Pockels Effect Research Articles

Generation and decay of surface charge in a background charge environment during surface dielectric barrier discharges

Previously, we reported on the decay mechanism of the positive charge filaments generated by the first microdischarge during surface dielectric barrier discharges using a high-speed camera combined with the Pockels effect of a bismuth silicon oxide crystal. With the existing work, the next milestone is achieved by using this powerful approach to the generation and decay of surface charge in a background charge environment. It is found that the generation locations of new positive charge filaments are influenced by the surface charge memory effect. The background charge environment is an important factor in the decay of surface charge.

Design and simulation of high modulation efficiency, low group velocity dispersion lithium niobate slow-wave electro-optic modulator based on a fishbone-like grating

Thin-film lithium niobate (LN) has emerged as an excellent platform for electro-optic modulators (EOMs) owing to its strong electro-optic (Pockels) effect. However, it remains an open challenge to achieve high modulation efficiency in chip-scale EOMs, primarily due to the limitation of light-matter interaction. Here, we propose an on-chip slow-wave LN EOM with a length of 3.4 mm with high modulation efficiency by using a fishbone-like grating. By assembling the fishbone-like grating, the Pockels effect is significantly enhanced as a result of the compression of the local density of states. Benefiting from this effect, the modulation efficiency of the modulator can be improved to 4.6 times of the original. In addition, a 3 mm matched micro-structure electrode is designed to realize the low group velocity of the microwave modulation signal. The simulation results show that the modulation efficiency of this slow-wave EOM is 1.42 V·cm. The slow-light effect is realized theoretically with a flat optical operating bandwidth of about 21 nm, group velocity dispersion < 2 ps2/mm, and low loss < 0.33 dB. Additionally, a 3 dB modulation bandwidth of 80 GHz is verified by simulation by virtue of the proposed micro-structure electrode.

Measurements of surface charge dynamics and surface-breakdown characteristics of surface dielectric barrier discharges

The surface charge distribution in a surface dielectric barrier discharge driven by repetitive pulse bias superimposed on AC voltage is measured using the Pockels effect of an electro-optic crystal. The impact of surface charge on surface-breakdown characteristics is investigated by varying the phase of the pulse superimposition. It is demonstrated that the surface charge accumulation varies at different superimposition phases depending on the potential difference between the two electrodes. The accumulated positive/negative surface charge will facilitate the following surface discharge when the AC voltage polarity changes. In addition, different spatiotemporal characteristics of the surface charge distribution are presented when changing the polarity of superimposed pulses. Positive surface discharges are usually easier to develop than negative surface discharges due to their lower breakdown voltage caused by the accumulation of negative surface charges near the edges of exposed electrodes. The decay of positive surface charge is dominated by neutralization of negative surface charge and negatively charged particles (free electrons and negative ions) from the volume above the dielectric. There are two decay modes of positive surface charge: exponential decay and linear decay.

Fano resonances generation in pyramidal lithium niobate metasurfaces with vertical symmetry-breaking

Fano resonance exhibits an asymmetric spectral profile with a sharp change between a dip and a peak. However, high quality factor Fano resonance is extremely difficult to be fabricated because of its ultra-sensitivity to geometrical imperfections. Here, we demonstrate the Fano resonances generation in all-dielectric pyramidal lithium niobate metasurface with vertical symmetry-breaking, which does not require tight geometrical tolerances and can be easily fabricated. The quality factor of the generated Fano resonance can reach up to 107 due to the reserve of horizontal symmetry. Our work provides a new method of achieving Fano resonances, which can find potential applications in a large variety of prominent optical devices, such as slow-light devices, susceptible sensors and ultrafast switches. Due to the large electro-optic coefficient of lithium niobate and the enhanced Pockels effect in the slow photon system, it has great potential for realizing tunable Fano resonance with extremely low voltage. These tuned Fano resonances, with a low voltage, will find many applications such as high-resolution spectroscopy, biomolecular detection, and tunable laser.

Smart Sensing Multifunctionalities Based on Barium Strontium Titanate Thin Films.

Sensors that have low power consumption, high scalability and the ability of rapidly detecting multitudinous external stimulus are of great value in cyber-physical interactive applications. Herein, we reported the fabrication of ferroelectric barium strontium titanate ((Ba70Sr30)TiO3, BST) thin films on silicon substrates by magnetron sputtering. The as-grown BST films have a pure perovskite structure and exhibit excellent ferroelectric characteristics, such as a remnant polarization of 2.4 μC/cm2, a ferro-to-paraelectric (tetragonal-to-cubic) phase transition temperature of 31.2 °C, and a broad optical bandgap of 3.58 eV. Capacitor-based sensors made from the BST films have shown an outstanding average sensitivity of 0.10 mV·Pa−1 in the 10–80 kPa regime and work extremely steadily over 1000 cycles. More importantly, utilizing the Pockels effect, optical manipulation in BST can be also realized by a smaller bias and its electro-optic coefficient reff is estimated to be 83.5 pmV−1, which is 2.6 times larger than in the current standard material (LiNbO3) for electro-optical devices. Our work established BST thin film as a powerful design paradigm toward on-chip integrations with diverse electronics into sensors via CMOS-comparable technique.

Dual-output kilohertz pump laser for high-energy picosecond OPCPA.

A dual-output thin-disk picosecond laser operating at 100 W with 1 kHz repetition rate is reported in this Letter. By electronically adjusting the amplitude of the optical seed pulses that are injected into the laser cavity, the energy extracted from the gain medium can be shared between two pulses. Amplified double pulses are subsequently spatially separated into two independent beams by a fast Pockels cell, compressed in one common compressor, and frequency-doubled with ∼70% efficiency. This approach significantly decreases strain on the optics, as well as nonlinear effects, and is advantageous for power scaling.

Electro-Optical Modulation in High Q Metasurface Enhanced with Liquid Crystal Integration.

Electro-optical tuning metasurfaces are particularly attractive since they open up routes for dynamic reconfiguration. The electro-optic (EO) modulation strength essentially depends on the sensitivity to the EO-induced refractive index changes. In this paper, lithium niobate (LiNbO3) metasurfaces integrated with liquid crystals (LCs) are theoretically investigated. Cylinder arrays are proposed to support quasi-bound states in the continuum (quasi-BICs). The quasi-BIC resonances can significantly enhance the lifetime of photons and the local field, contributing to the EO-refractive index changes. By integrating metasurfaces with LCs, the combined influence of the LC reorientation and the Pockels electro-optic effect of LiNbO3 is leveraged to tune the transmitted wavelength and phase spectrum around the quasi-BIC wavelength, resulting in an outstanding tuning sensitivity up to Δλ/ΔV ≈ 0.6 nm/V and relieving the need of high voltage. Furthermore, the proposed structure can alleviate the negative influence of sidewall tilt on device performance. The results presented in this work can foster wide application and prospects for the implementation of tunable displays, light detection and ranging (LiDAR), and spatial light modulators (SLMs).

Integrated Pockels laser

The development of integrated semiconductor lasers has miniaturized traditional bulky laser systems, enabling a wide range of photonic applications. A progression from pure III-V based lasers to III-V/external cavity structures has harnessed low-loss waveguides in different material systems, leading to significant improvements in laser coherence and stability. Despite these successes, however, key functions remain absent. In this work, we address a critical missing function by integrating the Pockels effect into a semiconductor laser. Using a hybrid integrated III-V/Lithium Niobate structure, we demonstrate several essential capabilities that have not existed in previous integrated lasers. These include a record-high frequency modulation speed of 2 exahertz/s (2.0 × 1018 Hz/s) and fast switching at 50 MHz, both of which are made possible by integration of the electro-optic effect. Moreover, the device co-lases at infrared and visible frequencies via the second-harmonic frequency conversion process, the first such integrated multi-color laser. Combined with its narrow linewidth and wide tunability, this new type of integrated laser holds promise for many applications including LiDAR, microwave photonics, atomic physics, and AR/VR.

All optical logic gates function by ring resonator properties aiding photonic crystal

Optical logic gates based on the Pockels effect are key components of light-wave communication networks and quantum computing because they are highly efficient and ultrafast. In this paper, we proposed a new hybrid platform of gallium arsenide and barium titanate (GaAs-BTO) for Ultraefficient Electro-Optic Tuning based on two-dimensional photonic crystals, the only proposed multifunctional structure is used to realize various very high-performance photonic logic gates such as BUFFER, NOT, AND, NAND, NOR, OR, XOR, XNOR. The functional parameters of these miniature logic gates are analyzed and optimized numerically by the FDTD method. The simulation results show that the contrast ratio is very high, with a very small footprint of 157 μm2, the response time is ultrafast 1 ps which corresponds to a bit rate of 1 Tbps.

Bulk second-order optical nonlinearities in centrosymmetric materials

The semiclassical theory of electrical susceptibility predicts null even-order susceptibilities for all centrosymmetric materials. However, second harmonic generation and other even-order nonlinear optical phenomena are often seen in them. Contributions due to magnetic dipoles, bulk quadrupoles, or symmetry ruptures describe many of these effects, but not all of them, as can be seen in some experiments recalled here. This work presents an extension of the theory that renders more general expressions for susceptibilities. According to these expressions, bulk even-order susceptibilities may eventually transform as pseudo-tensors and, therefore, may have nonzero values in centrosymmetric structures. We show examples of how this fact provides an alternative or simpler explanation of the conflicting experiments. Our result may have important implications in lasing, communications, imaging, quantum optics, quantum computing, and other fields, as it widens the family of materials in which to look for nonlinear effects such as second harmonic generation, the Pockels effect, spontaneous parametric downconversion, and other phenomena.

Microstructural analysis and electro-optic properties of thick epitaxial BaTiO3 films integrated on silicon (001)

Recent advances in epitaxial oxide deposition have enabled the fabrication of thick films of ferroelectric perovskite ${\mathrm{BaTiO}}_{3}$ capable of providing a robust electro-optic response via the Pockels effect in silicon photonic devices. We report a microstructure analysis of such films integrated on Si(001) by molecular beam epitaxy, showing how the crystallographic and polarization orientation change as a function of thickness. The measured electro-optic properties of the film correlate well with the microstructural analysis and demonstrate the potential of Si-integrated ${\mathrm{BaTiO}}_{3}$ for silicon photonics. An effective Pockels coefficient of up to 268 pm/V has been demonstrated in 110-nm-thick films in transmission measurements and 352 pm/V in waveguide measurements.

Assessment of alkali and alkaline earth metals doped cubanes as high-performance nonlinear optical materials by first-principles study

Novel organic materials have played a tremendous role in developing high-performance nonlinear optical materials. Herein, the geometric, electronic and nonlinear optical properties of designed alkali (Li, Na, and K) and alkaline earth metals (Be, Mg, and Ca) doped cubane (C 8 H 8 ) complexes have been explored by using density functional theory. Excess electrons generated by doping alkali/alkaline earth metals have significantly enhanced the NLO properties by reducing the crucial excitation energy of the cubane. The HOMO–LUMO energy gap of doped complexes is reduced up to 4.43 eV. It is revealed that the reduction in the HOMO–LUMO energy gap results from the development of the new highest occupied molecular orbital, which is confirmed by the density of state (DOS) analysis. The NBO analysis is carried out to confirm the charge transfer between metal atoms and the cubane ring. Further, the NCI and QTAIM analyses confirmed the nature of intramolecular interaction. The remarkable first hyperpolarizability ( β o ) of 3.01 × 10 4 au is observed for K@Cubane. Moreover, frequency dependent first hyperpolarizability ( β ( ω )), second harmonic generation β (-2 ω ; ω , ω ), electro-optic Pockel's effect β (- ω ; ω ,0), hyper-Rayleigh scattering coefficient ( β HRS ), second hyperpolarizability ( γ ( ω )), electric field-induced second harmonic generation γ (-2 ω ; ω , ω ,0) electro-optic Kerr effect γ (- ω ; ω ,0,0), and nonlinear refractive indices ( n 2 ) were also studied. The highest dc-Kerr (2.69 × 10 10 au ) and EFISHG (3.69 × 10 9 au ) values observed for K@Cubane along with large n 2 (1.73 × 10 −9 au ) justify the large NLO response. These intriguing outcomes will be advantageous for promoting the possible utilization of designed complexes in the field of high-performance NLO materials. • Alkali and alkaline earth metals doped cubane complexes have been investigated theoretically for better NLO response. • NBO analysis indicates the intermolecular charge transfer while NCI and QTAIM analyses validate non-covalent interactions. • All the doped complexes have deep ultraviolet transparency (≤200 nm). • First hyperpolarizability ( β o ) of doped cubane complexes have been enhanced to 3.01 × 10 4 au. • Hyper-Rayleigh scattering (upto 2.23×10 4 au ) and nonlinear refractive index (upto 1.15×10 −5 au ) reflect high NLO response.

Characterisation of surface charge density and net electric field during parallel-plate dielectric barrier discharge generated in atmospheric-pressure air

We measured the surface charge density in a parallel-plate dielectric barrier discharge (DBD) using the Pockels effect, and the axial and lateral components of the net electric field were evaluated for different gap lengths and applied voltages. The DBD was driven by a 5 kHz sinusoidal voltage in gap lengths of 0.5, 0.3, and 0.1 mm at atmospheric pressure with Bi4Ge3O12 crystal as a dielectric. Typical microdischarges (MDs) were observed for every gap length, and the number of MDs increased with the increasing applied voltage. As the gap length decreased, the spot radius of a single MD decreased, whereas the peaks of charge density were almost the same, indicating that the amount of charge transported per unit MD is limited for short gaps. The spatial memory effect, in which MDs occur at the same position in successive cycles, was not always observed under the experimental conditions, and it was evaluated considering the surface charge density distributions. Whether the memory effect works is determined by the surface charge density, and it is likely to occur under a balance between positive and negative charges across successive half-cycles. The net electric field was estimated from surface charge measurements. The axial component of the net electric field strength increased up to 150–170 Td before the MD occurred, and it decreased below 100 Td by the surface charge deposited by MD, being approximately 50%–60% of the external field amplitude. The maximum value of the lateral component of the electric field was approximately 150 Td at the edge of the MD spot with a gap length of 0.5 mm, and it decreased as the gap length decreased. As a negative surface charge generated a weaker lateral field than a positive one, the electric field distribution differed between anodic and cathodic dielectrics.

Electro-Optic Sensor for Measuring Electrostatic Fields in the Frequency Domain

Precise measurements of electrostatic fields in harsh environments are required in fields ranging from particle accelerators to industrial installations. Many techniques disrupt the field distribution due to the presence of conductors. We present a fully dielectric sensor for very harsh environmental conditions, that exploits the Pockels effect manifested by electro-optic crystals. This system is designed to allow DC measurements to be performed in the frequency domain. The paper discusses an analytical model and simulations of the system, validated with experimental results. The working principle of the measurement technique is explained in detail along the known limitations and possible solutions to further increase the performance.

Two-dimensional space–time terahertz memory in bulk SrTiO3

Polarizable materials with ultrafast responses are of great interest for the development of new sensors and memories under the influence of an electromagnetic field. Recent research efforts have demonstrated the role of optical excitation and intense terahertz (THz) pulses in inducing an ultrafast polar order and revealing a hidden phase transition in S r T i O 3 (STO), respectively. Here we show that the surfaces of STO crystals at room temperature act as ultrafast sensors that enable sub-picosecond switching through the Kerr effect and recording of polar THz intensity with spatial resolution below the diffraction limit through THz-field-induced dipole alignment followed by multi-picosecond relaxation time recovery. The contrast sensitivity and spatial resolution achieved by the STO sensor are significantly superior to those of present-day near-field THz sensors based on the linear Pockels effect, and more importantly, its ability to remain polarized for several picoseconds opens the door to a new strategy for building an ultrafast space–time THz memory.

Doppler compensation for cavity-based atom interferometry.

We propose and demonstrate a scheme for Doppler compensated optical cavity enhancement of atom interferometers at significantly increased mode diameters. This overcomes the primary limitations in cavity enhancement for atom interferometry, circumventing the cavity linewidth limit and enabling spatial mode filtering, power enhancement, and a large beam diameter simultaneously. This approach combines a magnified linear cavity with an intracavity Pockels cell. The Pockels cell induces a voltage-controlled birefringence allowing the cavity mode frequencies to follow the Raman lasers as they track gravitationally induced Doppler shifts, removing the dominant limitation of current cavity enhanced systems. A cavity is built to this geometry and shown to simultaneously realise Doppler compensation, a 5.8 ± 0.15 mm1/e2 diameter beam waist and an enhancement factor of >5× at a finesse of 35. Tuneable Gouy phase enables the suppression of higher order spatial modes and the avoidance of regions of instability. Atom interferometers will see increased contrast at extended interferometry times along with power enhancement and the reduction of optical aberrations. This is relevant to power constrained applications in quantum technology, alongside the absolute performance requirements of fundamental science.

Pulse-width-dependent dynamic charge deposition on quartz dielectrics interacted with atmospheric pressure He plasma jet

Surface processing with atmospheric pressure plasma jet (APPJ) is attracting attention from both academia and industry for its capability of flexible plasma release onto targets. It is significant to understand the characteristics and mechanism of interfacial phenomenon in plasma surface interaction. This paper reports the fundamental surface charging phenomenon on quartz dielectrics by a He APPJ excited by μs-width pulses with duty ratios from 0.5% to 75%. The targeted quartz plate is attached to an electro-optic crystal grounded in the back for charge measurement. The evolution of surface charges is detected with a reflective-type optical measurement platform based on Pockels effect and the fast charge inversion on 2D-FTA. Results show that ionization waves and quartz dielectric interaction generates a round positive charge deposition, whose lifetime greatly depends on the pulse widths. Under a fixed pulse width, higher voltage magnitudes encourage more charges with a higher deposition rate. An interesting polarity reversal of surface charging occurs when the pulse width increases to over half-cycle, with a reduced positive charge on pulse-on and more negative charges on pulse-off. Efforts are devoted to exploring the mechanisms of charge maintenance on pulse-on and the polarity reversal under longer pulses of several hundred microseconds. These results reveal that the unchanged charge density in dark channel is due to the much lower rate of charge decay compared with the fast ionization wave propagation. The abrupt decrease at the falling edge results from the charge neutralization in the negative conductive channel formed by the secondary discharge. By measuring the initial evolution during the foremost 1000 periods, we prove that the accumulative difference in dissipated charges between pulse-on and pulse-off periods is the main cause of the occurrence of polarity reversal under long pulses. This study provides a more compatible tool for in-depth insight into the charging process of plasma interacting with multiple dielectrics, and exhibits a potential strategy of regulating surface charging by adjusting pulse parameters, which are of interest to the plasma community.

Fiber electric double-layer platform for a phase shifter based on the Pockels effect of liquid molecules.

The electric double layer (EDL) was formed at the interface of the electrode and liquid and has been widely used in a series of applications, ranging from batteries to biosensors, based on the electrical property changes. In this paper, we demonstrate a simple microfiber phase shifter based on the Pockels effect of liquid in the electric double layer. By constructing an EDL around the microfiber, the phase shifter can be achieved. Furthermore, the effects of ion concentration and molecular polarity of liquids on this phase shifter were studied. The fiber electric double-layer platform has the advantages of low voltage modulation and simple fabrication, which has the potential for use in wearable sensing devices, biopotential detection, and biomolecule detection.

Pulse Picking PIV: A Single-Cavity Fiber Laser System For Highly Flexible Repetition Rates And Pulsing Schemes

A novel single-cavity laser system with flexible pulsing schemes suitable for particle image velocimetry (PIV) measurements is presented. The system is based on the concept of picking selected pulse pairs from an ultra-high repetition rate fiber laser which enables time-resolved and conventional dual-pulse PIV at highly flexible recording frame rates. Pulse picking PIV laser systems allow for the use of high-quality low speed dual-frame PIV cameras as well as highspeed cameras in both dual-frame and continuous recording modes, enabling the investigation of highly-transient phenomena at limited fields of view using time-resolved PIV as well as statistical PIV measurements with larger fields of view and higher spatial resolutions. The single-cavity output additionally avoids the alignment of laser beams of laser pulses, which is otherwise necessary in conventional dual-cavity PIV laser systems. Two pulse picking systems were set up and tested: An acousto-optic deflector selecting pulses using the diffraction across an acoustic wave and an electro-optic modulator rotating the polarization state of selected pulses in a Pockels cell. The performance of both systems was evaluated in terms of achievable inter-pulse durations, beam profile alterations, and pulse energy losses caused by the introduction of additional optical elements in the beam path.

Electro‐Optic Effect of ZnO Microcavity and Active Dynamic Lasing Mode Modulation

AbstractElectro‐optic effect, as a physical effect of electric field modulating refractive index, is widely applied to modulate lasing modes dynamically. However, the modulation is operated passively in general. It means that the lasing is generated in a resonance cavity and the modes are regulated externally in different materials and spaces. It will be highly favorable for optoelectronic integration and other applications when a gain medium with electro‐optic effect is applied to design an optical microcavity, integrating optical pumping and electro‐optic modulation. In this work, a hexagonal ZnO microrod is pumped optically to generate UV lasing with an electric field applied to modulate dynamically the resonance wavelength. When the electric field is parallel to the ZnO C‐axis, the refractive index variation is correlated linearly with the electric field strength (Pockels effect). When the electric field is perpendicular to the ZnO C‐axis, the refractive index variation shows a quadratic increase tendency with the increase of the electric field strength (Kerr electro‐optic effect). The whispering‐gallery lasing modes are dynamically modulated by applying an electric field successfully. In one word, lasing generation and modulation are integrated in the same microcavity based on both 1st and 2nd order electro‐optic effect.