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13 Dec 2002
A plastic lens with a high light-collecting efficiency could revolutionize infrared "point-and-pay" schemes.
Roger Green and Roberto Ramirez-Iniguez Warwick University, UK, have designed a polymer lens that they say could transform infrared "point and pay" schemes. Called the optical antenna, the lens has an acceptance angle in excess of 100 degrees and can filter out unwanted background light.
Prototype schemes that use an infrared remote control to carry out financial transactions such as paying at a motorway toll gate or buying a cup of coffee from a vending machine, are currently in trials in the Far East but prone to problems with beam alignment and detector sensitivity.
The Warwick duo says the optical antenna gets its enhanced performance from a shape based on complex mathematical curves and an integrated thin-film wavelength filter. The shape ensures that incoming off-axis light beams are directed onto the detector thanks to internal reflection.
At the base of the lens a narrow-band filter made from a multi-layer optical coating rejects all wavelengths outside the signal band. Green says that he got the idea for the lens shape from the optics used to maximise the collection efficiency of solar cells in the desert. He adds that the lens can be cheaply made using polymers and injection moulding, with the filter coating simply added afterwards.
The antenna is allegedly far superior to that used in existing short-distance infrared links used by televisions, mobile phones, PDAs and laptop computers. Green says that by tweaking the shape of the lens the performance of the antenna can be optimized to suit all kinds of specific communication applications, be it collecting a signal at a laptop computer, a road toll or any other kind of "point-and-pay" scheme.
"You can design the concentration [optical gain] to be anything from a factor of 80 down to a factor of 4 or 5 and the capture angle from 1 or 2 degrees up to +/- 50 degrees," he says.
"With an infrared link you're having to communicate in a bad environment, meaning that you've got room lighting, daylight and many sources of other wavelengths," explained Green. "If you put our antenna in front of your detector, alignment is much easier and it gives you the concentration power of a lens over a much wider range of angles. You could, for example, integrate it with a photodetector package, you've then got a very sensitive optical detector on a chip."
The technology has now being licensed to a UK start-up based in Nottingham. Optical Antenna Solutions (OAS), plans to market the technology and sub-license it to interested parties.
Author
Oliver Graydon is editor of Optics.org and Opto & Laser Europe magazine.
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