Showing papers on "Optical modulator published in 1990"

Electronic analog of the electro‐optic modulator

Abstract: We propose an electron wave analog of the electro‐optic light modulator. The current modulation in the proposed structure arises from spin precession due to the spin‐orbit coupling in narrow‐gap semiconductors, while magnetized contacts are used to preferentially inject and detect specific spin orientations. This structure may exhibit significant current modulation despite multiple modes, elevated temperatures, or a large applied bias.

Programmable femtosecond pulse shaping by use of a multielement liquid-crystal phase modulator.

Abstract: We report programmable shaping of femtosecond optical pulses by use of a multielement liquid-crystal modulator to manipulate the phases of spatially dispersed optical frequency components. Our approach provides for continuously variable control of the optical phase and permits the pulse shape to be reconfigured on a millisecond time scale. We use the apparatus to demonstrate femtosecond pulse-position modulation as well as programmable compression of chirped femtosecond pulses.

Dual parallel modulation schemes for low-distortion analog optical transmission

Abstract: The use of two integrated-optical modulators operated in parallel to attain low-distortion analog optical transmission is examined. This static feedforward approach achieves significantly improved linearity at the expense of small increases in the required optical power and moderate increases in the required drive voltage. A novel variation that uses the unique characteristics of an integrated-optical modulator to correct the dominant quadratic distortion of a directly modulated laser is proposed. >

Two-dimensional spatial light modulators: a tutorial

Abstract: Two-dimensional spatial light modulators (SLMs) modulate one of the properties of an optical wavefront (amplitude, phase, polarization) as a function of two spatial dimensions and time in response to information-bearing control signals that may be either optical or electrical. These devices form a critical part of optical information processing systems, serving as input transducers as well as performing several basic processing operations on optical wavefronts. A tutorial overview of the 2-D SLMs is given. their applications are outlined, a classification scheme for them is given, and major types of SLMs that are under active development are described. >

Quantum well optoelectronic switching devices

Abstract: Quantum well semiconductor structures allow small, fast, efficient optoelectronic devices such as optical modulators and switches. These are capable of logic themselves and have good potential for integration with electronic integrated circuits for parallel high speed interconnections. Devices can be made both in waveguides and two-dimensional parallel arrays. Working arrays of optical logic and memory devices have been demonstrated, to sizes as large as 2 048 elements, all externally accessible in parallel with free-space optics. This article gives an overview of the physics underlying the operation of such devices, and describes the principles of several of the device types, including self-electrooptic effect devices (SEEDs).

Coherent light modulation and detector

Abstract: A acousto-optic Fabry-Perot optical modulator (10) has a crystalline body (12) having a first partially reflective electrode (14) for receiving radiation, including laser radiation having a wavelength or wavelengths of interest, and a second, oppositely disposed partially reflective electrode (14) for emitting the received radiation including the laser radiation. The modulator is driven by an alternating source (16) at a resonant frequency of the crystalline body and intensity modulates at the resonant frequency only the emitted laser radiation. A detector (18) is positioned for receiving the emitted radiation, including the intensity modulated laser radiation, and has an output signal expressive of the intensity of the emitted radiation. Signal processing circuitry (20,34) is coupled to the detector output signal and is responsive thereto for identifying the intensity modulated laser radiation for indicating when laser radiation is received by the modulator.

Two-wavelength operation of the nonlinear fiber loop mirror.

Abstract: We describe the two-wavelength operation of the nonlinear fiber loop mirror. In this mode of operation a high-power signal at one wavelength switches a low-power signal at another wavelength. This device is investigated both theoretically and experimentally. The experimental results show that the nonlinear loop mirror performs as an optical modulator that consists of all-fiber components.

Tunable infrared modulator and switch using Stark shift in step quantum wells

Abstract: A tunable infrared modulator and/or switch using intersubband Stark shift in a step quantum well is discussed. The device utilizes the intersubband absorption and the large change of separation between energy levels in the step quantum well under an applied electric field. The incident infrared beam on the device is either absorbed or transmitted depending on the energy separation of the levels, and thus the modulation can be achieved by adjusting the energy levels with an applied electric field. The extremely short lifetime of the intersubband transition makes this modulator suitable for application in high-speed long-wavelength optical communications. >

Observation of room‐temperature blue shift and bistability in a strained InGaAs‐GaAs 〈111〉 self‐electro‐optic effect device

Abstract: We have observed room‐temperature exciton blue shift with applied voltage in a 〈111〉 In0.1Ga0.9As‐GaAs p‐i‐n multiple quantum well modulator. We have also observed optically induced bistability in a symmetric self‐electro‐optic effect device circuit composed of these modulators. Very large (2.5:1) ratios of photocurrent were obtained with only 0–3 V applied bias.

High modulation rate optical plasmon waveguide modulator

Abstract: A high-speed light modulator employing surface plasmon wave coupling comprises a metal-dielectric interface positioned adjacent to and externally of a waveguide carrying totally internally reflected light waves. A high frequency voltage applied to the interface causes the dielectric, in the preferred case an ultra-fast electro-optic polymer, to resonate, generating a surface plasmon wave at the interface. The plasmon wave couples with the evanescent wave portion of the light waves in the waveguide. The output intensity of the light waves varies inversely with the strength of coupling between the light wave and surface plasmon wave modes. The modulator eliminates bulk and alignment problems associated with state of the art modulators and can be employed in integrated optic circuits.

Spatial light modulator printer and method of operation

Abstract: A printing system and method which uses an unmodulated light focused on a spatial light modulator (SLM) device. The light modulator device, in one embodiment, can be a deformable set of mirrors monolithically integrated onto a semiconductor substrate which act, under control of data signals, to selectively modulate light onto a focusing lens which in turn images the light to the drum of the xerographic printing process. The deformable mirrors are formed in one or more parallel rows and the selective timing of the rows is controllable in order to compensate for variations in xerographic process speed. A stepped light baffle removes the unmodulated light further enhancing the dark field effect.

All‐optical modulation using an n‐doped quantum‐well structure

Abstract: The modulation of interband‐resonant light by intersubband‐resonant light using an n‐doped quantum well is proposed, and results of the theoretical analysis are reported. It is shown that a large change in absorption coefficient from 100 to 3160 cm−1 for interband‐resonant light can be obtained by changing the intensity of intersubband‐resonant light from 0 to 1 MW/cm2. Very fast modulation speed (∼ps) can be expected.

Optical amplifier and optical communication system provided with the optical amplifier

Abstract: An optical communication system transmits information with a pumping light beam acting as the carrier, and with a signal light beam. This optical communication system includes an optical fiber amplifier adapted to amplify the signal light beam by having the signal light beam and the pumping light beam propagate through a rare-earth-doped fiber doped with a rare-earth element. A modulating circuit modulates the pumping light beam with a high-frequency modulating signal having a period shorter than the life span of fluorescence resulting from an excited state. When the signal light beam and the pumping light beam are propagated in the same direction through the rare-earth-doped fiber, the transmission of information with the pumping light beam acting as the carrier, can provide transmission of a supervisory signal for an optical repeater. When the signal light beam and the pumping light beam are propagated in opposite directions through the rare-earth-doped fiber, a two-way transmission can be achieved by the transmission of information with the signal light beam and the transmission of information with the pumping light beam.

33 ps optical switching of symmetric self‐electro‐optic effect devices

Abstract: We describe a new method of operation of symmetric self‐electro‐optic effect devices (S‐SEEDs) using excitation pulses shorter than the diode sweep out times. We shall call this dynamic SEED switching. Previous SEEDs are optically bistable logic devices which use the unique properties of multiple quantum well structures placed in the intrinsic i regions of two p‐i‐n diodes reverse biased in series. Conventional operation of S‐SEEDs is at the exciton wavelength where absorption decreases with increasing electric field. Utilizing the dynamic properties of the S‐SEED we demonstrate that switching is possible at any wavelength where there is a nonlinear response showing a threshold. The major advantages of dynamic over conventional operation, is that it can be faster while requiring less optical energy, is automatically reset each cycle, and is less susceptible to saturation.

Multichannel AM video transmission using a high-power Nd:YAG laser and linearized external modulator

Abstract: A high-power Nd:YAG laser with a linearized external modulator-based system is demonstrated for a transmission of 50 channels of vestigal sideband amplitude modulated (VSM AM) video. The 1320-nm diode-pumped Nd:YAG laser is an attractive source for AM video transmission due to the high output power ( approximately 200 mW) and low relative intensity noise ( >

Ferroelectric-liquid-crystal/silicon-integrated-circuit spatial light modulator.

Abstract: We present the design and characterization of a spatial light modulator (SLM) comprising a ferroelectric-liquid-crystal light-modulating layer on top of a silicon integrated circuit. Our SLM consists of two electrically addressed arrays on the same integrated-circuit die. The first, a 1 x 128 linear array with a 20-microm center-to-center element spacing, used shift register addressing, while the second, a 64 x 64 square array with 60-microm pitch, used static random access memory addressing. The resulting SLM could be addressed at frame rates of up to 4.5 kHz and gave singleelement intensity contrast ratios of 12:1.

Polarization forming optical device and polarization beam splitter

Abstract: An optical device for forming a linear polarized light by dividing a light beam from a light source into two linear polarized light components, and rotating a plane of polarization of one of the light components at 90° to follow joining of both the light components Further, a polarization beam splitter for dividing a light beam into two linear polarized light components is employed in such an optical device

High-power and high-speed semi-insulating BH structure monolithic electroabsorption modulator/DFB laser light source

Abstract: By the use of a semi-insulating BH structure we have obtained a high-performance monolithic electroabsorption modulator/DFB laser light source having a bandwidth of 10.3 GHz and an output power of 17 mW. The chirp was only 0.1 A under 10 Gbit/s NRZ modulation.

High-speed InGaAlAs/InAlAs multiple quantum well optical modulators

Abstract: High-speed modulation over 22 GHz for waveguided InGaAlAs/InAlAs multiple quantum well (MQW) optical modulators is described. A large on/off ratio of over 25 dB is demonstrated with a low-drive voltage (6 V) operating in the 1.55- mu m wavelength region. The design and characteristics of MQW p-i-n modulators are discussed. The causes of large-insertion loss and the required drive voltage bandwidth figure of merit for the MQW modulator are discussed. The frequency response measurements show that the response speed is limited by the RC time constant of the device. This suggests that the speed can be further enhanced by decreasing the size and capacitance of the device. >

A semi-empirical model for electroabsorption in GaAs/AlGaAs multiple quantum well modulator structures

Abstract: A semiempirical model for electroabsorption in GaAs/AlGaAs quantum wells that is simple and has sufficient accuracy to make it suitable as a fast design tool for multiple quantum well (MQW) optical modulators is proposed. The model is based on a higher-order perturbation approach which includes all bound solutions of the unperturbed Hamiltonian. To complete the model, semiempirical relationships are set up for both the zero-field absorption peak and the half-width at half-maximum (HWHM) values of the heavy-hole exciton. Comparison with extensive experimental data shows a remarkable agreement for a range of wells between 5 and 20 nm and for photon energies on the long wavelength side of the absorption peak. These wavelength and well-size ranges coincide with those needed for practical design. >

Self-electro-optic device based on a superlattice asymmetric Fabry-Perot modulator with an on/off ratio >~ 100:1

Abstract: A self‐electro‐optic effect device based on a Fabry–Perot reflection modulator has been demonstrated for the first time. This modulator is a normally‐off high‐contrast asymmetric Fabry–Perot modulator using Wannier–Stark localization in a superlattice. Optical bistability has been achieved with a record‐high on/off ratio of 130:1 at the operating wavelength of 7620 A. The modulator with an appropriate reverse‐bias voltage supply was connected in series to a silicon photodiode which when illuminated with an appropriate light source acted as a current source load for the modulator.

Optimization of modulation ratio and insertion loss in reflective electroabsorption modulators

Abstract: We show theoretically that the maximum modulation ratio in Fabry–Perot reflective electroabsorption modulators for a given insertion loss is solely a function of the ratio of the maximum to minimum absorption. We increase this ratio by using thinner quantum wells than are conventionally used and obtain significantly improved performance. We obtain an insertion loss of 1.2 dB and a modulation ratio of 7.5 with a 5 V operating bias.

Optical memory disks in optical information processing.

Abstract: We describe the use of optical memory disks as elements in optical information processing architectures. The optical disk is an optical memory devicew ith a storage capacity approaching 1010b its which is naturally suited to parallel access. We discuss optical disk characteristics which are important in optical computing systems such as contrast, diffraction efficiency, and phase uniformity. We describe techniques for holographic storage on optical disks and present reconstructions of several types of computer-generated holograms. Various optical information processing architectures are described for applications such as database retrieval, neural network implementation, and image correlation. Selected systems are experimentally demonstrated.

InxGa1−xAs/GaAs multiple quantum well optical modulators for the 1.02–1.07 μm wavelength range

Abstract: We report the operation of strained‐layer InxGa1−x As/GaAs 50‐ and 100‐period multiple quantum well optical modulators at wavelengths ranging from 1.02 to 1.07 μm. Structures were grown on GaAs substrates, as well as on strain relief InxGa1−xAs buffer layers. Devices show favorable electrical characteristics and absorption contrasts up to 57% at the exciton peak. Optical modulation of a Nd:YAG laser is demonstrated, via operation of self‐electro‐optic effect devices at 1.064 μm.

Viscoelastic spatial light modulators and schlieren-optical systems for HDTV projection displays

Abstract: Thin metallized viscoelastic layers coated by a mirror electrode and addressed by an active matrix are proposed for ue in schlieren-optical light-valve projection systems for high-definition television (HDTV). Previously, the deformation behavior of such viscoelastic spatial light modulators (VSLMs) was analyzed extensively by use of the theories of electrostatics, linear viscoelasticity, and plate bending. In the meantime, most of the theoretical results could be qualitatively confirmed by interferometric deformation measurement. Of the many predictions derived from the theoretical treatment, only the deformation patterns to be expected with one bright line and with two bright lines separated by a dark line are demonstrated here. Furthermore, the number of grating periods per picture element as well as the ratio of electrode width and grating period are discussed in view of resolution limits. In addition, three concepts of full-color schlierenoptical projection systems for the above reflective VSLMS are described and compared. All three systems contain a light source, three spatial light modulators (one for each primary color), and a projection lens. The first concept is based on a very small light source and a correspondingly small stop; in the second concept, mirror bars as in the well-known Eidophor projector are employed; and parallel light is assumed in the third concept.

Optical distribution of analog and digital signals using optical modulators with complementary outputs

Abstract: A novel optical system is taught including an optical source, an optical modulator (128) having at least one optical input port for receiving the optical signal from the optical source, a modulation port for receiving the optical signal from the optical source, a modulation port for receiving a modulating signal, and complementary output port signals (132). The complementary modulated output signals are applied to one or more optical receivers at the other end of an optical transmission link. In one embodiment, the two complementary signals are provided to two separate optical receivers, thereby allowing distribution of optically modulated signals, for example, in a cable television or other type distribution system. In another embodiment, the two complementary modulated signals are applied to a single balanced receiver, thereby providing information content to the complementary receiver twice the power level available on either one channel alone. Furthermore, utilizing a balanced receiver, common mode error signals cancel, thereby increasing the signal to noise ratio of the system. In one embodiment of this invention, a single optical transmission channel is used, and the two optically modulated signals are separated in polarization (132) so as to be capable of being separately detected on the receiving end of the link. In one embodiment feedback means is used to insure proper polarization states for the two complementary signals.

High-speed optical modulator for application in instrumentation

Abstract: The design and characterization of the first integrated optic modulator for a commercial instrument application are described. Alternative forms of modulation, including direct laser current modulation and optical heterodyne techniques, are reviewed for the application, which requires modulation to 20 GHz. The advantages of an integrated optic modulator fabricated using titanium in-diffused lithium niobate are discussed. Performance tradeoffs between x-cut and z-cut LiNbO/sub 3/ including bandwidth, modulation efficiency, bias point stability, and acoustic resonances are detailed. The x-cut device is found to give the best overall performance for this instrument application. Device reliability and testing, including temperature cycling, humidity, electrostatic discharge, mechanical shock, and vibration are described for complete packaged and pigtailed devices. >

Silicon-based rib waveguide optical modulator

Abstract: An optical modulator (30) includes a waveguide region having, for radiation of a predetermined wavelength such as 1.3 microns, a variable optical transmittance characteristic. The optical transmittance characteristic is a function of a difference between an index of refraction of a first region (36) comprised of silicon having a first type of electrical conductivity and an index of refraction of a second adjacent region (34) comprised of an insulator such as a silicon dioxide. The modulator further includes a third region (38), also comprised of silicon, disposed adjacent to the first region. The third region has a second type of electrical conductivity for forming a p-n junction with the first region. Charge carriers are injected into the first region for varying the index of refraction thereof such that the optical transmittance characteristic of the waveguide region is varied.

How fast is excitonic electroabsorption

Abstract: Many semiconductor light modulators rely on changes in excitonic absorption induced by electric fields. We study their temporal response in the framework of a one-dimensional model, for which we solve exactly the timedependent Schrodinger equation. For a homogeneously broadened system, the electroabsorption response time is found to be simply the inverse of the (field-induced) exciton linewidth, which can be as short as 50 fsec.

Bistable spatial light modulator using a ferroelectric liquid crystal.

Abstract: A bistable spatial light modulator is developed by utilizing optical bistability of ferroelectric liquid-crystal molecules. Both positive and negative images are read out by changing the polarity of applied electric pulses. A binary image is stored for more than 2 h, and gray-level operation is also possible during the gradual decay after writing.