All optical wavelength converter and its application in optical network

All optical network （AON） is a hot topic in recent studies of optical fiber communications. Key techniques in AON include optical switching/routing, optical cross connection （OXC）, all optical wavelength conversion （AOWC）, all optical buffering, etc. Opti- cal switching/routing is in fact wavelength switching/ routing. OXC and wavelength conversion （WC） are introduced into cross nodes so that a virtual wavelength path is established. With WC, communication route is formed only if there is unused wavelength in an individual segment link. The rate wavelength usage is thus greatly increased. The blocking rate of network can be reduced by adding WCs, especially for huge capacity multiple nodes ones. Therefore, WC has attracted much attention in basic research of optical communication and is used in some experimental networks.This dissertation studies all optic wavelength conversion and its application, with the contributions in the following five aspects.

Module 3 Body Language and Non-verbal Communication

(满分120分;时间80分钟)第一部分听力(共两节,满分20分)第一节(共5小题;每小题1分,满分5分)听下面5段对话。每段对话后有一个小题,从题中所给的A、B、C三个选项中选出最佳选项,并标在试卷的相应位置。听完每段对话后,你都有10秒钟的时间来回答有关小题和阅读下一小题。每段对话仅读一遍。

Advanced modulation formats for underwater visible light communications [Invited]

In this paper, we present a detailed comparison of applying three advanced modulation formats including carrierless amplitude and phase modulation（CAP）, orthogonal frequency division multiplexing（OFDM）, and discrete Fourier transform spread orthogonal frequency division multiplexing（DFT-S OFDM） in underwater visible light communication（UVLC） systems. Cascaded post-equalization schemes are suggested to compensate the system impairments. For the first time, a two-level post-equalizer is presented to mitigate the nonlinear effect and improve the system performance of UVLC. The first post-equalization is based on a novel recursive least square Volterra. These modulation formats are all experimentally demonstrated with corresponding digital signal processing（DSP） algorithms. The experimental results show that single carrier modulations including CAP and DFT-S OFDM can outperform OFDM. Our experiment results show that up to 3 Gb/s over a 1.2 m underwater visible light transmission can be achieved by using DFT-S OFDM 64 QAM and CAP-64. The measured bit error rate is well under the hard decision-forward error correction（HD-FEC） threshold of 3.8 × 10;.

PDM-DPSK-MPPM hybrid modulation for multi-hop free-space optical communication

A hybrid polarization division multiplexed-differential phase shift keying-multipulse pulse position modulation(PDM-DPSK-MPPM) scheme for multi-hop free-space optical(FSO) communication is investigated. The analytical bit error rate(BER) of the proposed system in Gamma-Gamma turbulence channels is derived and verified using computer simulation. The results show that both multi-hop and hybrid modulation schemes are efficient techniques to improve the performance of FSO links. Compared with the traditional binary phase shift keying(BPSK) and MPPM, the hybrid scheme can improve the bandwidth-utilization efficiency and reliability of the system. Compared with the coherent demodulation of PDM-QPSK-MPPM, the system complexity is reduced at the cost of the degradation of BER performance, which can improve the practicality of hybrid modulation technology in FSO system.

A method of multichannel chaotic phase modulation spread spectrum and its application in underwater acoustic communication

Direct-sequence spread spectrum （DSSS） communication possesses low probability of detection and has been widely used in confidential communications. However, pseudo-noise （PN） sequences, used as spreading code in conventional DSSS communications, possess peri- odic character and binary value. In hostile environments, these distinct characters may lead to some important parameters of signals being estimated accurately, and then lead to the leakage of transmitted information. To solve the problem, we propose the chaotic phase modulation （CPM） sequence alternating the PN sequences. CPM sequence has complex values and constant envelope, and also possesses large quantity and good correlation characteristics. Moreover, it has more hidden features than conventional sequences by modulating its phases using chaotic sequence. To improve the data rate, we apply it into the technique of multichannel communica-tion. Simulation results show this scheme＇s superior bit error ratio （BER） performance, which demonstrates its feasibility in underwater acoustic communications.

Realization of OFDM modulation and demodulation for visible light communication based on FPGA

In order to ensure stable,correct and real-time high-speed transmission of indoor visible light communication(VLC),the key modulation and demodulation technologies of orthogonal frequency division multiplexing(OFDM) are studied in this paper. The time-domain synchronization,frequency synchronization and channel equalization of receiver are analyzed and optimized by utilizing short and long training preamble. Moreover,field programmable gate array(FPGA) development board(Xilinx Kintex-7) and Verilog hardware description language are used to realize the design of proposed OFDM-VLC system. Simulation and experiment both verify the feasibility of the hardware designs of this system. The proposed OFDM-based VLC system can process signal in real-time,which can be used in actual VLC application systems.