Shinji Yamashita

Sleep Mode for Energy Saving PONs: Advantages and Drawbacks

A common approach to reduce energy consumption in communication networks is to allow network elements to switch to sleep mode. While this technique has been widely utilized in wireless networks, recent studies have proposed to exploit sleep mode in wired networks to conserve energy as well. This paper focuses on some feasible implementations of sleep mode in passive optical networks (PONs). In particular, ONU sleep mode is considered. The paper first outlines the ONU wake-up process using current time division multiplexing (TDM) PON protocols. Current and novel optical network unit (ONU) architectures that selectively switch-off some elements are then described. Their advantages in terms of energy savings are analytically computed under different traffic scenarios. Using the proposed architectures, analytical results show more than 50% energy saving under realistic TDM traffic. Finally, possible drawbacks in terms of new scheduling challenges are also discussed and potential solutions are presented.

Energy Management Mechanism for Ethernet Passive Optical Networks (EPONs)

In the past few years, Ethernet Passive Optical Networks (EPONs) have rapidly gained large popularity in broadband access networks. However the current standard has no management protocols aiming at reducing power consumption. In this paper, we propose an Energy Management Mechanism (EMM) within the IEEE 802.3ah control scheme. The main idea is to switch Optical Network Units (ONUs) to sleep mode and determine a suitable wakeup time schedule at the Optical Line Terminal (OLT). In the proposed EMM there is a trade-off between maximizing the power saving and guaranteeing the network performance. We compare two types of downstream scheduling schemes, Upstream Centric Scheduling (UCS) and Downstream Centric Scheduling (DCS), which are different in the way they assign active and sleep states to ONUs. Simulation results in terms of energy consumption and queuing delay are shown for the EMM based EPON system.

Energy efficiency in passive optical networks: where, when, and how?

This article provides an overview of current efforts in reducing energy consumption in passive optical access networks. Both ITU-T and IEEE standardized PONs are considered. The current solutions proposed by standardization authorities, industry, and academia are classified based on the layer they address in the standardized architectures: physical layer, data link layer, and hybrid. Then, the article provides answers to major questions, such as where, when, and how to reduce PON energy consumption in TDM PONs by means of a quantitative evaluation. Results show that to reduce energy consumption, ONUs must be provided with physical devices that are not only power-efficient but also provide improved services (e.g., fast synchronization) to upper layers. For this latter purpose, novel physical ONU architectures are proposed to speed up the synchronization process and enable effective data link layer solutions. Finally, the feasibility of switching ONUs to low power mode in idle slots is assessed through a testbed implementation.

Photonic components for future fiber access networks

Fiber based access networks are recognized as promising technologies for solving broadband bandwidth bottlenecks. TDM-PONs, which are passive and non-reconfigurable, are the most widely deployed type of fiber access networks today. However, due to their passive nature, TDM-PONs encounter several issues such as inflexible coverage, lack of intelligence for control, and inability to counter security attacks. Based on current issues in optical access networks, we propose a novel non-volatile, reconfiguration node. The proposed remote node can reconfigure the network to adapt to varying degrees of deployment conditions and/or network attacks. Moreover, the proposed remote node incorporates a novel quasi-passive device that reconfigures using remotely supplied energy from CO. This quasi-passive device technology does not consume any energy once it reconfigures into a new latching states. Therefore, the proposed remote node has very low energy consumption and does not require local power supply to preserve the passivity of the passive distribution network. In particular, the proposed quasi-passive device technology is implemented using a novel tri-state Micro- Electro-Mechanical System (MEMS) actuator structure and the device demonstrates very small energy consumption requirement to enable energy be remotely supplied from CO. Also, the MEMS structure is shown to demonstrate acceptable insertion losses to makes it suitable for flexible energy distribution. Simulation study shows the proposed reconfigurable device would outperform traditional passive splitter in terms of maximum number of supportable users under realistic deployment conditions.

Effective Utilization of Network by Spectrum Defragmentation

We experimentally demonstrate hitless spectrum defragmentation and show the effectiveness of spectrum defragmentation through network simulations. In addition, we implement the OpenFlow extensions for spectrum defragmentation.

Spatial Light Phase Modulator With Bidirectional Tilt–Piston Micromirror Array—Part II: Fabrication and Experiment

In part I of this paper, we have proposed a novel structure of microelectromechanical-systems-based 1-D spatial light phase modulator (SLPM). We have discussed the design of the device and derived the optimum parameters to satisfy the target specifications. In part II, we focus on the fabrication process and experimental results of the device. We show that this device configuration allows us to use a simple fabrication process. We fabricated the device consisted of 24 micromirrors and realized the tilt and piston motions successfully. The measured dc (rotation angle and displacement on driving voltage) and ac (frequency response) characteristics matched well to the simulated data derived in part I. We also examined the distribution of the resonant frequencies over 24 micromirrors and verified that the variance was kept within 2%. As one of the applications of the device, we applied the device to optical beam shaping and succeeded in shaping the optical beam properly depending on the surface patterns of the SLPM. With these achievements, we show that the device can be adopted to a wide variety of applications in optical communication systems and optical signal processing.

Novel Spatial Light Phase Modulator with Bidirectional Tilt-Pistonmicromirror Array

We have proposed a novel structure of one dimensional spatial light phase modulator (SLPM) that consists of a micromirror array on an SOI wafer and ITO (Indium Tin Oxide) electrodes on a glass plate. Each micromirror can exhibit bidirectional single-axis rotation, as well as up- and down- translation motion. We have fabricated the device, and confirmed its motion experimentally.

Spatial Light Phase Modulator With Bidirectional Tilt–Piston Micromirror Array—Part I: Principle and Design

This paper proposes a novel structure of microelectromechanical-systems-based 1-D spatial light phase modulator (SLPM) that consists of a micromirror array on a silicon-on-insulator (SOI) wafer and indium tin oxide (ITO) electrodes on a glass plate. Each micromirror can exhibit bidirectional single-axis tilt, as well as up-and-down piston motions by combining the applied voltage on two ITO electrodes placed over the micromirror and the substrate of SOI (in the case that the substrate is energized, all micromirrors go down simultaneously). This device configuration enables SLPM to be fabricated by a simple process. Part I of this paper focuses on the principles and the design of the device. The optimum parameters of the device are derived to realize both tilt and piston motions, considering ways to reduce mirror warpage and crosstalk from the ITO electrode from the adjacent mirror. We simulate the dc and ac characteristics of the device and confirm that the designs that we optimized satisfy the target specifications to be widely used in optical communication systems.

Extension of OpenFlow protocol to support optical transport network, and its implementation

By having the OpenFlow protocol support Optical Transport Networks (OTN) and work as the unified control interface for multilayer (L0-L4) networks, a simple and cost-effective multilayer Software Defined Networking (SDN) controller can be created. Our aim is to propose and standardize the extended OpenFlow protocol to support OTN in Open Networking Foundation (ONF). We describe the approved specification, and the process from proposal to standard. We applied this extension to our OpenFlow controller and OpenFlow agent and succeeded in demonstrating that the extension works as desired in single- and multi-vendor environments. Future directions for OpenFlow extension and modeling of multilayer integrated nodes are also discussed.

Optical beam shaping by spatial light phase modulator with bidirectional tilt-piston micromirror array

We have succeeded in controlling the optical beam profile by MEMS spatial light phase modulator experimentally. The modulator proposed by our group has 1-D array of bidirectional tilt-piston micromirrors driven by electrostatic force.