Modified multi-wavelength optical orthogonal code for spectral efficiency improvement in two-dimensional optical CDMA system

Classical multi-wavelength optical orthogonal code (MWOOC) constructions impose several conditions on the code parameters. These limit the optical code division multiple access (OCDMA) system potentialities in terms of performance and practical implementation. A modified MWOOC construction is used to overcome these limitations. Indeed, this method permits the design of 2D codes with a low temporal code length value and a low number of wavelengths. Considering a multi-user receiver named parallel interference cancellation, the number of users and the data rate per user the system can provide for a low bit error rate value are evaluated. For a given performance, it is shown that the spectral efficiency using the modified MWOOC is significantly improved. Thus, the simplicity of the modified code design and the spectral efficiency increase constitute an advantage for practical implementation of OCDMA network.     

高效非成像聚光光学系统设计与性能分析

针对菲涅尔透镜存在实际光学效率偏低的问题,本文设计了一种由非球面透镜和棒锥镜组成的高效非成像聚光光学系统。在光学设计软件Zemax的序列模式下对非球面透镜进行了优化设计,通过最大程度地减小球差,像面光斑的几何半径从42 mm降到了1.7 mm。基于此,在Zemax的非序列模式下,完成了非球面透镜和棒锥镜的建模和优化,通过蒙特卡罗光线追迹分析实现了光学效率为87%、接收角为0.9°的非成像聚光光学系统。最后,基于非球面透镜阵列和棒锥镜样品,实现了高倍聚光型光伏模组的封装与测试。测试结果表明,该模组的光电转换效率达30.03%,与菲涅尔透镜构成的高倍聚光型光伏模组相比有显著提升。     

Design considerations of high performance optical code division multiple access: a new spectral amplitude code based on laser and light emitting diode light source

A new code of optical code division multiple access (OCDMA) based on spectral amplitude coding (SAC) is described and analysed. The coding technique is called random diagonal (RD) code. One of the important properties of this code is that the cross-correlation at data segment is always zero, which means that phase intensity induced noise (PIIN) is reduced. From the construction of RD code sequence, the authors can see that the RD code is constructed using code segment and data segment. Using this code property, RD code is implemented using coherent source (multi-laser) and incoherent source (light emitting diode) for the code segment and data segment, respectively. RD code using two multi-sources (incoherent and coherent) can be considered as an effective way for maximising the capacity while minimising the cost of SAC-OCDMA. It is shown that the system using this new code matrices not only suppresses PIIN, but also allows a larger number of active users compared with other codes.     

基于多维性能极限状态的概率地震需求分析

基于概率地震需求分析(PSDA),分别采用增量动力和非线性时程分析,得到某框架结构的最大层间漂移比和最大加速度响应,通过定义多维性能极限状态的性能水准,计算该结构的多维地震易损性,联合地震动危险性曲线,建立了年平均超越概率的三重积分公式,采用梯形法求得50年内地震需求(漂移)危险性曲线。在此基础上,进行了同时考虑性能极限状态的随机性和相关性对结构需求危险性的敏感性分析。在性能极限状态不确定性中选择适当的变异系数(cidrcpfa)及相互作用因子NID R,能够使年平均超越概率增加;相比单一极限状态,考虑二维极限状态的年平均超越概率也将提高。研究结果表明,所提方法可描述对多维响应参数敏感的结构破坏行为,可获得设计基准期内更加符合实际的结构需求危险性曲线,为震后损失估计提供可靠的理论依据。     

Construction and performance analysis of 2-D codes for M-ary OFFH?CDMA systems

A new family of two-dimensional (2-D) codes constructed by combining frequency-hop and time-spreading codes is presented. The proposed codes are designed to overcome the limitation imposed on the maximum permissible number of simultaneous users in optical code-division multiple-access (OCDMA) systems. To increase the data transmission rate, the 2-D codes employ a M-ary signalling scheme. The proposed family of codes has the favourable characteristics of a zero autocorrelation constraint and a cross-correlation constraint of one. The performance of the 2-D code is analysed in terms of the bit error rate (BER) and is compared with that of a conventional OCDMA system using optical orthogonal code (OOC). The numerical and simulation results reveal that the proposed system outperforms conventional OCDMA systems both in terms of the BER and the data transmission rate. In addition, the system capacity is sufficient to ensure reliable communication (BERles10^-9) in local area networks     

Priority-based CDMA system with variable code reservation periods for multiclass traffic

A priority-based CDMA system with variable code reservation periods for supporting multiple traffic types is presented. For the purpose of evaluation we build mathematical models for analysing two subsystems with different types of multimedia traffic. Two performance measures, the average packet dropping probability and the average packet transmission delay, are derived from the models based on equilibrium-point analysis. The effects of the two performance measures on system performance are discussed by varying the code reservation periods to adapt to multiple-class traffic with various priorities.     

Internally coded multicarrier frequency-hopping CDMA communication system and its performance analysis

A new internally coded scheme that combines frequency hopping (FH) and multicarrier (MC) code division multiple access (CDMA) techniques using a super-orthogonal encoder is proposed. In this method, the total bandwidth is partitioned into Ns₂ disjoint bands and each band is also segmented into Ns₁ subbands. On the basis of a super-orthogonal encoder output and a pseudorandom sequence, one of the Ns₁ bands is selected. The data bit is then transmitted in the band in the form of the multicarrier FH (MC-FH) CDMA scheme, that is, Ns₂ carriers are transmitted in the Ns₂ subbands of the selected band. At the receiver, both hard and soft detectors are used. The performance of the proposed method in the additive white Gaussian noise (AWGN) and fading channels is evaluated. The results indicate that the proposed method outperforms the previously presented uncoded and coded MC-FH-CDMA systems, where the data are transmitted over the whole bandwidth, keeping the same bandwidth (spectral efficiency). Further, in the new method, the carriers hop in part of the total bandwidth, and hence coherent detection is more feasible.     

新型高灵敏度GLV光学电流传感器设计与性能分析

本文结合GLV技术设计了一种适于检测高压交流电的新型光学电流传感器.这一设计具有温度稳定性好、大电流下灵敏度高、频率响应范围宽等特点,且测量芯片制作工艺简单、成本低廉.通过有限元分析和数值计算对器件的模态、工作性能、热膨胀特性等进行了分析模拟,结果表明:测量芯片量程达500A～2000A,并可通过改变设计参数灵活调整;一阶固有频率接近60kHz,大电流下灵敏度接近0.2dB/A,外界温度变化±50K时传感器测试误差在0.7%以内.     

Design of multi-rate optical code paths considering polarisation mode dispersion limitations

The authors propose an original design based on multi-rate optical code paths (OCPs) for transport in advanced wavelength-division multiplexing/optical code division multiplexing (WDM/OCDM) networks. The authors utilise multi-length optical orthogonal codes (OOC) to obtain multi-rate OCPs. The performance of the proposed scheme is analysed and the impact of multiple access interference (MAI) and polarisation mode dispersion (PMD) over these OCPs is evaluated. Results show that not only multi-rate operation can be achieved but also MAI effects can be reduced, while mitigating PMD effects.     

光通信系统中一种新颖的级联码型

基于级联码对光通信系统中级联码特性和ITU-T G.975.1中两种超强前向纠错(SFEC)码型进行分析和研究后,提出了一种新颖的RS(255,239) BCH(1023,963)级联码型.仿真表明,该码型与ITU-T G.975.1中RS(255,239) CSOC(k0/n0=6/7,J=8)码相比较,具有更低的冗余度和更好的纠错性能,并且在经过三次迭代且误码率(BER)为10-12时其净编码增益(NCG)比ITU-T G.975.1中RS(255,239) CSOC(k0/n0=6/7,J=8)码和BCH(3860,3824) BCH(2040,1930)码要分别大0.60 dB和0.57 dB.因而,它更适用于超长距离、超大容量和超高速的光通信系统中,并可以作为SFEC码的一种候选码型.     

Comparative performance analysis of time-frequency distributions for spectroscopic optical coherence tomography

The analysis of spectroscopic optical coherence tomography (SOCT) signals suffers the trade-off between time resolution and frequency resolution. Various joint time-frequency distributions (TFDs) can optimize this trade-off. Synthesized signals were generated and experimentally acquired data were obtained to compare and validate several different TFDs under different SOCT imaging schemes. Specific criteria were designed to quantify the TFD performance. We found that different SOCT imaging schemes require different optimal TFDs. Cohen's class TFDs generate the most compact time-frequency (TF) analysis, while linear TFDs offer the most reliable TF analysis. In both cases, if some prior information is known, model-based TF analysis can improve the performance.     

用于光学调整的二维纳米级微动台的设计分析

研究开发了一种用于光学调整的二维压电驱动的纳米级微动工作台,建立了工作台的力学模型,并利用结构力学理论推导出工作台沿X、Y方向刚度及前二阶固有频率的解析式。通过微动工作台固有频率及沿X、Y方向刚度的实验测试,验证了解析方法和有限元方法用于微动工作台设计分析的可行性。有限元分析结果表明,可通过改变直角平板柔性铰链的特征参数,达到控制和优化工作台固有频率、输出位移、应力分布及驱动力响应的目的,并提出一种初选微动工作台柔性铰链参数的简易方法。     

光学相关器系统的固化设计与性能分析

小型固化光学相关器,以偏振分光棱镜和反射型傅里叶透镜作为基本部件,并采用透明固体介质填充光学系统的空隙。该系统通过各元件端面相连,简化了校准难度;使用反射型透镜,具有色像差和轴外像差小的优势。模拟分析表明,这种固化结构具有良好的系统性能,并满足识别的需要。     

Internally coded time-hopping coherent ultra-short light pulse code division multiple access scheme with optical amplifier and its performance analysis using additive noise model

The internally coded time-hopping coherent ultra-short light pulse code division multiple access (CULP CDMA) scheme (recently introduced) with an optical amplifier is described and its performance in fibreoptic communication systems is analysed. In accordance with the important role of optical amplifiers in optical communication systems, a preamplifier at the input of the receiver is used in order to compensate the losses because of the spectral encoder, spectral decoder and optical fibre path. The authors evaluate the bit error rate of the system considering the effects of the multiple access interference, noise because of the optical amplifier and thermal noise using saddle point approximation, and compare the results with those of the conventional CULP CDMA system with and without an amplifier. The numerical results indicate a substantial improvement in the performance of the coded system in comparison with the uncoded one. In addition, the negative effect of amplifier noise in the proposed scheme is much less than that of the conventional CULP CDMA system.     

Mathematical modelling and performance analysis for average-based rapid search method for direct global position system precision code acquisition

Direct global position system precision code acquisition is desirable for providing stronger anti-jamming and anti-spoofing capabilities than the handover from a coarse acquisition code. Because of the high chip rate and long period of the precision code (P-code), direct acquisition is challenging. By averaging incoming and local signals respectively, to reduce the number of code phases to be searched, previously proposed direct and overlap average methods provide an efficient way to rapid acquisition. To further analyse the performance of average methods the previously proposed direct and overlap average methods are generalised, the corresponding mathematical modelling is established, the correlation properties of the averaged P-code are studied and the detection and mean acquisition time performances are investigated. By increasing the weighting of the local signal, which has a code phase shift in samples of half of the average length, improved overlap average methods are proposed. Compared with the previously proposed direct and overlap average methods, the improved overlap average methods have better detection performance and can further improve acquisition performance, that is, shorten the mean acquisition time. Numerical results demonstrate the enhancement.     

Design and analysis of hybrid optical and electronic buffer based optical packet switch

Optical packet switching has the potential to be used as next generation data transfer technology. This paper, introduces an Arrayed Waveguide Gratings (AWG) switch where hybrid buffer (electronic + optical) is used for the buffering of contending packets. Power budget analysis has been carried out under various switch designs. Comparison of optical and electronic buffering is done in terms of power required for the correct operation of the switch. Energy consumption per bit is also evaluated for both optical and electronic buffers for various buffering time ranges from nano-seconds to milli-seconds. In the switch analysis it has been found that, amplified switch requires five times less power, in comparison to un-amplified switch for correct operation. Energy consumption analysis reveals that for shorter duration storage, optical buffer would be a better choice.     

Design and analysis of an integrated optical sensor for scanning force microscopies

In this paper, a novel probe for displacement sensing will be introduced. It is based on a conventional GaAs cantilever, integrated with a Bragg grating as a photo-elastic strain sensor. The deflection of the cantilever is measured directly from the intensity modulation of the reflected light. The principle of the experimental setup and the sensor, as well as the theoretical investigation of the force and displacement sensitivity of the probe, is presented. Finite-element method simulations were performed to get the optimum sensor design. Transfer matrix method simulation of the waveguide grating have been described in detail. In order to enhance the sensitivity, different types of grating structures are discussed. Using this new design, it should be possible to achieve sensitivities, defined as the fractional change in detected optical power per unit displacement of the cantilever, as high as 10/sup -4/ /spl Aring//sup -1/ of cantilever deflection.     

Service differentiated drop code unit for metro ring optical networks

The authors demonstrate using both simulation and experiment, a drop code unit for metro ring optical networks with service differentiation capability. This is achieved by means of a spectral amplitude coding technique whereby the code weight in a particular channel is varied to provide different signal quality levels. Transmission of three channels with different weights operating at 10 Gbps per channel was simulated over a 68 km unamplified and 185 km amplified links of dispersion compensated fibre. Services are perfectly dropped at bit error rates from 10^-9 to 10^{-3, leaving the through service free from accumulated noise. The authors also present a 2.5 Gbps per channel proof-of-concept experiment over 40 km of single-mode fibre (SMF).}     

Geometrical-optics code for computing the optical properties of large dielectric spheres

Absorption of electromagnetic radiation by absorptive dielectric spheres such as snow grains in the near-infrared part of the solar spectrum cannot be neglected when radiative properties of snow are computed. Thus a new, to our knowledge, geometrical-optics code is developed to compute scattering and absorption cross sections of large dielectric particles of arbitrary complex refractive index. The number of internal reflections and transmissions are truncated on the basis of the ratio of the irradiance incident at the nth interface to the irradiance incident at the first interface for a specific optical ray. Thus the truncation number is a function of the angle of incidence. Phase functions for both near- and far-field absorption and scattering of electromagnetic radiation are calculated directly at any desired scattering angle by using a hybrid algorithm based on the bisection and Newton-Raphson methods. With these methods a large sphere's absorption and scattering properties of light can be calculated for any wavelength from the ultraviolet to the microwave regions. Assuming that large snow meltclusters (1-cm order), observed ubiquitously in the snow cover during summer, can be characterized as spheres, one may compute absorption and scattering efficiencies and the scattering phase function on the basis of this geometrical-optics method. A geometrical-optics method for sphere (GOMsphere) code is developed and tested against Wiscombe's Mie scattering code (MIE0) and a Monte Carlo code for a range of size parameters. GOMsphere can be combined with MIE0 to calculate the single-scattering properties of dielectric spheres of any size.     

光学加工中真空夹具设计及分析

为了在光学加工中快速、可靠地装夹光学元件,设计了真空夹具,对该真空夹具引起光学元件变形量进行了分析.首先,根据光学加工对夹具的要求,应用手动静压快速夹头以及传统真空吸盘结构,设计了真空夹具;接着,对真空夹具引起光学元件变形量进行了仿真分析,并根据分析结果改进了真空夹具结构;最后,针对改进后的真空夹具进行了仿真验证.仿真结果表明:有防护层的真空夹具引起光学元件表面最大变形量在0.1 μm～0.32 μm之间,是没有防护层的真空夹具引起光学元件表面最大变形量的1/14.该种真空夹具可以应用于高精度光学加工中.