Design and performance analysis of code families for multi-dimensional optical CDMA

A code design algorithm for application in multi-dimensional optical code division multiple access (MD-OCDMA) for asynchronous optical fibre communication is proposed. Two-dimensional (2D) wavelength-time or space-time OCDMA and three-dimensional (3D) space-wavelength-time OCDMA are subsets of MD-OCDMA. Some applications and the performance analysis of the algorithm in 2D multipulse per row codes and 3D multipulse per plane codes are shown. In the applications discussed, this design ensures a maximum cross-correlation of '1' between any two codes. The performance metrics studied are the probability of error due to multiple-access interference for different numbers of active users and optimum temporal length for different values of cardinality. The performance analysis shows that the proposed 2D design offers very low probability of error due to multiple-access interference at lower cardinality when compared with other 2D designs using equivalent code dimension. A comparison of the proposed 3D design with an existing 3D design shows better performance at lower cardinality. The 3D designs show better performance when compared with the 2D designs.     

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.     

多波长光网络的动态路由等效算法

针对多波长光网络的特点，提出了一种动态路由和波长分配的等效算法。采用波长图、增加虚拟源节点和目的节点等技术，把多波长网络转化为等效的单波长网络，避免了求解路由和波长分配两个复杂子问题，简化了算法的程序设计。利用最短径算法进行路由和波长分配可以求得问题的最优解，从而有效地降低了网络阻塞率。仿真结果表明：与FAR-2D算法相比，在4和8波长的全波长转换网络中，采用等效算法阻塞率最大降幅分别达到0．02、0．025。     

Multi-user adaptive orthogonal frequency-division multiplexing system for indoor wireless optical communications

An adaptive orthogonal frequency-division multiplexing (OFDM) system is proposed for multi-user communications over indoor wireless optical channels. The designed system uses multi-user least-squares detection techniques applied to space-division multiple access and OFDM schemes, in conjunction with angle-diversity reception. The system, which does not present an excessive increase in complexity with respect to the previous schemes, can support high bit rates for multiple users, beyond 100 Mbits/s. It also mitigates the channel fluctuations induced when either the space distribution or the number of emitters and receivers varies. The performance of the new proposed scheme is compared with that of a non-adaptive multi-user system and an adaptive single-user system, both described in the previous works, when they face similar environmental situations. The obtained results show a significant enhancement with respect to both the previous multi-user system and the adaptive single-user one, since the new scheme allows adaptively managing the system throughput on a multi-user environment     

光波导位相调制技术产生多波长光源

用Matlab软件模拟分析了高频光波导电光位相调制器的输出光谱特性。结果表明,在一定频率的微波源作用下,单色光通过光波导位相调制器后会产生光频谱展宽,展宽光谱中包括中心波长及各阶光边波带。随位相调制深度加大,边波带数目增多,光谱展宽增大;位相调制深度为3.3时,10dB展宽光谱中含边波带数为8个。实验制作了光波长1．55μm、微波频率10GHz的铌酸锂电光波导位相调制器;输出光谱中可清楚观察到正负三阶等频率间隔的边波带,即可实现七路光源输出,由此提出并验证了光波导位相调制技术用作多波长光源的可能性。利用位相调制器的光频谱展开得到多波长光源,具有成本低．易实现、促进系统集成等优点,有良好的应用前景。     

Laser-induced fluorescence detection system for microfluidic chips based on an orthogonal optical arrangement

In this work, a simple LIF detection system based on an orthogonal optical arrangement for microfluidic chips was developed. Highly sensitive detection was achieved by detecting the fluorescence light emitted in the microchannel through the sidewall of the chip to reduce scattered light interference from the laser source. A special crossed-channel configuration, with a 1.5-mm distance from the separation channel to the sidewall of the glass chip, was designed in order to facilitate collection of emitted fluorescence light through the sidewall. The significant difference in intensity distribution of scattered laser light on the chip plane observed in this study was fully exploited to optimize S/N ratio of detected signals by rejection of scattered light, both through systematic measurements and employing ray-tracing simulation. A fluorescence collection angle of 45 degrees in the chip plane gave the best result, with a scattered light intensity 1/38 of that obtained at an angle of 90 degrees. Sodium fluorescein and fluorescein isothiocyanate-labeled amino acids were used as model samples to demonstrate the performance of the LIF system. A detection limit (S/N = 3) of 1.1 pM fluorescein was obtained, which is comparable to that of optimized confocal LIF systems for chip-based capillary electrophoresis. Apart from the high detection power, the system also has the advantages of simple optical structure, compactness, and ease in building.     

Noncanonical vortex transformation and propagation in a two-dimensional optical system

We produced an axial and canonical optical vortex by using a computer-generated hologram and then converted it to a noncanonical vortex by passing it through a cylindrical lens. We conducted an experimental study of the shape and trajectory of the noncanonical vortex as it propagates in free space and obtained an analytical expression explaining our experimental results. The computed trajectory and shape of the noncanonical vortex agree quite well with our experimental results.     

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.     

Simulation-based performance analysis and improvement of orthogonal frequency division multiplexing - 802.11p system for vehicular communications

In this study, the physical layer (PHY) of the upcoming vehicular communication standard IEEE 802.11p has been simulated in vehicle-to-vehicle situation through two different scenarios. IEEE 802.11p wireless access in vehicular environment defines modifications to IEEE 802.11 to support intelligent transportation systems applications. The standard is being considered as a promising wireless technology for enhancing transportation safety and provides safety-related services like collision avoidance and emergency breaking. At first, this includes data exchange between high-speed vehicles and between the vehicles and the roadside infrastructure in the licensed ITS band of 5.9 GHz. Performance analysis of PHY model has been evaluated into different propagation conditions (AWGN, Ricean and Rayleigh fading). In particular, bit error rate (BER) and signal to noise ratio for all the data rates have been estimated. Simulation results reveal that our system can efficiently mitigate inter-symbol interference and inter-carrier interference introduced by multi-path delay spread in our high mobility environment but against frequency-selective fading BER values are on to increase. To overcome this problem, the authors propose to use a different value of guard interval (3.2 μs). Our initial results indicate that the performance with the larger cyclic prefix outperforms the performance of the initial value in our mobile channel profiles. Moreover, the authors investigated in which way the Doppler spread affects the performance with regard to the transmission distance.     

Multistage decoding for an internally coded fibre-optic time-hopping/optical code division multiple access communication system

A multistage decoder for the internally convolutionally coded fibre-optic time-hopping code division multiple access system recently introduced is considered. In this system, the decoder consists of several stages. The first stage is implemented using one of the single-user decoders introduced. The following stages are maximum likelihood (ML) decoders each of which use the decisions made by the previous stage. The performance of the proposed decoder is evaluated by a Monte Carlo simulation. Numerical results show that a multistage decoder with only two stages greatly outperforms the single-stage decoder with negligible increase in complexity. The authors also derive the Chernoff bound for the ML decoder with known interference, which is the ultimate performance of the multistage decoder.     

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.     

Strict optical orthogonal codes for purely asynchronous code-division multiple-access applications

Strict optical orthogonal codes are presented for purely asynchronous optical code-division multiple-access (CDMA) applications. The proposed code can strictly guarantee the peaks of its cross-correlation functions and the sidelobes of any of its autocorrelation functions to have a value of 1 in purely asynchronous data communications. The basic theory of the proposed codes is given. An experiment on optical CDMA systems is also demonstrated to verify the characteristics of the proposed code.     

A simple, robust orthogonal background correction method for two-dimensional liquid chromatography

Background correction is a very important step that must be performed before peak detection or any quantification procedure. When successful, this step greatly simplifies such procedures and enhances the accuracy of quantification. In the past, much effort has been invested to correct drifting baseline in one-dimensional chromatography. In fast online comprehensive two-dimensional liquid chromatography (LC×LC) coupled with a diode array detector (DAD), the change in the refractive index (RI) of the mobile phase in very fast gradients causes extremely serious baseline disturbances. The method reported here is based on the use of various existing baseline correction methods of one-dimensional (1D) liquid chromatography to correct the two-dimensional (2D) background in LC×LC. When such methods are applied orthogonally to the second dimension ((2)D), background correction is dramatically improved. The method gives an almost zero mean background level and it provides better background correction than does simple subtraction of a blank. Indeed, the method proposed does not require running a blank sample.     

Preservation of diagnostic information in synthesis of ECG signals for a standard lead system from signals measured by an orthogonal frank system: Minnesota code criteria

We show that using the three best known matrices for synthesis of ECG signals and their diagnostic interpretation in terms of the Minnesota code unfortunately cannot be considered valid. Translated from Izmeritel'naya Tekhnika, No. 4, pp. 68–71, April, 1997.     

Improvement of spectral efficiency based on spectral splitting in photonic quantum-well structures

The multiple photonic quantum-well structures are proposed by breaking the periodicity of a one-dimensional photonic crystal, in which the effect of spectral splitting is clearly observed. On the basis of the finite-difference time-domain method, the physical origin of the spectral splitting is explained, and the regularity of the formation of the multiple peaks is analysed. It is also found that both the well and barrier thicknesses have a marked influence on the positions and the number of the split peaks, and their relationships are carefully discussed. By using these proposed structures, the number of transmission peaks can be increased multiplicatively, and their spectral spacing can be finely tuned, resulting in high efficient utilisation of photonic band gap.     

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).}     

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。     

Power distribution in two-dimensional optical network channels

The power distribution in two-dimensional optical network channels is analyzed. The maximum number of allowable channels as determined by the characteristics of optical detector is identified, in particular, for neural-network and wavelet-transform applications.     

Nonlinear optical responses in two-dimensional photonic crystals

A two-dimensional (2D) highly nonlinear lithium niobate (LN) photonic crystal (PhC) waveguide is fabricated with the aim of studying its nonlinear optical properties. We show a large enhancement of the second-harmonic generation (SHG) in the 2D LN PhCs, originating from resonance between the external pump laser field and a photonic band mode. The SHG enhancement results agree well with the experimental photonic band structure obtained by an angle-dependent optical reflectivity and the theoretical band structure generated by three-dimensional finite-difference time-domain calculations. These results open new possibilities for the use of 2D LN PhC waveguide in integrated nonlinear optical applications.