17 Jan 2013

Dual-mode imaging could aid search-and-rescue missions

US-based researchers at the Northwestern University’s Center for Quantum Devices have now found a way to integrate active and passive infrared imaging capability into a single chip.

This paves the way to lighter and 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.

Existing cameras usually fall into one of two types; first is active cameras, which use an invisible infrared source to illuminate the scene, usually in the near or short-wavelength infrared.

And second, passive cameras, detect the thermal radiation given off by a warm object, typically in the mid- or long-wavelength infrared, without the need for any illumination.

Integrating both modes of imaging into a single camera has proven challenging as dual-mode active and passive infrared cameras have needed either two different infrared detectors or complex controllable filters to accommodate the different wavelengths.

The cameras have then required additional signal processing to reconstruct a single image from the two modes.

However, the Professor Manijeh Razeghi and colleagues have now built an imager that can simply switch from passive to active mode by 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 new structure incorporating two different superlattices with different layer spacings.

This enables detection with a cutoff wavelength of either 2.2µm (active mode) or 4.5µm (passive mode).

The researchers hope their new device will replace aging mercury-cadmium-telluride (HgCdTe) infrared camera technology in terms of both performance and cost.

  • A paper about the findings, “Active and Passive Infrared Imager Based on Short-Wave and Mid-Wave Type-II Superlattice Dual-Band Detectors,” was published January 1 in the journal Optic Letters.

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