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Shining a light on radio waves

Lasers and tiny membrane help detect faint signals

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1:00pm, March 5, 2014
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A new device, no bigger than a grain of salt, captures feeble radio waves and transforms them into laser pulses. The gadget is compact and works at room temperature, making it considerably more attractive than the bulky, expensive, cryogenically cooled amplifiers used today.

The contraption, which Eugene Polzik of the University of Copenhagen and colleagues describe in the March 6 Nature, converts incoming radio waves to light. At the heart of the gadget is a square film of silicon nitride, just 500 micrometers on a side, coated with aluminum.  A laser bounces off one side of the membrane. Radio waves impinging on the opposite side cause the membrane to vibrate like a drum. The vibrations change the brightness of the reflected laser beam, which a detector captures.

Fields as diverse as radio astronomy, medical imaging and navigation depend on detecting and transmitting weak radio waves.  Currently, faint signals get a boost by costly amplifiers cooled to a couple hundred degrees below zero Celsius and then travel along leaky copper wires to computers. Membrane-coupled lasers can bypass the amplifiers and replace antiquated wiring with fiber optics, dramatically reducing losses. 

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