[Laser] LASER diode embedded in tiny new atomic clock module

[bernieS]

Maybe when these get cheaper they could be used 
to synchronize free space LASER communications.

-ed


http://www.smartertechnology.com/c/a/Technology-For-Change/Smarter-Atomic-Clock-on-a-Chip-Debuts/

Smarter Atomic Clock on a Chip Debuts

R. Colin Johnson | Date: 05-11-11 |

Atomic clocks keep the world's processes on 
track­providing 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.

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.