Abstract: An optical fiber interferometric system includes a pair of single-mode, polarization-preserving fibers having distal and proximal ends. The cladding of a selected portion of one of the fibers having been removed to allow an evanescent portion of a light wave traveling within the fiber to interact with any medium surrounding the selected portion of the fiber. A light source for producing a light of known character is coupled to the proximal ends of the pair of optical fibers for introducing a source signal to the pair of fibers. A reflector at the distal ends of the optical fibers reflects the light from the distal ends back toward the light source. The return signals are used to construct an interferogram which is observed to detect any modulation in the phase of the light signals. The modulation is examined ratiometrically to derive a change in the index of refraction of the medium surrounding the selected portion substantially free of any environmentally induced phase noise.

Abstract: For measuring an angle of incidence of a luminous beam, one employs a polarized luminous beam which is brought to pass though a birefringent plate followed by an analyzing polarizer, in order to obtain succession of fringes of interference, and one analyzes by means of an appropriate detector and an electronic circuit the spacings between the crests of said fringes, said spacings being a direct function of the angle to be measured. One can utilize a measuring device of an angle of incidence for measuring the distance between said device and a reflecting surface of the object to be measured, by determining for a certain position of the object a spacing of reference between the crests of the fringes of interference and by measuring the variations of the spacings as a function of the position of the object, in order to display them in units of length.

Abstract: A fiber optic measuring device can be used, for example, as a rate gyro. Variation in a measured parameters engenders a phase difference between two waves. The measuring device includes a light source 1, a SAGNAC ring interferometer 2, a detector 3, a phase modulator 4, and a electronic unit 7. The electronic unit 7 includes a processing system 9 which furnishes a signal that is a function of the measured parameter and an electronic sub-unit 12 for controlling the phase modulator 4. The control signal for the modulator is a superposition of a first, periodic gating, bias signal .PHI..sub.b (t) with period 2.tau. and amplitude .PHI..sub.bm, and of a second, staircase, negative-feedback signal .PHI..sub.m (t) synchronized with .PHI..sub.b (t), each step of which has a duration equal to .tau. or to one of its sub-multiples, and an amplitude .PHI..sub.s, which is a function of the value of the measured parameter and which falls back to zero when its amplitude exceeds a predetermined value .PHI..sub.mm . .PHI..

Abstract: Apparatus and methods for reducing and preventing polarization fading in unbalanced measuring interferometers. An extended interferometer having a plurality of sensors and a compensating interferometer are used. They are driven from a pulsed optical signal source wherein the optical signal comprises sequences of two pulses each. To prevent polarization fading the polarization of a predetermined one of each two-pulse sequence is switched, preferably orthogonally, from sequence to sequence. Interference pulse output groups are produced for each two-pulse driving sequence. Each output group has the same number of usable pulses as the number of sensors in the interferometer.

Abstract: An optical heterodyne interference type detecting apparatus for measuring a displacement characteristic of a workpiece, including a device for applying a controlled physical quantity to the workpiece to induce a displacement of the workpiece, an optical heterodyne interference type displacement detecting device for detecting a difference in one of a frequency and a phase between a measuring light beam reflected by the portion of the workpiece and a reference light beam, and thereby detecting an amount of the displacement of the workpiece, and an arithmetic and control device for obtaining the displacement characteristic of the workpiece, based on the physical quantity and the amount of displacement detected by the displacement detecting device.

Abstract: A fast and effective way to step a relative position quantity by a reference interval. Each step in relative position includes open-loop and closed-loop control intervals. The invention contemplates an actuator capable of changing the relative position and a closed loop servo that acts on the actuator to keep the relative position centered on the nearest one of a series of reference values separated by the reference interval. The actuator is preferably capable of a fast response. Stepping the relative position is accomplished as follows, assuming an initial condition where the servo has locked the relative position to a particular initial reference value. First, the actuator is caused to change the relative position by an amount approximately equal to the reference interval in a manner that the servo cannot track the change, such as by disabling the servo. Servo control is then re-established, at which point the servo operates to keep the relative position centered on the nearest reference value.

Abstract: An object is typically illuminated by laser light, and reflected light carrying a speckle pattern is amplified by an image intensifier. First and second speckle patterns representing the object before and after its deformation, respectively are written by double writing into a ferroelectric liquid crystal spatial light modulator (FLC-SLM). The double-written image is read out from the FLC-SLM, and converted by a Fourier transform optical system into an output optical image, i.e., Young's fringe. The output optical image is detected by a photoelectric converter, and analyzed by an image processing device to determine a deformation of the object.

Abstract: For critical dimension (CD) metrology of photomasks, a laser scatterometer linewidth measurement tool provides noncontact rapid, and nondestructive measurement of linewidth. Calculation of the linewidth is based on a rigorous theoretical model, thus eliminating the need for calibrations. A chrome-on-glass diffraction grating is illuminated with a laser. A photodetector mounted behind the photomask measures the scattered power in each diffracted order. This provides data for the rigorous theoretical model which provides a relationship between the linewidth of the photomask grating and the fraction of total power diffracted into the transmitted zero-order. This scatterometer linewidth measurement technique provides a simple, rapid, nondestructive, and noncontact method of linewidth determination which takes into account the effect of the glass substrate on which the grating is placed.

Abstract: The present invention resides in method and apparatus for measuring a minute displacement, comprising applying a light of a first wavelength at a predetermined angle to a diffraction grating formed on an object whose position is to be detected, subjecting each of the resulting diffracted light and regular reflected light and a light of a second wavelength different from the first wavelength to heterodyne interference with each other to generate a measurement signal and a reference signal, and measuring a phase difference between the measurement signal and the reference signal to thereby determine a minute displacement of the object.

Abstract: A Fabry-Perot interferometer that is shear and tilt immune as well as being tunable. The basic design consists of a spherical semi-reflecting mirror and a planar array of retro-directive mirrors (referred to as phase or pseudo-phase conjugators). The focal point of the spherical mirror is located between the retro-array or phase conjugate mirror and the spherical mirror. In this configuration the Fabry-Perot is immune to tilting and shear displacement of its optical elements as well as being funable to change the optical path difference between interfering beams.

Abstract: A laser referencing system is disclosed which is used in a refractively scanning interferometer. The interferometer optics comprise a fixed wedge-shaped prism having a beamsplitter surface, a movable wedge-shaped prism, and two corner cube reflectors. A laser clocking beam enters the interferometer on a path below the infrared analytical beam, and leaves the interferometer on a path above the infrared beam. Quadrature control of the laser beams is used to control the ends of the scanning sweeps, eliminating the need for a third, "white light" interferometer beam. ZPD alignment is accomplished by horizontal adjustment of the fixed beamsplitter prism. The interferometer optics are supported three-dimensionally in a cast shell.

Abstract: A beam retarder positioned in the path of a superimposed linearly polarized working beam and an orthogonal linearly polarized reference beam, where the working beam and the reference beam have travelled over different optical paths, converts the linearly polarized superimposed working beam and reference beam components into circularly polarized beam components having opposite hands. A rotatable analyzer projects an analyzed beam having phase characteristics determined by the rotational orientation of the analyzer and by the optical path difference between the reference beam and the working beam. A radiation sensitive detector detects changes in intensity of the analyzed beam that are related to the beat frequency and phase of the analyzed beam. Signal processor apparatus relate the phase of the beat frequency to the rotation of the analyzer to adjust the variable path length traveled by the working beam.

Abstract: A method of determining regularity of a pattern array on a substrate to enable sequential positioning of patterns of the array relative to a reference position includes the step of calculating a reliability degree regarding a measured value of a pattern position, and the step of determining the regularity of the pattern array on the basis of the calculated reliability degree, and a design value and the measured value of the pattern position.

Abstract: Optical metrology method and apparatus wherein three optical wavelengths are generated and separated into a reference beam (RB) and an object beam (OB) having substantially equal optical path lengths. After reflecting from a surface being measured OB is combined with RB and provided to sensors which measure the intensity associated with each of the wavelengths. Any difference between the intensities is indicative of a difference in the optical path lengths of OB and RB and is a function of the polarization state of each of the three returned wavelengths. Differences in optical path length are shown to be indicative of a displacement of the object being measured. Preferably, two multimode laser diodes (12,14) are provided for generating the three optical wavelengths. Two synthetic wavelengths are derived from the three optical wavelengths and are employed to improve the precision of measurement while retaining a large dynamic range made possible by the use of a large synthetic wavelength.

Abstract: A Sagnac-type fiber-optic gyroscope having a light source, a fiber coil consisting of an optical fiber, and a receiver arrangement which are all connected with a directional coupler in such a manner that wide-band light of the light source is fed into the two ends of the fiber coil and passes through it in opposite directions, the light emerging from the ends of the fiber coil and forming an interference signal in the directional coupler which is detected. An auxiliary coil is also connected with the directional coupler into which light from the single light source is also coupled, the dimensions of the auxiliary coil and of the main coil with respect to their length and their diameter being such that a measuring range is obtained that is expanded by the auxiliary coil and in which, for the whole measuring range, unambiguous measuring values may be determined for the rate of rotation of the fiber-optic gyroscope.

Abstract: An object is tested for defects by interferometry, by comparing images of the object taken under stressed and unstressed conditions. The stress is applied by perturbing the object with acoustic waves, produced by a speaker directed towards the object, without any mechanical coupling to the object. The acoustic energy can be of a single frequency, or it can be distributed over a set of random frequencies (i.e. white noise), or it can be in the form of a signal which is "swept" through a range of frequencies. In the latter case, the results can be stored in a video buffer which records the maximum signal obtained, for each pixel, while the signal is swept through the frequency range. Different defects in the object may resonate at varying frequencies within the given range. By exciting the object at each frequency within the range, and superimposing the maximum signals obtained for each pixel, the resulting image is likely to show all the locations on the object which may be defective.

Abstract: An image receiving apparatus includes a light source for emitting a pulsed light beam, a shifting device for progressively shifting the light beam emitted from the light source, an imaging device for receiving image information related to an object illuminated by the shifted beam from the shifting device as electric signals, an image integrating unit for integrating the electric signals received by the imaging device to generate integrated image information, and a controller for controlling a repetition frequency of the pulsed emission of the light source and a shifting period of the shifting device in synchronization with a timing for receiving image information by the imaging device. The image receiving apparatus of the present invention can be utilized to perform alignment of an object. A method to perform such alignment is also disclosed.

Abstract: A displacement detection device has a laser unit. The laser unit has two semiconductor lasers formed on a single substrate through a single process. One of the lasers has an end coated with a reflection preventing film and facing a mirror provided at the end of a cantilever. The other end of the laser is coated with a film having a high reflectance film such that a light resonator is formed together with the mirror and the high reflectance film. The other laser has both opposite ends coated with films of a high reflectance, and a light resonator is formed between the opposite ends. Two laser beams emitted from the two semiconductor lasers interfere with each other, and the resultant interference light enters the light detector. The detector detects a variation in the interference light caused by displacement of the mirror, and outputs a signal indicative of a displacement in the cantilever.

Abstract: In a method and apparatus for linear transport of sheet and web material by piezotranslators, the longitudinal displacement is measured by an optical interferometer and the interferometer output is utilized to control the longitudinally acting piezotranslators.

Abstract: A positioning technique for grinding a conical tip on a fiber optic element includes rotatably mounting an end of the fiber optic element to be conically ground; detecting orbital motion of the optical axis of the fiber optic element about the mechanical axis of rotation; and adjusting the optical axis relative to the axis of rotation to minimize the orbital motion of the optical axis.