Electro-optic Coefficient R33 Research Articles

Phase Composition of HiVac-VPE Lithium Niobate Optical Waveguides Identified by Spectroscopic Investigations.

High-index contrast lithium niobate waveguides, fabricated by the High Vacuum Vapor-phase Proton Exchange (HiVac-VPE) technique, are very promising for increasing both the optical nonlinear and electro-optical efficiencies of photonic integrated devices. So as to play this role effectively, it is mandatory to know the crystallographic phase composition of waveguides and the position of protonated layers for appropriate tailoring and optimization based on the intended applications. In addition, the estimation of structural disorder and electro-optical properties of the waveguides are also of high interest. Benefiting from Raman spectroscopy, IR reflection, IR absorption, and UV-VIS absorption, the HxLi1-xNbO3 phase compositions, as well as the structural disorder in waveguides, were determined. Based on experimental data on the shift of the fundamental absorption edge, we have quantitatively estimated the electro-optic coefficient r13 in as-exchanged waveguides. The electro-optical properties of the waveguides have been found to be depending on the phase composition. The obtained results allow for reconsidering the proton exchange fabricating process of photonic nonlinear devices and electro-optic modulators based on high-index contrast channel waveguides on the LiNbO3 platform.

Evaluation of Optical Characteristics in Electro‐Optic Chromophores Designed for Applications at O‐Band

Herein, lots of electro‐optic (EO) chromophores designed for applications at O‐band are synthesized, and the first hyperpolarizability β of EO chromophores is evaluated by the hyper‐Rayleigh scattering (HRS) technique. EO chromophores are constituted of various tricyanofuran (TCF) derivatives as the electron acceptor unit, thienyl‐di‐vinylene or thienyl‐di‐vinylene with ethylenedioxy as the π‐conjugation unit, and aminobenzene with a benzyloxy group as the donor unit. Halogen phenyl group or trifluoromethyl‐phenyl group in TCF acceptor unit leads to a relatively large improvement in β values. Furthermore, EO polymers with some promising EO chromophores that are suitable for the applications at O‐band (1260–1360 nm) are synthesized, and EO coefficient r33 (or n3r33) and absorption loss α are evaluated. Considering the trade‐off relationship between r33 (or n3r33) and α, EO polymers with excellent EO chromophores in the C‐band (1530–1565 nm) are not necessarily suitable EO polymers in the O‐band (1260–1360 nm). EO polymers with the O‐band chromophores have small α and moderate r33 (or n3r33) at the O‐band, while EO polymers with the C‐band chromophores have large α and slightly modified r33 (or n3r33) at the O‐band. The development of suitable EO chromophores and polymers for O‐band and C‐band respectively is very important.

Characterization of electro-optic coefficients r13, r23 and r33 in single crystalline BaTiO3 thin films

We report experimental characterization of DC electro-optic coefficients r13, r23 and r33 in thin film single crystalline BaTiO3 on DyScO3. The epitaxial BaTiO3 thin film is sandwiched between a SrRuO3 bottom electrode and an indium tin oxide (ITO) top electrode. We characterize the DC electro-optic coefficients r13, r23, and r33 by the prism coupling method at 636.6 nm for the BaTiO3 thin film. The results show the DC coefficients r13 = 4.2 pm/V, r23 = 4.6 pm/V and r33 = 9.0 pm/V.

The important role of tetraphenylethene on designing bichromophores for organic nonlinear optical materials

Organic electro-optical (OEO) materials still exist huge challenges to achieve these materials for practical use. In this work, a novel bichromophores Y was synthesized via esterification reaction with julolidine donor chromophores and systematically studied. Chromophore Y presented good solubility, excellent thermal stability, and also with great transparency. Besides, the hyperpolarizability (β) of this new chromophore was computed by density functional theory. To our suprise, in electro-optic activities, the doped film containing chromophore Y performed an extremely small electro-optic coefficient (r33) with 13 pm/V. This outcome indicated that the nonplanar molecular structures of the TPE1 moieties can weaken the electrostatic interactions between molecules, but the size of this chromophore is too big to be polarized, thus leading the macroscopic EO activity decreased sharply.

Experimental evidence for preservation of electro-optic property in titanium-diffused lithium niobate waveguide

Abstract Electro-optic (EO) property of titanium-diffused LiNbO3 optical waveguide was studied using prism coupling technique. The EO-effect-induced increment ΔN of effective refractive index (at the wavelength 1311 nm) was measured as a function of externally applied electric field E for TM0 and TM1 modes guided in the titanium-diffused LiNbO3 planar waveguide. By using the linearity between ΔN and E, the EO coefficient r33 is determined. For reference, the measurement was also performed on a bulk material of congruent LiNbO3, yielding r33 = 24.9 ± 0.8 p.m./V, which is in qualitative agreement with that obtained by extrapolating previously reported result to the 1311 nm wavelength, ~24 p.m./V, confirming the feasibility of the measurement method. Measurements on the titanium-diffused planar waveguide give r33 = 25.7 ± 0.6 p.m./V for the TM0 mode and 25.7 ± 0.4 p.m./V for the TM1 mode. Both values can be considered as identical within the error, and are the same as that of the bulk material, indicating that the EO property is well preserved in the titanium-diffused LiNbO3 waveguide. The main reason is that the LiNbO3 crystalline phase is well preserved in the titanium-diffused waveguide layer.

Ultrahigh Electro-Optic Coefficients, High Index of Refraction, and Long-Term Stability from Diels–Alder Cross-Linkable Binary Molecular Glasses

The development of organic electro-optic (EO) materials that concurrently possess a high electro-optic coefficient (r33), high index of refraction, and long-term or high-temperature stability of ch...

Enhancement of electro-optic properties of nonlinear optical chromophores by introducing pentafluorobenzene group into the donor and π-bridge

Two isophorone-based chromophores A-B has been synthesized and investigated based on diethylaminophenyl donor and tricyanovinyldihydrofuran or phenyl-trifluoromethyltricyanofuran acceptors. The chromophores were modified with a bulky pentafluorobenzene group covalently attached to both the donor and bridge section of the chromophores to prevent close packing of molecules, which benefit the polarization efficiency. The ultraviolet absorption, Density functional theory (DFT) calculation, thermal stabilities and electro-optic activities of these chromophores were systematically studied. The chromophores A-B exhibited good thermal stabilities with the decomposition temperatures (Td) higher than 220 °C. Most importantly, the rigid steric hindrance groups can effectively reduce intermolecular electrostatic interactions to translate the hyperpolarizabilities of chromophore into large electro-optic (EO) coefficients (r33). Polymers doped with 30 wt% chromophore A-B have been poled to afford ultrahigh electro-optic coefficient (r33) of 115 pm/V and 213 pm/V, respectively at 1.31 μm, which is higher than that of analogue chromophores which without isolation groups.

Correction to “Electro-optic coefficients r13 and r33 of singly Er3+-doped and In3+/Er3+-codoped LiNbO3 crystals”

An error in the previous paper “Electro-optic coefficients r13 and r33 of singly Er3+-doped and In3+/Er3+-codoped LiNbO3 crystals” [J. Phys. Chem. Solids 100 (2017) 101–106] is corrected. The electro-optic coefficients γ33 and γ13 that were measured by applying a DC voltage to the crystal via the Al films coated onto the crystal surfaces are the unclamped instead of clamped coefficients.

Design and synthesis of novel H-Shaped chromophore for enhanced nonlinear optical properties

A novel H-shaped nonlinear optical chromophore B based on julolidinyl donors were designed and synthesized through Williamson ether reaction. The chromophore B is composed of two traditional rod-shaped chromophores A linked to each other through an isolation group, forcing chromophore separation through steric interaction. Chromophore B showed good thermal stability and film-forming ability. Besides, the reduction of intermolecular electrostatic interactions allows for increased active chromophore number density in the formulation of a host-guest doping material, thus enhancing electro-optic response. Polymers doped with 35 wt% chromophore B have been poled to afford large electro-optic coefficient (r33) of 180 pm/V at 1310 nm, which is nearly two times higher than that obtained from the chromophore A (92 pm/V) at the doping concentration of 25 wt%. These results indicated that the H-shaped chromophore B has the advantages over rod-shaped chromophore A in transforming the microscopic hyperpolarizability into a macroscopic electro-optic coefficient.

Optimizing the molecular structure of 1,1,7,7-tetramethyl julolidine fused furan based chromophores by introducing a heterocycle ring to achieve high electro-optic activity

Developing new organic chromophores with a large electro-optic coefficient (r33) is highly desirable for fabricating electro-optic (EO) materials.

Achieving excellent electro-optic activity of chromophores by introducing a stronger electron donor and modifying the π-bridge

We present here three chromophores with the same tricyanofuran acceptor, but with different donor moieties and bridges, synthesized by the conventional technique. Compared with chromophore without the substituted group, these modified chromophores show better stability. Structure analysis and photophysical properties were carried out to compare the molecular mobility and steric hindrance effect on chromophores. Density functional theory (DFT)was used to calculate the hyperpolarizability (β), and the results showed that the high molecular hyperpolarizability of these chromophores can be effectively translated into large electro-optic coefficients. By doping these chromophores with a high loading of 25 wt% in amorphous polycarbonate (APC), electro-optic (EO) coefficients (r33) of up to 163 pm V−1 at 1310 nm can be achieved. These results indicated that the introduced alkoxy group on the donor part or bridge part can enhance the donor ability and can also reduce intermolecular electrostatic interactions, thus enhancing the macroscopic electro-optic activity, which indicated that the structure–property relationship was essential.

Novel nonlinear optical chromophores based on coumarin: Synthesis and properties studies

Novel nonlinear optical chromophores JC-TCF and JC-FTCF using tetramethyljulolidine-based coumarin as the electron-donor and tricyanofuran derivatives as the electron acceptors were designed, synthesized and investigated. The obtained chromophores own good solubility in common solvents, and good compatibility with host polymers. The chromophores also have good thermal stability, and the decomposition temperature exceed 200 °C. The UV–vis spectra indicated that JC-TCF and JC-FTCF possess good intramolecular charge transfer ability. Density functional theory (DFT) was used to study the energy gap and first-order hyperpolarizability(β). After contact poling, the guest-host polymer films of polymethyl methacrylate containing 20% wt JC-TCF and 20% wt JC-FTCF exhibited the highest electro-optic coefficient (r33) up to 40 p.m./V and 76 p.m./V respectively, and the results indicated the chromophores’ microscopic β value could be effectively translated to macroscopic EO activity, and the tetramethyljulolidine-based coumarin could be an useful candidate in the development of NLO materials.

Structure–function relationship exploration for enhanced electro-optic activity in isophorone-based organic NLO chromophores

Four isophorone-based chromophores FLD1-FLD4 has been synthesized and investigated based on julolidinyl donors, with modified isophorone-derived bridges and tricyanovinyldihydrofuran or phenyl-trifluoromethyl-tricyanofuran acceptors. The chromophore FLD3 was modified with a 2-((tert-butyldimethylsilyl)oxy)ethanethiol group covalently attached to the π-conjugate bridge to ensure its all-trans conformation and prevent close packing of molecules, which benefit the macroscopic electro-optic efficiency. The chromophore FLD3 possesses better thermal stability than chromophore FLD1 without the isolation group on the bridge. Moreover, density functional theory calculations suggested that the hyperpolarizability (β) value of chromophore FLD3 is larger than that of chromophore FLD1. Polymers doped with chromophore FLD3 have been poled to afford ultrahigh electro-optic coefficient (r33) of 238 pm/V at 1.31 μm, which is nearly 60% higher than that obtained from chromophore FLD1 and three times higher than that of analogue chromophores FLD2 and FLD4.

Modification of indole by electron-rich atoms and their application in novel electron donor materials

Novel nonlinear optical (NLO) chromophore based on 6-(pyrrolidin-1-yl)-1H-indole as the electron donor group was designed and synthesized. The molecular structure of this chromophore was characterized by 1H NMR spectra, 13C NMR spectra, and MS spectra. The delocalized energy level was estimated by UV–Vis. spectra. The thermal property was studied by thermogravimetric analysis (TGA). The poled films containing chromophores ZML-1 with a loading density of 10wt% in amorphous polycarbonate (APC) afford an average electro-optic (EO) coefficient (r33) of 19pm/V at 1310nm. Compared to the reported aniline-based chromophore (r33=12pm/V) analogues, chromophore ZML-1 exhibits enhanced electro-optical activity.

The important role of the isolation group (TBDPS) in designing efficient organic nonlinear optical FTC type chromophores

Highly efficient and thermally stable nonlinear optical chromophores based on the same thiophene π-conjugation and tricyanofuran acceptor (TCF) possessing different isolation groups attached to electron-donating moiety have been synthesized and systematically investigated in this paper. Density functional theory (DFT) was used to calculate the HOMO–LUMO energy gaps and first-order hyperpolarizability (β) of these chromophores. These new chromophores showed excellent thermal stability with their decomposition temperatures all above 250 °C. Most importantly, the molecular hyperpolarizability of these chromophores can be effectively translated into large electro-optic (EO) coefficients (r33) in poled polymers. The doped films-B containing 25 wt % chromophore F1 displayed an r33 value of 52 pm/V at 1310 nm, and the doped films-C containing F2 showed a value of 91 pm/V at the concentration of 35 wt %. These values are all much higher than the traditional FTC chromophore (39 pm/V). These results revealed that the introduced isolation group can reduce intermolecular electrostatic interactions thus enhance the macroscopic EO activity. Besides, the position of the isolation group plays an equally important role in achieving the ultra large EO coefficients of materials. These properties, together with the good solubility, suggest the potential use of these new chromophores as advanced materials devices.

Electro-optic coefficients r13 and r33 of singly Er3+-doped and In3+/Er3+-codoped LiNbO3 crystals

A series of singly Er3+-doped and doubly In3+/Er3+-doped congruent LiNbO3 crystals were grown by Czochralski method. The Er3+-only doped crystals were grown from the growth melts doped with different concentrations of Er2O3 up to 1mol%, and the In3+/Er3+-codoped crystals from the melts doped with fixed 0.5mol% Er2O3 while varied In2O3 contents of 0.0, 0.5, 1.0 and 1.5mol%. The electro-optic coefficients γ13 and γ33 of these doped crystals were measured by Mach-Zehnder interferometry. Both clamped and unclamped coefficients were measured. The results show that both γ13 and γ33 reveal small Er3+ and In3+ doping effects. In the Er3+-only doping case, γ13 almost does not change within the experimental error of 3%, γ33 reveals a degradation tendency with a rise in Er3+ doping level, but the degradation is no more than 5% in the considered Er3+ concentration range 0–3.0mol% (in crystal). In the In3+/Er3+-codoping case, both γ13 and γ33 can be regarded as unchanged in the studied In3+ concentration range of 0–2.6mol% (in crystal) within the error. The small Er3+ or In3+ doping effect is desired in light of electro-optic application of these crystals. It is qualitatively explained on the basis of EO coefficient model and doping effect on defect structure of LiNbO3.

Synthesis of chromophores with ultrahigh electro-optic activity: Rational combination of the bridge, donor and acceptor groups

A series of high performance chromophores P1P3, based on N-(4-dibutylaminophenyl) tetrahydroquinolinyl or julolidinyl donors, and phenyl-trifluoromethyl-tricyanofuran acceptors linked together via π-conjugation through thiophene or vinylene moieties as the bridges, have been designed and synthesized. Density functional theory (DFT) was used to calculate the HOMO-LUMO energy gaps and first-order hyperpolarizability (β) of these chromophores. Chromophores P1 and P3 had good thermal stabilities with glass transition temperature higher than 110 °C. Most importantly, the high molecular hyperpolarizability of these chromophores can be effectively translated into large electro-optic (EO) coefficients (r33) in poled polymers with rational chromophore designs. In electro-optic activities, the poled films of P1/APC, P2/APC and P3/APC afforded r33 values of 223, 283 and 278 pmV−1, respectively, at 1310 nm at the doping concentration of 25 wt%, which showed significant enhancement over the similar EO polymer systems previously reported.

Enhanced electro-optic response in domain-engineered LiNbO3 channel waveguides

Substantial enhancement (36.7%) of the intrinsic electro-optic coefficient (r33) has been observed in lithium niobate channel waveguides, which are made to overlap with a pole-inhibited ferroelectric domain. The waveguide and the overlapping ferroelectric domain are both produced by a single UV irradiation process and are thus self-aligning. The enhancement of the electro-optic coefficient effect is attributed to strain, which is associated with the ferroelectric domain boundaries that contain the channel waveguide.

The effect of bulky groups on the electro-optic coefficient [formula omitted] of a pyridine-donor nonlinear optical chromophore

The effect of bulky groups attached to pyridine-donor chromophores on the electro-optic coefficient r33 of host-guest polymers was measured by modulation ellipsometry. Overall, the experimental results indicated no significant beneficial effect of the bulky groups on r33. The maximum r33 achieved was just under 6pm/V for the plain chromophore, compared with the expected 20pm/V based on the molecular properties. Decomposition of the chromophore absorption band revealed significant aggregation, with the monomer fraction estimated to be marginally less than 1/3 for all chromophores studied. We attribute the lower achieved r33 values to increased molecular aggregation.

Synthesis and characterization of two novel second-order nonlinear optical chromophores based on julolidine donors with excellent electro-optic activity

Second order NLO chromophores with julolidine donor.