Showing papers on "Optical filter published in 1969"

Thin-film optical filters

Abstract: Introduction. Basic theory. Antireflection coating. Neutral mirrors and beam splitters. Multilayer high-reflectance coatings. Edge filters. Band-pass filters. Tilted coatings. Production methods and thin-film materials. Factors affecting layer and coating properties. Layer uniformity and thickness monitoring. Specification of filters and environmental effects. System considerations: applications of filters and coatings. Other topics. Characteristics of thin-film dielectric materials.

Acousto-Optic Tunable Filter

Abstract: Electronically tunable lithium niobate optical filter utilizing collinear acousto-optic diffraction in anisotropic medium

Electronically tunable acousto‐optic filter

Abstract: Experimental results on a new type of electronically tunable optical filter are described. Tuning from 7000 to 5500 A has been obtained by changing an acoustic driving frequency from 750 to 1050 MHz. A band pass of less than 2 A, a corrected peak transmission of 50%, and an average skirt rejection ratio of about 45 dB have been obtained.

Anti-laser optical filter assembly

Abstract: A filter assembly for selectively removing preselected individual emission lines of laser energy from the visible spectrum comprising at least one pair of Fabry-Perot type filters which transmit laser energy emissions for dissipation in the filter assembly and reflect harmless radiation for transmission through the assembly. A plurality of these filter assemblies parallelly juxtaposed are also used to provide a filter screen for protection against laser energy emissions.

Optical frequency filters using disc cavity

Abstract: THIS APPLICATION DESCRIBES A VARIETY OF CIRCUIT COMPONENTS FOR USE AT OPTICAL FREQUENCIES. EACH OF THE COMPONENTS IS FORMED FROM ONE OR MORE TRANSPARENT DIELECTRIC STRIPS EMBEDDED IN A TRANSPARENT SUBSTRATE OF SLIGHTLY LOWER REFRACTIVE INDEX. BY SUITABLY SHAPING AND LOCATING THE GUIDING STRIPS, MODULATORS, DIRECTIONAL COUPLERS, AND A VARIETY OF FILTERS CAN BE REALIZED. TUNING ARRANGEMENTS ARE ALSO DISCLOSED.

Adjustable bandwidth optical filter

Abstract: THE OPTICAL APPARATUS USED IN A TELEVISION SYSTEM, FOR EXAMPLE, INCLUDES A SERIES ARRANGEMENT OF THREE BIREFRINGENT ELEMENTS OF DIFFERENT THICKNESS INTERSPERSED WITH TWO QUARTER WAVE DELAY ELEMENTS TO CONSTITUTE AN OPTICAL FILTER. THE FILTER IS PLACED IN THE LIGHT PATH BETWEEN AN OBJECT AND THE IMAGE FORMED AT THE PHOTOSENSITIVE ELEMENT OF A CAMERA TUBE. THE SPATIAL FREQUENCY BANDWIDTH OF THE LIGHT PASSING THROUGH THE FILTER IS CONTROLLABLE IN ONE OR MORE DIRECTIONS AND IN THE SAME OR DIFFERENT AMOUNTS IN A PLURALITY OF DIFFERENT DIRECTIONS BY SUITABLE DIMENSIONING OF THE BIREFRINGENT ELEMENTS AND/OR BY APPROPRIATE ROTATIONAL POSITIONING OF THE ENTIRE FILTER ABOUT THE OPTICAL AXIS.

Optical compensating filter with selective radial absorption distribution

Abstract: THERE IS DISCLOSED AN OPTICAL FILTER, PRIMARILY FOR USE WITHIN A LASER RECORDER, WHICH OPERATES TO SELECTIVELY ABSORB PORTIONS OF A LIGHT BEAM OF NONUNIFORM INTENSITY PASSING THERETHROUGH SO AS TO RESULT IN THE EMERGENCE THEREFROM OF A LIGHT BEAM OF UNIFORM INTENSITY.

Collinear heterodyning in optical processors

Abstract: The basic principles of several real-time optical processing schemes employing heterodyning are examined. In each case the method by which the correlation function is developed from the ultrasonic light modulator (ULM) is analyzed. It is shown that in some configurations it is possible to derive the heterodyne reference collinearly, thus increasing the mechanical stability and minimizing the effects of optical aberrations. Experimental results obtained with a correlator using a shear-wave ULM and collinear heterodyning confirm its stability and verify the fact that quality performance can be obtained with inexpensive optical components.

Contrast-enhancement in Imaging Devices by Selection of Input Photosurface Spectral Response

Abstract: Publisher Summary This chapter describes the contrast-enhancement in imaging devices by selection of input photosurface spectral response. The low light level performances of four hypothetical imaging devices possessing significantly differing input spectral responses are compared. At the lower light levels the use of image intensification, either direct view or a television technique, is of particular value because, firstly, the efficiency of the input photosurface is normally far greater than that of a photographic emulsion, and, secondly, the brightness of the output display can, in principle, be adjusted to a level suitable for photography or viewing directly . Spectral products obtained for concrete against a vegetation background are shown. If the current density is sufficiently high, a further improvement in the output display contrast could be obtained by including a band-pass optical filter at the input to the imaging system. This filter should be designed to accept wavelengths, either above or below the contrast inversion point at 0.7μm. The integrated responses to reflected night-sky radiation are also elaborated.

Far infrared interference filters.

Abstract: Capacitive meshes for far ir, low pass filters are prepared from Cu layers on 2.5 micro plastic film. The properties of these meshes of different mesh constants g with their different combinations in two-mesh, fourmesh, and eight-mesh filters are studied in the spectral region 160 cm(-1) to 10 cm(-1) by the use of a grating spectrometer. The applications of these meshes as low pass filters in the far ir spectral region in a grating spectrometer are described.

Electronically tunable acousto-optic filter

Abstract: The paper reports experimental results on a new type of electronically tunable optical filter (1). The filter makes use of collinear acoustic-optic diffraction in an optically anisotropic media. By changing the driving acoustic frequency, the band of optical frequencies which the filter will pass may be changed. A LiNbO 3 acoustic-optic filter with a pass band approximately 2 A wide, which is tunable from 750 A to 5500 A by changing the acoustic frequency from 750 Mc to 1050 Mc, has been demonstrated. Peak transmission at band center is about 30 percent and average rejection outside the pass band is about 50 db.

Light Propagation through a Turbulent Atmosphere: Measurements of the Optical Filter Function

Abstract: Two He–Ne lasers operating at 6328 A have been utilized to make simultaneous measurements of the effects of scintillation over homogeneous optical paths of 650 and 1300 m to study the transfer of laser radiation through a turbulent medium. At the path terminus, multiple sampling of each laser beam was effected by use of a photo-optical technique that records a 61-cm cross section of an optical beam. Concurrent with the optical data, wind-speed and direction recordings were made at multiple points along the optical path in order to estimate the homogeneity of meteorological conditions. Near the path terminus, measurements of wind shear and temperature lapse were taken. In addition, high-speed-thermometry techniques were utilized to compute one-dimensional temperature spectra as well as the thermal structure coefficient CT. Data were gathered during temperature-lapse, neutral, and inversion conditions. Log-irradiance scans derived from the optical data were used to compute log-irradiance power spectra, variance, and other statistical quantities. From these optical and meteorological data, optical-filter functions were calculated for spatial frequencies above 87 cycles/m and are used for comparison with current theories. The saturation of the log-irradiance data is again observed, and the isotropy of the irradiance fluctuations is examined.

Optical Processing of Underground Sound Waves in Seismic Exploration for Oil

Abstract: When coherent light from a laser beam is passed through a transparency on which pictorial information is impressed, the information itself acts as a complex grating to produce a Fraunhofer diffraction pattern which is the two-dimensional Fourier transform, or power spectrum, of the information in the picture. By properly obstructing the light in the transform, one can filter out undesired spatial frequencies or directions of inclinations in the original picture. The most widespread commercial application of this principle has been to the analysis and filtering of seismic reflection records made in exploration for oil. Removal of undesired noise from seismic recordings can often be accomplished more economically by optical filtering than by more conventional digital and electrical analog techniques. Examples are demonstrated where optical filters have substantially improved the quality of seismic data. Use of optical transforms for analysis and solution of geological problems is also illustrated. The most unique advantages of optical processing are in economy, flexibility, and convenience of monitoring. Principal disadvantages are limited dynamic range, and difficulty in constructing filters that behave as gradational rather than step functions.

A simplified optical correlator for radar-signal Processing

Abstract: Radar-signal processing is an interesting application of optical correlators. A simplified optical correlator is described and experimental results are presented.

Photographic printing of cathode-ray tube screen structure

Abstract: During the fabrication of a cathode-ray tube screen structure, a light field is projected through a photographic master, a correction lens and an optical filter incident upon a photosensitive layer. The filter is a relief image comprised of preformed, nonmetallic, light-absorbing particles having a mean diameter in the range of 5 to 50 millimicrons in a lighttransmitting binder. The filter has variations in light transmittance which produce predetermined variations in light intensity in the light filed tailored to the particular system.

Optical filter for suppressing noise which utilizes a graded optical fiber and means for controlling transverse position of iris

Abstract: A noise suppression optical filter having practical utility in increasing the signal-to-noise ratio of a laser communication system. The filter comprises a converging light guide element having an index of refraction which varies inversely with the square of the distance from the central axis. Irises having apertures of specified diameters are located at the input and output ends of that light guide, and means are provided to position these apertures in alignment with the light travelling through the guide.

Optical system for identifying pulses

Abstract: An optical system for identifying a pulse or wavetrain or for compressing the time duration of such a pulse. This is effected by passing monochromatic light through a cell containing a solid or liquid for sustaining an acoustic wave in the desired frequency spectrum. If the pulse to be identified is an electrical pulse, it may be coupled to the cell to set up the acoustic wave. Alternatively, the pulse may be already be an acoustic pulse. The resulting diffracted light wave is then optically filtered by an optical filter such as a hologram on which has previously been recorded a fringe or interference pattern of the pulse to e identified or to be compressed. Accordingly, if the acoustic wave corresponds to the desired electrical pulse, the light passing the hologram may be detected by a detector. If the time duration of the pulse is to be compressed, the hologram or optical filter is so arranged that it will focus the light from the laser substantially in a point or other predetermined area where its exact position may then be detected.

Ultraviolet oxygen sensor

Abstract: : The Ultraviolet Oxygen Sensor has been developed to quantitatively measure oxygen in a closed atmosphere. The essential elements of the instrument are: the ultraviolet source, an optical chopper, the sample cell, the photomultiplier tube, and the required electronic circuits. No monochromator or optical filter has been used. A Xenon discharge lamp with emission at 1470 angstroms is used with a sample path of 0.125 mm to provide a system sensitive to oxygen and insensitive to other gases found in a closed atmosphere environment. This configuration allows the use of a nondispersive optical system and an optical chopper to provide a double beam system. The oxygen concentration is determined by measuring the amount of energy absorbed through the sample cell. This measurement is compared to a reference signal obtained by directing the ultraviolet beam through an oxygen-free path to the photomultiplier. The electronic ratio of these two measurements results in a stable signal that is independent of variation in the source and detector.

Linear spatial filtering with crossed ultrasonic light modulators

Abstract: A new technique is described for realizing the optimum filter for spatial filtering in coherent optical systems. By employing two crossed ultrasonic modulators, this technique overcomes the inherent lack of adaptability of filters realized with photographic transparencies.

Transversal filters with continuously tapped delay lines (CTT filters)

Abstract: The properties of common transversal filters are well known. Transversal filters with continuously tapped delay lines have the advantage that they do not show a periodic continuation of the frequency characteristic. Therefore it is not necessary to use an additional filter for suppressing higher frequency components. After an introduction to CTT filter theory the realization of transversal filters with continuous inductive tapping (ICTT filters) is discussed. The description of the practical synthesis of a low-pass filter and a 90° wide-band phase shifter is followed by the interpretation of measured frequency characteristics.

Optical properties of fibrous and membrane filters

Abstract: The bi-directional and the directional-conical transmittances and reflectances of various materials used for sampling aerosols by filtration were measured, using directional incident light Observations were made with white light and, in some instances, with light filtered through broad-band optical filters The results are interpreted in terms of a one-dimensional model which incorporates a term taking account of absorption, as well as one involving scattering

Color video signal generating device

Abstract: 1,160,232. Colour television. NIPPON COLUMBIA K.K. 29 July, 1966, No. 34228/66. Heading H4F. The image of a coloured object 101, Fig. 1, recorded on a monochrome film 105 via striped colour filter 103 is converted into electrical signals by means of a photo-electric converter, e.g. a monochrome pick-up tube 50, Fig. 3, from which are derived colour video signals for transmission. Optical filter 103 comprises filter elements 103a and 103b having strip filter elements W and - R or - B respectively arranged alternately and crossing the horizontal scanning direction h of the photo-electric converter, Fig. 2 (not shown). The strip filter elements W, - R and - B are transparent, intercept red light and intercept blue light respectively and the "pitch" of the filter elements, i.e. the width of adjacent strip filter elements W are - R, and, W and- B are such that the photo-electric converter produces video signals having carrier frequencies f R and f B in addition to a non- carrier signal. These signals are separated by means of low pass filter 52, Fig. 3, and band pass filters 53 and 54 having centre frequencies f R and f B respectively. The characteristics of which are shown in Fig. 4. The outputs of filters 53 and 54 are demodulated in detectors 56 and 57 and the three primary colour video signals are obtained from matrix 55. Dur to cross modulation a beat frequency component appears in the output of low-pass filter 52 which is cancelled by means of a beat frequency generator 59. To increase the resolution obtained the upper limit frequency of the band of filter 52 may be raised to the centre frequency f R of filter 53, Fig. 5 (not shown), however as a result of this a component of filter 53 gets mixed in the output of filter 52 and a stripe pattern due to f R appears in the reproduced picture. The effect of this stripe pattern may be reduced by applying a rectangular current, Fig. 7B (not shown), derived from the vertical synchronizing signal circuit, to the horizontal deflection coil of the pick-up tube, thus causing the picture of one field to shift in a horizontal direction, and the amplitude of this rectangular current is determined so that the stripe patterns in adjacent fields are interleaved. The rectangular current may be derived from the horizontal synchronizing signal circuit and have a period corresponding to the horizontal deflection period, its phase being inverted every vertical deflection period. Instead of applying the rectangular currents to the horizontal deflection coils they may be applied to another coil provided around the pick-up tube or to a reproducing device. Deviations in the frequencies f R and f B which would result in distortion of the reproduced picture and deterioration of picture quality are reduced by applying the output of either one of filters 53 and 54 to a frequency discriminator (89), Fig. 9 (not shown), the output of which is fed to the horizontal deflection coil. Alternately the output of discriminator (89) may be fed to filter 53 and/or filter 54 to adjust a variable element, e.g. an inductance or capacitor, therein, to move their centre frequencies, Fig. 10 (not shown). In addition, the band of filter 52 may be made variable. To change the bandwidths and centre frequencies of the carriers the pitch of the optical filters is changed by adjusting the orientation of the optical filters, Fig. 12 (not shown). The low-pass filter 52 in Fig. 3 may be replaced by an adding circuit (52 1 , Fig. 13, not shown), and the outputs of band-pass filters (53) and (54) are applied thereto with the correct polarities so as to cancel these outputs from the output of the pick-up tube. With this arrangement further frequency components exceeding the pass-bands of filters (53) and (54) may be obtained so that the resolution may be enhanced. A colour filter 106 1 , Fig. 1, may be located in the light path between the object and the optical filter. Film 105 may be located in direct contact with optical filter 103, or optical fibres may be used, relay lens 104 being omitted.

High Current Vacuum System For Multilayer Filter Deposition

Abstract: The development of a high-current vacuum system suitable for deposition of multilayer acoustical and optical filters is described. Eight interchangeable sources using either a “wick” heater, a double coil, or a basket-type heater are arranged for sequential deposition of low- and high-temperature metals and dielectrics. Electrical contacts to the sources are externally operated to change sources. A liquid N2 cold can is situated on top of the evaporating source and it serves to funnel the vapor stream toward the target. This arrangement saves time and unrecoverable material since it considerably reduces spillage of vapor on the interior.

An imaging system exhibiting wavelength-dependent resolution

Abstract: The Christiansen filter consists of particles of a transparent solid immersed in a suitable liquid such that the two materials have different dispersions but equal indexes of refraction at some specified wavelength. This paper analyzes such a filter as an optical device for providing wavelength-dependent resolution. We derive the modulation transfer function of this filter by using the Huygens-Fresnel diffraction principle. General agreement is obtained with experimental measurements made using monochromatic light. One proposed single-tube color camera system for picture telephone service requires the three primary color component images to have different resolutions. An optical filter illustrating the characteristics required by this application was designed using the formulas developed in this paper. Subjective evaluation of the experimental results obtained with this filter indicates no unforeseen degradation of the composite image of the primary color components.

Development of a laboratory model gas analyzer using emission techniques

Abstract: : An instrument using emission spectroscopic techniques was designed and developed for monitoring the major components in air-type atmospheres. The essential components consist of a hollow cathode excitation source, four interference filters mounted in a filter wheel, a single photomultiplier tube and an electronic circuit, controlled by switching diodes and a gating circuit to record the response for each gas on individual meters.