Edwin L. Aguirre
Since night-vision devices were first introduced about 70 years ago at the beginning of World War II, the technology behind them has evolved by leaps and bounds. Advances in the field of optoelectronics now allow their users to see in virtual pitch-black darkness. These instruments are employed in a wide range of military and civilian applications -; from surveillance in law enforcement, counterterrorism and border patrol to search-and-rescue operations.
Electrical Engineering Assoc. Prof. Xuejun Lu and his team are developing a new generation of night-vision devices that offer not only high sensitivity but also smaller size and simpler, more economical manufacturing process. Physics Prof. William Goodhue, director of UMass Lowell's Photonics Center, supported their initial development efforts with material growths.
“Today’s night-vision devices generally operate in shortwave infrared [SWIR] wavelengths,” says Lu. “Our goal is to come up with high-performance photodetectors and imaging arrays that cover both the SWIR and longwave infrared [LWIR] in the one- to two-micron and seven- to 14-micron spectral bands, respectively.”
He says current LWIR imaging systems need to be cooled down to 320 degrees Fahrenheit, the temperature of liquid nitrogen. This requires a cryogenic system, which is heavy, bulky and requires a lot of power.
“Our sensor -; a thermoelectrically cooled quantum-dot infrared photodetector array -; can operate at higher temperatures,” explains Lu.
The sensor uses indium arsenide quantum dots in an indium arsenide/gallium arsenide substrate, and costs much less than the current mercury-cadmium telluride LWIR detectors. Furthermore, the sensor’s electronic circuitry is made of carbon nanotubes that can be printed directly on the sensor’s surface at room temperatures, without using any photolithography equipment.
“This simplifies the fabrication process and helps reduce the size, weight and power consumption of the imaging system,” he says. “Potential applications of this technology include handheld biochemical sensing and medical diagnostics.”
Lu says they also developed thermoelectrically cooled SWIR sensors working at the same wavelengths as night-vision goggles.
“Longwave IR can pass through the atmosphere, whereas shortwave IR cannot,” he says. “That is why longwave IR is used more in space and airborne systems for thermal remote sensing, target tracking, discrimination, space exploration and imaging.”
Lu and his team have been working on their project for more than six years and are making continuous improvements. Their next step is to apply for a research grant so they can build a prototype of the device for night-vision applications.