Signal-to-noise ratio analysis of 100 Gb/s demultiplexing usingnonlinear optical loop mirror

This paper investigates experimentally and theoretically the signal-to-noise ratio (SNR) characteristics of 100 Gb/s all-optical demultiplexing using a nonlinear optical loop mirror (NOLM). The analysis takes into account two effects that degrade the SNR associated with NOLM demultiplexing. First is channel crosstalk originating from the leakage of nontarget channels. Second is the intensity fluctuations of demultiplexed signals caused by the combined effects of timing jitter and a profile of the switching window. Considering these two effects, power penalties associated with NOLM. Demultiplexing are theoretically evaluated using the conventional noise theory of an optical receiver followed by an optical preamplifier. Experimental results of bit error rate measurements for 100 Gb/s demultiplexing using three different NOLMs with different intrinsic crosstalk values, defined by signal transmittance in the absence of control pulses, show that the power penalties are in good agreement with the evaluation based upon our proposed analysis. It can be found from our investigation in demultiplexing from 100 to 10 Gb/s that intrinsic crosstalk of less than -25 dB, corresponding to a coupling ratio, K, of |K-0.5|⩽0.03, is required for the power penalty of less than 1 dB. The root-mean-square (rms) value of the relative timing jitter necessary for obtaining a sufficient timing tolerance width for combining control and signal pulses is determined     

Sensitivity analysis of direct detection optical FDMA networks withOOK modulation

The authors analyze the sensitivity degradation in direct-detection optical FDMA networks as a result of signal filtering (both optical and electrical), interchannel crosstalk, channel beats (or nonlinear crosstalk), and intersymbol interference. The model used is valid for arbitrary linear time-invariant optical filters and received pulse shapes. The analysis is applied to on-off keying (OOK) systems using single-cavity Fabry-Perot filters and multistage Mach-Zehnder filters     

一种基于双通道自适应噪声对消的语音增强法

在自适应噪声对消(ANC)中,本文根据主辅通道噪声间的相关性,提出了一种自适应滤波语音增强算法。在低信噪比(-10～0dB)白噪声条件下,文中研究了辅助通道采集的噪声有无"串音"两种情况下的语音增强效果。研究表明:在无串音和有串音两种条件下,本文算法增强语音的信噪比分别比NLMS算法提高约14dB和5dB,PESQ_MOS得分分别比NLMS算法提高约1.13和0.83,同时增强语音的听觉质量得到了极大地改善。     

空间目标白天光电探测能力分析

天空背景在白天时的强光给空间目标的光电探测带来了很大的难度,针对白天探测的特点,基于极限探测信噪比、对比度及极限探测星等探测能力模型,说明了光谱滤波方法能有效提高白天探测能力,对比各种滤波效果,提出窄带滤波作为最优光谱滤波方法。从光学系统参数角度出发,通过分析计算得出在一定条件下综合权衡各参数的影响,减小视场,提高光学探测口径,增大焦距,有利于提高白天光电探测能力,为光学探测器的设计提供了一定的参考依据。     

An analysis of signal-to-noise ratio and design parameters of aterahertz optical asymmetric demultiplexer

Analysis of the signal-to-noise ratio (SNR) as a function of the component parameters in a terahertz optical asymmetric demultiplexer (TOAD) can help optimize its performance as a demultiplexer or as a router in an optical time division multiplexed network. The analysis presented here accounts for crosstalk due to deviation from a perfect 3 dB splitting ratio in the TOAD's 2×2 coupler, and the degradation of SNR due to fluctuations in the control pulse energy. The spontaneous emission noise output of the semiconductor optical amplifier (SOA) contained in the TOAD is simulated under different degrees of saturation. The analysis indicates that leakage due to the asymmetric placement of the SOA contributes significantly to the crosstalk. To achieve a SNR of 21.5 dB or higher in a 100 Gb/s system, one must use a 2×2 coupler that deviates less than 1% from a perfect 3 dB splitting ratio. Also, control pulse energy fluctuations must be less than 10% for a 20-GHz bandwidth electronic receiver. Novel crosstalk-free designs are proposed and analyzed which meet the stringent requirements of current TOAD devices. A significant enhancement in SNR is predicted when the SOA is operated near the optimal saturation point     

Analysis of direct-detection DPSK signal with homodyne crosstalk

When a differential-phase-shift-keying (DPSK) signal is directly detected using an asymmetric interferometer and balanced receiver, the exact error probability of the signal with homodyne crosstalk is derived analytically. Homodyne crosstalk from many interferers is Gaussian distributed, but the Gaussian model overestimates the signal-to-noise ratio (SNR) penalty for homodyne crosstalk from a single interferer. For the DPSK signal, the crosstalk ratio for a 1-dB SNR penalty must be less than -16.5 dB. For the same crosstalk ratio, the SNR penalty for a DPSK signal is far smaller than that for an ON-OFF keying (OOK) signal.     

Crosstalk performance of coherent time-addressed photonic CDMAnetworks

We report a theoretical investigation of the crosstalk performance of photonic code-division multiple access (CDMA) networks that are based on coherent matched filtering of optical pulses. We describe the importance of time gating in the reduction of noise in spread-time CDMA schemes. We give guidelines for the selection of codes in coherent matched filtering, and give a code set that produces low crosstalk. We present calculated bit-error rates (BERs) that show for individual user data rates in the gigabit per second range that crosstalk limits aggregate bit rates to the tens of gigabits per second range. This level of performance is a significant improvement over purely incoherent spread-time approaches. Such low crosstalk suggests that this scheme may be the first spread-time photonic CDMA scheme that is not crosstalk-limited     

Pulse-coded multiple access in space optical communications

There is interest in space-based wireless optical networks with nonsynchronous multiple access capability. Since space links are usually power-limited, pulsing is necessary to accomplish the multiple accessing and data transmission. In this paper, a nonsynchronous pulsed multiple-access optical-space system using code sequences for identifying stations is considered. Both OOK and PPM data encoding is considered and the link data rates and bit error probabilities (PE) are examined. It is shown that the achievable data rates are limited by the multiple access coding and the link SNR, while the PE can be either crosstalk or power-limited. It appears that moderate data rates (tens of Mb/s) are feasible with networks of about 5-20 stations even with low-link SNR     

Integrated-optic acoustically-tunable filters for WDM networks

The background needed to understand the integrated-optic collinear acoustically tunable optical filters (ATOFs) and the fabrication and performance of both simple and multielement acoustooptic tunable filters is presented. The most important sources of crosstalk between channels simultaneously selected by a single device are discussed. ATOFs have the combined virtues of narrow passband (subnanometer bandwidth), broad tuning range (hundreds of nanometers have been demonstrated), and simultaneous independent multiple-channel filtering. The theory and practice of collinear integrated optic acoustooptic filters is presented. Devices which involve higher-order integration are discussed, including multiple-state filters for enhanced sidelobe suppression and polarization-independent configurations. Various sources of interchannel crosstalk are derived and demonstrated in multiwavelength filtering experiments     

Design and Performance of WDM Transmission Systems at 6.3 Mbits/s

One- and two-way 6.3 Mbit/s optical transmission systems employing wavelength-division-multiplexing (WDM) are designed for application to telephone networks. Multiplexing at two wavelengths, 1200 and 1300 nm, as well as that at 810 and 890 nm, is found to be effective after taking the application fields and present fabrication techniques for optical multiplexers into account. Requirements for optical multiplexers are clarified through SNR design in which crosstalk is dealt with effectively. Optical multiplexers composed of newly developed dielectric multilayer thin-film filters are designed to meet the systems' requirements, and good transmission quality is confirmed for the systems by experiments.     

A Low‐Crosstalk Design of 1.25 Gbps Optical Triplexer Module for FTTH Systems

In this paper, we analyzed and measured the electrical crosstalk characteristics of a 1.25 Gbps triplexer module for Ethernet passive optical networks to realize fiber‐to‐the‐home services. Electrical crosstalk characteristic of the 1.25 Gbps optical triplexer module on a resistive silicon substrate should be more serious than on a dielectric substrate. Consequently, using the finite element method, we analyze the electrical crosstalk phenomena and propose a silicon substrate structure with a dummy ground line that is the simplest low‐crosstalk layout configuration in the 1.25 Gbps optical triplexer module. The triplexer module consists of a laser diode as a transmitter, a digital photodetector as a digital data receiver, and an analog photodetector as a cable television signal receiver. According to IEEE 802.3ah and ITU‐T G.983.3, the digital receiver and analog receiver sensitivities have to meet ‐24 dBm at BER=10^?12 and ‐7.7 dBm at 44 dB SNR. The electrical crosstalk levels have to maintain less than ‐86 dB from DC to 3 GHz. From analysis and measurement results, the proposed silicon substrate structure that contains the dummy line with 100 μm space from the signal lines and 4 mm separations among the devices satisfies the electrical crosstalk level compared to a simple structure. This proposed structure can be easily implemented with design convenience and greatly reduce the silicon substrate size by about 50 %.     

Impact of crosstalk in an arrayed-waveguide router on an opticaladd-drop multiplexer

The impact of crosstalk in an arrayed-waveguide (AWG) router on the performance of an N-channel optical add-drop multiplexer (OADM), with m add/drop channels and n-pass channels is theoretically investigated. A single arrayed-waveguide router is simultaneously used for multiplexing and demultiplexing. This results in crosstalk not only from the incoming channels, but from the outgoing channels as well. We show that the performance of the OADM degrades as either N or m are increased, suggesting that the number of channels in a network based on OADM's is limited by crosstalk in the AWG router. When an optical filter is added at the output of the OADM the digital signal-to-noise ratio Q is independent of N and m, and within a few tenths of a decibel of the perfect filtering case     

Investigation of Simultaneous 2R Regeneration of Two 40-Gb/s Channels in a Single Optical Fiber

We experimentally investigate the simultaneous all-optical signal processing of two 40-Gb/s wavelength-division-multiplexing optical streams spaced by 5 nm using self-phase modulation and offset filtering in a single highly nonlinear fiber to achieve a 2R optical regeneration. Using a bidirectional configuration, we demonstrate efficient mitigation of the interchannel crosstalk. We experimentally observe no degradation of the regenerator performance arising from the presence of the second channel as compared to the single-channel case.     

基于8PSK的新型高速正交光标记交换技术

提出了一种以八相移键控(8PSK)为净荷、ASK为标记的新型高谱效率高速正交光标记交换技术,首次实现了100 Gbit/s的高速正交光标记信号的80 km传输.分析了光信噪比(OSNR)、窄带滤波效应、信道中的非线性效应对标记与净荷性能的影响,并采用平衡相关探测和多符号相位估计(MSPE)技术实现了净荷8PSK信号的接收.与传统接收方式相比,8PSK净荷在相同误码率条件下,OSNR容限提升了约3 dB.经过80 km传输,ASK标记在BER=10~(-9),时OSNR为22.8 dB,8PSK相应的OSNR为20.3 dB.     

Modeling of in-band crosstalk in WDM optical networks

In this paper, we analyze three different simulation models which allow the impact of in-band crosstalk on the transmission performances of wavelength division multiplexing (WDM) optical networks to be evaluated: an accurate simulation (AS), a Gaussian correlated noise (GCN) model, and a Gaussian white noise (GWN) model. In the AS, an interfering channel is generated at each node and added to the signal after an optical filtering. The final result must be averaged with respect to the message transmitted on the interfering channels and to the phases of the optical carriers. In the GCN the crosstalk term is modeled as a Gaussian correlated noise, whose spectrum coincides with that of the interfering channel. This model can be further simplified if the noise is also assumed uncorrelated (GWN approximation). The results obtained by these simulation models are also compared with those produced by an analytical model allowing to evaluate the in-band crosstalk penalty     

Long-haul high-speed optical communication systems using asemiconductor laser amplifier

High-speed long-haul systems using semiconductor laser amplifiers, which eliminate the need for high-speed electronics in repeaters and are transparent to the transmission speed are considered for application in undersea high-speed transmission systems. The potential of laser-amplifier-repeated transmission systems has been explored by transmission experiments, showing that a high-speed system above 2 Gb is possible by filtering out the spontaneous emission power of the laser amplifier. A theoretical estimation of SNR degradation due to noise accumulation of chained laser amplifiers shows that systems are possible, using 30 to 40 laser amplifier repeaters, if narrow-bandwidth optical filters are used     

Advanced Modulation Formats for High-Capacity Optical Transport Networks

Advanced optical modulation formats have become a key ingredient to the design of modern wavelength-division-multiplexed (WDM) optically routed networks. In this paper, we review the generation and detection of multigigabit/second intensity- and phase-modulated formats and highlight their resilience to key impairments found in optical networking, such as optical amplifier noise, chromatic dispersion, polarization-mode dispersion, WDM crosstalk, concatenated optical filtering, and fiber nonlinearity     

Effects of polarization-mode dispersion on cross-phase modulation in dispersion-managed wavelength-division-multiplexed systems

This paper develops a vector theory of cross-phase modulation (XPM) in optical fibers and use it to investigate the impact of polarization-mode dispersion (PMD) on the crosstalk induced by XPM in wavelength-division multiplexed lightwave systems. Under certain reasonable approximations, the theory permits us to obtain an analytic expression for the amplitude of probe fluctuations induced by a copropagating pump channel through XPM. We use this expression to calculate the average level of XPM-induced crosstalk together with its variance for several dispersion maps. We show that PMD not only reduces the crosstalk on average, but also impacts the efficiency of a commonly used polarization-interleaving technique.