Chip Scale Atomic Clock (CSAC)

The basic physics of atomic clocks have been fairly well understood for some time, along with the macro-engineering challenges in creating a clock with frequency stability of one part in 10 billion (~1X10-¹¹) - equivalent to gaining or losing just one second every 300 years.

Taking advantage of the latest Micro Electro Mechanical Systems (MEMS) chip fabrication technology, it is now possible to produce an atomic clock with a volume of less than 0.1 cm³ and consumes only a few tens of milliwatts of power, enabling the clock to be operated on batteries, for military and civilian applications.

Applications range from friend-or-foe determination to commercial spread-spectrum communication and radar enhancements to secure UHF communication.

Like any clock, an atomic clock is designed to make the same event happen over and over. The repetition of this event produces a frequency, which is intended to be as stable as possible. The time-related quantity called frequency, basically the rate at which a clock runs, is the basis for a myriad of electronic systems that require the highest level of accuracy such as the Defense Department's GPS, radio observations of distant objects in the universe, event counters and power regulation.

To attain this kind of ultra-stability in an atomic clock of this size the injection current of a laser is modulated with a local RF oscillator, creating optical sidebands spaced by twice the modulation frequency. The light is directed through rubidium vapor and when the frequency difference between the two sidebands exactly equals the atomic ground-state hyperfine splitting of a rubidium atom, the absorption through the rubidium vapor decreases. This is known as "dark-line resonance" or "coherent population trapping" and is characterized by a very narrow transmission peak. The change in optical absorption of the cell is used to lock the modulation frequency of the local oscillator to the atomic transition.

A pioneer in MEMS design and production, Honeywell makes its advanced MEMS expertise and facilities available to customers who need any of a wide range of MEMS capabilities, from single process steps to complete turnkey design and volume production. Complex, precise MEMS product development requires more than a clean room, processing equipment and skilled operators. Over the past 10 years, Honeywell has established a portfolio of design expertise specializing in complex sensing and actuating devices.