Showing papers on "Optical modulator published in 1982"

Method and apparatus for converting phase-modulated light to amplitude-modulated light and communication method and apparatus employing the same

Abstract: A light modulator for generating a beam of amplitude-modulated light including a source of polarized light, at least one and preferably two liquid crystal cells having a thin layer of nematic liquid crystals of positive dielectric anisotropy through which the polarized light is directed to produce a beam of light having a phase shift corresponding to a modulating electrical signal which is applied to each of the liquid crystal cells. The liquid crystal cells in addition have a continuing electrical bias applied across the layers in order to achieve the rapid response times necessary to achieve phase modulation of the polarized light. The resulting phase-modulated light is converted in a linear polarizer to amplitude-modulated light corresponding to the modulating electrical signal. The amplitude-modulated light is detected in a suitable light detector which generates an electrical signal corresponding to the modulating electrical signal. The linear polarizer may be oriented with either the transmitter or the receiver. A communication system involving a transmitting modulator and a receiving demodulator transmits communication through light either as phase-modulated light or as amplitude-modulated light.

High efficiency optical tank for two-color liquid crystal light valve image projection with color selective prepolarization

Abstract: The invention provides a two-channel liquid crystal light valve image projection system with prepolarization using an oil coupled optical arrangement. A prepolarizing beam splitter is mounted the container in optical alignment with a first surface for splitting and prepolarizing light from a source into first and second beams having first and second polarization states respectively. First and second dichroic separators are mounted within the container for extracting light of a first color from the first beam and light of a second color from the second beam respectively. The separator outputs are recombined by the prepolarizing prism into a single beam which is directed to a second polarizing beam splitter mounted within the container. The second beam splitter splits the single beam and directs light of the first and second polarizations through the second and third apertures, respectively. Liquid crystal light valves mounted at the second and third apertures modulate the polarization state of the exiting light and return it to the second beam splitter to be directed through the output aperture to projection optics for display.

Light modulator, demodulator and method of communication employing the same

Abstract: A light modulator for generating a beam of phase modulated light including a source of polarized light, at least one and preferably two liquid crystal cells having a thin layer of nematic liquid crystals of positive dielectric anisotropy through which the polarized light is directed to produce a beam of light having a phase shift corresponding to a modulating electrical signal which is applied to each of the liquid crystal cells. The liquid crystal cells in addition have a continuing electrical bias applied across the layers in order to achieve the rapid response times necessary to achieve modulation of the polarized light. Demodulation of the polarized light occurs by splitting the modulated light beam into its quadrature components and developing an electrical signal corresponding to the phase difference between the two quadrature components. A communication system involving its modulators and demodulators delivers communication through light as a transmission medium.

Optical pulse radar for an automotive vehicle

Abstract: An optical pulse radar for an automotive vehicle of heterodyne detection-type which can detect an object ahead of the vehicle with an improved S/N radio even under the worst detection conditions in which sunlight or a strong headlight beam from a car is directly incident thereupon. The optical pulse radar according to the present invention comprises a laser system, a beam splitter for obtaining a carrier beam and a heterodyne beam, a beam deflector, a beam modulator, a beam mixer for obtaining a beat beam signal, a beam sensor and, a beat signal processing section, etc. An optical IC may incorporate the beam splitter and mixer, the beam modulator, and the beam deflector in order to miniaturize the system, while improving the sensitivity, reliability, massproductivity, and cost.

Electronically tuneable light source

Abstract: An electronically tuneable light source includes a source (10) of white light, an acousto-optic modulator (16) which includes a transparent medium and means (17) for generating an acoustical wave in the medium, and means for directing the collimated beam of the white light onto the medium at a preselected angle θ/2 to a line which is perpendicular to the direction of travel of the acoustical wave. Interaction of the light beam with the acoustical wave causes diffraction of the light beam. Means (22) are provided for selecting a visible band of the diffracted beam at an angle to the incident collimated beam of light equal to approximately 8.

Hybrid space/time integrating optical ambiguity processor

Abstract: A hybrid space/time integrating optical ambiguity processor in which time-sequential segments of a spatially modulated optical signal are received in a two-dimensional optical modulator. The output of the optical modulator is periodically imaged along one axis and transformed along a perpendicular axis, and the result is detected for further use. Two embodiments of the two-dimensional optical modulator are described; one utilizing an electrical-to-optical transducer and one utilizing an optical-to-optical transducer.

Controllable electro-optical modulator/phase shifter using an integrated optical interferometer

Abstract: An optical waveguide interferometer arrangement includes a single-mode optical waveguide device which diverges into two waveguide branches of identical optical length which converge into another single waveguide. The optical properties of the two branches are variable by electrical fields applied via adjacent electrodes, which are energized with a composite waveform comprising (for example) a symmetrical ramp superimposed on a square wave of the same period. The two component waveforms are in phase but of different amplitudes such that the output light is intensity modulated at a frequency which is some multiple of that of the input waveforms. Adjustment of the square wave amplitude provides the means to phase shift the optical output signal.

High Speed Guided-Wave Optical Modulators

Abstract: Design and fabrication techniques of wide-band or highspeed guided-wave electrooptic modulators are reviewed. It is shown that the traveling-wave type operation is promising because of the large bandwidth possible, even with velocity mismatching. Also the modulating electrodes, an asymmetrical planar strip line, is adequate for wide-band operation owing to the small discontinuity effect at the feeding and terminating ends.

Electrooptic polarization modulation in multielectrode Al x Ga 1-x As rib waveguides

Abstract: A single mode rib waveguide (RWG) polarization modulator is described with a measured extinction ratio ≳27 dB, a power conversion ≈0.99, and a switching voltage of 12.5 V at \lambda = 1.064 \mu m. The modulator is based on a modified step \Delta\beta -reversal configuration. Contact with CdO and an Au overlay ensures low optical losses ( \lsim1 cm-1) for both polarizations.

Recent developments in high resolution saturation spectroscopy obtained by means of acousto-optic modulators

Abstract: We present three applications of acousto-optic modulators to high resolution saturation spectroscopy. — First, an A/O modulator is used to improve both frequency and amplitude stabilization of Ar+ lasers outside the laser resonator. — Second, a new technique to detect saturation resonances is demonstrated. In this method the saturation beam is both frequency shifted and modulated and the induced modulation of the probe beam is detected resulting in a highly improved signal to noise ratio and a high degree of background cancellation. — Third, an auxiliary A/O modulator is used for line shape studies with a single laser.

Phase-modulated polarizing interferometer

Abstract: An interferometer for measuring optical surfaces which is capable of very high sensitivity. A HeNe laser light is converted into a circular polarized beam, spatially filtered and collimated. The light beam is passed through a photoelastic modulator for modulating the relative phase of the two polarization states of the optical field of the beam. The beam is then passed through a ROCHON prism which splits the beam into two orthogonally polarized components. One beam is reflected off the optical surface that is being measured and is recombined with the undeviated beam. The resulting irradiance distribution oscillates in the modulation frequency and the phase of the oscillation is dependent upon the optical path difference between the two beams. The detected interference signal is processed to extract the phase information.

Measurement and analysis of periodic coupling in silicon-clad planar waveguides

Abstract: Computer modeling studies indicate that planar dielectric waveguides clad with silicon exhibit a damped periodic oscillation in their attenuation and phase characteristics. The effect is due to a periodic coupling between the lossy, guided modes in the silicon film and the TE 0 mode of the dielectric waveguide. Experimental confirmation of the periodic coupling for a wavelength of 632.8 nm is presented. Propagation characteristics for a wavelength of 1150 nm were investigated for application in integrated optical modulators. Frequency filtering properties of silicon-clad waveguides are also examined and it is shown that the silicon thickness controls the filter response curve.

Optoelectronic system for measuring electric or magnetic quantities utilizing a dual light beam of different wavelengths

Abstract: A method and system for measuring quantities of electricity or magnetism by use of two light beams of different wavelengths and prescribed relative intensities. Emitted by respective light sources, the two beams are combined as by an interference filter to travel through a common optical fiber to a modulator station, where the beams are first plane polarized. The plane-polarized beams enter an optical modulator, therein to be modulated by the Pockels or Faraday effect in accordance with an electric or magnetic quantity to be measured. Then, after passing a quarter-wave plate as required, the modulated beams fall on a wavelength-dependent, selective polarizing filter, which polarizes only one of the incident beams into an intensity-modulated beam and which passes the other as a non-intensity-modulated beam. The beams are again sent over a common optical fiber to a beam splitter, which separates the beams from each other. Placed after the beam splitter, two photodetectors sense the intensities of the separated intensity- and non-intensity-modulated beams respectively. The electric or magnetic quantity is calculated, as by a digital computer, from the relative intensities of the intensity- and non-intensity-modulated beams falling on the photodetectors and the relative intensities of the beams as emitted by the light sources.

Linear Total Internal Reflection Spatial Light Modulator For Laser Printing

Abstract: This paper describes an alternative technique to laser scanning for nonimpact printing on a photosensitive medium. The laser light is formed into a line of illumination which illuminates a linear array of light modulators which in turn is imaged onto the photoreceptor. This array is implemented as a total internal reflection (TIR) spatial light modulator, with the electrodes and drive electronics fabricated on an integrated drive element which is placed against the total reflection surface of an electro-optic crystal. The localized change in index of refraction produced by the fringing field between each two electrodes is read out with Schlieren readout optics which image the TIR interface onto the photoreceptor. This paper will describe the basic device concept, present measurements on the required electrode spacing, length, and drive voltage, discuss analytically and experimentally the cacteristics of the relay imaging system, and show experimental results for modulators built with simple test electrode structures and a passively addressed full scale silicon device.

Apparatus for the production of a guide pattern of light beams

Abstract: An apparatus produces a guide beam pattern for a missile. The guide beam pattern comprises a plurality of bundles of light beams collectively surrounding the axis of the beam pattern. The bundles of beams are modulated differently by different electric modulating potentials from optical modulators. In order to produce the bundles of light beams without mechanical and aligning devices and to obtain a guidance system operating over the entire cross-section of the beam pattern, PLZT ceramic segments are provided as the modulators, each of which forms bundle of light beams. The segments collectively cover the entire cross-section of the beam pattern from a single source of light. A spearate modulating potential is applied to each of the segments.

Dielectric waveguide modulators at 95 GHz using LiNbO 3

Abstract: We describe electro-optic modulators at 95 GHz using LiNbO3 in an H-guide configuration. We have observed 70% amplitude modulation at l KHz in a bridge configuration, corresponding to an induced phase shift of ±29°. The prospects for improved device performance will be discussed.

Measurement and Analysis of Periodic Coupling in Silicon-Clad Planar Waveguides

Abstract: Computer modeling studies indicate that planar dielectric waveguides clad with silicon exhibit a damped periodic oscillation in their attenuation and phase characteristics. The effect is due to a periodic coupling between the lossy, guided modes in the silicon film and the TE/sub 0/ mode of the dielectric waveguide. Experimental confirmation of the periodic coupling for a wavelength of 632.8 nm is presented. Propagation characteristics for a wavelength of 1150 nm were investigated for application in integrated optical modulators. Frequency filtering properties, of silicon-clad waveguides are also examined and it is shown that the silicon thickness controls the filter response curve.

Film thickness monitoring device

Abstract: PURPOSE:To obtain a stable reflected light intensity signal without the effect of noises, by guiding the light from a powerful light source to an optical thin film and to a monitoring light receiving part which is separated from the light source through optical fibers, and guiding the reflected light from the optical thin film to a light receiving part which is separated from the light source through an optical fiber. CONSTITUTION:The light from an electronic flash discharge tube 44, which is controlled by a microcomputer 42, is guided to a monitor glass 30 in a vacuum evaporating device through an optical fiber 36 and also guided to a monitoring light detecting part 48, which is separated from the light source 44, through an optical fiber 46. Meanwhile, the reflected light from the monitor glass 30 is guided to a light detecting part through an optical fiber 38. The outputs of the light detectors 48 and 50 are processed in a processing circuit 52, and a reflected light intensity signal is inputted to the microcomputer 42. Since the powerful light source 44 and the light detecting parts 48 and 50, which are separated from the light source, are used, the stable reflected light intensity signal without the effect of noises can be obtained.

Fibre-optic phase modulator

Abstract: In the fibre-optic phase modulator according to the invention, an interfering polarisation modulation is avoided by ensuring that no state of polarisation of the light passing through is privileged in the phase modulator. Such a phase modulator can also be used as a pressure sensor.

Method and apparatus measuring absolute rotation

Abstract: Method for measuring absolute rotation with the aid of a light conductive fiber ring interferometer including a light source, a beam dividing arrangement, a light path formed by a light conductive fiber coil, an optical phase modulator which is disposed in the light path and which modulates the light circulating in the light path with a periodic, optical phase modulation at a fundamental frequency f 0 , and a photodetector for providing an electrical output signal. The light circulating in the light path or an electrical output signal from the photodetector is modulated with at least one mixing frequency f 2 in a manner such that an electrical evaluation signal results which has an evaluation frequency f 1 which is smaller than that of the fundamental frequency f 0 and which is evaluated to determine the absolute rotation of interest.

High efficiency precision laser beam switch

Abstract: An optical beam switch is provided in a multiple beam optical disc record and playback system. Current systems for very high data rate optical disc mass memory apparatus include requirements for near-continuous recording of data using two separate turntables in a single apparatus. To reduce cost and complexities in the system as well as power requirements, the optical system includes a beam switch that allows a single record laser and modulator to be shared between two turntables. In accordance with the system a half-wave plate is shifted into and out of the beam path to effect polarization change of the light beam. A polarizing beam splitter, which follows the half-wave plate in the beam path, shifts the light beam in one of two directions depending upon the polarization of the light beam or, in other words, the position of the half-wave plate.

Dynamic infrared scene projector

Abstract: A dynamic infrared scene projector for presenting cinematic, two-dimensional, spatially distributed scene data to an infrared sensor is provided comprising programmable, thermoptic infrared modulators which exploit thermally-induced changes in the infrared optical properties of a thin film of vanadium dioxide. Because of a hysteresis in the vanadium dioxide material, a stored scene can be created in the modulators by scanning a focused modulated visible or near-infrared laser beam across the thin film while it is thermally biased in the hysteresis loop. The scene is projected into the sensor by placing the modulators between an infrared source/condenser system and a system of projection optics. Dynamic scene projection is accomplished by an erase/rebias system and an optical framing switch to yield a flicker-free output. Erasing of the optical modulator is accomplished by momentarily cooling the VO 2 film to a temperature below the hysteretic loop. Rebiasing of the optical modulators is accomplished by reheating to increase the temperature of the thin film to a value not exceeding a thermal bias temperature.

Radiation picture reading system

Abstract: PURPOSE: To read picture information recorded on a storage type fluorescent material with a high S/N ratio by intercepting excitation light after irradiating the fluorescent material with the excitation light, and detecting emitted light from the fluorescent material CONSTITUTION: When a subject arranged between a radiation generator 11 and a radiation image conversion panel 13 is irradiated with radiation, a transmission image of the subject 12 is absorbed by the fluorescent material layer of the panel 13 to form a stored image Then, the panel 13 is excited by the excitation light modulated by an optical modulator 16 to radiate light of accelerated phosphorescence corresponding to the stored image This radiated light is converted photoelectrically by a photodetector 15 which turns on while delayed behind the optical modulator 16 by a specific phase and the picture is displayed on a display device 22 COPYRIGHT: (C)1984,JPO&Japio

Multibeam optical modulator and deflector

Abstract: PURPOSE:To maintain output beam intensity constant by summing up the number of the frequency components of a driving signal digitally with good accuracy by a high speed adder, and controlling the amplitudes of the respective frequency components of the driving signal by this total value. CONSTITUTION:If the signals of S1-S5 are applied from the printing signal generator 14 to the input terminals C0, A1, B1, A3, B3 of a total adder 15, and the output logics of output terminals SIGMA1-SIGMA4 of the adder 15 are set as shown in the table, one signal number out of the S1-S5 is encoded to the pure binary code of 3 bits and is outputted to the SIGMA1-SIGMA3. The OR outputs 17a-17c thereof are latched in latches 19, 20 by clock pulses 21 and a delay element 22 and are applied to an amplitude modulator 23 after timing adjustmemt and therefore the driving signal 8 of an ultrasonic optical modulator and deflector corresponding to the signal number of the on state is obtained.

Circuits with electro-optical feedback for display and a digitizer application

Abstract: A device for transforming information in electrical form into optical form, where the optical information consists of light intensity, light polarization or spectral composition varying with time. The transformation of information takes place from electrical into optical form by means of optical modulators, e.g. liquid crystals, and the transformation from optical form into electrical form is arranged to be carried out with photo-detectors, the device comprising components to control or sense said optical modulators in one, two or three-dimensions with time, and to sense or control said photo-detectors. The invention is characterized in that said components consist of one or more circuits with electro-optical feedback, in which at least one optical modulator is located in the ray path between at least one light source, for example a light-emitting diode or laser diode, and at least one photo-detector, for example a photo-resistor or a photo-diode, the photo-detector being connected into at least one electrical circuit, to which the optical modulator is connected in such a way that positive and negative feedback is obtained in a feedback loop. At least one light source is arranged to illuminate one photo-detector through one modulator and the other photo-detector through the other modulator, and one modulator is connected to the electric circuit of the other photo-detector, and the other modulator is connected to the electric circuit of the other photo-detector, thus obtaining a cross connection with electro-optical feedback.

Magnetooptical effect measuring device

Abstract: PURPOSE:To enable to measure a flash angle and ellipticity with one measuring device by applying the output electric signal of a photodetector to a coupled amplifier synchronized with at least one of the modulation frequency of an optical modulator and a frequency twice the said frequency. CONSTITUTION:A sample 6 arranged in an electromagnet 7 is irradiated with luminous flux from a light source 1 through a polarizer 4 and a circular polarized light modulator 5, and its reflected light or transmitted light is guided to a photodetector 9 through an analyzer 8. The output electric signal of the photodetector 9 is applied to a lock-in amplifier 11 synchronized with the modulation frequency (p) of the modulator 6 or a frequency 2p twice of it; when the lock-in amplifier 11 is synchronized with the frequency (p), ellipticity is measured and when with the frequency 2p, a flash angle is measured.

Multipoint fiber optic junction terminal

Abstract: In an intercom system, electrical noise interference is alleviated by interconnecting the tranceivers and receivers with the control sets via fibre optic lines. Audio signals are applied to a multiplexer which drives an optical modulator. The output of the optical modulator feeds a fiber optic line. Conversely, optical signals are fed to an optical demodulator whose output feeds a demultiplexer. Audio outputs from the demultiplexers feed the receivers and tranceivers and control sets.

Directional coupler type optical modulator

Abstract: PURPOSE:To enhance efficiency of modulation and to increase freedom of design of a directional coupler type optical modulator by a method wherein the first layer having a groove at a part thereof and having the refractive index n1, the second layer of which thickness becomes thicker at the edges of the groove part and having the refractive index n2, and the third layer and a buffer layer having the refractive index n3, n4 respectively are laminated in order on a substrat, and electrodes are provided at both end parts. CONSTITUTION:The first layer 32 (the refractive index is n1) consisting of N type AcGaAs is formed on the N type GaAs substrate 31, and the groove 33 is provided at a part of the longitudinal direction. The second layer (the refractive index is n2) is formed thereon as to make thickness thereof to become thicker at the edge parts of the groove 33. The waveguide path 35 (the refractive index is n3), the buffer 36 (the refractive index is n4) are formed samely, the electrode 37 is provided on the substrate side, and the Schottky electrode is provided at the end part of the buffer layer 36. Composition of the respective layers is selected properly as to hold the relation n3>n2>n1, n4. Accordingly efficiency of modulation becomes to favorable, and freedom of design, the allowable range of error are enlarged.

Amplification system for optical signal

Abstract: PURPOSE:To maintain the wavelength of output light in a low loss region without using any special fiber by inducing successively the Stokes light up to the n-th order by a stimulated Raman scattering effect in a single mode optical fiber. CONSTITUTION:The continuous laser light having a prescribed wavelength from a light source 11 is coupled to the output light of auxiliary light sources 13, 15, 17, 20 having the prescribed corresponding wavelengths by couplers 12, 14, 16, 18 respectively, and all of the output light of the light source 11 and the light sources 13, 15, 17, 20 are made incident to a single mode optical fiber 22. The output light of the light source 11 is induced by the output light of the light source 13, and the primary Stokes light having the output light wavelength of the light source 13 is generated by a stimulated Raman scattering effect. The output light energy of the light source 11 is converted to the light energy of the output waveform of the light source 13. The Stokes light of the 2nd, 3rd and 4th orders are generated similarly, and the amplified light signal converted to the wavelength of the output light from the light source 20 is emitted from the fiber 22. The light signal is amplified to the wavelength light in the low loss region of of the optical fiber without using any special fiber for phase matching by the above- mentioned constitution.