Duncan T. Moore

Gradient-index optics: a review.

The subject of gradient-index optics dates from the 1850s. However, only in the last 10 years has it been possible to design lenses, manufacture materials, measure the properties, and fabricate lens elements. The current status of gradient-index optics is reviewed.

50% Efficient Solar Cell Architectures and Designs

Very high efficiency solar cells (VHESC) for portable applications that operate at greater than 55 percent efficiency in the laboratory and 50 percent in production are being created. We are integrating the optical design with the solar cell design, and have entered previously unoccupied design space that leads to a new paradigm. This project requires us to invent, develop and transfer to production these new solar cells. Our approach is driven by proven quantitative models for the solar cell design, the optical design and the integration of these designs. We start with a very high performance crystalline silicon solar cell platform. Examples will be presented. Initial solar cell device results are shown for devices fabricated in geometries designed for this VHESC program

Design of Singlets with Continuously Varying Indices of Refraction

The use of a continuously varying index of refraction provides new degrees of freedom in the design of lens systems. By use of the third-order aberration theory developed by Sands, the effectiveness of these new degrees of freedom in correcting third-order aberrations is determined. After the theory is cast into a form suitable for a computer, two major designs are done. The first is a singlet with an axial gradient that is corrected for third-order spherical and chromatic aberrations and has no third-order distortion. A radial gradient is used in a singlet to correct all third-order monochromatic aberrations except Petzval curvature of field. The results of the study indicate that axial gradients have the same effect as aspheric surfaces for third-order aberrations. The study also shows that radial gradients are more effective in aberration correction than axial gradients and have a greater potential in lens design.

An intra-chip free-space optical interconnect

Continued device scaling enables microprocessors and other systems-on-chip (SoCs) to increase their performance, functionality, and hence, complexity. Simultaneously, relentless scaling, if uncompensated, degrades the performance and signal integrity of on-chip metal interconnects. These systems have therefore become increasingly communications-limited. The communications-centric nature of future high performance computing devices demands a fundamental change in intra- and inter-chip interconnect technologies. Optical interconnect is a promising long term solution. However, while significant progress in optical signaling has been made in recent years, networking issues for on-chip optical interconnect still require much investigation. Taking the underlying optical signaling systems as a drop-in replacement for conventional electrical signaling while maintaining conventional packet-switching architectures is unlikely to realize the full potential of optical interconnects. In this paper, we propose and study the design of a fully distributed interconnect architecture based on free-space optics. The architecture leverages a suite of newly-developed or emerging devices, circuits, and optics technologies. The interconnect avoids packet relay altogether, offers an ultra-low transmission latency and scalable bandwidth, and provides fresh opportunities for coherency substrate designs and optimizations.

Design of a gradient-index photographic objective

A two-element gradient-index photographic objective was designed. It operates at f/2 and has a focal length of 50 mm. The half-field of view is 21.8 degrees . The design is compared to the six-element new double Gauss photographic objective and performs well in comparison.

Phase-locked moiré fringe analysis for automated contouring of diffuse surfaces

Phase-locked moiré systems have the advantage of rapid data acquisition and accuracy of better than one twentieth of the fringe spacing. In conventional moire systems data acquisition is performed by making a photographic plate and taking measurements from the plate either visually or with a microdensitometer. This is slow, and the accuracy is about one-quarter of the fringe spacing. The phase-locked system is more accurate and permits a more favorable trade-off between accuracy and working depth. The equations governing moire contouring are examined, and the theory of phase-locked moire fringe analysis is presented. The design and operation of the phase-locked moire contouring system are described, and the results of measurements made with the instrument are presented.

Gradient infrared optical material prepared by a chemical vapor deposition process.

An axial gradient, infrared optical material, ZnSxSe1−x, has been developed by codepositing ZnS and ZnSe in a controlled manner via a chemical vapor deposition process. This material has been characterized by measuring the compositional and refractive-index profiles, visible, and IR transmission, microstructure, and hardness. Axial index gradients produced thus far range from 0.024 to 0.066 mm−1 over a thickness of ~4 mm. An analytical model of the deposition process has been developed and successfully used to derive a deposition algorithm to produce specific index gradients.

Interference imaging for aspheric surface testing

Peak-valley accuracy of lambda/20 over a range of 2lambda is not unusual in an interferometric null test. For the larger dynamic ranges of a nonnull test, however, the fringe-imaging optics degrades the accuracy. We classify the errors introduced and analyze them in the context of both general and third-order aberration theory. We can predict the measurement error from known interferometer parameters, and we illustrate this for a single mirror. The errors are tabulated for the specific case of a fourth-order asphere with 100 mum of sag. We show that the third-order approximation is comparable with exact ray-trace results for this case.

Ray tracing in gradient-index media

A new procedure for the tracing of rays in inhomogeneous media is described. The method is based on a polynomial solution of the differential equation for ray paths. The index of refraction is expressed in a polynomial in the optical-axis-direction coordinate and in the coordinate in the direction orthogonal to the optical axis. The technique is incorporated into a lens-design program to provide optimization of gradient indices. The results of the methods have been verified in two other ways.

3-D integrated heterogeneous intra-chip free-space optical interconnect

This paper presents the first chip-scale demonstration of an intra-chip free-space optical interconnect (FSOI) we recently proposed. This interconnect system provides point-to-point free-space optical links between any two communication nodes, and hence constructs an all-to-all intra-chip communication fabric, which can be extended for inter-chip communications as well. Unlike electrical and other waveguide-based optical interconnects, FSOI exhibits low latency, high energy efficiency, and large bandwidth density, and hence can significantly improve the performance of future many-core chips. In this paper, we evaluate the performance of the proposed FSOI interconnect, and compare it to a waveguide-based optical interconnect with wavelength division multiplexing (WDM). It shows that the FSOI system can achieve significantly lower loss and higher energy efficiency than the WDM system, even with optimistic assumptions for the latter. A 1×1-cm2 chip prototype is fabricated on a germanium substrate with integrated photodetectors. Commercial 850-nm GaAs vertical-cavity-surface-emitting-lasers (VCSELs) and fabricated fused silica microlenses are 3-D integrated on top of the substrate. At 1.4-cm distance, the measured optical transmission loss is 5 dB, the crosstalk is less than -20 dB, and the electrical-to-electrical bandwidth is 3.3 GHz. The latter is mainly limited by the 5-GHz VCSEL.