Showing papers on "Optical filter published in 1986"

Thin-film Optical Filters

Abstract: (1986). Thin-film Optical Filters. Optica Acta: International Journal of Optics: Vol. 33, No. 11, pp. 1336-1336.

Texture discrimination by Gabor functions

Abstract: A 2D Gabor filter can be realized as a sinusoidal plane wave of some frequency and orientation within a two dimensional Gaussian envelope. Its spatial extent, frequency and orientation preferences as well as bandwidths are easily controlled by the parameters used in generating the filters. However, there is an "uncertainty relation" associated with linear filters which limits the resolution simultaneously attainable in space and frequency. Daugman (1985) has determined that 2D Gabor filters are members of a class of functions achieving optimal joint resolution in the 2D space and 2D frequency domains. They have also been found to be a good model for two dimensional receptive fields of simple cells in the striate cortex (Jones 1985; Jones et al. 1985). The characteristic of optimal joint resolution in both space and frequency suggests that these filters are appropriate operators for tasks requiring simultaneous measurement in these domains. Texture discrimination is such a task. Computer application of a set of Gabor filters to a variety of textures found to be preattentively discriminable produces results in which differently textured regions are distinguished by first-order differences in the values measured by the filters. This ability to reduce the statistical complexity distinguishing differently textured region as well as the sensitivity of these filters to certain types of local features suggest that Gabor functions can act as detectors of certain "texton" types. The performance of the computer models suggests that cortical neurons with Gabor like receptive fields may be involved in preattentive texture discrimination.

What classical optics can do for the digital optical computer

Abstract: Recently, quite strong nonlinear optical configurations such as MQW have been invented. As a consequence, optical logic components with reasonable parameters are now feasible, but that is not enough to justify the development of a digital optical computer. The natural parallelism of optical instruments provides the impetus for developing a highly parallel digital optical computer. The optical technology is not so far behind the electronics technology as one might suspect. We show how varieties of computer subsystems can be implemented relatively easily by classical optical hardware.

Superresolving filters in confocally scanned imaging systems

Abstract: The limitations of superresolving filters in imaging systems are investigated. The constraints on such filters in the nonscanning imaging mode are discussed. The possible advantages of such filters in confocal scanning imaging are highlighted. It is shown theoretically and verified experimentally that simply designed complex-amplitude filters can be used effectively to double the exit pupil of a confocal imaging system and thus improve resolution. Superresolution can be achieved with acceptable energy losses and manufacturing tolerances.

Optical bistability, photonic logic, and optical computation.

Abstract: This paper presents new results and reviews the latest state of research in all-optical nonlinear logic switches, amplifiers, and memories. Optical circuit elements that perform the logic functions of the electronic computer are described. Switching speed on a picosecond time scale, the availability of fast high bandwidth consistent communication, and the application of optical parallelism in free space optical wiring are some advantages of the optical computing elements.

Narrowband grating resonator filters in InGaAsP/InP waveguides

Abstract: We report the first demonstration of efficient narrowband optical wavelength filters using InGaAsP/InP passive waveguide grating resonators. Filter bandwidths as narrow as 1 A, centered about λ=1.55 μm with excess resonator loss as low as 1 dB, have been achieved.

High-reflectivity monomode-fibre grating filters

Abstract: The fabrication and characterisation of efficient, narrowband fibre-optic filters utilising surface-relief gratings etched into monomode fibre are described. A device with 92% reflectivity and 1·8 nm bandwidth at 1·3 μm wavelength using a first-order Bragg grating with a high-index overlayer is reported.

Theoretical analysis of the crystalline colloidal array filter

Abstract: The major parameters of a crystalline colloidal array optical filter have been investigated theoretically, and the results compared to published experimental data. This filter consists of an aqueous suspension of polystyrene spheres in a lattice which produces Bragg diffraction of incident light. The development of expressions for the filter bandwidth and attenuation utilized both dynamical x-ray diffraction theory and light scattering theory. The theoretical attenuation function indicates that extremely high absorbance values are achievable with relatively thin filters.

Power generating optical filter

Abstract: A power generating optical filter (30) specially tuned to (1) transmit at least portions of selected wavelengths of incident light and (2) generate electrical power from absorbed portions of selected wavelengths of incident light. FlG.

All-fiber wavelength filter from successive biconical tapers

Abstract: We demonstrate the cascading of biconical fiber tapers as a simple method for converting monomode optical fibers into wavelength filters with a prescribed response. As an example, we made a narrow-bandpass filter consisting of four biconical tapers of different elongations made in succession on a single fiber. The transmission peak of the spectral response of the filter is centered on an arbitrary wavelength within the monomode domain of the fiber. The half-power width is approximately 6 nm.

A novel integrated optics wavelength filter in InGaAsP-InP

Abstract: An InGaAsP-InP integrated optics wavelength selective device is proposed and demonstrated. It utilizes coupling between epitaxial layers with different refractive indices and thicknesses. The device is suitable for integration to form, e.g., a monolithic receiver for wavelength division multiplexed optical communication systems. Design considerations are given. The filter bandwidth and center wavelength can be freely chosen, and bandwidths as narrow as 1.5 nm at 1.3 or 1.55 μm center wavelength are shown feasible. Electrical tuning is possible. Experimental filters show that devices can he fabricated with performance in good agreement with theory, The 22-nm -3-dB bandwidth at 1.12-μm center wavelength presently demonstrated is limited by the measurement system.

Scale, rotation, and shift invariant image recognition.

Abstract: A circular harmonic filter illuminated with white light illumination is used to achieve scale, rotation, and shift invariant image recognition. The circular harmonic expansion of an object is utilized to achieve rotation and shift invariant image recognition. Scale invariance is added using a broadband dispersion-compensation technique. When illuminated with broadband light, the frequency-plane filter simply selects the wavelength from the spectrum that produces the same size transform as that recorded in the filter. Laboratory experiments that demonstrate the operation of the technique are presented.

Optical implementation of the Hough transform by a matrix of holograms

Abstract: The Hough transform is a powerful feature extraction algorithm transforming parametric curves of objects into a smaller feature space called the parameter domain. Optical implementation of the Hough transform by space-variant holographic filters is discussed, and a computer controlled system for generating such filters is described. Employing this system, filters for images of space bandwidth product of 60 × 60 are generated and applied to recognize and detect straight lines and circles in parallel and real time.

Iterative technique for the synthesis of optical-correlation filters

Abstract: Optical-correlation filters that are translationally and rotationally invariant are made target specific by incorporating all the angular harmonics of the target image. An iterative design method similar to the technique of convex projections allows the image angular harmonics to be rephased so that the filter exhibits a constant-amplitude rotational response. Rotating this filter in the Fourier plane forms the Fourier summation of all angular harmonics of the input image. Ari image to be detected must have angular-harmonic terms that have an amplitude and a phase that are keyed exactly to the target image. This lock-and-tumbler filter exhibits excellent discrimination capability while preserving rotational invariance.

A Conceptional Design on Optical Frequency-Division-Multiplexing Distribution Systems with Optical Tunable Filters

Abstract: Optical frequency-division-multiplexing distribution systems providing more than ten frequency multiplexed optical signals separated by on the order of gigahertz, distribute signals to plural receivers, where one of the signals is selected by a frequency selection switch (FS-SW). This paper describes the design of an optical frequency-divisionmultiplexing distribution system. Investigation is made of periodic filters for frequency division multiplexers and FS-SW, and the optical source, as well as single-mode fiber polarization mode dispersion. Preliminary transmission experiments using a bit rate of 450 Mbits/s, fiber length of 13 km, and frequency spacing of 11 GHz are also demonstrated at a 1.5 μm wavelength to show the design's suitability.

Single crystal, epitaxial multilayers of AlAs, GaAs, and AlxGa1−xAs for use as optical interferometric elements

Abstract: We propose using single crystal multilayers of AlAs, GaAs, and AlxGa1−xAs for use as several different kinds of optical interference elements which include high reflectors, transmission filters, and Fabry–Perot cavities. We have grown many of these structures by molecular beam epitaxy and measured their optical characteristics. We find the characteristics of these structures to be very useful for a number of applications for integrated optical devices which we also propose.

Optical frequency filter for ultrashort pulses.

Abstract: We describe an optical filter based on prisms, which provides both spectral filtering and an adjustable correction to group-velocity dispersion. The low losses permit incorporation in a laser oscillator, and the group-velocity correction of the prism sequence has been used with pulses as short as 10 fsec.

Bar code reader with enhanced sensitivity

Abstract: In laser bar code scanners bright sunlight tends to overpower the reflected laser light, drastically reducing the difference between bar code and background signals. In the present bar code reader, a plurality of light detectors are utilized with different spectral response characteristics at the wavelength of the incident laser beam, such that the differential response of the detectors tends to minimize the effect of background illumination. Narrowband optical filters with offset passbands may be used with conventional light sensors. As another example, filters with long wavelength transmission characteristics and offset cutoff wavelengths may be employed if necessary with a neutral density filter to provide balanced responses under broadband illumination.

Visibility Of The Sea With Special Reference To The Secchi Disc

Abstract: A general visibility theory valid in inhomogeneous hydrosols is presented and experimentally verified for some special cases. The field measurements used in the experimental verification were obtained from both oligotrophic and eutrophic regions in the sea and comprise of a fairly large Danish and French data set consisting of spectral downward and upward irradiances, downward quanta irradiance, spectral light transmission, spectral radiance distributions and finally, spectral Secchi disc measurements.

Bias reduction by polarisation dispersion in the fibre-optic gyroscope

Abstract: In a ‘reciprocal architecture’ FOG a single-mode filter is used to reduce bias drift resulting from changing fibre birefringence. We show that if a birefringent element is combined with this filter the bias is reduced if the dispersion in the element exceeds the source coherence length. This significantly relaxes the requirements for mode filter extinction.

Color copying machine

Abstract: A color copying machine includes scanning device for applying illumination onto a color original to effect a scanning operation. A color separator includes a plurality of optical filters of different colors, each of the filters allowing a predetermined light component of the illumination to pass therethrough during each scanning operation so as to apply it onto a photoconductive drum charged uniformly to form an electrostatic image thereon. Color toner is applied to each of the electrostatic images during the rotation of the photoconductive drum. The toner image on the photoconductive drum is transferred to a record sheet on a transfer drum. Two sensors are provided for sensing the initiation of each scanning operation and the position of the record sheet on the transfer drum. A control circuit detects, in response to the outputs of the two sensors, start and end timings of the transferring of each of the toner images onto the record sheet. The control circuit controls the transfer drum to rotate at the same speed as the photoconductive drum during the transfer of each toner image to said record sheet, and controls the transfer drum to rotate, during a time interval between the two consecutive transfer operations, at such a speed that a leading edge of the record sheet on the transfer drum is brought into agreement with a leading edge of each toner image on the photoconductive drum.

Tunable optical filter in fiber-optic form.

Abstract: Light can be coupled between the two principal polarizations of birefringent fiber by using a traveling acoustic wave to produce a spatially periodic stress in the fiber. For a fixed acoustic frequency, maximum coupling occurs when the input optical wavelength is such that the beat length of the fiber equals the acoustic wavelength. By changing the acoustic frequency, the wavelength at which peak coupling occurs can be tuned. A prototype device has a passband 5 nm wide with a peak optical wavelength that can be tuned from 570 to 630 nm by changing the acoustic frequency from 2.85 to 2.55 MHz.

Optical filter for incoherent imaging systems

Abstract: An optical filter for use with an imaging lens in an incoherent imaging system operating in broadband illumination for increasing the depth-of-focus of the lens while maintaining energy thru-put is disclosed. The optical filter comprises a transparent support having on one surface thereof an array of transparent, discrete steps of substantially equal size, each step having a thickness that differs from all other steps by at least the coherence length of the radiation to be passed and the size of the array being equal to the size of the lens. In use, the optical filter is positioned in front of the imaging lens. When so positioned, the depth of focus of the imaging lens is proportional to the size of the individual steps rather than the size of the lens while the energy thru-put of the imaging remains the same as it would be without the optical filter.

Optical fiber type measuring instrument for temperature distribution

Abstract: PURPOSE:To measure the lengthwise temperature distribution of an optical fiber continuously and precisely by utilizing a temperature function of the intensity ratio of Stokes light and anti-Stokes light based upon the Raman scatter of the optical fiber itself. CONSTITUTION:Rayleigh scattered light and Raman scattered light generated in the optical fiber 7 return partially in the optical fiber 7 as back scattered light and are projected from an incidence end, and they are passed through a condenser lens 6, separated by a directional coupler 5, and sent to a detection system 13. The detection system 13 consists of a guide-in fiber 14, a half-mirror 15, optical filters 16 and 17, photodetecting elements 18 and 19, and an amplifier 21. Then, the intensity values of the Stokes light and anti-Stokes light inputted to a signal processing circuit 22 through the detection system 13 is corrected in consideration of wavelength characteristics of the loss of the optical fiber 7, transmission characteristics of the filters 16 and 17, gains of the photodetecting elements 18 and 19, etc., to obtain electric outputs. The ratio of them is calculated to find the temperature of the fiber 7 at a point (x) and the continuous lengthwise temperature distribution of the fiber 7 is obtained.

Coherent optical fibre delay-line processor

Abstract: The operation of an optical fibre tapped delay line with a long coherence length source is described. Optical phase is retained; thus the system can perform bipolar (or in general complex-valued) signal processing operations. Experimental results are presented that illustrate the operating characteristics and capabilities of the system for simple time-domain processing operations.

Rotationally invariant correlation filtering for multiple images

Abstract: A method is presented for designing translation-invariant optical correlation filters that have a specified rotational response for each of several input images. The correlation filter is postulated to have the form of an infinite linear combination of the angular Fourier harmonics of the input images. The corresponding response of the optical system to rotations of the multiple input images is described by a vector–matrix convolution equation. The solution of this equation for the unknown correlation filter is presented in terms of Fourier series. Use of one term in the Fourier series gives the multiple circular-harmonic filter that provides a specified rotationally invariant response for each of the multiple input images. Applications to rotationally invariant discrimination are described, and examples are given.

Optical Nonlinearity and Bistability of Wide-Gap II-VI Compounds

Abstract: We report on optical nonlinearity and bistability at room temperature in the wavelength range from 500 to 700 nm. The underlying physical mechanisms are discussed and low-power operation as well as fast switching on the ps time-scale is demonstrated.

Form-invariant linear filtering: Theory and applications

Abstract: The form-invariant filters are, by definition, those shift-variant filters such that their output, for any given input, turns out to be linearly scaled (implying that its "form" does not change) whenever the input is linearly scaled. In this paper the most general classes of 1- D and 2-D linear form-invariant filters are derived and their properties are discussed, together with their implementation techniques. Two main implementation approaches are considered: one based on the Mellin transform, the other on a combination of coordinate mappings and shift-invariant filtering. The paper also discusses the related works of other authors covering quite different fields such as optical pattern recognition, image restoration and image reconstruction from projections, radar signal processing, etc. It is shown that the mathematics of form-invariant filtering provides a common framework, if not a powerful unified approach, to the many signal processing techniques spread in the above-mentioned works and apparently different application areas. The paper ends with a processing example showing the usefulness of form-invariant filtering in a pattern recognition problem, that is, in the area where the most promising applications of such a filtering are foreseen.