Ben Layet

Design and fabrication of diffractive optical elements

An introduction to the design and fabrication of diffractive optical elements is presented. Design techniques for diffractive optic in the two theoretical design areas, the scalar and resonance domains, and the dominant methods of fabrications are described. Theoretical and experimental examples are given in each section.

Electromagnetic analysis of fan-out gratings and diffractive cylindrical lens arrays by field stitching

The field-stitching method introduced previously [Opt. Lett.21, 1508 (1996)] allows large-period gratings containing small-scale local structure to be analyzed without requiring excessive computing power. Multiple scattering and the polarization of the electromagnetic field are taken into account by standard rigorous analysis. A variety of calculations demonstrating the accuracy and the speed of the method are made. Also, we report on the optimization by simulated annealing of fan-out gratings with periods of up to 240λ and of diffractive cylindrical lenses with a period of 1200λ, which has been made possible by field-stitching analysis.

Analysis of gratings with large periods and small feature sizes by stitching of the electromagnetic field.

We present a new method for the analysis of diffractive optical elements, which we refer to as field stitching. It is suitable for use with grating structures of arbitrarily large period, even when the local feature size is of the order of a wavelength. Furthermore, the concept is straightforwardly extendable to aperiodic structures. To assess its applicability, we have calculated the diffracted orders from a 1 x 81 fan-out grating with periods of 100lambda and 10, 000lambda. The field-stitched calculations agree very well with independent rigorous predictions for the small-period element and scalar-regime predictions for the large-period element. We believe that a variety of areas within the diffractive-optics field will benefit from this new analytical tool. It promises accurate analysis and, by facilitating component optimization, high-performance designs.

Stripe color separation with diffractive optics

We describe a color separation optical element with potential display applications that is designed to separate light into an array of red, green, and blue stripes formed at a certain distance from the component. The stripe color separation grating is a surface-relief diffractive optical element composed of a repeated pattern of three constituent gratings. We describe the design principles and a numerical analysis of the component, showing that a maximum theoretical efficiency with which the colors are directed into the stripes is approximately 80%. We also examine the dependence of the efficiency on the grating feature size. In addition, we report on the fabrication of four of these components, using a combination of electron-beam lithography and photolithography with a backexposure technique. Measurements are presented to show the color separation property.

Comparison of two approaches for implementing free-space optical interconnection networks

Abstract A particular design choice in the implementation of free-space optical interconnection networks (e.g. photonic backplanes) based on cascaded image-relay lenses is investigated. In these systems, a communication link can be implemented either by a single hop between source and destination nodes with the signal remaining in the optical domain through many image-relay stages, or by multiple hops between adjacent nodes with the signal undergoing optical–electrical conversion and vice versa at intermediate nodes (which act as repeaters). These two approaches place different demands on the optical system and the optoelectronic interface. We compare the raw bandwidth-per-link available in two example networks (the mesh and the completely connected network) using a model of the bandwidth and power consumption of an optoelectronic data channel and considerations on the aggregate bandwidth of the optoelectronic interface chip. We find that the single-hop approach provides a higher bandwidth-per-link. For example, the single-hop bandwidth-per-link is three times greater than the multiple-hop value for a mesh network of 49 nodes and for a completely connected network of 13 nodes. The advantage can increase further as the network size grows. The methodology is also applicable to the investigation of other implementation choices in optoelectronic interconnects.

Application of resonance domain diffractive optics beam deflectors to high-power laser systems

We report on various novel uses of resonance domain diffractive optics. Here we primarily concentrate on the design of optical elements that act as 90° beam deflectors for a high-power laser. Two of the elements were binary surface relief gratings, one acting as a highly reflecting leaky waveguide and the second was a transmission grating operating at Bragg incidence. Both of these devices could be optimized for efficiencies approaching 100%. A third device consisting of dielectric micro prisms was also considered. The results have direct relevance to moderate to high power laser systems, where laser induced damage is a potential limiting factor for any multi-layer thin film or bulk optical element.

Diffractive optics development for application on high-power solid state lasers

This paper reports on the development of several diffractive optical elements (DOE) to fulfill applications on high power Nd glass laser systems. The measured performance for those components realized is discussed. These are focusing beam samplers, beam shapers, and harmonic separation filters (HSF). Designs of more demanding components operating in the resonance domain are also presented. These are linear polarizing elements and beam deflectors.

Smart optoelectronic networks for multiprocessors

An intelligent interconnection network with fine-grain parallelism is described that has the potential to support efficient, scalable algorithms running on associated coarse- grain processors. The approach is relevant to the emerging computational cluster systems. The support of concurrent operations within the network is discussed and their mapping onto smart-pixel array network interfaces is shown. Choices are considered in the design of the free-space optical interconnect that enables the inter-smart-pixel-array communication. In particular, a system that uses multi- element macro-lenses is studied and results of detailed modeling are given that quantify the smart-pixel density. These results are used, in an illustrative case study of the sorting problem, to compare potential system architectures. This is work in progress and throughout the paper, important issues in the design and use of the intelligent interconnect are raised that require more study.

Design and fabrication of diffractive optical elements for use in solid state laser systems

Scalar and resonance domain diffractive optical elements are proposed for use within high power laser systems. Resonance domain elements are described for beam deflection and polarization selection. Scalar domain elements for harmonic separation filtering and beam shaping in the near- and far- fields are also described. Experimental results are presented for far-field beam shaping and harmonic separation filtering elements.

Design of novel resonance domain diffractive optical elements

The key to effective utilization and systematic design of resonance domain diffractive elements lies in understanding the way in which the input beam interacts with the structure to produce the output field. This is straightforward in the paraxial, scalar, regime as the diffracted signal can be related directly to the physical parameters of the grating but resonance domain optics provides at least two exciting advantages over conventional optics. The first is the ability to use the wavelength scale structure to produce grating response functions with phase and/or amplitude modulations that cannot be realized conventionally. The second advantage is to use the polarization sensitivity of such devices to increase the functionality of a given element. We report on two novel uses of resonance domain diffractive optics. The first element is a diffractive optic beam deflector intended for high power laser systems, where laser induced damage limits the usefulness of conventional elements. The second element is a reflection grating operating as a polarization beam splitter. In the case of the beam splitter we present a simple model to explain the essential physics behind the operation of the device. This model leads to simple formulae for the design of other polarization sensitive devices.