This paper reviews advanced optical burst switching (OBS) and optical packet switching (OPS) technologies and discusses their roles in the future photonic Internet. Discussions include optoelectronic and optical systems technologies as well as systems integration into viable network elements (OBS and OPS routers). Optical label switching (OLS) offers a unified multiple-service platform with effective and agile utilization of the available optical bandwidth in support of voice, data, and multimedia services on the Internet Protocol. In particular, OLS routers with wavelength routing switching fabrics and parallel optical labeling allow forwarding of asynchronously arriving variable-length packets, bursts, and circuits. By exploiting contention resolution in wavelength, time, and space domains, the OLS routers can achieve high throughput without resorting to a store-and-forward method associated with large buffer requirements. Testbed demonstrations employing OLS edge routers show high-performance networking in support of multimedia and data communications applications over the photonic Internet with optical packets and bursts switched directly at the optical layer

Optical Packet and Burst Switching Technologies for the Future Photonic Internet

Lightwave communications is a necessity for the information age. Optical links provide enormous bandwidth, and the optical fiber is the only medium that can meet the modern society's needs for transporting massive amounts of data over long distances. Applications range from global high-capacity networks, which constitute the backbone of the internet, to the massively parallel interconnects that provide data connectivity inside datacenters and supercomputers. Optical communications is a diverse and rapidly changing field, where experts in photonics, communications, electronics, and signal processing work side by side to meet the ever-increasing demands for higher capacity, lower cost, and lower energy consumption, while adapting the system design to novel services and technologies. Due to the interdisciplinary nature of this rich research field, Journal of Optics has invited 16 researchers, each a world-leading expert in their respective subfields, to contribute a section to this invited review article, summarizing their views on state-of-the-art and future developments in optical communications.

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Roadmap of optical communications

The main bandwidth bottleneck in today's networks is in the access segment. To address that bottleneck, broadband fiber access technologies such as passive optical networks (PONs) are an indispensable solution. The industry has selected time-division multiplexing (TDM) for current PON deployments. To satisfy future bandwidth demands, however, next-generation PON systems are being investigated to provide even higher performance. In this paper, we first review current TDM-PONs; we designate them as generation C. Next, we review next-generation PON systems, which we categorize into C+1 and C+2 generations. We expect C+1 systems to provide economic near-term bandwidth upgrade by overlaying new services on current TDM-PONs. For the long term, C+2 systems will provide more dramatic system improvement using wavelength division multiplexing technologies. Some C+2 architectures require new infrastructures and/or equipment, whereas others employ a more evolutionary approach. We also review key enabling components and technologies for C+1 and C+2 generations and point out important topics for future research.

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Next-Generation Optical Access Networks

This paper reviews the future directions of next generation passive optical networks. A discussion on standardized 10 Gb/s passive optical network (PON) systems is first presented. Next, new technologies that facilitate multiple access beyond 10 Gb/s time division multiple access (TDMA)-PONs will be reviewed, with particular focus on the motivation, key technologies, and deployment challenges. The wavelength division multiplexed (WDM) PON will be discussed and in combination with TDMA, the hybrid WDM/TDMA PON will be reviewed in the context of improving system reach, capacity, and user count. Next, discussions on complementary high-speed technologies that provide improved tolerance to system impairments, capacity, and spectral efficiency will be presented. These technologies include digital coherent detection, orthogonal frequency division multiple access (OFDMA), and optical code division multiple access (OCDMA).

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Next-Generation Broadband Access Networks and Technologies

The wavelength-division-multiplexed passive optical network (WDM-PON) is considered to be the next evolutionary solution for a simplified and future-proofed access system that can accommodate exponential traffic growth and bandwidth-hungry new applications. WDM-PON mitigates the complicated time-sharing and power budget issues in time-division-multiplexed PON (TDM-PON) by providing virtual point-to-point optical connectivity to multiple end users through a dedicated pair of wavelengths. There are a few hurdles to overcome before WDM-PON sees widespread deployment. Several key enabling technologies for converged WDM-PON systems are demonstrated, including the techniques for longer reach, higher data rate, and higher spectral efficiency. The cost-efficient architectures are designed for single-source systems and resilient protection for traffic restoration. We also develop the integrated schemes with radio-over-fiber (RoF)-based optical-wireless access systems to serve both fixed and mobile users in the converged optical platform.

Key Technologies of WDM-PON for Future Converged Optical Broadband Access Networks [Invited]

In this work, the influence of the distribution element position and the reflective optical network unit (ONU) gain in wavelength-division-multiplexing passive optical networks are reported. After the theoretical and experimental analysis, it is determined that the best crosstalk-to-signal ratio is achieved if the multiplexer is placed either in the ONU or optical light termination vicinity, and the ONU gain has a new optimum value depending on the position. Also, it is demonstrated that Rayleigh backscattering is generally irrelevant in downstream transmission.

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Optimization of Rayleigh-Limited WDM-PONs With Reflective ONU by MUX Positioning and Optimal ONU Gain

We present a new remotely-amplified single-fibre-tree double-fibre-ring PON architecture for large capacity and scalability. We show its feasibility demonstrated by experimental results from our test-bed.

Remotely Amplified SARDANA: Single-fibre-tree Advanced Ring-based Dense Access Network Architecture

We explore a new wavelength management for ultradense wavelength division multiplexing-passive optical network with randomly distributed optical network unit (ONU) wavelengths, controlled with limited thermal tunability. Static and dynamic wavelength assignment paradigms and heuristic assignment schemes for spectrum management are proposed, simulated, and compared. ONU acceptances in activation processes and ONU availability ratios up to 99.99% are obtained in standard environmental conditions.

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Statistical UDWDM-PONs Operating With ONU Lasers Under Limited Tunability

A simple method for wavelength control of economical random non-preselected independent ONU source, by OLT monitoring and thermal tuning, is presented and dimensioned. It reduces the spectral overlap probability and increases the cost-effectiveness of an OFDMA-PON.

Dimensioning of OFDMA PON with non-preselected-independent ONUs sources and wavelength-control

A long-reach, high-density centralized-light access network using remote amplification and Reflective SOA for upstream remodulation in a user-single-fiber completely passive WDM-PON providing broadband to >1000 users distributed along large distances is presented.

Victor Polo

Papers

Optimization of Rayleigh-Limited WDM-PONs With Reflective ONU by MUX Positioning and Optimal ONU Gain

Remotely Amplified SARDANA: Single-fibre-tree Advanced Ring-based Dense Access Network Architecture

Statistical UDWDM-PONs Operating With ONU Lasers Under Limited Tunability

Dimensioning of OFDMA PON with non-preselected-independent ONUs sources and wavelength-control

Hybrid Dual-fiber-Ring with Single-fiber-Trees Dense Access Network Architecture using RSOA-ONU