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.

/pdf/roadmap-of-optical-communications-22jmvturxy.pdf

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.

/pdf/next-generation-optical-access-networks-41pmztcn8d.pdf

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).

/pdf/next-generation-broadband-access-networks-and-technologies-hinsjog43g.pdf

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]

Reflective ONUs by integration of Erbium Doped Waveguide Amplifiers

An ONU transmitter for UDWDM PONs based on direct phase modulated distributed feedback lasers (DFB) through digital beat signals is proposed and experimentally tested. The amplitude and duty cycle of the modulating signal are optimized for a DPKS signal. We achieved sensitivities of −50.5 dBm, and −45 dBm for bit rates of 2.5 Gb/s, and 5 Gb/s respectively at BER = 4×10−3 with an intradyne coherent receiver.

Direct Phase Modulation for UDWDM ONU with Beat Signals

The performance of a directly phase modulated RSOA and an equalized DFB is compared with homodyne coherent detection for udWDM-PONs. Both device produce similar signals but the receiver sensitivity improves by 1.5dB at BER=10−3 with the RSOA because of its flatter phase response and less intensity modulation residual than the DFB.

http://ieeexplore.ieee.org/iel7/7173926/7193279/07193364.pdf

Performance comparison between direct phase modulated DFB and RSOA for cost effective transmitter in udWDM-PONs

A coherent WDM-PON achieving ultra-dense spectral allocation is reported. The ONU at user premises is built of coherent transceivers with two paired low-cost DFB lasers, one as local oscillator and the other as transmitter, offering simplicity and economy hardware. The ONU DFB lasers are paired to realize a simple blind activation process, having wavelengths with limited thermal tunability controlled by thermo-electric coolers (TECs). A MAC at the OLT at central office manages the spectrum channel assignment: the OLT furnishes an optical carrier wavelength for the new active ONU to obtain reception in a Dynamic Wavelength Allocation (DWA) by a smart control algorithm, thus assigning a down-channel; subsequently, another paired up-channel is also allocated to the ONU laser transmitter. The MAC can reassign the channels because of interference, collision or any network needs. The channelization of the optical bandwidth is flexible, thus adapting to different user bandwidths, serving all sorts of bit rates and suited for 5G technologies. Measures in an activation process and in channel reassignment have been performed in environment conditions, demonstrating the system feasibility.

Practical Design of a Coherent Ultra-Dense WDM-PON with Paired DFB Lasers

We experimentally demonstrate a novel low-cost transmitter based on a directly modulated DFB with phase diversity in time. A sensitivity of −38dBm at 2.5Gb/s was achieved for 6.25GHz spaced UDWDM-PON with a simple intradyne receiver having 1 photodiode per polarization.

Victor Polo

Papers

Reflective ONUs by integration of Erbium Doped Waveguide Amplifiers

Direct Phase Modulation for UDWDM ONU with Beat Signals

Performance comparison between direct phase modulated DFB and RSOA for cost effective transmitter in udWDM-PONs

Practical Design of a Coherent Ultra-Dense WDM-PON with Paired DFB Lasers

Directly modulated DFB with phase diversity in time polarization independent intradyne receiver for UDWDM-PON