对于测量到的半高全宽（FWHM）为3.82 ps的脉冲,8个子脉冲堆积比4个子脉冲堆积更为有利;此外,对激光脉冲作近似椭球体整形可以进一步降低束流发射度。     

Spectral line‐by‐line shaping for optical and microwave arbitrary waveform generations

Spectral line‐by‐line shaping is a key enabler towards optical arbitrary waveform generation, which promises broad impact both in optical science and technology. In this paper, generation of optical and microwave arbitrary waveforms using the spectral line‐by‐line shaping technique is reviewed. Compared to conventional pulse shaping, significant new physics arises in the line‐by‐line regime, where the shaped pulse fields generated from one laser pulse now overlap with those generated from adjacent pulses. This leads to coherent interference effects related to the properties of optical frequency combs which serve as the source in these experiments. We explore such effects in a series of experiments using several different high‐repetition‐rate optical combs, including harmonically mode‐locked lasers and continuous‐wave lasers that are externally phase modulated either with or without the help of an optical cavity. As an application of line‐by‐line pulse shaping, we describe generation of microwave electrical arbitrary waveforms that can be reprogrammed at rates approaching 10 GHz.