Active and Passive Modes in One IR Camera
A new approach that integrates active and passive infrared (IR) imaging capability into a single chip has paved the way toward lighter, simpler dual-mode active/passive cameras with lower power dissipation.
High-performance infrared cameras are crucial for civilian and military applications such as night-vision goggles and search-and-rescue operations. The cameras usually fall into one of two types: active, which uses an invisible infrared source to illuminate the scene, usually in the near- or short-wavelength infrared, and passive, which detects the thermal radiation given off by a warm object — typically in the mid- or long-wavelength infrared — without the need for illumination.
A Center for Quantum Devices researcher holds a heater and a narrowband filter centered at 3.6 µm. The heater can be seen when imaged with the bandpass detectors sensitive up to 4.5 µm (left), but not in the ones with shorter detection wavelengths up to 2.2 µm (right). Courtesy of McCormick School of Engineering, Northwestern.
Integrating both modes of imaging into a single camera has proved challenging because dual-mode active and passive IR cameras have required either two different infrared detectors or complex controllable filters to accommodate wavelengths. The cameras would then require additional signal processing to reconstruct a single image from the two modes.
Now, however, Manijeh Razeghi and colleagues at Northwestern University’s Center for Quantum Devices have built an imager that can switch from passive to active mode with a very small change in bias. By engineering the quantum properties of novel semiconductor materials indium arsenide/gallium antimonide (InAs/GaSb) type-II superlattices, they have developed a structure incorporating two different superlattices with different layer spacings.
The new device — which the researchers hope will replace aging mercury cadmium telluride infrared camera technology in terms of both performance and cost — enables detection with a cutoff wavelength of either 2.2 µm (active mode) or 4.5 µm (passive mode).
The work, funded by DARPA, appeared in Optics Letters
For more information, visit: www.mccormick.northwestern.edu
For more on Razeghi’s work with IR cameras, see: Novel High-Res IR Camera Announced
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