Optical Data Path Research Articles

Non-display applications and the next generation of liquid crystal over silicon technology

The next generation of applications for liquid crystal (LC) over silicon technology will be non-display oriented systems such as adaptive optical interconnects, optical switches and optical image processors. These new non-display applications have a different set of material parameters, which means that existing display-based materials are not entirely optimal. This is particularly the case when the application is driven by phase modulation at high frame rates (more than 1 kHz). An example of such a non-display application is in adaptive optical interconnects. Optical data transmission between printed circuit boards is becoming more and more important as the data rate in electronic systems increases into the gigahertz region. One way of avoiding the data bottlenecks in board to board interconnects is to use optical links to transmit the data. Recent research into free-space optical links has shown that a high level of manufacturing tolerance must be used to maintain the link. However, one way of avoiding these limitations is to use a reconfigurable LC phase hologram as a beam-steering element to compensate for movement between the boards and maintain the optical data path.

Optical readout in a multi-module system test for the ATLAS pixel detector

The innermost part of the ATLAS experiment at the LHC, CERN, will be a pixel detector, which is presently under construction. The command messages and the readout data of the detector are transmitted over an optical data path. The readout chain consists of many components which are produced at several locations around the world, and must work together in the pixel detector. To verify that these parts are working together as expected a system test has been built up. It consists of detector modules, optoboards, optical fibres, Back of Crate cards, Readout Drivers, and control computers. In this paper, the system test setup and the operation of the readout chain are described. Also, some results of tests using the final pixel detector readout chain are given.

Validation studies of the ATLAS pixel detector control system

The ATLAS pixel detector consists of 1744 identical silicon pixel modules arranged in three barrel layers providing coverage for the central region, and three disk layers on either side of the primary interaction point providing coverage of the forward regions. Once deployed into the experiment, the detector will employ optical data transfer, with the requisite powering being provided by a complex system of commercial and custom-made power supplies. However, during normal performance and production tests in the laboratory, only single modules are operated and electrical readout is used. In addition, standard laboratory power supplies are used. In contrast to these normal tests, the data discussed here were obtained from a multi-module assembly which was powered and read out using production items: the optical data path, the final design power supply system using close to final services, and the Detector Control System (DCS).

Phase modulation with the next generation of liquid crystal over silicon technology

Liquid crystal materials are fast becoming the de facto standard in modern commercial display technology and large amounts of research and development have gone into optimising the materials used in these many types of display. One of the most exciting technologies based on liquid crystal materials is the combination of their optical modulation characteristics with the power and compactness of a silicon VLSI backplane. The next generation of applications for liquid crystal over silicon technology are already starting to emerge in laboratories, however there are severe limitations as the liquid crystal materials have all been optimised for amplitude or intensity modulation when in fact the ability to modulate the phase of the light is more desirable. One example of such an application is adaptive optical interconnects. Data transmission within and between printed circuit boards is becoming more and more important as the data rates in electronic systems increase into the GHz region. One way of avoiding potential data bottlenecks in board to board interconnects is to use optical links to transmit the data. Recent research into free-space optical links has shown that a high level of manufacturing tolerance must be used to maintain the link, however, this can be avoided by incorporating a liquid crystal phase hologram as a beam steering element to compensate for movement between the boards and maintain the optical data path.

Adaptive Optical Interconnect Using an FLC SLM

Optical interconnects between boards are becoming more and more important as the data rate in electronic systems increases into the GHz regions. One way of avoiding data bottlenecks in board to board interconnects is to use optical links to transmit the data. Such systems must be made from either guided wave technologies such as optical fibres or by using free-space propagation. Recent research into free-space optical links has shown that a high level of manufacturing tolerance and vibrational control must be used to maintain the link. One possible approach to avoiding these constraints is to use a reconfigurable liquid crystal phase hologram as a beam steering element to compensate for movement in the boards and maintain the optical data path.

Design of wavelength converting switches for optical burst switching

Optical burst switching (OBS) is an experimental network technology that enables the construction of very high-capacity routers, using optical data paths and electronic control. In this paper, we study wavelength converting switches using tunable lasers and wavelength grating routers, that are suitable for use in OBS systems and evaluate their performance. We show how the routing problem for these switches can be formulated as a combinatorial puzzle or game, in which the design of the game board corresponds to the pattern of permutation used at the input sections of the switch. We use this to show how the permutation pattern affects the performance of the switch, and to facilitate the design of permutation patterns that yield the best performance. We give upper bounds on the number of different wavelength channels that can be routed through such switches (regardless of the permutation pattern), and show that for 2/spl times/2 switches, there is a simple permutation pattern that achieves these bounds. For larger switches, randomized permutation patterns produce the best results. We study the performance of optical burst switches using wavelength converting switches based on several different permutation patterns. We also present a novel routing algorithm called the most available wavelength assignment and evaluate its benefits in improving the switch throughput. Our results show that for a typical configuration, the switch with the best permutation pattern has more than 87% of the throughput of a fully nonblocking switch.

Gemini: an optical interconnection network for parallel processing

The Gemini interconnect is a dual technology (optical and electrical) interconnection network designed for use in tightly-coupled multicomputer systems. It consists of a circuit-switched optical data path in parallel with a packet-switched electrical control/data path. The optical path is used for transmission of long data messages and the electrical path is used for switch control and transmission of short data messages. The paper describes the architecture of the interconnection network and related communications protocols. Fairness issues associated with network operation are addressed and a discrete-event simulation model of the entire system is described. Network performance characteristics derived from the simulation model are presented. The results show significant performance benefits when using virtual output queuing and quantify the tradeoffs between throughput and fairness in the system.