Large Electro-optic Response Research Articles

Effect of Ni doping on the electro-optic property in K(Ta0.6Nb0.4)O3 films

The rising of thin-film-based plasmonic electro-optic (EO) devices triggers considerable exploitation of ferroelectric oxide thin films with large EO response. In this study, epitaxial (001)-orientated Ni-doped K(Ta0.6Nb0.4)O3 (KTN) films were fabricated on SrRuO3/SrTiO3 substrates via pulsed laser deposition. In comparison with a pure KTN film, a larger withstand electric field was achieved by Ni doping. The EO measurements revealed that the doping of Ni ions induced a decrease in the effective EO coefficient. Instead, the variation of refractive index by the applicable maximum electric field was increased due to the increment of withstand electric field, particularly for the case of 2% Ni dopant.

Reconfiguration of three-dimensional liquid-crystalline photonic crystals by electrostriction.

Natural self-assembled three-dimensional photonic crystals such as blue-phase liquid crystals typically assume cubic lattice structures. Nonetheless, blue-phase liquid crystals with distinct crystal symmetries and thus band structures will be advantageous for optical applications. Here we use repetitive electrical pulses to reconfigure blue-phase liquid crystals into stable orthorhombic and tetragonal lattices. This approach, termed repetitively applied field, allows the system to relax between each pulse, gradually transforming the initial cubic lattice into various intermediate metastable states until a stable non-cubic crystal is achieved. We show that this technique is suitable for engineering non-cubic lattices with tailored photonic bandgaps, associated dispersion and band structure across the entire visible spectrum in blue-phase liquid crystals with distinct composition and initial crystal orientation. These field-free blue-phase liquid crystals exhibit large electro-optic responses and can be polymer-stabilized to have a wide operating temperature range and submillisecond response speed, which are promising properties for information display, electro-optics, nonlinear optics, microlasers and biosensing applications.

First-principles study of the linear electro-optical response in strainedSrTiO3

We report a density functional theory study of the Pockels effect (linear electro-optical effect) in epitaxially strained $\mathrm{SrTi}{\mathrm{O}}_{3}$. The electro-optical response is calculated for biaxial strain values ranging from \ensuremath{-}2.0 to 2.0% relative to the theoretically optimized lattice constant. Under 1.0% tensile strain, the Pockels tensor components increase dramatically, with the largest components reaching maximum values of ${r}_{111}={r}_{222}=505.64\phantom{\rule{0.16em}{0ex}}\phantom{\rule{4pt}{0ex}}\mathrm{pm}/\mathrm{V}$. Under 1.2% compressive strain, the Pockels tensor exhibits a similarly large peak with a maximum value of ${r}_{333}=236.55\phantom{\rule{4pt}{0ex}}\mathrm{pm}/\mathrm{V}$. These peaks in the electro-optical response originate from the softening of the phonon modes associated with ferroelectric phase transitions that result in the loss of inversion symmetry. Our results suggest that under the right circumstances $\mathrm{SrTi}{\mathrm{O}}_{3}$ can yield a very large electro-optical response, comparable to that of $\mathrm{BaTi}{\mathrm{O}}_{3}$, which has one of the largest known responses.

Large Pockels effect in micro- and nanostructured barium titanate integrated on silicon

The electro-optical Pockels effect is an essential nonlinear effect used in many applications. The ultrafast modulation of the refractive index is, for example, crucial to optical modulators in photonic circuits. Silicon has emerged as a platform for integrating such compact circuits, but a strong Pockels effect is not available on silicon platforms. Here, we demonstrate a large electro-optical response in silicon photonic devices using barium titanate. We verify the Pockels effect to be the physical origin of the response, with r42 = 923 pm V-1, by confirming key signatures of the Pockels effect in ferroelectrics: the electro-optic response exhibits a crystalline anisotropy, remains strong at high frequencies, and shows hysteresis on changing the electric field. We prove that the Pockels effect remains strong even in nanoscale devices, and show as a practical example data modulation up to 50 Gbit s-1. We foresee that our work will enable novel device concepts with an application area largely extending beyond communication technologies.

Large electro-optic response of bulk ferroelectric crystals enhanced by piezoelectric resonance in the high frequency range

Electro-optic (EO) devices with high EO coefficients at radio and microwave frequencies are integral components of the photonics industry. This work determines the EO effect of ferroelectric Li-doped niobium-rich potassium tantalate niobate (K0.95Li0.05Ta1-xNbxO3; KLTN) single crystals using improved dynamic EO measurement. The phase transitions of KLTN crystals were investigated via variable-temperature Raman spectroscopy. A full view of the surface displacement and velocity for the KLTN sample at the resonant frequency was studied using an ultra-frequency vibrometer. The KLTN sample with x=0.60 exhibits the enhanced effective EO coefficient (γc) ∼ 217 pm/V near the piezoelectric resonant peaks, which is comparable with the value at low frequency. The piezoelectric enhanced EO property of KLTN single crystals can be attributed to nonlinear polarization and nonzero stress, and showing promising for designing practical optical-piezoelectric-mechanism coupling devices.

High-power Broadband Organic THz Generator

The high-power broadband terahertz (THz) generator is an essential tool for a wide range of THz applications. Here, we present a novel highly efficient electro-optic quinolinium single crystal for THz wave generation. For obtaining intense and broadband THz waves by optical-to-THz frequency conversion, a quinolinium crystal was developed to fulfill all the requirements, which are in general extremely difficult to maintain simultaneously in a single medium, such as a large macroscopic electro-optic response and excellent crystal characteristics including a large crystal size with desired facets, good environmental stability, high optical quality, wide transparency range, and controllable crystal thickness. Compared to the benchmark inorganic and organic crystals, the new quinolinium crystal possesses excellent crystal properties and THz generation characteristics with broader THz spectral coverage and higher THz conversion efficiency at the technologically important pump wavelength of 800 nm. Therefore, the quinolinium crystal offers great potential for efficient and gap-free broadband THz wave generation.

Low-frequency–dependent electro-optic properties of potassium lithium tantalate niobate single crystals

A series of lead-free ferroelectric potassium lithium tantalate niobate K0.95Li0.05Ta1−xNbxO3 (x = 0.78, 0.69, 0.60, 0.52) single crystals were grown using the top-seeded melt growth method. The low-frequency–dependent linear electro-optic properties of K0.95Li0.05Ta1−xNbxO3 single crystals in the tetragonal state were investigated using the Senarmont method, autoscanning Mach-Zehnder interferometer technique and AC measurement method at room temperature. The electro-optic measurements were taken with continuous low frequency (from 1 kHz to 100 kHz) of a sinusoidal electric field, and large electro-optic responses were observed. For every component, the values of the electro-optic coefficients γ33, γ13 and γc decrease with the increase of frequency. However, the γ51 shows low sensitivity to the change of frequency. γ33, γ13 and γc increase with tantalum content, but γ51 decreases with the increase of tantalum content. The electro-optic properties of high-optical-quality K0.95Li0.05Ta1−xNbxO3 single crystals forecast their outstanding potential in various electro-optic applications.

Anomalously Large Bend Elastic Constant and Faster Electro-Optic Response in Soft Glassy Gels Formed by a Dipeptide

In this article, results of static/dynamic Freedericksz transformation and rheological studies on anisotropic thermoreversible gels formed by gelation of a nematic liquid crystal (NLC) with a monodisperse dipeptide are presented. Freedericksz transformation studies reveal a surprising result: the gel state possesses a very large Frank bend elastic constant value, order of magnitude higher than the sol state, whereas, the splay elastic constant shows relatively a small increase. The studies also demonstrate that the anisotropic gel to anisotropic sol transition can be tracked by simply monitoring the Freedericksz transformation. Other attractive features of the gel state include the vanishing of the undesirable backflow effect, and nearly an order of magnitude decrease of switching speed. Further, rheological studies bring out the soft glassy characteristics of these gels.

Linear electro-optic properties of orthorhombic PZN-8%PT single crystal

The optical transmittance spectra of relaxor ferroelectric 0.92Pb(Zn(1/3)Nb(2/3))O(3)-0.08PbTiO(3) (PZN-8%PT) single crystals poled along different directions have been systematically studied at room temperature. After being poled along the [011] direction, the transmittance of induced orthorhombic PZN-8%PT single crystal is more than 50% from 0.5 to 5.7 μm, which is much higher than that poled along the [001] and [111] directions. The refractive indices and linear electro-optic properties of the orthorhombic PZN-8%PT single crystal were characterized at a wavelength of 632.8 nm. Large electro-optic responses were observed, (γ33) = 220 pm/V, (γ13) = 62 pm/V, and (γ23) = 23 pm/V. Thus, orthorhombic PZN-8%PT single crystal is a promising material for high-performance electro-optic devices.

Frequency Dependent Electro-Optic Properties of Potassium Lithium Tantalate Niobate Single Crystal

Single crystals K0.95Li0.05Ta1-x Nb x O3 (KLTN) - x = 0.6 are grown and the transmission spectra show the UV absorption edge is about 400 nm for the transparent KLTN crystal sample. The refractive index and the frequency dependent of linear electro-optic coefficients of KLTN single crystals in the tetragonal phase are characterized at room temperature. The minimum deviation method is used for the refractive index measurements and the electro-optic properties have been investigated using the senarmont method and the auto scanning mach-zehnder interferometer technique. The EO measurements were taken with the continuous low frequency of applied ac field from 100 Hz to 100 KHz. Large electro-optic responses are observed and the coefficients, γ33 = 216.7 pm/V, γ13 = −21.2 pm/V, and γc = 242.9 pm/V at 1 kHz are measured for the crystals. The E-O properties show that the high quality KLTN single crystals have the potential in the field of optical modulation and deflection field devices.

Quantum Mechanical Design and Structure of the Li@B10H14Basket with a Remarkably Enhanced Electro-Optical Response

An innovative type of lithium decahydroborate (Li@B(10)H(14)) complex with a basketlike complexant of decaborane (B(10)H(14)) has been designed using quantum mechanical methods. As Li atom binds in a handle fashion to terminal electrophilic boron atoms of the decaborane basket, its NBO charge q (Li) is found to be 0.876, close to +1. This shows that the Li atom has been ionized to form a cation and an anion at the open end of B(10)H(14). The most fascinating feature of this Li doping is its loosely bound valence electron, which has been pulled into the cavity of the B(10)H(14) basket and become diffuse by the electron-deficient morphological features of the open end of the B(10)H(14) basket. Strikingly, the first hyperpolarizability (beta(0)) of Li@B(10)H(14) is about 340 times larger than that of B(10)H(14), computed to be 23,075 au (199 x 10(-30) esu) and 68 au, respectively. Besides this, the intercalation of the Li atom to the B(10)H(14) basket brings some distinctive changes in its Raman, (11)B NMR, and UV-vis spectra along with its other electronic properties that might be used by the experimentalists to identify this novel kind of Li@B(10)H(14) complex with a large electro-optical response. This study may evoke the possibility to explore a new thriving area, i.e., alkali metal-boranes for NLO application.

ROUTING LIGHT AT WILL

We present a comprehensive review on the routing of self-confined light-beams in liquid crystals, i.e., generation, propagation and angular steering of self-induced waveguides or spatial solitons in a nonlinear non local dielectric with a large electro-optic response. We describe all-optical routing through soliton-soliton or soliton-beam interactions, as well as voltage-controlled steering in an anisotropic geometry via birefringence or refraction/reflection at a graded interface.

Very large electro-optic responses in H-bonded heteroaromatic films grown by physical vapour deposition

A crucial goal for modern telecommunications systems is development of very high-speed components for broadband (>100 GHz), all-optical signal/information processing. The core component of such technologies is the electro-optic modulator, which encodes electrical signals onto fibre-optic transmissions. A significant challenge therefore is obtaining materials that have large electro-optic responses and that can be readily fabricated into devices at low cost. We report here on the realization of high-response heteroaromatic organic chromophores that can be straightforwardly self-organized from the vapour phase into intrinsically acentric, high-quality, micrometre-scale films. These pi-conjugated electro-optically active films (with second-order susceptibilities up to approximately 100 pm V(-1)) are thermally stable and conveniently grown by a simple physical vapour deposition process in a few hours. Supramolecular acentricity is achieved without electric field poling, enforced by biomimetic heterocycle-hydroxycarbonyl head-to-tail hydrogen-bonding.

First-Principles Study of the Electro-Optic Effect in Ferroelectric Oxides

We first present a method to compute the electro-optic tensor from first principles, explicitly taking into account the electronic, ionic and piezoelectric contributions. We then study the nonlinear optic behavior of three paradigmatic ferroelectric oxides. Our calculations reveal the dominant contribution of the soft mode to the electro-optic coefficients in LiNbO3 and BaTiO3 and its minor role in PbTiO3. We identify the coupling between the electric field and the polar atomic displacements along the B-O chains as the origin of the large electro-optic response in perovskite ABO3 compounds.

Stark effect measurements on monomers and trimers of reconstituted light-harvesting complex II of plants

The electric-field induced absorption changes (Stark effect) of reconstituted light-harvesting complex II (LHCII) in different oligomerisation states—monomers and trimers—with different xanthophyll content have been probed at 77 K. The Stark spectra of the reconstituted control samples, containing the xanthophylls lutein and neoxanthin, are very similar to previously reported spectra of native LHCII. Reconstituted LHCII, containing lutein but no neoxanthin, shows a similar electrooptical response in the Chl a region, but the Stark signal of Chl b around 650 nm amounts to at most ∼25% of that of the control samples. We conclude that neoxanthin strongly modifies the electronic states of the nearby Chl b molecules causing a large electrooptical response at 650 nm stemming from one or more Chls b in the control samples. Ambiguities about the assignment of several bands in the Soret region [Biochim. Biophys. Acta 1605 (2003) 83] are resolved and the striking difference in electric field response between the two lutein molecules is confirmed. The Stark effect in the carotenoid spectral region in both control and neoxanthin-deficient samples is almost identical, showing that the neoxanthin Stark signal is small and much less intense than the lutein Stark signal.

Observation of magnetic field-induced contraction of fission yeast cells using optical projection microscopy

AbstractThe charges in live cells interact with or produce electric fields, which results in enormous dielectric responses, flexoelectricity, and related phenomena. Here we report on a contraction of Schizosaccharomyces pombe (fission yeast) cells induced by magnetic fields, as observed using a phase-sensitive projection imaging technique. Unlike electric fields, magnetic fields only act on moving charges. The observed behavior is therefore quite remarkable, and may result from a contractile Lorentz force acting on diamagnetic screening currents. This would indicate extremely high intracellular charge mobilities. Besides, we observed a large electro-optic response from fission yeast cells.

Linear Electrooptic Properties of Pb(Mg1/3Nb2/3)O3–PbTiO3 Single Crystals at Compositions Near the Morphotropic Phase Boundary

The linear electrooptic coefficients of Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN–PT) single crystals in the rhombohedral and tetragonal phases were characterized at a wavelength of 632.8 nm. Large electrooptic responses were observed. The tetragonal 0.62PMN–0.38PT single crystals poled along the <001> direction (the spontaneous polarization direction) show r33=70 pm/V, r13=25 pm/V, and r51=558 pm/V. In addition, r33 and r13 of crystals of this composition show a slight increase with temperature, which originates from the temperature dependence of polarization and dielectric constant. The rhombohedral 0.67PMN–0.33PT single crystals poled along the <111> direction have r33=107 pm/V, r13∼0, and r51=1050 pm/V.

Realization of Expeditious Layer-by-Layer Siloxane-Based Self-assembly as an Efficient Route to Structurally Regular Acentric Superlattices with Large Electro-optic Responses

A new, expeditious siloxane-based layer-by-layer assembly process for the formation of intrinsically polar organic electro-optic thin films is described using highly reactive −SiCl2I-functionalized, silyl-protected donor−acceptor azo-benzene chromophore derivatives and octachlorotrisiloxane as a deprotecting reagent/interlayer precursor. This all-“wet-chemical” two-step process can be efficiently implemented in a vertical dipping procedure to yield polar films consisting of 40 alternating chromophore and capping layers. Each nanoscale bilayer (chromophore + polysiloxane layer ≈ 3.26-nm thick) can be grown in ≈40 minat least 1 order of magnitude more rapidly than previous siloxane-based solution deposition methodologies. Chromophore monolayer deposition from solution reaches completion in ≈15 min at 55 °C. The adherent, structurally regular assemblies exhibit appreciable electro-optic responses (χ(2) ∼ 180 pm/V and r33 ∼ 65 pm/V determined by SHG measurements at 1064 nm) and high chromophore surface densities (≈40 Å2/chromophore) and have been characterized by a full complement of physicochemical techniques: optical spectroscopy, aqueous contact-angle measurements, specular X-ray reflectivity, atomic force microscopy, and angle-dependent polarized second-harmonic generation.

Enhanced Electro-Optic Response Of Layered Composite Materials

electro-optic effect was measured to have the value x (3) 5(3.210.2i)310 221 625% (m/V) 2 . The real part of this value is a factor of 3.2 650% times larger than that of the doped polycarbonate, which is the dominant electro-optic component of the composite. We have modeled the experiment by using both effective medium theory and by solving the wave equation for our multilayered system, and we find that these approaches give consistent predictions which are in good agreement to the experimental results. © 1999 American Institute of Physics.@S0003-6951~99!03117-4# Many applications in modern optical technology require the use of materials with a large electro-optic response. Examples include the photonic control of phased array radar, 1 satellite-to-satellite data links that will require data transfer rates during the next decade of 50‐100 Gbits/s, 2 and optical fiber links of 1 Tbit/s. 3 The present approaches to improving materials ~e.g., improved organic chromophore design! have resulted in characteristics that are within a small factor of being satisfactory for application. Therefore, new approaches are in order and in this letter, we describe a technique that can be used to increase the value of essentially any electrooptic material by forming a composite out of that material. In the present work, we deal with the quadratic electro-optic effect, although the technique can be applied to the linear electro-optic effect as well. Our approach entails forming a composite material consisting of alternating layers of an electro-optic material ~designated material a in the ensuing analysis! and a buffer material ~designated material b! having a different linear dielectric constant. A theoretical analysis 4 of such a situation shows that the effective nonlinear susceptibility describing the quadratic electro-optic effect x ijkl (v8;v,V1 ,V2) is related

Thermally stable poled polyquinoline thin film with very large electro-optic response

Poled guest-host polyquinoline thin films are shown to demonstrate both exceptionally large electro-optic activity and long-term stability. After an initial drop from 45 to 26 pm/V in the first 100 h, the electro-optic coefficient r33 at 26 pm/V remained for more than 2000 h.