40-Gbit/s ETDM Channel Technologies for Optical Transport Network

We review recent progress and the future of 40-Gbit/s electrical time division multiplexed (ETDM) channel technologies for the optical transport network (OTN), where optical technologies, including high-speed ETDM channel transmission and wavelength division multiplexing (WDM), dramatically enhance network flexibility while reducing transport node cost as well as transmission cost. The 40 Gbit/s channel has recently been specified to be one of the optical channels in OTN. A new digital frame for the optical channels [optical channel transport unit (OTU)] was introduced for the network node interface of OTN in International Telecommunication Union-Telecommunication (ITU-T) standard. The specified data bit rates are 2.7 Gbit/s (OTU1), 10.7 Gbit/s (OTU2), and 43.0 Gbit/s (OTU3). These OTU frames have additional overhead bytes that support the network management overhead for OTN and out-of-band forward error correcting (FEC) codes. We discuss the feasibility and impact of the OTU3 frame in terrestrial networks. A newly developed 43-Gbit/s OTN line terminal prototype that confirms the feasibility of 43-Gbit/s ETDM channels and the OTU3 management capability is discussed. As a guide to the evolution of OTN, modulation formats for 43Gbit/s-based DWDM transmission are described for long distance application with the total capacity over one terabit per second.     

Differential precoder IC modules for 20-and 40-Gbit/s opticalduobinary transmission systems

This paper reports on 20- and 40-Gbit/s differential precoder modules for optical duobinary transmission systems. These precoder modules overcome the speed limit of a conventional precoder by parallel processing. The proposed precoders handle two or four parallel signals before multiplexing with data rates of one-half or one-quarter the transmission bit rate, and the final preceded signal is obtained by multiplexing the precoder output bit by bit, production-level 0.2-μm gate-length GaAs MESFET's were used to fabricate the precoders. The precoders are mounted in an RF package. They successfully performed 20- and 40-Gbit/s precoding for the first time, and the 20-Gbit/s precoder achieved a maximum precoding rate of 22 Gbit/s, which is 76% faster than that of the conventional circuit using the same MESFETs. The 40-Gbit/s precoder performs 40-Gbit/s precoding when combined with a 40-Gbit/s multiplexer unit. Twenty-Gbit/s optical duobinary transmitter and receiver circuits using the 20-Gbit/s precoder module successfully generate fully encoded optical duobinary signal at this rate for the first time. These circuits show a receiver sensitivity of -28.6 dBm for a bit error rate of 1×10^-9     

Key technologies for terabit/second WDM systems with high spectralefficiency of over 1 bit/s/Hz

To fully utilize a limited gain bandwidth of about 35 nm (4.4 THz) in an erbium-doped fiber amplifier, an increase in signal spectral efficiency is required. In this paper, we investigate the key technologies to achieve terabit/second wavelength-division multiplexing (WDM) systems with over 1 bit/s/Hz spectral efficiency. Optical duobinary signals, which have narrower optical spectra than conventional intensity modulation signals, were applied to such dense WDM systems. The measured minimum channel spacing for 20-Gbit/s optical duobinary signals was 32 GHz and a spectral efficiency of over 0.6 bit/s/Hz was reached. By using polarization interleave multiplexing, spectral efficiency was expected to reach 1.2 bit/s/Hz in an ideal case with no polarization dependencies along the transmission lines. In such ultradense WDM systems with narrower channel spacing, stabilizing the wavelengths of laser diodes is an important issue for achieving stable operation over long periods. To do this, we developed a simple and flexible wavelength stabilization system which uses a multiwavelength meter. The wavelengths for 116 channels with 35-GHz spacing were stabilized within ±150 MHz. The stabilization system is applicable to ultradense WDM signals with a spectral efficiency of over 1 bit/s/Hz by employing wavelength interleave multiplexing and an optical selector switch. On the basis of these investigations, we demonstrated a 2.6-Tbit/s (20 Gbit/s×132 channels) WDM transmission by using optical duobinary signals. In addition, 1.28-Tbit/s (20 Gbit/s×64 channels) WDM transmission with a high spectral efficiency of 1 bit/s/Hz was achieved by using polarization interleave multiplexing     

40 Gbit/s波分复用系统光转发单元的实现

利用子速率复用方案,研制了40Gbit／s密集波分复用系统的光转发单元,并进行了测试,测试结果表明该单元达到了设计要求。     

超高速光时分复用技术实现及发展

以单波道160Gbit／s传输为例，介绍了光时分复用技术的基本原理，对其中的关键技术进行了分断、比较，并对更高速的OTDM传输技术做了探讨。     

Field Trial of 640-Gbit/s-Throughput, Granularity-Flexible Optical Network Using Packet-Selective ROADM Prototype

Reconfigurable optical add/drop multiplexers (ROADMs) are able to provide flexible wavelength path provisioning in wavelength division multiplexing (WDM) networks. However, the capability of conventional ROADMs is limited to handling wavelength paths, and it does not support fine granularity in add/drop multiplexing of packets. Recently, we have proposed and demonstrated a packet-selective ROADM that combines an acoustooptic wavelength-tunable filter (AOTF) and an optical packet ADM (PADM) using optical code label processing. It provides more efficient utilization of wavelengths than conventional ROADMs. However, the bit rate of the demonstration was limited up to 10 Gbit/s. In this paper, we newly develop a label-selectivity-enhanced optical en/decoder, which allows the optical label recognition with 40-Gbit/s nonreturn-to-zero (NRZ) data packets, and a wide pass-band AOTF for 40-Gbit/s signals. Furthermore, we develop 640-Gbit/s throughput, packet-selective ROADM prototype, and demonstrate a field trial of granularity-flexible 3-node optical network over 173 km. error-free packet ADMs (error rate of under 10^-12) for all 16-wavelength channels at all nodes are obtained.     

Fully electrical 40-Gb/s TDM system prototype based on InP HEMTdigital IC technologies

This paper presents a fully electrical 40-Gb/s time-division-multiplexing (TDM) system prototype transmitter and receiver. The input and output interface of the prototype are four-channel 10-Gb/s signals. The prototype can be mounted on a 300-mm-height rack and offers stable 40-Gb/s operation with a single power supply voltage. InP high-electron mobility transistor (HEMT) digital IC's perform 40-Gb/s multiplexing/demultiplexing and regeneration. In the receiver prototype, unitraveling-carrier photodiode (UTC-PD) generates 1 V_pp output and directly drives the InP HEMT decision circuit (DEC) without any need for an electronic amplifier. A clock recovery circuit recovers a 40-GHz clock with jitter of 220 fs_pp from a 40-Gb/s nonreturn-to-zero (NRZ) optical input. The tolerable dispersion range of the prototype within a 1-dB penalty from the receiver sensitivity at zero-dispersion is as wide as 95 ps/nm, and the clock phase margin is wider than 70° over almost all the tolerable dispersion range. A 100-km-long transmission experiment was performed using the prototype. A high receiver sensitivity [-25.1 dBm for NRZ (2⁷-1) pseudorandom binary sequence (PRBS)] was obtained after the transmission. The 40-Gb/s regeneration of the InP DEC suppressed the deviation in sensitivity among output channels to only 0.3 dB. In addition, four-channel 40-Gb/s wavelength-division-multiplexing (WDM) transmission was successfully performed     

一种应用于波分复用无源光网络系统中的滤波片-PIN-TIA阵列光接收组件

设计并实现了一种将密集波分复用(DWDM)薄膜滤波片与光电探测器PIN以及前置放大器TIA集成封装的光接收组件。通过创新设计单模光纤双芯插针和自聚焦透镜的结构,解决了透过密集波分复用滤波片后的反射光偏离轴线带来的耦合问题。并基于该组件实现了32个密集波分复用通道的解复用与信号检测同时完成的波分复用无源光网络(WDM-PON)系统中上行信道阵列接收模块。测试表明模块满足国际电信联盟(ITU-T)中心波长,最小插入损耗为0.3 dB,最大插入损耗为6 dB,响应速率为100 Mbit/s~1.25 Gbit/s。     

Bidirectional Hybrid DWDM‐PON for HDTV/Gigabit Ethernet/CATV Applications

A new scheme for bi‐directional HDTV/Gigabit Ethernet/CATV transmission over a hybrid dense‐wavelength‐division‐multiplexing passive optical network (DWDM‐PON) is proposed and demonstrated. It is based on injection‐locked vertical‐cavity surface‐emitting lasers and distributed‐feedback laser diodes as transmitters. Services with 129 HDTV channels, a 1.25 Gbps Gigabit Ethernet connection, and 77 CATV channels are successfully demonstrated over 40 km single‐mode fiber links. Good performance of bit error rate, carrier‐to‐noise ratio, composite second order, and composite triple beat is achieved in our proposed bidirectional DWDM‐PON.     

正交频分复用无源光网络

认为当采用低频段的射频资源时,色散导致的双边带功率衰落对正交频分复用无源光网络(OFDM-PON)的影响很小。基于时分复用(TDM)架构的OFDMPON,充分利用正交频分复用(OFDM)技术的优势与TDM架构的无色性,与现有的以太网无源光网络(EPON)、千兆比无源光网络(GPON)兼容性高,是解决上行无色性传输的最优方案。基于OFDM的时波分复用无源光网络(TWDM-PON)充分利用了OFDM调制优势,用来提升单载波容量,在不改变TWDM-PON系统结构情况下,实现100 Gbit/s的高速接入,是未来无源光网络的重要候选方案。     

Study of 16 Tbit/s WDM transmission system derived from the CO-OFDM with PDM 16-QAM

In this paper,a wavelength division multiplexing (WDM) transmission system derived from the coherent optical orthogonal frequency division multiplexing (CO-OFDM) with polarization division multiplexing (PDM) and 16-order quadrature amplitude modulation (QAM) is studied. A simulation of 80-channel WDM transmission system with data rate of 200 Gbit/s is built, and the transmission performance of the system is analyzed. The simulation results show that the system Q value of the WDM channels at 16 Tbit/s with a spectral efficiency of 7.14 bit/s/Hz is potentially over 10.0 dB for a long haul transmission up to 1800 km in a standard single-mode fiber.     

Simple and spectrally-efficient design of high capacity hybrid WDM/TDM-PON with improved receiver sensitivity

A simple design of hybrid wavelength division multiplexed/time division multiplexed passive optical network （WDM/ TDM-PON） is demonstrated for the high capacity next generation access （NGA） network, having advantages of both WDM and TDM based PON techniques. A 10 Gbit/s differential quadrature phase shift keying （DQPSK） data signal is used at optical line terminal （OLT） for downstream, whereas a 2.5 Gbit/s inverse return-to-zero （IRZ） data signal with high extinction ratio is used for upstream signal by intensity re-modulation of downstream signal, no additional laser is used at optical network unit （ONU）. Simulation results verify that aggregated 100 Gbit/s downstream transmissions of 10 DQPSK channels and aggregated 25 Gbit/s upstream transmission of 10 IRZ channels, using spectrally-efficient 50 GHz channel spacing, can be successfully achieved over a distance of 20 km with less than 1 dB transmission power penalties and improved receiver sensitivity.     

Cost‐Effective Transition to 40 Gb/s Line Rate Using the Existing 10 Gb/s‐Based DWDM Infrastructure

In this paper, we propose and demonstrate a cost‐effective technique to upgrade the capacity of dense wavelength division multiplexing (DWDM) networks to a 40 Gb/s line rate using the existing 10 Gb/s‐based infrastructure. To accommodate 40 Gb/s over the link optimized for 10 Gb/s, we propose applying a combination of super‐FEC, carrier‐suppressed return‐to‐zero, and pre‐emphasis to the 40 Gb/s transponder. The transmission of 40 Gb/s DWDM channels over existing 10 Gb/s line‐rate long‐haul DWDM links, including 40×40 Gb/s transmission over KT's standard single‐mode fiber optimized for 10 Gb/s achieves successful results. The proposed upgrading technique allows the Q‐value margin for a 40 Gb/s line rate to be compatible with that of 10 Gb/s.     

Upgrading WDM Submarine Systems to 40-Gbit/s Channel Bitrate

The introduction of wavelength division multiplexing (WDM) has triggered a tremendous capacity growth in submarine systems, both by the increase of the number of WDM channels and by the increase of the channel bitrate. Starting from 2.5 Gbit/s in the mid-1990s, the bitrate was upgraded to 10 Gbit/s by the end of the century in commercial products. The next generation of submarine systems will likely be based on a 40-Gbit/s bitrate. However, transmissions at a 40-Gbit/s rate are more challenging than transmissions at 10 Gbit/s. The goal of this paper is to provide an overview of the technologies which could be required or used in next-generation submarine systems. In the first part of this paper, an overview of the history of submarine links is provided. Then the technologies used in current N /spl times/ 10 Gbit/s systems are described. Eventually, the challenges to overcome are discussed, whether they concern the type of fiber, the type of optical amplifier, or the nature of the modulation format.     

A 50-Gbit/s 450-mW Full-Rate 4:1 Multiplexer With Multiphase Clock Architecture in 0.13- μm InP HEMT Technology

A full-rate multiplexer (MUX) with a multiphase clock architecture for over 40 Gbit/s optical communication systems is presented. The 4:1 MUX is comprised of a re-timer based on a D-type flip-flop (DFF) and a clock tree system that uses EXOR-type delay buffers to match its skews well to those of the data. The supply voltage is reduced to -1.5 V by analyzing the voltage allocation. Fabricated in a 0.13-mum InP HEMT technology, a DFF test circuit achieved 75-Gbit/s operation and exhibited performance sufficient to re-time 50-Gbit/s serialized data. The 4:1 MUX measurement results demonstrate successful 50-Gbit/s operation at room temperature, and 40-Gbit/s operation, which has 10^-11 error free for 2³¹ - 1 pseudorandom bit stream (PRBS) data, up to an ambient temperature of 90 degrees or down to - 1.24 V of supply voltage. The circuit consumes 450 mW at a - 1.5-V supply and exhibits an output jitter of 283 fs rms at 50-Gbit/s operation. We also propose a multiphase clock generator for a MUX that has a serialization of more than four channels     

A Burst-Mode 3R Receiver for 10-Gbit/s PON Systems With High Sensitivity, Wide Dynamic Range, and Fast Response

The burst-mode 3R receiver using monolithic ICs for 10-Gbit/s-class optical access networks is reported. In a point-to-multipoint access system like a passive optical network (PON), the receiver at the optical line terminal (OLT) must be able to handle burst-mode optical packets with significantly different powers and phases. An OLT receiver with high sensitivity with instantaneous response to burst inputs is desired for widening the accommodation area and for high efficiency in PON uplinks. Currently, the diffusion of high-speed Internet connection services represented by fiber to the home services at 1.25 Gbit/s is remarkable and the standardization of the next-generation system operating at 10 Gbit/s has started in IEEE. We first discuss the issues in the implementation of 10-Gbit/s-class PON systems, focusing on securing the accommodation area and the quality of the service comparable with those of the deployed system. Against that background, we propose target specifications for sensitivity, a dynamic range and response speed of the 10-Gbit/s-class burst-mode receiver so as to secure the power budget and the upstream efficiency comparable with those of the already-installed systems. Our burst-mode 3R receiver was designed to meet the above requirements and developed using monolithic ICs of transimpedance amplifier, limiting amplifier, and clock and data recovery circuit fabricated by using SiGe BiCMOS technologies along with a p-i-n photodiode. High sensitivity of , a wide dynamic range of over 16.5 dB, and quick response time of 75 ns were confirmed for burst inputs with extremely different powers.     

1.6 Tbit/s(40×40 Gbit/s)光通信传输系统

在国家自然科学基金网(NSFCNet)上已实现由400 km×10 Gbit/s传输链路直接升级的一路400 km×40 Gbit/s光传输实验的基础上,采用自行研制的40×40 Gbit/s载波抑制归零(CS-RZ)码多波长光发送源,进行了160 km的1.6 Tbit/s(40×40 Gbit/s)波分复用(WDM)光传输实验。实验结果表明,对于常规中短距离10 Gbit/s传输链路可以直接升级至40 Gbit/s。但是由于40 Gbit/s传输系统的色散容限小于60 ps/nm,而且传输光纤与色散补偿模块的色散斜率不匹配,要实现40通道40 Gbit/s的传输,必须对40个信道分别进行精细的色散补偿。这也说明,对于宽带的40 Gbit/s多波长系统,有必要优化设计或更新传输链路。     

Technology of InP-based 1.55-μm ultrafast OEMMICs: 40-Gbit/sbroad-band and 38/60-GHz narrow-band photoreceivers

For future long-haul communication systems operating at bitrates of 40 Gbit/s and for broad-band mobile access systems using 38- or 60-GHz carrier frequencies, ultrafast photoreceivers have to be provided. Therefore, an integration concept for InP-based optoelectronic microwave monolithic integrated circuits for the 1.55-μm wavelength regime is demonstrated, which allows independent optimization of the constituting devices. Two different types of photodetectors (PDs), a waveguide-integrated PIN photodiode (PD) and a top-illuminated metal-semiconductor-metal PD, both having bandwidths of up to 70 GHz, have been developed. These are fabricated together with different amplifier designs employing high electron mobility transistors which exhibit transit frequencies of up to 90 GHz. The application to a 40-Gbit/s broadband photoreceiver for high-bit-rate time-division multiplexing systems is reported, as well as the application to 38- and 60-GHz narrow-band photoreceivers for use as optic/millimeterwave converters in mobile communication systems     

A Novel Scheme for Seamless Integration of ROF With Centralized Lightwave OFDM-WDM-PON System

We have experimentally demonstrated a novel transmission system for seamless integration of ROF with centralized lightwave OFDM-WDM-PON based on an integrated external modulator. At the one of two arms of the integrated external modulator, the optical carrier suppression (OCS) is realized to generate 40–GHz optical millimeter-wave (mm-wave) and up-converted baseband data signal as wireless signal. In another arm of the integrated external modulator, 16 quadrature amplitude modulation intensity-modulated OFDM signals at 10 Gbit/s are used for downstream transmission as wired signal based on double sideband modulation. By using one intensity modulator (IM), the downstream RF OFDM signal is remodulated for upstream on–off keying (OOK) data at 2.5 Gbit/s because of its downstream RZ shape waveform. The 10-Gbit/s wired signal, 2.5-Gbit/s wireless signal, and 2.5-Gbit/s upstream signal have been transmitted over 20-km single mode fiber (SMF) successfully.      

Simultaneous electrooptical upconversion, remote oscillatorgeneration, and air transmission of multiple optical WDM channels for a60-GHz high-capacity indoor system

The system concept and data transmission experiments for a mobile broad-band communication system at 60 GHz are presented in this paper. Dense wavelength division multiplexing (DWDM) is advantageously applied for simultaneous electrooptical upconversion of all optical channels carrying individual intermediate-frequency signals by means of a single external modulator. Thus, simple, but flexible, millimetric signal generation is obtained. Using this concept, data transmission experiments at 60 GHz have been carried out. Furthermore, the transponder noise performance is analyzed. Results of coded and uncoded 512-carrier orthogonal frequency division multiplex transmission with 50-Mb/s (subcarrier modulation quaternary phase-shift keying), 100 Mb/s (subcarrier modulation 16-quadrature amplitude modulation) as well as single-carrier modulation at 156 Mb/s utilizing three operational DWDM channels are presented. Uplink and downlink transmission has been realized. The significant performance improvement due to the application of coding is demonstrated in some experiments and line-of-sight transmission is compared to nonline-of-sight transmission. Low bit error rates, employing realistic air link conditions, have been obtained in all experiments