Abstract: A system for generating a spatially stable, small diameter light beam (18) which serves as a straight reference line over long distances may use the direction of propagation of light and one fixed point (11, 12) or may be between two fixed points (12, 21). In either instance, a light source (1) emits a beam (2) which is expanded, collimated and spatially filtered (3, 4). In the first instance, the collimated light wave (11) produced is diffracted by a sphere (12) to produce the small diameter light beam (18) which is constituted by a continuum of spots (16) which, in turn, produces a Poisson's spot (16) on a detector (21) which spatially samples the intensity of the spot (16). The resultant voltage (22) from each active detection are sent to a center locating electronics/computer (24) which processes the voltages (22) to give the position of the detector (21) relative to the straight reference line (18).

Abstract: An apparatus and method for controlling the length of a multioscillator cavity. A photodiode mixes a pair of beams rotating in the same direction, one of said beams being substantially left circularly polarized, and the other beam being substantially right circularly polarized. A local oscillator causes the mixed beams to be modulated. An amplitude demodulator demodulates the modulated beams. An error detecting device responds to the amplitude demodulators, and an active integrator integrates the detected error. A piezotransducer responds to the output of the integrator for controlling the length of the multioscillator cavity.

Abstract: A wavefront correction system is provided which uses an achromatic null lens to correct various aberrations introduced in a spherical wavefront when the wavefront is reflected off a non-spherical surface, particularly a parabola. Chromatic aberration, including spherochromatism, is corrected over a relatively wide bandwidth. When used in conjunction with an interferometer and a variable wavelength source, the wavefront correction system provides adequate means for determining relative position errors of the segments of a segmented mirror. The derivative of the phase error is obtained with wavelength by measuring interference for different wavelengths of light. This allows position errors of greater than one half wavelength to be accurately measured.

Abstract: A photoelectric measuring system measures relative movements between a diffraction grid and a substrate. An integrated semiconductor laser is formed on the substrate and emits radiation that is conducted via an optical waveguide and a focusing grating coupler onto the diffraction grid. The diffraction grid diffracts the incident radiation and directs it back onto the substrate. Diffracted component beams are received by waveguide horns having waveguide corrugation coupling gratings and are conducted via optical waveguides to a coupler, where the component beams are brought into interference to form a combined beam. This combined beam is transmitted from the coupler via optical waveguides to detectors which transform the combined beams into electrical signals that are displaced in phase with respect to one another. The electrical signals generated by the detectors can be processed in an evaluating circuit which may also be formed as an integrated circuit on the substrate, and then displayed.

Abstract: A method for endpoint detection in a semiconductor wafer etching system characterized by the steps of: (1) scanning a semiconductor wafer with a narrowly focussed laser beam; (2) analyzing a reflected portion of the beam to determine a preferred parking spot on a preferred flat area of the wafer; (3) parking the beam at the preferred spot; and (4) analyzing the reflected portion of the beam to determine when the preferred flat area has been etched through. The beam spot of the laser beam is smaller than the width of the preferred flat area to eliminate noise generated at the transition boundaries of the flat area. Preferably, the wafer is scanned several times along the same beam path to permit the comparison of several scans to determine the preferred parking spot.

Abstract: A lateral-shearing electro-optic field sensor in which a lateral-shearing terferometer is used in conjunction with an electro-optic crystal and a coherent light source to measure the waveform of an electro-magnetic pulse or a microwave pulse in free space. Depending on the size of the electro-optic crystal used, the device is adapted to measure frequencies as high as 20 GHz.

Abstract: A system for detecting abnormal patterns in a surface pattern on the surface of a sample wherein, when the abnormal pattern has a portion smaller than the surface pattern, the light for illuminating the sample is stopped down to an opening so that the abnormal pattern can be distinguished over the surface pattern, the surface pattern is limited to a predetermined opening by the illumination light to form an image on a detector, and the surface pattern detected by the detector is processed to detect the abnormal pattern in the surface pattern. Further, the plurality of light rays having good directivity are illuminated onto a point on the surface of the sample from dissimilar directions maintaining a predetermined angle of incidence, the detect signals are separated to be corresponded to said light rays, and the above processing is carried out to enhance the precision of detection.

Abstract: A device and method for modulating light intensity in response to a varying electrical signal which is particularly useful with optical fiber information sensing systems. The device includes a number of components positioned in seriatim in an elongated cavity in an insulating body. Means for receiving a light signal, such as from an optical fiber, is positioned at one end of the cavity. A lens receives the light and collimates it into a narrow collimated beam directed through the cavity. The beam is polarized, retarded by a wave plate to circular polarization and passed through a modulator material which is capable of rotating beam polarization in response to varying voltage signals imposed on the modulator through electrodes thereon. A mirror at the end of the modulator reflects the beam back through the system.

Abstract: Methods and apparatus for enhancing the accuracy of laser optical measuring instruments using fringe pattern spacing are disclosed. The apparatus in one embodiment includes a laser beam source 10, a beam splitter 14, and mirrors 22 to deflect the beams 18, 20 emitted from the beam splitter 14 to a sensing volume. Alternative embodiments include prisms 42, 44, gratings 62 or other optical devices in lieu of mirrors 22. Objects passing through the sensing volume scatter light which is detected by the instrument to determine, among other things, the velocity of the object. The emitted beams 18, 20 are automatically deflected in response to wavelength changes of the laser beam 16 such that variations in the fringe spacing, due to variations in laser beam 16 wavelength, are compensated by variations in the closing angle K of the emitted, deflected beams. The fringe pattern spacing is thereby held more nearly constant enhancing the accuracy of the instrument.

Abstract: A method and apparatus are disclosed for closed-loop phase modulation to measure rate and control phase modulator gain errors in an electrical signal representing the phase difference between first and second light signals from light waves counterpropagating in an interferometric rotation sensor including a closed light path with a phase modulator in the path. The disclosed method and apparatus correct phase modulator gain in a way that is independent of rate.

Abstract: Apparatus (10) and methods for measuring dark and bright reflectances of translucent sheet material (2) are disclosed. The apparatus (10) comprises first optical means for illuminating one side of the sheet material (2) with a source of electromagnetic radiation. A portion of the radiation is transmitted through the sheet material (2) and another portion of the radiation is reflected by the sheet material. The apparatus (10) also comprises optical gating means (30) that is positioned adjacent the other side of the sheet material (2) in a fixed position relative to the first optical means. The optical gating means (30) absorbs substantially all of the transmitted portion of the radiation when switched to a dark state and reflects substantially all of the transmitted portion of the radiation back through the sheet material (2) when switched to a bright state.

Abstract: An optical-fiber gyroscope of the Sagnac type consists of a fiber-optic loop and a 3.times.3 coupler, composed of three optically coupled fiber-optic guides, whereby a first fiber-optic guide of the 3.times.3 coupler is coupled to an optical radiation source and the two other fiber-optic guides of the 3.times.3 coupler are coupled on one end to one end of the fiber-optic loop and, on the other end, to a radiation detecting instrument. The first fiber-optic guide of the 3.times.3 coupler features a radiation detecting instrument on the end opposite the radiation source, with which interference-related variations in the light source, as well as in the 3.times.3 coupler, can be detected.

Abstract: An optical fiber rotation sensor includes a source of coherent light and a first polarizing beam splitter for transmitting a first component of the coherent light having a first polarization direction and reflecting a second component of the coherent light having a second polarization direction orthogonal to the first polarization direction. A coiled multimode optical fiber is coupled to the first beam splitter with the first and second components propagating in the fiber in opposite directions. A polarizer transmits a linearly polarized third component containing equal contributions from the first and second components. A half-wave plate rotates the polarization of the third component by 45.degree.. A self-pumped phase conjugating element reflects a phase-conjugated fourth component such that the fourth component retraverses the half-wave plate and the polarizer, then is divided by the first polarizing beam splitter into fifth and sixth components propagating in the fiber in opposite directions.

Abstract: Devices and methods for use in integrated optics waveguide circuits containing Y-junctions are presented for intercepting and either absorbing or otherwise removing radiation which has leaked into the substrate in order that such leaked radiation cannot re-enter the waveguide circuit and cause signal errors.

Abstract: A phase conjugate interferometer has a partially reflective conventional mirror placed in front of and in close proximity to a phase conjugate mirror using internally self pumped phase conjugation in barium titanate or other photorefractive material. The reflective surface may be the surface of the phase conjugate mirror. An optical system under test is illuminated with coherent light and the wavefront at the exit pupil thereof is imaged through a beam splitter onto the reflective surface (imaging being unnecessary if the distance between the exit pupil and the reflective surface is sufficiently small that negligible diffraction occurs over that distance). Part of the wavefront is reflected at the reflective surface of the partially reflecting conventional mirror. The transmitted portion of the wavefront is incident on the phase conjugate mirror where a wavefront reversed replica of the incident wave is produced and reflected.

Abstract: The invention relates to an interferometric displacement measuring device in which the reference norm is a diffraction grid (G). Diffracted partial beam bundles (+m, -m) are fed into a coupler (TBJ) by means of coupling grids (+HG, -HG) via beam waveguides (+LWL, -LWL) and there brought into interference. The interfering partial beam bundles are transmitted from the outputs (+A, A, -A) via beam waveguides (+LWL, LWL, -LWL) to detectors (+D, D, -D) which convert them into electric signals out-of-phase with each other. The displacement of the diffraction grid (G) is a standard for measuring the changes in position of machine components which are movable relative to one another.

Abstract: An apparatus for minimizing polarization-induced signal fading in an interferometric fiber-optic sensor is disclosed. The apparatus includes an optical source for providing an input light beam, a polarization modulator for modulating the state of polarization of the input light beam into at least three states represented by mutually perpendicular polarization vectors on a Poincare Sphere. The apparatus further includes means for conveying the input light beam with the at least three mutually perpendicular modulated states of polarization to the fiber-optic sensor, the interferometric fiber-optic sensor being responsive to the input light beam with modulated polarization states for developing an interference pattern output, wherein the interference pattern output has at least three visibilities corresponding to the input states of polarization.

Abstract: A measuring method and device are provided based on the analysis of a channelled light spectrum, particularly for measuring a low amplitude movement of a mobile surface, possibly representative of the variation of a physical magnitude convertible into such a movement.

Abstract: A proximity gap measuring system usable in a proximity mask aligner. The measuring system includes an illumination optical system for illuminating a mask and a wafer with white light, and an optical system, including a Wollaston prism, for dividing a wavefront of each of the light beams reflected from the mask and the wafer and causing relative inclination between the divided wavefronts to form a white light fringe on the Wollaston prism. Between the Wollaston prism and the mask or wafer, there is an anamorphic imaging system for forming an image of each of the mask and wafer on the Wollaston prism.

Abstract: An optical instrument has a low powered light point source mounted on a tube for orienting light point source along a predetermined viewing axis for one eye of an observer. An optical void surrounds the point light source, including the tube. The light point source is coherent and/or collimated so as to be substantially free of autokinesis effects. The tube is mounted on orientable support structure for the predetermined viewing axis for one eye of an observer whereby when said observer is viewing a scene through his other eye an optically fused image is presented to the observer with said predetermined viewing axis including the point in said scene wherein said point source appears.