High Electro-optic Coefficient Research Articles

Strain-concentration for fast, compact photonic modulation and non-volatile memory

A critical figure of merit (FoM) for electro-optic (EO) modulators is the transmission change per voltage, dT/dV. Conventional approaches in wave-guided modulators maximize dT/dV via a high EO coefficient or longer light-material interaction lengths but are ultimately limited by material losses and nonlinearities. Optical and RF resonances improve dT/dV at the cost of spectral non-uniformity, especially for high-Q optical cavity resonances. Here, we introduce an EO modulator based on piezo-strain-concentration of a photonic crystal cavity to address both trade-offs: (i) it eliminates the trade-off between dT/dV and waveguide loss—i.e., enhancement of the resonance tuning efficiency dv c /dV for the fixed EO coefficient, waveguide length, and cavity Q—and (ii) at high DC strains it exhibits a non-volatile (NV) cavity tuning Δvc,NV for passive memory and programming of multiple devices into resonance despite fabrication variations. The device is fabricated on a scalable silicon nitride-on-aluminum nitride platform. We measure dv c /dV=177±1MHz/V, corresponding to Δv c =40±0.32GHz for a voltage spanning ±120V with an energy consumption of δU/Δv c =0.17nW/GHz. The modulation bandwidth is flat up to ωBW,3dB/2π=3.2±0.07MHz for broadband DC-AC and 142±17MHz for resonant operation near a 2.8 GHz mechanical resonance. Optical extinction up to 25 dB is obtained via Fano-type interference. Strain-induced beam-buckling modes are programmable under a “read-write” protocol with a continuous, repeatable tuning range of 5±0.25GHz, allowing for storage and retrieval, which we quantify with mutual information of 2.4 bits and a maximum non-volatile excursion of 8 GHz. Using a full piezo-optical finite-element-model (FEM) we identify key design principles for optimizing strain-based modulators and chart a path towards achieving performance comparable to lithium niobate-based modulators and the study of high strain physics on-chip.

Design of RGB tunable narrowband metalens using BaTiO₃ material with high electro-optic coefficient

Design of RGB tunable narrowband metalens using BaTiO₃ material with high electro-optic coefficient

Giant electro-optic response in transparent rhombohedral ferroelectric Sm-PIN-PMN-PT crystal based on domain engineering

The relaxor ferroelectric crystal Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT), located near the morphotropic phase boundary (MPB), exhibits exceptionally high piezoelectric and electro-optic (EO) responses. Nevertheless, lower optical transparency and phase transition temperature of PMN-PT limit its optical applications. The ternary system Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) holds promise in addressing these challenges with a higher Curie temperature. Additionally, specific ferroelectric domain polarization techniques can eliminate domain scattering, substantially enhancing the transparency of the crystal. In this study, we explore the optical properties of Sm-doped PIN-PMN-PT. We achieve a 2R domain-engineered state by polarizing along the (110) direction of the crystal. The high transparency allows us to extract an effective EO coefficient of up to 431.5 pm/V from the Sm-PIN-PMN-PT crystal at the telecommunications wavelength. Second-harmonic generation (SHG) probing verified the domain-engineered state in Sm-PIN-PMN-PT. The temperature-dependent SHG reveals the ferroelectric phase transition process, laying the groundwork for studying the stability of the EO response. The Sm-PIN-PMN-PT crystal exhibits an exceptionally high EO coefficient, which is crucial for the development of enhanced EO devices with high integration and low driving voltages.

Integrated Optical Waveguide Electric Field Sensors Based on Bismuth Germanate.

Bismuth germanate (Bi4Ge3O12, BGO) is a widely used optical sensing material with a high electro-optic coefficient, ideal for optical electric field sensors. Achieving high precision in electric field sensing requires fabricating optical waveguides on BGO. Traditional waveguide writing methods face challenges with this material. This study explores using femtosecond laser writing technology for preparing waveguides on BGO, leveraging ultrafast optical fields for superior material modification. Our experimental analysis shows that a cladding-type waveguide, written with a femtosecond laser at 200 kHz repetition frequency and 10.15 mW average power (pulse energy of 50.8 nJ), exhibits excellent light-guiding characteristics. Simulations of near-field optical intensity distribution and refractive index variations using the refractive index reconstruction method demonstrate that the refractive index modulation ensures single-mode transmission and effectively confines light to the core layer. In situ refractive index characterization confirms the feasibility of fabricating a waveguide with a refractive index reduction on BGO. The resulting waveguide has a loss per unit length of approximately 1.2 dB/cm, marking a successful fabrication. Additionally, we design an antenna electrode, analyze sensor performance indicators, and integrate a preparation process plan for the antenna electrode. This achievement establishes a solid experimental foundation for future studies on BGO crystal waveguides in electric field measurement applications.

Organic Electro-Optic Materials with High Electro-Optic Coefficients and Strong Stability.

The preparation of high-performance electro-optical materials is one of the key factors determining the application of optoelectronic communication technology such as 5G communication, radar detection, terahertz, and electro-optic modulators. Organic electro-optic materials have the advantage of a high electro-optic coefficient (~1000 pm/V) and could allow the utilization of photonic devices for the chip-scale integration of electronics and photonics, as compared to inorganic electro-optic materials. However, the application of organic nonlinear optical materials to commercial electro-optic modulators and other fields is also facing technical bottlenecks. Obtaining an organic electro-optic chromophore with a large electro-optic coefficient (r33 value), thermal stability, and long-term stability is still a difficulty in the industry. This brief review summarizes recent great progress and the strategies to obtain high-performance OEO materials with a high electro-optic coefficient and/or strong long-term stability. The configuration of D-π-A structure, the types of materials, and the effects of molecular engineering on the electro-optical coefficient and glass transition temperature of chromophores were summarized in detail. The difficulties and future development trends in the practical application of organic electro-optic materials was also discussed.

Significantly enhanced transmittance and EO property in PMN-PT via optimized two-step pressure-free sintering

It is a great challenge to prepare Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN-PT) ceramics of very high transparency with only oxygen atmosphere pressureless sintering process. To address this issue, this work proposed an optimal low-cost two-step oxygen atmosphere sintering process with a first step at high temperature (T1) for minutes, followed by a second step at lower temperature (T2) for hours without applied pressure. High transmittance of 70 % in the near-infrared wavelength was achieved by our novel two-step process, which far exceeds the performance of PMN–PT ceramics prepared by only oxygen atmosphere sintering process reported in the past and demonstrates comparable performance compared to the costly hot-pressing sintering process. Meanwhile, it shows a high quadratic electro-optic (EO) coefficient of 42.1 × 10−16 m2 V−2, which is meaningful for applications in EO devices. Furthermore, the effect of the temperature difference between the first and second sintering step on the microstructure, transmittance, domain structure, ferroelectric and dielectric property, and polarization switching were discussed. The enhanced transparency is mainly attributed to the higher relative density, and weaker photoluminescence effect with lesser light absorption loss at optimal T1-T2. The improved EO property is due to greater polarization response originating from the interaction of defect dipoles and nanodomains. Such a process should facilitate the cost-effective preparation of other transparent electro-optic materials for practical applications.

Lithium niobate thin film electro-optic modulator

Abstract The linear electro-optic effect offers a valuable means to control light properties via an external electric field. Lithium niobate (LN), with its high electro-optic coefficients and broad optical transparency ranges, stands out as a prominent material for efficient electro-optic modulators. The recent advent of lithium niobate-on-insulator (LNOI) wafers has sparked renewed interest in LN for compact photonic devices. In this study, we present an electro-optic modulator utilizing a thin LN film sandwiched between top and bottom gold (Au) film electrodes, forming a Fabry–Pérot (F–P) resonator. This resonator exhibits spectral resonance shifts under an applied electric field, enabling efficient modulation of reflected light strength. The modulator achieved a 2.3 % modulation amplitude under ±10 V alternating voltage. Our approach not only presents a simpler fabrication process but also offers larger modulation amplitudes compared to previously reported metasurface based LN electro-optic modulators. Our results open up new opportunities for compact electro-optic modulators with applications in beam steering devices, dynamic holograms, and spatial light modulators, and more.

Synthesis and characterization of a julolidine-based electro-optic molecular glass.

Organic electro-optic (EO) materials have recently gained considerable attention owing to their advantages compared to inorganic EO materials. Among different kinds of organic EO materials, organic EO molecular glass exhibits desired prospect because of its high chromophore loading density and large macroscopic EO activity. The objective of this study is to design and synthesize a novel organic EO molecular glass JMG utilizing julolidine moiety as the electron donor, thiophene moiety as the conjugated bridge, trifluoromethyl substituted tricyanofuran derivate (Ph-CF3-TCF) as the electron acceptor. The JMG's structure was characterized through NMR and HRMS. The photophysical property, glass transition temperature, first hyperpolarizability (β) and dipole moment (μ) of JMG were determined through UV-vis spectra, DSC test and DFT calculation. JMG's Tg reached to 79 °C and it can form high-quality optical film. The theoretical calculation shows that the first hyperpolarizability (β) and dipole moment (μ) of JMG were calculated to 730×10-30 esu and 21.898 D. After connecting poling with the poling voltage of 49 V/μm at 90 ℃for 10 min, the highest EO coefficient (r33) of the poled JMG films reached to 147 pm/V. A novel julolidine-based NLO chromophore with two tert-butyldiphenylsilyl (TBDPS) groups was successfully prepared and characterized. TBDPS group is introduced as the film-forming group, and it also plays the role of isolation group, which can suppress the electrostatic interaction between chromophores, improve the poling efficiency and further enhance the EO activity. The excellent performances endow JMG with potential applications in device fabrication.

Synthesis, structure, growth, characterization and quantum chemical studies on 2-amino-5-bromopyridinium trichloroacetate: A novel phasematchable organic NLO single crystal

Organic crystals have become excellent candidates towards nonlinear optical (NLO) applications as they possess superior second and third order optical nonlinearities and high electro-optic coefficients when compared with their inorganic counterparts. In this direction, 2-Amino-5-bromopyridinium trichloroacetate (2A5BPT), a new organic second-order nonlinear optical compound is synthesized and optical grade single crystals are formed utilizing a slow evaporation solution growth approach at room temperature while using methanol as the solvent. Single crystal X-ray diffraction study shows that the title compound is assigned to monoclinic crystal system having non-centrosymmetric space group Cc. The crystal is transparent ( ̴ 85%) throughout the whole visible spectrum, according to the Ultraviolet-Visble (UV–Vis) spectra, with a cutoff wavelength of 367 nm and an optical energy band gap Eg of 3.32 eV. The crystal possesses good thermal stability. The compound has a 1.6 times greater powder second harmonic generation (SHG) efficiency than potassium dihydrogen phosphate (KDP). The phase matchability of the 2A5BPT is studied through particle size dependence of SHG. The intermolecular connection demonstrated by numerous inter contacts has been shown by a molecular Hirshfeld surface analysis of the crystal structure, and the related 2-dimensional finger print analysis further evaluates the individual contribution from each atom. In order to examine the first order hyperpolarizability, molecular electrostatic potential, and Highest occupied molecular orbital-Lowest unoccupied molecular orbital (HOMO-LUMO) energies, the quantum chemical calculations for the title molecule (2A5BPT) were carried out by density functional theory (DFT) utilizing the B3LYP/6–311++G(d,p) basis set. According to these results, the 2A5BPT crystal could be suitable for optoelectronic applications.

Epitaxial LiNbO3 growth and layer transfer for thin-film electro-optic modulator realization

The aim of the PhD project is to develop a new trend in modulation system for Exail company: thin film (<1 μm) lithium niobate (LN) electro-optic modulator. It exhibits better performance in term of bandwidth, power consumption and footprint than legacy ones [1-3]. This PhD is a cooperation between Exail photonics which is world-renowned for the performances of their electro-optic modulators and FEMTO-ST institute which can offer the possibility to grow stoichiometric LN thin film by means of direct liquid injection metalorganic chemical vapor deposition (DLI-MOCVD). This cooperation opens the possibility to obtain industrialization of optical device based on CVD LN stoichiometric layers which allow to have enhanced performances such as higher electro-optic coefficient than that of congruent compositions of commercial single crystals. Thus, all steps from MOCVD layer deposition to modulator realization can be done here in Besançon.

Design of optical phased array with low-sidelobe beam steering in thin film lithium niobate

Optical beam-steering devices are crucial components of complex optical control systems, which are widely used in diverse information-processing applications. Optical phased arrays (OPAs) as the promising beam-steering devices, have proven to alleviate current performance limitations in beam steering devices for ultra-small solid-state light detection and rangings (LiDARs) and free-space communication systems. The high electro-optic (EO) coefficient (γ33 = 30.9 pm/V) of lithium niobate (LiNbO3, LN) can be a useful platform for phase tuning of the OPAs, which is conducive to enable phase shifting for non-mechanical beam steering with high-speed and low power consumption. The design, configurations and LN-OPA corresponding performances are discussed in this paper. The OPA consisting of different waveguides array is optimized with a side lobe suppression lower than - 10 dB at the wavelength of 1.55 μm. Meanwhile, the OPA with grating emitters or adding silica cavity further improves the deflection quality of the beam. Then optical beam steering with an angle of 50° in one dimension controlled by the LN-OPA has been demonstrated. The proposed OPA on the LN platform in this work might hold significances for advanced LiDAR schemes based on EO tuning.

La-doped PMN–PT transparent ceramics with ultra-high electro-optic effect and its application in optical devices

Transparent electro-optic (EO) ceramics of La-doped 0.75Pb(Mg_1/3Nb_2/3)O₃–0.25PbTiO₃ (0.75PMN–0.25PT) were prepared successfully. High transparency of 69% in the near-infrared (IR) wavelength (1550 nm) was achieved at 2 mol% La doping, meanwhile it shows an extremely high quadratic EO coefficient of 45.4×10⁻¹⁶ m²·V⁻², which is indispensable for applications in EO devices. The distribution of a polar nanodomain structure of the samples experiences disorder–order–disorder evolution in a La doping range. It is found that a parallelly-stacked polar nanodomain structure with an easier and faster polarization switching in the 2 mol% La-doped sample suggests that an ordering distribution of polar nanoregions would be critical to inducing large EO effect, transparency, and piezoelectric response. A triple-cavity tunable optical filter (TOF) with a single transmission peak and a tuning voltage below 30 V in a tuning range of 190–197 THz was designed based on our ceramics. The work is believed to bridge the relationship among doping-engineering, EO properties, and polarization behavior, which would guide the further optimization of transparent EO ceramics.

Synthesis and Characterization of Electro-Optic Polyurethaneimide-Polyimide Copolymers

Polyurethaneimide prepolymer was synthesized using the synthesized chromophore C containing tricyanofuran, hexafluorodianhydride and phenyl diisocyanate as monomers. Polyimide prepolymers were synthesized using fluorinated aromatic diether dianhydride and fluorinated aromatic diamine as monomers. Polyurethaneimide-polyimide (PUI-FPI) copolymers were then synthesized by a polycondensation reaction of the polyimide and polyurethaneimide prepolymers. The electro-optic (EO) PUI-FPI copolymers had a special segment structure and concentrate the advantages of polyurethaneimide and polyimide. The copolymers exhibited good film-forming properties, high glass transition temperature (Tg =196 °C), and high thermal stability (Td up to 358 °C). The copolymers possessed a high EO coefficient (γ33 =72 pm/V) at the 1550 nm wavelength, good long-term electro-poled orientation stability, and low optical propagation loss (1.2–1.4 dB/cm) at 1550 nm. Mach-Zehnder interferometric electro-optic modulators were designed and fabricated using the synthesized copolymer as the waveguide material. The prepared polymer optical waveguide EO modulators showed a good low-frequency electro-optic modulation response. The results showed that the synthesized polyurethaneimide-polyimide copolymers meeted the performance requirements for the preparation of polymeric optical waveguide devices and were suitable as polymeric electro-optic waveguide materials.

Enhancement of the linear electro-optic effect by high pressure

It is challenging to design electro-optic (EO) crystals with both a large bandgap and a high EO coefficient. We propose that some semiconductors synthesized under a high pressure environment can present both a large bandgap and a high linear EO coefficient because of the enhanced strength of the valence bond. The electronic band structures and linear EO coefficients of the $II\mathrm{Si}{\mathrm{N}}_{2}$ ($II=\mathrm{Mg}$, Sr, Ba) compounds are studied using first-principles calculation. Our calculated results predict that both $\mathrm{SrSi}{\mathrm{N}}_{2}$ and $\mathrm{BaSi}{\mathrm{N}}_{2}$, under a high-pressure condition, will crystalize into an orthorhombic structure with the same space group of $\mathrm{MgSi}{\mathrm{N}}_{2}$ under ambient pressure. The calculated bandgaps are 5.48, 4.41, and 3.57 eV, respectively, for $\mathrm{MgSi}{\mathrm{N}}_{2}, \mathrm{SrSi}{\mathrm{N}}_{2}$, and $\mathrm{BaSi}{\mathrm{N}}_{2}$, while the calculated linear EO coefficients are 1.55, 12.09, and 21.60 pm/V at a fiber communication wavelength of 1550 nm. The increasing linear EO coefficients can be interpreted by the enhanced bond strength and a reduced bandgap. This work indicates that it is feasible to enhance the linear EO coefficient with high pressure.

Polarization independent high-speed spatial modulators based on an electro-optic polymer and silicon hybrid metasurface

Dynamical control of the constitutive properties of a light beam is important for many applications in photonics and is achieved with spatial light modulators (SLMs). Performances of the current demonstrations, such as liquid-crystal or micro-electrical mechanical SLMs, are typically limited by low (∼kHz) switching speeds. Here, we report a high-speed SLM based on the electro-optic (EO) polymer and silicon hybrid metasurface. The specially configured metasurface can not only support a high-Q resonance and large “optical–electrical” overlap factor, but also overcome the challenge of polarization dependence in traditional EO modulators. Combined with the high EO coefficient of the polymer, a 400 MHz modulation with an RF driving source of 15 dBm has been observed in the proof-of-concept device near the wavelength of 1310 nm. The device with the desired merits of high speed, high efficiency, and micrometer size may provide new opportunities for high-speed smart-pixel imaging, free-space communication, and more.

An ultrahigh sensitivity three-dimensional electric-field sensor with barium titanate crystal waveguides

The high-speed development and applications of modern automation production, high-capacity high-speed telecommunications, and aerospace are promoting the detection and sensing of various electric fields. In this article, we investigate a three-dimensional high-frequency electric-field sensor with a barium titanate (BaTiO3) crystal film waveguide due to an extremely high electrooptic (EO) coefficient, r51 = r42. First, the dependences of the lowest electric field, namely, the sensitivity of the sensor to the electric field and the most sensitive direction, are modeled through the nonlinear EO modulation equation of the EO coefficient, r51, and birefringence, beo, with an embedded waveguide/electrode regime. Then, for the given r51/beo values, broad dependences of device sensitivities are numerically simulated with a broad design of electrodes. Thus, as a result, for a given BaTiO3 crystal thin-film having an EO coefficient value of r51 = ≥500 pm/V and an absolute beo value of ≤0.01, the lowest electric field of tens of kilovolt/m level and the electric-field direction could also be detected with a sensing length of millimeters. Meanwhile, the frequency dependence of a scattering parameter of the microwave sensor antenna, S11, is simulated and the frequency point of 2.15 GHz for the highest gain antenna is found.

Ferroelectric crystals with giant electro-optic property enabling ultracompact Q-switches.

Relaxor-lead titanate (PbTiO3) crystals, which exhibit extremely high piezoelectricity, are believed to possess high electro-optic (EO) coefficients. However, the optical transparency of relaxor-PbTiO3 crystals is severely reduced as a result of light scattering and reflection by domain walls, limiting electro-optic applications. Through synergistic design of a ferroelectric phase, crystal orientation, and poling technique, we successfully removed all light-scattering domain walls and achieved an extremely high transmittance of 99.6% in antireflection film-coated crystals, with an ultrahigh EO coefficient r33 of 900 picometers per volt (pm V-1), >30 times as high as that of conventionally used EO crystals. Using these crystals, we fabricated ultracompact EO Q-switches that require very low driving voltages, with superior performance to that of commercial Q-switches. Development of these materials is important for the portability and low driving voltage of EO devices.

Reporting Excellent Transverse Piezoelectric and Electro‐Optic Effects in Transparent Rhombohedral PMN‐PT Single Crystal by Engineered Domains

Transparent ferroelectric crystals with high piezoelectricity are challenging to build because of their complex structure and disordered domains in rhombohedral relaxor ferroelectrics. There are eight domains along the <111> direction, which cause light scattering. In this study, perfect transparency is achieved along the [110] and [001] directions in [110]-poled rhombohedral 0.72Pb(Mg1/3 Nb2/3 )O3 -0.28PbTiO3 (PMN-PT) crystals, which have a high d31 value of 1700 pC N-1 and a high electro-optic coefficient γ33 of 320 pm V-1 . This implies that the [110]-oriented rhombohedral PMN-0.28PT crystal can realize the mode of transverse modulation, whereas the [001]-oriented PMN-0.28PT crystal is more suitable for the longitudinal mode. Through piezoresponse force microscopy (PFM), it is confirmed that the [110]-poled rhombohedral PMN-PT crystals form 71° layered domains, which are similar to the 109° layered domains of the [001]-oriented transparent crystal. Combined with PFM and birefringence microscopy, the degradation of domains and thickness dependence of piezoelectricity provide clear evidence for the relationship between the engineered domain structures and piezoelectric properties, which should be considered in the design of piezoelectric or electro-optic devices with excellent performance. This work enriches the research on ferroelectric domain engineering for excellent transparency and high piezoelectricity to provide new ideas for photoacoustic devices.

Electro-optic polymer and silicon nitride hybrid spatial light modulators based on a metasurface.

Spatial light modulators (SLMs) are important for various applications in photonics, such as near-infrared imaging, beam steering and optical communication. After decades of advances, current commercial devices are typically limited to kilohertz modulating speeds. To realize higher operating speeds, an electro-optic (EO) polymer and silicon nitride hybrid SLM has been demonstrated in this work. We utilize a specially designed metasurface to support a relatively high quality resonance and simultaneously confine most of the incident light in the active EO polymer layer. Combing with the high EO coefficient of the polymer, a clear modulation at 10 MHz with a driving voltage of Vp-p=±10 V has been observed in the proof-of-concept device. Our first-generation device leaves vast room for further improvement and may open an attractive route towards compact SLM with an RF modulation higher than 100 GHz.

Tunable polarization mode conversion using thin-film lithium niobate ridge waveguide.

Lithium niobate on insulator (LNOI) waveguides, as an emerging technology, have proven to offer a promising platform for integrated optics, due to their strong optical confinement comparable to silicon on insulator (SOI) waveguides, while possessing the versatile properties of lithium niobate, such as high electro-optic coefficients. In this paper, we show that mode hybridization, a phenomenon widely found in vertically asymmetric waveguides, can be efficiently modulated in an LNOI ridge waveguide by electro-optic effect, leading to a polarization mode converter with 97% efficiency. Moreover, the proposed device does not require tapering or periodic poling, thereby greatly simplifying the fabrication process. It can also be actively switched by external fields. Such a platform facilitates technological progress of photonics circuits and sensors.