High efficiency wireless optical links in high transmission speed wireless optical communication networks

Power link budgets are prepared for wireless optical communication systems to illustrate the optical losses that happen during transmission. This paper has presented optical wireless links, which offer ultra multi gigabit per second data rates and low system complexity. For ground space and/or terrestrial communication systems, these links suffer from atmospheric loss mainly due to fog, and scintillation. Optical wireless links provide high bandwidth solution to the last mile access bottleneck. However, an appreciable availability of the link is always a concern. Wireless optical links are highly weather dependent, and fog is the major attenuating factor reducing the link availability. Link margin, received signal power, transmission bit rate, bit rate distance product, signal‐to‐noise ratio, and BER are the major interesting design parameters in the current study. Copyright © 2013 John Wiley & Sons, Ltd.     

A cross-layer optimized adaptive modulation and coding scheme for transmission of streaming media over wireless links

In this paper, a novel cross-layer Adaptive Modulation and Coding scheme that optimizes the overall packet loss (by both transmission errors and excessive delays) probability under a given arrival process is developed. To this end, an improved Large Deviations approximation for the fraction of packets that suffer from excessive queuing delay is proposed. This approximation is valid for G/G/1 queues with infinite buffers that are driven by stationary arrival and service processes which satisfy certain conditions. Such models can capture the time correlations in the amount of traffic generated by streaming media sources and the time varying service capacity of a wireless link. Through numerical examples, the proposed AMC policy is shown to achieve a significant reduction in the overall packet loss rate compared to previously proposed schemes. This algorithmic performance gain can be translated into a sizeable decrease in the required transmit power or an analogous increase in the rate of the arrival process, subject to a given maximum packet loss rate Quality of Service constraint. Furthermore, the proposed AMC policy can be combined with ARQ in order to achieve an even lower overall packet loss probability.     

Evaluation of 4-Gbit/s optical fiber transmission distance with direct and external modulation

Transmission characteristics for a recently modulated measured distributed-feedbacked (DFB) laser and an externally modulated DFB laser using a Ti:LiNbO/sub 3/, Mach-Zehnder modulator at 4 Gb/s are discussed. The transmission characteristics are estimated by an advanced eye-pattern analysis method. The maximum measured fiber dispersion with a directly modulated laser is 100 to 140 ps/nm when the chirp power penalty is 1 dB. However, for external modulation, there is no power penalty after transmission over a 2220-ps/nm dispersive fiber. This confirms that external modulation has superior transmission characteristics. The modulation scheme for 4-Gb/s systems in terms of these results is discussed.<>     

基于Nyquist脉冲副载波调制的短距离光纤传输技术研究

提出了一种适用于强度调制直接检测(IM/DD) 光系统的信号调制格式。这种基于Nyquist脉冲half cycle副载波调制(SCM)信号能有效提高频谱效率,为了减少传递函数引起的系统的性能 恶化,采 用了数字预均衡和后均衡实现对光纤损伤的补偿;建立了偏振复用(PDM)IM/DD系统 平台, 分析了Nyquist脉冲SCM信号在系统中的PAPR性能,实现了72Gbit/s 64-QAM N yquist脉冲SCM信号经过20km标准单模光纤(SMF)传输后其误码性能 小于前向纠错(FEC)阀值3．8×10－3。     

光纤传输在脱靶量测量系统中的应用

在某脱靶量测量系统中,在测量雷达和测量数据处理、存储模块之间必须实现50m距离分离,根据使用要求,利用一个光收发器HFBR5208和一个串行/解串行芯片TLK1501设计实现了一种光纤传输摸块,详细介绍了DSP硬件实现和传输差错控制方法,在实际应用中达到了预期目的.     

Extending transmission distance of high-density WDM systems usingpost transmitter fiber Raman amplifiers

The authors investigate the behavior of multichannel signals in a high-density wavelength division multiplexing (WDM) system with the consideration of stimulated Raman scattering. A parameter to evaluate the depth of Raman crosstalk is provided, and the transmission distance limitation imposed by Raman crosstalk is analyzed. To extend the system transmission distance, a post-transmitter fiber Raman amplifier is used. The allocation of signal channels on the pump gain profile is discussed. It is found that there exists an optimum pump power which results in a maximum amplifier gain. The example shows that the transmission distance limitation imposed by Raman crosstalk can be extended by 20 km for a 30-channel system with 0.25-dB/km fiber loss     

Video transmission in optical fiber communication systems usingpulse frequency modulation

A design procedure has been developed to determine the required operating conditions for a pulse-frequency modulation (PFM) system (modulation index, required system bandwidth, and receiver carrier-to-noise ratio (CNR) for a specified receiver SNR (signal-to-noise ratio) and number of clicks per second. The PFM processing gain (=SNR/CNR) was measured to be 40 dB for a modulation index of β=2.5, which agrees closely with the theory. The theoretical processing gain advantage of PFM over FM is 15.9 dB for a modulation index of β=2.5 with receiver bandwidth B_rx =50 MHz     

短距离通信中的塑料光纤无源器件技术

阐述了塑料光纤的真正优势在于其器件和连接的低价与便捷.着重介绍应用在短距离通信中的塑料光纤无源器件的研究进展,包括塑料光纤连接器、耦合器、塑料光纤放大器、塑料光纤光栅等.分析比较各种器件的技术特点,并指出今后面临的问题与挑战.     

基于OFDM调制和Nyquist滤波的超宽通道大容量光传输

文章首先概述了产生超宽通道的行业背景,接着介绍了产生超宽通道的两种主要方式;分别阐述了OFDM(正交频分复用)调制方式和Nyquist(奈奎斯特)滤波方式的基本原理和产生途径,分析了这两种方式的优劣特点并进行了比较;最后综述了两种方式的研究现状及今后展望。     

高精度远程光纤传输延时测量系统研究

介绍了当前的光纤传输延时测量方法和发展现状,针对远程光纤传输延时测量设计了一种高精度的测量系统,详细地阐述了系统的总体设计、工作机理及关键技术的解决等方面问题,最后介绍了系统的验证实验方法和系统所能达到的测量精度.     

光纤传输光电检测脉冲间隔与宽度双重调制

文章给出了脉冲时间调制的分类方法及实现方案。推导了非同步型脉冲间隔与宽度双重调制（ Ｐ Ｉ Ｗ Ｍ） 的频谱及其特点。说明了 Ｐ Ｉ Ｗ Ｍ 是模拟信号测量的一种经济有效的调制方法,在光纤传输光电检测中有广泛应用前景     

Bidirectional optical fiber transmission systems using Ramanamplification

Bidirectional optical fiber transmission systems using Raman amplification are discussed. Analytical expressions for signals amplified by both forward and backward Raman scattering are presented. It is found that there exists an optimal pump power for the maximum unrepeated transmission length in a bidirectional system and that the maximum length is about 450 km, which is about the same as that of the unidirectional system     

Nondestructive optical fiber modulation using radiation modecoupling phenomena

We demonstrate a nondestructive optical fiber modulation technology based on a radiation mode coupling (RMC) interference effect that modulates the phase difference between a guided mode and recoupled radiation modes. Because of high sensitivity of the RMC effect in the buffer layer, deep signal modulation in frequency region to the order of MHz is successfully generated by applying slight lateral deformation of a few μm to the fiber with the piezoelectric device. Modulation index of 30 was achieved for an applied voltage of 14 V_pp and no signal fading was observed for all the states of polarization. This technique enables a free access modulation at any points along optical fibers with a wide frequency band response and low applied voltages and requires no complex composition such as polarization diversity     

Millimeter wave narrowband optical fiber links using externalcavity semiconductor lasers

We present the theoretical analysis and the experimental implementation of a narrowband millimeter wave optical fiber communication system using an external cavity semiconductor laser. We derive analytic expressions and present experimental data for the modulation response, relative intensity noise, carrier-to-noise ratio, and harmonic distortion for a semiconductor laser in an external cavity operating as a transmitter in the millimeter wave frequency range. We present a system implementation of this capable of transmitting 40-Mbt/s digital data at a 35-GHz subcarrier frequency with bit-error rates below 10^-9 over a 6.3-km-long optical fiber link     

Multiple-subcarrier modulation in optical wireless communications

This article overviews multiple-subcarrier modulation techniques in optical wireless communications. The basic principles and characteristics of MSM techniques in optical wireless communications are presented. MSM optical wireless systems are explained where some block codes that convert information bits to be transmitted to the symbol amplitudes of subcarriers are used to increase the minimum value of the MS electrical waveform. MSM optical communications systems using subcarrier signal point sequences (SSPS) that can improve the power efficiency of MSM systems are also explained. The performance of MSM optical communications systems is presented in the intensity modulation with direct detection (IM/DD) channel without dispersion and in atmospheric optical communications where the effects of scintillation exist.     

Phase shift keying using optical delay modulation formillimeter-wave fiber-optic radio links

We propose a novel phase shift keying technique that uses optical delay modulation for fiber optic radio links. Using only a 2×1 switch and a delay line, this technique enables modulation of a millimeter-wave carrier at bit rates of several gigabits per second or higher, where high-speed devices are not needed. Binary phase shift keying (BPSK) was experimentally demonstrated, 2-Gb/s data signal on a 40-GHz carrier was transmitted over a 5-km optical fiber without any error. The coherent crosstalk noise, due to insufficient extinction ratio of optical switches, was evaluated. The BPSK modulation technique can he extended to multiphase shift-keying modulation     

FM subcarrier fiber optical transmission system design and itsapplication in next-generation wireless access

This paper presents a design method of optical frequency modulation (FM) subcarrier (with super carrier) transmission modem. The nonideal link characteristics, including laser chirping, fiber dispersion, voltage controlled oscillator (VCO) phase noise, relative intensity noise (RIN), and equivalent network model of laser diode of such a system that may bring about signal distortion are discussed first. We then propose a hierarchical methods to establish the system equivalent model. Finally this FM modem is applied to a GSM wireless system, in which multichannel signals are transmitted over fiber between radio port and basestation, and system performance is appraised by its dynamic range. It is found that optical FM subcarrier (with super carrier) transmission technique can improve the system dynamic range, compared with the intensity modulated direct detection (IMDD) method, and this is a economical and efficient method     

OTDR in optical transmission systems using Er-doped fiber amplifiers containing optical circulators

Fault location in optical amplifier transmission systems is described. Optical time-domain reflectometry (OTDR) cannot be used for an optical transmission line containing traditional Er-doped fiber amplifiers (EDFAs) because they contain optical isolators. The authors propose an OTDR scheme that uses new EDFAs containing optical circulators and return transmission lines. The new EDFAs support both OTDR and digital signal transmission. A 280.9 km transmission line containing three of the proposed EDFAs was constructed and tested. Experimental results demonstrated the feasibility of OTDR fault location and 1.8-Gb/s digital signal transmission.<>     

High-performance optical phase modulation using piezoelectricZnO-coated standard telecommunication fiber

Optical phase modulation in a standard telecommunication fiber coated with a piezoelectric ZnO jacket has been investigated both experimentally and theoretically. The frequency response of the modulator exhibits 18 peaks between 20 and 800 MHz, which correspond to radial resonances of the coated fiber composite. A theoretical model was developed to explain the experimental results. The model takes into account the geometry of the modulator, nonuniform strain distributions, and the structure of the ZnO film. The calculated positions of the resonances and cancellation of phase modulation at frequencies higher than 800 MHz agree well with the measured data. The analysis also demonstrates the capability of tuning the resonances positions by varying the thickness of the ZnO jacket or the metal electrodes     

Cross-phase modulation in fiber links with multiple opticalamplifiers and dispersion compensators

We have theoretically and experimentally investigated the cross-phase modulation (XPM) effect in optical fiber links with multiple optical amplifiers and dispersion compensators. Our theory suggests that the XPM effect can be modeled as a phase modulator with inputs from the intensity of copropagating waves. The frequency response of the phase modulator corresponding to each copropagating wave depends on fiber dispersion, wavelength separation, and fiber length. The total XPM-induced phase shift is the integral of the phase shift contributions from all frequency components of copropagating waves. In nondispersive fibers, XPM is frequency-independent; in dispersive fibers, XPM's frequency response is approximately inversely proportional to the product of frequency, fiber dispersion, and wavelength separation. In an N-segment amplified link, the frequency response of XPM is increased N-fold, but only in very narrow frequency bands. In most other frequency bands, the amount of increase is limited and almost independent of N. However, in an N-segment amplified link with dispersion compensators, the frequency response of XPM is increased N-fold at all frequencies if the dispersion is compensated for within each fiber segment. Thus, the XPM-induced phase shift is smaller in systems employing lumped dispersion compensation than in systems employing distributed dispersion compensation