Infrared Light Emitting Diode Extraction Efficiency

Description:

TECHNOLOGY AREA(S): Weapons 

OBJECTIVE: Develop technologies to improve extraction efficiency of high density infrared light emitting diode arrays to improve radiance output, self-heating, and wall-plug efficiency. 

DESCRIPTION: This SBIR topic seeks to identify and demonstrate technologies that can improve the light extraction efficiency of high density mid-wave infrared (MWIR) and long wave infrared (LWIR) light emitting diode (LED) arrays designed to be used in infrared (IR) scene projectors without affecting the ability to control the radiance on a per-pixel level. The enhancements must be applicable for incorporation into projector systems suitable for use in hardware-in-the-loop (HITL) simulation and Installed System Test Facility (ISTF) applications. The ability to stimulate advanced infrared weapon and aircraft sensors and seekers with high radiance, high resolution IR imagery of targets, backgrounds, and countermeasures in dynamic hardware-in-the-loop simulation and installed systems test facilities is critical in the development, test, and evaluation of those systems. Current IR scene projectors are based on resistive emitter array technology that has numerous limitations including output radiance, frame rates, and frame size. Infrared (IR) LED arrays have shown great potential for application to advanced IR scene projectors. LED arrays may improve radiance levels, operating speed, and frame size over other existing technologies. Developmental LED arrays range from 512x512 pixels on a 48 micron pixel pitch (~1 inch square array) to 2048x2048 arrays on a 24 micron pitch (~2 inch square array) with potential growth to larger arrays. The LED arrays are driven by a read-in integrated circuit (RIIC) which provides control of the radiance output of each pixel based on the desired IR image from a scene generation system and the ability to provide non-uniformity correction across the array. A significant issue with current generation IR LED arrays is the light extraction efficiency (LEE) which is typically less than 1%. Even slight improvements to the LEE would greatly increase maximum radiance, reduce waste heat which must be removed from the arrays, and increase wall-plug efficiency. An example is a 512x512 superlattice LED array with about 1% extraction efficiency where each pixel at full power consumes 15 milliamps at 12 volts. If all quarter million pixels were turned on, the one inch square array would be required to dissipate 47 kW. The low efficiency significantly impairs the utility of the LED arrays. Not only does the reduced radiance limit the types of imagery that can be projected, a very large amount of waste heat is generated that, even with extensive cooling, can affect operation of the array and even permanently damage the devices. 

PHASE I: Identify factors that limit extraction efficiency, define concepts that may increase the efficiency, determine the technical feasibility of the concepts, and design a follow-on test program for the most promising concepts. Required deliverables will include reports and briefings documenting the analysis and the results 

PHASE II: Complete design and fabricate small prototype IR LED arrays using the most promising concepts developed in Phase I. Perform characterization experiments quantifying the effects on extraction efficiency and on overall LED performance including output radiance, self-heating, and wall-plug efficiency. Required deliverables will include reports and briefings on the results of the experiments. 

PHASE III: Military Applications: DT&E of IR guided weapons, threat warning and aircraft self-protection systems, electro-optical sensors. Commercial Applications: DT&E of IR sensors and systems including autonomous guidance, vision, and collision avoidance systems. 

REFERENCES: 

1. Norton, Dennis Thomas Jr. "Type-II InAs/GaSB superlattice LEDs: applications for infrared scene projector systems." PhD thesis, University of Iowa, 2013.

2. Norton, Dennis, et al., "Development of a high-definition IR LED scene projector." Proc. SPIE 9820, Infrared Imaging Systems: Design, Analysis, Modeling, Testing XXVII, 98200X, 3 May 2016.

3. Lange, Corey Wyatt. "Design and Development of 512 512 Infrared Emitter Array System." Master's thesis, University of Delaware, 2011.

 

KEYWORDS: Extraction, Efficiency, Light, Emitting, Diode, LED, Infrared, Emitter, Array, Mid-wave, MWIR, Long-wave, LWIR, Hardware-in-the-loop, HITL, Scene, Projector, IRSP, Optoelectronics 

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