Analog+digital phase and frequency detector for phase locking of diode lasers

We describe a type of phase and frequency detector employing both an analog phase detector anda digital phase and frequency detector. The analog and digital detectors are mutually exclusive sothat only one of them is active at any given time, resulting in a phase detector with both the broadcapture range of digital circuits and the high speed and low noise of analog mixers. The detector hasbeen used for phase locking the diode lasers generating the sequence of Raman pulses in an atominterferometer. The rms phase error of the phase lock is about 100 mrad in a 5 Hz-10 MHzbandwidth. The limit set on the interferometer phase resolution by the residual phase noise is 1.1 mrad. Since the digital circuitry is implemented with a programmable logic device the detector canbe easily adapted to other experiments requiring frequency/phase stabilization of lasers sources.