DEPARTMENT OF THE NAVY WASHINGTON D C
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The patent application concerns an improved system and technique for detecting and stabilizing long term thermal and mechanical drifts in a swept Fabry-Perot interferometer. Under the control of a timing circuit the distance between two interferometer optical surfaces is changed by periodically sweeping a first surface while the second surface is rocked in a positive and negative direction about two orthogonal axes. The light transmitted by the interferometer is detected to provide a train of uniform pulses of random spacing having a maximum count when the surfaces are substantially parallel. A counter circuit senses the number of pulses during rocking in both the positive and negative direction about each axis and provides each count to a summing circuit for providing a difference output. The difference output for each axis is applied to individual long time constant integrating circuits to provide correction voltages for repositioning the second surface about both orthogonal axes so that both surfaces remain substantially parallel in spite of thermal and mechanical deviations over long time periods.
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