Showing papers on "Optical modulator published in 1984"

High‐speed optical modulation with GaAs/GaAlAs quantum wells in a p‐i‐n diode structure

Abstract: A new type of high‐speed optical modulator is proposed and demonstrated An electric field is applied perpendicular to GaAs/GaAlAs multiple quantum well layers using a ‘‘p‐i‐n’’ diode doping structure of 4‐μm total thickness The optical absorption edge, which is particularly abrupt because of exciton resonances, shifts to longer wavelengths with increasing field giving almost a factor of 2 reduction in transmission at 857 nm with an 8‐V reverse bias The shifts are ascribed to changes in carrier confinement energies in the wells The observed switching time of 28 ns is attributed to RC time constant and instrumental limitations only, and fundamental limits may be much faster

Optical-Image Correlation With A Binary Spatial Light-Modulator

Abstract: The use of a binary, magneto-optic spatial light modulator as an input device and as a spatial filter in a VanderLugt correlator is investigated. The statistics of the correlation that is obtained when the input image or the spatial filter is thresholded are estimated. Optical correlation using the magneto-optic device at the input and Fourier planes of a VanderLugt correlator is demonstrated experimentally.

Velocity-matching techniques for integrated optic traveling wave switch/modulators

Abstract: We propose and analyze a new technique for achieving velocity match between the traveling wave electrical drive and guided optical signal for modulators in substrates for which there is an inherent mismatch. The traveling wave electrodes are laterally shifted periodically to reverse the direction of the applied electric field within the optical waveguide which exactly compensates for the polarity reversal caused by the microwave-optical walkoff. Consequently, the electrooptically induced phase shifts of each section add in phase and several sections can be used to reduce the required drive voltage at the design frequency. This artificial velocity-matching technique moves the mismatch-limited bandwidth to an arbitrarily high design frequency. In addition, we extend the new concept of phase reversal and the previously suggested technique of intermittent interaction by proposing electrode structures with large inactive to active aspect ratios. This generalization provides increased flexibility for manipulating the total available bandwidth to, for example, allow efficient modulation by a train of arbitrarily short electrical pulses. These techniques are ideally suited for several proposed integrated optic devices, including picosecond samplers and gates, which require strong overmodulation at a single high frequency.

Linear interferometric modulators in Ti:LiNbO 3

Abstract: Measurements are described on asymmetric interferometric channel waveguide modulators in Ti:LiNbO 3 at 0.83-μm wavelength. Modulation voltages and device transmissions are compared for X-, Y- and Z -cut substrates. An interferometer intrinsic phase bias of \sim\pi/2 allows linear modulation and we have observed linearity over 67 dB for a 3-kHz bandwidth. This dynamic range is limited by optical damage effects, of which the photovoltaic effect is the most critical.

Multi-spot modulator using a laser diode

Abstract: A multi-spot light modulator using a laser diode is disclosed in which a single light pulse from the laser diode generates a multi-spot image of a data pattern, each spot corresponding to an active bit of the data pattern. The ability of a pulsed laser diode to generate a narrow light pulse is used to image an acoustic wave corresponding to the data pattern without the normal degradation in resolution caused by the motion of the acoustic wave.

Sequential optical logic implementation

Abstract: An optical system that performs sequential binary logic operations is described. The system consists of a spatial light modulator (SLM) used to provide a nonlinear threshold response and a computer-generated hologram to provide interconnections between logic gates. A 2-D array of logic gates with binary inputs and outputs is formed on the active surface of the SLM. These gates are interconnected by a 2-D array of subholograms, one for each gate. Arbitrary logic circuits consisting of NOR gates and inverters can be implemented, and the system can be reconfigured by changing a single holographic element. The system is demonstrated using a twisted-nematic liquid crystal light valve as the SLM. A test circuit is implemented that includes a synchronous master–slave flip-flop and an oscillator consisting of five inverters in a feedback loop. Experimental results of this test circuit are presented.

Fiber optical modulator and data multiplexer

Abstract: A data gathering system comprising a single optical fiber having one or more modulators formed thereon, means for launching into the fiber an interrogating light pulse which propagates in a first direction, means for generating at each modulator an optical return signal which propagates in the fiber in a second direction opposite the first direction and which has an intensity which is variable in response to variations in an external signal incident at the modulator, and means for detecting and processing each such return signal. The return signal comprises a portion of the interrogating light pulse which is coupled into the fiber in the second direction via evanescent coupling. The return signal from each modulator (or array of modulators) is identified via time division multiplexing. A signal processing means may be coupled to the fiber for generating a unique return signal from each of one or more modulator arrays, each array comprising a selected subset of the modulators. In a preferred embodiment, each modulator comprises a looped section of the fiber having a coupling region in which the distance between adjacent fiber segments is variable in response to variations in an external signal incident thereon. In another embodiment, each modulator comprises a short fiber segment positioned adjacent to the main fiber and separated therefrom by a distance variable in response to pressure changes incident on the modulator.

Traveling‐wave electro‐optic modulator with maximum bandwidth‐length product

Abstract: A traveling‐wave Ti‐indiffused LiNbO3 guided‐wave Mach–Zehnder interferometric modulator has been fabricated and characterized at λ=0.85 μm. The modulator achieves the theoretical 3‐dB linear small‐signal bandwidth limit of 16 GHz for a 4‐mm‐long interaction length. With a ±2.25‐V drive signal, an extinction ratio of 22 dB is achieved. Linear small‐signal measurements made with a swept‐frequency technique are compared to previously reported measurements.

Broad-band guided-wave electrooptic modulators

Abstract: Lumped-element Mach-Zehnder interferometric modulators have been designed, fabricated in LiNbO 3 , tested and analyzed. These modulators had 3 dB bandwidths from 280 MHz to 2.75 GHz and V π 's from 1 V to 4 V, respectively. A simple RLC equivalent circuit is utilized to model the packaged modulator performance and results are compared with those measured using a swept-frequency technique. The model is seen to break down at the higher frequencies due to a frequency-dependent resistance and the electrode and parasitic inductances are seen to limit the overall modulator performance. The effects of varying the electrode capacitance, resistance, or inductance on modulator performance are demonstrated.

Optical-level shifter and self-linearized optical modulator using a quantum-well self-electro-optic effect device.

Abstract: We demonstrate an optical-level shifter and a modulator whose transmission varies linearly with drive current, both based on a new, negative-feedback mode of operation of the recently discovered quantum-well self-electro-optic effect device. The system is compatible with both laser diodes and low-power semiconductor electronics and is applicable in both analog and digital optical processing. An extension of the system gives inverted, linear modulation of a coherent beam by an incoherent light source.

Microwave integrated optical modulator

Abstract: A Ti‐diffused lithium niobate, traveling wave modulator has been fabricated and tested at microwave frequencies. A Mach–Zehnder interferometer optical configuration and a coplanar waveguide electrical transmission line are used. For a 4‐mm interaction length, the modulator has a 3‐dB bandwidth of 13 GHz and requires only 2 V to switch at λ=840 nm. The frequency response is measured directly using an ultrahigh speed photodiode, and the test setup therefore constitutes the highest bandwidth efficient electro‐optical transmission system ever reported.

Review of All-Fiber Phase and Polarization Modulators

Abstract: For at least ten years now workers have been contributing techniques for modulating light signals in optical fibers1'2'3'4. These techniques have been of the phase, polarization and frequency variety. However, whereas the phase and polarization modulation techniques can be accomplished in a very efficient manner in what is referred to as the "all-fiber" approach (i.e., an unbroken or unspliced fiber), frequency modulation schemes have not been very efficient (under 2%) using an all-fiber techniques '6. To date, practical frequency modulation is limited to accomplishment in bulk Bragg Cell media external to the fiber. Hence discussion of frequency modulation within an optical fiber is premature at this time. This paper therefore will survey those signal modulation techniques which apply to demonstrated in situ optical fiber modulation techniques, i.e., all-fiber phase and polarization modulation.

Fabrication and characterization of GaAs Schottky barrier photodetectors for microwave fiber optic links

Abstract: High‐Speed GaAs Schottky barrier photodiodes have been fabricated and characterized. These detectors have 3‐dB bandwidths of 20 GHz and quantum efficiencies as high as 70%. The response of the detectors to light modulated at 1–18 GHz has been directly measured. Microwave modulated optical signals were obtained by using a LiNbO3 traveling wave modulator and by heterodyning two laser diodes.

Two-dimensional propagating beam analysis of an electrooptic waveguide modulator

Abstract: Diffused waveguides are analyzed employing the propagating beam method. By reducing the problem to two dimensions by the effective index method, a reduction of the computer time by a factor of 100 is achieved. The method has been exemplified by a Y - branch electrooptic waveguide modulator. The calculated output power versus applied voltage is in good agreement with results found in the literature. We expect the method to be a powerful tool when optimizing the geometry of modulators and similar waveguiding circuits with respect to physical dimensions and losses.

Improved mode extinction modulator using a Ti in‐diffused LiNbO3 channel waveguide

Abstract: An efficient, linear mode extinction modulator has been demonstrated using a weakly guided, near cutoff, channel waveguide. Modulation slopes as high as 16% per volt have been measured. Deviation from a linear voltage‐intensity relationship of less than 1% has been observed over a 77% modulation range. Over 97% modulation has been achieved with ±4 V applied. An optical bias is also demonstrated. A coupled mode analysis for the modulator is reported which includes propagation loss effects.

Theoretical resolution limitations of electrooptic spatial light modulators. I. Fundamental considerations

Abstract: The sensitivity and resolution of electrooptic spatial light modulators (ESLM’s) such as the Pockels Readout Optical Modulator (PROM) and Microchannel Spatial Light Modulator (MSLM) are shown to be functions of the potential distribution arising from charges located within the active electrooptic-crystal layer. The Fourier transform of the potential distribution (which can be directly related to the modulation transfer function) is derived as a function of the charge location within the electrooptic crystal. The resultant analytic expression in addition exhibits the dependence of sensitivity and resolution on the dielectric constants of the blocking layers and electrooptic crystal and on the thicknesses of the three layers. It is shown that the overall sensitivity and resolution are affected strongly by charge storage in the bulk away from the electrooptic-crystal/dielectric-blocking-layer interfaces. In particular, the effects of various operating modes can be qualitatively explained by utilizing superposition to calculate the potential distribution for a positive–negative charge pair located at various positions in the electrooptic crystal. The implications of these results for device design and operation are discussed.

Gigahertz-bandwidth InGaAsP/InP optical modulators/switches with double-hetero waveguides

Abstract: A new kind of InGaAsP/InP electro-optic directional coupler modulator/switch with double-hetero plano-convex waveguides, which is suitable for monolithic integrated optics, has been proposed and demonstrated The fabricated devices have shown low optical loss (4 dB/cm) and high modulation bandwidth of 1 GHz at 13 μm wavelength

Optical element in semiconductor laser device having a diffraction grating and improved resonance characteristics

Abstract: The disclosure is directed to an improved semiconductor laser device which includes a first light deriving optical waveguide connected approximately perpendicularly to a light exit face at one side, a second light deriving optical waveguide connected approximately perpendicularly to another light exit face at the other side and having an optical axis different from that of the first light deriving optical waveguide, and a light emitting optical waveguide subjected to optical coupling with a periodical diffraction grating for optical resonance, and connected to end portions of the first and second light deriving optical waveguides within the semiconductor laser device.

Length measuring apparatus based on the dual laser beam interferometer principle

Abstract: Length measuring apparatus with position sensor (12), in accordance with the dual beam laser interferometer principle, having a laser light source (16) supplied by a power source (48), a beam splitter (18) disposed in its optical axis for dividing the light beam into a measuring light beam and a reference light beam aligned at an angle thereto, a movable mirror (19) joined to the position sensor and reflecting the measuring light beam parallel to the optical axis with a transverse offset, and an at least partially reflecting additional optical element (20). This optical element (20) can be either in the form of a second mirror or in the form of a second beam splitter. In the area of interference of the beam paths lies at least one photodetector (21) whose output or outputs are connected to an evaluating circuit (37) which has a counting system for counting the light/dark sequences including a detection of direction of movement, and to a digital display system (3). In accordance with the invention, the laser light source is a laser diode (16 ) for the production of laser light which is essentially monomodal both laterally, transversely and longitudinally and has a coherence length that corresponds at least to the length to be measured. The evaluation circuit (37) also has at least one system for eliminating the influences of operational and environmental parameters of the length measuring apparatus. The apparatus is extraordinarily compact, and easy to learn to operate as regards signal processing and regulation. It is consequently suitable both for manual measuring devices (gauges) and for machine devices.

Reactive ion etched GaAs optical waveguide modulators with low loss and high speed

Abstract: Single-mode rib waveguides and modulators for operation at 13 ?m have been fabricated by reactive ion etching (RIE) The antireflection-coated devices show very low coupling and propagation loss (2 dB/cm) and are suitable as extracavity digital modulators in the Gbit/s range for single-mode system applications

Electrically stimulated optical switching of NbO2 thin films

Abstract: For the first time, electrically stimulated optical modulation in a thin‐film NbO2 device is demonstrated. NbO2 thin‐film deposition by reactive ion‐beam sputtering, device fabrication, and device performance as a 120‐Hz continuous‐wave modulator are described.

Two dimensional electro-optic modulator for printing

Abstract: A two dimensional electro-optic modulator comprises an electro-optic element and a two dimensional planar array of individually addressable electrodes for spatially modulating a light beam along a plurality of transverse axes or for imparting a geometric phase front to the light beam. Such a modulator may be used, for example, (1) in a real time or in a time delay and integration mode as a multigate light valve for (a) electro-optic line printing or (b) optical displays, or (2) in a real time mode as (a) a beam focusing and tracking device for optical memories or (b) an arcal input device, a Fourier plane filter, or an image plane correlation mask for optical processing.

Light modulation device

Abstract: A light modulation device comprises a substrate (1), a substrate layer (2), an optical waveguide layer (3) and buffer layers (4), in that order, formed of either all n-type or all p-type compound semiconductor crystal. In orderto capture the light in the optical waveguide layer, the composition ratio of the compound semiconductor is so determined that the refractive index is at least approximately 0.1% higher in the optical waveguide layers than in the substrate layer and in the buffer layers. Furthermore, the carrier density is low in the optical waveguide layer and in the buffer layers, so that the applied voltage is effectively applied mainly to the optical waveguide layer. Due to the construction of the light modulation device, strict control of the etching process is not required, the device has a low absorption loss of light, and it can be made as a monolithic optical integrated circuit.

Aperture compensation signal processor for optical recording

Abstract: A signal processor and method for frequency compensating the drive signal for an optical modulator in an optical recording apparatus to make the exposure level modulation amplitude on the medium independent of the spatial frequency of the information being recorded. The processor compensates for exposure level modulation roll off at high spatial frequencies due to the finite size of the recording spot by increasing the amplitude of the modulator drive signal at high frequencies. The compensation is preferably the inverse of the modulation transfer function of the recording objective lens.

High-speed low-loss low-drive-power travelling-wave optical modulator for λ = 1.32 μm

Abstract: We report a Ti: LiNbO 3 travelling-wave optical switch/modulator for λ = 132 μm that requires only 45 V to switch, has ~55 GHz bandwidth, a power per bandwidth figure of merit of 109 mW/GHz and a fibre-device-fibre insertion loss of only -23 dB

Thermo-optic waveguide interferometric modulator/switch in glass

Abstract: We demonstrate a novel optical waveguide interferometric modulator/switch in glass, which uses the thermo-optic (TO) effect based on the temperature dependence of refractive index The TO modulation and switching characteristics are discussed experimentally In particular, TO switching of the order of 50 μs was successfully obtained under an overdriven operation

Independent acoustooptic modulation of the two wavelengths of a bichromatic light beam.

Abstract: When a single acoustooptic modulator is used to independently modulate the two nearly equal optical wavelengths of a bichromatic laser beam, each with a given acoustic frequency bandwidth, both the acoustic frequencies as well as the transducer width must be large. A general expression for this bandwidth, valid for both isotropic and anisotropic acoustooptic interactions and whatever the acoustic power and the bandwidth definition are, is derived. In uniaxial crystals, a special configuration of anisotropic interaction is shown to lead to a small acoustic frequency bandwidth with a reasonable transducer width at moderate central frequency. A practical 6-MHz bandpass modulator using the slow shear wave in paratellurite is designed, and experimental results for independent modulation of 0.5145- and 0.4880-μm wavelengths of an Ar laser are reported.

Controlled Optical signal absorber apparatus and method using quantum well layer structure

Abstract: An optical device having controllable absorption for an optical signal having a wavelength corresponding to a photon energy not exceeding 1.2 ev comprises (i) a semiconductor structure including one or more quantum well layers and (ii) means adapted for applying to the quantum well layers(s) an electric field such that the component of the field normal to the layer(s) may be controlled so as to determine the absorption edge of the quantum well layer(s) to be on either side of the optical signal wavelength. The device may be used as an optical modulator or switch and in optical demultiplexing.

Amplifier-modulator integrated with a cleaved-coupled-cavity injection laser

Abstract: We have demonstrated an external amplifier-modulator integrated with a cleaved-coupled-cavity injection laser on the same 13 μm InGaAsP/InP laser chip The maximum available gain was 20 at an input power of −192 dBm, and it reduced to 10 at an input power of −105 dBm High on/off extinction ratios and side-mode suppression >100:1 were achieved at about 1 Gbit/s (NRZ) modulation rate

Polarisation-independent modulators with Ti:LiNbO3 strip waveguides

Abstract: In the letter we demonstrate experimentally the operation of a polarisation-independent amplitude modulator based on the evolution of the electro-optical modulation efficiency against the position of the mode with respect to the electrode system. For a 20 mm-long Mach-Zehnder interferometer command voltages of 5 V have been obtained at the polarisation-insensitive configuration.