Influence of extinction ratio on performance of optical receivers incorporating laser preamplifiers

Reports the performance degradation of optical receivers incorporating semiconductor laser amplifiers (SLAs) caused by the nonzero extinction ratio of the input optical signal. The resulting sensitivity penalty dependencies on bit rate, SLA gain and facet reflectivity are also investigated. The results clearly show that the new receiver can be more affected by a finite extinction ratio compared to a conventional pin or APD receiver. Using a bandpass optical filter to reduce amplifier spontaneous emission noise will increase the extinction ratio penalty.<>     

波分复用-光时分复用波长转换信号的消光比研究

对基于半导体光放大器(SOA)交叉增益调制(XGM)效应的全光波分复用一光时分复用(WDM—OTDM)转换后的两路时分复用输出信号的消光比(ER)特性进行了分析。研究了两路波分复用的输入抽运光和探测光的功率、波长、抽运光的消光比、数据速率以及半导体光放大器的偏置电流、腔长和模场限制因子对转换信号消光比的影响。模拟结果表明，增大抽运光输入功率，选择长波长抽运光，可以增加转换光相应信道消光比，但减小了相邻信道的输出消光比；增加抽运光消光比，可以提高转换光消光比，但各个信道增长幅度不同；减小探测光输入功率，选取短波长探测光波长，增加半导体光放大器的腔长和模场限制因子以及大的偏置电流可提高转换光消光比；对于两路或多路波分复用信号转换时分复用信号的过程中，一定要考虑转换光每个信道消光比的均衡。     

Vertical-cavity amplifying modulator at 1.3 μm

The modulation/switching properties of a vertical-cavity semiconductor optical amplifier operating at 1.3 μm wavelength are investigated. The device was optically pumped and operated in reflection mode. A 150-mV (100 mA) modulation of the drive to the pump source produced a 7-dB modulation of the pump power, which produced a 35-dB modulation in the output signal. The maximum extinction ratio was 35 dB, and limited by device heating. Frequency response measurements revealed a modulation bandwidth of 1.8 GHz when the amplifier was saturated. This enabled 2.5-Gb/s modulation of a -10 dBm input signal with 5.5-dB fiber-to-fiber gain     

采用SOA-Sagnac光纤干涉仪的AOWC研究与实验

对采用SOA—sagnac光纤干涉仪的全光波长变换器(AOWC)从理论上进行了较为详细的研究，首次根据光路合成法求出SOA—Sagnac光纤干涉仪的响应函数。并构成了一套实验系统，测量了SOA的增益、带宽与输入光功率的关系，测量了输出信号的消光比以及输入、输出信号的波形和眼图。并对它们进行了比较。     

Comprehensive analysis of two cascaded semiconductor optical amplifiers for all-optical switching operation

This paper presents numerical calculations and experimental results for two cascaded semiconductor optical amplifiers (SOAs) in a counterpropagating configuration for an all-optical switching operation. A detailed theoretical analysis with regard to the gain evolution and the extinction ratio (ER) through the SOAs' cavities show that the two cascaded SOAs have improved performance over the single SOA configuration. A measured ER up to 20 dB is obtained for close contra-directional signal wavelengths and for a wide range of optical input powers. An all-optical switching operation is realized for 2.5-GHz data pulses, and its feasibility is demonstrated with an ER higher than 12 dB over a wide range of wavelength.     

Optical narrow-band filters using optical amplification withdistributed feedback

The amplification characteristics of the distributed-feedback (DFB) laser amplifier are studied. The amplifier has a narrow, single-frequency gain-bandwidth product and the maximum-gain frequency tunability. With these advantages, the amplifier can be applied as an optical narrowband filter. This filter has optical frequency selectivity with an extinction ratio of better than -15 dB for optical inputs separated by 9.8 GHz having different optical input powers. By using a multielectrode DFB laser amplifier, the wide-range tunability of a gain maximum frequency (33.3 GHz) can be obtained while maintaining a constant gain and a constant gain-bandwidth product. Optical frequency selection with an extinction ratio of better then -20 dB can be obtained for two optical inputs separated by 15.4 GHz and having the same input power     

Investigation on the combined orthogonal FSK/ASK labeled signal based on cross gain modulation in a SOA

An optical frequency shift keying(FSK) transmitter performed by the cross gain modulation(XGM) in a semiconductor optical amplifier(SOA) is used in an optical label switching(OLS) system with 622 Mbit/s FSK label and 10 Gbit/s amplitude shift keying(ASK) payload.The key parameters in this system are optimized to achieve the best performance of FSK/ASK signal,including the input power of LD,the extinction ratio(ER) of the control light and that of the ASK payload.Besides,the transmission performance of ASK p...     

半导体光放大器的偏振光开关性能改进

半导体光放大器(SOA)非线性偏振旋转效应的光开关具有开关速度快、易集成等优点,其开关操作可以通过改变注入SOA中的电流而获得。这种偏振光开关的性能主要受注入光功率与控制电流的大小范围来决定。基于SOA中的偏振主态的概念,分析了非线性偏振旋转效应与控制电流的关系,并对不同功率的注入光进行了偏振旋转实验,分别实现了偏振光开关的操作。实验结果表明:随着注入光功率的增加可以提高光开关的分光比,有效改进光开关的性能。当注入光为5 dBm时,光开关的分光比与消光比均可达到30 dB。     

Coupled-waveguide exchange-Bragg resonator filters: coupled-modeanalysis with loss and gain

Novel resonator filters made of two closely coupled asymmetric waveguides with phase-shifted exchange-Bragg grating, are investigated. Coupled-mode theory based on the normal modes is used to examine the effects of loss and gain on the filter spectral responses. The filter exhibits a total transmission at central wavelength and a rejection to the adjacent waveguide with high extinction ratio for other signals in the absence of loss and gain. Material loss reduces the transmitted power level and increases the filter bandwidth. With a certain amount of optical gain, good transmission can still be maintained in the presence of material loss. Proper control of the optical gain can lead to the amplification of both the transmitted and reflected powers at the central wavelength     

SOA Fiber Ring Laser-Based Three-State Optical Memory

By exploiting three coupled semiconductor optical amplifier (SOA) fiber ring lasers, a compact, integratable, and polarization-independent three-state all-optical memory is demonstrated, with 40-dB extinction ratio for each state. Dynamic flip-flop operation between states is also demonstrated with switching pulse energy of 13.6 nJ. Due to the broad bandwidth of SOA gain spectrum, the wavelength range of set pulses is large. Finally, the transition behavior of state switching is investigated.      

WDM transmission system performance: influence of non-Gaussiandetected ASE noise and periodic DEMUX characteristic

This paper presents the first unified wavelength division multiplexing (WDM) transmission model for systems incorporating cascaded optical amplifiers and a realistic demultiplexing (DEMUX) characteristic with periodic transfer function. The bit error ratio (BER) is evaluated accounting in rigorous form for the influence of non-Gaussian detected amplified spontaneous emission (ASE) noise, noise correlation between stochastic noise samples in the receiver, the bandwidth of the electrical receiver noise filter, the gain tilt and effective noise figure of optical amplifiers (with as well as without optical ASE noise filtering), channel crosstalk, signal extinction ratio and a one-or two-stage DEMUX implementation. The model is compared to the Gaussian receiver model in realistic design cases providing important information as to the validity of the Gaussian model. Practical design results indicate the link budget dependence on the DEMUX design and the ASE noise filtering     

Analysis of wavelength conversion using a multisection DBR laserwith a saturable absorber

The static performance of a wavelength converter obtained by a multisection distributed Bragg reflector (DBR) laser with a saturable absorber between two gain sections is analyzed. For this device an optical input signal at one given wavelength is converted into an output signal at the lasing wavelength. The performances are evaluated in terms of conversion efficiency, suppression ratio, and minimum input power needed for wavelength conversion. It is shown that a proper choice of the injected signal wavelength with respect to the lasing wavelength enhances the conversion efficiency and the suppression ratio and reduces the switching power. The performance can be enhanced also by increasing the electrical current applied to the first gain section provided that the second gain section is biased above the transparency level. The authors have shown that reduction of the front facet reflectivity results in a dramatic increase for the conversion efficiency. The sensitivity to the electrical bias condition and to the resonant condition of the injected signal with respect to the cavity has also been investigated     

Performance analysis of LMS adaptive prediction filters

The conditions required to implement real-time adaptive prediction filters that provide nearly optimal performance in realistic input conditions are delineated. The effects of signal bandwidth, input signal-to-noise ratio (SNR), noise correlation, and noise nonstationarity are explicitly considered. Analytical modeling, Monte Carlo simulations and experimental results obtained using a hardware implementation are utilized to provide performance bounds for specified input conditions. It is shown that there is a nonlinear degradation in the signal processing gain as a function of the input SNR that results from the statistical properties of the adaptive filter weights. The stochastic properties of the filter weights ensure that the performance of the adaptive filter is bounded by that of the optimal matched filter for known stationary input conditions     

A high-speed 4×4 Ti:LiNbO3 integrated optic switchat 1.5 μm

The operation of a fully packaged and pigtailed polarization dependent Ti:LiNbO₃ 4×4 integrated optic switch with an operating wavelength of 1.5 μm is demonstrated. The switching matrix is fast, with a measured 3-dB small-signal bandwidth greater than 1 GHz. Unwanted cross modulation between channels due to coupling between switching elements was measured and found to be less than -20 dB of the signal strength. The switch is composed of balanced bridge switching elements having a 17-V switching voltage, an 18 dB extinction ratio, and an excess optical loss of 0.6 dB     

采用移频反馈的SOA多波长光纤环形激光器

文章报道了一种基于移频反馈的半导体光放大器(SOA)多波长光纤环形激光器,其环腔内插入声光调制器作为移频器,用自制的光纤马赫-曾德干涉仪进行梳状滤波,在输出光谱1.5 dB带宽为21.7 nm范围内,获得了间隔50 GHz的54个稳定的多波长连续光激射,消光比为28 dB.该激光器具有工作稳定性好、输出光谱宽和不同波长功率平坦度高的优点.实验证明,移频反馈技术能够实现激光器不同起振波长间的增益均衡,使输出光谱带宽增大21.7%.     

VCSOA动态开关特性的理论研究

区别于常规的法布里-珀罗（F—P）腔增益公式,本文结合传输矩阵和载流子速率方程从理论上研究了垂直腔半导体光放大器（VCSOA）的动态开关特性。模拟结果发现,VCSOA作为光开关应用时,可以达到ns级的开关延时和15dB以上的消光比;在满足增益需求的前提下减小顶部分布布拉格反射镜（DBR）的膜层周期,以及正确设置关状态下的抽运电流密度值略高于增益截止区水平,是同时得到较好的开关延时和输出消光比的重要因素。     

Tunable coherent optical transversal EDFA gain equalization

In this paper, we propose a fiber amplifier gain equalizer using a coherent optical transversal filter. The gain equalizer is tunable and has a bandwidth in the order of 30 nm. We also study the effects of different parameters such as input signal power pattern and the input pump power on the gain profile of the amplifier. The results show that, when the input signal power pattern changes, the amplifier does not maintain its gain profile. The gain profile has to be maintained in order to make the gain equalization effective. We show that, the pump input power can be adjusted so that the changes in the gain profile are compensated for. The gain profile varies quite slowly, hence compensation is feasible. As an example, we discuss the design of a gain equalizer for a system consisting of seven wavelength channels     

垂直腔半导体光放大器带宽特性研究

为了研究垂直腔半导体光放大器(vertical cavity semiconductor optical amplifiers,VCSOA)中抽运光功率、分布布喇格反射镜(distributed Bragger reflector,DBR)周期数以及输入信号强度对其带宽特性的影响,采用传输矩阵法进行了数值模拟。计算模型中考虑了载流子和光强沿纵向的分布,以及腔内介质折射率的不均匀性对光波传输的影响。得到的结果与文献中的结论符合较好。结果表明,提高VCSOAs的抽运水平可以增大其峰值增益,同时会缩小其增益带宽;减小DBR周期数可以获得更大的增益带宽积。另外,输入光信号强度对VCSOA带宽的大小也有较大的影响。     

Power penalty assessment in optically preamplified receivers witharbitrary optical filtering and signal-dependent noise dominance

The assessment of the power penalty of optically preamplified receivers with signal-dependent noise (SDN) dominance is often accomplished by neglecting the influence of the optical filtering of the amplified spontaneous emission (ASE) noise on the signal-ASE beat noise. In this paper, it is shown that the optical filtering of the ASE noise can have a strong impact on the signal-ASE beat noise and remarkably affect the power penalty, even for optical filter bandwidths five times wider than the signal bandwidth. A simple expression to analytically evaluate the power penalty due to optical filtering, which describes reasonably well the influence of the optical filter on the signal-ASE beat noise variance, is proposed. The accuracy of the new expression is investigated, in the case of assessment of the optical filter detuning impact on receiver performance and the case of optical filter bandwidth optimization, and its predictions are satisfactory in comparison with rigorous estimates. Two new expressions of power penalty due to extinction ratio and to eye closure are also presented. It is shown that the power penalty due to eye closure depends on the extinction ratio and vice versa. Our results show also that the power penalty due to eye closure is remarkably dependent on the eye closure asymmetry