Electro-optic Light Modulator Research Articles

Device-quality second-order nonlinear optical poly(ester-imide) for electro-optic applications

Abstract A side-chain second-order nonlinear optical (NLO) poly(ester-imide) (PEI) possessing good organo-solubility, excellent film-forming property, high glass transition temperature (186 °C) and high thermal stability was synthesized. The NLO chromophore orientation in the polymer film achieved via corona poling showed high long-term stability at elevated temperatures up to 120 °C. A reflective electro-optic (EO) light modulator using this polymer as the EO material was fabricated and encoded electrical signals onto reflected light successfully. The EO coefficient γ33 of the PEI layer in the EO modulator was determined to be 11.5 pm/V at 650 nm by an improved attenuated-total-reflection method.

Characterization of a nematic liquid crystal light modulator for mid-infrared applications

We characterize an electro-optical light modulator intended for applications in the middle infrared spectral region (10.6 μm) based upon the transition to turbulence in a nematic liquid crystal with negative dielectric anisotropy. The modulation mechanism is analyzed when the thickness of the liquid crystal layer is comparable with the light wavelength. The characteristic response times of the device are measured for various thicknesses of the liquid crystal layer.

Electric field sensing system using coherence modulation of light

This paper describes an experimental setup for detecting electric fields using electrooptic lithium niobate (LiNbO/sub 3/) sensors and coherence modulation of light. In this detection scheme, the sensed electric fields modulate optical delays, which are introduced by LiNbO/sub 3/ coherence modulators when associated to low-coherence optical sources. The optical delays act as coherence-multiplexed carriers of the sensed electric fields and are transmitted through an optical fiber channel. At the receiver, the electric fields are detected by measuring the auto-correlation of the received light by using two-wave interferometers, which are matched to the introduced optical delays on the sensing devices.

Phase measurements of a twisted nematic liquid crystal spatial light modulator with a common-path interferometer

We present a novel and high accuracy (±1°) technique for measuring the difference in phase delay between the positive and negative eigenvectors of a twisted nematic liquid crystal spatial light modulator (LCSLM) as a function of applied voltage. We show a new architecture for a common-path interferometer where we simultaneously generate both the positive and negative eigenvectors of the LCSLM. We use an electro-optic light modulator to provide a time varying phase shift between the two eigenvectors and measure the phase delay difference between the two eigenvectors. We compare the phase delay values with those obtained using a Mach–Zehnder interferometer and find good agreement.

Electro-Optic Modulation of Light by a Planar Waveguide Based on Ferroelectric Liquid Crystals

We present electro-optic switching from a planar waveguide with a ferroelectric liquid crystal overlayer and discuss the operating principle and the parameters significant for the operation of the device. We have found electro-optic response times of about 20 μs at best as well as a high (5.7%) transmittance in the ON-state of the device. The contrast ratio was 4:1 ON to OFF state.

Interferometric phase measurements for polarization eigenvectors in twisted nematic liquid crystal spatial light modulators

We show interferometric measurements of the phase delays for both eigenvectors in a twisted nematic liquid crystal spatial light modulator (LCSLM). These polarization eigenvectors are of interest for newer LCSLMs that are thinner and consequently have a lower birefringence compared with earlier devices. We use a new technique in which an electro-optic light modulator provides a time varying phase shift between the electric field components in the two arms of a Mach–Zehnder interferometer. The appropriate eigenvectors are generated and detected for a LCSLM located in one arm of the interferometer. We then use a lock-in amplifier to accurately measure the phase delay for the LCSLM as a function of applied voltage. Our experimental results show agreement with the theory.

Enhanced electrooptic modulation efficiency utilizing slow-wave optical propagation

The use of slow-wave optical propagation to promote highly efficient electrooptic modulation of light is investigated theoretically. The proposed modulators utilize a traveling wave (TW) design in which a grating integrated with a single-mode waveguide induces coupling between forward- and reverse-propagating waves. This contradirectional coupling leads to a reduction in the average optical propagation speed in the forward direction. The "slow" waveguide structures provide two features which facilitate improved modulator performance over conventional "fast" TW designs: (1) optical/microwave velocity matching in substrates with high electrooptic coefficients and dielectric constants and (2) enhancement of electrooptic phase shift due to the "dwell time" of the light in the modulation region. For the ideal case of perfect velocity matching, these two factors lead to a potential improvement of nearly an order of magnitude in electrical power dissipation over velocity-matched designs in the conventional lithium niobate (LN) substrate material. Additional orders-of-magnitude improvement in the required electrical power could result from the use of tungsten bronze substrates such as strontium barium niobate (SBN), which have such higher electrooptic coefficients than LN. The prediction of a large reduction in electrical power dissipation is confirmed by calculations for specific slow-wave designs utilizing multireflector etalons in SBN, although response speed limitations result from the fact that perfect velocity matching is not achieved.

Electro-optic modulation of laser diode light by mode interference in a multilayer waveguide including a 2-docosylamino-5-nitropyridine Langmuir–Blodgett film

A hybrid four layer guide (FLG) including a glass guide and a 2-docosylamino-5-nitropyridine Langmuir–Blodgett film is described, and some tests are reported on an electro-optic modulator based on this FLG. The modulation of laser diode light was obtained by guided mode interference, without a Mach–Zehnder configuration of the device. From the modulated signal the r22 electro-optic coefficient was calculated as 11 pm/V.

X-ray imaging with amorphous selenium: theoretical feasibility of the liquid crystal light valve for radiography.

A novel radiographic imaging system based on a liquid crystal light valve is described. A liquid crystal light valve is a photon addressed spatial light modulator that consists of a high resolution, solid-state electrostatic detector (photoconductor) and an electro-optic light modulator (liquid crystal cell) physically coupled in a sandwich structure. We propose a light valve with a thick, x-ray sensitive photoconductive layer and call the system under study the x-ray light valve (XLV). The image formation in the XLV is based on x-ray exposure controlled modulation of light from an external source; the XLV is essentially an x-ray image intensifier that allows the image brightness to be adjusted independently from the x-ray exposure. Thus the XLV may be coupled to an optical imager, such as a charge coupled device (CCD), for image digitization without a secondary quantum sink. A model of the XLV operation is developed to investigate its sensitivity, speed, noise, and resolution. The imaging properties of the XLV are found to be time dependent, which leads to an unusual transmission versus exposure characteristic. The feasibility of clinical use of the XLV based on amorphous selenium (a-Se) photoconductor and a twisted nematic liquid crystal cell is analyzed, and the device is shown to be adaptable to a variety of radiographic imaging tasks.

Electro-optical and photorefractive devices for optical information processing systems

The operating principles of electro-optic and photorefractive spatial-temporal light modulators (STLMs) having electrical and light control are considered. An analysis of the characteristics of STLMs shows that they make it possible to carry out basic mathematical operations on 2-D optical signals in real time as well as providing for the entry, processing, and display of information. The presence of an optical memory for information in the form of images makes it possible to carry out multichannel spectral analysis of ratio signals, multichannel correlation, pattern recognition, etc.

Glass fiber poling and applications

Recent developments in the application of poled optical fibers to second harmonic generation and electrooptic light modulation are reviewed.

Electro-optic modulation and frequency translation of light in a gyrotropic medium

The solution of coupled-mode equations is obtained for a strong coupling and a short interaction length. It is used in an analysis of electro-optic modulation in a gyrotropic or optically active medium. The gyrotropy and electro-optic interaction make it possible to transform phase modulation into intermode coupling and also to translate the phase matching from low to high frequencies and thus achieve efficient hf mode conversion. This can be used in wideband electro-optic modulators of the state of polarisation and in optical frequency translators operating in the gigahertz range.

Modelling of the dynamics of parameters of nematic liquid-crystal layers

Equations describing the dynamics of a nematic liquid-crystal layer are derived and investigated. These equations are suitable for a qualitative description of the dynamic characteristics of electrooptic light modulators based on liquid-crystal layers. A theoretical model is compared with the experimental results.

Electrooptic light modulation and second-harmonic generation in novel diazo-dye-substituted poled polymers

The nonlinear-optical susceptibilities, x/sup (2)/, of a diazo-dye-substituted polymer poled with high electric fields were determined experimentally and theoretically. The electrooptic modulation of He-Ne laser light in a traveling-wave channel-waveguide modulator using the diazo-dye-substituted poled polymer is reported, and the linear electrooptic coefficient of the poled polymer is estimated from a measured half-wave voltage. The polymer studied is a poly(methyl methacrylate) copolymerized with a methacrylate ester of the dicyanovinyl-terminated diazo dye derivative. This polymer is called 3RDCVXY. The corona-poled 3RDCVXY polymer exhibits a x/sup (2)/ value of 1*10/sup -6/ esu at 1.06 mu m. The thermal stability is excellent even at 80 degrees C. The poled 3RDCVXY polymer film shows a linear electrooptic coefficient as high as 40 pm/V at 0.633 mu m. An electrooptical light modulation in the channel 3RDCVXY polymer waveguides with a half-wave voltage as low as 5 V was obtained. >

Integral optical digital computers

The specific features of optical digital computers in integrated circuit form, whose principle of operation is based on electrooptic light modulation, are considered. The design of an array processor unit is described. It is shown that the optical communication channels introduced into integrated circuit structures with the help of thin film light modulators enable one to reduce, compared to electronics with equivalent functional capability, the total number of device components by 2 orders of magnitude, the interconnections area by an order of magnitude, and to increase performance by a factor of m (m is the image dimension). The experimental results of studying a cell of dynamic memory constructed with the above components are presented.

Electronic analog of the electro-optic modulator

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.

Growth of large diameter lithium niobate single crystals by czochralski method

Abstract An attractive combination of piezoelectric and optical properties has made lithium niobate one of the most extensively studied materials. Nowadays, application of these crystals in various fields such as acoustic wave propagation, electro-optic light modulation, optical second harmonic generation and parametric oscillation demands the bulk single crystal production. Solid State Physics Laboratory has grown large diameter (2 inch) lithium niobate (LiNbO3) single crystals successfully. Colourless, transparent, good optical quality crystals weighing up to 1.3 kg have been grown by Czochralski method. A computer controlled crystal puller equipped with R.F. heating has been used to pull these crystals from melt. An after heater wound with Kanthal A1 wire has been used. The growth parameter to develop crack free, good optical quality crystals have been optimized and will be discussed in detail. Grown crystals were sliced into 1 mm thick wafer and polished. Grown crystal surfaces were observed through o...

Waveguide electrooptic microwave modulator with a low control power

Characteristics of a traveling-wave electrooptic light modulator, controlled by a microwave power amplifier, were investigated. The input control power was 7.5 mW in the modulation frequency range 4–5 GHz. Optimization of the modulator characteristics made it possible to reduce the control power to 2–3 mW at 4–5 GHz and to less than 10 mW at 9–11 GHz.

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.