The Boeing Company

John A McGarvey

Peter J De Groot

Ronald L Hagman

Raymond G Beausoleil

Barbara A Capron

John A Bell

William D Sherman

Paul Frederic Sjoholm

Peter J deGroot

W Randall Babbitt

The invention performs coordinate measurement employing multiple-frequency intensity-modulated laser radar. A laser diode source is intensity modulated by variation of its excitation current. Its output beam is directed to a target using scanning mirrors or other opto-mechanical means, and the light returned from the target is detected. The modulation frequency is alternated between two or more values, creating a dataset of several relative phase measurements that uniquely determine the distance to the target without ambiguity. A device for carrying out such a method includes a laser whose output is modulated by a high frequency signal generator, optics for directing the output signal to the target to a detector, a signal generator which generates reference signals offset in frequency from the intensity modulation frequencies by a predetermined amount; mixers for combining the return signals with the reference signals to form a first set of intermediate frequency signals, and for combining the modulation signals with the reference signals to form a second set of intermediate frequency signals, and a computer which calculates phase differences between the output beam and the return signals for each modulation frequency from the intermediate frequencies, and determines the distance to the target from the phase differences.

Method and apparatus for measuring distance to a target

The frequency separation between two light signals, one having a first and the other having a second frequency, is determined by first forming three light beams, each including both frequencies; directing the three beams through an interferometer in which they traverse three optical paths having three different known optical path lengths; determining the interferometric phases for each of the three optical paths at both frequencies; and determining the difference between the first and second frequencies from the interferometric phases and known optical path lengths. The light signals may be light from two lasers operating at different frequencies. The optical path lengths can be predetermined by calibration using two light sources of know frequencies. An apparatus for carrying out this method is also disclosed.

Method and apparatus for use in measuring frequency difference between

An interferometer with a dual laser source having a tunable frequency separation between the laser emissions is used to measure absolute distance to weakly-reflecting targets. A dual-laser source is commonly characterized by a synthetic wavelength, which is equal to the speed of light divided by the frequency separation with time over a total frequency range that is small compared to the average frequency separation. Simultaneously, a high-speed phase modulator generates a signal whose amplitude is proportional to the interferometric fringe visibility, and data acquisition means are used to record the fringe visibility as a function of time during the synthetic wavelength chirp. Signal processing means are then used to extract the frequency and phase of the resultant quasi-periodic fringe-visibility curve. The optical path is then determined to high accuracy without the phase ambiguity problems of prior-art synthetic-wavelength techniques. An optical fiber implementation of a preferred embodiment of the invention operates over a 0.1 to 10 inch range, using a 0.01-inch diameter 100 .mu.W laser beam, with an absolute error of less than 0.001 inch (25 .mu.m). The invention can be used for dimensional gauging, surface profiling and position measurement, and will improve productivity and quality control in manufacturing.

Chirped synthetic wavelength laser radar

A system for tuning a narrow-linewidth semiconductor laser such that the laser produces a laser beam at its output port having a desired frequency. The system includes an optical resonator and an optical system for coupling a portion of the laser beam into the resonator along a feedback optical path. The resonator may comprise a pair of faces, an electro-optic material between the faces, and an electrode for generating an electric field in the electro-optic material in response to a control voltage. The laser beam portion that enters the resonator causes the resonator to produce a feedback beam that is coupled into the input port of the laser, to provide optical feedback that causes the laser to lock to a resonance of the optical resonator. Tuning is accomplished by varying the resonance by applying a voltage to the electrode. The optical feedback also reduces the laser's linewidth. In another embodiment, a fiber-optic cable ring resonator is used to produce the feedback beam.

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Bellevue, WA, United States of America

John A McGarvey