Patent ID: 6556509
Filing Date: 2003-04-29
Classification: G01B

Abstract:
An apparatus for determining the phase of a phase shifting interference signal between a phase modulated sensor signal and a sinusoidal feedback signal including:means for sampling successive cycles of phase shifting interference signals; an odd modulation component amplitude generator operatively connected to receive some of the samples of the phase shifting interference signals centered on each successive sampling cycle, and to produce therefrom odd modulation amplitude signals; an even modulation component amplitude generator operatively connected to receive some of the samples of the phase shifting interference signals of each sampling cycle and at least one phase shifting interference signal from the next sampling cycle, and to produce therefrom even modulation amplitude signals for times centered with the samples of the phase shifting interference signals used to produce the odd modulation amplitude signals; an octant generator operatively connected to receive the magnitudes of the even and odd modulation amplitude signals and from the magnitudes of the even and odd modulation amplitude signals and the difference between the magnitudes of the even and odd modulation amplitude signals produce octant signals which represent the octant of a phase vector having the even modulation amplitude signal as a first orthogonal ordinate and the odd modulation amplitude signal as a second orthogonal ordinate; means to produce the sinusoidal feedback signal from the octant signals and the successive phase shifting interference signals, for feeding back to an interferometer producing the phase shifting interference signal to stabilize the modulation depth and the phase of the modulation of the interferometer; and an inverse tangent generator connected to the octant signals and the magnitudes of the even and odd modulation amplitude signals to produce therefrom output phase signals representing the phase of the phase modulated sensor signal.