Optics: measuring and testing – By particle light scattering – With photocell detection
Patent
1991-08-19
1994-02-01
Turner, Samuel A.
Optics: measuring and testing
By particle light scattering
With photocell detection
356350, 25022727, G01B 902
Patent
active
052836258
ABSTRACT:
A phase modulation control apparatus is taught in combination with an interferometer excited by a coherent light source providing a light beam to the interferometer having first and second optical paths. The interferometer senses a physical quantity such as pressure. The interferometer is coupled to provide an optical signal containing information providing a measure of the physical quantity via first and second interfering beams to a detector. The detector provides a composite output signal. The invention phase modulation control apparatus has a modulation means responsive to a modulating frequency signal and a phase modulation control signal to provide a frequency modulating factor signal for frequency modulating at least a portion of the light beam to provide a phase modulation between the first and second interfering beams at a carrier frequency. The composite output signal has at least four harmonic signals referenced to the carrier frequency. A synchronous detection means responsive to the carrier frequency signal and to the composite output signal provides a pair of even harmonic filtered signals and a pair of odd harmonic filtered signals. A reference channel means and quadrature channel means each respond to the even and odd harmonic pairs of filtered signals and respectively provide first and second integrator input error signals which have null values in response to their respective harmonic pairs having a predetermined ratio. An integration means combines and integrates the first and second integrator input error signals to provide the phase modulation control signal to the modulation means.
REFERENCES:
patent: 4883358 (1989-11-01), Okada
Carpenter M. Michael
Cline Gerald L.
Kirk James F.
Litton Systems Inc.
Turner Samuel A.
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