Showing papers on "Optical modulator published in 1970"

Modulators for optical communications

Abstract: This paper reviews the field of high-speed small-aperture modulators for applications in optical communications, with emphasis on electrooptic modulation. The capabilities and limitations of electrooptic modulators are discussed based on a review of the physical origin of the electrooptic effect. Thermal and photoconduction phenomena, which may severely limit the operation of practical devices, are emphasized. The modulation power and bandwidth limitations using various schemes of electrooptic interaction are derived and compared. It is shown that lumped modulators are capable of efficient modulation for bandwidths up to about 1 GHz for visible wavelengths and are also attractive for their simplicity. For broader bandwidth capability the traveling wave or zigzag types of interaction become more efficient but with added complexity. Finally, acoustooptic and magnatooptic modulators are briefly discussed and compared with electrooptic modulators.

Wide-band optical communication systems: Part II—Frequency-division multiplexing

Abstract: Frequency-division multiplexing techniques offer means for circumventing the bandwidth limitations of optical modulators and detector. Practical broad-band long-distance optical communication system of this type appear feasible and some possible embodiments are described. Calculations are made to determine the approximate information capacity and other characteristics of several 4000-mile repeaterad systems.

Light beam polarization modulator

Abstract: A parallel cell electro-optical phase modulator is used in combination with two birefringent crystals and a half wave plate to produce polarization modulation of an incident light beam. A first birefringent crystal provides a lateral relative displacement between the two orthogonal components of the incident light beam to form two spaced light paths, one through each of the respective electro-optical crystals. The half wave plate rotates the linear polarization of the orthogonal components to allow a second birefringent crystal to recombine the orthogonal components into a single light beam.

Acoustooptic interactions and devices

Abstract: A review of recent advances in the understanding of the interaction of light and ultrasonic waves in solids and liquids is presented, emphasizing the Bragg diffraction regime wherein the diffracted optical energy is confined near one angular direction. The usefulness of optical beam probing techniques, using laser light sources, for investigating such subjects as ultrasonic attenuation and diffraction, acoustic nonlinear phenomena, magnetoelastic interactions, and photoelastic properties of materials is described. The application of the acoustooptic interaction for the design of devices intended to perform optical information processing functions is also mentioned. Present applications include optical modulators, switches, sequential scanners (such as are useful for television display), random access optical deflectors, and optical correlators. An attempt is made to describe the assets and liabilities of acoustooptic devices and to speculate concerning their future in the practical world.

A Coherent Optical Computer System Using the Membrane Light Modulator

Abstract: A 32-input coherent optical computer system is described which is driven by a membrane Light modulator (MLM). The MLM has an active area of 4 by 4 mm containing a 32 by 74 array of 2368 38-pm diameter light modulating elements. The optical computer calculates the one-dimensional Fourier transform over 32 points of a phase function in 1 ?s. Both the theoretical and actual operating characteristics of the computer are presented.

Apparatus for measuring current in high-voltage lines

Abstract: An apparatus for measuring the current flowing through a highvoltage line and transferring the result to a low-potential locality has at the high line-voltage side a magnetic or electric field which varies in dependence upon the current to be measured. An optical modulator controlled by the field variations is interposed in one of two beams of coherent light to modulate this one beam relative to the other. An interferometer or the like device superimposes the modulated and unmodulated beams to produce an interference fringe pattern of alternately bright and dark stripes which travel from one to the other side of the pattern area. Light conductors transmit the resulting optical pulses to photoelectric sensors on low potential. The corresponding electric pulses control a device for counting the interference stripes. At any time the count corresponds to the then obtaining intensity value of the current.

Efficient octave-bandwidth microwave light modulators

Abstract: The use of wide-bandwidth interdigital microwave circuits to provide electrooptic modulation of light is discussed. Two models employing lithium niobate crystals of different aspect ratios have been constructed and tested. Both have nominal bandwidth from 1.0 to 2.0 GHz but actually give somewhat greater modulation bandwidth. Single-pass modulation tests made using 6328-A light at RF drive power level of 5 watts show that 30 percent modulation depth over a 1.5-GHz frequency band is obtained for one model while approximately 50 percent modulation depth over a 1.1-GHz band is obtained for the other. These results show excellent agreement with analytical predictions. Measurement techniques are also discussed.

Acousto-optic band reject light filter and apparatus using same

Abstract: An acousto-optic band reject light filter is disclosed. The light filter includes an optically anisotropic medium, such as a birefringent crystal, in which an acoustic wave is excited at a certain selected radiofrequency corresponding to a selected optical frequency to be rejected. The crystal is disposed to receive an incident light beam containing the selected optical frequency to be rejected. The light beam is collinearly diffracted on the acoustic wave within the optically anisotropic medium to diffract light of a first polarization and of the selected optical frequency related to the acoustic frequency into light of a second polarization. The diffracted light beam is then passed through a polarization analyzer to reject from the diffracted light beam light of the second polarization while retaining in the diffracted light beam light of the first polarization. The selectable frequency in the light beam which is to be rejected can be tuned over a wide band by tuning the frequency of the acoustic wave within the crystal.

Acousto-optic light spectrum analysis

Abstract: An acousto-optic light spectrum analysis method and apparatus is disclosed. A linearly polarized unknown light beam to be spectrum analyzed is collinearly diffracted on an acoustic wave in an optically anisotropic medium to diffract light of the first linear polarization and of a frequency related to the frequency of the acoustic wave into light of a second polarization. The diffracted unknown light beam is polarization analyzed to separate the light of the second polarization from the light of the first polarization. The frequency of the acoustic wave is swept and the light of the second polarization is detected as a function of the sweep to obtain a spectrum analysis of the unknown light beam. The output spectrum of the unknown light beam is calibrated by switching a known light source through the acousto-optic system for calibration of the output spectrum.

Refraction-measuring apparatus utilizing common optical modulator

Abstract: Modulated light containing components of two different wavelengths is transmitted over a path and the modulation phase difference at the receiving end of the path is determined. A common optical modulator is used for demodulating both of the received light components in order to minimize differences in phase between these two components.

Device for measuring currents in a high voltage conductor including a controlled optical arrangement

Abstract: A control unit derives a control magnitude from a current to be measured in a high voltage conductor. A controlled optical arrangement utilizes the control magnitude for converting a light beam into light pulses having an information content corresponding to the current to be measured. A light beam is directed into the controlled optical arrangement. A receiver converts the light pulses to output signals corresponding to the current to be measured. The controlled optical arrangement comprises an electro-optical or a magneto-optical device including a double refractor or a polarization plane rotator for transverse double refracting and rotating of the plane of polarization of the light beam. A polarizer polarizes the light beam after rotation of the plane of polarization thereof.

Resonant self-pulsing acousto-optical modulator

Abstract: A self-pulsing acousto-optical modulator system produces acoustical pulses in the modulator which are capable of deflecting an optical beam. Multiple resonances in the modulator are phase locked by means of an electrical feedback path, thereby producing a continuous series of traveling pulses in the modulator. When this modulator system is placed in a laser cavity it causes the laser beam to be repetitively switched out of the cavity, producing laser pulses.

Optimisation of electro-optic crystal modulators

Abstract: A general method is given for the optimum design of electro-optic light modulators in respect of minimum halfwave voltage for crystals of any class. Examples are given for materials of class 42m (XDP).

Distortion and its compensation in a varactor-controlled frequency modulator

Abstract: The nonlinearity of the voltage-frequenc characteristic of a frequency modulator is a factor of primary importance when designing, for example, high-quality modulators for large-capacity microwave links. The nonlinearities of a varactor-controlled oscillator are derived. A theory of various distortion-conpensation circuits is developed. Distortion compensation is applied to push-pull modulator, and 1800–2700-channel radio links, are shown.

Optical correlation apparatus

Abstract: An optical correlation system in which an optical modulator modulates a collimated monochromatic beam of light in accordance with an input reference signal to the modulator. An output light beam having sinusoidal light intensity variation versus phase retardation characteristics with the modulation quiescent operating point being positioned within a predetermined region of the characteristic by means of a fixed wave filter having a spatial pattern thereof applying amplitude and/or phase shift to the elements of the beam is applied to a cathode ray tube whose scanning beam is modulated in accordance with information, such as a radar signal, to be correlated with the reference signal source as modified by the modulator and wave filter to produce an output having a multiplication of the two signals.

Novel type of cut for KDP crystals for low-voltage light modulation

Abstract: It is shown that a new type of cut of KDP, ADP and their isomorphs is useful for low-voltage operation of a light modulator.

Light modulator for producing light beam having sinusoidally varying intensity

Abstract: A light modulator for producing a light beam having a sinusoidal intensity modulation comprising a rotating, uniaxial crystal disposed between a pair of polarizers having mutually orthogonal transmission axes. To produce a light beam having a sinusoidal intensity modulation of a substantially constant modulation frequency, an unmodulated light beam is passed through the modulator only during some portions of each revolution of the uniaxial crystal. Passage of the light beam through the modulator during the portions of each revolution of the uniaxial crystal is achieved either by an electro-optic crystal plus a polarizer located between the source of the unmodulated light beam and the polarizer nearer to the source or by a rotating, slotted cylinder encircling the rotating crystal and having the same angular velocity as the rotating crystal.

An experimental laser-photochromic display system

Abstract: A laser display system is described which can produce real-time television standard pictures, or alternatively reversible, stored images using photochromic film. The development of components for the modulation of laser beams is also described. The spatial modulators are acousto-optic diffraction cells, and the amplitude modulator uses the electro-optic effect in ADP.

Extinction ratio of electrooptic light modulator

Abstract: The dependence of the extinction ratio on the angle of inclination between the end surfaces of electrooptic crystals with natural birefringence and on the light spot size is described in the electrooptic light modulators.

Lighting device comprising two optical systems and a radiation sensitive detector

Abstract: A sighting device equipped with two optical systems which each comprise an optical modulator and a lens and the optical axes of which intersect at an acute angle and with a radiation-sensitive detector is described. It is shown that by inserting auxiliary radiation sources between the lenses of the optical systems and the radiation-sensitive detector and by using the lenses as catadioptric systems for imaging the auxiliary radiation sources asymmetrical errors can be eliminated.

The design of broadband light modulators

Abstract: Curve sets are presented for the design of collinear travelling-wave light modulators using KDP, KDA, ADP(r63), ADP(r41), LiNbO3, LiTaO, as electro-optic materials. The transverse dimensions ratio, the characteristic impedance and the bandwidth-length product are plotted versus the velocity mismatch. The attenuation of modulating signal is plotted versus mismatch for the peak voltage and modulating power for different lengths of the electro-optic materials. Examples of the use of these curves are reported.

Acoustically absorbent mounting method for optical modulator

Abstract: Acoustical ringing which results from piezoelectric effects in an electro-optical modulator is suppressed by mounting the modulator crystal between massive, acoustically absorbent, support members which also provide an electric circuit interface for applying electric signals to the modulator. Solder provides such an absorbent mounting for a lithium tantalate electrooptical modulator crystal. Both solder support members are applied during the same heating interval and permitted to cool simultaneously. In one embodiment the solder application is accomplished in a first step wherein mounds of solder are applied adjacent to the crystal at a first temperature and in a second step wherein additional solder is applied at a lower temperature between the crystal and the solder mounds.