Performance of single-electrode 1.5-μm DFB lasers in noncoherentFSK transmission

The author reports the results of an investigation of the performance of single-electrode 1.5-μm DFB (distributed feedback) lasers in 1.7-Gb/s noncoherent frequency-shift-keyed (NC-FSK) transmission. Sixteen commercial laser transmitters were characterized in terms of FSK transmission sensitivity, eye-margin, chromatic dispersion penalty and pattern dependence. Using amplitude-shift-keying (ASK) performance as a baseline, FSK is shown to outperform ASK when dispersion is present, while ASK is slightly better with no dispersion. FSK transmitters with commercial single-electrode DFB lasers are shown to provide an attractive alternative to ASK in dispersion limited systems. The FSK degradations mainly result from an inadequate FM modulation index and a thermal-FM index manifested as a pattern length dependence     

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...     

Performance Evaluation of the Physical Layer of the DSRC Operating in 5.8 GHz Frequency Band

In this paper, the theoretical as well as experimental results of BER characteristics of three different modulation schemes, ASK, FSK and BPSK, in a multi‐path Rician channel are addressed. These BER characteristics are analyzed as a function of E_b / N_o and the power ratio of the line of sight (LOS) component to the Rayleigh scattered component. The theoretical as well as computer simulation results shows the ASK is the most suitable modulation scheme for the dedicated short range communication (DSRC) in terms of implemental cost and system complexity. The decision feedback equalizer is proved to be very effective in canceling the multi‐path interference in the DSRC channel environment. The simulation result of the equalized ASK, reveals the performance enhancement achievable with decision feedback (DFE) equalizer for the first generation DSRC system. The multi‐ray DSRC channel model is also provided to predict the received carrier power and fluctuation, which are quite dependent on the surroundings of a cell.     

ASK／FSK光标记交换系统中的OBPF谱均衡法

基于幅移键控／频移键控（ASK／FSK）正交调制光标记交换（0LS）系统工作原理,提出了一种利用光带通滤波器（OBPF）对FSK标记进行谱均衡的方法,从而有效改善ASK净荷接收灵敏度。利用仿真,对40Gb／sASK／FSK正交调制OLS系统,在使用3种不同类型OBPF进行谱均衡时的传输性能进行了验证与比较分析。结果表明...     

Why FSK and CPFSK have identical linewidth requirements

CPFSK is the most widely used modulation scheme in coherent optical transmission. Theoretical analyses so far predicted a much more stringent linewidth requirement compared to ASK and FSK systems with noncoherent IF-detection. In this paper we present a unified linewidth analysis of ASK, FSK, CPFSK, and DPSK receivers, with leads to the conclusion that the linewidth performance of these different schemes is to a large extent identical. The inclusion of post-detection filtering in the analysis is critical for obtaining these results, which are supported by practical system measurements on a 1 Gbit/s phase diversity CPFSK receiver     

Computer simulation of FSK laser spectra and of FSK-to-ASKconversion

The performance of binary frequency shift keyed (FSK) modulated two-segment semiconductor injection lasers is simulated by generating a 64-b pseudorandom step-function bit pattern. This signal, superimposed on a DC bias, is used to drive a two-segment distributed feedback (DFB) laser. To obtain the optical laser spectrum, the input signal is passed through the laser's small-signal transfer function. The resulting spectrum is passed through a Fabry-Perot filter that rejects one of the two principal peaks of the wide-deviation optical spectrum and converts the FSK modulation to amplitude shift keying (ASK) modulation. This simulation determines how different system parameters influence the performance of a laser system used for signal transmission by means of FSK-to-ASK conversion     

Study of Optical Transmission Performance in IP‐over‐WDM Networks Based on FSK/ASK Combined Modulation Format

The transmission performance of optical labeling based on a combined frequency shift keying/amplitude shift keying (FSK/ASK) format is studied by numerical simulation. The simulation demonstrates that the bit‐error ratio (BER) characteristic of an ASK signal is limited by the extinction ratio, received optical power, and dispersion, simultaneously. However, an FSK signal is mainly limited by the extinction ratio (ER) and received optical power when the peak spectrum, which is used to detect the FSK signal, is relatively narrow.     

高阶累积量和分形理论在信号调制识别中的应用研究

提出了将信号高阶累积量和分形盒维数相结合的特征提取方法。信号高阶累积量特征具有良好的抗噪性能,被广泛应用于调制识别。2ASK和BPSK的高阶累积量、以及2FSK,4FSK,8FSK的高阶累积量相等,使得只提取信号高阶累积量不足以区分信号。针对这一问题,引入信号的分形盒维数,提取信号的高阶累积量和分形盒维数构成联合特征参数,构建级联神经网络分类器,对信号进一步进行分类。对2ASK, 4ASK, BPSK, 4PSK, 2FSK, 4FSK, 16QAM七种信号进行了仿真,结果表明,该方法提取的特征参数计算复杂度低,具有较好的抗噪性能。在信噪比不低于5dB、测试样本数不少于200的条件下,正确识别率达到了85%以上。      

Optical FSK heterodyne detection using image rejection mixer

A new optical FSK heterodyne detection scheme is proposed and demonstrated. This scheme uses an optical image rejection mixer. The intermediate frequency bandwidth is the same as ASK heterodyne detection while equalling dual filter FSK detection receiver sensitivity.<>     

Sensitivity penalty in multichannel coherent optical communications

The error rates and sensitivity penalties for multichannel coherent optical communications systems are evaluated for amplitude-shift keying (ASK), phase-shift keying (PSK), and frequency-shift keying (FSK) modulation, taking into account adjacent channel interference. Both time-domain and frequency-domain analysis are used, the latter being based on a Gaussian approximation. Both techniques yield similar results for sensitivity penalties below 1 dB. For FSK systems, larger values of the modulation index Δ do not necessarily lead to larger channel spacings. ASK and PSK systems both require larger channel spacings than FSK systems with Δ=1. The study was conducted for sources with linewidths narrow enough so that phase noise does not degrade the performance of receivers with matched filter demodulators     

Performance of directly modulated DFB lasers in 10-Gb/s ASK, FSK,and DPSK lightwave systems

A comparison is presented of the performance of amplitude-shift-keying (ASK), frequency-shift keying (FSK), and differential-phase-shift-keying (DPSK) lightwave systems which operate at 10 Gb/s with directly modulated 1550-nm distributed feedback (DFB) laser transmitters and conventional 1310-nm dispersion-optimized fiber. Computer modeling techniques were used to accurately simulate the amplitude modulation response and the frequency modulation response of DBF lasers. The system performance is evaluated from simulated eye patterns for both direct and heterodyne detection. With the narrow-optical spectral widths of these signal formats, fiber chromatic dispersion limits up to 70 km were obtained for transmission at 1550-nm using conventional 1310-nm optimized fiber     

Error Probability and Bandwidth of Digital Modulation

The bandwidth in which 99 percent of the power is contained is presented for ASK, QASK, OQASK, PSK, FSK, and MSK. An example is given in which the bandwidth of FSK is one eighth the bandwidth of ASK and of the modulating signal. Error probability is presented for the various types of modulation with various detectors, detector filters and Butterworth receiver filters of orderN = 4orinfty. Comparisons are made between the performance and bandwidth efficiency of the various systems.     

Theoretical analysis of heterodyne optical receivers for transmission systems using (semiconductor) lasers with nonnegligible linewidth

We present a general theoretical model of receivers for coherent optical communication systems where transmitters and local oscillators having nonzero linewidth are used. Key issues in the model are the concept of single realization measurements of a stochastic intermediate frequency, and development of the probability density function for this stochastic process. Analytical results are derived for heterodyne ASK and dual filter FSK receivers and include the shot-noise limit, the asymptotic error-probability limits in ASK and FSK receivers, the influence of the IF on receiver noise, and the effective local oscillator strength. Detailed numerical results for typical p-i-n-FET wide-band receivers illustrate the influence on receiver sensitivity of IF filter bandwidth and relative threshold setting in ASK systems and of modulation index and IF filter bandwidth in FSK systems. A receiver sensitivity penalty for nonzero linewidth is found to be, for IF linewidths of 0.1 to 0.3 of the bit-rate, 3 to 9 dB in optimum ASK receivers, and 2 to 8 dB in optimum FSK receivers. Thus DFB lasers of linewidth 5 to 20 MHz could be used without external cavities in simple systems with near-ideal performance, which could find application wherever the great multiplexing advantage of coherent systems is a prime advantage. We present some guidelines for system design based on the results of this work.     

Input power limits of single-mode optical fibers due to stimulatedBrillouin scattering in optical communication systems

Stimulated Brillouin scattering (SBS) limits the optical power that can be transmitted through a single-mode fiber in long-distance optical communication systems, the authors have investigated SBS gain and threshold characteristics with amplitude-shift-keying (ASK), frequency-shift-keying (FSK), and phase-shift-keying (PSK) modulated lights to estimate the input power limitation set by SBS. It was shown that maximum fiber-input powers or the SBS thresholds for fixed-pattern (1010 . . .) ASK, FSK, and PSK modulated lights are 2, 4, and 2.5 times higher, respectively, than the threshold for unmodulated light. Theoretical predictions were experimentally verified by SBS gain measurements with FSK and PSK modulated lights. The first direct observation of SBS with FSK modulated light pumping is also described     

New techniques for the suppression of the four-wave mixing-induced distortion in nonzero dispersion fiber WDM systems

The performance of a wavelength-division multiplexing (WDM) optical network can be severely degraded due to fiber nonlinear effects. In the case where nonzero dispersion (NZD) fibers are employed, the four-wave mixing (FWM) effect sets an upper limit on the input power, especially in the case of narrow channel spacing. In order to reduce FWM-induced distortion two new techniques, the hybrid amplitude-/frequency-shift keying (ASK/FSK) modulation and the use of prechirped pulses are investigated. It is shown that both techniques can greatly improve the Q-factor in a 10 Gb/s WDM system. This happens even for very high input powers (/spl sim/10 dBm), where the degradation of the conventional WDM system is prohibitively high. The proposed methods are also applied and tested in higher bit rates (40 Gb/s). It is deduced that although the hybrid ASK/FSK modulation technique marginally improves the system performance, the optical prechirp technique can still be used to greatly increase the maximum allowable input power of the system.     

基于高阶累积量和循环谱的信号调制方式混合识别算法

为了识别当前通信系统所采用的主要调制方式,该文结合高阶累积量和循环谱的特点,采用混合识别算法,同时应用智能决策算法(神经网络)对信号进行识别。该算法基于四阶和六阶高阶累积量构造出一个新的特征参数,将数字调制信号分为{BPSK, 2ASK}, {QPSK}, {2FSK, 4FSK}, {MSK}和{16QAM, 64QAM}5类。然后利用高阶累积量的其它特征参数以及循环谱特征对{OFDM}, {16QAM, 64QAM}, {2ASK, BPSK}及{2FSK, 4FSK}进行识别。为便于工程实现,该文采用半实物仿真以及LabVIEW和MATLAB混合编程来验证算法。仿真结果证明,该算法能够在较低信噪比下实现对{OFDM, BPSK, QPSK, 2ASK, 2FSK, 4FSK, MSK, 16QAM, 64QAM}等多种信号的分类,在信噪比高于 5 dB时,调制方式识别率可达94%以上,由此证明了该方法的有效性。     

4-Gb/s heterodyne transmission experiments using ASK, FSK and DPSKmodulation

An experimental heterodyne lightwave transmission system operating at 4 Gb/s is described. The optical sources were 1.5-μm-wavelength DFB (distributed feedback) and DBR (distributed Bragg reflector) semiconductor lasers. ASK, FSK, and DPSK modulation formats were investigated; baseline receiver sensitivities of 175, 191, and 209 photons/bit, respectively, were achieved. Transmission experiments through up to 160 km of conventional single-mode fiber and up to 175 km of dispersion-shifted fiber are also reported     

一种2FSK信号参数估计的方法

文中在研究信号循环平稳特性的基础上给出了一种2FSK信号参数估计方法。基于2FSK信号频域上的单个谱峰与2ASK信号谱的相似性,首先在频谱上将2FSK信号的两个谱峰分离,然后根据2ASK信号的循环谱特征对单个谱峰做参数估计,最后将上述估计值做加权平均得到原2FSK信号的参数估计值。仿真结果表明该算法在信噪比（SNR）高于0dB时,信号参数估计MSE低于10^-4。     

Accurate performance evaluation of weakly coherent optical systems

An accurate performance evaluation approach which uses a closed-form exact analytical expression of the phase noise moments is presented. This enables one to derive a high-order Gaussian quadrature rule for the integrations needed to take into account the phase noise in the computation of error probability. A systematic comparison with results obtained through a Monte Carlo simulation shows that the approach is more accurate than previous methods. The analysis is performed on ASK and FSK heterodyne receivers with integrate-and-dump filtering, envelope detection, and optimized postdetection low-pass filtering. The feasibility of ASK and FSK heterodyne systems at bit rates comparable to the spectral line bandwidth of the laser sources is confirmed. The theory applied seems to be adequate to attack other problems, such as the evaluation of the effects of crosstalk between the FSK filters or among frequency division multiplexed channels     

FSK with direct detection in optical multiple-access FDM networks

High-performance optical data networks of the future may interconnect hundreds of users at gigabit rates for a reasonable cost. A novel approach is described that utilizes a passive star coupler for distribution, a multiplicity of frequency-shift keyed (FSK) tunable lasers to provide a frequency division multiplexed (FDM) network, and a tunable optical fiber Fabry-Perot filter to select the channels and convert the FSK signal to ASK (amplitude-shift keying) for direct detection. The design of high-speed FDM-FSK direct detection networks and the performance of critical devices, such as tunable FM lasers, tunable filters, integrated star couplers, and optical amplifiers, are reviewed and discussed