Designers of advanced digital imaging systems are frequently challenged with considering not only the optics and sensor, but also the effects of image processing in the selection of the best architecture to meet their system objectives. Leveraging the image processing degree of freedom presents a considerable opportunity if one incorporates system-level metrics in the design and optimization process. Including the image processing degree of freedom also significantly expands the set of solutions and enables different trades of performance, cost, size, weight, and power. Here, we demonstrate the opportunity available to the system designer by exploring the design of a wide angle system intended to maximize a system-level human visual performance metric. The resulting system solutions span a range of optical, optomechanical, and signal processing complexity and show systems with a wide range of size and cost.
With reductions in microbolometer size and cost, long-wave infrared (LWIR) systems are increasingly being developed
for platforms with challenging size, weight, power, and cost (SWAP-C) constraints, such as helmet-mounted systems
and unmanned vehicles. Past optimization of imaging systems toward the simultaneous objectives of improved stand-off
detection and low size, weight, and power required an iterative, multi-disciplinary design process. Here we demonstrate
the direct optimization of the full LWIR system model including the optics, sensor, signal processing, and display
degrees of freedom with system level metrics including SWAP-C and detection range. The end result is a system with
superior size and weight for a given detection range.
The DRS Tamarisk® 320 camera, introduced in 2011, is a low cost commercial camera based on the 17 µm pixel pitch 320×240 VOx microbolometer technology. A higher resolution 17 µm pixel pitch 640×480 Tamarisk®640 has also been developed and is now in production serving the commercial markets. Recently, under the DARPA sponsored Low Cost Thermal Imager-Manufacturing (LCTI-M) program and internal project, DRS is leading a team of industrial experts from FiveFocal, RTI International and MEMSCAP to develop a small form factor uncooled infrared camera for the military and commercial markets. The objective of the DARPA LCTI-M program is to develop a low SWaP camera (<3.5 cm3 in volume and <500 mW in power consumption) that costs less than US $500 based on a 10,000 units per month production rate. To meet this challenge, DRS is developing several innovative technologies including a small pixel pitch 640×512 VOx uncooled detector, an advanced digital ROIC and low power miniature camera electronics. In addition, DRS and its partners are developing innovative manufacturing processes to reduce production cycle time and costs including wafer scale optic and vacuum packaging manufacturing and a 3-dimensional integrated camera assembly. This paper provides an overview of the DRS Tamarisk® project and LCTI-M related uncooled technology development activities. Highlights of recent progress and challenges will also be discussed. It should be noted that BAE Systems and Raytheon Vision Systems are also participants of the DARPA LCTI-M program.
The zoom lens design problem for the 2012 Zoom Lens IV conference is a first of its kind. The challenge is to design a
lens operating at a single wavelength of 587.6 nm with a 20:1 zoom ratio using only four elements; akin to the 1990
IODC Monochromatic Quartet design problem. The lens design offers several degrees of freedom including a range of
glass and aspheric elements in order to achieve the continuous zoom through effective focal lengths from 4 mm to 80
mm, with a back focal length > 16 mm. Throughout the zoom motion, the first element and the aperture stop are kept in
fixed positions relative to the image plane and lens operates at a constant f/10. The goal of the problem is to minimize
the length of the system as measured from the vertex of the front element to the image plane. The design is required to
meet an RMSWFE < 0.07 waves to a field height of 1.25 mm, while supporting a full field height of 2.5 mm with less
than 5% magnitude distortion. The winning entry met the specifications with a length of only 22.195 mm.
A foveated imager providing a panoramic field of view with simultaneous region of interest optical zoom for use on a
micro unmanned aerial vehicle is described. The foveated imager reduces size, weight and power by imaging both wide
and telephoto fields onto a single detector. The balance of resolution between panoramic and zoom fields is optimized
against the goals of threat detection and identification with a small unmanned aerial system, resulting in a 3X reduction
in target identification time compared to conventional systems. A description of the design trades and the evaluation of a
prototype electro-optical system are provided.
Several methods have been demonstrated for desensitization of a lens design to manufacturing errors with the result of
increased as-built performance at the expense of a slightly reduced nominal performance. A recent study demonstrated a
targeted desensitization method tuned for the most sensitive lens parameters can greatly increase yield for a known set of
manufacturing tolerances. The effectiveness of such a targeted desensitization relies on two key pieces of information;
lens sensitivities and manufacturing tolerance distributions. Targeted desensitization to known and unknown
manufacturing tolerances is examined with an example demonstrating the impact of designing to unknown, bounded
manufacturing tolerance distributions.
A new method of optimization using the thru-focus MTF is described. Operands based on the thru-focus MTF peak and
distance from the evaluation plane to the peak are investigated for their insensitivity to local minima in DLS
optimization. The new optimization method is generally compared to conventional MTF optimization and demonstrates
a significantly reduced optimization failure rate. The method is tested and shown to optimize a highly aspheric four
element mobile lens design.
Miniature camera lenses are currently manufactured at volumes over 1 billion units per year. In this high volume
industry, design methods that improve tolerance to manufacturing errors result in improved yield and significantly
reduced cost. Few, if any, design for manufacture methods have been developed for this solution space, which is vastly
different than traditional design as it is dominated by highly aspheric optics and compact design forms. In this paper, five
design for manufacture methods that were developed for traditional designs are examined for their efficacy in improving
the as-built performance of a well-corrected injection molded miniature camera lens. Building on the results of the
evaluation, a new design for manufacture method is developed which is highly correlated to the sensitivities associated
with this solution space and requires little computational overhead. The new method generates 1.3 times the number of
improved solutions and produces a design with 1.7X looser tolerances than the starting point.
The Terrestrial Planet Finder Coronagraph (TPF-C) is a future NASA mission to search for earth-like planets around nearby stars. Detecting a planet that is almost 10 billion times fainter than its parent star is extremely difficult, and it has been shown that polarization effects can cause stellar leakage which threatens that sensitivity goal. Building on our earlier work, we now show the combination of basic polarization effects with a representative coronagraph masking system, the eighth order linear field mask and Lyot stop, results in adequate performance.
Interferometric testing of large-sized optics in a thermal vacuum environment poses challenges not normally found in an optical metrology lab. Unless the test equipment is thermal-vacuum compatible, it must be installed in an ambient environment with the test item viewed through a window in the thermal-vacuum chamber. Limitations in chamber port size preclude normal-incidence viewing of the full aperture of large-sized optical elements. This necessitates the use of a mechanical translation of the test item to acquire multiple overlying interferograms. The interferograms are then concatenated in order to produce a full-aperture surface map of the test item. This is then used to confirm surface deformation of the entire test mirror. This paper will discuss the challenges, solutions, and results of a series of thermalvacuum tests performed on a large-scale (>40cm) silicon carbide mirror at ambient temperatures.
The optical telescope for a spaceborne coronagraph to detect terrestrial to Jovian-sized planets has unusually stringent phase and amplitude requirements - far exceeding a "conventional" telescope like Hubble or the James Webb Space Telescope. The key engineering requirements will be summarized based on probable mission science objectives and an engineering solution with a monolithic primary mirror on the order of 6 meters by 4 meters. We will also present an optical design for a sub-scale coronagraphic simulator as a logical and essential step in examining the system sensitivities. Testbed simulations will include F, G, and K stars and companion planets ranging in size from earth-like up to Jovian-like.
One of NASA's two planet-finding missions will be an optical coronagraph. Due to the stringent science requirements, i.e., detecting a planet that is more than a billion times fainter than its parent star, effects that normally do not enter into instrument design must now be considered. One such effect is polarization. This paper has several goals. First, we review scalar diffraction theory (PSFs and Strehl ratios) and extend it to include polarization. Second, we employ a systems-engineering approach to subdivide and categorize instrumental effects, ultimately concentrating on polarizing non-coronagraph components (mirrors). Third, we push the limits of Code-V commercial optical-engineering software to model the polarization behavior for on- and off- axis configurations, using protected-silver and bare-gold mirror coatings at four wavelengths. Last, we present a brief discussion of future tasks: easing polarization requirements, source polarization, and coronagraph masks and stops.
The telescope for a Terrestrial Planet Finder (TPF) coronagraph has exceedingly stringent phase and amplitude requirements, especially for the large, monolithic primary mirror (possibly as large as 4 meters by 10 meters). The pertinent derived engineering requirements will be summarized based on a described set of science objectives to simulate solar type stars and their companion earth-size planets. We will also present an optical design for a sub-scale coronagraphic testbed as an essential step in examining the system sensitivities. The major subassemblies of the testbed include: 1) a star/planet simulator that affords variation in contrast, adjustable relative separation and angular orientation and 2) a relay optical system representative of a TPF 3-mirror telescope that allows the imposition of known optical perturbations over the desired wavefront spatial frequencies. We will compare these TPF testbed mirror wavefront requirements with levels recently achieved on the Advanced Mirror System Demonstrator and planned for the James Webb Space Telescope (JWST).