An optical system for measuring distance and for range-finding is provided. This single beam system uses a polarization selector and a retardation plate to take advantage of the polarization properties of light from a transmit source and of light reflected to a receiver. Another embodiment of the system uses the properties of certain types of transmit sources to further reduce the dimensions of the system. Methods for using the system are also provided.

The invention relates to an optical measurement device designed notably to evaluate the velocity of an aircraft by detection of a Doppler shift. The device for measurement by optical probe comprises at least two light beams of different wavelengths .lamda.1 , .lamda.2, denoted as first beam and second beam, the device illuminating a reference medium MILREF (60) by the first beam and receiving a light echo Sr reflected back by the reference medium, and the device comprising: an optical coupler COUPL (70) receiving, on the one hand, the light echo Sr reflected back by the reference medium MILREF and, on the other, the second beam, the coupler delivering a resultant wave Or comprising the second beam and the light echo Sr; an optical amplification unit AMPLI (80), of bandwidth B.sub.opt, receiving the resultant wave Or and delivering an amplified resultant wave Ora.

A method and apparatus for finding a relative direction to, a radial speed of, and a distance to a target is described. A laser source illuminates the target and the Doppler shifted return beam is incident upon a window system at an angle and is transmitted therethrough. The magnitude of the transmitted Doppler shifted beam decreases due to Fresnel transmittance. Opposing photomixers then detect this transmitted Doppler shifted beam, thereby creating a pair of detection signals that are mixed with a local oscillator signal. The mixing process creates Doppler frequency signals that are subsequently processed to determine the radial speed of the target. Due to the Doppler frequency component of the signals, objects in the same direction, but moving at different radial speeds, can be discriminated, as the relative direction processing occurs after the Doppler processing.

The present invention provides a vibration measurement method and apparatus capable of accurately measuring displacement even if the displacement is very small. The vibration measurement method according to the present invention comprises: a laser beam application step (step S1) for applying a laser beam of a first wavelength to an object to be measured; a beat wave generation step (step S2) for mixing a laser beam of a second wavelength which is different from the first wavelength and the return beam reflected from the object to be measured; and a vibration information output step (step S3) for outputting the beat wave thus generated as a vibration information of the object to be measured.

A method and apparatus for finding a relative direction to, a radial speed of, and a distance to a target is described. A laser source illuminates the target and the Doppler shifted return beam is incident upon a window system at an angle and is transmitted therethrough. The magnitude of the transmitted Doppler shifted beam decreases due to Fresnel transmittance. Opposing photomixers then detect this transmitted Doppler shifted beam, thereby creating a pair of detection signals that are mixed with a local oscillator signal. The mixing process creates Doppler frequency signals that are subsequently processed to determine the radial speed of the target. Due to the Doppler frequency component of the signals, objects in the same direction, but moving at different radial speeds, can be discriminated, as the relative direction processing occurs after the Doppler processing.