Plasmonic modes provide the potential for routing information with optical speeds and bandwidth at the nanoscale. The inherent tradeoff between modal energy confinement and energy dissipation, however, makes realizing this potential an extreme challenge. For decades, researchers have investigated compensating losses in plasmonic systems with active gain media. In recent years, progress has increased dramatically, as nanoscale plasmonic amplifiers and lasers have emerged. We review this progress and offer our prospective on the challenges ahead.

Recent proposals have employed optical circuit switching (OCS) to reduce the cost of data center networks. However, the relatively slow switching times (10--100 ms) assumed by these approaches, and the accompanying latencies of their control planes, has limited its use to only the largest data center networks with highly aggregated and constrained workloads. As faster switch technologies become available, designing a control plane capable of supporting them becomes a key challenge.

Recently, there have been proposals for constructing hybrid data center networks combining electronic packet switching with either wireless or optical circuit switching, which are ideally suited for supporting bulk traffic. Previous work has relied on a technique called hotspot scheduling, in which the traffic matrix is measured, hotspots identified, and circuits established to automatically offload traffic from the packet-switched network. While this hybrid approach does reduce CAPEX and OPEX, it still relies on having a well-provisioned packet-switched network to carry the remaining traffic. In this paper, we describe a generalization of hotspot scheduling, called traffic matrix scheduling, where most or even all bulk traffic is routed over circuits. In other words, we don't just hunt elephants, we also hunt mice. Traffic matrix scheduling rapidly time-shares circuits across many destinations at microsecond time scales. The traffic matrix scheduling algorithm can route arbitrary traffic patterns and runs in polynomial time. We briefly describe a working implementation of traffic matrix scheduling using a custom-built data center optical circuit switch with a 2.8 microsecond switching time.

We designed and constructed a 24x24-port optical circuit switch (OCS) prototype with a programming time of 68.5 μs, a switching time of 2.8 μs, and a receiver electronics initialization time of 8.7 μs [1]. We demonstrate the operation of this prototype switch in a data center testbed under various workloads.

This paper presents an analysis of the post fabrication performance for a Bragg-mirrors-based photonic allpass filter. The development subsequently leads to a first definition of the stochastic measures in a realistic system implementation. A Digital Signal Processing (DSP) approach to examining photonic integrated circuitry is explored in depth. The physical origins of error that manifests in an unbalanced phase error is mathematically described in detail. We describe the details of error analysis and demonstrate a stochastic measure for the expected behavior of first-order allpass filter as well as high complexity systems. Our findings show that the frequency performance under error can be characterized by a convolution of the ideal response with a probability function based kernel.

This paper presents an approach to designing narrowband digital filters that are realizable using optical allpass building blocks. We describe a top-down design method by explicitly examining the derivation of an Infinite Impulse Response (IIR) architecture. Our result demonstrates a design that can achieve a 0.0025π passband edge while providing 60dB stopband attenuation. The design is aimed to reduce filter pole magnitudes, providing tolerance for waveguide losses and fabrication errors. The narrowband filter is based on the foundation of latticed allpass sections, which makes it naturally realizable using basic photonic components. Furthermore, analysis is performed on delay length variations that can result from the fabrication process.

The basic building block of ever larger data centers has shifted from a rack to a modular container with hundreds or even thousands of servers. Delivering scalable bandwidth among such containers is a challenge. A number of recent efforts promise full bisection bandwidth between all servers, though with significant cost, complexity, and power consumption. We present Helios, a hybrid electrical/optical switch architecture that can deliver significant reductions in the number of switching elements, cabling, cost, and power consumption relative to recently proposed data center network architectures. We explore architectural trade offs and challenges associated with realizing these benefits through the evaluation of a fully functional Helios prototype.

For pt.I see ibid., vol.50, p.2018-31 (2002). In part I, we proposed and investigated a hybrid pulse position modulation/ultrashort light pulse code-division multiple-access (PPM/ULP-CDMA) system for ultrafast optical communication networks. In this scheme, the large bandwidth of a ULP is efficiently utilized by virtue of the very high time resolution of a time-space processor. More detailed analysis and discussion on the receiver scheme using the time-space processor is now presented; nonideal performance of the time-space processor, including the reference pulse realization problem, as well as amplifier and detector noise, are taken into account. Discussions on physically achievable ranges of the system parameters that determine the performance of the proposed PPM/ULP-CDMA system are also made based upon current, state of the art technology. As remedies to overcome the physical limitations on the system parameters, two modified modulation/demodulation schemes are proposed and investigated to enhance the performance of the hybrid PPM/ULP-CDMA system.

We propose a hybrid pulse position modulation/ultrashort light pulse code-division multiple-access (PPM/ULP-CDMA) system for ultrafast optical communications. The proposed system employs spectral CDMA encoding/decoding and PPM with very short pulse separation. The statistical properties of the encoded ULP are investigated with a general pulse model, and the performance of the proposed PPM/ULP-CDMA system is investigated. It is shown that we can improve upon the performance of other ULP-CDMA systems, such as those using on-off keying, by employing PPM. It is also shown that we can improve the performance of the proposed system by increasing the effective number of chips, by increasing the number of PPM symbols, and by reducing the ULP duration. The performance analysis shows that the aggregate throughput of the proposed PPM/ULP-CDMA system could be over 1 Tb/s.

Probability density functions are estimated by an exponential family of densities based on multilayer feedforward networks. The role of the multilayer feedforward networks, in the proposed estimator, is to approximate the logarithm of the probability density functions. The method of maximum likelihood is used, as the main contribution, to derive an unsupervised backpropagation learning law to estimate the probability density functions. Computer simulation results demonstrating the use of the derived learning law are presented.

A method that determines the absolute position of a mobile system with a hybrid optoelectronic processor has been developed. Position estimates are based on an analysis of circular landmarks that are detected by a TV camera attached to the mobile system. The difference between the known shape of the landmark and its image provides the information needed to determine the absolute position of the mobile system. For robust operation, the parameters of the landmark image are extracted at high speeds using an optical processor that performs an optical Hough transform. The coordinates of the mobile system are computed from these parameters in a digital coprocessor using fast algorithms. Different sources of position estimation errors have also been analyzed, and consequent algorithms for improving the navigation performance of the mobile system have been developed and evaluated by both computer simulation and experiments.>

A mobile system with a hybrid opto-electronic processor has been studied. The position estimation is based on analysis of landmarks being detected by a TV-camera attached to the mobile system. The difference between the known real shape of the landmark and its image provides the information necessary for determining the relative position of the mobile system to the landmark. The parameters of the landmark image are extracted at high speed using an optical processor that performs an optical Hough transform, while the coordinates of the mobile system are computed from these parameters in a digital coprocessor using fast and simple algorithms. Different sources of errors have been analyzed, and algorithms to improve the performance of the mobile system have been developed and evaluated by computer simulation.>