Electro-optic Light Modulator Research Articles

ВЛИЯНИЕ ПРИРОДЫ ЗАМЕСТИТЕЛЯ В АЗОБЕНЗОЛЬНЫХ ХРОМОФОРАХ НА ДИФРАКЦИОННУЮ ЭФФЕКТИВНОСТЬ ПОЛЯРИЗАЦИОННЫХ ГОЛОГРАММ

The films of polymeric composites containing monomers of azobenzene dyes or azobenzene lateral groups chemically bonded to the main polymer chain demonstrate photoactive properties, and can be used in electrooptical light modulators and in recording media (RM) for polarization holography. Photoinduced optical anisotropy (PIA) appears under influence of linearly polarized light caused by the processes of trans-cis-izomerization of the azobenzene groups. This process is determining for application of the considered materials as RM for polarization holography. The films of polymeric polarization sensitive media based on a copolymer of styrene with nonyl methacrylate doped with azobenzene-type dyes with different electron-acceptor substituents are obtained in this work. In the films of copolymer the holograms of the plane wave front were registered for parallel and orthogonal orientations of polarization vectors of the object and reference light beams. Their photoelectrophysical, in particular photodielectric, and information properties are investigated. It was established, that when the mutual orientation of the recording beams changes from the orthogonal to parallel orientation the diffraction efficiency of the holograms increases in the case of using azo dye with the maximum number of auxochromic substituents in the molecule. The effect of the diffraction efficiency dependence on the chromophores structure is connected with the deepening of dye color. The photo-induced optical anisotropy in the films appears due to a change of the concentration ratio of trans- and cis-isomers of azobenzene dye fragments. This conclusion is confirmed by the photodielectric measurements data, namely, by the negative sign of the photodielectric effect, observed experimentally in the investigated thin film structures. It was shown, that investigated compositions can be used as information media for polarization holography.

Electro-optic combs rise above the noise.

Electro-optic modulation of light can have a precision equivalent to one optical-field cycle

Dynamic Response of Graphitic Flakes in Nematic Liquid Crystals: Confinement and Host Effect.

Electric field-induced reorientation of suspended graphitic (GP) flakes and its relaxation back to the original state in a nematic liquid crystal (NLC) host are of interest not only in academia, but also in industrial applications, such as polarizer-free and optical film-free displays, and electro-optic light modulators. As the phenomenon has been demonstrated by thorough observation, the detailed study of the physical properties of the host NLC (the magnitude of dielectric anisotropy, elastic constants, and rotational viscosity), the size of the GP flakes, and cell thickness, are urgently required to be explored and investigated. Here, we demonstrate that the response time of GP flakes reorientation associated with an NLC host can be effectively enhanced by controlling the physical properties. In a vertical field-on state, higher dielectric anisotropy and higher elasticity of NLC give rise to quicker reorientation of the GP flakes (switching from planar to vertical alignment) due to the field-induced coupling effect of interfacial Maxwell-Wagner polarization and NLC reorientation. In a field off-state, lower rotational viscosity of NLC and lower cell thickness can help to reduce the decay time of GP flakes reoriented from vertical to planar alignment. This is mainly attributed to strong coupling between GP flakes and NLC originating from the strong π-π interaction between benzene rings in the honeycomb-like graphene structure and in NLC molecules. The high-uniformity of reoriented GP flakes exhibits a possibility of new light modulation with a relatively faster response time in the switching process and, thus, it can show potential application in field-induced memory and modulation devices.

Algebraic approach to electro-optic modulation of light: exactly solvable multimode quantum model

We theoretically study electro-optic light modulation based on the quantum model where the linear electro-optic effect and the externally applied microwave field result in the interaction between optical cavity modes. The model assumes that the number of interacting modes is finite and effects of the mode overlapping coefficient on the strength of the intermode interaction can be taken into account through dependence of the coupling coefficient on the mode characteristics. We show that, under certain conditions, the model is exactly solvable and, in the semiclassical approximation where the microwave field is treated as a classical mode, can be analyzed using the technique of the Jordan mappings for the su(2) Lie algebra. Analytical results are applied to study effects of light modulation on the frequency dependence of the photon counting rate. We also establish the conditions of validity of the semiclassical approximation by applying the methods of polynomially deformed Lie algebras for analysis of the model with quantized microwave field.

Direct generation of 12.5-GHz-spaced optical frequency comb with ultrabroad coverage in near-infrared region by cascaded fiber configuration.

We generated a 12.5-GHz-spacing optical frequency comb that can be resolved over 100 THz, from 1040 to 1750 nm, without spectral mode filtering. To cover such a broad spectrum, we used electro-optic modulation of single frequency light and line-by-line pulse synthesis to produce a clear pulse train and subsequent spectral broadening in highly nonlinear fibers (HNLFs). We numerically and experimentally investigated a configuration of the HNLFs and find that a two-stage broadening through different HNLFs is required when using limited pulse energy at a high repetition rate. We designed and fabricated solid silica-based HNLFs with small zero-dispersion wavelengths to obtain strong spectral broadening, especially at the shorter wavelengths. The individual lines of the proposed frequency comb are resolvable with high contrast over the entire spectral range. The results described in this paper should lead to the development of multicarrier sources for wavelength-division-multiplexing communication and super-multi-point frequency calibration for spectrometers, especially in astrophysics.

High sensitivity electro-optic modulation of slow light in ellipse rods PC-CROW

A tunable slow light with low group velocity, high buffer performance and high sensitivity is realized in photonic crystal coupled resonator optical waveguide (PC-CROW) with elliptical rod around cavity. By adjusting the long axis and short axis of the elliptical rods, the slow light and buffer performance of PC-CROW are optimized. As ae=0.42a, be=0.20a, the group velocity is below 2.3053×10−4c, simultaneously, the buffer capacity C and delay time Ts reach the optimum value of 9.8214bit and 354.8ps. Then the dynamic modulation of the slow light and buffer performance based on this optimized structure has been discussed systematically. Thanks to the electro-optic effect of the polystyrene substrate, the guided mode shifts linearly to short wavelength in sensitivity of 3.0nm/mV around 1550nm, as the applied voltage increases. The modulation sensitivities of delay time and buffer capacity are 0.445ns/mV and 0.051bit/mV, respectively. These results show a considerable potential for this structure that can be dynamically controlled according to the practical requirements by electro-optic effect in PC-CROW.

High-contrast electro-optic modulation of spatial light induced by graphene-integrated Fabry-Pérot microcavity

We have proposed a graphene-integrated Fabry-Pérot microcavity for efficient modulation of spatial light. A simplified theoretical model is established to analyze the performance of our system, and the calculated results agree well with the simulation results. It is shown that the plasmon-induced transparency (PIT) effect is achieved in the proposed microcavity and the central frequency of PIT window can be dynamically tuned by gate voltages. In particular, the PIT spectra exhibit extremely large modulation depths (∼90%) across a broad range of frequencies. The proposed ultracompact configuration demonstrates a type of cavity-induced high-contrast and frequency-selective electro-optic modulators, offering opportunities in exploiting active chip-integrated high-performance devices operating at frequencies from terahertz to mid-infrared.

Electro-optic light modulation and THz generation in locally plasma-activated silicon nanophotonic devices

Silicon is not an electro-optic material by itself but the required second-order optical nonlinearity can be induced by breaking the inversion symmetry of the crystal lattice. Recently, an attractive approach has been demonstrated based on a surface-activation in a CMOS-compatible HBr dry etching process. In this work, we further investigate and quantify the second-order nonlinearity induced by this process. Using THz near-field probing we demonstrate that this simple and versatile process can be applied to locally equip silicon nanophotonic chips with micro-scale areas of electro-optic activity. The realization of a first fully integrated Mach-Zehnder modulator device - based on this process - is applied to quantify the nonlinearity to an effective χ((2)) of 9 ± 1 pm/V. Analysis of the thermal stability of the induced nonlinearity reveals post-processing limitations and paths for further efficiency improvements.

Dynamic electro-optic response of graphene/graphitic flakes in nematic liquid crystals

Electric field induced dynamic reorientation phenomenon of graphene/graphitic flakes in homogeneously aligned nematic liquid crystal (NLC) medium has been demonstrated by optical microscopy. The flakes reorient from parallel to perpendicular configuration with respect to boundary plates of confining cells for an applied field strength of as low as tens of millivolt per micrometer. After field removal the reoriented flakes recover to their initial state with the help of relaxation of NLC. Considering flake reorientation phenomenon both in positive and negative dielectric anisotropy NLCs, the reorientation process depends on interfacial Maxwell-Wagner polarization and NLC director reorientation. We propose a phenomenological model based on electric field induced potential energy of graphitic flakes and coupling contribution of positive NLC to generate the rotational kinetic energy for flake reorientation. The model successfully explains the dependence of flake reorientation time over flake shape anisotropy, electric-field strength, and flake area. Using present operating scheme it is possible to generate dark field-off state and bright field-on state, having application potential for electro-optic light modulation devices.

Light emitting diodes: Light engines to simplify and economize advanced microscopy

THE old adage, ‘‘A picture is worth a thousand words,’’ is especially true in biological research, with microscopic images serving to mark the development of key concepts in biology since Hooke first described ‘‘cells’’ in thin slices of cork (1). More than 400 years later, microscopic imaging still serves as a primary data source for biological research, with increasingly advanced techniques that provide information on molecular scale interactions and dynamics. Such advanced molecular imaging techniques take advantage of ever more sophisticated light sources, optics, detectors, and image processing methods, many of which can be quite complex and expensive. At the same time, new technologies and production methods, many driven by the consumer market, have resulted in key components of imaging systems becoming smaller, simpler, and cheaper. The convergence of these effects is having profound effects on our options for light sources for microscopic imaging. The properties of the illumination source are critical to many advanced optical microscopy methods. Lasers play a key role in many of these owing to the monochromatic and coherent nature of their light, plus their ability to be pulsed and otherwise controlled. However, illumination with high-pressure mercury gas discharge or xenon lamps is still the standard for most imaging applications. These light sources provide bright, broad-spectrum excitation (300–900 nm) that can be easily selected by excitation filters for fluorescent imaging applications. However, there are quite a few disadvantages that limit the wide-spread of mercury or xenon lamps-based microscopy system in biological applications. First, sometimes these traditional light sources are too bright and harmful for the living organisms being studied. Excessive brightness can cause rapid photo-bleaching of the dyes used to stain the cells/ tissues. UV light especially, if not blocked, can have significant deleterious effects on live cells. Second, there are substantial costs involved in using mercury or xenon lamps because of their relatively short lifespan. The life of a mercury lamp is usually several hundred hours, and the intensity of these lamps decays progressively during this time. In addition, gas discharge lamps require some time to warm up before lamp intensity reaches steady state. Therefore, once mercury lamps are turned on, they have to be left on for hours to enable fluorescent measurements as needed without delay, thereby further shortening the lamp lifetime. Third, there are also some hazards issues of using mercury or xenon lamps. These lamps generate a significant amount of heat and therefore introduce complications when used in a confined space. When mercury lamps die, they can explode and damage the lenses or mirrors within the lamp housing. These factors combine to make gas discharge lamps inconvenient for lab-based applications and impractical for field applications, including use in portable, miniature, or low cost imaging devices. By contrast, light-emitting diodes (LEDs) show great pro

A multi-layer electro-optic field probe

We present a novel design method and sensing scheme for an electro-optic field probe using multi-stratified layers of electro-optic wafers. A serial stack of cascaded layers is found to be capable of enhancing the performance of interferometric electro-optic light modulation that utilizes the slopes of interference fringe patterns and field-induced electro-optic phase retardations within wafers. The absolute sensitivity of the probe is also characterized with a micro-TEM cell that generates electric fields distributions with accurate, calculable strength for use in probe calibration. The sensitivity of a multi-layered probe-per unit electro-optic wafer volume--was enhanced by 6 dB compared to that of a single-layer one.

Simulation study of surface-plasmon-resonance electro-optic light modulator based on a polymer grating coupler

An electro-optic light modulator design based on a grating-coupled surface-plasmon-resonance structure is numerically investigated using finite-difference time-domain simulation. The thickness effect of a dielectric layer acting as a waveguide on metal structures is investigated. The results show that the new structure has much higher modulation index than the conventional one and can implement an electro-optic modulator with low operating voltage.

A heterodyne laser interferometer for dilatometer measurements

A dilatometer measuring system based on heterodyne laser interferometry is described. An electrooptical light modulator based on the double transverse Pockels electrooptical effect in a crystal of lithium niobate and operating in the quarter-wave mode is used as the optical heterodyne. The electronic measuring system uses modern microelectronic components with a high degree of integration.

Investigation of Electro-optic Light Modulators with PLZT Thin Films Prepared by Aerosol Deposition Method

We investigated a fabrication process and optical properties of electro-optic (EO) light modulators with Fabry-Perot structure, which consisted of PLZT [(Pb0.91, La0.09)(Zr0.65, Ti0.35)O3] thick films by aerosol deposition method. A supernatant elimination process for small size PLZT powder with diameter of 0.125-0.175 μm was effective in order to obtain a transparent film. In the fabricated Fabry-Perot type EO light modulator with a ITO (Indium Tin Oxide))/PLZT/ITO defect layer, a wavelength of resonant localized mode was shifted about 1.0 nm from 788 nm by applying an electric field of +400 kV/cm in reflectance mode, and consequently the reflectance difference of 7.2 % was observed. The Fabry-Perot type EO light modulator had the advantage of contrast of light in the reflection mode.

Fullerene-containing liquid crystal spatiotemporal light modulators with surface-electromagnetic-wave-treated conducting layers

We have studied the switching characteristics of multilayer electrooptical structures comprising quartz substrates, transparent conducting layers, and an oriented nematic liquid crystal (NLC) film doped with photosensitive charge-transfer complexes based on electrooptically active organic monomer or polymer molecules and fullerenes. The transparent conducting layers treated with surface electromagnetic waves are used for the orientation of NLC molecules. The surface relief with variable permittivity, which is created by this treatment, not only ensures the alignment of NLC molecules, but also significantly influences the relaxation times of the electrooptical mesophase, thus making possible effective control over the switching times of the electrooptical light modulator within 1–1.5 ms.

Electro-optic modulation of light propagating near the optic axis with any polarization in uniaxial crystals

The electro-optic effect in uniaxial crystals for light propagating near the optic axis with any polarization has been analyzed. The passive and the electrically induced birefringences and the rotation of polarization direction in crystals have been calculated, and the conoscopic interference figures under orthogonal polariscopes for different polarizer directions have been plotted. The extinction areas caused by the rotation of polarization direction in crystals change with the polarizer direction, but the two heads of the induced optical axes do not vary, which are always on the induced principal axis with bigger refractive index. The directions of polariscopes are always extinction, and the ±45° directions with polarizer are always complete transmission. The conoscopic interference figures for LiNbO3 crystals have been demonstrated experimentally by rotating polariscopes directions, which accord with the theoretically calculating plots.

Polymeric electrooptic light modulator based on grating-coupled surface plasmon resonance

In summary, in this work, we demonstrated the application of the grating-coupled SPR for the fabrication of an EO light modulator. SPR-based EO modulators reported to date have mostly used the Kretchmann configuration. To the best of authors’ knowledge, this work reports the first fabrication and demonstration of a grating-coupled EO modulator. By switching on and off of the applied voltage of 5 V, the subsequent variation of SPR was observed clearly. It should be mentioned that currently our study was limited to show the feasibility of our concept. For practical applications, further optimization of SPR signal will be required, which is a subject of our ongoing research.

Ferroelectric Barium-Strontium Niobate Films and Multi-Layer Structures

A brief review of the research on the barium-strontium niobate films and multilayer structures performed in the institutes of the Siberian Branch of Russian Academy of Sciences is presented. The electrophysical properties of the films are studied, as well as characteristics of the microelectronic components such as memory elements, pyroelectric radiation receivers, electrooptic light modulators and electrostatic micromotors that are based on these films.

Generation of flat power-envelope terahertz-wide modulation sidebands from a continuous-wave laser based on an external electro-optic phase modulator

Flat power-envelope terahertz-wide modulation sidebands are generated by only electro-optic phase modulation of continuous-wave laser light. Generation and power equalization of widespread sidebands are realized simultaneously by spatial distribution of the modulation index within a laser beam cross section by use of simple domain-engineering processes in LiTaO3 electro-optic crystal. Generation of 46 sidebands spaced by 16.25 GHz within a -3-dB bandwidth (over a 1-THz span for a +/- 3-dB bandwidth) is demonstrated.

Fabrication and metrology of an electro-optic polymer light modulator based on waveguide-coupled surface plasmon resonance

This study presents a novel high-efficiency electro-optic (EO) light modulator whose operation is based on the attenuated total reflec- tion effect, in which the surface plasmon wave is excited by an incident waveguide light wave. The EO light modulator is fabricated using a non- linear optical polymer material that is a side-chain EO polyimide with 2-(N-ethyl-4-(tricyanovinyl)anilino)ethanol chromophore. The modulator is characterized, and its performance tested, in terms of the thickness and dielectric constant of the polymer thin film, the EO coefficient, the insertion loss, and the modulation index. Additionally, the dynamic re- sponse of the EO light modulator is fully investigated and discussed. © 2005 Society of Photo-Optical Instrumentation Engineers. (DOI: 10.1117/1.1868775) Subject terms: surface plasmon resonance; attenuated total reflection; electro- optic polymer; waveguide-coupled; nonlinear optical.