Optical Transport Systems Research Articles

Theoretical and experimental study of passive spatiotemporal shaping of picosecond laser pulses

We report the results of theoretical and experimental studies on passive spatiotemporal shaping of cw mode-locked picosecond laser pulses for driving the photocathode of a high-brightness, high-current energy recovery linear accelerator. The temporal pulse shape is modified using birefringent crystals, while a refractive optical system is used to generate a flattop spatial beam profile. An optical transport system is designed and implemented to deliver the flattop pulse onto a photocathode sited 9 m away from the shapers. The alignment tolerances on the beam shaper and the temporal pulse stacker have been studied both theoretically and experimentally. The experimental results agree well with theoretical simulations.

CSO/CTB PERFORMANCE IMPROVEMENT BY USING FABRY-PEROT ETALON AT THE RECEIVING SITE

An externally modulated NTSC 77-channel erbium-doped fiber amplifier (EDFA)-repeated system employing Fabry-Perot (FP) etalon at the receiving site to improve system performance was proposed and demonstrated. In comparison with conventional externally modulated fiber optical CATV transport systems, good performance of carrier-to-noise ratio (CNR), composite second order (CSO), and composite triple beat (CTB) were achieved for the full channel band over a 100-km single-mode fiber (SMF) transmission. Our proposed systems are suitable for the long-haul fiber optical CATV transport systems.

PMD Compensation/mitigation techniques for high-speed optical transport

In high-speed long-haul optical transport systems with channel data rates at 40Gb/s and beyond, polarization mode dispersion (PMD) is one of the major obstacles that limits system performance. It is desired or in most cases required to increase the system tolerance to PMD through PMD compensation and mitigation. In this paper, we review the techniques of PMD compensation and mitigation, including per-channel based optical PMD compensators (PMDCs), analog and digital electronic PMDCs, and all-channel PMD mitigation using distributed fast polarization scrambling and forward error correction (FEC). With the emergence of digital coherent detection, the signal optical field becomes digitally available, enabling powerful digital PMDC techniques to be applied. Digital PMDC techniques in optical single carrier coherent systems and orthogonal frequency division multiplexing (OFDM) systems are briefly reviewed.

Intra-symbol frequency-domain averaging based channel estimation for coherent optical OFDM

We present an efficient channel estimation method for coherent optical OFDM (CO-OFDM) based on intra-symbol frequency-domain averaging (ISFA), and systematically study its robustness against transmission impairments such as optical noise, chromatic dispersion (CD), polarization-mode dispersion (PMD), polarization-dependent loss (PDL), and fiber nonlinearity. Numerical simulations are performed for a 112-Gb/s polarization-division multiplexed (PDM) CO-OFDM signal, and the ISFAbased channel estimation and the subsequent channel compensation are found to be highly robust against these transmission impairments in typical optical transport systems.

Optical fiber transport systems and networks: fundamentals and prospects

Abstract This article presents first the history of the optical fiber transport networks, from the introduction of the first high capacity systems in the 1990s to the 10 Gbit/s per channel WDM (Wavelength Division Multiplexing) systems deployed today, and the tremendous evolution of performance within this period. The effects of propagation in optical fibers and their consequences for optical system engineering, the architecture of today's optical transport networks, the choices made in France are recalled. We then have a look at the future of optical transport networks from an operator's point of view: the expected evolutions in terms of transmission system capacity and network architecture are presented. We conclude that capacity, transparency, and agility are the main drivers of the evolution of optical fiber transport systems and networks and that a lot of changes have yet to be expected in these domains during the next decade. To cite this article: M. Joindot, S. Gosselin, C. R. Physique 9 (2008).

Employing split-band and only one sideband techniques to improve fiber optical CATV system performance

A directly modulated NTSC 77-channel fiber optical CATV transport system based on split-band and only one sideband techniques is proposed and demonstrated. Good performances of carrier-to-noise ratio (CNR), composite second-order (CSO) and composite triple beat (CTB) were obtained in our proposed systems over a 100 km standard single-mode fiber (SMF) transmission. Since an expensive externally modulated transmitter, sophisticated optical single sideband (SSB) modulation and stimulated Brillouin scattering (SBS) suppression techniques are not used, it reveals an outstanding system with simplicity and economic advantages over that of an externally modulated transport system.

Special issue on mathematical methods in network management

Special issue on mathematical methods in network management

Reed-Solomon Turbo Product Codes for Optical Communications: From Code Optimization to Decoder Design

Turbo product codes (TPCs) are an attractive solution to improve link budgets and reduce systems costs by relaxing the requirements on expensive optical devices in high capacity optical transport systems. In this paper, we investigate the use of Reed-Solomon (RS) turbo product codes for 40Gbps transmission over optical transport networks and 10Gbps transmission over passive optical networks. An algorithmic study is first performed in order to design RS TPCs that are compatible with the performance requirements imposed by the two applications. Then, a novel ultrahigh-speed parallel architecture for turbo decoding of product codes is described. A comparison with binary Bose-Chaudhuri-Hocquenghem (BCH) TPCs is performed. The results show that high-rate RS TPCs offer a better complexity/performance tradeoff than BCH TPCs for low-cost Gbps fiber optic communications.

Transmission in optically transparent core networks

Optical fiber transmission systems have become critical in facilitating the rapid growth in high-speed services in the consumer and commercial markets. It is apparent that as higher-speed services, such as IPTV, become available there will be even greater demand for capacity in the distribution and core transport networks. Hence, it is no wonder that underlying optical transport infrastructures need to be scalable and robust to reliably and economically support these services. Service providers have long recognized the importance of transmission capacity in the design of their networks. However, technological limitations often obscure the role of transparency in meeting their requirements. We review and clarify the critical role that optical transparency will have in facilitating the types of optical infrastructures required to support future services and highlight the technologies that enable it. In particular, we summarize recent advances in broadband Raman amplification, transmitter and receiver technologies with advanced modulation formats, dispersion management, signal processing, reconfigurable optical add-drop multiplexing, and dense wavelength-division-multiplexed transmission with mixed 10, 40, and potential 100Gbits/s channels. Network planning tools that facilitate fast and optimal deployment of optical transport systems are also discussed.

Employing split-band technique and Fabry–Perot etalon filter to improve directly modulated fiber optical CATV system performances

We proposed and demonstrated a directly modulated NTSC 77-channel fiber optical CATV transport system using split-band technique at the transmitting site and Fabry–Perot (FP) etalon filter at the receiving site to improve system performance. Good performance of carrier-to-noise ratio (CNR), composite second-order (CSO), and composite triple beat (CTB) were obtained in our proposed systems over a 100-km standard single-mode fiber (SMF) transmission. Employing a FP etalon filter in fiber optical CATV transport systems is useful in real network, as it is simple, passive, and potentially low cost. This proposed system reveals an outstanding one with simpler and more economic advantages than that of externally modulated transport system.

Intelligent and Reliable Photonic Cross-Connect System Based on Overlay Model

We developed a carrier-based photonic cross-connect (PXC) system based on an optical switch, which provides wavelength-division-multiplexing transmission, generalized multiprotocol label switching, and optical-transport-network management. This system uses an overlay model in which the administrative authority between the client-network-element (NE) layer and the carrier's PXC layer is completely separated. The PXC system provides user-network interface signaling between the client NEs and the PXCs, which enables automatic optical path setting between the two client NEs through a PXC network. We considered new protection schemes for the PXC system and successfully carried out an experiment in a testbed network using one of the discussed schemes. The new concept of policy control in the control-plane management is introduced, and the feasibility of our PXC system is demonstrated. This system is promising as a prototype for a next-generation optical transport system. Furthermore, the PXC system will enable the creation of a new type of optical transport layer service, accommodate increased Internet traffic demand, and reduce network operation loads and costs for Internet service providers and carriers in the near future.

Directly modulated fiber optical CATV transport systems without optical amplification

We propose and demonstrate a repeaterless directly modulated fiber optical CATV transport system based on half-split-band and remote light injection techniques. Good performances of carrier-to-noise ratio (CNR), composite second order (CSO) and composite triple beat (CTB) were obtained over a 50-km single mode fiber (SMF) transmission without optical amplification. Our proposed repeaterless directly modulated fiber optical CATV transport systems are simpler and cost lower than conventional externally modulated ones.

The Realization of Large-Scale Photonic Integrated Circuits and the Associated Impact on Fiber-Optic Communication Systems

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Large-scale photonic integrated circuits (LS PICs) have been extensively deployed throughout the fiber optic communication network. This paper discusses the properties of the LS PICs, the interaction between them, and what is necessary to create an optical transport system that fully utilizes the properties of the LS PIC. </para>

Design and Architectural Concepts for Border Model Based IP/Optical Multi-Layer Service Networks

The bandwidth explosion ushered in by the popularity of the Internet has spurred the recent acceleration in the development and deployment of equipment supporting packet based broadband services. This coupled with the widespread deployment of WDM based Optical Transport Systems in the core network to satisfy the corresponding increase in capacity demand, has led network planners for tighter coordination between IP and Optical layers to increase reliability, robustness of next generation backbone network. In this paper, we propose a solution known as border model, which is tailored to address deployment concerns associated with GMPLS technology in existing networks. We extend our proposal to include, Border model based Multi-layer service network architecture, to provide coordinated multi-layer IP and Optical services, for different network design scenarios. Resource Control is an important aspect of multi-layer service networks. This paper examines next generation requirements for resource control, defines resource control architecture and presents some evaluation results for multi-layer recovery techniques in the context of Multi-layer service network based on border model.

ENHANCED NETWORK SIGNALING FOR 10 GIGABIT ETHERNET TO ACHIEVE A LAN-WAN SEAMLESS INTERFACE AND ITS IMPLEMENTATION IN THE PHY-LSI/TRANSCEIVER MODULE

This paper describes Inter-frame Ling Signaling (ILS) protocol technology and its implementation in a 10-Gigabit Ethernet (10GbE) physical layer (PHY) LSI and optical transceiver module. The ILS can realize SDH/SONET-compatible operations, administration, maintenance, and provisioning (OAM&amp;P) functions for PHY of 10GbE networks by inserting OAM&amp;P information in the inter-frame gap periods. The coding features include 10GbE PHY upper compatibility, error detection capability, and disparity neutral characteristics. The 10GbE PHY LSI with the ILS function was fabricated using 0.18-um SOI CMOS technology to achieve high-speed and low-power performance. The main features of the high-speed circuit design are an inductive-load buffer, high-speed clock and data recovery (CDR), and pre-emphasis/equalizer circuits. The LSI function meets IEEE 802.3ae specifications with the very low-power consumption of about 1.2W. An XENPAK transceiver with ILS function using the LSI was also fabricated to make it easy to implement the ILS function in optical transport network systems such as WDM, OADM, OXC systems and L2/L3 switches. The key features of the module include a 1.3-um DFB laser module with highly reliable transmission performance and a small EML driver integrated module. ILS protocol operation is verified by experiment with XENPAK modules emulating the optical transport system.

Simulation of power evolution and control dynamics in optical transport systems

The design and analysis of control strategies for high-capacity, reconfigurable optical transmission systems require an understanding of optical system dynamics involving the time-dependent interaction of many components. This paper describes system simulation software that couples continuous physical-layer models of optical transmission components with discrete models for events such as channel add/drops. The simulator computes detailed time traces of signal and noise power propagation along a line system consisting of multiple controlled transmission elements and monitoring devices in response to a particular discrete event. Examples are given illustrating the rich variety of experimentation modes the software supports, including the evaluation of control algorithms, systematic exploration of design parameters, and investigation of cost reduction plans. Details of the development effort are presented, illustrating the contributions of the optical physicists, applied mathematicians, system engineers, and computer scientists who were involved in this collaborative project.

Implementation of IPv6 services over a GMPLS-based IP/optical network

In recent days, there has been considerable interest in deploying IPv6-based services. Trial and commercial IPv6 services offering has already begun, especially in Japan, Korea, China, and other parts of the world. At the same time, many service providers have embraced MPLS as the enabler for the required multiservice capabilities of their next-generation packet networks. Also, the widespread deployment of DWDM-based optical transport systems in the core network to satisfy the tremendous need and increase in capacity demand has led network planners to reconsider traditional approaches to provisioning and network restoration, and plan integration of the optical layer into the MPLS infrastructure according to the emerging GMPLS technology. The purpose of this article is to discuss next-generation network architecture evolution and present a detailed architecture for transport of emerging IPv6 services and applications over next-generation GMPLS multiservice backbone networks. This article also presents an implementation and demonstration of this technique for IPv6 transport over a GMPLS backbone network as well as interoperability verification of IPv6 and GMPLS using a GMPLS network testbed.

Field trial of all-optical 40 Gbps transmission system for next-generation networks

The National Institute of Informatics (NII) has been conducting joint research with JapanTelecom to develop a 40 Gbps optical transport system for the next-generation SuperSINET. We report on the recent results of field trials focused on automatic chromatic dispersion compensation and path protection/restoration applied to the future SuperSINET as key technologies required to maintain the quality of transmission, to reduce operational costs, and to facilitate the enhancement of network capabilities. From the results of the field trial, we have confirmed that an automatic optical path control system is essential in an all-optical wavelength path network.

Large-scale photonic integrated circuits

100-Gb/s dense wavelength division multiplexed (DWDM) transmitter and receiver photonic integrated circuits (PICs) are demonstrated. The transmitter is realized through the integration of over 50 discrete functions onto a single monolithic InP chip. The resultant DWDM PICs are capable of simultaneously transmitting and receiving ten wavelengths at 10 Gb/s on a DWDM wavelength grid. Optical system performance results across a representative DWDM long-haul link are presented for a next-generation optical transport system using these large-scale PICs. The large-scale PIC enables significant reductions in cost, packaging complexity, size, fiber coupling, and power consumption.

Highly Spectral-Efficient Optical Code-Division Multiplexing Transmission System

A highly spectral-efficient transmission system based on optical code-division multiplexing (OCDM) technique is investigated. To meet the rapid increase in the demand of data bandwidth, spectral efficiency is becoming a key factor in optical transport systems. Several modulation formats along with the optical receiver design have been proposed to upgrade the spectral efficiency. OCDM is one of the promising techniques for this purpose. OCDM is the other class of multiplexing technique than optical time-division multiplexing and wavelength-division multiplexing (WDM). OCDM provides unique features such as asynchronous transmission, secure communication, soft capacity on demand, and high degree of scalability. In this paper, we apply OCDM technique to the highly spectral-efficient transmission system by quaternary phase-shift keying optical encoding/decoding along with ultrafast optical time-gating and optical hard thresholding. As a result, a transmission of 6.4 Tbit/s OCDM/WDM (4 OCDM/spl times/40 WDM/spl times/40 Gbit/s) using only C-band wavelength region is experimentally demonstrated with 1.6-bit/s/Hz spectral efficiency.