多波长OCDMA系统频谱效率的改善

分析了色散效应对多波长OCDMA系统频谱效率的影响。在相同的扩频因子条件下,色散效应将降低多波长OCDMA系统的频谱效率峰值,同时达到频谱效率峰值的波长信道数也将相应减少。提出了将前向纠错码用于改善多波长OCDMA系统的频谱效率,分析结果表明,该方案将有效改善多波长OCDMA系统的频谱效率,特别是频谱效率峰值将明显提高。     

Performance analysis of a hybrid fiber Bragg grating-based spectral-amplitude-coding/successive interference cancellation for optical CDMA systems

Successive interference cancellation (SIC) scheme is proposed as a new technique that has the potential to reduce the interference and suppress the multiple-access interference (MAI) in spectral-amplitude-coding (SAC) optical-code-division-multiple access (OCDMA) systems. The proposed receiver-based on fiber Bragg gratings (FBGs) techniques. The performance of the proposed system is theoretically analyzed, taking into account various types of noise and interference, including both multiple-access interference (MAI) and receiver noise. Analytical results show that the proposed system offers significant improvement in terms of bit error rate and system capacity (number of users). We have tested our results with both modified prime codes (MPR) and modified quadratic congruence (MQC) codes. In addition, we have compared our proposed system with the corresponding one without cancellation. It has been shown that the proposed scheme gives a substantial increase in capacity.     

DWDM混合光学系统中帧间和信道内四波混频效应的抑制

本文提出了光码多分址（CDMA）和光密集波分复用（DWDM）的混合系统,全面研究了四波混频（FWM）的影响。在这个系统中,主要存在两个四波混频问题：包括多址干扰（MAI）和码间干扰（ISI）的帧间四波混频和信道内四波混频。结果表明,综合考虑信道间和信道内四波混频的影响,最佳发射功率可选为18 dBm。当发射功率大于18 dBm时,混合系统的误码率（BER）将增加。基于此,本文提出了一种电光相位调制器（EOPM）模块,将其放置在波分复用器之后,通过抑制信道内四波混频的影响,同时调制所有波长信号的相位,从而增加混合系统的非线性容限,这极大地改善了基于OOK传输的光学CDMA-DWDM混合系统的性能。此外,由于多对角线（MD）结构具有零互相关特性,通过使用多对角线识别序列码可以减少多址干扰的影响。结果还表明,CDMA技术与色散相结合有助于降低信道间四波混频的影响。此外,识别序列码间隔在减轻码间干扰中起着至关重要的作用,如结果所示,当识别序列码间隔压缩至比特持续时间的25%时,可以避免码间干扰,此时所提出的混合系统的性能最佳。     

关于OCDMA系统安全性的研究

简要介绍了OCDMA系统的原理,分析了码型和码容量、地址序列的扩频作用对OCDMA安全性的影响,结合完全无差错探测几率给出完全探测到正确地址码所需探测次数的期望值,并以此重点分析了码字探测对OCDMA安全性的影响,比较分析了OCDMA技术与现代光纤保密通信技术的关系,给出了增加OCDMA系统安全性而采取的一些措施。     

Power control of optical CDMA star networks

In this paper, we apply the power control concept to optical CDMA star networks. Two approaches are considered, namely, centralized and distributed power control. Both approaches are used to optimize the optical transmit power and to maximize network capacity in terms of the number of users satisfying a target signal to interference (SIR) ratio. Centralized algorithms result in the optimum power vector while distributed algorithms are more suitable for practical system implementation and eliminate the need for a centralized control node. Both analytical and simulation results show significant improvement in the performance of the power controlled optical CDMA system. For instance, in a network of 31 nodes, a doubling of the capacity as compared to the non power control case is obtained. Furthermore, we show in the interference-limited case that the network performance is upper bounded by the number of nodes and the correlation properties of the employed code rather than network attenuation and optical fiber lengths. The concept of network partitioning is then introduced to simplify optimum power calculations. Using network partitioning, we find in the interference-limited case that the optical fibers after the star coupler are irrelevant to the optimum power evaluation.     

Enhanced performance analysis of optical CDMA communication system

Optical CDMA technique is required to meet the increased demand for high speed, large capacity communications in optical networks. OCDMA assures data access security and supports asynchronous burst data transmission. In this paper, improvement in optical CDMA has been done by implementing forward error correction technique and a distance of 100 km was achieved BER 10⁻¹⁹ at bit rate 3.75 Gbps with forward error correction in optical CDMA.     

Novel cobweb-topology WDM access network architecture featuring ultra-high reliability and easy scalability

A wavelength division multiplexing access network architecture with cobweb topology is proposed in this paper. It can be a candidate for metro access network with high reliability in the future. This architecture can provide two protection methods. The protection strategy which can maximize the protected traffic is elaborated in the context. Mathematical models of system performance such as network scale and link reliability are established and analyzed in this paper.     

Novel family of prime codes for synchronous optical CDMA

In this paper we have proposed a novel prime spreading sequence family hereby referred to as “new-Modified Prime Code (n-MPC)” for direct-detection synchronous optical code-division multiple-access (OCDMA) networks. The new code has been applied to Overlapping Pulse-Position Modulation (OPPM) CDMA system and the performance of system is evaluated. In addition, we have analyzed the system throughput and also introduced a new interference cancellation technique which significantly improves the bit error probability (BEP) of OPPM-OCDMA systems.     

Evaluation of coherent homodyne and heterodyne optical CDMA structures

This paper evaluates the coherent optical code-division multiple-access (OCDMA) techniques and examines the overall system performance in terms of signal-to-noise ratio (SNR) penalty as a function of simultaneous users accommodated to maintain an appropriate value of the bit-error rate (BER) for homodyne and heterodyne detections. As spreading codes, the proposed structures are utilizing a recently introduced prime code family hereby referred to as double-padded modified prime code (DPMPC). As a coherent modulation, binary phase-shift keying (BPSK) format is deployed. In homodyne detection, two different phase modulations are studied including either an external phase-modulator or injection-locking methods. The phase limitation and the performance for two methods plus multiple-access interferences (MAI) and receiver noise in a shot-noise limited regime are investigated. In heterodyne detection, BER analysis of the system based on only external phase modulator is examined. It is found that by maintaining BER = 10⁻⁹, this system can accommodate an increased number of simultaneous users to compare with systems which employ conventional bipolar codes.     

Performance evaluation of the phase encoded optical CDMA system

Recently, there has been increasing interest in field of Optical CDMA due to its potential for offering unmatched features at ultra high data rates in field of local and metro area networks. In this paper, a very simple method of Optical CDMA encoding known as the Temporal Phase Encoding is discussed and the performance of the system with this encoding technique is evaluated on the basis of number of users, length of the spreading code for 4-phase and 8-phases. Simulation results for the system are presented for upto seven users. Bit error rate curves are plotted with data rate of 1 Gbps. This has been found that performance improves if normalized threshold higher than 0.5 is used.     

数字光开关网络中四功能交换开关光学Omega网络

本文提出了一种用于数字光开关网络中，四功能交换开关光学Ｏｍｅｇａ网络。文中详细地阐述了用液晶空间光调制方法实现光学四功能交换开关，和Ｏｍｅｇａ互连网络的原理，并给出了光学系统和实验结果。     

WDM-OTDM based spectral efficient hybrid multiplexing technique inherent with properties of bandwidth elasticity and scalability

In this paper a hybrid multiplexing technique has been presented that merges WDM and OTDM multiplexing technologies. The WDM-OTDM hybrid realizes wavelength parallel bus architecture and is inherent with features of high spectral efficiency, high scalability and bandwidth elasticity. Simulations and experiments were carried out to investigate the selection of most suitable modulation format, dispersion compensation technique and erbium doped fiber amplifier (EDFA) noise figure for WDM-OTDM hybrid, where link lengths exceeding 500 km at high Q-values was achieved.     

Towards integrated semiconductor optical parametric oscillators

Microelectronic grade semiconductors display excellent figure of merits for second-order optical nonlinearity effects. However, most of them are not birefringent and cannot be properly phase-matched for efficient optical frequency conversion. This paper describes the different phase-matching scenarios which are currently developed in different laboratories to solve this problem. If successful, this field of research will open the way to future complete integrated optical parametric oscillators.     

Design and performance analysis in multiuser optical CDMA systems

The article presents comparative performance analysis of the proposed Optical CDMA system for 32 and 16 users with two dimensional codes. Numerical simulations have been done under interference significant environment, considering noise and dark current at data rates 2.5, 5, 7.5 and 10 Gbps over single mode fiber for transmission distance of more than 270 km. Results illustrate overall good performance, degraded with augment in bit rate and transmission distance, impervious with raise in number of simultaneous active users. Depicts significant performance improvement with inclusion of forward error correction RS (255,239), for low attenuation and chirp factor. It perceived, this is one of the efficient functional techniques for next generation broadband optical networks together with higher security owing to encoding and decoding, as it allow multiple users in the network to access the same fiber channel asynchronously.     

Utilization of spatial ternary coding scheme in optical CDMA system

In this paper, we propose a spatial ternary coding scheme for optical code-division multiple access systems. Since the multiple access interference (MAI) and beat noise leads to the error floor effect, using error correction mechanism is a preferable manner to further enhance the system performance. The proposed spatial ternary coding scheme possesses larger free distance, which is an effective way to relieve such deteriorating effect. It is expected that more users accommodated in the network can obtain higher throughput, while the side effects of MAI and beat noise will turn out to be more serious. To further reduce such adverse impact, the optical hard-limiter is also proposed. Once the channel condition is improved, it will give rise to the more powerful utilization of error correction code. The countermeasures utilized in the proposed system can effectively fight against the MAI and beat noise, and can allow more simultaneous users accommodated in the network. Therefore, it is a promising way for future high-speed optical access networks.     

A new family of two-dimensional codes for optical CDMA systems

The design of a new family of two-dimensional single pulse per column codes for optical code division multiple access (OCDMA) networks is reported. The 1-D modified pseudo-noise codes have been known to be orthogonal and their generation and system design based on these codes is rather simple. But their performance is limited due to the bandwidth constraints if the code length increases. Hence, using these 1-D modified pseudo-noise codes, modified 2-D pseudo-noise matrix codes (MPMCs) are generated. The system performance is evaluated for two, three and four simultaneous users using the link with all the sources responsible for degradation included: attenuation, chromatic dispersion, non-linear refractive effects, non-linear scattering and four-wave mixing. The effect of the non-linear and lossy dispersive medium over the system performance is shown by plotting the BER with respect to the link length for the systems designed using encoders/decoders base on 1-D modified pseudo-noise codes and our MPMCs. The performance is compared for the two types of codes by finding the crosstalk due to interfering users simultaneously operating in the network.     

Low-distortion hybrid optical shuffle concept

A hybrid micro-macro-optical shuffle interconnection approach is described. The new concept minimizes distortion in multichip smart-pixel shuffle interconnection systems that use macro-optics to link dense arrays of vertical-cavity surface-emitting laser (VCSEL) sources and matching arrays of detectors. The typical narrow-beam cones of VCSEL's are exploited by use of beam-deflecting micro-optics to create an optical system that is symmetric about its aperture. Since symmetric systems are well known to cancel distortion, this novel concept provides the means to achieve the required high degree of interchip registration accuracy.     

Overview of hybrid optical neural networks

This paper reviews optical architectures for the implementation of hybrid neural networks. Optics is mainly applied to implementing the matrix-vector or tensor-matrix multiplication. In addition, the general background of neural networks as well as a brief discussion on holographic associative memory are also given.     

Placement of hybrid optical amplifier in fiber optical communication systems

In this paper, we investigated the post-, pre- and symmetrical power compensation methods for a different position of hybrid optical amplifier RAMAN–EDFA in fiber link. The effect of increase in signal input power for three power compensation methods is compared in terms of bit error rate, eye closure penalty and output received power. It is found that the post power compensation method is superior to pre- and symmetrical power compensation methods. Further, the effect of variation in length of the standard single mode fiber and dispersion-compensated fiber for three power compensation configurations has also been observed. We observed that RAMAN–EDFA as post power compensation method provides least bit error rate (10^?40) and high output power (12 dBm) at ?15 dBm signal input power at fiber link.