A newly patented invention could help the Department of the Air Force (DAF) enhance its infrared sensing capabilities.
Dr. Igor Anisimov, a senior research physicist in the Air Force Research Laboratory (AFRL) Information and Spectrum Warfare Directorate (RF), recently received a patent from the United States Patent and Trademark Office for “photodetector focal plane arrays with enhanced detection capability” technology. Included in the patent issuance were several other RF personnel along with Dr. Vasily Astratov, a professor of Physics and Optical Science at the University of North Carolina at Charlotte (UNC Charlotte). Dr. Astratov participated several years ago in the DAF’s Summer Faculty Fellowship Program, where he connected with AFRL researchers pursuing similar objectives and interests. His UNC Charlotte graduate students have developed their own connections with the laboratory and have accumulated valuable research experiences helping them to begin their careers. For example, Dr. Kenneth Allen, the chief technology officer of the Georgia Tech Research Institute, in 2014 worked as a member of Dr. Astratov’s laboratory on the integration of photodetector focal plane arrays with dielectric microspheres in collaboration with AFRL personnel.
The inventors’ innovation helps night vision cameras operate more effectively. Infrared night vision cameras are designed to detect heat-emitting objects. However, the cameras themselves create heat, generating thermal “noise” that reduces the cameras’ reliability. They must therefore be outfitted with cooling apparatuses, which can make the cameras expensive. Dr. Anisimov and his collaborators aimed to develop technologies that would reduce the need for cooling, which would make the cameras much more affordable to produce and therefore more abundant.
The researchers focused their efforts on focal plane arrays, which help receive heat signals from external objects. Smaller photovoltaic photodetectors used in such arrays have less thermal noise. In addition, they can be combined with light concentrating structures to collect photons from a wide area and focus it more efficiently on detectors. As a result, signal-to-noise ratio is improved in such photodetector arrays, allowing them to operate at elevated temperatures. Previous light related to focusing light on individual pixels has been mainly reduced to use of microlenses, microspheres, micro-cones, meta-lenses, nano-plasmonic arrays, and phonic crystals. All these designs possessed limitations related to angle of view, alignment issues, and complex fabrication.
The patented invention uses arrays of truncated silicon micro-pyramids – instead of flat surfaces- to concentrate light received by photodetectors. These arrays contain tens of thousands of pyramids and can be fabricated with extraordinary uniformity by anisotropic wet etching of silicon and monolithically or heterogeneously integrated with various photodetectors placed at the frustums of the truncated pyramids.
This approach creates a larger angle of view, solves alignment problems, and relies on simple, fast, and well-established fabrication methods. It can also be realized in the top layer of silicon-on-insulator wafers, where photons are confined inside silicon pyramids. Trapping light inside these pyramids allows the light to “circle around” inside them, increasing the probability that it will be detected.
This invention helps detectors operate far more efficiently, without the need for external cooling or compact electrothermal cooling. The invention is applicable in detecting both “mid-wave” heat signatures emitted at temperatures of approximately 300 to 700 degrees Celsius, as well as “long-wave” signatures created by the human body, engines, and other pieces of machinery. Although more trial-and-error research is necessary to further optimize the invention, this initial innovation has created a promising foundation indeed.
The invention will likely have important implications for the DAF. Drones, for example, are rapidly assuming extremely important roles in defense and warfare. Drones equipped with infrared sensors could help assess the presence of adversary personnel and materiel, thereby producing valuable intelligence.
However, the invention could also have wide applications across many other potential use cases. For example, infrared detectors can be used to locate missing people during search-and-rescue operations. People can use them to help locate lost pets. Mechanics could detect the presence of “hot spots” in car engines requiring attention. Emergency responders could pinpoint the locations of forest fires. In fact, if infrared detectors become inexpensive enough, they could be installed into every smartphone, infinitely multiplying the number of potential uses.
The inventors’ patent application was facilitated by their local Office of Research and Technology Applications (ORTA). DAF ORTAs conduct outreach related to technology transfer and facilitate the development of formal technology transfer agreements, including patent licensing agreements, to protect the DAF’s intellectual property interests as related to innovative technologies. The DAF Technology Transfer and Transition (T3) Program Office provides DAF ORTAs with training and guidance, and it also performs ORTA services for DAF laboratories lacking their own ORTA.
United States Patent and Trademark Office Patent #12,672,366
About AFRL
The Air Force Research Laboratory, or AFRL, is the primary scientific research and development center for the Department of the Air Force. AFRL plays an integral role in leading the discovery, development, and integration of affordable warfighting technologies for our air, space, and cyberspace forces. With a workforce spanning across nine technology areas and 40 other operations across the globe, AFRL provides a diverse portfolio of science and technology ranging from fundamental to advanced research and technology development. For more information, visit afresearchlab.com.