Flatband Slow Light in Asymmetric Line-Defect Photonic Crystal Waveguide Featuring Low Group Velocity and Dispersion

In this paper, an asymmetric photonic crystal (PC) waveguide is proposed for slow light transmission. A row of air holes is removed to form a line-defect waveguide, and the lateral symmetry of the waveguide is broken by shifting the holes in the PC cladding on one side along the waveguide axis. Two structural parameters are carefully adjusted: the amount of shift compared with the array of holes in the cladding on the other side, and the radius of the holes closest to the waveguide core in the shifted PC cladding. In the asymmetric waveguide, it is possible to obtain flat band modes with low group velocity (c/50) and low dispersion (on the order of 10⁴ ps²/km) over a signal bandwidth of 40 GHz. The delay-bandwidth product (DBP) of the proposed slow-light device is analyzed and compared with the DBP of the PC waveguides reported in literatures. We find that our structure yields a significant increase in DBP, and improves the effective bandwidth in which we can obtain slow modes with both low group velocity and vanishing dispersion.     

高速相干光正交频分复用系统实现方案研究

相干光正交频分复用系统（Coherent Optical Orthogonal Frequency Division Multiplexing, CO-OFDM）作为未来高速光通信的重要解决方案,是近年来光传输领域的研究热点。高速CO-OFDM系统需要较高带宽的模数/数模转换器（DAC/ADC）,目前技术水平难以达到。文章改进了正交频带复用技术（Orthogonal Band Multiplexing , OBM）的光域实现方案;结合偏振复用技术和偏振分集接收,提出了基于OBM的100Gb/s高速CO-OFDM系统;并对系统传输性能进行数字仿真。结果表明：基于OBM技术的MIMO CO-OFDM系统可有效降低对DAC/ADC的处理速度要求,在不需任何在线色散补偿和偏振控制器件条件下,通过单模光纤传输800km,系统Q值保持在13dB以上。     

Coupling properties in a 2-D photonic crystal slab directional coupler with a triangular lattice of air holes

Two-dimensional (2-D) photonic crystal (PC) directional couplers (DCs) that have a triangular lattice pattern of air holes in a planar dielectric slab are theoretically and experimentally analyzed. Unlike the 2-D PC DC structure with a dielectric rod in air, which is frequently used in theoretical studies, more practical PC DCs tend to be multimode in nature and exhibit a large group velocity dispersion, thus creating decoupling points in the dispersion relation without any additional modifications to the structure. The multimode nature and large dispersion lead to interference which degrades the coupling properties. By inserting three rows of air holes between neighboring line-defect waveguides in order to separate them, we have successfully reduced the multimode region and obtained a single-mode region. In this case, the large dispersion allows the creation of a PC DC with wavelength selectivity and a coupling length as short as 30 a,/spl sim/10 /spl mu/m for a=345 nm, where a is the lattice constant. The transmission spectra obtained experimentally showed good agreement with the theory whereas their transmission ranges were restricted to those of bent waveguides. These results are encouraging for practical application to optical communications.     

One-Dimensional Photonic Crystal Rib Waveguides

We analyze an optical waveguide that consists of a 1D photonic crystal (PC) embedded in a large cross-sectional rib waveguide. The PC provides control over the dispersion properties of the waveguide, while the rib geometry provides a low loss and versatile mechanism for confining light. The structure is analyzed using the 3D finite-difference time-domain method. The simulation results indicate that extremely low-loss waveguiding is possible over a defect band. Moreover, the PC has a complete 1D photonic band gap with a gap-midgap ratio (Deltaomega/omega_mid) of 0.913, which is one of the largest ratios ever reported for a PC.     

3-D FDTD Analysis of Gold-Nanoparticle-Based Photonic Crystal on Slab Waveguide

In this paper, metallic photonic crystals (PC) based on 2-D periodic arrays of gold nanoparticles were investigated on indium tin oxide slab waveguides using 3-D finite-difference time domain simulations with nonuniform mesh techniques. The PC effects were studied by changing the lattice constants from 300 to 500 nm. The results obtained indicate that the waveguide-excited plasmon absorption peak of periodic array of gold nanoparticles is tunable from 672 to 707 nm due to the second grating order propagating backward at the grazing angle. The nanoparticle-induced extinction of the waveguide mode was also investigated by varying the slab thickness from 100 to 375 nm. The results show that the extinction peak shifts from 650 to 705 nm. The theoretical results predict that the interactions of the periodic array of gold nanoparticles are strongly affected by the dispersion of the waveguide.      

通过恒包络调制提高相干光OFDM系统的光纤非线性容限

相干光正交频分复用(CO-OFDM)对光纤链路中 的色度色散(CD)和偏振模色散(PMD)具有较强的容忍性,但 是OFDM信号高峰均功率比(PAPR)的特点使其对光纤非线性效应 非常敏感,严重影响了系统传输性能。 本文提出了基于恒包络(CE)调制的方法使得系统中光信号PAPR降低为0dB,从而提高了CO-OFDM系统的非 线性传输性能。仿真结果表明,子载波采用16QAM调制的40Gbit/s单信道CE调制CO -OFDM系统,在经800km无色散补偿、欠色散补偿和周期全色散补偿 标准单模光纤(SSMF)链 路传输后,虽然较传统CO-OFDM存在约1.8dB的代价,但是系统最大 发射光功率分别提高 了6.2、9.3dB。并且,将本文方案应 用 到CO-OFDM和10Gbit/s NRZ-OOK混合传输WDM系统中,信道最大发 射光功率仍获得了5.2dB的提高。因此,本文提出的CE调制方法能有 效地提高CO-OFDM系统在不同传输环境中的光纤非线性容限。     

Chromatic-dispersion compensator using virtually imaged phasedarray

A new method for chromatic-dispersion compensation is proposed and demonstrated. This method can produce a chromatic dispersion practically in a wide range from -2000 to +2000 ps/nm and can compensate simultaneously for the dispersion of over 60 wavelength channels with 100-GHz spacing in a wavelength-division multiplexed (WDM) system that has a total bandwidth of over 50 nm. This method has further attractive features such as very small polarization-state dependence, mechanically variable chromatic dispersion, and potential for small packaging. It was experimentally confirmed that this method compensated for the chromatic dispersion accumulated through 110 km standard single-mode fiber (SMF) at 1.55-μm wavelength and that 10-Gb/s signal quality was clearly recovered after the 110-km transmission     

Dispersion-flattened photonic crystal fiber with large effective area and low confinement loss

A photonic crystal fiber (PCF) can realize a flat dispersion over a wide wavelength range that cannot be realized with a conventional single-mode fiber. However, the confinement loss tends to increase in a conventional dispersion-flattened PCF (DF-PCF) that has uniform air holes. In this paper, a novel PCF that has two cladding layers with different effective indices is proposed. The authors numerically show that the proposed PCF can achieve an ultralow dispersion variation of less than 0.8 ps/nm/spl middot/km in all telecommunication bands, with both a large effective area greater than 100 /spl mu/m/sup 2/ and a low confinement loss less than 0.01 dB/km.     

40G比特/秒 FSK传输链接的理论和实证研究

A novel Frequency Shift Keying (FSK) transmitter that can operate at 40Gb/s and above is proposed. The transmission characteristics of a FSK signal at 40Gb/s are investigated under varying dispersion management. The resilience of compensation ratio and power level is obtained. We also experimentally demonstrate transmission over 100km SMF and transparent wavelength conversion based on a semiconductor optical amplifier.     

Enhanced Optical Generation of 42.7 Gbps Phase Shaped Binary Transmission

A novel method for optical phase shaped binary transmission (PSBT) generation has been recently reported and experimentally evaluated. An amelioration of the optical signal‐to‐noise ratio (OSNR) sensitivity of the optical PSBT modulation format is proposed with the application of the concepts of enhanced electrical PSBT signal generation. Enhanced optical PSBT is proposed here as a modulation format producing a 0.7 dB gain in OSNR sensitivity compared to OPSBT, while maintaining a good robustness to group velocity dispersion: 100 ps/nm for enhanced optical PSBT and 120 ps/nm for optical PSBT, compared to 50 ps/nm for standard NRZ signals.     

基于光子晶体光纤中自相位调制效应的6×40 Gbit/s 全光波长组播实验研究

基于非线性效应的全光组播,以其能直接在光域内将信息从单节点路由到多目标节点而受到广泛关注。实验证实了利用色散平坦高非线性光子晶体光纤级联光学滤波器实现全光波长组播的新方案,通过使用窄带光学滤波器次选择自相位调制加宽光谱分量,对速率为40 Gbit/s 的归零信号实现了极性保持、通道间距100 nm 的1 到6 信道全光波长组播。进一步研究了所设计全光波长组播器的动态特性,结果表明,它具有20 nm 的宽带波长调谐范围,同时,对输入信号的光功率波动具有较强的容忍性,系统整体结构简单,在未来透明光子网络中很有应用潜力。     

Low chromatic-dispersion flat-top arrayed waveguide grating filter

A low chromatic dispersion (CD) flat-top arrayed waveguide grating (AWG) filter with a novel parabolic waveguide horn is proposed, and a 100 GHz-spacing 16-channel flat-top AWG that reduces the CD from -20.9 to -3.2 ps/nm has been successfully fabricated.     

Compensation for chromatic dispersion and nonlinear effect in highdispersive coherent optical repeater transmission system

A design for a chromatic dispersion equalizer that provides 4.4 times higher efficiency in the dispersion compensation characteristics, compared with a conventional equalizer, is proposed. In addition, the amplitude response slope in the frequency domain is less than half of the conventional characteristic. This extends the compensation limit for chromatic dispersion up to 82500 ps/nm for a 2.5-Gb/s heterodyne system, which corresponds to a 4900-km normal dispersion fiber transmission system. A compensation method for modulational instability is also proposed. The method was confirmed by a 2.5-Gb/s continuous-phase frequency-shift-keying (CPFSK) 764-km normal dispersion fiber transmission experiment, with the abovementioned chromatic dispersion equalizer. Employing computer simulations, an over-1000-km normal dispersion fiber optical repeater transmission system with 2.5-Gb/s CPFSK heterodyne detection was shown to be feasible     

Demonstration of Ultraslow Modes in Asymmetric Line-Defect Photonic Crystal Waveguides

We propose an asymmetric photonic crystal (PC) waveguide, formed by moving the PC cladding on one side of the line defect along the waveguide core. By adjusting the structural parameters, we flatten the slow-mode dispersion curve, exclude the extreme points from the flat band, and avoid the unacceptably large dispersion induced by extreme points. We obtain an ultra-flat band with an inflection point corresponding to a slow-light mode with reduced distortion. We utilize the finite-difference time-domain method to verify the inflection-point ultraslow wave.     

基于悬臂梁啁啾调谐的光纤光栅滤波器

提出并发展了一种基于悬臂梁结构的啁啾光纤Bragg光栅(CFBG)啁啾调谐方案,获得了一系列性能优异的可调谐CFBG滤波器,包括调谐范围达到36 nm(1.8～37.8 nm)的带宽可变反射滤波器、色散在178～2 100ps/nm范围内可调的色散补偿器、基于取样CFBG或重叠写入CFBG的信道间隔可调谐滤波器等。这些FBG滤波器不但能维持较高的反射率,还能保持中心波长基本不变。     

Compensation of dispersion in optical fibers for the 1.3-1.6 μmregion with a grating and telescope

The transmission of ultrashort optical pulses over long distances in optical fibers is limited by pulse broadening due to group velocity dispersion. A grating and telescope dispersion compensator with group velocity dispersion of equal magnitude and opposite sign can compensate for the fiber dispersion. The possible benefits of such dispersion compensation in the 1.3-1.6-μm wavelength region are investigated. The results show that compensation of first-order dispersion at 1.55 μm in a fiber with zero dispersion near 1.3 μm is primarily limited by the second-order dispersion of the grating and the telescope compensator. For a wavelength slightly greater than the zero dispersion wavelength, both the first- and second-order group velocity dispersion can be canceled by the grating and telescope dispersion compensator, allowing transmission exceeding 100 Gb/s over 100 km     

Coherent Equalization and POLMUX-RZ-DQPSK for Robust 100-GE Transmission

We discuss the use of a coherent digital receiver for the compensation of linear transmission impairments and polarization demultiplexing in a transmission system compatible with a future 100-Gb/s Ethernet standard. We present experimental results on the transmission performance of 111 Gbit/s POLMUX-RZ-DQPSK. For a dense WDM setup with channels carrying 111 Gbit/s with a 50 GHz channel spacing (2.0 bits/s/Hz), we show the feasibility of 2375 km transmission. This is enabled through coherent detection which results in excellent noise performance, and subsequent electronic equalization which provides the high tolerance to polarization mode dispersion and chromatic dispersion (CD). Furthermore, we discuss the impact of sampling and digital signal processing with either 1 or 2 samples/bit. We show that when combined with low-pass electrical filtering, 1 sample/bit signal processing is sufficient to obtain a large tolerance towards CD. The proposed modulation and detection techniques enable 111 Gbit/s transmission that is directly compatible with the existing 10 Gbit/s infrastructure.     

基于LonWorks技术的暖通空调监控系统

本文介绍了一个基于LonWorks总线技术和组态王的暖通空调监控系统的建立。由LonWorks总线连接智能控制节点,iLON600作为网关联接LonTalk协议和TCP／IP协议,实现上位机和智能控制节点之间的通讯。利用组态王KingView设计上位机监控软件,构成性能可靠、易扩展以及操作界面友好的监控系统,达到控制温度的目的。结果证明,该系统为教学和工程实践环节提供良好的平台。     

Increase of the SBS threshold in a short highly nonlinear fiber byapplying a temperature distribution

We evaluate numerically and experimentally the stimulated Brillouin scattering (SBS) threshold increase for a short, highly nonlinear GeO₂-doped fiber by applying different temperature distributions along the fiber. The temperature coefficient for the Brillouin frequency downshift is measured to 1.2 MHz/°C. A threefold SBS threshold increase is obtained for a 100-m long highly nonlinear fiber with a 140°C temperature gradient. The proposed scheme is implemented in a wavelength converter based on fiber optical four-wave mixing (FWM). The SBS suppression scheme shows negligible influence on the FWM efficiency as well as the wavelength conversion bandwidth. The temperature coefficient for the zero dispersion wavelength is measured to 0.062 nm/°C     

Compact Terahertz Wave Collimator Design with Photonic Crystal Slabs

A compact terahertz (THz) wave collimator is proposed,which works under the frequency from 2.4 THz to 2.7 THz with a photonic crystal (PC) slab based on the self-collimation effect.The plane wave expansion (PWE) method is used to calculate the dispersion surfaces and the equal-frequency contours (EFCs) and optimize the structure.The propagation of the THz waves in the structure is simulated and the normalized transmission is calculated by using the finite-difference time-domain (FDTD) method with perfectly matched layer (PML) absorbing boundary conditions.Numerical simulations show that the designed collimator has a good collimation property and a high transmittance.