The very broad bandwidth of low-loss optical transmission in a single-mode fiber and the recent improvements in single-frequency tunable lasers have stimulated significant advances in dense wavelength division multiplexed optical networks This technology, including wavelength-sensitive optical switching and routing elements and passive optical elements, has made it possible to consider the use of wavelength as another dimension, in addition to time and space, in network and switch design The independence of optical signals at different wavelengths makes this a natural choice for multiple-access networks, for applications which benefit from shared transmission media, and for networks in which very large throughputs are required Recent progress in multiwavelength networks are reviewed, some of the limitations which affect the performance of such networks are discussed, and examples of several network and switch proposals based on these ideas are presented Discussed also are critical technologies that are essential to progress in this field >

Dense wavelength division multiplexing networks: principles and applications

In this tutorial overview, the principles, advantages, challenges, and practical requirements of optical orthogonal frequency division multiplexing (OFDM)-based optical access are presented, with an emphasis on orthogonal frequency division multiple access (OFDMA) for application in next-generation passive optical networks (PON). General OFDM principles, including orthogonality, cyclic prefix use, frequency-domain equalization, and multiuser OFDMA are summarized, followed by an overview of various optical OFDM(A) transceiver architectures for next-generation PON. Functional requirements are outlined for high-speed digital signal processors (DSP) and data converters in OFDMA-PON. A techno-economic outlook for such a “software-defined,” DSP-based optical access platform is also provided.

OFDM for Next-Generation Optical Access Networks

Feature Issue on
Optical Access Networks (OAN) The passive optical network (PON) is
an optical fiber based network architecture, which can provide much higher bandwidth
in the access network compared to traditional copper-based networks. Incorporating
wavelength-division multiplexing (WDM) in a PON allows one to support much higher
bandwidth compared to the standard PON, which operates in the "single-wavelength
mode" where one wavelength is used for upstream transmission and a separate one is
used for downstream transmission. We present a comprehensive review of various
aspects of WDM-PONs proposed in the literature. This includes enabling device
technologies for WDM-PONs and network architectures, as well as the corresponding
protocols and services that may be deployed on a WDM-PON. The WDM-PON will become a
revolutionary and scalable broadband access technology that will provide high
bandwidth to end users.

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Wavelength-division-multiplexed passive optical network (WDM-PON) technologies for broadband access: a review (Invited)

5G is the next cellular generation and is expected to quench the growing thirst for taxing data rates and to enable the Internet of Things. Focused research and standardization work have been addressing the corresponding challenges from the radio perspective while employing advanced features, such as network densification, massive multiple-input-multiple-output antennae, coordinated multi-point processing, inter-cell interference mitigation techniques, carrier aggregation, and new spectrum exploration. Nevertheless, a new bottleneck has emerged: the backhaul. The ultra-dense and heavy traffic cells should be connected to the core network through the backhaul, often with extreme requirements in terms of capacity, latency, availability, energy, and cost efficiency. This pioneering survey explains the 5G backhaul paradigm, presents a critical analysis of legacy, cutting-edge solutions, and new trends in backhauling, and proposes a novel consolidated 5G backhaul framework. A new joint radio access and backhaul perspective is proposed for the evaluation of backhaul technologies which reinforces the belief that no single solution can solve the holistic 5G backhaul problem. This paper also reveals hidden advantages and shortcomings of backhaul solutions, which are not evident when backhaul technologies are inspected as an independent part of the 5G network. This survey is key in identifying essential catalysts that are believed to jointly pave the way to solving the beyond-2020 backhauling challenge. Lessons learned, unsolved challenges, and a new consolidated 5G backhaul vision are thus presented.

5G Backhaul Challenges and Emerging Research Directions: A Survey

The next-generation passive optical network stage 2 (NG-PON2) effort was initiated by the full service access network (FSAN) in 2011 to investigate on upcoming technologies enabling a bandwidth increase beyond 10 Gb/s in the optical access network. The FSAN meeting in April 2012 selected the time- and wavelength-division multiplexed passive optical network (TWDM-PON) as a primary solution to NG-PON2. In this paper, we summarize the TWDM-PON research in FSAN by reviewing the basics of TWDM-PON and presenting the world's first full-system 40 Gb/s TWDM-PON prototype. After introducing the TWDM-PON architecture, we explore TWDM-PON wavelength plan options to meet the NG-PON2 requirements. TWDM-PON key technologies and their respective level of development are further discussed to investigate its feasibility and availability. The first full-system 40 Gb/s TWDM-PON prototype is demonstrated to provide 40 Gb/s downstream and 10 Gb/s upstream bandwidth. This full prototype system offers 38 dB power budget and supports 20 km distance with a 1:512 split ratio. It coexists with commercially deployed Gigabit PON (G-PON) and 10 Gigabit PON (XG-PON) systems. The operator-vendor joint test results testify that TWDM-PON is achievable by the reuse and integration of commercial devices and components.

Time- and Wavelength-Division Multiplexed Passive Optical Network (TWDM-PON) for Next-Generation PON Stage 2 (NG-PON2)

We demonstrate a passive optical network (PON), based on a wavelength-division multiplexing router, with modulators (instead of lasers) at the subscriber terminals. A single, cost-shared, tunable laser is time-division multiplexed to provide bidirectional switched WDM services for N subscribers with independent formats and bit-rates for each. Simultaneous support of telephony and compressed digital video are presented in which RF subcarrier multiplexing is used to provide service segregation and resolve upstream packet contention. >

A wavelength-division multiplexed passive optical network with cost-shared components

An optical frequency-division-multiple-access (FDMA) star network is analyzed and demonstrated experimentally using two 45-Mb/s frequency-shift-keyed (FSK) laser channels at 1.5 mu m. A tunable fiber Fabry-Perot (FFP) filter is used to select channels and convert FSK to intensity modulation for direct detection. The analysis predicts and experiment supports a minimum channel spacing of about six times bit rate B for a single FFP. These constraints are similar to those for more complex heterodyne demultiplexing. Estimates show that a network with 1000 users, independent of bit rate, is feasible with a tandem FFP. For B=1 Gb/s per channel the network capacity would be 1 Tb/s. >

FDMA-FSK star network with a tunable optical filter demultiplexer

We investigate using Fabry-Perot lasers as the upstream transmitters in a wavelength-division-multiplexed passive optical network (WDM-PON). We demonstrate transmission of a 10-Mb/s signal through each port of a wavelength-grating router followed by 18 km of fiber using an uncooled Fabry-Perot laser. These signals could be subcarrier multiplexed together, so that each user would have a dedicated radio-frequency channel. Since Fabry-Perot lasers provide more output power than low-cost light-emitting diodes, this may enable deployment of WDM-PON's in areas where optical loss prohibits the use of other low cost optical sources. The bit-rate is limited by mode-fluctuations being converted into intensity noise when transmitted through the router.

A spectrally sliced PON employing Fabry-Perot lasers

A passive optical network is provided that spectrally slices optical signals transmitted in both upstream and downstream directions utilizing wavelength division multiplexing routing. The passive optical network preferably includes an incoherent signal source at both ends to provide signals that are spectrally sliced according to optical frequency. The downstream information may be transmitted in a conventional data format. The upstream transmissions may be segregated by subcarrier multiplexing, time scheduling or wavelength division multiplexing. A broadcast signal can be overlayed with point-to-point information for transmission to plural network units.

Wavelength division multiplexing passive optical network including broadcast overlay

A passive optical network is provided that spectrally slices optical signals transmitted in both upstream and downstream directions utilizing wavelength division multiplexing routing. The passive optical network preferably includes a broadband optical signal source at both ends to provide signals that are spectrally sliced according to optical frequency. The downstream information may be transmitted in a conventional data format. The upstream transmissions may be segregated by subcarrier multiplexing, time scheduling or wavelength division multiplexing. At the subscriber end of the network there is an optical network unit which includes a device coupling the downstream fiber to the upstream fiber. Such coupling allows the passive optical network to perform enhanced diagnostic tests.

Patrick P. Iannone

Papers

A wavelength-division multiplexed passive optical network with cost-shared components

FDMA-FSK star network with a tunable optical filter demultiplexer

A spectrally sliced PON employing Fabry-Perot lasers

Wavelength division multiplexing passive optical network including broadcast overlay

Passive optical network with diagnostic loop-back