THE BOEING COMPANY
Fiber optic Boeing 87Rb Compact Optical Atomic Clock
This is the 87Rb compact optical atomic clock developed at The Boeing Company. It was developed by myself, Scott Sullivan, and Fred Sharifi. The clock uses 780 nm light from a fiber laser to excite the Rb atoms.
The clock is based on a two-photon transition. The electron starts on the 5S1/2 state. The first photon transitions the electron to the 5P3/2 state (a virtual state). A second photon will transition the electron to a 5D5/2 state. Two photons of wavelength 780 nm are shown on 87Rb atoms. It will relax into two photons, the first of 5460 nm and a second of 420 nm.
The quality factor for this transition is ~109, while the quality factor for an oven-controlled crystal oscillator is. The larger the quality factor, the higher the accuracy of the clock.
Factors such as temperature and density of the 87Rb and background gas, electric and magnetic fields, and laser intensity will reduce the quality factor of the transition.
The 420 nm light is detected by a PMT, which is then used to maintain the input laser frequency centered on the excitation frequency. The output of the clock is then used as a standard frequency for a clock.
A Vascent optical comb is used to generate a 100 MHz signal with the stability of the laser frequency in the atomic clock.
The frequency comb converts the 780 nm light (385 THz) to 100 MHz. Although there is some error associated with the optical combs, the error that results from this conversion is on the order of 10-17, much smaller than the clock error of around 10-15.