Low-loss pure-silica-core fibers and their possible impact on transmission systems

Low-loss optical fibers are now indispensable transmission media for transmission systems. Recently, the ultralow-loss performance for long transmission systems, the water-loss-free performance for wide-band wavelength-division-multiplexing (WDM) systems, the hydrogen-loss-insensitive performance for system reliability, and the bending-loss-insensitive performance for access or indoor applications have attracted much interest. In this regard, pure-silica-core fibers (PSCFs) are suitable, and unprecedented low-loss PSCFs have been successfully fabricated. This paper introduces the recent progress of low-loss PSCFs and their possible impact on transmission systems.     

Experimental 1.5 μm coherent optical fibre transmission systems

The authors consider the design requirements for 1.52 μm coherent optical fibre transmission systems. Some of the essential requirements are: narrow linewidth sources, polarisation stable transmission media, low insertion loss optical mixers and frequency tracking or phase locked local oscillators. Having been successful in reducing the linewidth of semiconductor lasers to less than 30 kHz, by using injection locking techniques, and in fabricating optical mixers with insertion losses of the order of dB, they have been able to experiment with coherent optical fibre transmission systems to assess their practicability. In this paper it will be shown that coherent systems can be operated over long lengths of conventional low loss monomode fibre without any polarisation penalty and give far better performance than direct detection systems.     

Reliability of optical components for use in submarine optical fiber transmission systems

This paper presents the reliability test results for LD modules, optical couplers, and APD modules, which are fabricated through methods for achieving and assuring a high degree of reliability for use in 400-Mbit/s submarine optical fiber transmission systems. In particular, the paper presents methods for evaluating the optical component reliability as well as an investigation into the degradation factors in the coupling circuits. From the reliability test results obtained, the paper also discusses the mechanism and test acceleration of wear-out degradation following reliability tests conducted for more than 8000 h on the fabricated optical components. These optical components are consequently confirmed to be highly reliable for a system life of 25 years.     

Reliability-Growth Programmes For Undersea Communication Systems

This paper deals with the unique problems encountered when managing reliability growth programmes on expensive capital equipment components destined for use in a relatively inaccessible environment. Continuous operation of these components in predominantly non-redundant configurations is required for up to 25 years; and repair costs and/or lost revenues incurred by single failures at anytime during this period can amount to several $100 000. After a brief review of the history and philosophy of reliability growth programmes on components for coaxial cable systems, the planning, development, and implementation of reliability assurance procedures for undersea systems designed for 1.3 ?m optical transmission at 280 Mbit/s are addressed. The challenge involved in proving electro-optic and electronic components suitable for undersea optical PCM systems is not to be underestimated. Even in a relatively benign environment, these systems have specific problems with respect to operating temperatures, voltage stresses, heat dissipation factors, and the lack of escape routes for trapped contaminants. The components themselves are not only relatively new, or just emerging from the development phase, they also demand innovative reliability assessment techniques because of the inadequacy of traditional methods of accelerated testing. This paper gives an insight into some of these problems from a reliability management viewpoint. It is increasingly evident that QC and RA programme leadership cannot now, if it ever could, be accomplished without detailed knowledge of sophisticated component design.     

Optical Digital High-Speed Transmission: General Considerations and Experimental Results

Laboratory experiments on digital optical transmission systems at bit rates of 1 and 2 Gbits/s are described. Systems with graded-index and single-mode fibers in the optical short and long wavelength region were investigated. All systems include complete circuits for clock and signal regeneration. Special emphasis was laid on the development of electronic circuits for gigabit signal processing and on the investigations of the noise sources of the optical channel, which appear especially pronounced in broad-band systems. The experimental results confirm the possibility to set up reliable high-speed optical transmission systems under laboratory conditions with available components. The remaining problems are of optical and not of electronic nature, despite the fact that monolithic integrated circuits for gigabit applications are hardly commercially available today.     

Optical time division multiplexing: systems and networks

The recent advances in optical time division multiplexed (OTDM) systems and components research show the technique to be highly suited to the generation and transmission of high capacity data on a single optical carrier. This approach uses a single wavelength to carry capacities of at least 40 Gb/s. Such systems are based on a clock frequency and tributary data rates which are easily accessible using electronic components. Short optical pulses are used in a return-to-zero data transmission format with temporal interleaving to map a number of optical data channels into a single electronic clock cycle. It is an approach that can be used to achieve extremely high data-rate bit interleaved systems. This article summarizes the developments in this field and outlines a possible methodology to evolve transport networks to encompass the potential that both WDM and OTDM have to offer     

Nonlinear surface waves on the interface of two non-Kerr-likenonlinear media

In recent years, there has been growing interest in studying nonlinear guided-wave propagation as they present potential, yet not fully-explored, applications for high-speed optical signal processing and transmission. In this paper, analytical solutions for nonlinear surface waves on the interface of two nonlinear non-Kerr-like media are derived. The dispersion relations and their relations to the transmission power and initial field distributions are calculated. Several observations are made on the behaviors of the surface waves and their potential applications     

Fiber Optic Video Transmission Employing Square Wave Frequency Modulation

Investigations are carried out on the performance of video transmission systems employing square wave frequency modulation (SWFM). A simple formula for the signal-to-noise ratio (SNR) in the SWFM video transmission systems is derived. The SNR performance is compared to that of frequency modulation (FM) and pulse frequency modulation (PFM). SWFM is shown to display the greatest receiver sensitivity when the fiber 6 dB bandwidth is less than 100 MHz. Video transmission experiments demonstrate the advantages of the SWFM, including 1) degree of simplicity in modulation/demodulation circuits as well as in optical transmitter and receiver circuits, 2) tolerance to nonlinearities in the system, and 3) insensitivity to the fiber baseband frequency-phase characteristics. Both the theoretical and experimental results have made clear the superiority of SWFM optical video transmission systems in application to CATV distribution systems and subscriber loop systems.     

Fundamental limitations caused by RF propagation

Propagation phenomena affect the design of radio frequency (RF) transmission systems. Propagation phenomena limit the suitability of portions of the frequency band for some applications, limit the reliability of RF transmission systems, and provide a means of coupling unwanted signals from one system to another with the potential of producing interference. The possiblity of interference is the fundamental limitation to the unrestricted use of the frequency band. Phenomena affecting suitability, reliability, and the potential for interference are considered for frequencies in the 1- to 300-GHz range.     

无线光DH-PIM与DPIM调制方式的性能研究

为了解决目前无线光通信采用的调制方式误包率大、传信率低等问题,研究了双头脉冲间隔调制(DH-PIM)和数字脉冲间隔调制(DPIM)的性能。分析了DPIM和DH-PIM两种调制方式的符号结构,比较了二者的传信率以及给定模型下的误包率。仿真与分析结果表明,DH-PIM的传信率较高,适合于实时性要求较高的传输系统,而DPIM的平均发射功率低,误包率较小,适合于要求低功率或高可靠性的系统。     

基于频域均衡的Tb/s级相干光单载波系统

对相干光单载波频域均衡系统(CO-SCFDE)、相干光单载波频分复用系统(CO-SCFDM)以及相干光正交频分复用系统(CO-OFDM)的理论和实验进行了对比研究,结果表明基于频域均衡的相干光单载波系统既保留了正交频分复用方式计算复杂度较低、频谱效率高和抗色散性能好的优点,又有效地减小了光纤非线性带来的传输损伤,是高速长距离光纤传输的一种有潜力的技术方案。     

Optical lithography stalls X-rays

The revival in optical lithography resulting from continuing advances in photoresists, phase-shifting masks, high-numerical-aperture step-and-repeat optical systems, multilevel-resist processing, and top-surface imaging techniques is discussed. Optical lithography is being used to make advanced IC chips, with 0.35 μm geometries in research, 0.5 μm in production. Ultraviolet (UV) light in the 200-400 nm range is the predominant system for IC manufacturing technology. Deep-UV lithography is not yet accepted for production processes, mostly due to the lack of commercially available positive and negative-tone photoresist systems for deep-UV wavelengths. In addition, negative-tone resists are temperature-sensitive and therefore hard to handle in a manufacturing environment, extensive gas-handling facilities are required for deep-UV excimer laser sources, and optical components have to be replaced often because the intense laser energy devitrifies lenses quickly     

A remote supervisory system based on subcarrier overmodulation forsubmarine optical amplifier systems

A supervisory (SV) signal transmission scheme for long haul optical amplifier systems is described. The scheme is based on subcarrier overmodulation of the line signal and features simple configuration; due to the use of EDFA gain modulation, no additive optical components are required in a submarine repeater to transmit a response signal. This paper discusses the subcarrier modulation index and frequency used for the SV signaling, the most significant design parameters. The dependence of the signal-to-noise ratio (SNR) on the modulation index in SV signal transmission is analyzed to clarify the modulation index value required for reliable SV signaling. In addition, the line signal impairment caused by subcarrier overmodulation is also analyzed to show the system's in-service feasibility. The subcarrier frequencies used for command and response signal transmission are discussed from the experimental results on the frequency response of an optical amplifier system and EDFA gain modulation efficiency     

The multi-hop multi-rate wavelength division multiplexing ring

Transparency of the optical layer offers the possibility to design a network that operates at varying transmission bit rates. While variable bit rate interfaces are being tested and will soon provide the possibility to optimally select the transmission rate for each optical channel, the potential advantages of relying upon multiple transmission rates in the optical network have yet to be fully explored. In this paper, we define the concept of multi-hop and multi-rate (M&M for short) network in which the tributary signal is transmitted over a concatenation of optical channels, with each optical channel operating at its own transmission rate. The optimal rate of each optical channel is determined by a number of factors including the end node's interface, amount of multiplexed traffic and cost of the network components. The potential advantages provided by the M&M network when compared to first generation optical networks (i.e., SONET/SDH), to single- and multi-hop (constant bit rate) optical networks, are discussed in general and demonstrated numerically in a WDM ring. Presented results show that the network cost reduction achieved by the M&M design is a function of the cost ratio between the optical bandwidth (wavelengths) and the optical terminals     

Photonic integrated circuits: A technology update

A photonic integrated circuit (PIC) monolithically integrates many optical components, such as lasers, modulators, detectors, attenuators, multiplexers, demultiplexers, and amplifiers, into a single photonic substrate and device. PICs thus provide important benefits for optical transmission systems, including packaging consolidation, increased system density, reduced power consumption, reduction in fiber couplings, and improved reliability.     

Tunnel generation and locking stimulated Raman radiation components

Stimulated Raman radiation is considered in a ring optical resonator. It is supposed that the resonator is partly filled with a condensed medium at the full length of the medium close to several tunnel lengths. A Raman-active medium and an optical waveguide are assumed to occupy a part of the condensed medium. The feasibility is shown of tunnel generation and synchronization of a great number of Stokes components of stimulated Raman radiation. Here, femtosecond light pulses are shown to be formed in a spacing adjacent to the Raman-active medium, the pulses being single over the periodT = 2pi/omega_{R}(ωRis the Raman frequency shift). Predicted and considered also are tunnel generation and locking of new light modes in an optical parametric oscillator. The effects are due to a correction for the dispersion of the full effective refractive index of the medium inside the resonator. Numerical calculations of the correction for a glass thin-film optical waveguide, quartz, and the Raman-active media CaCO3, C6H6, CS2inside the resonator are represented. Here, five or six Stokes components are shown to be generated and locked for CaCO3and C6H6, eight Stokes components for CS2. A similar numerical calculation is represented for the active medium LiNbO3in the corresponding optical parameteric oscillator. Here, new modes covering a frequency bandwidth of 5000 cm^-1are shown to be feasible. Noted and discussed is also a higher-order correction for the effective refractive index dispersion making it feasible to broaden the frequency bandwidth for tunnel generation and locking.     

Digital optical networks using photonic integrated circuits (PICs) address the challenges of reconfigurable optical networks

To reduce costs and simplify operations, carriers are deploying flexible optical networks that can be easily reconfigured and managed remotely. This article provides an overview of typical all-optical reconfigurable optical add/drop multiplexer (ROADM) systems and their associated network issues. We describe a novel digital optical network architecture based on digital ROADM systems, which use photonic integrated circuits (PICs) to overcome many of these issues. Digital ROADM systems use monolithic PICs to integrate over 60 discrete optical components, including lasers, modulators and detectors, into a single pair of optical components, allowing cost-effective optical-electrical-optical conversion at every node. This also allows key functions such as service reconfiguration, add/drop and protection to be implemented in the digital domain, and enables de-coupling of service provisioning from optical link engineering, termed bandwidth virtualization. Finally, key deployment, reliability and operational metrics for PIC-based digital ROADM systems are presented.     

Optical componentry utilized in field trial of single-mode fiber long-haul transmission

Realization of large-capacity long-haul transmission systems is now quite promising due to rapid development in the field of optical fibers. This paper describes single-mode fiber optical components for use in the above-mentioned system. In particular, LD modules and optical connectors are most important for construction of a practical system. Thus, they are explained in detail along with their development procedures. Important field trial results of these components are also presented.     

射频信号光纤传输技术研究现状及进展

随着现代战场中电磁环境的日趋复杂化,情报侦察、电子对抗、通信和遥感等系统中不同频率、制式的射频(RF)信号密集交叠,RF信号光纤传输技术所具有的宽带、抗干扰和信号损耗小等优势将在这些系统中发挥关键性的作用。概述了RF信号光纤传输技术的特点和优势,介绍了国内外的研究现状及进展情况,展望了RF信号光纤传输技术的发展前景。     

基于非正交多址的室内可见光通信系统性能优化方法

室内可见光通信(Visible Light Communication, VLC)系统常用的非对称限幅光OFDM(Asymmetrically Clipped Optical Orthogonal Frequency Division Multiplexing, ACO-OFDM)与直流偏置光OFDM(DC-biased Optical OFDM, DCO-OFDM)采用加循环前缀、信道均衡和载波复用等方法解决信道干扰及多用户复用问题,但均以牺牲有效性为代价。非正交多址(Non-orthogonal Multiple Access, NOMA)通过功率域复用提高频谱利用率,利用串行干扰消除(Successive Interference Cancelling, SIC)进行多用户信号处理,有效兼顾可靠性与有效性。将NOMA应用于室内可见光系统,建立基于NOMA-DCO-OFDM的可见光信号传输及信道增益模型。通过功率域多用户信道差异计算信道增益,进行功率分配实现功率域复用,提高系统容量和通信速率;利用SIC按功率分配算法对用户逐一解调,减弱信道干扰,提高可靠性。通过理论分析和仿真实验验证表明:该系统的通信速率达到6.8×107 bit·s?1,且合速率受用户数量的影响不显著。2用户下,误码率(Bit Error Rate, BER)为10?4时用户1有5.2 dB左右的性能提升,用户2有2.3 dB左右的性能提升,通信可靠性也明显提高。