This paper describes a compressive sensing strategy developed under the Compressive Optical MONTAGE Photography Initiative. Multiplex and multi-channel measurements are generally necessary for compressive sensing. In a compressive imaging system described here, static focal plane coding is used with multiple image apertures for non-degenerate multiplexing and multiple channel sampling. According to classical analysis, one might expect the number of pixels in a reconstructed image to equal the total number of pixels across the sampling channels, but we demonstrate that the system can achieve up to 50% compression with conventional benchmarking images. In general, the compression rate depends on the compression potential of an image with respect to the coding and decoding schemes employed in the system.
With this work we show the use of focal plane coding to produce nondegenerate data between subapertures of an imaging system. Subaperture data is integrated to form a single high resolution image. Multiple apertures generate multiple copies of a scene on the detector plane. Placed in the image plane, the focal plane mask applies a unique code to each of these sub-images. Within each sub-image, each pixel is masked so that light from only certain optical pixels reaches the detector. Thus, each sub-image measures a different linear combination of optical pixels. Image reconstruction is achieved by inversion of the transformation performed by the imaging system. Registered detector pixels in each sub-image represent the magnitude of the projection of the same optical information onto different sampling vectors. Without a coding element, the imaging system would be limited by the spatial frequency response of the electronic detector pixel. The small mask features allow the imager to broaden this response and reconstruct higher spatial frequencies than a conventional coarsely sampling focal plane.
The Compressive Optical MONTAGE Photography Initiative (COMP-I) is an initiative under DARPA's MONTAGE program. The goals of COMP-I are to produce 1 mm thick visible imaging systems and 5 mm thick IR systems without compromising pixel-limited resolution. Innovations of COMP-I include <b>focal-plane coding, block-wise focal plane codes, birefringent, holographic and 3D optical elements for focal plane remapping</b> and <b>embedded algorithms for image formation</b>. In addition to meeting MONTAGE specifications for sensor thickness, focal plane coding enables a reduction in the transverse aperture size, physical layer compression of multispectral and hyperspectral data cubes, joint optical and electronic optimization for 3D sensing, tracking, feature-specific imaging and conformal array deployment.
Previously, a method of incorporating a microlens within a standard fiber optic ferrule was described. In this paper, the micro-rod and wafer fabrication concepts are explained, the wafer mapping/layout processes used to create the microlens substrate are detailed, and packaging in standard ferrules and v-grooves are described along with coupling results.
Optical connectors utilize microlens elements for coupling light into and out of fibers. Typically, these lenses are based on sapphire ball lenses or Gradient Index lens elements.However, lenses that are on the same scale as the single-mode fiber itself have not been previously realized. This paper introduces an optical lens element that fits into the single-mode optical ferrule, without any modifications to the connector package. This approach offers substantial performance and cost benefits over other methods.Both theoretical and experimental results are presented.
The design of a 1.2 Gbit/sec CMOS laser driver with a novel temperature controlled feedback loop is presented. It was designed to be used for digital fiber applications, e.g. fiber-to-the-curb telecommunications or for datacom. The laser-driver operates at a maximum speed of 1.2 Gbit/sec between the temperature ranges of -40 C to 85 C using low-cost CMOS technology. Simulation results at these speeds, and experimental results at a lower speed of 200Mbit/sec, are presented.
Diffractive optical elements (DOEs) have many advantages over refractive optical elements including the ability to implement exotic function (such as flat-tops, line generators and splitting and combining functions), the ability to easily incorporate a variety of functions in to one element, lower volume and less weight. In addition to these advantages, diffractives offer 3 potential positive characteristics which are sometimes cited as drawbacks. These are: diffraction efficiency, dispersion and cost. In some applications, such as wavelength division multiplexing (WDM) or other applications in which it is desirable for different wavelengths of light to be affected in different manners, the highly dispersive nature of diffractives is an advantage. In other applications when the spectral width of the illumination is large (e.g. laser diodes when the case temperature varies over a wide range), the dispersion of DOEs can be a disadvantage. Diffraction efficiency, defined as the power diffracted into the desired diffraction order divided by the power incident on the DOE, can be very high or low depending on the application and design procedure. This paper focuses on these 3 potential advantages of diffractives. In the remainder of this paper each characteristic is discussed individually in order to show how the negative effects of each can be minimized and the positive effects enhanced.
Diffractive optics is becoming a standard part of the optical designer's toolkit. The transition from design to manufacturing, especially for elements larger than a few millimeters in diameter, has been impeded by the relatively high cost of producing diffractive elements by standard photolithographic means. Replications techniques, such as injection molding, have the potential to significantly lower the cost for such elements. We report on results of the application of injection molding techniques to the replication of diffractive elements. Several examples of diffractives fabricated by these techniques, as well as present process capability, are discussed.
Diffractive optics have the potential to play a key role in several areas of head mounted displays. They can reduce size and weight while providing some unique optical functions that would be difficult to implement with conventional refractives. There are four areas in which diffractive optics may contribute: Magnifier optics, combiner optics, head and hand tracking, and optical data interface. This paper is primarily concerned with the introduction of a new image combiner element based on Babinet's principle.
The design and fabrication of a low cost laser diode to fiber optic coupler is discussed. A single diffractive optical element was used to provide uniform coupling efficiency over a 40 nm bandwidth. The element was optimized to maintain constant coupling efficiency with small tilts and decenters. An iterative method referred to as radially symmetric iterative discrete on-axis (RSIDO) encoding was used to determine optimum fringe placement and profile.
For the past few years we have been working on the development of an optically interconnected multichip module (MCM). The MCM is composed of a planar transparent substrate, containing thin film electrical connections. GaAs laser array chips and silicon CMOS VLSI chips with integrated photodetectors are flip-chip bonded to one side of the substrate, while computer generated holograms (CGHs) are fabricated on the other side of the substrate. The purpose of this work is to develop the technology to enable high speed and high density connections between chips, MCMs, and PC boards. We believe that the basic approach we use, based on flip-chip and CGH technology, will provide 1-2 orders of magnitude increase in connection performance when compared with conventional electrical connectors.
In this paper we focus on the design of optically interconnected MCMs for gigabit ATM switching networks. Our approach is to design a generic hardware module that can be used to implement ATM switches with application-specific functionality, cost, and performance requirements. The module design is partitioned on the MCM such that it can be built using VLSI chips interconnected with holographic free-space optical interconnects. Holographic optical interconnects are also used for inter-MCM communication. A comparison of our approach with electrical MCM, all-optical, and guided-wave implementations of ATM switches is presented. A detailed review of the technology used in our design and various switch architectures that can be achieved can be found in references 1 and 2, respectively.
The development of an optical interconnected multichip module (MCM) is underway at UNC- Charlotte. The approach is to use optical interconnects within a digital multichip module for connections that are longer than a certain length (break even line length). For these connections the optical link dissipates less power than the corresponding electrical link. One of the main goals of this project is to develop a technology for optical interconnects that can be implemented with minimal modification to current devices. We are currently in the process of developing a series of MCM systems. System 1 will be a testbed that enables testing of hologram encoding techniques, alignment tolerances, optical link efficiency, and thermal properties. System 2 will use the knowledge gained in the development of system 1 to build a small functional system to demonstrate the technology.
In this paper we describe the design and testing of a high speed photodetector that is fully integrated into a CMOS chip, with a response time of 2.6 ns and an operating speed of 112 MHz. The photodetector is to be used in an optically interconnected multi-chip module.
An optically interconnected multichip module designed specifically to meet the demands of high performance processor array systems is proposed. The system consists of computer generated holograms GaAs laser array chips and Si VLSI chips containing processing elements and integrated photodetectors. All components are incorporated into a package (similar to an existing multichip module design) with a water-cooled heat sink. All intramodule chip-to-chip connections longer than a particular line length and all intermodule connections are implemented optically. Limitations on power dissipation bandwidth connection density and alignment tolerances are discussed. The performance is compared with both electrical thin film interconnects and guided wave optical interconnects.