Jong-Dug Shin

Optical packet switching in core networks: between vision and reality

The research on optical packet switching (OPS) has witnessed considerable progress in the 1990s. We examine the future potential of OPS in the core network by discussing this switching approach and the current status of a number of its enabling technologies. Many of these technologies are still in the stage of research and experimentation. We see that optical packet switching may be deployed in the long-term future subject to satisfaction of three main conditions/developments. First, additional technological developments have to take place to overcome remaining implementation challenges while making OPS cost-effective to deploy. Second, a rational migration scenario of the network toward gradual deployment of packet-based optical switching approaches should exist. Finally, carriers have to become more interested in packet-based optical switching solutions.

Fiber-optic matched filters with metal films deposited on fiber delay-line ends for optical packet address detection

We fabricated compact fiber-optic matched filters by directly depositing metal thin films on fiber delay-line ends. Average reflectance of the metal film was measured to be 88% in the wavelength region of 1400-1600 nm. Detection of 10 Gb/s, 8-b optical packet addresses has been successfully demonstrated using the matched filters composed of four metal-coated fiber delay lines and three fused biconically tapered fiber couplers. Experimental results on correlation outputs of the matched filters showed an excellent agreement with those of theoretical analyzes.

Optical true time-delay feeder for X-band phased array antennas composed of 2/spl times/2 optical MEMS switches and fiber delay lines

We proposed an optical true time-delay (TTD) feeder for X-band linear phased array antennas (PAAs), which possesses high-speed beam scan capability by selecting different lengths of fiber delay lines with fast 2/spl times/2 optical microelectromechanical system switches. For proof of concept, a 3-bit optical TTD has been built for a 10-GHz linear PAA composed of two antenna elements. Experimental results show that the maximum time-delay error is less than 0.2 ps, corresponding to a radiation angle error of less than 0.84/spl deg/, which is within the equipment resolution. We have also designed a 10-GHz linear PAA composed of eight microstrip patch antenna elements driven by the proposed TTD. The radiation patterns of this PAA have been obtained by simulation.

Optical True Time-Delay for Two-Dimensional

An optical true time-delay (TTD) scheme for two-dimensional (2-D) X-band phased array antennas (PAAs) has been proposed. It is composed of a multiwavelength optical source and a delay line matrix consisting of 2times2 optical microelectromechanical system (MEMS) switches with fiber-optic delay lines connected between cross ports. A 2-bit times 4-bit optical TTD for 10-GHz 2-D PAAs has been implemented by cascading a wavelength-dependent TTD (WD-TTD) with a unit time delay of 12 ps in the x-direction and a wavelength-independent TTD (WI-TTD) with that of 6 ps in the y-direction. The time delay error for WD-TTD was measured to be less than 2.8 ps, mainly due to jitter incurred from gain-switching. On the other hand, the error for WI-TTD was less than 0.8 ps, which is within the equipment resolution. Insertion loss of both delay line matrices was less than 1 dB due to the column-wise control of the MEMS switches. This prevents the feed current applied to each antenna element from fluctuating at any radiation angles so that antenna gain and sidelobe level do not deteriorate in this scheme

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To date, all of the proposals for burst-scheduling techniques have considered scheduling individual bursts. We introduce a new scheme called OBS group scheduling. In this approach, a burst is represented by an interval of time. The process of scheduling a number of bursts, thus, turns to be a process of fitting a set of the corresponding time intervals on a channel time line that represents a channel-time resource. By doing so, we can formulate the scheduling process as a combinatorial optimization problem. Then, graph theory is applied to schedule as many non-overlapping intervals as possible onto the channel time line. The underlying concept of the group scheduling is that of briefly delaying the scheduling of a burst so that a much better decision can be made about a number of bursts all-together. This scheme is shown, through simulations, to improve performance in terms of burst loss probability and channel utilization over existing schemes.

-Band Phased Array Antennas

An in-line submillimeter hole fabricated by micro-drilling plastic optical fiber (POF) directly has been proposed as a compact refractive index sensor. Since the hole behaves as a concave lens if it is filled with a liquid having lower refractive index than that of the fiber core, transmittance increases in proportion to the refractive index. Analysis of the sensor transmittance has been performed using a simple ray optics model. Through immersing a 1.5-mm POF with a 0.35-mm-radius hole into various liquids, transmittance of the sensor has been measured at 670 nm. It has been shown that the experimental and analytical results are in excellent agreement.

Group-scheduling for optical burst switched (OBS) networks

We discuss a number of operation and maintenance (OAM) issues in optical burst-switched (OBS) networks and propose an OAM framework in this respect. Four OBS functions are identified as bases for the proposed framework. These are the burst termination function, the burst transmission function, the switching function, and the routing and switching control function. The study focuses on the unique aspects of OBS networks and how they can be addressed from an OAM point of view. We propose an OAM architecture and investigate the functional, network, and node aspects of it. Novel OAM-capable structures for core and edge OBS nodes are introduced for the first time.

Plastic Optical Fiber Refractive Index Sensor Employing an In-Line Submillimeter Hole

Very little work has been carried out so far in the area of operation and maintenance (OAM) schemes for optical bursts switched (OBS) networks. We continue to discuss OAM issues for OBS networks. The spectral and temporal de-coupling of data and control in an OBS network calls for special OAM attention. In this paper, OAM procedures, functions and sessions based on specific network and node architectures are discussed. An OAM information model, encompassing OAM-specific packet/burst formats is also presented.

Operation and maintenance issues in optical burst-switched networks

We propose a new burst scheduling mechanism for Optical Burst-Switched (OBS) networks. The new approach is made possible by gathering data bursts into groups and performing the scheduling decision for each group collectively. In OBS group-scheduling, bursts will not be considered for scheduling until a pre-defined time period elapses, during which the group of burst header packets would be gathered. By transforming a set of data bursts into a set of corresponding time intervals, the problem of scheduling these bursts is transformed into a combinatorial optimization problem. Graph algorithms are applied to obtain the maximum number of non-overlapping bursts. The proposed OBS group-scheduling scheme is shown to improve the performance of OBS networks over existing scheduling schemes in terms of burst loss probability and channel utilization. With an extension through a sequential optimization, using a Branch-and-Bound technique, the proposed scheme can support multiple classes of service. It is shown that the new scheduling approach has several desired characteristics including fairness and service differentiability among classes in terms of burst loss probability and channel utilization.

Procedures and functions for operation and maintenance in optical burst-switching networks

The problem of operation and maintenance (OAM) in optical burst switched (OBS) networks is not addressed by the optical-networking community even though OBS has been gaining research interest in recent years. In this paper, we introduce a functional model of OBS networks and an OAM architecture that is designed to meet the operational requirements based on this model. We present the first framework to realize OAM in OBS networks, including OAM activities, OAM-aware OBS nodes, OAM information and communication models and protocols. A number of practical examples of possible network failures and the corresponding reactions are presented.