This PDF file contains the front matter associated with SPIE
Proceedings Volume 7096, including the Title Page, Copyright
information, Table of Contents, Introduction (if any), and the
Conference Committee listing.
With the trend to seek solutions for persistent surveillance based on exploiting
unmanned aircraft, there is interest in combining as many sensing functions in as
small a system as possible, so that the endurance of the platform can be increased as
far as possible. The challenge is to provide the means of discriminating diverse sets
of targets in relation to their environments and to enable the identification of those
targets with a reasonable level of confidence. Multifunctional systems can provide
a way forward, especially if several sensors can be exploited through a common
aperture. This paper provides a review of progress in the field, building on a
process of bio-inspiration with some emphasis on the benefits that multi-spectral
EO systems provide in relation to improved target recognition.
We describe an approach to polarimetric imaging based on a unique folded imaging system with an annular aperture.
The novelty of this approach lies in the system's collection architecture, which segments the pupil plane to measure the
individual polarimetric components contributing to the Stokes vectors. Conventional approaches rely on time sequential
measurements (time-multiplexed) using a conventional imaging architecture with a reconfigurable polarization filter, or
measurements that segment the focal plane array (spatial multiplexing) by super-imposing an array of polarizers. Our
approach achieves spatial multiplexing within the aperture in a compact, lightweight design. The aperture can be
configured for sequential collection of the four polarization components required for Stokes vector calculation or in any
linear combination of those components on a common focal plane array. Errors in calculating the degree of polarization
caused by the manner in which the aperture is partitioned are analyzed, and approaches for reducing that error are
investigated. It is shown that reconstructing individual polarization filtered images prior to calculating the Stokes
parameters can reduce the error significantly.
We describe a novel method to track targets in a large field of view. This method simultaneously images multiple,
encoded sub-fields of view onto a common focal plane. Sub-field encoding enables target tracking by creating
a unique connection between target characteristics in superposition space and the target's true position in real
space. This is accomplished without reconstructing a conventional image of the large field of view. Potential
encoding schemes include spatial shift, rotation, and magnification. We briefly discuss each of these encoding
schemes, but the main emphasis of the paper and all examples are based on one-dimensional spatial shift encoding.
Simulation results are included to show the efficacy of the proposed sub-field encoding scheme.
We consider direct minimum mean-squared error (MMSE) reconstruction of difference images without explicit
reconstruction of the two images at the two time instants. We first derive the MMSE reconstruction operator
and show that it depends on the cross-correlation between the two images taken at different times. We then
consider the reconstruction performance of different strategies for measuring linear spatial projections of the two
images. Performance is evaluated by using measured video imagery of an urban intersection as the input into a
simulation that models the linear projections.
An earlier paper  discussed the merits of adaptive coded apertures for use as lensless imaging systems in the thermal
infrared and visible. It was shown how diffractive (rather than the more conventional geometric) coding could be used,
and that 2D intensity measurements from multiple mask patterns could be combined and decoded to yield enhanced
imagery. Initial experimental results in the visible band were presented. Unfortunately, radiosity calculations, also
presented in that paper, indicated that the signal to noise performance of systems using this approach was likely to be
compromised, especially in the infrared.
This paper will discuss how such limitations can be overcome, and some of the tradeoffs involved. Experimental results
showing tracking and imaging performance of these modified, diffractive, adaptive coded aperture systems in the visible
and infrared will be presented. The subpixel imaging and tracking performance is compared to that of conventional
imaging systems and shown to be superior. System size, weight and cost calculations indicate that the coded aperture
approach, employing novel photonic MOEMS micro-shutter architectures, has significant merits for a given level of
performance in the MWIR when compared to more conventional imaging approaches.
The design of novel imaging systems for wide area surveillance poses unique challenges that range from
practical aperture design to the sheer number of pixels that must be sensed. Towards this end, we have
developed an imaging system that employs interleaved sparse-apertures with multiplexed look directions to
achieve wide area coverage while simultaneously achieving resolution. Point Spread Function (PSF)
engineering is key to combating the effects of chromaticity and recovering resolution in such a system.
Specifically, we show that a combination of micro-prisms and micro-piston arrays can be optimized to
approximate the PSF of bulk prisms over a range of wavelengths. The resulting optics is much smaller and
lighter than bulk prisms, and also easier to fabricate for interleaved surfaces. The proposed technique maps
many resolution cells to the same pixel, and is motivated by the desire to reduce the number of focal plane
arrays as well as the overall size, weight and power requirements for the sensor system.
Coded aperture imaging has been used for astronomical applications for several years. Typical implementations used a
fixed mask pattern and are designed to operate in the X-Ray or gamma ray bands. Recently applications have emerged in
the visible and infra red bands for low cost lens-less imaging systems and system studies have shown that considerable
advantages in image resolution may accrue from the use of multiple different images of the same scene - requiring a
Previously we reported on the early feasibility of realising such a mask based on polysilicon micr-opto-electromechanical
systems (MOEMS) technology and early results in the visible and near IR bands. This employs interference
effects to modulate incident light - achieved by tuning a large array of asymmetric Fabry-Perot optical cavities via an
applied voltage whilst a hysteretic row/column addressing scheme is used to control the state of individual elements.
In this paper we present transmission results from the target mid-IR band (3-5μm), compare them with theory and
describe the scale up from a 3x3 proof-of-concept MOEMS microshutter array to a 560 x 560 element array (2cm x 2cm
chip) with the associated driver electronics and embedded control - including aspects of electronic design, addressing
control and integration. The resultant microsystem represents a core building block to realise much larger reconfigurable
masks using a tiled approach with further integration challenges in the future.
The use of coded apertures in a large area MWIR system introduces a number of difficulties including the effects of
diffraction and other distortions not observed in shorter wavelength systems. A new approach is being developed that
addresses the effects of diffraction while gaining the benefits of coded apertures, thus providing the flexibility to vary
resolution, possess sufficient light gathering power, and achieve a wide field of view (WFOV). The photonic MEMS
artificial eyelid array technology is currently being applied as the coded aperture in this program for surveillance
enabling technology development. Speed, lifetime, packaging and scalability are all critical factors for the MEMS eyelid
technology to determine system efficacy as well as military and commercial usefulness. The electronic eyelid is the
fundamental addressable unit for adaptive code generation and will allow the system to multiplex in time for increased
resolution. The proposed system consists of four subsystems in parallel with each subsystem consisting of four subapertures.
Each sub-aperture contains an artificial eyelid array capable of 36 different, independent patterns of open
500µm eyelids corresponding to 36 different look directions. Dynamic aperture arrays were fabricated on both quartz
and sapphire substrates for operation in the visible to MWIR. Both 8x8 and 40x40 element arrays were designed,
fabricated, and tested with the capability of 4, 8, and 16 unique pattern combinations. Process and device improvements
have been implemented to improve the yield of the MEMS arrays. In addition to mechanical evaluations, the eyelid
arrays were tested optically to demonstrate the capability of multiple look directions.
This paper will investigate micro-shutter MEMS "fabrication techniques" and processes to identify opportunities and
barriers for successful implementation of micro-shutter technologies to enable adaptive coded aperture imaging and nonimaging
systems. The use of photonic MEMS for creating adaptive coded apertures has been gaining momentum since
2007. Both Industry-based1, 2 and University-based3 studies have demonstrated their unique solutions for implementing
MEMS-based micro-shutter technologies; however, there are many unique and novel MEMS-based "fabrication and
characterization" processes and solutions that will be considered herein as we explore micro-shutter technologies. This
paper discusses challenges and opportunities that may arise from in-house fabrication of MEMS which may prevent
and/or improve structural uniformity, reproducibility, & reliability. This paper will also discuss characterization of the
micro-shutters to include mechanical, electrical and optical properties. The "open and close" speeds of the micro-shutter
device will also be assessed from a scaling perspective to determine usability.
Photonic MEMS technology as it pertains to adaptive coded aperture sensing is an emerging technology offering an
increase to imaging performance compared to a fixed system in the EO/IR wavelength region. In this paper we address
the effects of potential manufacturing yield and defects. A 1-d first order optical model is developed in an attempt to
correlate the optical/system performance to the manufacturing defects and yield output. The imager is found to be
extremely robust to both random and correlated failures in the coded aperture, so long as the aperture code is adapted to
the aperture failures.
This paper will investigate micro-shutter developments for IR applications. By demonstrating a interrupter mechanism
MEMS design, we will show how to implement a micro-shutter technology to enable adaptive coded aperture imaging
and non-imaging systems. The use of Photonic MEMS for creating adaptive coded apertures, for surveillance systems,
has been gaining momentum since 2007 1,2. Through the investigation of the interrupter mechanism 3,4, we will
demonstrate a novel approach for IR applications. This paper discusses challenges and opportunities that may arise from
the fabrication of a MEMS interrupter mechanism. We discuss the characterization of the micro-shutter to include
mechanical, electrical and IR properties. The "open and close" speeds of the micro-shutter device will also be assessed
from a scaling perspective to determine usability through modeling and simulation.
This paper will investigate a novel agile-pitch diffraction grating array design and phenomenology, for micro-shutter
Photonic MEMS technologies, to enable adaptive coded aperture imaging and non-imaging systems. The use of Photonic
MEMS for creating adaptive coded apertures, for surveillance systems, has been gaining momentum since 2007 1,2. The
use of the agile-pitch diffraction grating has also been used previously to perform beam-dispersion which is a critical
step in imaging processing 3. Through the investigation of new diffraction grating approaches, we hope to show a
reconfigurable capability for agile beam steering for adaptive coded apertures surveillance imaging and non-imaging
systems. This paper discusses challenges and opportunities that may arise from in-house fabrication of agile-pitch
diffraction grating array micro-shutter designs which may prevent and/or improve structural uniformity, reproducibility,
& reliability. This paper will also discuss characterization of the micro-shutters to include mechanical, electrical and
optical properties. The "open and shut" speeds of the micro-shutter device will also be assessed from a scaling
perspective to determine usability.