An optical method and optical device for distance measurement, comprising the steps of emitting an incident light beam (13) comprising at least two waves of differing wavelengths (.lambda.1 and .lambda.2); separating this beam into a reference beam (15) and a measurement beam (17) which are reflected on, respectively, a reference reflector (16) and a zone (18) of a part (19), of which it is desired to measure the position in the direction of the measurement beam and recombine into a resultant beam (20), in which said waves exhibit conditions of polarization, the components of which rotate when the optical path of the aforementioned measurement beam varies and which determine, in the direction of the measurement beam, adjacent ranges at the ends of each one of which the angular positions of two corresponding components of these conditions of polarization are identical; determining, in the resultant beam (20), the angular positions (.alpha.1 and .alpha.2) of two corresponding components of said conditions of polarization of said waves; and computing, as a function of said angular positions, the distance separating the aforementioned zone of said part from a reference position, preferably the image of the reference reflector. Their application to the positioning of parts, especially of a chip inserted in a substrate.
A method and apparatus for distance measurement includes an optical interferometer, a two-color source characterized by a synthetic wavelength, and processing means for acquiring and analyzing phase information. The synthetic wavelength, which corresponds to the spatial period of phase coincidence in two-color interferometry, is commonly used in metrology to increase the unambiguous distance-measurement range. The invention provides a greatly enhanced unambiguous measurement range, for a given synthetic wavelength, over the unambiguous range of prior-art techniques. This extended range is achieved by analysis of a phase couple formed by a combination of the synthetic and optical phases. This phase couple repeats at spatial intervals which may be very much larger than the synthetic wavelength. Detailed computational methods for illumination source selection and for data analysis are provided, and several specific embodiments of the invention are described.
The apparatus and method for measuring a small spacing down to contact uses an interferometric fringe intensity calibration to calibrate maximum and minimum intensity of two or more monochromatic or quasi-monochromatic interference patterns caused by a spacing between two articles, one of which is transparent. The intensity calibration is done by measuring maximum and minimum fringe intensity of each color while altering the spacing by at least 1/4 of the wavelength of the light or other electromagnetic radiation being used. The calibration by changing spacing allows the fringe order to be calculated for each wavelength of the radiation being used. This calibration procedure allows the maximum and minimum intensity of the radiation to be known, as well as the fringe order of the interference patterns to be calculated. With the maximum and minimum intensities and the fringe orders known, the spacing is readily calculated from interferometric theory.
A distance-measuring system includes a light source for transmitting a beam of light to a target, thereby generating a received beam. A calibration unit periodically calibrates the system by positioning a calibration target between the light source and the target so that the transmitted beam is interrupted, thereby generating a received calibration beam. The calibration unit also generates a calibration signal which is indicative of when the calibration target is generating the received calibration beam. A target sensor receives the reflected target and calibration beams and provides a target signal indicative of the reflected target and calibration beams. A reference sensor receives light from the light source and provides a reference signal to the processing circuitry. Processing circuitry receives the calibration, target, and reference signals and calculates the distance to the target based upon the target and reference signals and/or calibrates the system based upon the calibration signal. The processing circuitry may provide data based upon the calibration and target signals to a computer for distance calculations and calibration. A beam splitter may be provided between the light source and the target to allow the transmitted beam to be incident on the target while deflecting the received beam to be incident on the target sensor, so that the light transmitted to the target and reflected back to the target sensor is substantially coaxial.
A slider is mounted to a rotary drive mechanism. The slider is loaded, i.e., moved toward and positioned near a disk surface, by rotary movement of the rotary drive mechanism in a first rotary direction. Similarly, the slider is unloaded, i.e., moved away from the disk surface, by rotary movement of the rotary drive mechanism in a second rotary direction which is the reverse direction of the first rotary direction.
