Dual-band cameras aid IR system

Developed in the mid-1980s in several university and industry labs, quantum-well-infrared-photodetector (QWIP) technology arose from the need to simultaneously acquire synchronous pixel-registered images in both the mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) spectrum.

Jul 1st, 2007
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Andrew Wilson, Editor, andyw@pennwell.com

Developed in the mid-1980s in several university and industry labs, quantum-well-infrared-photodetector (QWIP) technology arose from the need to simultaneously acquire synchronous pixel-registered images in both the mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) spectrum. For several years, single-band QWIP IR cameras have been available in the consumer market.

The first dual-band IR camera was brought to the market in 2005. “Since dual-band technology permits the direct comparison of MWIR and LWIR images,” says Mónica López Sáenz, managing director of IRCAM (Erlangen, Germany; www.ircam.de), “precise characterizations of materials, smoke, gases, and temperatures can be made with a single camera.”

“Dual-band focal-plane arrays (FPAs) are capable of simultaneous thermal imaging in two spectral bands, for example, MWIR (3-5 µm) and LWIR (8-12 µm),” says López Sáenz. “Dual-band imaging systems allow accurate temperature measurements and the identification of reflections and background clutter by comparing the signal intensities in both bands.”


IRCAM dual-band IR camera imaged Freiburg, Germany, at daytime (top) and nighttime (bottom). MWIR and LWIR images are overlayed with complementary colors.
Click here to enlarge image

At the April 2007 SPIE Security & Defense Symposium (Orlando, FL, USA), IRCAM introduced a series of cameras based on QWIP technology. The detector used in these cameras is based on GaAs III-V QWIP technology originally developed at the Fraunhofer Institute for Applied Solid-State Physics IAF (Freiburg, Germany; www.iaf.fraunhofer.de). “After completion of front-side processing, the FPAs are diced into single chips and hybridized with the silicon readout integrated circuits (ROICs) using indium solder-bump technology,” says López Sáenz. The detector design, layer growth by molecular-beam epitaxy, and processing of FPAs is performed at the Fraunhofer Institute.

IRCAM has used this technology in the development of Geminis, its cooled 110k ML Pro QWIP-based camera that features a 384 × 288-pixel array and operates at frequencies of 4.4-5.5 µm (MWIR) and 7.8-8.8 µm (LWIR). With a Camera Link interface, the camera supports data rates up to 130 Mbytes/s and is targeted toward high-speed IR imaging applications.

These cameras are not new. Three years ago, QmagiQ (Nashua, NH, USA; www.qmagiq.com) showed a “dual-color” IR camera based on a 320 × 256 dual-color or dual-wavelength detector array (see Vision Systems Design, September 2004, p. 10). What is new about the IRCAM Geminis 110k ML Pro is the real-time image overlay of images of two spectral bands. Because the device can detect IR images in both the 4-5-μm MWIR and 8-9-μm LWIR spectral bands simultaneously, the device is useful in military applications that previously required two different IR detectors. Furthermore, in the overlay-mode, more information can be delivered within the 8-bit information than when using two single IR cameras.

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