Parameter Estimation of Phase-Modulated Signals Using Bayesian Unwrapping

Parametric estimation of phase-modulated signals (PMS) in additive white Gaussian noise is considered. The prohibitive computational expense of maximum likelihood estimation for this problem has led to the development of many suboptimal estimators which are relatively inaccurate and cannot operate at low signal-to-noise ratios (SNRs). In this paper, a novel technique based on a probabilistic unwrapping of the phase of the observations is developed. The method is capable of more accurate estimation and operates effectively at much lower SNRs than existing algorithms. This is demonstrated in Monte Carlo simulations.     

异步取样在光数字信号监测中的应用

报道了2．5Gb／s光数字信号的异步取样实验,并通过软同步算法,得到了待测光数字信号眼图、Q值和误码率（BER）,实验结果与采用高速示波器测量的结果较为一致。通过异步取样结合数据的软同步算法,具有实现更高速率光数字信号在线监测的潜力。     

NRZ-DPSK and RZ-DPSK Signals Signed Chromatic Dispersion Monitoring Using Asynchronous Delay-Tap Sampling

In this paper, we demonstrated a signed chromatic dispersion (CD) monitoring method of 10 GHz nonreturn-to-zero differential phase-shift keying (NRZ-DPSK) and return-to-zero differential phase-shift keying (RZ-DPSK) signals by using asynchronous delay-tap sampling and an imperfect tuned delay interferometer. This method could monitor not only the value but also the polarity of residual CD. The demodulated signals show amplitude shoulders on the rising edge or the trailing edge with CD accumulation. Delay-tap sampling scatter plots could reflect this signal distortion by a unique characteristic and realize the signed CD monitoring. The monitoring range can be up to plusmn400 and plusmn720 ps/nm for NRZ-DPSK and RZ-DPSK signals, respectively. Simulation and experimental results are also proposed.     

Start-Bit Detection and Gate-Pulse Generation Using Phase-Modulated Preamble for Asynchronous Packet Processing

Start-bit detection and a single gate pulse generation scheme scalable to high-speed operation for asynchronous packet processing have been achieved. It is based on phase-modulated two-bit preamble for a coder and one-bit-delayed detection combined with a balanced photodetector as exclusive or (xor) function for a decoder. By using pi/2 phase-shifted first-bit and a pi/2 phase-shifted one-bit delay line, a single gate pulse can be generated with high speed, regardless of packet period. We have successfully achieved the single gate-pulse generation with bit rate of 10.72 Gb/s and various packet periods from 12.8 to 120 ns. Amplitude of the gate pulse was almost constant with fluctuation of plusmn5%. Suppression ratio of a gate pulse could be improved up to 9.5 dB via nonlinear absorption characteristics of an electroabsorption modulator. Autonomous gating operation for an optical digital-to-analog converter was also verified for two-bit operation     

All-Optical Chromatic Dispersion Monitoring for Phase-Modulated Signals Utilizing Cross-Phase Modulation in a Highly Nonlinear Fiber

We propose and experimentally demonstrate an all-optical chromatic dispersion (CD) monitoring technique for phase-modulated signals utilizing the cross-phase-modulation effect between the input signal and the inserted continuous-wave probe. The probe's optical spectrum changes with the accumulated CD on the input signal, indicating that the optical power variations can be measured for monitoring. The experimental results show that this technique can monitor up to 120 ps/nm of CD for a 40-Gb/s return-to-zero differential phase-shift keying (RZ-DPSK) transmission system, with the maximum measured optical power increment of 16.5 dB. The applicability of this monitoring technique to higher bit-rate phase-modulated signals, such as 80-Gb/s RZ differential quadrature phase-shift keying and 80-Gb/s polarization-multiplexed RZ-DPSK, is also investigated via simulation.      

双硬限幅器异步光码分多址系统误码性能分析

针对基于单硬限幅器（OHL）异步光码分多址（OCDMA）系统的解码器不能完全消除信道串扰产生的误码,提出了具有双OHL的解码器结构来优化系统传输性能。通过数值分析给出了地址码（光正交码,OOC）的码长、码重、用户数与系统误码率的关系,结果表明：双OHL异步OCDMA系统误码率相对于单OHL系统误码率下降明显,系统传输性能得到改善。     

Complex Spectrum Analysis of Modulated Optical Signals Using Stimulated Brillouin Scattering

We introduce a novel method for the measurement of the spectral phase of modulated optical signals based on double-pump stimulated Brillouin scattering interaction and direct homodyne detection. This technique is combined with Brillouin high-resolution analysis to achieve a complete characterization of the complex optical spectrum. A 10-Gb/s nonreturn-to-zero signal with a 32-bit pattern modulated with an electroabsorption modulator is measured using this technique and its time-domain information (power and chirp) is obtained by inverse Fourier transform.      

新型光数字信号取样测量与两步分析模型

提出将电吸收调制器(EAM)应用于数字光通信信号监测的频差法测量中，大大简化了传统频差法测量的复杂性。在实验中，对10GHz正弦光信号序列取样，得到100MHz的低频信号波形。分析了EAM的取样窗口宽度与测量系统带宽之间的关系，并提出利用两步模型分析取样宽度对伪随机码信号取样测量的系统带宽的影响，提出采用高斯低通滤波器能够很好的估算EAM取样窗口宽度与取样系统带宽的关系。分析表明，EAM同步取样系统在测量实际数字光通信系统中具有很大的应用潜力。     

光网络性能监测技术

光网络性能监测(OPM)已成为下一代光网络发展的关键技术,构建满足光网络发展需求的OPM系统也已成为物理层技术的发展重点。本文在介绍光网络性能监测主要内容、关键技术、光采样技术的基础上,总结了目前光网络发展对光性能监测技术的主要要求,同时分析了目前应用的部分技术难点和后续发展趋势。     

Optical Signal-to-Noise Ratio Estimation Using Reference Asynchronous Histograms

This paper presents and experimentally demonstrates a novel method for the estimation of optical signal-to-noise ratio (OSNR) based on the comparison of an asynchronous histogram of the signal under analysis with a reference asynchronous histogram. The latter is acquired from the signal under analysis at a calibration stage. The proposed method allows the use of optical amplification to increase the sensitivity of the optical monitoring system (OMS) by a factor 20 dB, when using an erbium doped fiber preamplifier. In addition, the use of a semiconductor optical preamplifier, initially designed for nonlinear operation at 2.5 Gb/s is used in the OMS to preamplify 40-Gb/s signals, achieving a sensitivity gain of 10 dB. It will be experimentally demonstrated that the proposed method is applicable to 40-Gb/s nonreturn to zero (NRZ) signals arbitrarily degraded by group velocity dispersion (GVD). Furthermore, accurate monitoring of the OSNR of return-to-zero (RZ) signals will also be possible using a simple RZ-to-NRZ converter based on narrow-band optical filtering within the OMS. The proposed method also allows estimating of the GVD-induced OSNR penalty between the signal under analysis and the signal at the calibration stage.     

Improved Large Signal Analysis of the Dual-Wavelength Linearization Technique of Optically Phase-Modulated Analog Microwave Signals

This paper presents simple closed-form expressions, in terms of the ordinary Bessel functions, for the amplitudes of the third- and fifth-order intermodulation products of the dual-wavelength linearized phase modulated link for any scenario of the microwave driving voltage. The results obtained for a microwave driving voltage comprising equal-amplitude two- and three-tones show that the third-order intermodulation can be minimized for values of phase modulation depth less than 0.2 over a relatively wide range of the ratio between the powers in the TM and TE waves of the link. Using these results it is possible to adjust the phase modulation depth and/or the ratio between the powers of the TM and TE waves to achieve a dual-wavelength linearized phase modulated link with a predetermined intermodulation performance.     

Statistical Analysis of Optical Signal-to-Noise Ratio Monitoring Using Delay-Tap Sampling

We derive analytical expressions for the optical signal-to-noise ratio (OSNR) monitoring using delay-tap sampling for intensity-modulated direct-detection (IM/DD) systems. We demonstrate through our theoretical analysis and experimental results that modeling of noise correlation due to low-pass filtering between delay-tap samples enables accurate monitoring of OSNR, without recalibration for each system setup. Effects of chromatic dispersion (CD) and polarization-mode dispersion on the proposed technique are investigated through numerical simulations. The monitoring error remains within $pm$ 1 dB for CD up to 400 ps/nm and differential group delay up to 45 ps.      

Linearization of Phase-Modulated Analog Optical Links Employing Interferometric Demodulation

We present a linearized phase-modulated analog photonic link that utilizes parallel interferometric demodulation to suppress the third-order intermodulation distortion present in the link. By utilizing two parallel interferometers with different differential delays, we are able to balance the third-order distortion in the output photocurrent and achieve a fifth-order limited link response. We demonstrate shot noise-limited spurious-free dynamic ranges of ~ 130 dB (1-Hz bandwidth) at ~ 1 GHz for a total DC photocurrent I_dc~ 8 mA and ~ 131 dB (1-Hz bandwidth) at ~ 5 GHz for a total DC photocurrent I_dc ~ 7 mA . These results represent a nearly two order-of-magnitude improvement in dynamic range over conventional intensity- or phase-modulated analog photonic links for a fixed received photocurrent.     

Performance of Nonlinear Receivers in Asynchronous Spectral-Phase-Encoding Optical CDMA Systems

Because of limits on the speed of the photodetector, a nonlinear thresholder is needed at the receiver of a spectral-phase-encoding optical code-division multiple-access system to discriminate between the correctly decoded short pulse and the low-intensity interference. The two most common nonlinear receivers based on second harmonic generation and self-phase modulation effects are analyzed in this paper. Mathematical models are provided, and analytical results are obtained to estimate the receivers' performances. Numerical simulations are carried out for both receivers with different system parameters. Both m-sequences and random binary codes are examined for spreading. The results provide a profile of how these nonlinear receivers perform with various system settings. It is found that, when an m-sequence is used as the spreading code, the encoded signal does not obey Gaussian statistics, and the system performs better than an equivalent system using a random code.     

光传送网的性能监测方案

在简要回顾传统性能监测方案的基础上,引入了插入型(Intrusive )和非插入型(Non-intru-sive)在线性能监测的分类方式,着重阐述了基于模拟量监测的非插入型光性能监测方案。     

异步光分组交换的缓存排序方案及性能

分析了简单的先到先服务(FCFS)光纤延迟线(FDL)循环占用方案性能,发现其分组丢失率(PLR)较高,提出3种输入分组按长度排序,寻找最小的FDL缓存优化分配方案.分析和仿真结果表明:约10%的分组排序后使3种方案都大大地能减小PLR,最小长度分组占用最小可用FDL缓存方案的性能最好.业务负载低于0.8时,排序的缓存方案对管理有限的FDL是有效的.     

光正交码在LDPC码中的应用性能分析

主要分析LDPC（低密度奇偶校验）码日矩阵不同构造的译码性能,通过在4／5码率、990码长、AWGN（加性高斯白噪声）信道、BP（置信传播）译码算法条件下,先采取随机构造的方式进行仿真分析,然后将光正交码的概念引入H矩阵的设计,并进行相应的改进,通过计算机仿真,发现通过光正交码改进H矩阵构造设计的LDPC码不仅性能优于随机构造的LDPC码,而且还具有循环结构。     

DWDM光纤通信网络中光发射单元的智能化监控

实现了密集波分复用 (DWDM)光纤通信网络中光发射单元 (OTU)的智能化监控 ,设计了以80 C5 5 2单片微机为核心的盘控 (MCU)部分 ,实现了激光器输出波长、光功率、偏置电流等重要参数的随时监控 ,并能在激光器工作状态异常时 ,及时上报网管、控制告警灯并自动调节激光器 ,以保证通信系统的顺利进行。成功地完成了 16× 10 Gb/ s的系统实验 ,各波长信道的传输功率代价均小于 2 d B(误码率 =10 - 1 0 )     

一种新型异步数据通路性能分析方法

介绍了一种新型的异步数据通路性能分析方法。这种方法在进行性能分析时基于多延迟模型、SPICE和逻辑仿真 ,可以作为异步数据通路设计和分析的一种有效工具。为了进一步的阐述和验证这种分析方法 ,文中举例分析了 4比特和 8比特异步比较器。     

Translation of Gbps Phase-Modulated Optical Signal From Near-Infrared to Visible Band

Phase-coded optical signal was spectrally translated from the conventional near-infrared communication band to the visible band. Spectrally narrow 780-nm pump was combined with phase-modulated 1575-nm signal in a small core photonic crystal fiber (PCF), to generate 518-nm idler through parametric process. The phase-modulated idler carrying 1-Gbps information was received in an error-free manner. The onset of the stimulated Brillouin scattering (SBS) was found to be a major limitation for conversion efficiency and noise performance. The SBS effect and the birefringence properties of the small core PCF were studied at both 780 and 1550 nm and their impact on the parametric process was analyzed.