Nikkei Electronics Asia -- September 2009
Features
NEC, NICT Develop T-Wave Camera with High Sensitivity

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Sept 7, 2009 00:00 Tetsuo Nozawa

NEC Corp of Japan and the National Institute of Information & Communications Technology (NICT) of Japan have jointly developed a portable camera with high sensitivity to terahertz (T-wave) electromagnetic radiation. The longest part of the case is only 18cm, for portability. It requires no special cooling in operation, and can shoot a fast 60 frames/s (fps) at Quarter Video Graphics Array (QVGA) resolution (320 x 240 pixels). Prior T-wave cameras had complex optics, pushing case dimensions into the meter-range, and requiring several seconds per shot. 

NEC hopes to commercialize the product in the near future, making it likely that T-waves will finally enter practical use. A source at the firm also commented that it would be fairly simple to increase resolution to VGA (640 x 480 pixels). NICT has already developed the quantum cascade laser used as the radiation source for the T-waves.

T-waves are electromagnetic waves with a frequency of about 1THz, placing them in the region between sub-millimeter waves (radio) and deep infrared radiation, which is generally classified as a type of light (Fig 1). As steady progress is made in the application of radio, light and similar radiation, the utilization of THz radiation has been lagging. Reasons for this include the fact that the frequency was believed to be too high from the viewpoint of electronics technology, such as semiconductors; while engineers experienced in handling light, infrared, etc, have had difficulty developing emitters, receptors, transmission methods, etc, for the waveband. Research and development into T-waves is active, however, because if they can be utilized they would have potential in ultra-high-speed (such as 100Gbps) wireless communication, not to mention new applications unique to the THz waveband.

Infrared Camera Modified

NEC and NICT approached the problem from the light waveband. In the fall of 2006, NEC noticed that its infrared camera was sensitive to T-waves at about 3THz. Sensitivity as a camera, however, was quite low, and commercialization would have been difficult.

NEC engineers modified the lens and imaging device (Fig 2) in response. Normally lenses are made with monocrystalline germanium, but this was replaced by a thinfilm of high-purity silicon and parylene. According to Naoki Oda, executive expert, Guidance & Electro-Optics Division of NEC, this approach boosted T-wave transmissivity from about 30% to 95%. The design of the imaging device was not changed, but the imager face was coated with a metallic thinfilm that improved sensitivity to T-waves by six to ten times.