Insertion loss and misalignment tolerance in multimode tapered waveguide bends

Experimental measurements of laterally tapered multimode waveguide bends fabricated photolithographically on FR4 printed circuit board establish that the product of the mean insertion loss (in linear units) and the mean source misalignment tolerance is a constant which depends only on the taper ratio TR (input width/output width) and not on the radius of curvature R. The minimum loss of 0.78 dB occurs in the special case of TR = 0.8, R = 14 mm. Together, these form waveguide layout design rules for board-to-board and chip-to-chip optical interconnects

Matrix Elements and Few-Body Calculations within the Unitary Correlation Operator Method

We employ the Unitary Correlation Operator Method (UCOM) to construct correlated, low-momentum matrix elements of realistic nucleon-nucleon interactions. The dominant short-range central and tensor correlations induced by the interaction are included explicitly by an unitary transformation. Using correlated momentum-space matrix elements of the Argonne V18 potential, we show that the unitary transformation eliminates the strong off-diagonal contributions caused by the short-range repulsion and the tensor interaction, and leaves a correlated interaction dominated by low-momentum contributions. We use correlated harmonic oscillator matrix elements as input for no-core shell model calculations for few-nucleon systems. Compared to the bare interaction, the convergence properties are dramatically improved. The bulk of the binding energy can already be obtained in very small model spaces or even with a single Slater determinant. Residual long-range correlations, not treated explicitly by the unitary transformation, can easily be described in model spaces of moderate size allowing for fast convergence. By varying the range of the tensor correlator we are able to map out the Tjon line and can in turn constrain the optimal correlator ranges.Comment: 16 pages, 9 figures, using REVTEX

Optimal Time-Inconsistent Beliefs: Misplanning, Procrastination, and Commitment

We develop a structural theory of beliefs and behavior that relaxes the assumption of time consistency in beliefs. Our theory is based on the trade-off between optimism, which raises anticipatory utility, and objectivity, which promotes efficient actions. We present it in the context of allocating work on a project over time, develop testable implications to contrast it with models assuming time-inconsistent preferences, and compare its predictions to existing evidence on behavior and beliefs. Our predictions are that (i) optimal beliefs are optimistic and time inconsistent; (ii) people optimally exhibit the planning fallacy; (iii) incentives for rapid task completion make beliefs more optimistic and worsen work smoothing, whereas incentives for accurate duration prediction make beliefs less optimistic and improve work smoothing; (iv) without a commitment device, beliefs become less optimistic over time; and (v) in the presence of a commitment device, beliefs may become more optimistic over time, and people optimally exhibit preference for commitment

FirstLight: Pluggable Optical Interconnect Technologies for Polymeric Electro-Optical Printed Circuit Boards in Data Centers

The protocol data rate governing data storage devices will increase to over 12 Gb/s by 2013 thereby imposing unmanageable cost and performance burdens on future digital data storage systems. The resulting performance bottleneck can be substantially reduced by conveying high-speed data optically instead of electronically. A novel active pluggable 82.5 Gb/s aggregate bit rate optical connector technology, the design and fabrication of a compact electro-optical printed circuit board to meet exacting specifications, and a method for low cost, high precision, passive optical assembly are presented. A demonstration platform was constructed to assess the viability of embedded electro-optical midplane technology in such systems including the first ever demonstration of a pluggable active optical waveguide printed circuit board connector. High-speed optical data transfer at 10.3125 Gb/s was demonstrated through a complex polymer waveguide interconnect layer embedded into a 262 mm × 240 mm × 4.3 mm electro-optical midplane. Bit error rates of less than 10-12 and optical losses as low as 6 dB were demonstrated through nine multimode polymer wave guides with an aggregate data bandwidth of 92.8125 Gb/s

Self-assembled porous polymer films for improved oxygen sensing

Absolute oxygen sensors based on quenching of phosphorescence have been the subject of numerous studies for the monitoring of biological environments. Here, we used simple fabrication techniques with readily available polymers to obtain high performance phosphorescent films. Specifically, evaporation-based phase separation and the breath figure technique were used to induce porosity. The pore sizes ranged from ∼ 37 nm to ∼ 141µm while the maximum average porosity achieved was ∼ 74%. The oxygen sensing properties were evaluated via a standarised calibration procedure with an optoelectronic setup in both transmission and reflection based configurations. When comparing non-porous and porous films, the highest improvements achieved were a factor of ∼ 7.9 in dynamic range and ∼ 7.3 in maximum sensitivity, followed by an improved linearity with a half-sensitivity point at 43% O2 V/V. Also, the recovery time was reduced by an order of magnitude in the high porosity film and all samples prepared were not affected by variations in the humidity of the surrounding environment. Despite the use of common polymers, the fabrication techniques employed led to the significant enhancement of oxygen sensing properties and elucidated the relation between porous film morphologies and sensing performance