Elsevier

Optical Fiber Technology

Volume 26, Part A, December 2015, Pages 126-134
Optical Fiber Technology

WDM PONs based on colorless technology

https://doi.org/10.1016/j.yofte.2015.08.002Get rights and content

Highlights

  • WDM PONs will be introduced with applications in business and mobile fronthaul segments.

  • Fixed wavelength technologies will first be deployed such as CWDM dual fiber and CWDM single fiber.

  • When higher density of ports will be required, colorless technologies will be essential.

  • A WDM PON system based on self-seeded RSOAs is experimented with CPRI3 links.

  • Good performances demonstrated with long reach and coexistence with legacy PONs.

Abstract

Wavelength Division Multiplexing (WDM) Passive Optical Network (PON) is foreseen to be part of the Next Generation Passive Optical Networks. Business and mobile fronthaul networks already express the need to develop WDM PONs in the access segment. Fixed wavelength transceivers based on Coarse WDM are already available to respond to today’s market needs but Dense WDM technologies will be needed and colorless technologies are essential to provide simple and cost-effective WDM PON systems. We propose in this paper to demonstrate the capabilities of a DWDM PON system prototype based on self-seeded RSOAs and designed to transmit CPRI over 60 km of fiber at 2.5 Gbit/s.

Introduction

The International Telecommunication Union ITU-T is finalizing the upcoming standard for optical access networks on Next Generation Passive Optical Networks 2. Several technological options are discussed within this standard to be delivered under references G989.x: Time and Wavelength Division Multiplexing PONs and also some point-to point WDM links as depicted on Fig. 1. This represents a first step towards the standardization of solutions for WDM in access networks.

Alternatively, WDM is already rolling out in optical access networks with several use cases and a common objective: to avoid deploying new fibers in the case of a lean fiber infrastructure. WDM is also foreseen to be the topology used particularly when symmetrical bit rates and secured architectures are required. In particular, two use cases have been identified for WDM PONs: business Ethernet links as Fiber to The Office (FTTO) and mobile fronthaul links as Fiber To The Antenna (FTTA) as depicted in Fig. 2.

Optical fiber for enterprises (FTTO) is a decisive and essential factor in economic development of regions, aiming in a long term perspective to deliver attractive digital services to the companies. The FTTO offer is realized with a point to point topology, using dual-fiber mediums and offering symmetrical bitrates from a few Mbit/s to 10 Gbit/s. Bitrates requirements are proportional to the increase of the service usage and type of service (File sharing, data saving, videoconferencing, High Definition Voice over IP, Cloud computing, etc.). This point to point link connects an access Ethernet router placed at the enterprise site and an Edge Node router at the central office. This offer is for offices, computer sites, call centers, factories, medical centers, etc… Increased quality of service is guaranteed by FTTO offers (performance, service classes adapted to each needs, commitments on the service availability and guarantee of low recovery time). The evolution of this offer is going towards the optimization of the user’s connections to a central office: it is intended to densify the number of users per central and avoid systematic connection to the nearest one. This will cause a large number of fibers to be connected to a single central, but often fiber resource is not available between central offices. To reduce this fiber need, it is possible to use passive multiplexing technology offering point to point connectivity and symmetrical bandwidth such as WDM PONs.

Most of mobile antenna sites are already connected with optical fibers to realize the backhaul of the Radio Access Network (RAN). Driven partly by a lack of space and climatic dispositions at the antenna sites, the evolution toward Centralized RAN (C-RAN) proposes to remove part of the RAN equipment from the antenna sites to a common central office. This operation creates a new optical access segment called “Mobile fronthaul” between the Remote Radio Heads (RRH) placed at the antenna site and the Base Band Unit (BBU) placed at the Central office [1]. At the antenna site, for the operator Orange France, up to 5 RAN technologies exist (2G and 3G both at 900 MHz and 2100 MHz) or will be deployed (4G at 800 MHz, 1800 MHz and 2.6 GHz) and 3 sectors for each technology are required to cover all the area around the antenna site. This represents up to 15 point to point links to create between each RRH and the BBU at the central office. In order to optimize the use of fiber resources, a Wavelength Division Multiplexing (WDM) technology is foreseen to realize those multiple point to point links. Mobile fronthaul links use Common public Radio Interface (CPRI) or Open Base Station Architecture Initiative (OBSAI) protocols with bitrates from 614.4 Mbit/s for CPRI1 to 10.137 Gbit/s for CPRI8. The line bitrate depends on the RAN technology, the frequency bandwidth of the radio carrier (10 MHz or 20 MHz) and the Multiple Input Multiple Output (MIMO) option.

Wavelength Division Multiplexing technique is already used in access networks, particularly in a field trial of mobile fronthaul in Orange France using Coarse WDM technologies. The main advantage of this solution is that its infrastructure remains passive using multiplexers (MUX) and de-multiplexers (DMUX) for bidirectional transmissions. The CWDM technology, based on 20 nm spacing between channels, has been chosen to reduce the number of fibers to deploy and is, up to now, the only cost-effective WDM solution supporting bitrates at 2.5 Gbit/s and compliant with outdoor conditions (I-temp ranges [−40 °C;+85 °C] required at an antenna site for example). The CWDM grid offers up to 16 channels from 1270 nm to 1610 nm, with a possibility to avoid the OH peak (high insertion losses). In a mobile fronthaul application setup, 15 CWDM links are dedicated to cover a full antenna site with 15 RRH (2G, 3G and 4G) and the sixteenth link can be reserved for the management of the optical link, as shown on Fig. 3. Indeed, the mobile operator owning the RRHs + BBUs can be different from the fixed operator owning the optical fiber. In this case, some demarcation point needs to be defined to provide service level agreements between multiple operators. An example of semi-passive monitoring is depicted on Fig. 3: using a passive loop back at the antenna site and a dedicated CWDM channel to realize a signal round trip monitoring from the central office.

Recent commercial products are available with a major technical advance on the CWDM channel: evolution of the Small Form Pluggable (SFP) transceiver from dual fiber to a single fiber output. Several techniques have been identified:

  • Single Wavelength Single Fiber (SWSF): the same wavelength is used to transmit the downstream and upstream signals. A special technique is used to separate the signals before the receiver. Also, a specific product has been developed to enhance the performances of this transceiver: SWSF with Reflection Immune Operation (RIO) [2]. This SWSF transceiver can detect and lower reflected signals and thus reduces the impact of back-reflections due to connectors or Rayleigh back scattering in the fiber.

  • Cooled Single Channel (CSC) [3]: the CWDM channel is sub-divided in two sub-bands of 6 nm wide. The transceiver at each side of the network is chosen to emit in the “high” sub-band or the “low” sub-band and vice versa for the other network termination. Then, in order to maintain the laser in this sub-band, a thermoelectric cooler is required.

With the advent of multiple sizes of cells on mobile antenna sites (macro, micro, small cells), in the future, the number of CWDM channels available might be unsufficient and a Dense WDM technique (DWDM) could be required. In order to re-use the deployed WDM infrastructures, a first step towards DWDM in access networks could be to transmit several DWDM channels within a CWDM channel. When green-field areas are use cases, pure DWDM technologies can be foreseen. The main challenge to deploy DWDM technologies relies on the cost of DWDM transceivers. Fixed wavelength DWDM technologies are out of scope for operational reasons: complex management of the products in the network information system, require a lot of spare parts for the technician in the field, not outdoor compatible today (no I-temp products). Then, the key technology for DWDM in access is a cost effective colorless optical source: using the same device at each user termination will permit mass production and reduce the operational costs compared to fixed wavelength items. Moreover, the exploitation of colorless transceiver would overcome inventory problems, which could burden the mobile network administration, limiting inventory and maintenance costs [4]. The wavelength management of the source also needs to be efficient with regards to climatic changes and relies on simple technical tools to reduce the operational expenditure of the network. Many DWDM colorless technologies have been studied in research laboratories: Spectrum slicing [5], [6], Injection locked Fabry-Pérot [7], [8], wavelength reuse [9], Tunable Lasers [10], Reflective Semiconductor Optical Amplifier (RSOA) self-seeding [11], etc. Only a few of these technologies have been exploited recently to realize a commercial system and they are still limited to a prototype system: ADVA developed a WDM PON system with transmissions at 1 Gbit/s base on tunable lasers [10], Transmode proposed a 1.25 Gbit/s DWDM PON system based on Injection Locked Fraby-Pérot [12], Aeponyx realized transmissions at 1.25 Gbit/s with a WDM PON technology using RSOA associated with Fiber Bragg Gratings [13] and finally Huawei Technologies worked on self-seeded RSOA technologies with a prototype system transmitting 1.25 Gbit/s [14].

Section snippets

Experimentation of a DWDM system prototype based on self-seeded RSOAs technologies

We report the evaluation of a new WDM PON prototype system [17]. This system is dedicated to mobile fronthaul applications transporting CPRI links and the DWDM technology adopted is based on Self-seeded RSOAs.

Conclusions

After the ascension of fixed wavelength transceivers for optical networks, colorless technologies in DWDM PONs are essential to maintain a cost-effective access network. We demonstrated in this paper the error free transmission of CPRI3 with a DWDM PON system based on self-seeded RSOAs. This colorless technology delivers an automatic assignment of the DWDM wavelength, by a simple connection to a multiplexer. Up to 16 mobile fronthaul links can be realized with this system in order to decrease

Acknowledgments

The authors would like to thank Huawei technologies for their help and support with the DWDM system prototype. This work was also supported by the French research program ANR project LAMPION under grant agreement ANR-13-INFR-0002.

References (18)

  • P. Parolari

    Self-tuning transmitter for fibre-to-the-antenna PON networks

    Opt. Switch. Netw.

    (2014)
  • A. Pizzinat et al.

    Things you should know about fronthaul

    IEEE J. Lightwav. Technol.

    (2015)
  • ...
  • ...
  • K.-H. Han et al.

    Bidirectional WDM PON using light-emitting diodes spectrum-sliced with cyclic arrayed-waveguide grating

    Photon. Technol. Lett., IEEE

    (2004)
  • D.K. Jung et al.

    Wavelength-division multiplexed passive optical network based on spectrum-slicing techniques

    Photon. Technol. Lett., IEEE

    (1998)
  • M. Presi, A. Chiuchiarelli, E. Ciaramella, Polarization independent self-seeding of fabry-perot laser diodes for...
  • Q.T. Nguyen, L. Bramerie, G. Girault, O. Vaudel, P. Besnard, J. C Simon, A. Shen, G.-H. Duan, and C. Kazmierski,...
  • Jea-Hoon Yu, Byoung whi Kim, Nam Kim, “Wavelength Re-use Scheme with Reflective SOA for WDM-PON Link”. 10th...
There are more references available in the full text version of this article.

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