Under a U.S. Navy SBIR solicitation, a need was
identified for the development of a fieldable two-color midwave
infrared (MWIR) simulator to test a host of different IR target
tracking technologies, forward looking infrared cameras, and night
vision systems. Within this application, the simulator would be used at
various ranges to illuminate the aperture of the unit under test (UUT)
with a dynamic IR scene simulating the target. The system must be able
to simulate the spectral, spatial, temporal, and radiant intensity
characteristics of various targets for different test applications. Of
particular importance for this development effort is the ability to
simulate a change in the spectral properties of the target over the
duration of the event. More specifically, the simulator must project in
two independently controllable MWIR spectral bands loosely called "red"
and "blue". OPTRA proposed and successfully
demonstrated a two-color simulator concept based on digital micromirror
device (DMD) technology. A breadboard simulator was designed, built,
and tested under a Phase I, the results from which are shown here. This
work has transitioned to Phase II.
The above photo shows the two-color dynamic scene generator Phase I breadboard. MWIR light originating from the simulator module (center) is spectrally filtered and directed onto the DMD (right) which causes the scenes of the two bands. The scenes are then overlayed by the simulator module and projected onto an IR camera (left). The Phase II system will employ separate DMDs for the two spectral bands.
OPTRA proposed the development of a two-color MWIR source simulator based on fused projected images of two DMDs, one for each spectral band. The system employs a broadband IR (thermal) source whose energy is spectrally filtered via a bandpass filter (BPF) centered on the blue band prior to being imaged onto each DMD. The “on” reflected image from each DMD is then recombined by a second BPF centered on the red band, and the fused beam is expanded by a telescope and transmitted towards the UUT. The relative intensities of the two bands are controlled through the duty cycle of “on” versus “off” images reflected by each micromirror in the same manner that a commercially available digital light projector (DLP) controls intensity. Because we are not changing the IR source temperature, response is fast relative to resistive based simulators; in the same vein, thermal management issues are less complex than with resistive arrays whose time constant depends on thermal management. Simplified thermal management may ultimately result in a lower power, more fieldable system. At the same time, this approach provides a broadband simulation, unlike laser simulators, resulting in a more representative target with which to challenge an IR tracker.
Above are MWIR images generated with the beardboard simulator in overlayed two-color ("Red" and "Blue") bands. These images are created by turning corresponding micromirrors on within each channel. The images were recorded with an IR camera.
The overall approach offers the ability to
realistically simulate the spectral, spatial, temporal, and radiant
intensity properties of a number of targets for IR tracker test
applications.
(Left) Dynamic scene generated with the breadboard
simulator in Red, Blue and two-color bands. The scene represents a
point source approaching the UUT, increasing in angular subtense as
well as in intensity. The simulation demonstrates the ability to
independently control the two channel's spatial and intensity
properties. The scene was recorded with an IR camera.
(Right) Dynamic
scene generated with the breadboard simulator in two-color bands. The
"Red" and "Blue" simulated images are rotated in turn to demonstrate
the ability to independently control the two channels. This scene was
also recorded with an IR camera.
OPTRA, Inc. 461 Boston Street, Topsfield MA 01983-1234 fax: 978-887-0022 | sales: 978-887-6600 | e-mail: info@optra.com
