Martin P. O'Boyle

Active control of slow light on a chip with photonic crystal waveguides

It is known that light can be slowed down in dispersive materials near resonances. Dramatic reduction of the light group velocity—and even bringing light pulses to a complete halt—has been demonstrated recently in various atomic and solid state systems, where the material absorption is cancelled via quantum optical coherent effects. Exploitation of slow light phenomena has potential for applications ranging from all-optical storage to all-optical switching. Existing schemes, however, are restricted to the narrow frequency range of the material resonance, which limits the operation frequency, maximum data rate and storage capacity. Moreover, the implementation of external lasers, low pressures and/or low temperatures prevents miniaturization and hinders practical applications. Here we experimentally demonstrate an over 300-fold reduction of the group velocity on a silicon chip via an ultra-compact photonic integrated circuit using low-loss silicon photonic crystal waveguides that can support an optical mode with a submicrometre cross-section. In addition, we show fast (∼100 ns) and efficient (2 mW electric power) active control of the group velocity by localized heating of the photonic crystal waveguide with an integrated micro-heater.

Uncovering energy-efficiency opportunities in data centers

The combination of rapidly increasing energy use of data centers (DCs), which is triggered by dramatic increases in IT (information technology) demands, and increases in energy costs and limited energy supplies has made the energy efficiency of DCs a central concern from both a cost and a sustainability perspective. This paper describes three important technology components that address the energy consumption in DCs. First, we present a mobile measurement technology (MMT) for optimizing the space and energy efficiency of DCs. The technology encompasses the interworking of an advanced metrology technique for rapid data collection at high spatial resolution and measurement-driven modeling techniques, enabling optimal adjustments of a DC environment within a target thermal envelope. Specific example data demonstrating the effectiveness of MMT is shown. Second, the static MMT measurements obtained at high spatial resolution are complemented by and integrated with a real-time sensor network. The requirements and suitable architectures for wired and wireless sensor solutions are discussed. Third, an energy and thermal model analysis for a DC is presented that exploits both the high-spatial-resolution (but static) MMT data and the high-timeresolved (but sparse) sensor data. The combination of these two data types (static and dynamic), in conjunction with innovative modeling techniques, provides the basis for extending the MMT concept toward an interactive energy management solution.

Shallow trench isolation double-diobe electrostatic discharge circuit and interaction with DRAM output circuitry

Abstract Electrostatic discharge (ESD) performance of a shallow-trench-isolation double-diode protection circuit in CMOS technology is discussed. This paper highlights the sensitivities of these devices to semiconductor process parameters, interaction with chip circuitry and advanced failure analysis techniques.

Rapid Three-Dimensional Thermal Characterization of Large-Scale Computing Facilities

We demonstrate a mobile measurement technology which allows for fast and systematic 3-D temperature mapping of data centers. This technology yields the first experimental 3-D temperature images of an actual data center. The experimental temperature distributions reveal strong hot spots in the data center suggesting that current cooling schemes can be readily improved.

The impact of air flow leakage on server inlet air temperature in a raised floor data center

One of the most important parameters in the optimal ventilation of a raised air cooled data center is the amount of cool air that is delivered to the front of a server. It is very common in data centers for a significant fraction of the conditioned cool air to bypass the desired locations, i.e. the perforated tiles in front of the IT racks, and leak out through cable cutouts and other openings. This represents energy inefficiencies of two kinds: firstly, the wastage of blower pumping power at the air conditioning units, and secondly, the misdirection of the refrigeration work to create sub-ambient air which performs limited cooling function. The characterization of this leakage flow is the focus of this study. A representative CFD numerical model of a 12000 square foot facility, comprising of 100 server racks, at a heat flux of 100 W/ft2, was utilized for the thermal characterization to provide data to concretize the trends. For a fixed total volumetric air flow rate for a given data center, the amount of leakage air flow was varied and its impact on the inlet air temperature to the servers was quantified. The results showed a decrease in average rack inlet temperature of 0.7-0.9degC for every 10% reallocation of leakage flow to a desired rack inlet location. Observed trends for rack air inlet temperatures for different rack positions within a row, and for different groups of rack or aisles located in different parts of the data center, are also presented. In addition to studying the effect of leakage flow, two perforated tile layouts were characterized; a traditional one and a novel guard tile design, and the new design was shown to yield better data center thermal designs.

Ultra-compact wavelength division multiplexing devices using silicon photonic wires for on-chip interconnects

Ultra-compact four-channel wavelength division multiplexing (WDM) devices in add/drop filter and multi-mode interferometer configurations were demonstrated on silicon-on-insulator for future on-chip optical interconnects. Both devices show a crosstalk level les-13 dB and a footprint les0.006 mm2.

Group velocity engineering in silicon nanophotonic circuits

We report over-300-fold reduction of the group velocity in photonic crystal waveguides measured with integrated Mach-Zehnder interferometer. We show fast (100ns) and efficient (2mW electric power) tunability of the group velocity with an integrated micro-heater.