Regenerative 40 Gbit/s wavelength converter based on similariton generation

We present an all-optical regeneration technique based on spectral filtering of self-similar parabolic pulses (similaritons). In particular, we demonstrate numerically and experimentally that ghost pulses, which occur in the zero bit slots of telecommunication pulse trains, can be effectively suppressed. These results are obtained with a 40 Gbit/s pulse train.     

Recent progress in soliton transmission technology

Recent progress on time-division multiplexed (TDM) and wavelength-division multiplexed (WDM) soliton transmission is described, in which dispersion management plays an important role in increasing the power margin and the dispersion tolerance. The characteristics of the dispersion-managed soliton are compared with those of return to zero and nonreturn to zero pulses. With a small dispersion swing, the system can still be described as an average soliton using the nonlinear Schrodinger equation, while with a large dispersion swing, the solitonlike steady-state pulse becomes a chirped Gaussian pulse, in which the governing equation is closer to a linear Schrodinger equation with a parabolic potential well. We describe an in-line modulation scheme for up to 80 Gbit/s per channel and its two channel WDM transmission over 10 000 km. Finally, we describe 640 Gbit/s (40 Gbit/sx16 channels) WDM soliton transmission over 1000 km with a dispersion-managed single-mode fiber. (c) 2000 American Institute of Physics.     

二阶偏振模色散对高速高斯光脉冲在单模光纤中传输的影响

研究二阶偏振模色散（PMD）对高斯光脉冲在单模光纤中传输产生的影响，给出输出光脉冲的时域表达式。分析表明，输出光脉冲在每个基本偏振态上仍保持高斯形状，但其频率啁啾及脉宽等特性都已改变，文中对这些变化与二阶偏振模色散之间的关系进行了讨论。通过比较10Gb/s和40Gb/s的光传输系统中二阶偏振模色散的影响，可以发现，若规定脉冲展宽不能超过脉宽的十分之一，40Gb/s系统所能容忍的二阶偏振模色散极限值比10Gb/s系统小一个数量级。     

2R regeneration study in a microcavity with a saturable absorber

We theoretically study the dynamical response of a saturable absorber (SA) in a microcavity realizing a non-linear mirror (NLM). We compare the effects of the SA response time on the extinction ratio of a single pulse crossing a single NLM and a two NLM based device. We also study 2R regeneration of a 40 Gbit/s pulses train with a single NLM.     

Experimental observation of a 1.5 microm band wavelength conversion and logic NOT gate at 40 Gbit/s based on sum-frequency generation

We have experimentally verified a new idea for 40 Gbit/s wavelength conversion within the 1.5 microm band based on sum-frequency generation (SFG) in a periodically poled LiNbO3 waveguide. The spectrum and the temporal waveform of the output pump reveal that the input cw pump is converted to an optical pulse during SFG. Not only wavelength conversion but also a logic NOT gate at 40 Gbit/s are experimentally observed.     

10 Gbit/s all-optical non-return to zero-return-to-zero data format conversion based on a backward dark-optical-comb injected semiconductor optical amplifier

By using a semiconductor optical amplifier backward injected by a dark-optical-comb pulse train at 10 GHz, we demonstrate a 10 Gbit/s all-optical nonreturn-to-zero (NRZ) to return-to-zero (RZ) format conversion of an incoming optical pseudorandom binary sequence (PRBS) data stream. Both the polarity and the wavelength of data are conserved during format conversion. Without any pre-amplification, the extinction ratio of degraded optical NRZ PRBS data is greatly improved from 7.13 to 13.6 dB after NRZ-to-RZ conversion. An ultralow bit-error rate of 10(-12) at a data rate as high as 10 Gbits/s is obtained with a received optical power of -18.3 dBm. The converted RZ PRBS data exhibit a negative power penalty of >3.7 dB compared with the NRZ PRBS data at a bit-error rate of 10(-12).     

Optical 3R regeneration of 40 Gbit/s degraded data signals

A 40 Gbit/s optical 3R regenerator is proposed and demonstrated. The 3R regenerator consists of a dual-ring injection mode-locked fiber ring laser as the clock recovery module and an electroabsorption modulator (EAM) as the decision gate. The clock recovery module extracts the optical short pulse clock with low timing jitter from degraded 40 Gbit/s optical data streams, while the decision gate restores their signal quality. A numerical model describing the cross-absorption modulation effect in a bulk EAM is developed to explore the operating conditions, such as bias voltage, pump signal power. The timing jitter tolerance for the EAM optical gate is also investigated. Significantly improvement of BER is obtained from 40 Gbit/s RZ signals which are degraded by polarization mode dispersion or chromatic dispersion.     

基于电吸收调制晶体(EAM)的超短光脉冲特性研究

数值模拟了两种形式的基于电吸收调制晶体(EAM)的超短光脉冲源(单EAM)和级联EAM形式)的输出脉冲宽度及消光比与外加反向偏压、射频信号幅度之间的变化关系.数值模拟结果表明,在重复率为10GHz情况下,对于单EAM形式,可以获得的最小脉宽大约为13ps,其消光比大于20dB,脉冲波型接近sech2孤子波型;对于级联EAM形式,我们得到了小于5ps的超短脉冲,消光比也较单EAM形式有较大的提高.因此,单EAM形式的超短脉冲源可以满足20Gb/s的OTDM系统需求,也同样适合于超长距离的光孤子通信系统;级联形式EAM可以满足40Gb/s的OTDM系统光源需求.     

Demultiplexing of OTDM-DPSK signals based on a single semiconductor optical amplifier and optical filtering

We propose and demonstrate the use of a single semiconductor optical amplifier (SOA) and optical filtering to time demultiplex tributaries from an optical time division multiplexing-differential phase shift keying (OTDM-DPSK) signal. The scheme takes advantage of the fact that phase variations added to the target channel by cross-phase modulation from the control signal are effectively subtracted in the differential demodulation scheme employed for DPSK signals. Demultiplexing from 80 to 40 Gbit/s is demonstrated with moderate power penalty using an SOA with recovery time twice as long as the bit period at 80 Gbit/s. Large dynamic ranges for the input power and SOA current are experimentally demonstrated. The scheme is expected to be scalable toward higher bit rates.     

40-Gbits transmission in dispersion-management links with step-index fiber and linear compensation

The dynamic behavior of single-channel transmission in standard fibers with strong dispersion management and linear compensating devices was theoretically and numerically analyzed. We compared a single pulse and a pseudorandom sequence to highlight the relevant roles played by nonlinearity-induced spectrum distortion and pulse interaction. As a result, 40/Gbit/s transmission on an 1800-km dispersion-management link with 100-km spans of standard fiber was obtained.     

Ultrafast all-optical signal processing with Symmetric Mach–Zehnder type all-optical switches

We present Symmetric Mach–Zehnder (SMZ) type all-optical switches: an SMZ all-optical switch, a polarization-discriminating SMZ (PD-SMZ) all-optical switch, and a delayed interference signal wavelength converter (DISC). These switches are capable of ultrafast, low control power, and low chirp switching, which is not restricted by slow relaxation of highly efficient nonlinearities. High repetition operation unrestricted by slow relaxation is also possible for these switches. This is because of a push–pull modulation scheme or sometimes called a differential phase modulation scheme. These three devices are similar, but different in some important aspects, thus a comparison is made among the three. Then semiconductor optical amplifiers (SOAs) are discussed as a nonlinear phase shifter for these devices. Then, ultrafast all-optical signal processing using SOA based SMZs is demonstrated. Error-free demultiplexing from 168 to 10.5 Gbit/s is presented, in which a hybrid-integrated SMZ (HI-SMZ) is used as a demultiplexer. In pulse regeneration experiment, the signal pulses at 84 Gbit/s are regenerated by the PD-SMZ and the regenerated pulses are demultiplexed to 10.5 Gbit/s by the HI-SMZ to verify error-free operation. The retiming capability of this scheme is quantitatively demonstrated. Also presented is error-free all-optical wavelength conversion at 168 Gbit/s using the DISC. These results represent the fastest error-free operations reported to date in each category.     

利用魏格纳分布对光脉冲在40Gbit/s系统中传输特性的研究

使用时频域联合分析的方法对光脉冲在40Gbit/s光纤通信系统中的传输特性进行了分析。在进行时频域联合分析时,利用著名的魏格纳分布。利用魏格纳分布的时频域联合分析是在时频交合平面上对光脉冲进行分析,即光脉冲在此平面上同时是时间和频率的二维函数。具体实例证明,这个独有的属性使得基于魏格纳分布的时频域联合分析法能够提供信号的各个频谱分量的时域分布,即提供了各个频谱分量的瞬时特性。为此,利用魏格纳分布的时频联合分析法可以较为全面地描述光脉冲的信息,进而较为全面地描述光纤通信系统的性能。     

Gbit/s rate bipolar pulse modulation of semiconductor injection lasers

Using a bipolar drive current pulse shape and very low threshold (9 mA) lasers, zero-background pseudorandom optical pulses were generated and detected at a rate of up to 4 Gbit/s without a pattern effect. The drive current pulse consists of a forward pulse followed by a reverse pulse, each of 70 ps duration and about 400 mA amplitude. No DC bias was applied, which is a necessary condition for pattern-effect-free modulation.     

Demonstration of an 8×10-Gb/s OTDM system

An 8×10 Gb/s optical time-division-multiplexing (OTDM) system was demonstrated with an electroabsorption modulator (EAM) based short pulse generator followed by a two-stage nonlinear compression scheme which generated stable 10-GHz, 2-ps full-width at half-maximum (FWHM) pulse train, an optoelectronic oscillator (OEO) that extracted 10-GHz clock with a timing jitter of 300 fs from 80-Gb/s OTDM signal and a self cascaded EAM which produced a switching window of about 10 ps. A back-to-back error free demultiplexing experiment with a power penalty of 3.25 dB was carried out to verify the system performance.     

用电吸收调制器实现标记擦除的新方法

提出一种结构简单、易于实现的正交光标记擦除的新方法.利用频移键控调制产生80 Gbit/s载荷,采用强度调制产生2.5 Gbit/s标记,然后利用电吸收调制器在分组交换网络核心节点处擦除旧标记,再加入新标记实现信息在网络中继续传输.理论分析和数值模拟验证了此方案擦除标记的可行性.     

Simple and Practical Approaches for Upgrading Installed Electronic-Repeater-Based Fiber Systems to Optically Amplified Systems

We propose simple and practical approaches to upgrade electronic-repeated systems by using optical amplifiers and zero-dispersion wavelength transmission. Possibility of increasing data rate from 560 Mbit/s to 80 Gbit/s in 1,318-km-long Thai-Malaysia system is demonstrated.     

研制超宽带全光取样示波器设备

全光取样示波器是研究与开发超高速光通信系统和光子交换网络的关键性测试仪器设备. 本文简介了我们自行设计和研制出的超宽带全光取样示波器设备的实验样机系统, 并报道了我们已取得的初步实验结果. 采用自主研发的高稳定性被动锁模飞秒光纤激光器作为该光学示波器的光脉冲取样源, 我们通过利用高度非线性光纤中的四波混频效应, 成功地实现了对脉宽为1.8ps、重复频率分别为10GHz和40GHz的光脉冲信号的全光取样. 然后通过数字信号处理和计算机图形处理, 得到了再现后的超短光脉冲信号波形, 并测出了其脉冲宽度值为2.3ps. 借助于该光学取样示波器实验样机, 我们还成功地完成了对脉宽为1.8ps、经过伪随机数据序列调制后的10Gbit/s和40Gbit/s光数据信号眼图的精确测量. 这是我国首次报道有关超宽带全光取样示波器设备的实际研制工作及其相应的实验测试结果. 所得到的有关超短光脉冲信号波形的测试结果也与用70GHz宽带电子示波器和超快光电探测器组成的常规光电测量系统所获得的结果进行了比较, 清楚地表明了我们研制出的全光取样示波器实验样机比后者具有更高的时间分辨率和更大的测量带宽.     

Investigation of Intrachannel Nonlinear Distortion in 40 Gbit/s Transmission over Standard Fiber

We describe new distance-dependent experiments investigating intrachannel nonlinear distortion in 40 Gbit/s optical time division mulitplexed transmission over standard fiber. Simulation results predicting significant reduction in the distortion due to intrachannel four-wave mixing by using alternating pulse polarization were experimentally confirmed.     

Investigation of Intrachannel Nonlinear Distortion in 40 Gbit/s Transmission over Standard Fiber

We describe new distance-dependent experiments investigating intrachannel nonlinear distortion in 40 Gbit/s optical time division mulitplexed transmission over standard fiber. Simulation results predicting significant reduction in the distortion due to intrachannel four-wave mixing by using alternating pulse polarization were experimentally confirmed.     

Optical Sampling at 80 Gbit/s Using a Highly Non-Linear Photonic Crystal Fiber

Optical sampling using four-wave mixing in 50m of newly developed highly non-linear photo niccrystal fiber has been achieved at 80 Gbit/s with an Extinction Ratio of 12 dB. A basic characterization is also included.