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.
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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.
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.