Advanced Imaging

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Advanced Imaging Magazine

Updated: January 12th, 2011 10:01 AM CDT

Using the Earth's Atmosphere for High-Performance Night Vision

Germanium-enhanced CMOS sensor overcomes traditional obstacles of SWIR technology
Germanium vs. Silicon chart
© NoblePeak Vision
Standard CMOS cameras use silicon (yellow) as a sensor, which is adequate for daytime use. For night vision-only applications, InGaAs (red) is effective and very costly—used almost exclusively by the military. TriWave uses Germanium, (blue) which offers a broad spectral response to see day and night. Even on moonless (green) and cloudy (pink) nights, TriWave still receives ample light from night glow to provide quality night imaging.
These images show the night glow at work when compared to a low-light EMCCD camera.
© NoblePeak Vision
These images show the night glow at work when compared to a low-light EMCCD camera. The EMCCD picture on the left relies on ambient light from stars or illumination and, in this case, is benefiting from snow on the ground that provides a reflected light source of light to enhance picture quality. The image below is from a camera that can see into the SWIR band utilizing only the night glow. Because the night glow is uniform, there are significantly fewer shadows. Note the brightness of the sky in the image from the SWIR camera in contrast to the EMCCD camera image.
A technology comparison of EMCCD
A technology comparison of EMCCD, thermal, InGaAs and TriWave. Click here to view larger image.
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By Stephen Germino, NoblePeak Vision

They can be seen on buildings and toll booths, hidden within streetlight enclosures on traffic light poles and even on the Statue of Liberty. They are becoming a critical part of security on college campuses, commuter parking lots and in busy downtown districts. Security cameras are everywhere these days, and there are high expectations from law enforcement and homeland security agencies as well the private sector that these cameras provide quality images day and night. And while the daytime camera market is very mature and great images are easily obtained, the nighttime market still faces limitations. Light is the No. 1 obstacle. Without enough light, cameras just cannot reliably generate clear images.

Broader limitations for current night vision cameras include:

  • Expensive illumination installation and maintenance
  • Limited field of view (FOV) that illumination provides
  • Limited visibility (shadows)
  • Limited range/monitoring of large security perimeters
  • Inability to identify, only detect
  • Inability to read vehicle license plates and other markings
  • High cost

Imaging Using Night Glow

"Night Glow" is a naturally occurring light source that is emitted from the night sky. The source of light in question is created by the interaction of the earth's atmosphere with the solar winds. It starts with the solar winds agitating hydrogen and oxygen ions 90 km high in the earth's atmosphere, causing these ions to release their energy in the form of light. This naturally occurring but relatively unknown phenomenon results in a considerable amount of light or "night glow" that comes from the entire night sky. However, the light is emitted in the short wave infrared (SWIR) band with wavelengths of 1200 to 1800nm. Therefore this light is not visible to the human eye, which sees at wavelengths of 400 to 700nm. The SWIR light also is undetectable to the many millions of installed security cameras around the world. Typical CMOS or CCD image sensors cannot detect SWIR as they fade out at around 1000nm wavelengths.

Germanium-enhanced CMOS

A new and revolutionary single-chip CMOS TriWave™ image sensor technology solves the complexity and cost problems associated with prior SWIR sensing technology. Using this single chip technology enables security and surveillance video cameras to see in the harshest zero-light conditions surpassing the capabilities of even the most sensitive low-light cameras currently on the market.

The breakthrough is in the dramatically improved wavelength response of a standard CMOS image sensor when germanium is introduced to the CMOS process. Germanium is an element that is sensitive to SWIR and its longer wavelength sensitivities are due to its smaller band gap properties. Unlike the very expensive multi-chip complex semiconductor image sensors, this unique silicon-based process, produces hundreds of visible-to-SWIR imaging chips on a single CMOS wafer, manufactured with high uniformity, reliability and low cost. Additional advantages of the CMOS process are that it enables small pixel sizes that allow high-resolution imagers, smaller optics and condensed camera size, weight and cost.

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