A secure transmission scheme on link level for optical fiber communication systems

In secure communication systems, a very important problem is how to prevent wiretapping. Lots of researches on cryptography give good solutions on secure communications. But if a wire tapper can detect the existence of the transmitted information and get enough eavesdropped frames, cryptanalysis techniques can help to blindly recover the frame structures, error-control coding parameters and passwords. In this paper we propose a novel secure transmission scheme on the link level for optical fiber communication systems. Based on the blind frame synchronization technique, we propose to drop the traditionally strict frame structures in fiber communications and conceal the error-correcting-encoded blocks among random data, so that wire tappers cannot get enough coded packets to analyze and recover the transmitted information. Therefore, the proposed method is very suitable for secure communications and military communications.     

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.     

A high efficiency construction method of multilength optical orthogonal codes with correlation constraint two for OCDMA multimedia network

In order to construct multilength optical orthogonal codes (ML OOCs) with correlation constraint 2 for multi-rate OCDMA passive optical networks, a high efficiency construction method is presented. The main idea is to construct high efficiency mapping sequences to map optimal short length OOCs with cross correlation 2 into long length OOCs with cross correlation 2. Fundamental of constructing high efficiency mapping sequence is derived, and the mapping sequences based on multiplication table of integer domain is examined. Simulations based on the method show that the cardinality of long length OOCs is just slightly lower than Johnson bound. Therefore, it has very high variable length efficiency.     

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.     

Performance analysis of OTDM system in the presence of FEC using symmetric Mach-Zehnder switch

Optical time division multiplexing is an emerging and promising alternative for future high-speed photonic networks because of its ability to accommodate higher bit rate and flexible bandwidth. SMZ have been found to be the most suitable switching element than all the available de-multiplexing switches because of compact size, thermal stability, and low-power operation. In this paper, we simulate four channel OTDM systems (all-channel multiplexer and de-multiplexer) with a Mach-Zehnder modulator and an SMZ de-multiplexer to investigate the impact of FEC on the OTDM system. It is observed that the presence of FEC in OTDM transmission can greatly improve the system performance.     

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 model to characterize the effect of cross phase modulation on polarization in an optical fiber transmission system

This paper presents a model that described the process of inter-influence between cross phase modulation (XPM) and polarization effects such as polarization mode dispersion (PMD) and polarization dependant loss (PDL) in an optical fiber communication system. Previous papers have discussed PMD-PDL and PMD-XPM effects in separate models, but in this work we developed a model that is capable of characterizing and evaluating PMD, PDL and XPM simultaneously. From the model, we found that PMD and PDL can be affected by XPM. The presence of XPM changed the vector directions of PMD and PDL in Stokes space.     

从高等教育的发展到光学工程类专业研究型人才培养方案再调整的思考

浙江大学信息工程(光电)专业自1952年建立以来,为促进国家经济建设和光学工程学科的发展培养了大量的专业人才。21世纪之初,中国的高等教育进入了大众化阶段,科技的进步和社会的发展对光学工程学科人才的培养呈现出了知识多元化和能力专业化的需求,光电信息工程领域对高端研究型人才的培养要求呼之欲出。从中国高等教育的发展背景出发,分析了光学工程类本科人才培养的变迁和现状,介绍了浙江大学本科层次研究型人才培养的新模式,阐述了浙江大学信息工程(光电)专业的整体调整思路和培养方案。     

A Model for the Passive Infrared Detection of Naval Targets through FLIR: Model Description and Preliminary Results Applicable in the Eastern Mediterranean Sea

The maritime environment is a very unique system with respect to the environmental conditions that affect the transmission of electromagnetic energy, and especially the part of the spectrum that falls in the infrared band. This paper proposes an end-to-end model for the detection of ships at the environmental conditions of the eastern Mediterranean Sea, with the use of a Forward Looking Infrared (FLIR) system. The model: a) covers the issues regarding the detection and classification of simple model targets in various states of temperature conditions, by applying the Moser and O’Neill criteria, b) takes into account existing environmental conditions, by using data obtained from the Hellenic National Meteorological Service (HNMS) and the British Atmospheric Data Centre (BADC) for the years 2004–05, and c) uses the LOWTRAN 7 code for the calculation of the transmission through the maritime atmosphere. In the calculation of the atmospheric transmission, turbulence is taken into account through the introduction of a Modulation Transfer Function (MTF), to model the specific phenomenon. The FLIR system is also modeled as a series of MTF functions, with each one of those covering the characteristics of major subsystems of the detection device. Finally, the observer’s MTF is included in the model, and the probability of completing the specific task is calculated and presented for a range of observer to target distances. LOWTRAN computer model generated by the U.S. Air Force Geophysics Laboratory, is now in its 7th version and may be purchased in a PC version from the ONTAR Corporation, 9 Village Way North Andover 01845, Massachusetts. MATLAB and SIMULINK are registered trademarks of The Math Works Inc. 3 Apple Hill Drive, Natick 01760-2098 Massachusetts. S. E. Lagaras is currently pursuing the PhD degree in Electrical Engineering at the National Technical University of Athens.