Lloyd LaComb

Design and Preliminary Implementation of an N

We have demonstrated a diffraction-based nonblocking, scalable N × N optical switch employing a digital micromirror display (DMD) with 12 μs switching speed, performing 100 times faster than the currently available technology. The distributed nature of diffraction makes this switch more robust than one-to-one reflective systems where a single mirror failure incapacitates an entire connection. We thereby address a key bottleneck in data centers and optical aggregation networks by decreasing circuit-switching speed and allowing for facile port count scalability.

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We have recently demonstrated several improvements in material properties and optical design to increase the resolution, size, brightness, and color range of updatable holograms using photorefractive materials. A compact system has been developed that is capable of producing holograms with brightness in excess of 2,500 cd/m2 using less than 20mW of CW laser power. The size of the hologram has been increased to 300mm × 150mm with a writing time of less than 8 seconds using a 50 Hz pulse laser. Optical improvements have been implemented to reduce the hogel size to less than 200 μm. We have optimized the color gamut to extend beyond the NTSC CIE color space through a combination of spatial and polarization multiplexing. Further improvements could bring applications in telemedicine, prototyping, advertising, updatable 3D maps and entertainment.

N Diffractive All-Optical Fiber Optic Switch

Organic photorefractive polymer composites can be made to exhibit near 100% diffraction efficiency and fast writing times, though large external slants are needed to project the applied field onto the grating vector. We show here that the use of interdigitated electrodes on a single plane provides similar performance to these standard devices and geometries but without a external slant angle. This new devices structure also greatly improves the diffraction efficiency and sensitivity compared to less slanted standard devices necessary for some real applications, such as holographic displays, optical coherence imaging, and in-plane switching.

Recent advancements in photorefractive holographic imaging

Optical functionality is being used to realize new data center architectures that minimize electronic switching overheads, pushing the processing to the edge of the network. A challenge in optically interconnected data center networks is to identify the large, bandwidth hungry flows (i.e., elephants) and efficiently establish the optical circuits. Moreover, the amount of optical resources to be provisioned during the network planning phase is a critical design problem. Flow classification accuracy affects the efficiency of optical circuits. Optical channel bandwidth, on the other hand, directly relates to the additive-increase, multiplicative-decrease congestion control mechanism of the transmission control protocol and affects the effective bandwidth allocated to elephant flows. In this paper, we simultaneously investigate the impact of two important mechanisms on data center network performance: traffic flow classification accuracy and optical bandwidth aggregation (i.e., the consolidation of several low-capacity channels into a single high-capacity one by employing advanced modulation formats for short-reach communications). We develop a discrete-event simulator for a hybrid data center network, enabling the tuning of flow classification parameters. Our simulations indicate that data center performance is highly sensitive to the aggregation level.We could observe up to a 74.5% improvement in network throughput only due to consolidating the optical channel bandwidth. We further noticed that the role of flow classification becomes more pronounced with higher bandwidth per wavelength as well as with more hot-spot traffic. Compared to a random classification benchmark, adaptive flow classification could lead to throughput improvements as large as 54.7%.

Interdigitated coplanar electrodes for enhanced sensitivity in a photorefractive polymer

National Aeronautics and Space Administration (NASA) Small Business Technology Transfer (STTR) Phase II [NNX15CP19C]; National Science Foundation Engineering Research Center for Integrated Access Networks [EEC-0812072]; Technology Research Initiative Fund (TRIF) Photonics Initiative of the University of Arizona

TCP flow classification and bandwidth aggregation in optically interconnected data center networks

In this paper, we analyze the optical performance of a commonly used 1-step recording geometry for stereograms and compare it to the fully fringe rendered case, taking a published optical model of the human eye into account. We compare our results to a model that conserves wavefront curvature. We then demonstrate how to optimize hogel sampling parameters as a function of image depth, size, and viewer distance. We conclude that stereograms suffer from little degradation from a viewing distance larger than 2 meters, but that nearer field images can significantly benefit by adding a second order phase correction.

Yb^3+-doped double-clad phosphate fiber for 976 nm single-frequency laser amplifiers

Cladding pumped single-frequency Yb3+-doped fiber amplifiers at 976 nm were investigated. Over 4 W output power was obtained and further power scaling can be achieved by reducing the cladding diameter of the Yb3+-doped fiber.

Are stereograms holograms? A human perception analysis of sampled perspective holography

Hybrid networking, based on electronic packet switching and optical circuit switching, has been proposed to resolve the existing switching bottlenecks in data centers in an energy-efficient and cost-effective fashion. We consider the problem of resource provisioning in hybrid data centers in terms of optical circuit switching capacity and granularity. The number of fibers connected to server racks, the number of wavelengths per fiber, and the ratio of capacity provided by the optical circuit-switched portion of the network to that of the electronic packet-switched portion are crucial design parameters to be optimized during the data center planning phase. These parameters in conjunction with the additive-increase, multiplicative-decrease (AIMD) congestion control mechanism of the Transmission Control Protocol (TCP) pose a significant impact on data center network performance. In this paper, we examine the combined impact of optical bandwidth settings and TCP dynamics using event-driven simulations. Our analysis reveals the strong dependence of overall network throughput on channel capacity (i.e., the bit rate per wavelength channel) and points to the advantages of optical bandwidth consolidation employing higher-order modulation formats.