Two-wavelength phase control system

摘要

In accordance with the present invention, output beams from a plurality of optical amplifiers in an oscillator-amplifier optical configuration are phase matched utilizing a feedback system employing phase error signals generated by optically heterodyning a frequency shifted, two-wavelength reference beam, with a portion of the output from each of the plurality of amplifiers. Electrical signals from detectors responsive to the optical heterodyned signals are processed in control circuits to provide coarse and fine phase error signals to control elements for controlling the optical path difference of the beams of radiation passing through each of the amplifiers for phase matching the beams. Coarse error signals having a synthetic wavelength with an extended phase range of many wavelengths are generated by dividing the electrical signal from the detectors, homodyning the divided signals from each detector to provide a beat signal, passing the beat signal through a low-pass band filter centered at the frequency difference of the frequency shifted reference beams and heterodyning the filtered beat signals from two detectors. Fine error signals are generated by passing the divided electrical signal from each detector through a band-pass filter centered at the frequency of one of the frequency shifted reference beams and heterodyning the filtered signal from each detector with the filtered signal from a standard detector. The synthetic wavelength of the coarse error signal enables the control system to drive the optical path difference of the output beams toward zero with minimal 2 pi N phase ambiguity.