Showing papers on "Optical modulator published in 1977"

Acoustooptic modulator for optical fiber waveguides

Abstract: An acoustooptic modulator is disclosed in which light may be modulated while propagating through an optical fiber waveguide through the use of focussed acoustic waves. The modulator is formed by encircling a portion of the optical fiber waveguide in an optical communications system with an acoustic transducer. Due to the encircling of a portion of the waveguide by the transducer, the acoustic waves which are generated in the optical fiber waveguide material are focussed inwardly to the center so that the energy densities where acoustooptic modulation occurs are high. Therefore, the acoustic driving powers and modulation efficiencies are highly favorable.

Bias control circuit for light modulators

Abstract: A bias control circuit for light modulator includes a feedback control loop through which a measure of the modulated laser beam is processed to derive an error correction signal which is superimposed on the normal bias potential to shift the bias point in the same direction as the direction of shift of the operating curve of the light modulator due to the heat generated therein during operation. A feed-forward control loop is also provided to cancel an error signal in the feedback control loop resulting from an intentional gradial variation of the laser beam intensity prior to the modulation so that the average light intensity of the modulated laser beam is correspondingly varied.

Multimode optical modulator/switch

Abstract: A multimode optical waveguide having refractive index n, width a, and length L is provided with branches on either side of each end and has an electrode pattern capable of differentially delaying the even modes and the odd modes of light of wavelength λ in the waveguide when voltage is applied. When the length L is a half-critical length, calculated to be (2na 2 /λ), or multiple thereof, the device acts as an amplitude modulator or switch. At least one of the electrodes typically is very slender and has a width less than about one-fourth the waveguide width a, so as to achieve different effects on the different modes by causing a laterally nonuniform but bilaterally symmetric refractive index change in the waveguide.

The Electrogyration Effect in Crystalline Quartz

Abstract: A linear electrogyration effect has been identified in crystalline α -quartz. This is an effect whereby the polarization direction of a linearly polarized light wave propagating in the crystal is rotated by the application of a transverse electric field. It is thus an electric field dependence of the optical activity in quartz. The third rank tensor characterizing the effect has been fully quantified. The effect has potential usefulness in measurement transducers and in optical modulators.

Closed loop laser noise elimination for optoelectronic recording

Abstract: In an optoelectronic audio/video recording system wherein a laser beam which is subject to undesired broad-spectrum noise is intensity modulated by a light modulator with an audio/video intelligence signal, a feedback control loop is provided including a half-silvered mirror disposed in the path of the beam to transmit a greater part of the light energy to the light modulator and to reflect some of the light to a photoelectrical transducer to convert the reflected light into corresponding electrical signal, a plurality of filter-amplifier circuits for dividing the frequency spectrum of the signal into a plurality of separate frequency bands to provide outputs accentuated such that each output has a particular amplitude versus frequency characteristic corresponding to a portion of the noise spectrum, and a second light modulator disposed in the path of the beam incident to the half-silvered mirror to effect the intensity modulation of the beam with the outputs from the separate filter-amplifiers to suppress the undesired broad-spectrum noise, to an acceptable level.

Waveguide optical modulator

Abstract: Light propagating in a waveguide is modulated by deforming a cladding on at least one surface of the waveguide. The cladding has a thickness at least equal to the exponential depth of the evanescant field of the propagating light. A pair of electrode means is used to impress a field across the waveguide and cladding so that the cladding is deformed to a degree sufficient to interfere with the evanescant field and to modulate the propagating light.

Optical inspection system employing spherical mirror

Abstract: An optical system having a spherical mirror is used to collect light from the surface of a turbine blade or the like which is to be contoured. The spherical mirror is located at an equal optical distance from both the test specimen and the linear diode array so that it operates at a one-to-one magnification ratio. The linear diode array is positioned behind the spherical mirror and it receives light focused by the mirror and reflected by a beam splitter through an opening in the center of the mirror. None of the optical elements of the inspection system are located in the plane of movement of the test specimen so that even particularly long items such as a helicopter rotor blade can be contoured. Indentical upper and lower optical systems allows both surfaces of the test specimen to be contoured simultaneously and each system is independently operable and oriented to prevent optical interference. An automatic gain control is provided to adjust the optical modulator so that the effective intensity of the spot presented to the diode array is maintained within predetermined limits.

Optical inspection system employing dual path pickup system with single spherical mirror

Abstract: An optical system having a single spherical mirror for collecting light from two directions combined by a beam splitter after the light has been scattered from the surface of a turbine blade or the like. The spherical mirror is located at an equal optical distance from both the surface of the test specimen and a linear detector array so that it operates at a one-to-one magnification ratio. The linear detector array receives light focused by the mirror along a path folded by the beam splitter. This arrangement is helpful in contouring the surface of a turbine blade near a vertical obstruction such as a shroud of a turbine blade since the collection axes of the pickup legs view the incident spot from different directions. None of the optical elements of the inspection system are located in the plane of movement of the test specimen so that even particularly long items such as a helicopter rotor blade can be contoured. Identical upper and lower optical systems allow both surfaces of the test specimen to be contoured simultaneously. An automatic gain control is provided to adjust the optical modulator so that the effective intensity of the beam incident on the detector array is maintained within predetermined limits.

An application of Pb(Zr, Ti)O 3 Ceramic to opto-electronic devices

Abstract: A lead-zirconate-titanate ceramic is used in an electrically controllable diffraction (ECD) grating for reflection of parallel polarized light. The ECD grating used consists of a PZT ceramic with ten pairs of interdigital electrodes having 400 μm period on its surface. The characteristics of the grating and its application to an optical modulator are demonstrated experimentllly with a He−Ne 0.63 μm laser, obtaining a modulation of 60% with the applied peak voltage of 60 V at 24 kHz signal for the incident angle of 60°.

Multiplexed optical communication system

Abstract: The system permits the multiplex telecommunication through the medium of an optical carrier wave. The system comprises a source of coherent light whose optical spectrum is dispersed in an optical device comprising a pair of diffraction gratings. A plurality of light modulators are disposed in the path of the spread out beams and controlled by electric signals which carry items of information. Output optical means collect the modulated spectral components.

Liquid-Crystal Electro-Optical Modulators For Optical Processing Of Two-Dimensional Data

Abstract: In the face of the increasing need to be able to process two-dimensionally organized data, the present electronic digital processing and coherent optical data processing techniques have proven inadequate. The potential advantage of coherent optical data processing (CODP) is that, as opposed to the serially organized electronic digital computers, it can simultaneously process data on a very large number of parallel channels. The limitation to the usefulness of CODP has been the lack of a high-speed, high-spatial-bandwidth input device. This paper describes the development of a new CODP input device capable of the required speed and spatial bandwidth. The device employs an integral CCD input to accept serial electronic signals and a liquid-crystal light valve output for CODP.© (1977) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Spatial Light Modulators And Their Use In Optical Data Processing

Abstract: Real time and reusable coherent spatial light modulators for use in optical data processing are summarized. The status of the six leading candidate real time devices that have seen use in coherent light are included. Three electron beam addressed devices are described (the dielectric oil film valve, the thermoplastic optical phase recorder, and electron beam DKDP). Three optically addressed spatial light modulators are also included (the liquid crystal lightvalve, the PROM, and photo DKDP). The operation, specifications, applications, and remarks on directions for future research are included for all of these devices.© (1977) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The dispersive modulator - A new concept in optical pulse compression

Abstract: A description of a new method of optical pulse compression, named the dispersive modulator, is given. In this device, amplitude modulation and temporal compression of light were achieved by passage through a Stark-modulated, near-resonant dispersive medium. The relationship between the dispersive modulator and the chirp compression scheme is discussed. Experimental results on modulation of 10-μ CO 2 and N 2 O laser light, including a case where 100 percent modulation was observed, are presented.

Design and comparison of single-mode planar and ridge type electro-optic waveguide modulators

Abstract: Electro-optic waveguide modulators utilizing phase retardation of two orthogonally polarized optical modes in LiNbO3 and LiTaO3 waveguides have been designed taking into consideration the optical field distribution in the waveguides and the electrical properties of the electrodes. The analysis has revealed that a driving-voltage to frequency-bandwidth ratio of 1 V/GHz is attainable at the wavelength of 1.05 μm using presently available embedded and ridge waveguides. Improvement in waveguide fabrication techniques may reduce the ratio by at least a half. Thus, LiNbO3 and LiTaO3 waveguide modulators are considered to be promising candidates for practical application to single-mode optical-fibre transmission systems of higher than 1 Gbit/s.

Polarization-Dependent Light-Scattering Measurements Using An Electro-Optical Modulator-Based Instrument

Abstract: We have developed an instrument which permits the direct measurement of all sixteen ele-ments of the 4 x 4 phase matrix. This is accomplished using four electro -optic modulatorsto modulate the polarization of the incident and scattered light. Synchronous detectionis then used to measure each of the sixteen individual matrix elements. The instrument andbrief theory of its operation will be discussed, along with possible applications.IntroductionThe determination of the complete light scattering properties, including all polariza-tion effects, of a light scattering medium has received little experimental attention.We have knowledge of only three instruments, other than our own, which have been construc-ted for this purpose. Of these, only ours makes use of polarization modulation. The other three use conventional polarizers and quarter -wave plates to effect the measurements.It is this difference which makes our instrument superior.To facilitate the discussion of polarized light, it is convenient to use the Stokes

Improved Design and High-Frequency Modulation Experiment of the Coupled-Waveguide Optical Modulator withp-nJunction

Abstract: Improved design theory of the coupled-waveguide optical modulator with p-n junction and planar guides is presented with some design examples of GaAs homojunction and GaAs–AlxGa1-xAs heterojunction devices. It becomes clear that P/Δf (modulating power per unit bandwidth) decreases a great deal by reducing the carrier concentration and the width of guide layer. High-speed pulse and high-frequency modulation experiments have been carried out at 1.06 µm using improved GaAs homojunction devices with mesa-etched guides (50 µm wide and 2 mm long) and reduced junction capacitance. At reverse bias of 15 V, the half power bandwidth is 670 MHz for load resistance of 50 Ω, and is in good agreement with the calculated value. Furthermore a new improved structure with strip-loaded channel waveguides is proposed. Some designed examples with more reduced P/Δf are shown.

Modulating and deflecting device of light beam

Abstract: PURPOSE:To automatically correct power fluctuations and shading of a scanning beam by providing a light modulator for correction between a light source and an optical light modulator. CONSTITUTION:A light modulator 3 for correction is provided between a light beam source 1 and an acousto-optic modulator 5. As a result, a light beam 2 passes through the light modulagor 3 for correction and is converged by a converving lens 4, after which it is divided to first order diffracted light and zero order diffracted light by the acousto-optic light modulator 5. The divided light passes through a rotary polyhedral mirror 8 and beam splitter 10 and is radiated to the surface to be scanned 13. At the same time, part thereof is detected with a detector 15 and is compared with a reference value in a comparator 16. The deviation thereof is fthen inputted to the light modulator 3 for correction. Hence, the power fluctuations of the scanning beam caused by the variations in the reflectsnces of the mirror faces of the rotary polhedral irror 8 and the shanding based on the vignetting of the beam by the ridges of the mirror faces are auftomatically corrected.

Intensity modulation of light transmitted in curved optical fibres

Abstract: Coupled-mode theory is used to explain the intensity modulation of transmitted light which results from small changes in the radius of curvature. It is shown that the mode coupling induced by bends in small-V fibres introduces an uncertainty into light-transmission measurements.

Automatic polarisation analysis appts. - has two optical modulators controlled by square wave AC

Abstract: The automatic polarisation analysis system has alight source (1) and a collimator lens system (2) followed by a monochromatic filter (3) passing light of 546 m u. There is a polariser whose optical axis is rotatable, it is driven by a servomotor. The polariser is followed by a quarter wave plate (2). The test sample (5) follows the quarter wave plate and is followed by a light modulating crystal (6). This is controlled by AC from a switching network (11). A square wave is produced. The first crystal (6) is followed by a quarter wave plate (7), a second crystal modulator (6') and an analyser (8). Lenses (9) focus the light onto a photocell (10).

Light beam switching and modulation using a built-in dielectric channel in LiNbO 3 planar waveguide

Abstract: The results of light beam switching and modulation experiments utilizing electrooptic control of the refractive index of a built-in dielectric channel in a Y-cut LiNbO3 planar waveguide are reported. The resulting device is capable of simultaneously providing a combination of desirable characteristics.

Revolving drum optical modulator for moving target location - fixes direction of incident beam using intermediate annular strip corresponding to common factor of frequencies of outer annular strips

Abstract: A revolving drum optical modulator used to locate a moving target, has on its wall two annular strips (A, C) with regions (a, c) through which an optical beam may pass. An incident beam is transformed into two amplitude modulated beams with fundamental frequencies FA and Fc which correspond to the distribution of the two regions (a, c) The two strips (A, C) are separated by an intermediate annular strip having regions (b) through which the beam may pass. The fundamental frequency of the beam intercepted by this intermediate strip is a common factor, pref. the highest common factor, of the frequencies of the beams intercepted by the two other strips.

Improved contrast for acousto-optical modulators by using spatial filtering

Abstract: As a means of modulating lasers, acousto-optical cells are a relatively simple and generally satisfactory solution. When used in the zero-order mode to modulate the undiffracted light, they do suffer from the disadvantage that the maximum contrast between the on and off states is typically 10 to 1. This cannot be improved by increasing cell length because it orginates from rediffraction of once-diffracted light. By spatial filtering the light between passes through multiple cells, or alternatively, multiple passes through a single cell, this contrast can be improved by removing the once-diffracted orders before they can be rediffracted into the zero-order beam. Experimentally we have demonstrated an improvement of a factor of 10 in contrast by using two cells, each of which by itself produces only a 10 to 1 contrast. In addition to using filters consisting of stops and apertures, it is possible to achieve similar results with polarization filters. Multiple applications of this filtering improve contrast as the power of the contrast of a given step, thus contrast of modulation in zero order can be improved to any desired degree.

Acoustic optical modulator

Abstract: PURPOSE:To provide an acoustic optical modulator for laser mode rock of highly efficient and low power characteristics by forming a co-focus resonator for sound wave with a piezo-electric crystal having an acoustic optical effect.

Optical information recording system

Abstract: PURPOSE:To provide an optical information recording system, in which there are provided in the opticalpath of a laser beam a aplurality of optical modulators having a colsed loop circuit for removal of the laser noises and drifts so as to remarkably inprove the S/N ratio of the recorded signals in an information recording disc.

Semiconductor optical modulator

Abstract: PURPOSE:To obtain small sized and effective unit by forming a vacant layer by means of semiconductors located at the both ends of the curved semiconductor optical conduction path.

Waveguide type optical modulator

Abstract: PURPOSE:By making a part of the section between two linear optical waveguides arranged in a close contact a concave shape and mounting an electrode at a part of the oncave section at least, a modulator of which optical propagation loss is few and insertion loss is few shall be constructed.

Highly Sensitive Optical Modulators with Distributed Bragg-Reflectors

Abstract: Optical modulators with distributed Bragg-reflectors using the electro-optic effect are investigated by applying coupled mode equations. The modulation characteristics are calulated for various values of the modulator length, the optical wavelength, and the coupling coefficient of the corrugated waveguide. It is shown that the modulated light intensity changes from 0.9 to 0.4 as the applied voltage changes from 2.5 V to 8 V, provided that the modulator length and the coupling coefficient are chosen appropriately. Also, modulation characteristics, where the optical wavelength λ shifts from the Bragg condition λ0, and stability of the optical wavelength are discussed to obtain a highly sensitive optical modulator.

Wideband Thin Film Modulators For Optical Communications

Abstract: The development of optical modulators and switches is reviewed with emphasis placed on the comparison of conventional bulk modulators and thin film devices. It is shown that the primary motivation for such a development is the major reduction in the electrical drive power requirements for high bandwidth devices. The thin film devices are first discussed with acousto-optic and electro-optic devices in LiNb03 and LiTa03 given primary emphasis. The application of these devices to high speed scanning is shown to be quite promising. The problems of efficient coupling and optical power handling are shown to be important areas where improvements have been made. The development of directional couplers is then discussed with stress placed on the cross-talk performance and speed of the devices. The problem area of fiber-to-channel coupling is also discussed.© (1977) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.