New design of spectral amplitude coding in OCDMA with zero cross-correlation

A zero cross-correlation (ZCC) code is proposed to reduce the impact of system impairment and multiple access interference (MAI) in spectral amplitude coding optical code division multiple access (SAC-OCDMA) system. Bit-error-rate (BER) performance is derived taking into account the effect of some noises. The key to an effective OCDMA system is the choice of efficient address codes with good or almost zero correlation properties for encoding the source. The use of ZCC code can eradicate phase induced intensity noise (PIIN) which will contribute to better BER. Thus, we demonstrate, theoretically, the performance of optical ZCC code. It is shown that optical ZCC code can accommodate more users simultaneously for the typical error rate of optical communication system of 10⁻⁹. The result indicates that the established system not only preserves the capability of suppressing MAI, but also improves bit-error-rate performance as compared to the conventional coders.     

基于成像光通信的时间-空间扩频混合光码分多址编码方案

为了在成像光通信中充分利用时间和空间两种频带资源,以成像光通信为基础,提出一种利用二维光正交Pattern码结合时域扩频实现光码分多址(OCDMA)编码的新方案。分析在该方案中存在的多址干扰噪声,并给出了噪声的概率密度函数,然后讨论由多址噪声引起的误码率与判决门限、用户数、码长积和码重积之间的关系。在相同的码容量下与时域扩频光码分多址编码和空间扩频光码分多址编码方案相比,该方案能降低对相关器件性能(时域码片数量和空间像素规模)的要求,而且还可获得更小的误码率。最后给出编码解码的光学实现方案。     

A novel scheme of two-dimension time-stacked wavelength-time optical code label for optical packet switching network

A novel scheme of time-stacked optical code label based on optical code division multiple (OCDM) technique for optical packet switching network is proposed, in which two-dimensional wavelength-time OCDM code is used as the optical label. Packet loss rate and system characteristic based on the proposed scheme are studied. Results show that less packet loss rate of proposed scheme can be achieved as compared with that of one-dimension time-stacked optical code label system.     

BCH信道编码对降低快跳频OCDMA系统中色度色散的影响

提出BCH信道编码的方案来降低色度色散对降低快跳频OCDMA系统性能的影响.采用BCH信道编码后,单重合码的长度将变短,即可以用较少的波长数来构造码字,因此降低了色度色散的影响.分析结果表明,在相同的信息比特速率、脉元间隔、资用波长数的情况下,BCH信道编码能显著改善FFH-OCDMA系统的误码率性能.同时,由于单重合码的长度将变短,大大降低了光纤光栅的制作难度.由于BCH信道编码在电域中实现,其硬件技术已相当成熟,所以对整个BCH/FFH-OCDMA系统的代价影响不大.     

多噪音背景下引入光硬限幅器及并行干扰抑制器的光码分多址系统

为了抑制光码分多址中的多址干扰及多噪音,提出了一种引入光硬限幅器及基于最大值判决的并行干扰抑制器的光码分多址系统.在系统中存在APD噪音及热噪音的情况下,研究了系统对多址干扰的抑制作用.系统采用光正交码作为地址码,APD作为光电检测器,分析推导了系统的误码率表达式.根据所得的误码率表达式,进行了数值仿真,比较了该方法与其他方法的多址干扰抑制效果.研究结果表明:与现有其他有效方法(单比特引入一个光硬限幅器、单比特引入两个光硬限幅器、多比特传输、多比特引入光硬限幅器、基于最大值判决的并行干扰抑制器等)相比,本系统对多址干扰的抑制作用优于并行干扰抑制器、多比特传输、多比特引入光硬限幅器方法;当接收功率较低时,该系统优于引入双光硬限幅器的方法,因此可以有效的抑制多址干扰及多噪音.     

基于三种调制模式下的turbo码光无线通信系统分析

从分析大气对光无线通信系统的影响出发,研究了大气信道特性,建立了大气信道信噪比和能见度的关系.为降低系统误码率,提出了基于OOK、BPSK、BPPM三种调制模式的turbo码的编码方案,推导出三种不同方案对应的turbo码迭代MAP算法.应用建立的信噪比关系,分析和计算了基于三种不同方案的系统的误码率.结果表明,基于BPSK的turbo码系统比OOK和BPPM系统的信噪比降低约3dB,且在高的信噪比情况下,BPSK系统能显著降低系统的误码率.因此,基于BPSK的turbo码方案较适合光无线通信系统.     

多噪音背景下引入光硬限幅器及并行干扰抑制器的光码分多址系统

为了抑制光码分多址中的多址干扰及多噪音,提出了一种引入光硬限幅器及基于最大值判决的并行干扰抑制器的光码分多址系统.在系统中存在APD噪音及热噪音的情况下,研究了系统对多址干扰的抑制作用.系统采用光正交码作为地址码,APD作为光电检测器,分析推导了系统的误码率表达式.根据所得的误码率表达式,进行了数值仿真,比较了该方法与其他方法的多址干扰抑制效果.研究结果表明:与现有其他有效方法(单比特引入一个光硬限幅器、单比特引入两个光硬限幅器、多比特传输、多比特引入光硬限幅器、基于最大值判决的并行干扰抑制器等)相比,本系统对多址干扰的抑制作用优于并行干扰抑制器、多比特传输、多比特引入光硬限幅器方法|当接收功率较低时,该系统优于引入双光硬限幅器的方法,因此可以有效的抑制多址干扰及多噪音.     

Optical coding scheme for all-optical analog-to-digital conversion using asymmetrical Y-branch waveguide

The novel optical coding scheme for all-optical analog-to-digital conversion has been proposed, in which asymmetrical Y-branch waveguide structures have been introduced to achieve the desired optical power splitting. The optical performance has been simulated by using finite-difference beam propagation method (FD-BPM), which shows that the designed component exhibits good coding performance. Experimentally, the optical coding component has been fabricated and measured. The optical power contrast between bit code 1 and 0 at output port is more than 37 dB, and measured imbalance of output power is less than 1.5 dB for bit code 1.     

频域反射法光纤延时精密测量

本文提出了一种应用于光纤延时系统中实现光纤延时精密测量的新方法,用以提高光纤延时测量的精度和准确性.该方法以1064 nm激光调制信号作为光源,通过测量回波信号的幅值和相位信息得到被测通道的频率响应,采用快速傅里叶逆变换得到被测目标的延时信息,实现光纤延时测量.本文通过理论分析和延时测量实验对频域反射法与传统的时域测量方法进行对比,使用频域反射法在调制频率范围10—200 MHz,采样频率间隔0.5 MHz的实验条件下,实现了3.3 ps延时测量分辨率,并证明了该方法具有比时域方法更高的测量精度,测量结果的准确性更好.     

基于超结构光纤光栅的正交四相光码分多址编/解码器

正交四相序列编码相比于二相序列具有更大的码字容量和更好的互相关特性,因此更适用于光码分多址(OCDMA)无源光接入网.提出并实现了一种基于超结构光纤光栅的正交四相光码分多址编/解码器.该编/解码器采用A族四相序列作为地址码,在制作的过程中仅需一个均匀相位掩模板即可实现编码功能,并且在性能上与传统工艺制作的编码器相当.为了与不同波长信道相匹配,提出了变信道编码技术,仿真结果表明采用该技术的编码器具有更高频谱效率,因此得到更好的编/解码性能.对一个码长63,长度4.1 cm的正交四相编/解码器进行了信息速率为2.5 Gb/s.码片速率为156 Gchip/s的编/解码实验,取得了较好的编/解码效果.     

A new coding scheme of QC-LDPC codes for optical transmission systems

Based on Galois Field (GF(q)) multiplicative group, a new coding scheme for Quasi-Cyclic Low-Density Parity-Check (QC-LDPC) codes is proposed, and the new coding scheme has some advantages such as the simpler construction, the easier implementation encoding, the lower complexity of the encoding and decoding, the more flexible adjustment of the code length as well as the code rate and so forth. Under the condition of considering the characteristics of optical transmission systems, an irregular QC-LDPC (3843,3603) code to be suitable for optical transmission systems is constructed by applying the proposed new coding scheme. The simulation result shows that the net coding gain (NCG) of the irregular QC-LDPC (3843,3603) code is respectively improved 2.14 dB, 1.19 dB, 0.24 dB and 0.14 dB more than those of the classic RS (255,239) code in ITU-T G.975, the LDPC (32640,30592) code in ITU-T G.975.1, the regular SCG-LDPC (3969,3720) code constructed by the Systematically Constructed Gallager (SCG) coding scheme and the regular QC-LDPC (4221,3956) code at the bit error rate (BER) of 10-8. Furthermore, all the five codes have the same code rate of 93.7%. Therefore, the irregular QC-LDPC (3843,3603) code constructed by the proposed new coding scheme has the more excellent error-correction performance and can be better suitable for optical transmission systems.     

Performance Enhancement for Optical Fast Frequency-hopping CDMA Systems by BCH Channel Coding

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基于傅里叶变换的光纤探头光谱特性校正方法的研究

针对光纤自身对光谱的非线性衰减的影响，提出了一种基于傅里叶变换的光谱校正方法。首先对是否经过光纤的两种情况下光电倍增管的输出电流进行傅里叶变换，得到光谱频域中的校正函数，然后通过傅里叶逆变换得到光谱域中的校正函数。为实现测试，建立一个光电检测系统，在可见光范围内进行测试。分别对是否带有光纤的两种情况下数据进行采集，使用该校正方法可以使光线的衰减得到较好的修正，误差小于1．54％。实验结果表明，该方法对特定的光纤传导系统的光谱非线性衰减有较好的校正效果。     

Performance analysis of electronic code division multiple access based virtual private networks over passive optical networks

A solution for implementing multiple secure virtual private networks over a passive optical network using electronic code division multiple access is proposed and experimentally demonstrated. The multiple virtual private networking capability is experimentally demonstrated with 40 Mb/s data multiplexed with a 640 Mb/s electronic code that is unique to each of the virtual private networks in the passive optical network, and the transmission of the electronically coded data is carried out using Fabry-Perot laser diodes. A theoretical scalability analysis for electronic code division multiple access based virtual private networks over a passive optical network is also carried out to identify the performance limits of the scheme. Several sources of noise such as optical beat interference and multiple access interference that are present in the receiver are considered with different operating system parameters such as transmitted optical power, spectral width of the broadband optical source, and processing gain to study the scalability of the network.     

Design of strict optical orthogonal codes with nonconstant weights for use in optical code-division multiplexing multimedia systems

We report the design of a new family of strict optical orthogonal codes (SOOCs) that permit the use of nonconstant code weights in optical code-division multiplexing (OCDM) systems. Because this new code can possess any number of pulses (i.e., 1s) in each codeword while still maintaining the minimum autocorrelation and cross-correlation constraints (i.e., “1”) for incoherent optical processing, its use can flexibly support multimedia applications in an OCDM system to meet varieties of transmission performance and traffic requirements which are demanded by different types of communication services. The method of designing the proposed codes is presented, and the bound on code length is also given.     

A new alternative approach of all optical frequency encoded clocked S-R flip-flop exploiting the non-linear character of semiconductor optical amplifiers

In all optical networking and computing system, the role of all-optical flip-flops is very much essential. For signal synchronization with a reference clock and for storage of digital bits the flip-flop has no alternative. In this communication the authors propose a method of developing an all optical frequency encoded clocked R-S flip-flop using the non-linear character of semiconductor optical amplifiers. Frequency is the basic character of light and several encoding/decoding problems in computations and communications can be solved using the frequency encoding principle of optical data. The proposed system is all-optical and therefore it can extend a super fast speed of operation (far above THz limit).     

A novel construction algorithm of the LDPC code for high-speed long-haul optical transmission systems

According to the transmission characteristics of high-speed long-haul optical transmission system, the main construction method of Low-Density Parity-Check (LDPC) code for optical transmission system is presented and a novel construction algorithm of LDPC code is proposed, the theoretical analysis shows that the parity check matrix of the LDPC code constructed by the proposed construction algorithm has no four-girth phenomenon, this is also theoretically proved out. Both the novel LDPC(3969,3720) code with 6.69% redundancy and the novel LDPC(8281,7920) code with 4.56% redundancy for optical transmission systems are constructed by using the presented construction method and proposed construction algorithm. The simulation results show that the net coding gain (NCG) of the two novel LDPC codes at the eighteenth iteration for the BER of 10^?12 are respectively 1.63 dB and 1.49 dB more than that of the RS(255,239) code in ITU-T G.975. Moreover, the decoding of the LDPC code in the hardware can parallel be implemented, so the decoding speed of the two novel LDPC codes are very rapid, the complexities of implementing the two novel LDPC codes, compared with the concatenated codes in ITU-T G.975.1, are relatively lower, furthermore, the hardware overhead and storage space can relatively be saved and the computation complexity can be reduced in implementing the hardware in the future. As a result, the two novel LDPC codes can better be suitable for high-speed long-haul optical transmission systems.     

A New Algorithm for Development of Dynamic Cyclic Shift Code for Spectral Amplitude Coding Optical Code Division Multiple Access Systems

Abstract

This article presents a new code—the dynamic cyclic shift code—for spectral amplitude coding–optical code division multiple access systems. One of the important properties of the dynamic cyclic shift code is that the number of users can be increased without increasing the weight value. System performance was evaluated by using both theoretical analysis as well as the simulation experiment. The analysis results show that the proposed dynamic cyclic shift code can support more users in spectral amplitude coding–optical code division multiple access systems compared to spectral amplitude coding–optical code division multiple access codes. It was ascertained by performance evaluation that the dynamic cyclic shift code possesses ideal properties for use in spectral amplitude coding–optical code division multiple access systems.     

Method of implementing frequency encoded multiplexer and demultiplexer systems using nonlinear semiconductor optical amplifiers

Multiplexing and demultiplexing are the essential parts of any communication network. In case of optical multiplexing and demultiplexing the coding of the data as well as the coding of control signals are most important issues. Many encoding/decoding mechanisms have already been developed in optical communication technology. Recently frequency encoding technique has drawn some special interest to the scientific communities. The advantage of frequency encoding technique over any other techniques is that as the frequency is fundamental character of any signal so it remains unaltered in reflection, refraction, absorption, etc. during transmission of the signal and therefore the system will execute the operation with reliability. On the other hand, the switching speed of semiconductor optical amplifiers (SOA) is sufficiently high with property of best on/off contrast ratio. In our present communication we propose a method of implementing a ‘4-to-1’ multiplexer (MUX) and a ‘1-to-4’ demultiplexer (DEMUX) exploiting the switching character of nonlinear SOA with the use of frequency encoded control signals. To implement the ‘4-to-1’ MUX and ‘1-to-4’ DEMUX system, the frequency selection by multiquantum well (MQW)-grating filter-based SOA has been used for frequency routing purpose. At the same time, the polarization rotation character of SOA has also been exploited to get the desired purpose. Here the fast switching action of SOA with reliable frequency encoded control input signals, it is possible to achieve a faithful MUX/DEMUX service at tera-Hz operational speed.     

Frequency encoded optical four-bit adder/subtractor with control input using semiconductor optical amplifiers

Optical adder/subtractor for two four-bit frequency encoded binary numbers are proposed and designed based on four wave mixing, add drop multiplexing and frequency conversion in semiconductor optical amplifier. The input bits and the control input are intensity-modulated signal of two specific frequencies suitable for optical communication in the C band of wavelength. The device can distinguish negative and positive results and controlled operation are most promising in this proposal. The use of semiconductor optical amplifiers along with frequency encoding makes the system very fast and useful for future optical communication and computation systems.