Wednesday, May 11, 2011

#CHIPS: "Smarter Atomic Clock on a Chip Debuts"

Atomic clocks keep the world's processes on track—providing a universal time base with which everything from satellite communications to demolition explosions are synchronized. Now chip-scale atomic clocks are small enough to install inside mobile devices.

Symmetricom atomic clock on a chip based on Sandia National Laboratories technology (Source: Symmetricom)

Today accurate atomic clock readings are most commonly obtained from global positioning system (GPS) signals, but a new atomic clock on a chip will work where GPS does not reach, such as indoors, in tunnels, underground, under the sea and in outer space.

Miners, for instance, must set many charges that need to be blown up in perfect synchronization, necessitating atomic clocks that can time simultaneous processes down to a millionth of a second. Deep sea operations likewise often need precise time keepers to synchronize operations with the ships above them. Also military applications often require super precise timing, such as when clearing mines. This operation cannot depend on GPS signals that are often being blocked by electromagnetic jamming.

Telecommunication applications could also benefit from having integrated atomic clocks, for instance, to synchronize data streams when packets traverse different routes. And relay stations for cross-country telephone and Internet connections could use atomic clocks to reassemble packets into the correct order even during GPS outages.
A new atomic clock on a chip offers a solution for these applications.

Atomic clocks today are bigger than a breadbox and require a car battery to power them in the field, but Sandia National Labs, Draper Laboratory and Symmetricom have been working for almost a decade to reduce them to a chip-scale package running off two AA batteries.
The matchbook-sized atomic clock is 100 times smaller than previous commercial models, measuring only 1.5 inches square and half an inch thick, and consuming just 100 milliwatts, compared with 10 watts for conventional atomic clocks.

The secret to the new atomic clock on a chip is a solid-state laser illuminating a tiny container holding normal non-radioactive cesium vapor. The laser interrogates the cesium gas, causing its atoms to vibrate at a precise frequency that can be sensed and used to keep the clock accurate within a millionth of a second per day.

The team achieved the atomic clock on a chip by integrating a vertical-cavity surface-emitting laser (VCSEL) next to the cesium container. This reduced the power needed to illuminate the cesium by a thousand times over the rubidium atomic vapor lamp used by conventional atomic clocks. A microwave generator splits the laser beam into two closely related frequencies, which cause the cesium atoms to "beat" at their difference. A photodiode monitors the light passing through the cesium gas, counting the beats until they add up to 4,596,315,885, which is equal to one second.
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