Dr. Stewart A. Clark Profile

Dr. Stewart A. Clark

Director, Advanced Programs at Excelitas Canada Inc

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Proceedings Article | 16 November 2004 Paper

Adaptive packet switch with an optical core (demonstrator)

Ahmad Abdo, Vadim Bishtein, Stewart Clark, Pino Dicorato, David Lu, Sofia Paredes, Sareh Taebi, Trevor Hall

Proceedings Volume 5579, (2004) https://doi.org/10.1117/12.567581

KEYWORDS: Switches, Field programmable gate arrays, Computer architecture, Switching, Network architectures, Process modeling, Adaptive optics, Programmable logic devices, Clocks, Electronic components

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In this paper, a three-stage packet switch architecture is implemented consisting of a reconfigurable optical center stage surrounded by two electronic buffering stages grouped into sectors to ease contention. A Flexible Bandwidth Provision algorithm is used to change the configuration of the optical center stage to form the requested bandwidth desired by incoming traffic. The switch is modeled by a bipartite graph built from the service matrix. The bipartite graph is decomposed by solving an edge-coloring problem and the resulting permutations are used to configure the central stage removing the requirement for a per-time slot scheduler. Flexible Bandwidth Provision (FBP) algorithm requires dynamically reconfigurable technology readily available in programmable logic devices. The designed packet switch being a collection of discrete entities is most easily implemented on separate programmable logic devices forming electronic “islands” interconnected by photonics technology. The demonstrator itself contains 64 inputs and 64 outputs with reconfigurable central stage crossbars. The switch is a collection of input and output sectors each implemented on a single FPGA. Each sector is an 8 x 8 sub-switch with shared buffer memory. The interface between the sectors and the central stage will use VCSEL technology for O-E-O conversion. The input sectors together with the central stage form the adaptive portion of the switch configured by an embedded soft-core processor implementing the FBP algorithm of which is entity are located on an Ethernet local area network. This switching architecture has also been simulated and results show that this architecture result in a dramatic reduction of complexity, at the price of only a modest spatial speed-up (<2).

Proceedings Article | 24 March 2000 Paper

Thermo-optic phase modulators in SIMOX material

Stewart Clark, Brian Culshaw, Emma Dawnay, Ian Day

Proceedings Volume 3936, (2000) https://doi.org/10.1117/12.379940

KEYWORDS: Modulators, Waveguides, Modulation, Thermal optics, Silicon, Phase shifts, Polarization, Phase shift keying, Etching, Electrodes

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An investigation of a series of low-power thermo-optic phase-modulating devices fabricated in SIMOX material suitable for use in distributed sensing or as optical variable attenuators is presented. These devices are integrated in a balanced Mach-Zehnder Interferometer utilizing multi-micron vertical sidewall rib waveguides and exhibit low polarization dependence. The investigation highlights the power consumption of various lengths of devices with low-lateral heat diffusion operated by ohmic heating and quantifies the attainable modulation depths under quasi-static operation. Non-linear device behavior is demonstrated and explained with a proposal for these characteristics giving rise to devices which would operate with further power reductions. AC characteristics are also investigated, showing the modulation to have 3 dB bandwidths of approximately 40kHz. A second device geometry is presented which was fabricated utilizing an under-etching technique to suspend the arms of the Mach-Zehnder. Results indicate lower power operation with a corresponding reduction in bandwidth to approximately 1kHz. An improvement in overall device geometry provides modulation depths in excess of 99 percent, independent of both bandwidth and power.

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