Single fiber colorless symmetric WDM-PON architecture using time interleaved remodulation technique for mitigating Rayleigh backscattering resilience

A time interleaved differential phase shift keying (DPSK) remodulation technique is proposed to mitigate the effect of Rayleigh backscattering (RBS)-induced noise in a single fiber colorless wavelength-division-multiplexing passive optical network (WDM-PON). In order to achieve a cost effective optical network unit (ONU) solution without dedicated laser sources for upstream signals to provide optimum symmetric capacity in a colorless WDM-PON, remodulation becomes the core attraction. Also as the performance of colorless WDM-PON systems suffers from the transmission impairments due to RBS, it is mitigated by using this remodulation scheme. Simulation results show that downstream and upstream signals achieve the error-free performance at 10 Gbit/s with negligible penalty, and enhance the tolerance to RBS-induced noise over a 25 km single-mode fiber.     

Wavelength filter detuning for improved carrier reuse in loop-back WDM-PON

Negative detuning of the passband frequency of the wavelength filter, particularly used as a wavelength demultiplexer at the central office in the loop-back WDM-PON, is demonstrated. This method is experimentally proved to suppress further the residual downstream component included in the optical upstream data in the remodulation scheme, resulting in improvement of the upstream performance.     

Reliable wide-area wavelength division multiplexing passive optical network accommodating gigabit ethernet and 10-Gb ethernet services

This paper proposes and demonstrates a reliable wide-area wavelength-division-multiplexing passive optical network (WDM-PON) with a wavelength-shifted protection scheme. This protection scheme utilizes the cyclic property of 2/spl times/N athermal arrayed-waveguide grating and two kinds of wavelength allocations, each of which is assigned for working and protection, respectively. Compared with conventional protection schemes, this scheme does not need a 3-dB optical coupler, thus leading to ensure the large loss budget that is suited for wide-area WDM-PONs. It also features a passive access node and does not have a protection function in the optical network unit (ONU). The feasibility of the proposed scheme is experimentally confirmed by the carrier-distributed WDM-PON with gigabit Ethernet interface (GbE-IF) and 10-GbE-IF, in which the ONU does not employ a light source, and all wavelengths for upstream signals are centralized and distributed from the central office.     

A novel AWG-based WDM-PON architecture with full protection capability

The higher bandwidth utilization of wavelength-division-multiplexing passive optical networks (WDM-PONs) can be problematic if the link failure is not repaired in a timely manner since major data losses may occur in the event of link failure. Therefore, developing robust WDM-PON architectures with an effective protection capability is an essential task when designing optical access networks. Although the literature contains many proposals for WDM-PON protection schemes, the majority of these schemes protect either the feeder fibers or the distribution fibers, but not both. By exploiting the cyclic properties of the AWG and establishing appropriate interconnections between matched pairs of ONUs such that one ONU in the pair can use the distribution fiber assigned to its partner for backup purposes, the proposed scheme can protect both the feeder fibers and the distribution fibers through the designated protection streams in feeder fiber 3. Additionally, five operational modes of the proposed scheme are detailed with the proposed wavelength assignment scheme, the operational sequence, and the operation flow chart of decision circuit in the ONU/OLT. The analytical results have shown that the proposed scheme not only provides a full protection capability for WDM-PON networks, but also has a lower unavailability, a lower construction cost, and a reduced wavelength requirement than existing representative protection schemes. Finally, an analysis of the power budget and the recovery time has confirmed the practical feasibility of the proposed scheme.     

A Wavelength-Division-Multiplexed Passive Optical Network With Flexible Optical Network Unit Internetworking Capability

We propose and experimentally demonstrate a novel flexible optical network unit (ONU) internetworking architecture over a wavelength-division multiplexed passive optical network (WDM-PON). By employing our designated wavelength assignment and remodulating the downstream differential phase-shift keying signal as the ONU internetworking carrier, one ONU can broadcast its own message to all other ONUs, with negligible signal interference. Moreover, the inter-ONU communication can further be partitioned into arbitrary virtual private groups of ONUs by employing designated RF tones for identification and control. It was experimentally demonstrated that the performance degradation due to the introduction of RF tones is negligible compared with the full broadcast case. Our proposed scheme can provide high flexibility and practical implementation for WDM-PONs.     

Improving upstream transmission performance using a receiver with decision threshold level adjustment in a loopback WDM-PON

We have experimentally demonstrated that the use of an optical receiver with decision threshold level adjustment (DTLA) improved the performance of an upstream transmission in reflective semiconductor optical amplifier (RSOA)-based loopback wavelength division multiplexing-passive optical network (WDM-PON). Even though the extinction ratio (ER) of the downstream signal was as much as 9 dB and the injection power into the RSOA at the optical network unit was about ?24 dBm, we successfully obtained error-free transmission results for the upstream signal through careful control of the decision threshold value in the optical receiver located at optical line terminal (OLT). Using an optical receiver with DTLA for upstream signal detection overcame significant obstacles related to the injection power into the RSOA and the ER of the downstream signal, which were previously considered limitations of the wavelength remodulation scheme. This technique is expected to provide flexibility for the optical link design in the practical deployment of a WDM-PON.     

PON in adolescence: from TDMA to WDM-PON

Passive optical networks are used for fiber-to-the-home/curb/cabinet/building applications. Today, two PON variants with time-domain multiple access, GPON and EPON, are being used for mass roll-outs. WDM-PONs are the next step up from these PONs to accommodate traffic growth and new applications. This article analyzes WDM-PON variants and proposes they be used for a unified optical access and back-hauling network.     

Coherent passive optical network for 5G and beyond transport

Building low-latency and high-capacity optical networks is vital for new high-speed cellular technologies. Coherent wavelength division multiplexing passive optical networks (WDM-PONs) are expected to play a key role in these applications. In this article, an overview of PON technologies for the 5th generation (5G) transport systems has been given. Moreover, a modified scheme based on coherent WDM-PON has been investigated using a dual polarization quadrature phase shift keying (DP-QPSK) transceiver. The aim of the scheme is to build a 1 600 Gbit/s network that will be used in the construction of the transport architecture of 5G and beyond cellular networks either in mobile front haul (MFH) or mobile back haul (MBH). The results indicate that the proposed scheme offers a promising solution for future 5G transport systems.     

Tunable OTDR Based on Direct Modulation of Self-Injection-Locked RSOA for In-Service Monitoring of WDM-PON

We propose a tunable optical time-domain reflectometer (OTDR) for in-service monitoring of wavelength- division- multiplexing passive optical networks (WDM-PONs). The proposed method uses a reflective semiconductor optical amplifier, which is self-injection-locked by a tunable fiber Bragg grating. The proposed tunable OTDR has a tuning range of 30 nm and a resolution of 50 m. The performance of the proposed scheme is experimentally evaluated to demonstrate the in-service monitoring of WDM-PON.     

WDM-PON Architectures With a Single Shared Interferometric Filter for Carrier-Reuse Upstream Transmission

We propose two novel wavelength-division-multiplexed passive-optical-network (WDM-PON) architectures where subcarriers are employed to transmit downstream data and optical carriers are reused for upstream transmission. Architecture I is designed for the situation where two short distribution fibers are available between the remote node (RN) and each optical network unit (ONU), whereas Architecture II is devised for the case where there is only one distribution fiber between the RN and each ONU. Both architectures use only one interferometric filter located at the RN to simultaneously separate all downlink optical carriers and subcarriers, leading to a considerable cost reduction in the implementation of the WDM-PONs. Separated optical carriers are then reused and injected into reflective semiconductor optical amplifiers as the uplink light sources, which eliminates the necessity of specific wavelength sources at the ONUs. The downstream subcarrier signals are directly detected using baseband receivers. Two multichannel upstream and downstream transmission experiments are carried out at 1.25 Gb/s using the proposed schemes. The impact of optical carrier-to-subcarrier ratio of downlink signal, Rayleigh-backscattering noise, and wavelength mismatch between laser source and filter on system performance is also investigated.     

Wavelength Remodulation Using DPSK Down-and-Upstream With High Extinction Ratio for 10-Gb/s DWDM-Passive Optical Networks

We propose and demonstrate a novel wavelength remodulation scheme using differential phase-shift keying (DPSK) modulation format in both downstream and upstream signals for ldquocolorlessrdquo dense wavelength-division-multiplexed (DWDM) passive optical networks (PONs). The scheme enables high extinction ratio in both downstream and upstream remodulated signals. Error-free operation was achieved in a 20-km-reach 10-Gb/s DWDM-PON without dispersion compensation. Timing misalignment tolerance between downstream and upstream remodulated signals and maximum launched optical power for the proposed scheme are studied. Comparison with other wavelength remodulation schemes for DWDM-PONs is also performed, showing the proposed scheme can be a potential candidate for next-generation wavelength reuse DWDM-PONs.     

A total-cost-of-ownership analysis of l2-enabled WDM-PONs - [Topics in optical communications]

Next-generation access networks must provide bandwidths in the range of 50-100 Mb/s per residential customer. Today, most broadband services are provided through copper-based VDSL or fiber-based GPON/EPON solutions. Candidates for next-generation broadband access networks include several variants of WDM-PONs. The total cost of ownership of these solutions is determined mainly by operational expenditures, where the cost of energy is one of the major contributors. We show that a combination of WDM-PON with active L2 switching can minimize the total cost of ownership while at the same time offering the highest scalability for future bandwidth demands.     

Broad-band light source using mutually injected Fabry-Pe/spl acute/rot laser diodes for WDM-PON

We propose and demonstrate a new broad-band light source (BLS) for a wavelength division multiplexing-passive optical network (WDM-PON) based on the wavelength locked Fabry-Pe/spl acute/rot laser diodes (F-P LDs). By mutual injection between two antireflection-coated F-P LDs, we realized a broad-band light with a low relative intensity noise. By using the proposed BLS for wavelength locking of the F-P LD, we achieve color-free operation of the optical network termination with Manchester coded data. We also demonstrate a WDM-PON based on the proposed BLS.     

WDM-PON接入技术及其最新进展

本文首先从时分复用无源光网络（TDM—PON）的不足引入波分复用无源光网络（WDM—PON）,接着介绍了ONU波长固定和可调WDM—PON,随后阐述了ONU无色和无光源WDM—PON。鉴于目前WDM-PON难以推广使用的现状,上行用TDMA替代WDMA会使WDM—PON看起来更加现实,所以本文也介绍了混合使用WDM和TDM的HPON。最后对WDM—PON与功率分配PON（PS—PON）的技术进行了比较。     

基于RSOA再调制技术的WDM-PON系统仿真研究

WDM-PON作为下一代PON技术,能充分利用光纤丰富的带宽资源来满足不断增加的高带宽网络应用业务的需求。文章在简要介绍WDM-PON工作原理的基础上,重点分析了基于反射式半导体光放大器(RSOA)再调制技术的WDM-PON系统结构,并利用光通信仿真软件Optisystem对该系统进行仿真,验证了该系统的可靠性。最后提出了WDM-PON的应用前景。     

TWC and AWG based optical switching structure for OVPN in WDM-PON

Considering the influence of more random atmospheric turbulence,worse pointing errors and highly dynamic link on the transmission performance of mobile multiple-input multiple-output(MIMO)free space optics(FSO)communication systems,this paper establishes a channel model for the mobile platform.Based on the combination of Alamouti space-time code and time hopping ultra-wide band(TH-UWB)communications,a novel repetition space-time coding(RSTC)method for mobile 2×2 free-space optical communications with pulse position modulation(PPM)is developed.In particular,two decoding methods of equal gain combining(EGC)maximum likelihood detection(MLD)and correlation matrix detection(CMD)are derived.When a quasi-static fading and weak turbulence channel model are considered,simulation results show that whether the channel state information(CSI)is known or not,the coding system demonstrates more significant performance of the symbol error rate(SER)than the uncoding.In other words,transmitting diversity can be achieved while conveying the information only through the time delays of the modulated signals transmitted from different antennas.CMD has almost the same effect of signal combining with maximal ratio combining(MRC).However,when the channel correlation increases,SER performance of the coding 2×2 system degrades significantly.     

Extended-reach WDM-PON based on CW supercontinuum light source for colorless FP-LD based OLT and RSOA-based ONUs

We investigate the benefits of using our proposed continuous-wave supercontinuum (CW SC) as a broadband wavelength-locking source for the implementation of extended-reach, colorless, wavelength division-multiplexed passive optical networks (WDM-PONs). More specifically, first, an extended reach WDM-PON architecture based on both the CW SC and our devised C-/L-band beam combiner is proposed, in which the optical line terminal (OLT) is based on Fabry–Pérot laser diodes (FP-LDs), whereas the optical network units (ONUs) are reflective semiconductor optical amplifiers (RSOAs). Second, a theoretical investigation on the maximum reach achievable with the proposed architecture is carried out considering Rayleigh backscattering noise and injection power limits. Only upstream signal performance is compared for the following four cases: (1) superluminescent diode (SLD) broadband source and FP-LD ONU, (2) SLD and RSOA, (3) CW SC and FP-LD, and (4) CW SC and RSOA. The combination of a CW SC injection source and RSOA-based ONUs is found to allow for the longest distance coverage. Finally, the feasibility of the proposed architecture is experimentally analyzed over a 60-km transmission fiber at 622 Mbit/s.     

一种基于相位调制环的多波长产生器的WDM-PON

本文首先简单介绍了WDM-PON的技术背景,在此基础上分析WDM-PON的劣势为造价成本高,通过对现存关键技术的研究和对比,提出了一种基于相位调制环的多波长产生器,将这种技术应用于WDM-PON中,大大降低了成本。     

An Automatic Wavelength Control Method of a Tunable Laser for a WDM-PON

We propose a novel automatic wavelength control method of a tunable laser for a wavelength-division-multiplexed passive optical network (WDM-PON). By sending a low-power amplified spontaneous emission light generated from a broadband light source (BLS) to a tunable laser through a wavelength-division multiplexer, we match the wavelength of the tunable laser to a peak transmission wavelength of the multiplexer. The deviation of the wavelength of the tunable laser was less than 0.05 nm from the center of the target channel. We demonstrate up to 10-Gb/s transmission in a WDM-PON by using the proposed method. We also show that system impairments induced by the BLS are negligible.      

一种基于相位调制环的WDM-PON

本文首先简单介绍了WDM-PON的技术背景,在此基础上分析WDM-PON的劣势为造价成本高,通过对现存关键技术的研究和对比,提出了一种基于相位调制环的多波长产生器,将这种技术应用于WDM-PON中,大大降低了成本。