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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Abstract: The steady-state model of thermally induced optical bistability, presented in a previous paper, is extended to describe transient phenomena. A nonlinear integral equation is derived which can be readily solved for arbitrary time dependence of the input power. We apply the model to switching processes in bistable ZnSe interference filters. The corresponding experimental results are found to be in good agreement with the theoretical predictions.

Abstract: An optical filter for use in a solid state color camera containing a plurality of solid state image sensing devices having a predetermined horizontal scanning direction, the filter including a first crystal plate for separating an incident ray into an ordinary ray and extraordinary rays in a direction of 45° with respect to the horizontal scanning direction of said solid state image sensing devices, a second crystal plate for separating the incident ray thereof into an ordinary ray and extraordinary rays in a direction which coincides with the horizontal scanning direction, and a third crystal plate for separating the incident ray into an ordinary ray and extraordinary ray in a direction of -45° with respect to the horizontal scanning direction. The second crystal plate is located between the first and third crystal plates, and the three plates are bonded together in the form of a laminate. The optical filter thus produced provides a point diffusion for an incident ray to direct the diffused rays on the solid state image sensing devices. The optical filter then forms first and second trap straight lines and a third trap straight line extending along the vertical scanning direction of the solid state image sensing devices for distributing a spatial frequency spectrum of a sampled output from the solid state sensing device.

Abstract: A binary phase-only optical correlation system incorporating therein a binary phase-only filter. The binary phase-only optical filter is made by mathematically generating preselected phase-only information by a fast Fourier Transform technique. This generated phase-only information is binarized into a function having two values. This binarized function is utilized to produce a mask which in turn is used in conjunction with an appropriate optical substrate to produce the binary phase-only filter. The manufacture of the binary phase-only filter is substantially easier than the production of a phase-only filter yet virtually the same correlation results when the binary phase-only filter when it is used in an optical correlation system.

Abstract: A computing device for computing the accumulated solar or sunlamp radiation over a period of time has an indicating device (8) as well as a means for measuring the radiation received. Said means has at least one opto-electronic converter. It is combined with an information device (S, D, E, 14) for a tolerable residual dosage which can contain an information output device (14), preferably with visual display of the tolerable residual dosage, and also an information input device (S, D, E). A filter (2) for the UV-B range is preferably installed in front of the opto-electronic converter. The time may be displayed, and the zenith angle of the sun calculated and displayed. The device may be used as a photographic exposure meter, as well as during suntanning sessions. A process of producing optical filters comprises simultaneously moulding a plurality of filter bodies as a single structure, the filter bodies being connected by runner portions, coating the filter bodies, and separating the coated filter bodies from each other.

Abstract: An optical filter is formed by providing a plurality of gaps, which have a desired width and such a depth that is larger than the thickness of the waveguide layer, in a slab or a waveguide layer in a three-dimensional optical waveguide so as to extend in the light propagating direction at desired period intervals. These gaps are filled with a film of a material, the refractive index of which is different from that of the waveguide layer, to complete the optical filter. A multiplex wavelength transmission device is formed monolithically by providing at least one optical filter, which is formed in the above-mentioned manner, in an optical waveguide, and arranging one or both of a light-emitting semiconductor element and a photodetector on the side of an optical signal which has passed through the optical filter, and on the side of an optical signal which has been reflected on the same optical filter.

Abstract: We describe the theory of a narrowband electrooptic tunable filter based on a Fabry-Perot etalon with distributed Bragg reflectors. The filter can be in either bulk or waveguide form. The input to the filter must be prefiltered to the stop-band of the Bragg mirrors. Once this is accomplished, the etalon possesses a very narrow notch in the Bragg filter stop-band. The notch width is extremely narrow when the Bragg reflectance is high. The location of the notch in the Bragg stop-band is determined by the etalon cavity length and can be tuned by application of an electric field to the electrooptic material comprising the etalon cavity. Absorption in the cavity and Bragg reflectors is included in the theoretical model of the filter. The filter can be constructed from any one of several existing electrooptic organic polymer crystals, if the gratings are made either by partial polymerization of the monomer in crossed-UV beams or by corrugating the surface of the polymer. We show a theoretical example of a notch filter operating at a center wavelength of 1 microm that is 62.75 microm thick, with a notch width of under 1 A and a transmission of 35%. This type of filter should have applications in high-speed optical modulation and Q-switches for lasers.

Abstract: An optical filter for blocking radiation of preselected wavelength is described which comprises a colloidal suspension of an optical medium and a multiplicity of microspheres of optical dimensions in a substantially regular three-dimensional array, the optical medium and microspheres comprising materials having matched indices of refraction in the absence of incident radiation, but at least one index of which varies nonlinearly with incident electric field whereby an index mismatch and resulting Bragg diffraction within the suspension is produced by incident radiation of the selected wavelength.