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]

The network dimensioning for a TDM-PON deployment based on reflective ONUs is presented in order to optimize number of users for efficient exploitation. Due to wavelength reuse, the study is focused on the power budget and DS-ER/US-oSRR critical relation. These and other parameters are analyzed theoretical and experimentally and optimal design values are presented. A TDM-PON for 32 users/20km is possible at BER = 5E-4 reference level.

Network dimensioning for a TDM-PON deployment Single-fibre single-wavelength-reuse based on reflective ONUs

Coherent ultra-dense wavelength division multiplexing (UDWDM) architecture constitutes an approach to serve hundreds of users in a passive optical network (PON) with high spectrum efficiency. We propose and experimentally test a directly phase modulated distributed feedback (DFB) laser with a Nyquist shaped beat signal. An Rx sensitivity of −44 dBm at BER=10e-3 is achieved for dedicated 2.5 Gb/s/user in only 6.25 GHz spaced. Even more, the proposed technique tolerates a differential link-loss of 15 dB.

Coherent Nyquist UDWDM-PON with 2.5 Gb/s/user and 15 dB differential link-loss

We apply digital pre-emphasis to compensate for the frequency response non-idealities of low-cost optical transmitters. It enables transmission beyond 10Gb/s with 2/4/8-DPSK using directly modulated lasers and coherent detection for optical access.

Digital pre-emphasis for 10Gb/s with low-cost directly phase-modulated lasers for PONs

Digital Nyquist-WDM is experimentally demonstrated using RSOA-based colorless ONUs, providing a 6-fold enhancement of transmission capacity through 25km fiber, and showing digital Nyquist-WDM as promising candidate for cost-effective flexible bandwidth allocation in PONs.

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Digital Nyquist WDM for access networks using limited bandwidth reflective semiconductor optical amplifiers

Flexible bandwidth allocation strategies in a statistical OFDM-PON are experimentally shown to compensate for differential link loss allowing for proper detection of ONUs separated up to 55km (11.4dB).

Victor Polo

Papers

Network dimensioning for a TDM-PON deployment Single-fibre single-wavelength-reuse based on reflective ONUs

Coherent Nyquist UDWDM-PON with 2.5 Gb/s/user and 15 dB differential link-loss

Digital pre-emphasis for 10Gb/s with low-cost directly phase-modulated lasers for PONs

Digital Nyquist WDM for access networks using limited bandwidth reflective semiconductor optical amplifiers

Differential link-loss compensation through dynamic bandwidth assignment in statistical OFDMA-PON