Effective Electro-optic Coefficient Research Articles

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.

Electro-optic effect in thin film strontium barium niobate (SBN) grown by RF magnetron sputtering on SrTiO3 substrates

Ferroelectric strontium barium niobate (SrxBa1−xNb2O6 or SBN) is a material with high electro-optic (EO) response. It is currently of interest in low voltage silicon-integrated photonics (SiPh). We have grown strongly textured SBN films with x = 0.65 by radio frequency sputtering on (100)-oriented SrTiO3 substrates where grains with mixed (310) and (001) out-of-plane orientation form. For these mixed orientation films, we observed a maximum effective EO coefficient of 230 pm/V using a transmission EO measurement geometry that is responsive only to the in-plane polarization component coming from the (310)-oriented grains. We also demonstrate that by growing SBN on TiO2-terminated SrTiO3 substrates, we can obtain predominantly (001)-oriented SBN films with out-of-plane polarization. Transmission EO measurements on such (001)-oriented films show a reduced effective Pockels coefficient of 88 pm/V, which is consistent with the overall ferroelectric polarization becoming out-of-plane. This work shows that controlling substrate termination is effective in controlling the grain orientation of SBN films grown on top and that one can readily integrate SBN films on SrTiO3-buffered Si for use in SiPh.

Linear Electro-Optic Effect in 2D Ferroelectric for Electrically Tunable Metalens.

The advent of 2D ferroelectrics, characterized by their spontaneous polarization states in layer-by-layer domains without the limitation of a finite size effect, brings enormous promise for applications in integrated optoelectronic devices. Comparing with semiconductor/insulator devices, ferroelectric devices show natural advantages such as non-volatility, low energy consumption and high response speed. Several 2D ferroelectric materials have been reported, however, the device implementation particularly for optoelectronic application remains largely hypothetical. Here, the linear electro-optic effect in 2D ferroelectrics is discovered and electrically tunable 2D ferroelectric metalens is demonstrated. The linear electric-field modulation of light is verified in 2D ferroelectric CuInP2S6. The in-plane phase retardation can be continuously tuned by a transverse DC electric field, yielding an effective electro-optic coefficient rc of 20.28 pm V-1. The CuInP2S6 crystal exhibits birefringence with the fast axis oriented along its (010) plane. The 2D ferroelectric Fresnel metalens shows efficacious focusing ability with an electrical modulation efficiency of the focusing exceeding 34%. The theoretical analysis uncovers the origin of the birefringence and unveil its ultralow light absorption across a wide wavelength range in this non-excitonic system. The van der Waals ferroelectrics enable room-temperature electrical modulation of light and offer the freedom of heterogeneous integration with silicon and another material system for highly compact and tunable photonics andmetaoptics.

Huge piezoelectricity and electro-optic effects in rhombohedral relaxor ferroelectric single crystals by Sm3+ doping

In recent years, relaxor ferroelectric single crystals have attracted people's attention and research because of their excellent piezoelectric properties at morphotropic phase boundary(MPB). The ternary system Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) crystals have higher Curie temperature and coercive field, which have the opportunity to be applied in high-temperature devices. The crystals of the rhombohedral phase have better stability, but their performance is not as good as that of the MPB component crystals. In this paper, the piezoelectric properties of rhombohedral PIN-PMN-28PT single crystals are improved by Sm3+ doping. The piezoelectric coefficient d33 after AC polarization along [001] direction can reach 3125pC/N, which is 60% higher than that of undoped crystals. Meanwhile, the crystal exhibits excellent optical performance after DC polarization along [110] direction. The crystal has an effective electro-optic coefficient of 386 pm/V at room temperature and a stable frequency-dependent characteristic, which is expected to be an ideal material for electro-optic devices.

Combined effect of piezoelectric, elastic, dielectric, and electro-optical properties on single-domain potassium tantalate niobate single crystals

The complete matrix parameters of the elastic, dielectric, and piezoelectric constants of high-quality Fe-doped KTa1-xNbxO3 (KTN) single crystals poled along [001]PC were successfully confirmed. The piezoelectric coefficients d33 and k33, which are of interest for various applications, are 137 pC/N and 50.4 %, respectively. The orientation dependence of these properties for the single-domain Fe:KTN samples was calculated, and it was found that the [001]PC direction is the optimal orientation for the highest performance with a single-domain state, at which the sample exhibits good transparency. Further, the single-domain sample exhibits a large effective electro-optical coefficient (γc = 126.6 p.m./V), and the combined piezoelectric and electro-optical effects provide a 0.4 % electro-optical coefficient. This is beneficial for applying high-response speed modulators with an effective electro-optical working mode and a low contribution of the inverse piezoelectric effect, owing to slower frequency response characteristics.

Strain engineering of the electro-optic effect in polycrystalline BiFeO3 films [Invited

Electro-optic thin film materials, which change their refractive index upon the application of an electric field, are crucial for the fabrication of optical modulators in integrated photonic circuits. Therefore, it is key to develop strategies to tune the linear electro-optic effect. Strain engineering has arisen as a powerful tool to optimize the electro-optic coefficients in ferroelectric thin films. In this report, the electro-optical properties of polycrystalline bismuth ferrite (BiFeO3) thin films are studied. The electro-optic coefficients (reff) of low-cost solution-processed BiFeO3 films under different substrate-induced thermal stress are characterized using a modified Teng-Man technique in transmission geometry. The influence of poling state and substrate stress on the electro-optical properties are discussed. The films show a notable piezo-electro-optic effect: the effective electro-optic coefficient increases both under compressive and tensile in-plane stress, with compressive stress having a much more profound impact. Electro-optic coefficients of 2.2 pm/V are obtained in films under a biaxial compressive stress of 0.54 GPa.

Strong electro-optic effect in Mg incorporated ZnO thin films

a-axis oriented ZnMgO epitaxial thin films with a strong linear electro-optic (EO) effect were developed by radio frequency magnetron sputtering. The Mg incorporation into ZnO thin films not only obviously increases the transmittance at the wavelength range of 400–800 nm but also reduces the leakage current by 3–6 orders of magnitude. Furthermore, with the increase in the Mg content, the linear EO response enhances significantly. In particular, the derived effective EO coefficient rc of the Zn0.72Mg0.28O thin film is (7.6 ± 0.2) pm/V, which is over three times larger than the reported values for ZnO-based thin films and over twice larger than that of ZnO single crystals. The results and discussion conclude that an enhanced intrinsic contribution can be responsible for the increase in rc with Mg incorporation. These findings open the way for the ZnO-based thin films to EO devices in optical communication and optical interconnects.

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.

Enormous electro-optic effect in paraelectric nanodisordered KTa1-xNbxO3 crystal.

Recent experiments have revealed that the order of the electro-optic (EO) effect depends on the frequency of electric field in paraelectric nanodisordered KTa1-xNbxO3 (KTN) crystal. Through the dielectric frequency spectrum under the bias electric field, enormous linear and quadratic EO effects were discovered at the resonance frequencies, which changed the perception that only the quadratic EO effect exists. Applying just a small AC electric field of 6 V/mm, the effective linear EO coefficient reached 478 pm/V at 609 kHz, and the effective quadratic EO coefficient reached 4.39*10-13m2V-2at 302 kHz. The reason why an extremely low electric field results in an enormous EO coefficient is attributed to the resonance between the polar nanoregions (PNRs) and the electric field, induced by the field-driven reorientation of free dipoles on the boundary of the PNRs. In addition, the order of EO effect depending on the frequency of electric field was attributed to the motion modes of the PNR. This finding improves the understanding of how the EO effect is caused by field-driven PNR dynamics, but also provides a basis for the development of EO devices.

Crystal growth and photoelectric performance of γ-CuCl by the vertical Bridgman method

The cuprous chloride (γ-CuCl) crystal exhibits wide optical transmittance and electro-optic property with Pockels effect, which shows a great potential application in the infrared band. In this paper, a large transparent γ-CuCl crystal with Φ22 mm × 35 mm has been grown by the vertical Bridgman method without flux for the first time. The crystal was further characterized by the X-ray diffraction of the powder measurement, thermal analysis, optical and electric properties. The results indicate that γ-CuCl crystal crystallize in the F4¯3m space group of the cubic system and wide direct band gap (Eg = 3.1 eV). The effective electro-optic coefficient is 2.91 pm/V at 60 Hz.

An effective optoelectronic mixing method based on bulk KTN crystal

An effective optoelectronic mixing (OEM) method based on bulk potassium tantalate niobate (KTN) crystal was proposed. The optical isotropy of the cubic phase rendered KTN insensitive to the incident angles of collected beams. Consequently, effective electro-optic (EO) modulation could be realized under a large incident range of 20°. The massive quadratic EO coefficient of 3.7 × 10−15 m2/V2 could effectively reduce local oscillation (LO) voltage, such that OEM could be achieved under low power consumption. On the basis of the above advantages, a mixing efficiency model for KTN mixer was proposed to describe mixing characteristics. Simultaneously, a mixing efficiency of 44% within the 20° incident range was achieved at a power consumed for each pixel of 230 μW.

Electro-Optic Intensity Modulation in Fe-Doped KTa0.65Nb0.35O3 Crystals

KTa0.65Nb0.35O3 and Fe-doped KTa0.65Nb0.35O3 crystals were grown by the top-seeded solution growth method (TSSG). Fe ion doping significantly improves the electro-optic properties of cubic KTN crystals. We describe their electro-optic modulation theory and experimental research. The electro-optic modulation waveform deduced by theoretical calculation is basically consistent with the waveform measured in the experiment. We observed the attenuation of light modulation under multiple voltage cycles. The modulation curve of the crystal is inconsistent when the crystal voltage is boosting and bucking. Under the same voltage condition, the higher the incident light power, the faster the modulation depth attenuation. In this experiment, the size of the KTN crystal chip is 6 mm × 5 mm × 2 mm. We obtain the effective electro-optic coefficient as s11 − s12 = 1.34 × 10−15 m2/V2; the half-wave voltage near the Curie temperature is 39 V.

Achieve single domain state in (111)-oriented rhombohedral phase PMN-PT relaxor ferroelectric single crystals for electro-optical application

An electro-optic (EO) modulator is one of the most important optical devices and has been widely used in the photonic industry. Performance of EO modulators mainly depends on the property of EO materials. Here, the EO property of the (111)-oriented single domain rhombohedra phase (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT) single crystal is investigated. Due to the light scattering by domain walls, a single domain crystal is essential and has been well prepared here by a thermal annealing and high temperature poling process. It is found that domains become irregular with significantly decreased dimension after annealing, which indicates that the ferroelastic domain walls are eliminated. A crack-free single domain crystal shows excellent optical quality, with a high transmittance of approximately 70% in near-infrared regions. Finally, the effective EO coefficient of the (111)-oriented rhombohedral phase PMN-PT crystal is measured by a Senarmont compensator amplitude modulator. An effective EO coefficient of 112 pm/V is obtained in the (111)-oriented rhombohedral phase PMN-PT crystal, which is much higher than that of the commercial LiNbO3 crystal, indicating the potential for use in compact and low driving voltage EO devices.

Electro-optic properties of singly and doubly doped lithium niobate crystal by rare earth elements for optoelectronic and laser applications

Congruent lithium niobate (LN) doped with rare-earth elements is a promising host for integrated optic combining the properties straightforwardly associated to the dopant with the good electro-optic (EO) properties. By direct technique based on interferometric optical arrangement at a wavelength of 633 nm and at room temperature, we have experimentally determined the figure of merit F = n3reff, (n is the refractive index and reff, the effective EO coefficient) and finally calculated the EO coefficients reff of the third-column of the unclamped EO tensor of three series of singly doped LN with Yb3+, Ho3+, Tm3+ and two series of doubly doped Er3+–Yb3+. It is found that in all the studied opto-geometric configurations, the unclamped figure of merit and consequently the corresponding EO coefficients are relatively constant in the considered dopant concentration range. As the figure of merit, F qualifies crystals for EO modulation and laser applications, all reported results confirm that the LN singly or doubly doped with rare-earth elements are very promising versatile candidates for several multifunctional nonlinear devices in optoelectronic and laser applications.

Measuring effective electro-optic coefficient at 1040 nm by spectral intensity modulation with THz time-domain spectroscopy

We report a single method for measuring the effective electro-optics (EO) coefficient only by spectral intensity modulation with a terahertz time-domain spectroscopy (THz-TDS) device. Compared with conventional methods, the measuring device based on THz-TDS by probing the spectral intensity modulation is simple, rapid, and highly sensitive. It does not require special preparation process, electrode contact or applying high voltage on the sensor samples. The EO coefficients of four kinds of materials, namely, ZnTe and GaP crystals, DAST wafer and GaSe film, are measured at 1040 nm. The results showed good agreement with literature data by the conventional methods.

Giant Electro-Optical Effect through Electrostriction in a Nanomechanical Metamaterial.

Electrostriction is a property of all naturally occurring dielectrics whereby they are mechanically deformed under the application of an electric field. It is demonstrated here that an artificial metamaterial nanostructure comprising arrays of dielectric nanowires, made of silicon and indium tin oxide, is reversibly structurally deformed under the application of an electric field, and that this reconfiguration is accompanied by substantial changes in optical transmission and reflection, thus providing a strong electro-optic effect. Such metamaterials can be used as the functional elements of electro-optic modulators in the visible to near-infrared part of the spectrum. A modulator operating at 1550 nm with effective electrostriction and electro-optic coefficients of order 10-13 m2 V-2 and 10-6 m V-1 , respectively, is demonstrated. Transmission changes of up to 3.5% are obtained with a 500 mV control signal at a modulation frequency of ≈6.5 MHz. With a resonant optical response that can be spectrally tuned by design, modulators based on the artificial electrostrictive effect may be used for laser Q-switching and mode-locking among other applications that require modulation at megahertz frequencies.

Demonstration of wide frequency bandwidth electro-optic response in SBN thin film waveguide

The dynamic modulation of effective electro-optic (EO) coefficient in pulsed laser deposited SBN thin film was investigated using Senarmont Compensation method. Prism coupling technique was used to realize a waveguide to guide the light in SBN thin film. The dynamic variation of effective electro-optic coefficient over a wide frequency range (10 Hz–20 MHz) was investigated with the maximum value of 198 pm/V. This wide frequency bandwidth obtained in the present article opens up avenues to design an EO modulator using ferroelectric SBN thin film. A lower value of half wave voltage (38 V) along with high figure of merit (0.9×106V2) were obtained for the fabricated SBN60 thin film based EO modulator.

Fabrication and electro-optic properties of 0.9Pb[(Mg,Zn)1/3Nb2/3]O3–0.1PbTiO3 transparent ceramics by a conventional sintering technique

0.9Pb[(Mg1−xZnx)1/3Nb2/3]O3–0.1PbTiO3 (x = 0–0.4) ceramics were fabricated by a conventional sintering technique. The ceramics became transparent at x = 0, 0.1, and 0.2, and the transmittances were 47, 43, and 53% at an infrared wavelength of 1310 nm, respectively. Birefringence of the transparent ceramics was quadratically increased as a function of electric field, with some deviations observed beyond certain electric fields at x = 0 and 0.2. An effective quadratic electro-optic (EO) coefficient was calculated with a half-wave electric field, and it was 6.30, 25.5, and 13.8 × 10−16 m2/V2 at x = 0, 0.1, and 0.2, respectively. The large EO effect at x = 0.1 was associated with the composition where a transition from a relaxor state to a ferroelectric state occurred. Microstructure, density, refractive index, and dielectric and ferroelectric properties were also investigated.

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.

$\chi ^{(2)}$ Modulator With 40-GHz Modulation Utilizing BaTiO3 Photonic Crystal Waveguides

Future telecommunication and data center networks as well as quantum optical communication systems will require optical modulators with wide bandwidths, large extinction, low operating voltage, and small size. We report the first quantitative demonstration of slow light enhancement of the electro-optic (EO) coefficient in a χ (2) ferroelectric waveguide at microwave modulation frequencies. This is demonstrated in a compact (1 mm) photonic crystal (PC) device with a voltage-length product (Vπ·L) of 0.66 V-cm at 10 GHz and measured EO modulation out to 40 GHz. A local enhancement factor of 12 and effective EO coefficient of 900 pm/V is measured in the PC region at a wavelength of 1530 nm. By further optimizing the PC structure, devices with EO 3-dB bandwidths greater than 40 GHz and voltage-length product of 0.16 V-cm are predicted with 100-μm interaction length.