US 5,371,587 A · Chirped synthetic wavelength laser radar

Abstract

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.

Claims12

Dependent claims

An apparatus for generating continuous fringe contrast data comprising:

two lasers, wherein wavelengths of laser beams generated by said lasers are each separated from a central wavelength in an equal magnitude, but in opposite directions, whereby one of said wavelengths is larger and the other of said wavelengths is smaller than said central wavelength;
a beam combining device receiving said laser beams and outputting a combined beam;
means for directing said combined beam onto a target, wherein light scattered from said target interferes with a portion of said combined beam to form an interference beam;
means for modulating the phase of said interference beam;
means for linearly tuning both lasers in opposite directions around said central frequency over a tuning period;
and
a detection means for receiving said modulated interference beam and for outputting an interference signal proportional to fringe contrast over an acquisition period corresponding to the tuning period.

4 more elements

A method for measuring a distance to a target, comprising the steps of:

generating two laser beams at different wavelengths, wherein said wavelengths are each separated from a central wavelength in an equal magnitude, but in opposite directions, one of said wavelengths being smaller and one larger than said central wavelength;
combining said laser beam to form a combined beam;
splitting said combined beam into a reference beam and a target beam;
delivering said target beam to said target;
producing a target interference pattern between said target beam scattered by said target and a portion of said target beam;
detecting said target interference pattern;
producing a reference interference pattern from a reference interferometer using said reference beam;
detecting said reference interference pattern;
continuously tuning both laser beams in opposite directions around said central wavelength over a tuning period;
acquiring both interference patterns over an acquisition period corresponding to the tuning period;
and
processing said target interference patterns and said reference interference patterns to determine the distance from a predetermined point to said target.

9 more elements

Dependencies are inferred from the claim text.

Chirped synthetic wavelength laser radar

Life of this patent

Chirped synthetic wavelength laser radar

Life of this patent

Abstract

Claims12