Pockels Effect Research Articles

Non-volatile electrically programmable integrated photonics with a 5-bit operation

Scalable programmable photonic integrated circuits (PICs) can potentially transform the current state of classical and quantum optical information processing. However, traditional means of programming, including thermo-optic, free carrier dispersion, and Pockels effect result in either large device footprints or high static energy consumptions, significantly limiting their scalability. While chalcogenide-based non-volatile phase-change materials (PCMs) could mitigate these problems thanks to their strong index modulation and zero static power consumption, they often suffer from large absorptive loss, low cyclability, and lack of multilevel operation. Here, we report a wide-bandgap PCM antimony sulfide (Sb2S3)-clad silicon photonic platform simultaneously achieving low loss (<1.0 dB), high extinction ratio (>10 dB), high cyclability (>1600 switching events), and 5-bit operation. These Sb2S3-based devices are programmed via on-chip silicon PIN diode heaters within sub-ms timescale, with a programming energy density of sim 10,{fJ}/n{m}^{3}. Remarkably, Sb2S3 is programmed into fine intermediate states by applying multiple identical pulses, providing controllable multilevel operations. Through dynamic pulse control, we achieve 5-bit (32 levels) operations, rendering 0.50 ± 0.16 dB per step. Using this multilevel behavior, we further trim random phase error in a balanced Mach-Zehnder interferometer.

Electric-Field Mapping of Optically Perturbed CdTe Radiation Detectors.

In radiation detectors, the spatial distribution of the electric field plays a fundamental role in their operation. Access to this field distribution is of strategic importance, especially when investigating the perturbing effects induced by incident radiation. For example, one dangerous effect that prevents their proper operation is the accumulation of internal space charge. Here, we probe the two-dimensional electric field in a Schottky CdTe detector using the Pockels effect and report on its local perturbation after exposure to an optical beam at the anode electrode. Our electro-optical imaging setup, together with a custom processing routine, allows the extraction of the electric-field vector maps and their dynamics during a voltage bias-optical exposure sequence. The results are in agreement with numerical simulations, allowing us to confirm a two-level model based on a dominant deep level. Such a simple model is indeed able to fully account for both the temporal and spatial dynamics of the perturbed electric field. This approach thus allows a deeper understanding of the main mechanisms affecting the non-equilibrium electric-field distribution in CdTe Schottky detectors, such as those leading to polarization. In the future, it could also be used to predict and improve the performance of planar or electrode-segmented detectors.

Diamondoid as potential nonlinear optical material by superalkali doping: A first principles study

Adamantane (C10H16), the smallest diamondoid molecule, has sparked considerable scientific interest due to its symmetric, single cage-shaped structure. In the current work, the geometric, electronic, and nonlinear optical responses of Li3O, Na3O and K3O clusters doped adamantanes have been investigated via DFT simulations. The calculated values of interaction energies (−5.50 to −6.91 kcal/mol) and vertical ionization energies (3.01–3.56 eV) reflected that the designed M3O-Ada complexes are thermodynamically and chemically stable. Charge transfer is probed through natural population analysis and the highest charge transfer (0.038 |e|) is observed for K3O-Ada complex. The electride nature of M3O-Ada complexes is confirmed through their electron density distribution and their energy gaps (2.19–3.06 eV) are reduced significantly. Interestingly, the absorption maxima (1387–1629 nm) of M3O-Ada electrides fall in the near infrared region. The highest first and second hyperpolarizability values of 5.9 × 105 au and 2.6 × 108 au are observed for K3O-Ada electride. The maximum hyper-Rayleigh scattering and second harmonic generation values of 1.3 × 107 au and 6.5 × 106 au are obtained at 1907 nm whereas the electro-optical Pockel's effect (6.5 × 106 au) is maximum at 1064 nm. Moreover, the dynamic second hyperpolarizability co-efficients (EOKE, EFISHG) are also computed at varying wavelengths. The M3O-Ada electrides exhibit the maximum nonlinear refractive index n2 of 1.9 × 10−7 cm2 W−1 at 1064 nm. This study will pave the way to the designing of stable superalkali doped diamondoids with enhanced NLO response.

Perspective: Nanophotonic electro-optics enabling THz bandwidths, exceptional modulation and energy efficiencies, and compact device footprints

The growth of integrated photonics has driven the need for efficient, high-bandwidth electrical-to-optical (EO) signal conversion over a broad range of frequencies (MHz–THz), together with efficient, high bandwidth photodetection. Efficient signal conversion is needed for applications including fiber/wireless telecom, data centers, sensing/imaging, metrology/spectroscopy, autonomous vehicle platforms, etc., as well as cryogenic supercomputing/quantum computing. Diverse applications require the ability to function over a wide range of environmental conditions (e.g., temperatures from &amp;lt;4 to &amp;gt;400 K). Active photonic device footprints are being scaled toward nanoscopic dimensions for size compatibility with electronic elements. Nanophotonic devices increase optical and RF field confinement via small feature sizes, increasing field intensities by many orders of magnitude, enabling high-performance Pockels effect materials to be ultimately utilized to their maximum potential (e.g., in-device voltage-length performance ≤0.005 V mm). Organic materials have recently exhibited significant improvements in performance driven by theory-guided design, with realized macroscopic electro-optic activity (r33) exceeding 1000 pm/V at telecom wavelengths. Hybrid organic/semiconductor nanophotonic integration has propelled the development of new organic synthesis, processing, and design methodologies to capture this high performance and has improved understanding of the spatial distribution of the order of poled materials under confinement and the effects of metal/semiconductor-organic interfaces on device performance. Covalent coupling, whether from in situ crosslinking or sequential synthesis, also provides a thermally and photochemically stable alternative to thermoplastic EO polymers. The alternative processing techniques will reduce the attenuation of r33 values observed in silicon organic hybrid and plasmonic organic hybrid devices arising from chromophore-electrode electrostatic interactions and material conductance at poling temperatures. The focus of this perspective is on materials, with an emphasis on the need to consider the interrelationship between hybrid device architectures and materials.

Nonlocal electro-optic metasurfaces for free-space light modulation

Abstract Dynamic optical metasurfaces with ultrafast temporal response, i.e., spatiotemporal optical metasurfaces, provide attractive solutions and open fascinating perspectives for modern highly integrated optics and photonics. In this work, electro-optically controlled optical metasurfaces operating in reflection and utilizing resonant waveguide mode excitation are demonstrated from the viewpoint of free-space propagating light modulation. The modulation of reflected light power with superior characteristics in comparison with prior research is achieved by identifying a suitable low-loss waveguide mode and exploiting its resonant excitation. The electro-optic Pockels effect in a 300 nm-thick lithium niobate (LN) film sandwiched between a continuous thick gold film and an array of gold nanostripes, serving also as control electrodes, is exploited to realize fast and efficient light modulation. The fabricated compact (active area &lt;1000 µm2) modulators operate in the wavelength range of 850–950 nm, featuring a maximum intensity modulation depth of 42 % at the driving voltage of ±10 V within the bandwidth of 13.5 MHz (with the potential bandwidth of 6.5 GHz). The introduced nonlocal electro-optic metasurface configuration opens new avenues towards the realization of ultrafast, efficient, and robust free-space light modulators based on an LN flat optics approach.

Background suppression for CARS thermometry in highly luminous flames using an electro-optical shutter.

An electro-optical shutter (EOS), comprising a Pockels cell located between crossed-axis polarizers, is integrated into a nanosecond coherent anti-Stokes Raman scattering (CARS) system. The use of the EOS enables thermometry measurements in high-luminosity flames through significant reduction of the background resulting from broadband flame emission. A temporal gating ≤100 ns along with an extinction ratio >10,000:1 are achieved using the EOS. Integration of the EOS enables the use of an unintensified CCD camera for signal detection, improving upon the signal-to-noise ratio achievable with inherently noisy microchannel plate intensification processes previously employed for short temporal gating. The reduction in background luminescence afforded by the EOS in these measurements allows the camera sensor to capture CARS spectra at a broad range of signal intensities and corresponding temperatures, without saturation of the sensor, thus enhancing the dynamic range of these measurements.

A Novel Millimeter Wave Receiver Enhanced by a Metallic Dipole Antenna and an Electro-Optic Polymer Waveguide Ring Resonator

The ever-demanding requirement for higher data transmission rate has pushed the carrier frequency in wireless communications from centimeter to millimeter waves (MMW) or even terahertz band. Hybrid integration between the wireless and fiber-optic systems can then help realize a seamless signal transition between the access and backbone networks. In this work, we propose a novel MMW receiver with a simple structure consisting of an electro-optic polymer racetrack waveguide ring resonator (WRR) and a metal dipole antenna. Due to Pockels effect within the polymer waveguide, the presence of the MMW electric field can introduce minor refractive index changes in the waveguide, which can affect light phase and the transmission through the WRR. This effect can be employed to effectively detect the presence of MMW based on the optical method. The phase changes can be highly improved by the dipole antenna resonating at the MMW frequency in order to achieve an enhanced detection of the MMWs. As a result, a low-cost, compact and reliable MMW receiver can be realized, which provides an effective functional interface between MMW and optical fiber-optic systems.

Investigation of the electro-optic effect in high-Q 4H-SiC microresonators.

Silicon carbide (SiC) recently emerged as a promising photonic and quantum material owing to its unique material properties. In this work, we carried out an exploratory investigation of the Pockels effect in high-quality-factor (high-Q) 4H-SiC microresonators and demonstrated gigahertz-level electro-optic modulation for the first time. The extracted Pockels coefficients show certain variations among 4H-SiC wafers from different manufacturers, with the magnitudes of r 13 and r 33 estimated to be in the range of (0.3-0.7) pm/V and (0-0.03) pm/V, respectively.

Improved fabrication of scalable hybrid silicon nitride–thin-film lithium niobate electro-optic modulators

Strategies for improved fabrication of integrated thin-film lithium niobate electro-optic (EO) Mach–Zehnder modulators (MZMs) are reported using scalable processes and designs. The MZM devices utilize direct bonding of unetched and unpatterned thin-film lithium niobate to patterned and planarized silicon photonic microchips. The latter contains silicon nitride waveguide structures of various widths that are used to form hybrid modes that are suitable for high-bandwidth low-voltage EO modulators based on Pockels effect. We report that the incorporation of appropriately designed outgassing channels and certain modifications to key processing steps helped achieve a greater than 99% reduction in void density during bonding. Void reduction is critically important for these traveling-wave hybrid MZM devices in which the optical mode is controllably distributed between multiple thin layers and propagates over millimeter-scale lengths.

Nonlinear optical properties of superalkali@teetotum boron clusters with potential applications on the electro-optic modulator

The development of nonlinear optics has revolutionized the photonic and optoelectronic fields in recent years.In this paper, we have designed a new class of donor–acceptor frameworks with enhanced nonlinear optical (NLO)properties using a series of superalkalis including Li3O, Li2NaO, LiNa2O, Li2KO, LiK2O as donors and three sizes of teetotum boron clusters (B14, B18, and B22) as acceptors. A systematic first-principles study has been performed on the electronic, linear, and NLO properties of superalkali@Bnassemblies. Besides the static non-linearity, the frequency-dependent electro-optic Pockel's effect (EOPE), second harmonic generation (SHG), and nonlinear refractive index have also been evaluated. In the case of dynamic NLO, the SHG process has a stronger NLO response than EOPE. At the typical experimental frequency of the Nd:YAG laser (ω = 0.04282) a.u., the SHG coefficients are about 2–3 times larger than the corresponding EOPE at this wavelength. Also, the nonlinear refractive index shows a remarkable response atω = 0.04 a.u. for LiK2O@B14.

A comparative study on nonlinear optical properties of zinc porphyrins analogs: Coordination atoms and group effects

AbstractDensity functional theory (DFT) has been carried out to investigate the electronic characteristics, UV–VIS–NIR absorption spectra, and nonlinear optical (NLO) properties of two series of zinc porphyrin analogs (FPD‐Nxand TPD‐Nx,x = 0–4) with donor‐π‐donor frameworks. The design of these analogs is based on previously synthesized furan‐linked zinc porphyrins (FPDs) and thiophene‐linked zinc porphyrins (TPDs). It is noted that their electro‐optical features are sensitive to the numbers of N‐coordination atoms and the attached groups. A dramatic enhancement of static first and second hyperpolarizabilities (β0andγ0) occurs when two furan/thiophene rings are attached to the zinc porphyrin. Among the two series, FPD‐N3 and TPD‐N3 have the largestβ0values of about 7600 a.u. The staticγ0values of these complexes range from 0.41 × 106to 1.79 × 106 a.u. The FPD‐Nxhas a largerγ0value than the corresponding TPD‐Nx, but theγ0value of FPD‐N2 is close to that of TPD‐N2. In the dynamic NLO process, the electro‐optical Pockels effect, second harmonic generation, and electro‐optic Kerr effect can be enhanced at the wavelength of 1907 nm. This study provides a new strategy for the experimental design of high‐performance NLO materials.

Simultaneous Manipulation of the Temporal and Spatial Behaviors of Nanosecond Laser Based on Hybrid Q-Switching

A hybrid Q-switching method based on a special-shaped saturated absorber was proposed for simultaneous manipulation of the temporal and spatial behaviors of a solid-state pulse laser. The temporal–spatial rate equation model of the laser was given and used to optimize the design parameter of the saturated absorber. Best spatial intensity homogenization performance can be expected using an active-passive hybrid Q-switched laser, comprising a Pockels cell and a cylinder Cr:YAG crystal with one end cut as a spherical concave surface. The optimized laser pulse width could be narrowed to 2.39 ns and the laser radial intensity distribution became quasi-super-Gaussian distribution with a radial intensity distribution ratio of 0.91, while that for the Gaussian beam was 0.84. In principle, the laser coherence can be maintained, and the laser spatial intensity distribution can be kept in a long propagation distance.

Distribution and evolution of surface charges in nanosecond pulsed dielectric barrier discharge under the quiescent air and airflow

The surface charges in nanosecond pulsed dielectric barrier discharge under quiescent air and airflow are detected based on the Pockels effect of electro-optical crystals. In quiescent air, it is found that the surface charge spot propagates and moves in a certain direction due to the combination of the transverse electric field and the thermal accumulation during dozens of consecutive discharge cycles. However, the position of the surface charge spot remains fixed throughout a single discharge cycle (0.83 ms). At the same time, the noticeable decay of surface charges emerges in the above time scales. Furthermore, when the airflow is introduced into the discharge gap, the propagation and movement of surface charges are accelerated. With the increase of airflow velocity, the discharge transforms from a filamentary mode to a diffuse mode, and the distribution of surface charges varies from discrete to uniform. The transition point of the discharge state and charge distribution corresponds to the airflow velocity of 10 m s−1. The airflow accelerates the decay of surface charges, resulting in the shrink and dispersion of surface charges, which is considered to be the fundamental reason for the airflow’s potential to improve discharge uniformity. The inherent mechanism for achieving uniform discharge is revealed in this study.

Surface charge characteristics in surface dielectric barrier discharge actuators with thin cylindrical exposed electrode

The influence of the cylindrical exposed electrode diameter on distribution and attenuation of the surface charge in surface dielectric barrier discharges is experimentally investigated using the Pockels effect of the Bi12SiO20 crystal. For the actuator with the smaller exposed electrode diameter, more positive charges accumulate closer to the exposed electrode after positive half periodic discharge, while the quantity of positive charges deposited on the surface in a discharge period at the same distance away from the exposed electrode is smaller. At the same time, the smaller the exposed electrode diameter is, the shorter decay time the positive charge filament needs. Combined with thrust generation of actuators, it can be indicated that a positive residual surface charge closer to the exposed electrode may play a more crucial role in the discharge and consequent thrust than one far away from the exposed electrode does. Also, the effect on the discharge of the positive residual surface charge may be greater than that of the negative residual surface charge. More explorations of the residual surface charge have been done by selectively enhancing the discharge of the actuator with a 10 μm exposed electrode using the pulse-AC dual power supply, drawing the same conclusions.

Optical Isolation of the Amplifier Cavity in XG-III PW Beamline

Optical isolation with high-quality, large-aperture polarizers is commonly used in high-power laser facilities to suppress retro-reflected pulses. However, it is hard to manufacture these polarizers. We propose an approach of optical isolation with two plasma-electrode Pockels cells instead of large-aperture polarizers. In this approach, Nd:glass slabs placed at the Brewster′s angle are used as polarizers. The analysis results and the application performances in the Xingguang (Star Light) XG-III PW beamline indicate that this approach can supply good protection to optical components in laser facilities.

OPTICAL VOLTAGE TRANSDUCERS

The paper presents basic operating principles of optical transducers for the measurement of high voltage. It was observed by Pockels that the change in refractive indexes in certain crystals is proportional to the applied electric fi eld. The main parts of the sensor based on Pockels effect are: polarizer, Pockels crystal and analyzer. These are passive elements to and from which the light is taken by means of optical fibers from an electronic device at the earth potential. The polarized light that vibrates in two mutually perpendicular planes passes through the crystal at different speeds that change under the infl uence of the electric fi eld, which is detected by an electronic circuit. The longitudinal and transverse effect are distinguished with respect to the applied electrical field.

Enhanced Pockels Effect in AlN Microring Resonator Modulators Based on AlGaN/AlN Multiple Quantum Wells

Enhanced Pockels Effect in AlN Microring Resonator Modulators Based on AlGaN/AlN Multiple Quantum Wells

Design of Novel Resonant Optical Voltage Sensor Based on Pockels Effect

A novel resonant optical voltage sensing scheme based on Pockels effect with less optical elements is proposed to pave the way for the miniaturization of voltage sensors in a high-voltage power grid, which can improve the voltage detection accuracy by using the multiple propagation of light in the resonator composed of Bi4Ge3O12 (BGO) crystal and reflector. Based on the multiple beam interference theory, the optical sensing model is analyzed to explore the influence of the key parameters such as the propagation loss and the resonator reflectivity on the performance of resonant optical voltage sensor. Considering the propagation loss and reflectivity, a resonator is designed to promote the limit sensitivity of the resonant optical voltage sensor. Also, based on the theoretical analysis results, we obtained that the design parameters (propagation loss <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula> and reflectivity <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${r}$ </tex-math></inline-formula> ) of the resonator are, respectively, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \le0.5$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${r} \ge0.83$ </tex-math></inline-formula> . Finally, the experimental equipment of the novel resonant optical voltage sensor is built, and the measured resonator finesse shows that the limit sensitivity of the resonant optical voltage sensor can achieve <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.689\times 10^{-{5}}$ </tex-math></inline-formula> V. Furthermore, the experimental results of the resonant optical voltage sensor demonstrate that the resonant frequency of the resonator is linear with the applied voltage. The proposed resonant sensing scheme has the potential to lay the foundation for the miniaturization of high-precision optical voltage sensors in the future.

Lithium niobate optical beam deflectors operating at both electro-optic and thermo-optic modes

A novel optical beam deflector based on a Lithium niobate (LN) waveguide is demonstrated, which can operate at both electro-optic and thermo-optic modes. At the electro-optic mode, the microstructured serrated electrodes induce inhomogeneous change in the refraction index of LN waveguide via the Pockels effect when a voltage is applied. The incident beam is thus deflected with the deflected distance changing linearly with the applied voltage. A high deflection speed up to 2.5 GHz is observed experimentally. The optical beam deflector can operate at the thermo-optic mode, where the deflected distance depends on the applied electric power; thus it varies quadratically with the applied voltage. The deflection capacity at the thermo-optic mode is much higher than electro-optic mode, since the deflection distances are respectively 27.19 and 2.53 μm for the thermo-optic and electro-optic modes at a 4 V applied voltage. Therefore, the distinct electro-optic and thermo-optic operating modes enable the LN optical beam deflector to be qualified for various tasks, such as optical scanning, optical modulator.

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.