Abstract: An apparatus for optically detecting a security thread embedded in a paper-like material, e.g., a paper currency. The paper-like material is carried through a detection region defined by an infrared radiation source and two infrared radiation detectors. Two optical filters are mounted on the detectors, respectively. Those filters have different infrared transmission characteristics. Therefore, one detector can detect infrared rays having wavelengths only within a specific range determined by that one filter, and the other detector can detect infrared rays having wavelengths only within another specific range determined by the other filter. When the infrared radiation source projects infrared rays to the paper-like material, the detectors deliver the respective detection signals. A processor processes these detection signals to determine whether or not a security thread is embedded in the paper-like material and also what a detected security material is made of.

Abstract: Part 1 Introduction to acousto-optics: introduction to acousto-optic interaction theory acousto-optic device technology - basic principles acousto-optic device technology - design. Part 2 Acousto-optic processing fundamentals: the theory of acousto-optic spectrum analyzers acousto-optic tunable filters space-integrating acousto-optic signal processors using surface-acoustic-wave delay lines incoherent-light time-integrating processors coherent time-integration processors. Part 3 Acousto-optic processing implementation: optical information-processing applications of acousto-optics acousto-optic spectrum analyzers acousto-optic wide band correlator system signal delay and compression. Part 4 New directions: image processing applications of acousto-optics low-loss acousto-optic photonic switch.

Abstract: Dielectric multilayer thin-film (DMF) filters for a wavelength-division-multiplexing (WDM) system are discussed. It was found that a 23-layer 3-cavity bandpass-type DMF-filter made of TiO 2 and SiO 2 is most suitable for this type of system. An optical multi/demultiplexer employing this type of bandpass DMF-filter is applicable to a two-way WDM transmission system.

Abstract: A spatial frequency filter apparatus for suppressing spurious signals of the type generated in a color television camera incorporating a mosaic color encoding filter for multiplexing color signals includes two double refraction plates for filtering natural light introduced through a lens system in both the horizontal and vertical directions and an optical plate, such as a quarter wavelength plate or a rotatory polarization plate, interposed between the two double refraction plates. By causing natural light to transmit through the two double refraction plates and the optical plate before being introduced to the mosaic color encoding filter, the spurious signals are suppressed, whereby false color which may otherwise make an appearance at the contours of an image picked up by the color television camera can be significantly reduced.

Abstract: The velocity components of individual macroparticles (molten droplets) moving through the interelectrode plasma of copper vacuum arc were measured by applying the forward-scattering laser Doppler anemometry method (LDA). The arc was sustained between two cylindrical copper electrodes, 14 mm in diameter and spaced 4 mm apart. Two current waveforms, with rise times to peak currents of 1 and 6 ms and duration of about 5 and 30 ms, respectively, were used in the experiment, while in both cases peak currents were either 1 or 2 kA. Macroparticles traversing through the ellipsoid shaped "probe-volume," which was produced by the intersection of the two He-Ne laser beams, scattered the laser light, through a monochromator, used as a 1.7-A bandpass filter, onto a photomultiplier. The Doppler-frequency component of the photomultiplier was recorded after appropriate filtering and amplification. The macroparticle velocity component obtained from the Doppler frequency was in the plane defined by the illuminating laser beams and directed perpendicularly to the optical axis. Macroparticles were detected during the whole period of the discharge, and their velocity was determined either at the instant of peak current or when the current decreased to 10 percent of its peak value, at several spatial locations inside the discharge volume. The measured macroparticle velocity components ranged from about 10-20 m/s up to about 700 m/s, showing a systematic dependence on the instantaneous value of the arc-current and on the spatial position of the "probe-volume," e. g.

Abstract: The optical properties of thirty-five all-dielectric spectral filter coatings for the visible spectrum have been investigated and correlated with the deposition conditions of the constituent layers of cryolite and zinc sulfide and with the processes which occur when the coatings are exposed to atmosphere. It will be shown that the results of measurements of transmittance and reflectance over the passband wavelengths can be predicted theoretically only if account is taken of absorption in the layers and scattering at the rough boundaries and of changes in the refractive indices of the layers due to water penetration.

Abstract: A solid state color imaging device comprising a two dimensional array of stacked thin film photovoltaic devices with devices in each stack responsive to selected color bands. Color discrimination may be enhanced by design of intermediate transparent conductive layers to act as optical filters.

Abstract: An optical filter includes a first polarizer for transmitting light having a first polarization direction and a first birefringent element for receiving the light transmitted by the first polarizer. A second birefringent element, of a different material having a different birefringence, receives the light transmitted by the first element, while a second polarizer receives the light transmitted by the second element and transmits the portion having a second polarization direction. The birefringences and the thicknesses of the elements are arranged to effect a predetermined amount of net phase retardation, preferably zero, for light of a wavelength λ in traversing the first and second elements.

Abstract: A novel single mode optical fiber tapped delay line that uses silicon V‐groove substrates to align an array of directional coupler taps has been demonstrated as a transversal filter. The device was used to generate and correlate 4‐bit, 400‐Mb/s coded sequences. The generated codes exhibited an amplitude uniformity of ±0.04 dB. The electrical correlation output was linear over a range of 25 dB and was limited by electronic components external to the fiber filter itself. Extension of the fabrication technique to include hundreds of taps at intervals as short as several picoseconds may be possible.

Abstract: A real-time coherent optical correlator is mounted inside a 15- × 23- × 38-cm enclosure and features laser diode light sources and a liquid crystal incoherent-to-coherent image converter. Each of four reference filters is illuminated by a separate laser diode, real-time operation is achieved by the image converter, and a zoom lens forming the incoherent image allows a scale search. The correlator can be mounted on a tripod and performs correlations indoors or outdoors.

Abstract: Narrowband grating filters were fabricated in GeO2 thin-film optical waveguides by optically induced changes in the refractive index. Intense counterpropagating laser beams inside the waveguide resulted in distributed feedback reflectors having a peak efficiency of 40%. The spectral response of the filters was measured by thermal tuning of the center frequency and agreed with the results of a coupled-mode analysis. The filter bandwidths were <0.01 nm.

Abstract: We propose to use computer-generated matched-filter holograms for the analysis of arbitrary fibre fields in terms of suitable orthogonal functions. In preliminary experiments true graded-index fibre modes were analysed in terms of Gauss-Laguerre functions.

Abstract: A fiber optical measuring device for measuring primarily electric voltage or magnetic field, comprises a transducer having a sensor element, the transducer being connected by means of at least one optical fiber to a measuring electronic unit provided with at least two light sources having different emission spectra for excitation of photo-luminescence in the sensor element and at least one photo-detector for detection of photo-luminescene emanating from the sensor element. The sensor element includes at least one luminescent layer arranged so that light from said optical fiber is arranged to fall towards the surface of the layer. Between the end surface of the optical fiber in the transducer and the surface of the luminescent layer, there is arranged at least one optical filter perpendicular to the ray path of the light. The luminescent layer is provided with at least two electrodes to generate, in the layer, a lateral electric field for the purpose of accelerating charge carriers which are excited by light emitted from the measuring electronic unit and transmitted to the luminescent layer via the optical fiber and through at least one of the filters.

Abstract: A television camera which carries out color separation by use of vertical correlation in a picture, comprises a pickup element for scanning a target, a color separating stripe filter, and an optical filter for separating a single incident light beam in a direction which is the same as the scanning direction of the pickup element and a direction perpendicular to the scanning direction, by acting on the single incident light beam in two dimensions. The optical filter comprises a first double refraction transparent plate for separating a light beam in a direction which coincides with the scanning direction of the pickup element, a second double refraction transparent plate for separating a light beam in a direction which is rotated by 45° with respect to the scanning direction, and a third double refraction transparent plate for separating a light beam in a direction perpendicular to the scanning direction. The first, second, and third double refraction transparent plates are stacked.

Abstract: This communication describes a method of referencing out adventitious intensity variations in an optical fibre intensity-modulated sensor by measuring the transmitted light intensity at two wavelengths, one of which carries the signal information and the other being used to normalise the intensity.

Abstract: Disclosed is an optical device producing single mode laser emission. The device includes a semiconductor laser which would normally emit a number of closely spaced longitudinal modes and a filter which receives light from the laser active layer and reflects light back to the active layer. The filter includes at least one thin, optically absorbing layer, a dielectric layer, and a reflecting layer. The thickness and refractive indices of the layers are such that the filter reflectivity has a number of narrow maxima, but only one which lies within the gain bandwidth of the laser. The width of the peak and the background amplitude between peaks is such that only a single longitudinal mode of the laser is allowed to oscillate.

Abstract: Extraction of wanted parts from optical images is performed by matched intensity filters of spatial frequiencies. The aim of the procedure is to enhance the recognition power of similar images.© (1983) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Abstract: An optical filter device is disclosed made up of a specially designed bandpass filter and a circularly polarizing filter and is typically used in front of the faceplate of a cathode ray tube in a high intensity ambient light environment, such as with navigation displays in some aircraft cockpits, to reduce the high intensity ambient light striking the phosphor of the cathode ray tube and thus effect a reduction in the level of the scattered light that causes a washout of the display thereon, thereby permitting observation of the display on the tube.

Abstract: An electronically tunable optical filter using acousto-optic interaction in a dispersive birefrigent crystal. The strong wavelength dispersion of birefringence in a class of uniaxial semiconductors near the band gap is utilized to enhance the spectral resolution of the tunable acousto-optic filter. The dispersive tunable acousto-optic filter provides a very large aperture while maintaining an extremely narrow bandwidth.

Abstract: Diseased areas of human teeth are identified by an orange-red fluorescence which is produced when the teeth are illuminated with visible light having a wavelength of less than approximately 434.5 nm. The teeth are viewed directly through an optical filter which blocks transmission at the illuminating wavelength. A peaking filter may be used to enhance the visibility of the fluorescence.

Abstract: Optical filters which are capable of performing discrete two-dimensional coordinate transformations for space-variant image processing are described. Several examples of space variant image processing are given, including the application of conformal mapping to a problem in potential flow theory. With simple optical arrangements, both the forward and inverse transformations can be performed with the same filter. Production of these filters by a microcomputer controlled scanning Interferometric Pattern System is detailed.© (1983) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Abstract: An advanced airborne pushbroom scanner, MEIS II, has been developed and operated by the Canada Centre for Remote Sensing. The imaging scanner uses charge-coupled device linear array detectors, and covers the near infrared and visible spectral regions, spectral bands being readily selected by means of optical filters. MEIS II has a low noise equivalent radiance and high spatial resolution, and its real-time data processor provides radiometric gain and offset corrections, together with geometric and aircraft roll compensation. The sensor shows an improvement in noise equivalent radiance of at least two orders of magnitude when compared to the rotating-mirror scanner presently in use at CCRS as well as improvements in the geometric fidelity and spatial measurements, with inter-channel registration to within a fraction of a pixel.

Abstract: AMeasurement AssumanceProgramrforspectrophotometry is being established in orderto assistlaboratories involved in spectrophotometric calibrations. This paper deals with the preparation and calibration of neutral density glass filters for checking the linearity of photometric response, as applied to spectral transmittance measurements. Several sets of filters were prepared from suitable neutral glass to provide nominal tramnmittances of 92, 70, 50, 25, 10, 1, and 0.1% at a wavelength of 548.5 nm. These filter sets will be available in three sizes: these are, 38 mm diameter aperture in 51 x 51 mm holder, 25 mm diameter aperture rn 51 x 28 mm holder, and 30 x 8 mm aperture in a cuvette holder. The filters were calibrated for spectral transmittance on the NBS Reference Spectrophotometer for high accuracy transmittance measurements Measurements were made with a 1.5 nm passband collimated sample beam> The filters were checked for uniformity and measurements were made to determine the effects of sample beam polarization. The tranarmittance data for the wavelength range of interest were analyzed by statistical methods to determine the effecs of pasaband for a range of 1.5 nm to 10.5 nmm passband. The results of these measurements are presented in tabular and graphical detail for the master filter set.

Abstract: This paper reports on recent progress on invariant pattern recognition. Circular harmonic component (CHC) matched filters allow pattern recognition that is invariant under translations and rotations of the objects, and does not require segmentation of the object from its background. Now that the problem of the proper center for expansion of the filter has been solved, it has become easier to use such filters. The performance of the filter may be improved without using multiple filters by using composite CHC filters. When both target discrimination and sidelobe reduction are required, a composite filter that is an average between two composite filters must be used. The use of other invariant features is discussed.

Abstract: An automated control system for evaporation and sputtering plants is presented. It consists of an optical monitoring system (OMS 2000) and a control unit (LEYCOM) based on a 16 bit microprocessor.This system has been successfully in operation since three years. The OMS 2000 is a single wavelength monitoring system designed for measuring the reflectance or transmittance of a test glass during deposition of the coating. It has the additional capability of terminating the evaporation when a preselected intensity value is reached or when the measured intensity passes through an extremum. Different optical monitoring methods, which can be executed with the OMS 2000, are discussed with respect to their error compensation effect. When using a special 6 fold test glass changer a special monitoring method is possible which makes monitoring of non-quarterwave layer systems rather easy and which exhibits a useful error compensation effect for edge filters.© (1983) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Abstract: The object of the invention is an optical component which consists of an optical fibre and a (fibre-optic) graded-index rod lens, which is coupled thereto and whose other end surface is inclined relative to the optical axis. Such a component can be used in manifold ways, e.g. in multiplexers, splitters, optical filters and optical switches.