Dynamic infrared scene projector

Details Dynamic infrared scene projector Dynamic infrared scene projector

1998-03-27

1999-09-07

Nguyen, Kiet T.

Radiant energy

Radiant energy generation and sources

2504941, 2504951, 250504R, H05B 320

Patent

active

059490810

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a Dynamic Infrared Scene Projector (DIRSP) for use in testing infrared detection systems.
Infrared detection systems generally fall into the category of either thermal imaging systems, where an infrared scene is presented to an observer, or seeker systems, where the information from the focal plane is acted upon directly by a computer. Dynamic Infrared Scene Projectors DIRSP), also known as thermal picture synthesizers, are currently used for the dynamic testing of these infrared focal plane detector array systems.
It is essential that any infrared system undergoes static testing to determine performance capabilities, such as Minimum Resolvable Temperature Difference (MRTD), Noise Equivalent Temperature Difference (NETD) and spatial resolution (MTF), and to monitor any deterioration of the system in time. Such testing requires the simulation of one or more thermal scenes, typically with varying temperature differences and spatial frequencies. One existing means of performing this test makes use of a pseudo blackbody source, involving electrically heated regions or bars of differing temperature. The temperature difference between the bars may be varied so as to establish the MRTD or NETD, whilst the MTF is determined from the apparent size of the structure. Typically, the sources comprise heated bars several centimeters in size which have a low frequency response and therefore can not be used for the dynamic testing of infrared detection systems.
Dynamic testing is useful for all infrared detection systems and, in particular, for missile seeker systems, in order to test the function of the whole system, comprising infrared detector, optics, signal processing, gimbals and tracking algorithms. The requirement is to simulate, and project, a two dimensional infrared scene which can be altered at a frame rate of up to 1 kHz. Temperature ranges of up to 350.degree. C. may typically be required.
There are no DIRSP systems currently available which meet the requirements. One class of conventional DIRSP system under development is based on two dimensional arrays of resistively heated pixels, driven by silicon integrated circuitry. However, such systems dissipate a significant and inconvenient amount of heat and the maximum frame rate achievable is approximately 100 Hz. Furthermore, real thermal scenes frequently contain objects which are very cold compared to ambient temperature, arising from the cold sky which is seen both directly by the detector and as reflections from metal objects in the scene. Resistor projector arrays are not capable of simulating such cold temperatures unless expensive and bulky cryogenic cooling equipment is employed.
U.S. Pat. No. 5,214,292 discloses a dynamic infrared scene display comprising an array of heated infrared radiation emitting elements which have an array of microlens structures coupled to the elements. Again, this display is not capable of simulating very cold temperatures without additional cooling equipment.
The present invention relates to an array of infrared light emitting diodes for use as a Dynamic Infrared Scene Projector for the testing of infrared detection systems. The device has particular use in the testing of thermal imaging systems or seeker systems. The light emitting diodes are heterostructure devices capable of negative luminescence. For example, such devices are described in U.S. Pat. No. 5,016,073. Also, infrared light emitting diodes based on the InAlSb and HgCdTe materials systems are described in T. Ashley et al., Proc. of the 7th Int. Conf. on II-VI compounds and devices, Edinburgh, UK, published Journal of Crystal Growth, vol. 159, Nos 1-4 (Feb 1996).
The invention overcomes several of the problems associated with conventional systems. For example, the power dissipation is lower, therefore reducing the need for excessive cooling, and the fundamental switching speed of the electroluminescence is such that very fast frame rates are possible. Furthermore, cold scene temperatures well below ambient can be simulated by the

REFERENCES:
patent: 5214292 (1993-05-01), Hendrick, Jr.
patent: 5864144 (1999-01-01), Laine
7.sup.th International Conference II-VI Compounds and Devices, Edinburgh, UK, Aug. 13-18 1995, vol. 159, No. 104, ISSN 0022-0248, Journal of Crystal Growth, Feb. 1996, Elsevier, Netherlands, pp. 1100-1103, XP002022420 Ashley T et al: "Room temperature narrow gap semiconductor diodes as sources and detectors in the 5-10 mu m wavelength region" see whole document.
Journal of Optical Technology, Oct. 1994, USA, vol. 61, No. 10, ISSN 1070-9762, pp. 711-719, WP000613694 Dmitriev I et al: "Dynamic infrared scene simulators" see p. 713, paragraph 3.2.1.

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