Chirped synthetic wavelength laser radar

US5371587A · kind A · utility

Assignee

• The Boeing Company · US

Inventors

• Peter De Groot · Middletown, US
• John A. McGarvey · Bellevue, US

Key dates

• Filing date: May 6, 1992
• Grant date: Dec 6, 1994
• Expiry date: May 6, 2012

Classification

• Technology area (CPC G): Physics
• CPC primary: G01B2290/60
• WIPO field: Measurement
• WIPO sector: Instruments

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…