Using a novel computational imaging architecture, we double the field of view of a long-wave infrared microbolometer camera while maintaining resolution. Due to the compact designs enabled by this architecture and the critical impact of resolution on classification performance, this approach is compelling for surveillance applications where low size, weight, power and cost (SWaP-C) systems are desired. We detail the optical design, characterization, and performance of a compact, refractive, optically multiplexed imaging system for use in the long-wave infrared (8-12 μm). A pair of prisms are used to divide the aperture and expose the uncooled microbolometer focal plane to two fields of view simultaneously, doubling the number of output pixels and the horizontal field of view. The image is reconstructed by rotating the prisms about the optical axis, inducing opposing vertical shifts in the two channels. Focal length, field of view, MTF, and NEDT are used to compare performance to a conventional camera. Shifting methods for proper demultiplexing are discussed, and reconstructed images are offered as a demonstration of system performance.
In a multiplexed image, multiple fields-of-view (FoVs) are superimposed onto a common focal plane. The attendant gain in sensor FoV provides a new degree of freedom in the design of an imaging system, allowing for performance tradeoffs not available in traditional optical designs. We explore design choices relating to a shift-encoded optically multiplexed imaging system and discuss their performance implications. Unlike in a traditional imaging system, a single multiplexed image has a fundamental ambiguity regarding the location of objects in the image. We present a system that can shift each FoV independently to break this ambiguity and compare it to other potential disambiguation techniques. We then discuss the optical, mechanical, and encoding design choices of a shift-encoding midwave infrared imaging system that multiplexes six 15×15 deg FoVs onto a single one megapixel focal plane. Using this sensor, we demonstrate a computationally demultiplexed wide FoV video.
We describe the optical design and characterization testing of an optically multiplexed imaging system operating in the 3.4 to 5 micron waveband. The optical design uses a division of aperture method to overlay six images on a single focal plane and produce a 90 by 15 degree 6-megapixel field of view. Image disambiguation is achieved through image shifting enabled by piezo-actuated mirrors in the multiplexing assembly. This paper provides an overview of the optical design including focal plane selection, image resolution and distortion, pupil imaging, and aperture division geometry. A method of applying one and two-point non-uniformity correction using radiometric test data is suggested. Sensor-level per-channel image quality and sensitivity tests including MTF, 3D-noise and NEDT are shown to validate the design assumptions.
Optically multiplexed imagers overcome the tradeoff between field of view and resolution by superimposing images from multiple fields of view onto a single focal plane. In this paper, we consider the implications of independently shifting each field of view at a rate exceeding the frame rate of the focal plane array and with a precision that can exceed the pixel pitch. A sequence of shifts enables the reconstruction of the underlying scene, with the number of frames required growing inversely with the number of multiplexed images. As a result, measurements from a sufficiently fast sampling sensor can be processed to yield a low distortion image with more pixels than the original focal plane array, a wider field of view than the original optical design, and an aspect ratio different than the original lens. This technique can also enable the collection of low-distortion, wide field of view videos. A sequence of sub-pixel spatial shifts extends this capability to allow the recovery of a wide field of view scene at sub-pixel resolution. To realize this sensor concept, a novel and compact divided aperture multiplexed sensor, capable of rapidly and precisely shifting its fields of view, was prototyped. Using this sensor, we recover twenty-four megapixel images from a four-megapixel focal plane and show the feasibility of simultaneous de-multiplexing and super-resolution.
Constraining the Seidel aberrations of optical surfaces is a common technique for relaxing tolerance sensitivities in the optimization process. We offer an observation that a lens’s Abbe number tolerance is directly related to the magnitude by which its longitudinal and transverse color are permitted to vary in production. Based on this observation, we propose a computationally efficient and easy-to-use merit function constraint for relaxing dispersion tolerance sensitivity. Using the relationship between an element’s chromatic aberration and dispersion sensitivity, we derive a fundamental limit for lens scale and power that is capable of achieving high production yield for a given performance specification, which provides insight on the point at which lens splitting or melt fitting becomes necessary. The theory is validated by comparing its predictions to a formal tolerance analysis of a Cooke Triplet, and then applied to the design of a 1.5x visible linescan lens to illustrate optimization for reduced dispersion sensitivity. A selection of lenses in high volume production is then used to corroborate the proposed method of dispersion tolerance allocation.
The Gabor Superlens (GSL) combines light from an array of micro-telescopes to form a single composite image. This is achieved through an initial selection of micro-telescope and array parameters that satisfy a set of first order imaging conditions. Designing a GSL presents two design challenges that are not encountered in conventional (single-aperture) lens design: the array parameters couple design characteristics such as the F/# and field of view to the paraxial design, and the composite image quality can be dominated by aberration of individual elements rather than a summation of aberration contributions throughout the design. This paper begins with an assessment of the highly parameterized design space of the Gabor Superlens to clearly identify relationships between the initial selection of first order design geometry and the consequences they have on system performance. An overview of a streamlined design method follows. Increasingly sophisticated GSL designs are then investigated to demonstrate the effectiveness of using individually corrected lens groups to improve composite image quality.
We describe an advanced computational imaging system with an optical architecture that enables simultaneous and dynamic pupil-plane and image-plane coding accommodating several task-specific applications. We assess the optical requirement trades associated with custom and commercial-off-the-shelf (COTS) optics and converge on the development of two low-cost and robust COTS testbeds. The first is a coded-aperture programmable pixel imager employing a digital micromirror device (DMD) for image plane per-pixel oversampling and spatial super-resolution experiments. The second is a simultaneous pupil-encoded and time-encoded imager employing a DMD for pupil apodization or a deformable mirror for wavefront coding experiments. These two testbeds are built to leverage two MIT Lincoln Laboratory focal plane arrays – an orthogonal transfer CCD with non-uniform pixel sampling and on-chip dithering and a digital readout integrated circuit (DROIC) with advanced on-chip per-pixel processing capabilities. This paper discusses the derivation of optical component requirements, optical design metrics, and performance analyses for the two testbeds built.
Plastic lenses are widely used in visible imaging systems and provide a number of advantages including reduced
weight. However, their use in the short-wave infrared (SWIR) has been limited due to the presence of strong material
absorption bands occurring at wavelengths above 1 micron. This paper explores the viability of using plastic optics in
broadband SWIR imaging applications and the efficacy of using plastic lenses as a method of weight reduction. A design
study is presented to reveal combinations of plastic and glass lenses suitable for aberration correction. Weight savings is
quantified via a comparison to glass lenses to investigate the trade-off between using lower density plastic materials and
the faster F/#s (i.e. larger lenses) required to compensate for the signal loss caused by their absorption.
With the increasing availability of InGaAs detectors for imaging applications in the short wave infrared (SWIR, 0.9 - 1.7 μm), the need for diffraction limited lenses optimized for this spectrum is rising as well. With an abundance of commercially available optical glasses that are transparent in the SWIR, correcting chromatic aberration over the broader SWIR waveband might seem only a moderately difficult task for the optical designer. As it turns out, it is considerably more difficult because the dispersive nature of most of the common glass flints is decreased in the SWIR, limiting the
availability of strong flints for achromatization. Fortunately, a limited selection of highly dispersive SWIR transparent materials can be found among materials used for mid-wave and long wave infrared (IR) optics. However, some of these IR materials have a strong absorption edge in close proximity to the SWIR waveband which presents the optical designer with a different challenge. This paper examines challenges and tradeoffs specific to material selection for color correction in the design of diffraction limited lenses for the SWIR. Solutions are proposed for achromatic and apochromatic lenses. A discussion of material properties and the SWIR glass map is included.
KEYWORDS: Monte Carlo methods, Modulation transfer functions, Aspheric lenses, Tolerancing, Spindles, Single point diamond turning, Data modeling, Code v, Error analysis, Stars
Single point diamond turning of optical surfaces is becoming more commonly used, especially in infrared systems. However, the process introduces its own peculiar forms of figure error that can compromise performance. These errors include tool misalignment error, thermal effects, low frequency surface ripple, and mounting effects. Techniques have been developed to model these effects in Monte Carlo simulations using conventional optical design codes to predict the changes in optical performance.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.