Experimental demonstration of security-improved OCDMA scheme based on incoherent broadband light source and bipolar coding

Experimental demonstration of security-improved optical code-division-multiplexed-access (CDMA) scheme based on spectrally encoded incoherent broadband light source with bipolar coding is presented. Incoherent bipolar encoding is achieved with amplified spontaneous emission (ASE) noise of erbium-doped fiber amplifier. We show details of coding scheme and investigate security issues by measuring eye-diagrams and bit-error-rates for various cases. In addition, we present analytical and numerical simulation results for secure transmission of spectrally encoded incoherent optical CDMA signal.     

Analysis of the spectral efficiency of frequency-encoded OCDMA systems with incoherent sources

This paper presents the spectral efficiency of frequency-encoded (FE) optical code-division multiple-access (OCDMA) systems with incoherent sources. The spectral efficiency of five code families compatible with FE-OCDMA is calculated as a function of the number of users. Analytical equations valid in the limiting case of Gaussian noise are also developed for the bit-error rate and the spectral efficiency. Among the code families considered, the modified quadratic congruence code leads to the maximum achievable spectral efficiency.     

非相干OCDMA系统地址码的比较

地址码的选择是光码分多址系统中的一项关键技术，为此介绍了非相干光码分多址系统中的各种地址码，对它们的基本参数、性能和应用等进行了比较，最后指出了今后的发展方向。     

Performance analysis of 2-D time-wavelength OCDMA systems with coherent light sources: code design considerations

The performance of two-dimensional (2-D) time-wavelength (TW) optical code-division multiple access systems at both physical and data link layers is considered in the presence of a multitude of noise sources. Particular consideration is given however to both beat noise (BN) and multiple-access-interference effects. A general procedure for calculating BN is presented. Comparisons between several 2-D TW codes comprising single-pulse-per-column/row and multiple-pulse-per-column/row strategies are performed. Results reveal that BN is strongly dependent on the code properties and the distribution of wavelengths within a code. Several aspects for 2-D TW code design are presented that mitigate the effect of BN.     

Coupling light from incoherent sources to optical waveguides

Spatially coherent laser light can be coupled into an optical waveguide with nearly 100 percent efficiency. However, coupling light from a spatially incoherent source to a waveguide can be frustrating. Here the author describes how to efficiently couple blackbody radiation to optical fiber waveguides. The same basic principles hold for other types of waveguides, such as integrated optic waveguides. Radiation emitted from other types of extended sources, such as surface emitting LEDs or ionized gases, can be efficiently coupled to waveguides using the same techniques     

Performance improvement of bandwidth-limited coherent OCDMA system

The performance of an optical code division multiplexing access (OCDMA) system employing the differential phase shift keying (DPSK) data format and turbo code is investigated and simulated. A bandwidth-limited coherent time spreading (TS) OCDMA system is considered. Theoretical results show that performance degradation due to bandwidth limitation could be effectively restrained by the application of the DPSK data format in a coherent OCDMA system, and further performance improvement could be achieved by incorporating turbo coding into the OCDMA system.

Performance analysis on phase-encoded OCDMA communication system

The performance of an asynchronous phase-encoded optical code-division multiple-access system is evaluated on the condition that the impact of fiber channel is neglected. Phase-encoded optical signal (pseudorandom optical signal with low intensity) is analyzed in the view of stationary random process. The pseudorandom optical signal with low intensity is seen as a sample function of a certain stationary random process which is ergodic in strict sense. The analysis results reveal that the variance of the corresponding random process is only inversely proportional to the code length while the root-mean-square width of the phase-encoded optical signal is proportional to the width of initial optical pulse and the code length F. The numerical results demonstrate that the better system performance can be achieved in case of larger code length and shorter initial optical pulse.     

Spectral efficiency of OCDMA systems with coherent pulsed sources

We present a model to evaluate the upper limit of the spectral efficiency of optical code-division multiple-access (OCDMA) systems with coherent sources. Phase-encoded and direct-sequence OCDMA systems are evaluated using this model. The results show that a spectral efficiency of 2.24/spl times/10/sup -2/ b/s/spl middot/ Hz can be achieved with a maximum bit error rate of 10/sup -10/ in these systems of the number of users. This result demonstrates that the maximum spectral efficiency of OCDMA systems with coherent sources is at least a factor of 5 higher than OCDMA systems with incoherent sources.     

Analysis of beat noise in coherent and incoherent time-spreading OCDMA

The effect of beat noise and other types of additive noise in time-spreading optical-code-division multiple-access (TS-OCDMA) networks is analyzed in this paper. By defining the coherent ratio kt, the ratio of the chip duration to the coherence time of the light source, TS-OCDMA systems are classified into incoherent, partially coherent, and coherent systems. The noise distributions and the bit-error rates are derived, and system performance is discussed for different cases. The performance of coherent systems is limited by the beat noise. With increasing kt, the effect of beat noise decreases in incoherent systems, and they eventually become free of beat noise. Possible solutions to the beat noise problem in coherent and partially coherent systems are also proposed and discussed.     

S+C+L超宽带光源的研究

为了得到一种高性能的S+C+L波段的超带宽光纤光源,采用一种新型的混合掺杂的光纤作为传输媒质,通过用激光二极管作为抽运源抽运掺铒光纤和掺铥光纤,用两个3dB宽带耦合器作为光纤反射镜,同时利用功率控制电路让光源输出光稳定,对设计的光源进行了实验和理论验证,得到了总功率为28mW、带宽1460nm～1610nm的S+C+L波段的超带宽光纤光源。结果表明,光纤环形镜的使用,不仅改善了光源的平坦度,并且大大提高了光光转换效率。     

基于OCDMA的改进型室内可见光无线局域网分析

在原有的室内可见光无线通信网络结构的基础上,提出将用户终端适配器光源改为激光。用激光通信实现系统的上行链路,采用可见光通信与激光通信相结合的方式实现室内无线局域网,并基于光码分多址(OCDMA)技术,用光正交码(OOC)作为地址码对信号进行编码。仿真结果表明,改进后的系统误码率明显降低,能较好地满足通信的需求。     

OCDMA/DWDM混合系统接入网的参数配置

研究了接入网中光码分多址/波分多址(OCDMA/DWDM)混合系统影响系统性能的因素,通过理论分析和仿真,得出系统比特差错概率(BER)的半解析表示,最终仿真结果表明,为了满足通信质量,在配置系统时要严格控制同时在线的地址码用户数K,而复用信道数M可在成本允许的范围内灵活选择.初步解决了满足系统正常传输所需要的系统配置问题,为以后实际系统的用户数设计提供了一定的参考价值.     

一种具有平衡互补结构的新型OCDMA解码器

提出了一种新的具有平衡互补结构的解码器,与相应的编码器配合可以在一个光学信道上实现双极性编码的容量和多址干扰指标,给出了解码器的结构,分析了其工作原理,并与其它方案进行了比较。     

Security performance analysis of an M-code keying OCDMA system

In this article, an M-code keying OCDMA system with parallel encoders/decoders is presented and its security performance is quantitatively analyzed. Under brute-force searching techniques, the formula about the average searching time is derived. The bit-correct-interception possibilities for tapping individual and multiple users’ signals are calculated, respectively. By analysis, it is shown that the security performance of an OCDMA system can be enhanced by employing M-code keying.     

新型激光光源染料HA宽带调谐发光物理机制

为了研究和揭示竹红菌甲素(HA)的宽带调谐发光物理机制,采用强激光激发的方法,主要研究了HA的强激发辐射效应,从一个侧而证实了激发态质子转移(ESIPT)的存在,同时进行了理论分析和实验验证,并给出了HA分子能级模型.结果表明,对于HA分子需要舣光子吸收才能实现ESIPT过程.这一结果对进一步认识HA的发光物理机制是有...     

Performance Analysis of an Integrated Spectral OCDMA Technique Including Coupler Imbalance

In this letter, we show, for the first time, that an integrated spectral optical code-division multiple-access (OCDMA) technique has a comparable performance with respect to coherent OCDMA techniques based on a crosstalk analysis. The code set is further studied on its resilience against imbalances in the 3-dB couplers of the en/decoders (E/Ds). The orthogonality remains acceptable for imbalance penalties up to 1 dB. The analysis done in the letter considers a cascade and a tree E/D which shows negligible differences in performance.     

波分复用OCDMA系统的性能分析

分析了波分复用(WDM)光码分多址(OCDMA)系统的归一吞吐量性能。当同时用户数均匀分配到不同的波长时,得到了WDM OCDMA系统归一化吞吐量性能的上界;当同时用户数尽量分配到同一个波长时,得到了WDM OCDMA系统归一化吞吐量性能的下界。在所有用户均匀分配到不同波长信道的条件下,比较了WDM OCDMA与多波长(MW)OCDMA系统的归一化吞吐量性能。结果表明,当负载较小时,两者的性能基本相当;当负载较大时,WDM 0CDMA的性能优于MW OCDMA系统。同时,WDM OCDMA的归一化吞吐量峰值高于MW OCDMA系统的归一化吞吐量峰值。     

采用改进的PIC技术的OCDMA系统性能分析

文章提出改进的并行干扰消除(PIC)技术来减少多址干扰时光码分多址(OCDMA)系统性能的影响.以光正交码(OOC)为地址码,推导出改进的PIC技术的系统误码率表达式.通过仿真分析给出了误码率与OOC的码长、码重和并发用户数的关系.结果表明,采用改进的PIC技术,能大大降低OCDMA系统的误码率,改善系统性能,且系统满足误码率≤10<'-9>时所需的最小OOC码长远远小于PIC所需的最小OOC码长.     

Absorption measurement of methane gas with broadband light source using fiber-optic sensor system

The absorption coefficient of methane is very important for measuring the concentration of methane.We theoretically analyzed the general expression of methane absorption coefficient for a given condition,at room temperature of 296K,and we simulated the relationship between the absorption and the wavelength of the light source.The experimental results we obtained are consistent with the simulation.The discrepancy between the experimental results and the simulation results is also discussed.