公开(公告)号：US06597458B2

公开(公告)日：2003-07-22

申请号：US09775945

申请日：2001-02-02

申请人： Tristan J. Tayag ,  Christopher A. Belk

发明人： Tristan J. Tayag ,  Christopher A. Belk

IPC分类号： G01B902

CPC分类号： G01B9/02084 ,  G01B9/02067

摘要： A method and system for stabilizing and demodulating an interferometer at quadrature are described. In response to receipt of a signal indicative of optical power of the interferometer, an interferometer control system determines an optical path length correction required to stabilize the interferometer at quadrature utilizing signal amplitudes appearing at multiple harmonics of the signal. In a particularly preferred embodiment, the signal amplitudes are calculated utilizing the Goertzel algorithm, a computationally efficient discrete Fourier transform. The interferometer control system then outputs an error signal indicative of the optical path length correction. In a preferred embodiment, the error signal forms the DC component of a composite stabilization signal, whose AC component is the reference modulation signal utilized to excite a transducer to modulate the optical path length of the interferometer. With the interferometer stabilized at quadrature, the interferometer control system determines a first signal amplitude of a particular harmonic without target oscillation and a second signal amplitude of the same harmonic with target oscillation. Based upon the relative magnitudes of the first and second signal amplitudes, the interferometer control system determines a solution set for the displacement amplitude of the interferometer target. Any ambiguity in the displacement amplitude can then be eliminated utilizing additional information gained from the signal amplitude present at a harmonic of a target oscillation frequency.