Electro-optic Light Research Articles

Pyrooptic converter, a new device for wavelength conversion of electromagnetic radiation

Abstract The operation of a “pyrooptic” converter based on the combined utilization of a pyroelectric detector and an electrooptic light modulator is demonstrated. In the device investigated the intensity changes of an electromagnetic radiation incident to a triglycine sulphate pyroelectric detector induce a pyroelectric signal, and this signal controls the intensity of a light beam passing through a liquid crystal light modulator, i.e. a modulated radiation is converted into modulated light. With impedance matching between the two elements of the converter but without amplifying the pyroelectric voltage a minimum detectable intensity of radiation of 0.3–0.6 W/m2, and an intensity required for total opening of the light modulator of 17–47 W/m2 is found in the chopper frequency range of 5–20 Hz.

Active-matrix-addressed spatial light modulators based on the longitudinal pockels effect in oblique-cut perovskites

Abstract Oblique-cut layers from the perovskite crystals potassium tantalate niobate and barium titanate and from the tungsten-bronze crystal strontium barium niobate are suggested as control layers for active-matrix-addressed electro-optic spatial light modulators. Since all these materials consist of oxygen octahedra as building blocks and since they all exhibit their highest electro-optic effect in the tetragonal (4mm) phase, a common theoretical treatment is used to determine the optimal oblique-cut angle. Preliminary experimental results on oblique-cut crystals are presented and a compact and efficient optical system for their use is proposed.

Large-scale use of ferroelectricity in microelectronics is reality

Abstract Some specific features characterizing ferroelectric films (FF) use in microelectronics are discussed taking Ba0.5SR0.5Nb2O6 films as an example. The most rapid and effective introduction of the high quality FF into microelectronics can be expected from production of pyroelectric matrix detectors for 8 ÷ 50 μm wavelength, read-only memory elements reprogrammable by electrical field, and optical communication channels by arrangement of electrooptical ferroelectric light modulators.

Droplet shape and reorientation fields in nematic droplet/polymer films

Abstract Polymer films containing droplets of nematic liquid crystal form an important class of new electro-optic light valves and displays. While previous work has shown that the nematic droplet size is an important factor in the electro-optic properties of these films, here we report that the droplet shape is equally important in determing the electro-optics of the film. Electron micrographs show that for films using polyvinyl alcohol as the polymeric binder the cavities formed by the polymer matrix are oblate in nature, and aligned with the minor axis perpendicular to the film plane. In oblate cavities the elastic-deformation free energy is minimized when the director field in the droplet is aligned along a major axis of the spheroid; the electric field performs work on the nematic in reorienting the nematic into a higher-energy state, equal to the elastic-free-energy difference between the two configurations. Calculations and experiment are used to estimate the elastic and electric field free-energy-d...

Bistable spatial light modulator using liquid crystal and Bi12SiO20 crystal layers

A compact spatial light modulator having optical bistability has been constructed with a twisted nematic liquid-crystal layer, a polarizing film, and a Bi12SiO20 crystal layer. The optical bistability is produced by combining the nonlinear optical transmittance property of the liquid-crystal electro-optic light modulator with the photoconductive property of the Bi12SiO20 crystal layer. The device performs optically bistable operations in a controllable manner, and parallel processing of intensity-level image thresholding is also demonstrated for several threshold levels.

A novel type of electrooptic light modulator

Abstract A new type of electrooptic modulator is presented. The modulation of optical waves is obtained by variation of one of the parameters ruling the excitation conditions of a guided mode during the coupling of an optical beam into a planar structure. The performances obtained with a prism coupler are discussed.

Low voltage, resonant-mode electrooptic light shutter

A doubled electrooptic light shutter is described, the operation of which is controlled by the electrically induced mechanical oscillation of two plates of an electrooptic material (e.g. ADP) having slightly different resonant frequencies. When the plates are kept oscillating at their resonant frequencies, the amplitude of the transmission of the system oscillates in time with the beat frequency. The voltage necessary for the operation of the system is of 2-3 orders of magnitude lower than that of the ordinary light shutters. The beat frequency can be continuously tuned by changing the temperature of the system.

KDP Q-Switch with decreased piezooptic influences

Disturbing piezooptic transients caused by impulse driving in KDP Pockelscell electrooptic light modulators are reduced by orientation, shaping and sizing methods based on crystal-acoustic considerations.

Doubled electro-optic light shutter

The disturbing effect of piezoelectrically induced acoustic transients in longitudinal electro-optic light shutters is eliminated by the use of two light shutters working in coincidence.

Quadratic electro-optic light modulation in a GaAs/AlGaAs multiquantum well heterostructure near the excitonic gap

The electro-optic effect has been investigated in a GaAs/AlGaAs multiquantum well waveguide structure 50 meV from the excitonic transition. We extract r41=−1.6×10−10 cm/V and (R11−R12)=6×10−16 cm2/V2, nonlinear optical characteristics that differ from homogeneous GaAs layers. This (R11−R12) value is similar in magnitude but opposite in sign to that found in InGaAsP 130 meV from the band gap.

Time-division optical power divider using electrooptic light switches

A time-division optical power divider (TDPD), which chops an analog optical signal with an electrooptic light switches to produce pulsed optical signals and distributes them to output ports, is proposed. It is shown theoretically and experimentally that the TDPD is capable of dividing a signal with less deterioration of a signal-to-noise ratio (SNR) compared with a conventional optical divider, if the original signal is recovered through a sample/hold circuit and low-pass filters. It is also demonstrated that the SNR degradation due to the signal distribution is remarkably improved with an increase of output ports by using the TDPD system.

KDP Q-switches and second harmonic generator for high-power solid-state lasers

KDP electrooptic light modulators and optical second harmonic generators have been developed for high power solid-state laser applications. The device parameters and the results in switching and frequency doubling of Nd-glass lasers are reported.

Optical Devices Based on Ferroelectric Single Crystals

Optical devices based on the electrooptic effect of the ferroelectric crystals are described for the application to the information processings, including the analog to digital converter using the electrooptic light modulators, the distributor and demultiplexer of optical signals and the electrooptic bistable device. The spatial light modulators are also discussed. Finally, the microscopic mechanism of the electrooptic effect in LiNbO3 and LiTaO3 is introduced through the observation of the ionic and electronic contributions by the X-ray diffraction method.

Measurement of the Mueller matrix for ocean water

The normalized light scattering polarization matrix has been measured for ocean water using an electrooptic light scattering polarimeter. Measurements were done on samples from the Atlantic and Pacific Oceans and the Gulf of Mexico. The polarization effects in the matrices were found to have, in general, a form which is similar to polarization effects in the Rayleigh scattering approximation; for example, all off-diagonal matrix elements except S12 and S21 were zero. Mueller matrix elements were calculated using a Mie computer code and compared to the measured matrices for ocean water. A simple one-component distribution was found to produce a reasonably good fit.

Theoretical resolution limitations of electrooptic spatial light modulators I Fundamental considerations

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.

Theoretical resolution limitations of electrooptic spatial light modulators II Effects of crystallographic orientation

The point-spread function (PSF) of an electrooptic spatial light modulator (ESLM), such as the Pockels Readout Optical Modulator (PROM) or the PRIZ, is derived for various electrooptic crystal orientations and for charge distributions consisting of one or two point charges located in the electrooptic-crystal bulk. It is shown that phase modulation occurs for crystallographic orientations other than 〈001〉, resulting in signal-dependent phase distortions in the image plane and increased harmonic distortion in the Fourier plane. By utilizing linear systems theory, ESLM sensitivity and resolution are analyzed by means of generalized voltage transfer functions. Strikingly strong dependences on crystallographic orientation and charge position are shown. The effects of readout polarization on the angular dependence of the phase and amplitude of the PSF for various crystallographic orientations are also derived.

Self-heating effects in electro-optic light modulators

The performance of an electro-optic light modulator under high average laser power is studied theoretically and experimentally. Absorption of laser radiation produces a thermal gradient in the electro-optic crystal which degrades the performance of the modulator. Measurements on modulators using KDP and KD*P crystals support the analytical results.

Coherent-optical signal processor based on a spatial light modulator with multichannel optical addressing

A study was made of the use of a combined coupling-in device in a coherent-optical processor for signals from antenna arrays. This device included a multichannel electrooptic light modulator made of lithium tantalate, a mechanical deflector, and an optically controlled transparency in the form of a Fockels readout optical memory (PROM).

A New Electrooptic Light Deflection Phenomenon

A new electrooptic light deflection phenomenon has been investigated. This is presumably due to the spatial distribution in the refractive index, induced by the nonuniform electric field under the surface electrodes. 100% deflection efficiency is attained and a large deflection angle can be provided at low driving voltage, either AC or DC. This phenomenon was observed in various materials, including crystals and glasses.

Subharmonic resonances in KDP electrooptical light shutters

Acoustic resonance vibration generated by the inverse piezoelectric effect was investigated in longitudinal KDP electrooptic light shutters driven by a series of high voltage pulses. Although the repetition rate of the driving pulses was far below the mechanical frequencies of the modulator crystals significant resonances were observed.