Showing papers on "Optical modulator published in 1978"

Calibration of optical modulator frequency response with application to signal level control.

Abstract: A swept frequency technique for measuring the frequency response of an optical intensity modulator and its application to modulation level control are outlined. The technique is precise and suited for wideband measurements. Experiments have been performed up to 2-GHz frequency. The measured response confirms the theoretical prediction. In the experiment on level control, a modulation depth flatness of ±0.3 dB was obtained for 0.1–2-GHz rf sweeping.

Polarization-independent optical switches/modulators

Abstract: Optical channel waveguide switches/modulators having polarization-independent operation are disclosed. Electrodes are disposed in proximity to the waveguide channels to provide an electric field that is primarily horizontally directed in at least one channel and an electric field that is primarily vertically directed in at least one channel. Since the different electric-field orientations electrooptically induce different changes in the index of refraction for waves of different polarization in the guides, this permits improved electrooptic control over both TM-like and TE-like modes. Embodiments of both modal interference switches/modulators and branching waveguide switches/modulators are disclosed.

Precision phase modulators utilizing cascaded amplitude modulators

Abstract: The present invention relates to a precision phase modulator wherein a carrier signal of constant amplitude and frequency and a modulating signal are applied to the two inputs of the first one of a cascade of linear suppressed-carrier amplitude modulators. Each subsequent modulator of the cascade arrangement concurrently modulates the output signal of the previous modulator of the cascade with the modulation signal. The input carrier signal and the output signal of each modulator of the cascade is tapped-off and weighted, the weighted carrier input and outputs of the even-numbered modulators and the weighted outputs of the odd-numbered modulators are separately added and are combined in quadrature to provide a phase modulated output signal.

Optical scanner and recorder

Abstract: A flat field laser recorder includes means to direct a beam from a laser through an acousto-optic light modulator, an acousto-optic light deflector/modulator, and a beam scanner, to scan-lines on a linearly-moving light-sensitive film The acousto-optic light modulator is operated by electrical oscillations which are amplitude modulated by a video information signal The acousto-optic light deflector/modulator is operated by electrical oscillations which are amplitude modulated to provide an automatic brightness control of the beam, and are frequency modulated to provide an automatic scan-line spacing control In addition, a plurality of simultaneous oscillation frequencies are selectively applied to the deflector/modulator to provide beam spot elongation control in the direction perpendicular to the scan-lines

Light retro-reflecting responser and data modulator arrangement

Abstract: A light retro-reflective responser and data modulator arrangement which, in particular, allows expected incident radiation to be reflected back with no contour field within the operating field and which enables an optical modulator of very small size to be used. It comprises a retro-reflective system formed by an optical objective and in the corresponding focal zone, a lens, an electronically controlled optical modulator, and a reflective mirror, the two latter items being produced as layers deposited on at least one face of the lens and preferably on the plane face of a plano-convex lens.

Distributed Bragg deflector: a multifunctional integrated optical device.

Abstract: The properties of wide-angle integrated optical Bragg deflectors which utilize slab-coupled optical waveguides, are analyzed. Specifically considered is the interaction that occurs, via the intermediary of a periodic waveguide perturbation, between an incident wave guide within the core region of the structure and a Bragg deflected beam guided within the slab region of the structure. The deflection efficiencies and far-field deflected-beam intensity patterns characteristic of this device configuration, which we term a distributed Bragg deflector or DBD, are derived for both T.E.-polarized and T.M.-polarized incident waves and for deflection angles between π/4 and 3π/4 rad. Following these derivations, discussion is made of the potential device applications of the basic DBD structure, including its use as an integrated optical modulator, polarizer/analyzer, beam divider, beam deflector, and intrawaveguide beam expander.

Amplitude modulation of light beam

Abstract: An optical modulator suitable for use with a collimated light beam having a moderate cross section and a fast response time and operational at relatively low voltage includes, for example, a glass prism and a smooth metal surface that are separated by an adjustable gap. The gap is filled with a medium, for example, air, having an index of refraction lower than the prism. A beam of monochromatic light is passed into the prism at a specific angle of incidence to undergo total internal reflection at the glass prism-gap interface. A change of approximately 1 micron in the thickness of the gap is sufficient to change the reflectivity from greater than 95% to essentially zero. The size of the gap is mechanically adjusted and this mechanical device determines the frequency response of the light modulation.

Multimode optical-fibre phase modulators and discriminators: I-theory

Abstract: Low-moded optical fibres are very microphonic when guiding highly coherent light. Acoustic signals applied to the fibre cause phase modulation of the optical carrier. This phase modulation is then converted to a related amplitude modulation by a fibredyne (fibre-optic self-homodyne) detection process at the photodiode. A simple theory is presented which describes the causes and characteristics of three p.m. to a.m. discriminator effects in coherent multimode fibre systems. Possible applications for fibredyne systems include data highways and low-fidelity distributed microphones.

Acoustic-optic coherent modulator and detection system

Abstract: The intensity of light beams transmitted through a tunable acousto-optic modulator is controlled by modulating the center wavelength of the filter passband. Such wavelength modulation can be obtained by modulation of the acoustic frequency or the crystal birefringence. An acousto-optic modulator of this type is sensitive to the temporal coherence of the light beam. When used in an optically coherent detection system, it can provide detection of very weak laser beams in the presence of strong incoherent background radiations.

Coherent optical correlator

Abstract: Reference scenes stored in a filter set containing an array of sets of suimposed, holographic, matched filters are optically correlated with input images displayed on an optically-addressed, liquid crystal, light modulator 34. In operation, a selected laser diode is energized to direct a polarized light beam through the collimating lens L1 to the reflecting surface of a polarizing beam splitter 35. After reflecting off the beamsplitter surface, the beam is expanded by positive lens L2 and passed to the liquid crystal modulator. There it is modulated by the input image and reflected; after which it is recollimated by positive lens L2, transmitted by the beamsplitter, and directed to a particular array location of the filter set dependent upon which particular laser diode is energized. The filter set is positioned to be in the back focal plane of lens L4 so that the Fourier-transform of the input image is incident on the particularly located, superimposed matched filter at 31. If the Fourier transformed input image corresponds to one of the superimposed matched filters the incident light beam is diffracted by that particular hologram matched filter to form a spot of light at a predetermined array location of a detector array. The optical correlator finds use as a terminal guidance system in guiding a missile to its target.

Apparatus for optically recording signals on a recording medium

Abstract: An optical recording apparatus comprises a light source for emitting a light beam, a modulator for modulating the light beam with a signal to be recorded, and an optical system for conducting the light beam thus modulated through a specific light path. The light beam has a specific cross-sectional shape which is projected onto a recording medium. The optical system also includes a restricting plate having a slit or hole for restricting the cross-sectional shape of the modulated light beam to the specific shape. A pair of light detectors are irradiated by the modulated light beam of the restricted cross-sectional shape to detect the intensities of the light beam in the vicinity of two end parts. Any difference between the outputs of the two light detectors control the optical system, in response to the detected difference, so that the light intensity distribution of the modulated beam in the restricted cross-sectional shape is maintained symmetrical with respect to the center of light distribution.

Optical Information Storage And Spatial Light Modulation In PLZT Ceramics

Abstract: Spatial light modulation in PLZT ceramics involves variation of the ferroelectric properties in conjunction with the related electrooptic, light scattering, surface deformation, and photosensitive properties of the material Several combinations of these properties have been used to design a variety of spatial light modulators Most PLZT light modulators are also capable of non-volatile storage of digital or analog information which can be read out with transmitted or reflected visible light This paper surveys several types of modulators and compares some of their important characteristics

Temperature stabilized optical waveguide modulator

Abstract: A low drive-voltage optical modulator using a Ti-diffused UNbO3 optical waveguide has been fabricated. Stabilization against ambient temperature change was realized by using a miniature halfwave plate. The halfwave voltage, 3 dB bandwidth, optical insertion loss and extinction ratio were 3·8 V (at 1·06μm wavelength), 850 MHz, 10 dB and 13 dB, respectively. A reduction scheme for the optical absorption caused by metallic electrodes, and an analysis of the modulator high frequency response are also reported.

Monolithic integration of GaAs-(GaAl)As light modulators and distributed-Bragg-reflector lasers

Abstract: Integration of an intensity light modulator and a LOC‐DBR laser on a single chip has been demonstrated. The injection‐type modulator gives a variable loss (or gain) to the laser light, coupled to it via an interconnecting waveguide, and thus modulates its intensity in accordance with the injected current of the modulator. An extinction ratio of more than 10 was obtained.

Spatial coding of laser beams by optically biasing electro-optic modulators

Abstract: Apparatus for encoding a laser beam with information indicative of position in the beam. A linearly polarized laser beam passes through a birefringent wedge which encodes a continuously varying polarization across one dimension thereof. The polarization-encoded laser beam is applied to an electro-optic modulator which induces a second harmonic component of an applied modulation signal to appear in the beam due to optical biasing by the polarization encoding. On beam center, only the fundamental appears, while going away from beam center the second harmonic appears, having a varying magnitude and phase. A polarizer transmits a linearly polarized component of the encoded beam. To encode a second dimension of the beam orthogonal to the first, a second wedge and modulator are provided. To provide discrimination between the two, the second modulator operates at a different fundamental modulation frequency. The doubly-encoded beam is applied to a polarizer which transmits a linearly polarized component of the laser beam. A receiver detects and separates the encoded signals by frequency, and the fundamental signals are frequency-doubled and compared with the second harmonic signals. A signal is developed which is a function of the magnitude and phase of the second harmonic of each encoded dimension. These signals are indicative of the receiver position in the beam, and may be used as error signals, as in a missile guidance system or the like.

Method for stabilizing a modulated light ray

Abstract: A light ray emitted by a light source and which is to be modulated by an acoustic-optical modulator element is stabilized by its intensity being detected before it enters the acoustic-optical modulator element and being used to produce correction signals. The correction signals are used to amplitude-modulate a high-frequency carrier in reverse phase to the change of intensity of the light ray, to produce corrected carrier signals. Then the corrected carrier signals are further amplitude-modulated by control signals to produce modulator signals which are used to modulate the light ray in the acoustic-optical modulator element.

Optical system for use with apparatus for contouring surfaces with coherent light

Abstract: An optical system having a spherical mirror (34 used to collect light from the surface of a turbine blade (141 or the like which is to be contoured. The spherical mirror (34) is located at an equal optical distance from both the test specimen and the linear diode array (36) so that it operates at a one-to-one magnification ratio The linear diode array (36) is positioned behind the spherical mirror (34) and it receives light focused by the mirror and reflected by a beam splitter (32) through an opening (38) 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 Identical upper and lower optical systems allow 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 (40, 31, 42 1 is provided to adjust the optical modulator (22) so that the effective intensity of the spot presented to the diode array is maintained within predetermined limits.

Acoustooptic snapshot PROM: a real-time optical-signal spectrum analyzer.

Abstract: This paper describes a system which performs real-time optical processing of electrical signals. The signals of interest are recorded in a raster format on the Itek PROM (Pockels Readout Optical Modulator), a light addressed electrooptic imaging device. The PROM is then read out with laser light to perform optical Fourier transformation, achieving spectrum analysis in near real time. A technique called acoustooptic snapshot recording is used to generate the required low distortion raster at rf bandwidths.

New coupled-waveguide optical modulators with Schottky contacts

Abstract: Coupled‐waveguide optical modulators with Schottky contacts are proposed in two waveguide configurations, namely, in the embedded‐waveguide configuration and in the rib‐waveguide configuration. It is shown that the heterostructured embedded‐waveguide device is suitable for efficient modulation and that the homostructured rib‐waveguide device has fairly small modulating power per bandwidth P/Δf in spite of its simpler structure. GaAs homostructured rib‐waveguide devices were fabricated, and optical modulation was carried out at a light wavelength of 1.06 μm.

Interferometer gyro using heterodyne phase detection without severe light source coherence requirements

Abstract: An interferometer gyro employing a coiled optical fiber includes a pair of acousto-optic modulators to modulate first and second frequencies onto two components divided from the light of a light source. The light source need not exhibit the high degree of source coherence heretofore required, and can be an incandescent bulb in many applications. The first and second modulated light components are injected in opposite or counter-rotating directions into the optical fiber wherein they experience phase changes due to the apparent change in optical length of the optical fiber upon rotation of the fiber about an axis of sensitivity. The light components are then, after being removed from the fiber, combined and compared with the signals applied at the input. The phase difference therebetween is then established to measure the rate of rotation of the optical fiber about the axis of sensitivity.

New Coupled-Waveguide Optical Modulators with Schottky Contacts

Abstract: Coupled‐waveguide optical modulators with Schottky contacts are proposed in two waveguide configurations, namely, in the embedded‐waveguide configuration and in the rib‐waveguide configuration. It is shown that the heterostructured embedded‐waveguide device is suitable for efficient modulation and that the homostructured rib‐waveguide device has fairly small modulating power per bandwidth P/Δf in spite of its simpler structure. GaAs homostructured rib‐waveguide devices were fabricated, and optical modulation was carried out at a light wavelength of 1.06 μm.

Limitations of zinc sulphide leaky waveguide electro-optic modulators

Abstract: Design criteria for relative-phase optical-waveguide modulators are established for single-crystal thin films of zinc sulphide grown on silicon. It is found that the minimum guide length is limited by voltage breakdown to 2 mm while for high frequency applications, because of the leaky nature of the guiding region, the maximum available length and thickness of zinc sulphide are the limiting factors.

Real-Time Spatial Modulators for Optical/Digital Processing Systems

Abstract: The real-time functional features of optically addressed electrooptical spatial modulators such as the Pockels Readout Optical Modulator (PROM) are described and applied to hybrid optical/digital processing of photographic information. The current and predicted performance of developed hardware and R&D devices for optical image sampling, incoherent-to-coherent conversion, stored image manipulation and computer-controlled Fourier plane filtering are presented. The utility in image exploitation of adjusting the dynamic range of a stored image under interactive

Optical sweep signal generator

Abstract: PURPOSE:To secure a flat and wide-band modulation performance by extracting the information on the modulation performance and giving a negative feedback to the information to the optical modulator driving circuit.

A total internal reflection modulator using small glancing light angles

Abstract: Techniques to amplitude modulate a light beam using the total internal reflection light modulators are now well-established. A proposition is developed to improve the performance of such a device by using the small incident glancing angles and thereby lowering the operating voltage. Experimental observations are included.

Space Light Modulators

Abstract: Many characteristics of systems including information transmittance of coherent optical processing systems depend on space light modulators (SLM) characteristics to a considerable degree. Therefore it is necessary to have a satisfactory match between SLM characteristics and parameters of a system including SLM. Some of these parameters were evaluated in [1–3], the other papers [4–6) give characteristics of SLM. However, it is evident that the problem of matching SLM with other parts of systems of processing, recording and.reconstruction of information needs studying.

Beam position detecting device for recorder

Abstract: PURPOSE: To improve the scanning speed of incident lights and to reduce the discrepancy of a synchronous timing by guiding the scanning light into and out of an optical scanner several times with respect to a beam detector. CONSTITUTION: The modulated light from an optical modulator is scanned with a rotary polygonal mirror 4, and the output light is converted by an f-θ lens 8 such that the scanning speed upon a photosensitive element 5 has a linearity. On the other hand, the lens 8 is so arranged that the beam spot of the scanning light from the polygonal mirror 4 is focused upon the photosensitive element 5. The end portion of the scanning light from the lens 8 is cut by a mirror 9, and the remainder is guided through a mirror 10 into the mirror 4 so that the reflected light is detected by a beam detector 6. At this time, the mirror 10 is so arranged that the reflected light from the mirror 9 does not pass through the lens 8 and that the second reflected light from the mirror 4 does not enter the lens 8. thus, the discrepancy of the synchronous timing can be deduced with the use of a simple construction. COPYRIGHT: (C)1979,JPO&Japio

Dielectric and Optical Properties of Thin Films.

Abstract: : For several years, Itek Corporation has been developing an electro-optic imaging device, the Itek PROM (Pockels Readout Optical Modulator). The device required an insulating layer, which acts with an electro-optic photoconductor to provide a voltage division that is detectable through the Pockels effect. The original insulating layer was Parylene C, a vapor-deposited linear polymer. The purpose of this paper is to identify other insulating or blocking layers that possess higher dielectric constants and greater breakdown fields, are more durable, and are capable of being vacuum evaporated. The materials investigated were SiO2, Al2O3, Ta2O5, ZrO2 and TiO2.