Front Matter: Volume 8646

In this paper, we review emerging technologies to build up Tb/s per channel transmission capacity. We discuss the appropriate choice of modulation formats as well as options for generation and multiplexing of multiple lower bit rate subchannels. Different multiplexing approaches, mainly based on various implementations of orthogonal frequency division multiplexing and Nyquist wavelength division multiplexing are introduced. Their main strengths and weaknesses are discussed by means of selected experimental demonstrations.

High degree of heterogeneity of future optical networks, such as services with different quality-of-transmission requirements, modulation formats and switching techniques, will pose a challenge for the control and optimization of different parameters. Incorporation of cognitive techniques can help to solve this issue by realizing a network that can observe, act, learn and optimize its performance, taking into account end-to-end goals. In this letter we present the approach of cognition applied to heterogeneous optical networks developed in the framework of the EU project CHRON: Cognitive Heterogeneous Reconfigurable Optical Network. We focus on the approaches developed in the project for optical performance monitoring and power consumption models to implement an energy efficient network.

In Metropolitan Area Networks (MANs), point-to-multipoint applications, such as IPTV, video-on-demand, distance learning, and content distribution, can be efficiently supported through light-tree-based multicastcommunications instead of lightpath-based unicast-communications. The application of multicasting for such traffic is justified by its inherent benefits of reduced control and management overhead and elimination of redundant resource provisioning. Supporting such multicast traffic in Flexible optical WDM (FWDM) networks that can provision light-trees using optimum amount of spectrum within flexible channel spacing leads to higher wavelength and spectral efficiencies compared to the conventional ITU-T fixed grid networks. However, in spite of such flexibility, the residual channel capacity of stranded channels may not be utilized if the network does not offer channels with arbitrary line rates. Additionally, the spectrum allocated to guard bands used to isolate finer granularity channels remains unutilized. These limitations can be addressed by using traffic grooming in which low-rate multicast connections are aggregated and switched over high capacity light-trees. In this paper, we address the multicast traffic grooming problem in FWDM networks, and propose a novel auxiliary graph-based algorithm for the first time. The performance of multicast traffic grooming is evaluated in terms of spectral, cost, and energy efficiencies compared to lightpath-based transparent FWDM networks, lightpathbased traffic grooming-capable FWDM networks, multicast-enabled transparent FWDM networks, and multicast traffic grooming-capable fixed grid networks. Simulation results demonstrate that multicast traffic grooming in FWDM networks not only improves spectral efficiency, but also cost, and energy efficiencies compared to other multicast traffic provisioning approaches of FWDM and fixed grid networks.

This paper reviews techniques used for optical passive circuits and the integration components adopted for DQPSK / DPQPSK receivers using silica based planar lightwave circuit technology.

Through the recent progress in information oriented society, the required information volume is expanding rapidly. Under these circumstances, high-speed and high-capacity optical communication systems are deployed in the industry. Especially high speed optical transceiver is the key device to realize high-speed system, and the practical development is accelerated in the industry. In order to develop these leading edge products timely, the establishment of the global standards is strongly demanded in the industry. Based on these backgrounds, Forum standardization bodies such as OIF/IEEE802.3 are energetically creating the standards in the industry. With regard to 40G/100G standardization activities, OIF leads telecom field and IEEE802.3 leads datacom field, and both activities become important recently. The recent topics of these two standardization bodies are reviewed and its future direction is discussed. Two organizations have completed the 1st gen 40G/100G standards, and soon after they starts creating the 2nd gen 40G/100G standards for targeting more compact size and low power consumption transceivers, mainly because the unexpected huge increase of the information volume. Key factor for the 2nd gen is the low power consumption technology such as new CMOS technology and the design improvement of the heat dissipation. Also from the mechanical point of view, the development of the new electrical interface such as 25G/50G and the brand-new hybrid integration technologies are strongly expected in the industry. New configurations using silicon-photonics are reported by many organizations in the recent standardization meetings.

Dynamic path switching in lower layers such as optical or sub-wavelength layer-1 path connections is essential for future networks to provide end-to-end, bandwidth-guaranteed, large-capacity services without energy crunch. While this is almost generally agreed, the number of ports in optical switches tends to be limited by technological difficulties, severely restraining the scale of the network. However, video-related services, that occupies most of the traffic nowadays, could significantly alleviate such restraints if we utilized the nature of video usage. In most cases, video-related services are virtually provided through prior reservation scheme in which a relatively high call-blocking probabilities or long latency for a connection can be tolerated. This situation allows us to accommodate a relatively high number of subscribers with a limited number of switch ports. This paper shows that a network using optical switches with a technologically feasible number of ports, multi-granular paths, and a hierarchical network topology can be of a national scale accommodating several tens of millions of subscribers. The purpose of detailing a plausible network topology is to show that such a network offers a benefit of energy efficiency approximately three orders of magnitude compared with that extrapolated from recent router-based networks. We then discuss important technical aspects of such dynamic optical path networks including our several research activities. We emphasize the importance of vertically integrated research activities from application to device layers to develop the dynamic optical path networks.

After the East Japan Great Earthquake, Tohoku University has established Research Organization of Electrical Communication to achieve the most advanced disaster-resistant information communication network in the world. In this paper, we will introduce our projects of “Disaster-Resistant Information Communication Network” based on industry-academia-government collaboration.

Latency is an important figure to describe performance of transmission systems for particular applications, such as data transfer for earthquake early warning, transaction for financial businesses, interactive services such as online games, etc. Latency consists of delay due to signal processing at nodes and transmitters, and of signal propagation delay due to propagation of electromagnetic waves. The lower limit of the latency in transmission systems using conventional single mode fibers (SMFs) depends on wave propagation speed in the SMFs which is slower than c. Photonic crystal fibers, holly fibers and large core fibers can have low effective refractive indices, and can transfer light faster than in SMFs. In free-space optical systems, signals propagate with the speed c, so that the latency could be smaller than in optical fibers. For example, LEO satellites would transmit data faster than optical submarine cables, when the transmission distance is longer than a few thousand kilometers. This paper will discuss combination of various transmission media to reduce negative impact of the latency, as well as applications of low-latency systems.

Computational intelligence techniques have appeared as efficient alternatives to solve complex problems, such as in optimization of multi-objective problems. These techniques have been used to solve hard problems in optical networks, such as the impairment-aware routing and wavelength assignment problem, the design of the physical and the logical topology, and the placement of high cost devices along the network where necessary, such as regenerators and wavelength converters. This paper presents some examples of the use of evolutionary computation, swarm intelligence and neurocomputing to solve these optical network problems.

Next generation metro aggregation systems are expected to use integrated lambda, circuit and packet switching platforms. We analyzed a typical Tier 1 aggregation scenario using a converged transport platform offering OTN, MPLS-TP and lambda switching. Vertical integration (multiple transport technologies) and horizontal integration (multiple service types) yielded about one third savings over a traditional L3 over DWDM approach. The number of wavelengths needed was roughly halved. The usage of hybrid interfaces which allow sharing the wavelength between OTN and MPLS services leads to additional savings which will increase as the line rate shifts from 10G to 40G and 100G.

The Internet is entering an era of cloud computing to provide more cost effective, eco-friendly and reliable services to consumer and business users and the nature of the Internet traffic will undertake a fundamental transformation. Consequently, the current Internet will no longer suffice for serving cloud traffic in metro areas. This work proposes an infrastructure with a unified control plane that integrates simple packet aggregation technology with optical express through the interoperation between IP routers and electrical traffic controllers in optical metro networks. The proposed infrastructure provides flexible, intelligent, and eco-friendly bandwidth on demand for cloud computing in metro areas.

In conventional optical FMCW fiber network monitoring the spatial resolution is limited by the laser linewidth. To overcome this limitation, two different approaches of optical network monitoring based on FMCW are eval- uated and their performance is experimentally compared in terms of spatial resolution, dynamic range and multiple-target detection capability. Additionally, the FMCW monitoring system is combined with a signaling scheme for reconfigurable optical networks based on optical chirp slope detection. This opens the possibility to simultaneously monitor the optical network and to switch network key components from a central point hence paving the way to greener photonic networks.

We experimentally evaluated the transmission performance of discrete multi-tone (DMT) modulation at wavelengths in the 1300-nm and 1550-nm regions and analyzed the degradation factors. By using their countermeasures to extend transmission distance, we realized the capacity of 100 Gbps with 2WDM x 50 Gbps over 80 km. To our knowledge, this work is the highest capacity in 80-km transmission system using direct modulation and direct detection. These results show that the DMT modulation can be used to realize high capacity transceiver with simple and cost effective configuration for the bi-directional transmission system like a passive optical network.

The overall spectral efficiency in optical transmission systems need to be enhanced by employment of advanced modulation and coding schemes as well as the advanced detection techniques. In parallel, novel networking concepts with the griddles and elastic bandwidth allocation are needed to increase the network dynamics and flexibility. In this paper we provide an overview of these techniques and concepts, which have been or may be used in the next generation high-speed optical network.

Visible Light Communication (VLC) has received more and more attention in recent years. In this paper, we propose a novel configuration of unidirectional subcarrier multiplexing (SCM) -wavelength division multiplexing (WDM) -VLC system adopting quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM) modulation. Based on this configuration, we successfully demonstrate a 3x1 multiple-input single-output (MISO) OFDM-VLC transmission experiment using three blue phosphor LEDs. The transmission distance can be as long as 140cm. We also demonstrate an 800-Mb/s MISO SCM-WDM VLC transmission experiment based on RGB-LED with 66-cm transmission distance. In the two experiments, pre-equalization and post-equalization both are implemented to compensate for the poor frequency response of LEDs. And the properties of EVM and BER in all channels are measured and analysed.

Discrete multi-tone (DMT) technology is an attractive modulation technique for short reach optical transmission system. One of the main factors that limit the performance of the 1.5-m band DMT system is the interplay between the chromatic dispersion of the transmission fiber and the chirp characteristic of the transmitter. We experimentally measured and compared the chirp characteristics of various modulator configurations, which are lithium-niobate Mach-Zehnder modulator, directly modulated laser, and electro-absorption modulator, by the frequency discriminator method using MZ interferometer. We also measured and compared the transmission characteristics of the transmitters using above-mentioned modulators and discuss the suitable transmitter configuration for DMT technology.

We report Nyquist-wavelength-division-multiplexed (Nyquist-WDM) seven-channel 192-Gb/s polarization-divisionmultiplexed 16-QAM transmission. The transmitter comprises high-speed digital-to-analog converters (DACs) fabricated with 0.5-μm indium phosphide (InP) heterojunction bipolar transistors and an FPGA-based multi-channel digital signal generator, and enables us to perform transmitter-side digital signal processing (DSP) for spectrally efficient WDM transmission. The transmitter generated 24-Gbaud electrical waveforms for optical 16-QAM signals with a digital pre-filter. Using low-loss and low-nonlinear pure silica core fiber, we achieved 25-GHz-spaced seven-channel 192 Gb/s transmission distance of 480 km with a spectral efficiency of 7.17 b/s/Hz.

Capacity demand has continued to increase exponentially. For the system capacity expansion, increasing the spectral efficiency by using multi-level modulation formats may be a good candidate. One drawback of multi-level formats is the requirement of higher signal-to-noise ratio. This requests more frequent OEO regenerations due to its shorter reach. Optical regeneration using phase sensitive amplifier (PSA) has a possibility to prolong the reach by suppressing phase noise generated through fiber transmission. In this paper, we discuss a network architecture having optical restoration process, and its advantages and merits. Then, we show proposed PSA and optical restoration schemes and their system tolerance against chromatic dispersion.

We successfully developed the Quantum Dot (QD) light source in the T- and O-band (Thousand-band: 1.000–1.260 μm and O-band: 1.260–1.360 μm).We used the optical gain chip properties of a single InAs/InGaAs QD to develop a 1.3 μm waveband QD optical frequency comb laser (QD-CML) as the novel functional wavelength divisio nmultiplexing (WDM) light source. The QD-CML can be used for stable generation of multiple-wavelength peaks that the QD-CML can be selected and controlled using the optical interference of the etalon filter. We used holey fiber (HF) transmission line to successfully demonstrate an O-band photonic transport system. In this experiment, each single peak could be clearly selected in the wavelength range the 1286- to 1302 nm. An error-free data transmission of the 10-Gb/s signal with stable multiple-wavelength channels that were generated from a newly developed 1.3 μm waveband multiple-wavelength quantum dot light source was achieved over the low-loss HF that was 8 -km long. We suggest that the low cross-talk for a data transmission can be achieved using the multiple-wavelength peaks from the QD light source. Based on these experimental results, it is clear that the generation of multiple-wavelength peaks in the 1.3 μm waveband can be successfully achieved using from the multiple-wavelength QD light source, which acts as a single QD optical gain device.