A centralized-light-source WDM access network utilizing inverse-RZ downstream signal with upstream data remodulation

We propose and demonstrate employing inverse-return-to-zero (IRZ) downstream signal format to facilitate upstream data remodulation in a wavelength division multiplexing (WDM) passive optical network (PON) architecture with centralized light sources. The finite optical power in each downstream IRZ bit can be simply remodulated by the upstream data at the optical network unit. This can make each downstream and upstream pair share a single light source and such light reuse can be easily realized. An experiment on 10-Gb/s downstream IRZ signal generation, 2.5-Gb/s upstream signal remodulation, and two-way transmission is successfully demonstrated. The downstream/upstream signal performance in such a PON has also been analyzed, which is useful for system design.     

Centralized light-wave WDM-PON employing DQPSK downstream and 00K remodulated upstream signals

A novel architecture for wavelength-division-multiplexing passive optical network (WDM-PON) with centralized light-wave is proposed and demonstrated. At the optical line terminal (OLT) session of this architecture, optical differential quadrature phase shift keying (DQPSK) modulated signal with constant-intensity at 10 Gbit/s is utilized for downstream transmission. At the optical network unit (ONU), part of the downstream optical power is remodulated with on-off keying (OOK) intensity modulation at 10 Gbit/s for upstream without additional laser. Simulation results show that the power penalties of the downstream for 20 km single-mode fiber (SMF) transmission and multi-channels are negligible. While for the upstream, the power penalties are obvious. The simulation results and analysis also reflect that by reducing the launch power of DQPSK transmitters, power penalties can be reduced, although the transmission distance is limited.     

Centralized light-wave WDM-PON employing DQPSK downstream and OOK remodulated upstream signals

A novel architecture for wavelength-division-multiplexing passive optical network(WDM-PON)with centralized light-wave is proposed and demonstrated.At the optical line terminal(OLT)session of this architecture,optical differential quadrature phase shift keying(DQPSK)modulated signal with constant-intensity at 10 Gbit/s is utilized for downstream transmission.At the optical network unit(ONU),part of the downstream optical power is remodulated with on-off keying(OOK)intensity modulation at 10 Gbit/s for upstream without additional laser.Simulation results show that the power penalties of the downstream for 20 km single-mode fiber(SMF)transmission and multi-channels are negligible.While for the upstream,the power penalties are obvious.The simulation results and analysis also reflect that by reducing the launch power of DQPSK transmitters,power penalties can be reduced,although the transmission distance is limited.     

Effects of Upstream Bit Rate on a Wavelength‐Remodulated WDM‐PON Based on Manchester or Inverse‐Return‐to‐Zero Coding

We compare the performance of a wavelength remodulated wavelength‐division‐multiplexed passive optical network implemented using Manchester‐coded or inverse‐return‐to‐zero (IRZ)‐coded signal downstream and non‐return‐to‐zero remodulated signal upstream. We investigate the effects of varying differences between downstream and upstream bit rates on the two coding schemes. When the bit rate ratio of upstream to downstream is less than or equal to 50%, the performance of Manchester coding is better than that of IRZ coding. However, when the bit rate ratio of upstream to downstream is higher than 50%, Manchester code requires appropriate time delay between upstream and downstream signals, whereas IRZ code needs reduced extinction ratio in the downstream signal.     

WDM PON using 10-Gb/s DPSK downstream and re-modulated 10-Gb/s OOK upstream based on SOA

A signal remodulation scheme of 10-Gb/s differential phase-shift keying(DPSK) downstream and 10-Gb/s on-off keying(OOK) upstream using a semiconductor optical amplifier(SOA) and a Mach-Zehnder intensity modulator(MZ-IM) at the optical networking unit(ONU) side for wavelength division multiplexed passive optical network(WDM PON) is proposed.Simulation results indicate that error-free operation can be achieved in a 20-km transmission,and the receiver sensitivity of return-to-zero differential phase-shift keying(RZ-DPSK) is higher than nonreturn-to-zero differential phase-shift keying(NRZ-DPSK) in the proposed scheme.     

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.     

Colorless ONU implementation for WDM-PON using direct-detection optical OFDM

A novel architecture for the colorless optical network unit (ONU) is proposed and experimentally demonstrated with direct-detection optical orthogonal frequency division multiplexing (DDO-OFDM). In this architecture, polarization-division multiplexing is used to reduce the cost at ONU. In optical line terminal (OLT), quadrature amplitude modulation (QAM) intensity-modulated OFDM signal with x-polarization at 10 Gbit/s is transmitted as downstream. At each ONU, the optical OFDM signal is demodulated with direct detection, and y-polarization signal is modulated for upstream on-off keying (OOK) data at 5 Gbit/s. Simulation results show that the power penalty is negligible for both optical OFDM downstream and the on-off keying upstream signals after over 50 km single-mode fiber (SMF) transmission.     

Rayleigh backscattering minimization in single fiber colorless WDM-PON using intensity remodulation technique

The performance of colorless wavelength-division multiplexed passive optical network(WDM-PON) systems suffers from the transmission impairments mainly due to Rayleigh backscattering(RB).In this paper,we propose and demonstrate a single fiber colorless WDM-PON which enhances the tolerance to RB induced noise.The high extinction ratio in both return-to-zero(RZ)-shaped differential phase shift keying(DPSK) downstream(DS) data signal and intensity-remodulated upstream(US) data signal helps to improve the tolerance to RB induced noise.Simulation results show that downstream and upstream signals can achieve error-free performance at 10 Gbit/s with negligible penalty and improve the tolerance to RB induced noise over 25 km standard single-mode fiber.     

Eight-channel bidirectional WDM add/drop multiplexer

The authors propose and demonstrate an eight-channel reconfigurable bidirectional wavelength division multiplexed (WDM) add-drop multiplexer in which all channels can be added/dropped independently in either direction. The performance of the bidirectional WDM add/drop multiplexer is experimentally studied for a data rate of 10 Gbit/s per channel, providing an overall capacity of 80 Gbit/s. It is found that the performance of the add/drop multiplexer is not degraded by a backward propagating signal     

A WDM-PON with DPSK modulated downstream and OOK modulated upstream signals based on symmetric 10 Gbit/s wavelength reused bidirectional reflective SOA

We investigate a wavelength-division-multiplexing passive optical network (WDM-PON) with centralized lightwave and direct detection. The system is demonstrated for symmetric 10 Gbit/s differential phase-shift keying (DPSK) downstream signals and on-off keying (OOK) upstream signals, respectively. A wavelength reused scheme is employed to carry the upstream data by using a reflective semiconductor optical amplifier (RSOA) as an intensity modulator at the optical network unit (ONU). The constant-intensity property of the DPSK modulation format can keep high extinction ratio (ER) of downstream signal and reduce the crosstalk to the upstream signal. The bit error rate (BER) performance of our scheme shows that the proposed 10 Gbit/s symmetric WDM-PON can achieve error free transmission over 25-km-long fiber transmission with low power penalty.     

Spectral slicing WDM-PON using wavelength-seeded reflective SOAs

A method of implementing wavelength division multiplexed-passive optical network (WDM-PON) upstream channels based on spectral slicing with wavelength-seeded travelling-wave reflective semiconductor optical amplifier (SOA) modulators is described. A dense WDM comprising eight 1 nm slices, each modulated at a data rate of 1.25 Gbit/s are shown to operate over 25 km of standard fibre with negligible crosstalk and <1 dB dispersion penalty     

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.      

Gain transient control for wavelength division multiplexed access networks using semiconductor optical amplifiers

Gain transients can severely hamper the upstream network performance in wavelength division multiplexed (WDM) access networks featuring erbium doped fiber amplifiers (EDFAs) or Raman amplification. We experimentally demonstrate for the first time using 10 Gb/s fiber transmission bit error rate measurements how a near-saturated semiconductor optical amplifier (SOA) can be used to control these gain transients. An SOA is shown to reduce the penalty of transients originating in an EDFA from 2.3 dB to 0.2 dB for 10 Gb/s transmission over standard single mode fiber using a 2³¹–1 PRBS pattern. The results suggest that a single SOA integrated within a WDM receiver at the metro node could offer a convenient all-optical solution for upstream transient control in WDM access networks.     

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。     

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.     

30 Gbit/s downstream capacity of cost-effective colourless WDM-PON based on injection-locked Fabry-Perot lasers

A 100 GHz spaced comb, generated by a quantum dash passively modelocked laser, is used as a low-noise coherent seeding source for the colourless wavelength-division-multiplexed passive optical network based on injection-locked Fabry-Pe rot laser diodes. Error-free downstream transmission over 25 km singlemode fibre of 12 WDM channels at 2.5 Gbit/s with 100 GHz channel spacing is experimentally demonstrated.     

A WDM Passive Optical Network With Centralized Light Sources and Multicast Overlay

We propose a novel wavelength-division-multiplexed passive optical network (WDM-PON) architecture to provide a downstream multicast overlay on the conventional point-to-point data service. The differential-phase-shift-keying multicast data is modulated on the same optical downstream carrier with the inverse return-to-zero point-to-point data signal, thus additional light sources are saved. Broadcast or multicast control is realized at the optical line terminal. For each WDM channel, part of the downstream power is re-used as the upstream data carrier, and thus realizes a colorless optical network unit. We successfully demonstrate the proposed WDM-PON with 10-Gb/s downstream point-to-point signals,10-Gb/s downstream multicast signals, and 2.5-Gb/s upstream signals.     

A novel WDM passive optical network architecture supporting two independent multicast data streams

We propose a novel scheme to perform optical multicast overlay of two independent multicast data streams on a wavelength-division-multiplexed (WDM) passive optical network. By controlling a sinusoidal clock signal and shifting the wavelength at the optical line terminal (OLT), the delivery of the two multicast data, being carried by the generated optical tones, can be independently and flexibly controlled. Simultaneous transmission of 10-Gb/s unicast downstream and upstream data as well as two independent 10-Gb/s multicast data was successfully demonstrated.     

Impact of Fiber Non-linearity in High Capacity WDM Systems and in Cross-Connected Backbone Networks

The rapidly increasing data traffic volumes will demand for very high transmission capacity and network nodes throughput. Wavelength division multiplexing (WDM) technology will be asked to support many channels on the same fiber, both in point-to-point links and in WDM optical networks. The transmission of a high number of wavelength channels in all these systems is a key issue. This paper analyzes this topic, in both high capacity links and optical networks, highlighting the impact of fiber non-linearity, and addressing the main source of impairments. This is done through the use of a semi-analytical model recently upgraded to account for all the contributions deriving from Kerr effects, particularly four-wave mixing and cross-phase modulation. The analysis reveals that more than one hundred of channels at 2.5 Gbit/s can be transmitted in point-to-point links whose length can span until the order of 1000 km, and 32 channels per fiber, at the previous bit rate, can be handled in WDM networks, without dispersion compensation. For a higher number of channels (e.g., 64) dispersion compensation is needed.     

基于光相位信号延时自相干的相位信息高速实时取样系统

提出了一种基于光相位信号自相干的高速光相位实时取样方案。利用时延为10ps的延时干涉仪(DI),将待测光信号的相位信息转换为强度信息;再在高非线性光纤(HNLF)中,利用四波混频(FWM)效应对强度信号进行取样。在接收端,利用不同中心波长的光滤波器(OBPF)即可滤出不同时间点的取样信号,从而在光域同时完成高速光相位信息的实时取样和取样信号的串-并转换。本文方案具有成本低、对测信号码率和波长不敏感的优点。实验中,对9GHz正弦调制以及10Gb/s非归零码调制的光相位信号实现了100G/s的高速实时取样系统,并转换为10路10G/s取样信号输出,最终恢复取样光信号的相位波形。