Active computational imaging for circumventing resolution limits at macroscopic scales.

Macroscopic imagers are subject to constraints imposed by the wave nature of light and the geometry of image formation. The former limits the resolving power while the latter results in a loss of absolute size and shape information. The suite of methods outlined in this work enables macroscopic imagers the unique ability to capture unresolved spatial detail while recovering topographic information. The common thread connecting these methods is the notion of imaging under patterned illumination. The notion is advanced further to develop computational imagers with resolving power that is decoupled from the constraints imposed by the collection optics and the image sensor. These imagers additionally feature support for multiscale reconstruction.

Dispersion design in gradient index elements using ternary blends.

We show that a gradient-index element designed from a blend of three materials allows a designer to specify independently the element's refractive index and its change in refractive index with respect to wavelength. We show further the effectiveness of this approach by comparing modeled chromatic performance of deflectors consisting of a single material, a binary blend of materials, and a ternary blend.

Chromatic analysis and design of a first-order radial GRIN lens.

From the expression for optical power of a radial first-order graded-index (GRIN) lens with curved surfaces, we derive an expression for chromatic aberration. Our expressions for optical power and chromatic aberration are valid under the paraxial approximation. By applying a series of further simplifying assumptions, namely a thin lens and thin GRIN, we derive a set of equations with which one can design an achromatic GRIN lens. We also derive expressions for the dispersive property of a GRIN element. Our analysis enables us to derive the relationship between material pairs that indicate their suitability as a material pair for a GRIN achromat. We use this relationship to search a standard glass catalog for attractive GRIN material pairs for a particular achromat design. We compare the optical performance of our GRIN design to that of a conventional homogeneous doublet and demonstrate that our approach is capable of identifying material pairs that perform well for achromatic GRIN lenses which would not generally be considered for conventional achromatic design. We also demonstrate our approach is capable of designing GRIN achromats with superior performance.

Review of multiscale optical design.

Multiscale optical design is an approach that has been successfully utilized for over 100 years by optical designers and engineers to overcome challenges and achieve desired optical system performance. The benefits of the design paradigm include improving light collection, creating specific symmetries that can be exploited, collecting additional information about the object space, partitioning the optical field to enable piecewise correction of aberrations, and alleviating packing constraints. The purpose of this paper is to review the historical emergence of the use of multiscale optical design and present key examples of developments that have expanded its capabilities over the years.

Space-bandwidth scaling for wide field-of-view imaging.

We examine the space-bandwidth product of wide field-of-view imaging systems as the systems scale in size. Our analysis is based on one conducted to examine the behavior of a plano-convex lens imaging onto a flat focal geometry. We extend this to consider systems with monocentric lenses and curved focal geometries. As a means to understand system cost, and not just performance, we also assess the volume and mass associated with these systems. Our analysis indicates monocentric lenses imaging onto a curved detector outperform other systems for the same design constraints but do so at a cost in lens weight.

Trade-offs between lens complexity and real estate utilization in a free-space multichip global interconnection module.

The FAST-Net (Free-space Accelerator for Switching Terabit Networks) concept uses an array of wide-field-of-view imaging lenses to realize a high-density shuffle interconnect pattern across an array of smart-pixel integrated circuits. To simplify the optics we evaluated the efficiency gained in replacing spherical surfaces with aspherical surfaces by exploiting the large disparity between narrow vertical cavity surface emitting laser (VCSEL) beams and the wide field of view of the imaging optics. We then analyzed trade-offs between lens complexity and chip real estate utilization and determined that there exists an optimal numerical aperture for VCSELs that maximizes their area density. The results provide a general framework for the design of wide-field-of-view free-space interconnection systems that incorporate high-density VCSEL arrays.

Analysis of a hybrid micro/macro-optical method for distortion removal in free-space optical interconnections.

Eikonal analyses are applied to a hybrid micro/macro-optical shuffle interconnection approach that minimizes distortion in a multichip smart-pixel shuffle interconnection system. The optical system uses off-axis imaging elements to link clusters of dense arrays of vertical-cavity surface-emitting laser (VCSEL) sources to matching clusters within arrays of detectors. A critical requirement for such a system is that the images of the two-dimensional arrays of the VCSELs must be registered on their associated detector arrays with a precision of the order of 10 microm across the entire multichip array. The hybrid approach exploits the typical narrow-beam cone angles of VCSELs by use of beam-deflecting micro-optics to create a distortion-canceling symmetry about a central aperture in the optical system for each VCSEL-detector link. The second- and third-order aberrations of the plane-symmetric system created by the global off-axis imaging system are analyzed. The results prove that the hybrid concept cancels distortion and minimizes the spot size at the detector array plane.

Experimental validation of hybrid micro-macro optical method for distortion removal in multi-chip global free-space optical-interconnection systems.

Experimental validation of a distortion removal technique for multi-chip free-space optical shuffle interconnections is presented. The free-space fabric links dense two-dimensional arrays of vertical cavity surface emitting laser(s) (VCSEL)(s) and detectors and must achieve full field registration on the order of 10 microns across the entire array. The new hybrid micro-macro optical concept realizes the required high-registration accuracy by simultaneously eliminating distortion in each of the interleaved off-axis imaging systems that comprise the complete fabric. This is achieved by exploiting the typically low numerical aperture of VCSELs. Individually tailored beam-deflecting micro-optical elements were used to create symmetry about a central aperture for VCSEL beams in the optical system. Experiments were developed to quantify the registration accuracy, the VCSEL images, and the associated spot sizes. The experimental results show that beam steering can be implemented to remove distortion in off-axis free-space optical-interconnection systems.

ACTIVE-EYES: an adaptive pixel-by-pixel image-segmentation sensor architecture for high-dynamic-range hyperspectral imaging.

The ACTIVE-EYES (adaptive control for thermal imagers via electro-optic elements to yield an enhanced sensor) architecture, an adaptive image-segmentation and processing architecture, based on digital micromirror (DMD) array technology, is described. The concept provides efficient front-end processing of multispectral image data by adaptively segmenting and routing portions of the scene data concurrently to an imager and a spectrometer. The goal is to provide a large reduction in the amount of data required to be sensed in a multispectral imager by means of preprocessing the data to extract the most useful spatial and spectral information during detection. The DMD array provides the flexibility to perform a wide range of spatial and spectral analyses on the scene data. The spatial and spectral processing for different portions of the input scene can be tailored in real time to achieve a variety of preprocessing functions. Since the detected intensity of individual pixels may be controlled, the spatial image can be analyzed with gain varied on a pixel-by-pixel basis to enhance dynamic range. Coarse or fine spectral resolution can be achieved in the spectrometer by use of dynamically controllable or addressable dispersion elements. An experimental prototype, which demonstrated the segmentation between an imager and a grating spectrometer, was demonstrated and shown to achieve programmable pixelated intensity control. An information theoretic analysis of the dynamic-range control aspect was conducted to predict the performance enhancements that might be achieved with this architecture. The results indicate that, with a properly configured algorithm, the concept achieves the greatest relative information recovery from a detected image when the scene is made up of a relatively large area of moderate-dynamic-range pixels and a relatively smaller area of strong pixels that would tend to saturate a conventional sensor.