High Electro-optic Activity Research Articles

Nano-clustering mediates phase transitions in a diastereomerically-stabilized ferroelectric nematic system

In recent years, ferroelectric nematic liquid crystals have attracted considerable attention owing to their unique properties such as a colossal polarization, high electro-optic activity, and high fluidity. However, despite large efforts in designing and developing new ferrofluid molecules based on molecular parameters, the control and stabilization of ferroelectric nematic phase transitions remain challenging. Here, we discuss the impact of mixing 1,3-dioxane-tethered fluorinated (DIO) diastereomer molecules, namely transDIO and cisDIO, in controlling the ferroelectric nematic phase transition, using X-ray diffraction to investigate the effect of smectic cybotactic cluster formation. Our results show that the ferroelectric nematic phase transition can be tuned by a smooth exchange of the ferroelectric nematic transDIO and non-liquid crystal cisDIO components, where the similar dipole and molecular backbone of the two components ensures a consistent macroscopic polarization of the diastereomeric-controlled ferroelectric nematic phase.

Bis(4-dialkylaminophenyl)heteroarylamino donor chromophores exhibiting exceptional hyperpolarizabilities

Theory-guided design enables new organic electro-optic (OEO) materials with record hyperpolarizability and high electro-optic activity.

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.

A hybrid electro-optic polymer and TiO2 double-slot waveguide modulator.

An electro-optic (EO) modulator using a TiO2 slot hybrid waveguide has been designed and fabricated. Optical mode calculations revealed that the mode was primarily confined within the slots when using a double-slot configuration, thus achieving a high EO activity experimentally. The TiO2 slots also acted as an important barrier to induce an enhanced DC field during the poling of the EO polymer and the driving of the EO modulator. The hybrid phase modulator exhibited a driving voltage (Vπ) of 1.6 V at 1550 nm, which can be further reduced to 0.8 V in a 1 cm-long push-pull Mach–Zehnder interferometer (MZI) structure. The modulator demonstrated a low propagation loss of 5 dB/cm and a relatively high end-fire coupling efficiency.

A straightforward electro-optic polymer covered titanium dioxide strip line modulator with a low driving voltage

An electro-optic (EO) modulator composed of an EO polymer/titanium dioxide (TiO2) hybrid waveguide has been designed and fabricated. By using a TiO2 strip line (0.3 × 0.3 μm2 cross-section) as the core, the confinement factor in the EO polymer is optimized, thus achieving a high EO activity. The coplanar electrode spacing is tuned to enable an effective poling and a small propagation loss. The measured in-device EO coefficient is 100 pm/V at 1550 nm, with a driving voltage (Vπ) 3.2 V for the 12 mm-electrode length. The results also predict a possible Vπ of ∼1 V in a push-pull MZI structure. The EO activity of the modulator exhibited an excellent temporal stability at 85 °C for 500 h due to the high glass transition temperature of the EO polymer and the temperature-insensitive TiO2 strip line.

Reinforced Site Isolation Leading to Remarkable Thermal Stability and High Electrooptic Activities in Cross-Linked Nonlinear Optical Dendrimers

A series of cross-linkable electro-optic (E-O) dendrimers have been developed with anthracene- and acrylate-containing dendrons functionalized on the periphery of chromophores that can form thermally stable Diels−Alder adducts. These new E-O dendrimers with a high density of standardized AJL8-type chromophore are originally prone to thermo-decomposition in their thermoplastic form but can be converted into thermally stable networks to provide excellent site isolation for these chromophores. After poling, large E-O coefficients (up to 84 pm/V at 1310 nm) can be obtained in these dendrimers. These poled E-O dendrimers can maintain their alignment stability at 200 °C for 30 min and also possess impressive long-term stability at 150 °C for more than 200 h. This result provides a very effective molecular engineering approach to systematically increase the thermal stability of highly polarizable dipolar chromophores for high temperature on-chip applications.

Broadband electro-optic polymer modulators with high electro-optic activity and low poling induced optical loss

A screening method is reported for electro-optic (EO) polymers with an emphasis on broadband device suitability. The method is based on comparing the signal from second harmonic generation (SHG) and the leak through current (LTC) during poling. Plots of the SHG and LTC are used to define high EO activity-low current poling windows that are critical for low driving voltage, broadband devices with relatively low optical loss. The screening procedure was used to select an EO polymer core that resulted in a 40Gbits∕s broadband modulator with a driving voltage of 1.3V and an insertion loss of <8dB.

Tri-component Diels–Alder polymerized dendrimer glass exhibiting large, thermally stable, electro-optic activity

A novel, thermally curable, tri-component organic glass for electro-optic applications was designed and synthesized. The system employed the Diels–Alder cycloaddition reaction to effect efficient cross-linking. The first component was a dendrimer containing multiple electro-optic chromophore substituents surrounded by an outer periphery possessing diene functionality. The second was a furan-protected, bis-dienophile electro-optic chromophore, introduced in order to function as a nonlinear optically-active cross-linking agent. The initial glass-transition temperature of the material was tuned by the addition of the third component, an optically-inert, maleimide-based dienophile cross-linking agent. Tuning of this mixture allowed optimum poling temperature to coincide with optimum thermal conditions for promotion of the Diels–Alder cross-linking reaction. The electro-optic properties of the material were evaluated in real-time, using a reflection-based single-beam ellipsometry apparatus that was modified to perform in situ signal monitoring. The high electro-optic activity observed (r33 of 150 pm V−1), was thermally stable up to 130 °C (a 48 °C improvement over similar uncross-linked materials). After processing, materials were insoluble in acetone, retained 90% of their original r33 after 15 months at room temperature, and performed well in accelerated operational testing at 85 °C in air.

Photodefinable electro-optic polymer for high-speed modulators

We present a series of polymeric electro-optic (EO) materials based on the tricyanovinylidenediphenylaminobenzene (TCVDPA) chromophore which exhibits an exceptionally high photostability combined with a high EO activity. The EO properties of these derivatives are given and the best result was obtained with the di-tBut derivative 2, which showed a nearly doubling effect of $r_{33}$ (14 pm/V to 25 pm/V), while increasing the concentration from 25 wt% to 37.5 wt%. A microring resonator design was made based on the PC-TCVDPA system. Waveguides were fabricated by photodefinition of inverted ridges in VSC, a negative epoxy based photoresist with low refractive index.

Synthesis of Chromophores with Extremely High Electro-optic Activity. 1. Thiophene-Bridge-Based Chromophores

We have successfully synthesized several new substituted thiophene-based electro-optic chromophores. All of these chromophores have structures similar to FTC but they incorporated our newly designed tricyanovinyldihydrofuran acceptors. Since these acceptors possess an anisotropic structure, all of the chromophores are very soluble in a wide range of organic solvents. Thermal study of these chromophores by TGA shows all of them are very stable in air. UV spectra indicate the chromophores have a large solvatochromic effect, implying very large molecular nonlinearities.

Synthesis of Chromophores with Extremely High Electro-optic Activities. 2. Isophorone- and Combined Isophorone−Thiophene-Based Chromophores

Four new isophorone and combined isophorone and thiophene bridged chromophores have been synthesized. All of these new high μβ chromophores possess our newly synthesized tricyanovinyldihydrofuran acceptors. Because of our unique acceptor design, all of our chromophores show high solubility in all organic solvents due to minimized chromophore−chromophore electrostatic interactions. These chromophores have also been studied with respect to their solvatochromism and thermal behavior by TGA in air. Preliminary EO characterization of one of these chromophores in polycarbonate has demonstrated an extremely high r33 of 70 pm/V at 1550 nm. We believe that this is the largest r33 reported at this wavelength.

Synthesis of second-order nonlinear optical chromophores with enhanced thermal stability and nonlinearity: a conformation-locked trans-polyene approach

A facile synthesis that combines the use of an easily polarizable thiophene ring and a ring-locked triene as efficient conjugating moieties is employed to simultaneously enhance molecular nonlinearity (as high as 13000 × 10–48 esu) and thermal stability; incorporating this highly nonlinear chromophore in polyquinoline results in high electrooptic activity and long-term alignment stability at 100 °C for more than 1000 h.

Polymer Integrated Optic Zero-Gap Directional Coupler

ABSTRACTIntegrated optic zero-gap directional couplers (ZGDC‘s) offer orders of magnitude shorter device lengths than conventional directional couplers. Researchers are currently striving to simultaneously optimize several properties of nonlinear optical (NLO) polymers that are viewed essential for the fabrication of commercially viable polymer electro-optic devices, including high electro-optic activity, low propagation loss and high temperature poling retention. Fabrication of zero-gap directional couplers using NLO polymers show the potential to realize devices with interaction lengths as short as 100 μm, operating at TFL level switching voltages. Hence, NLO polymer ZGDC‘s will possess the ability to tolerate large propagation losses. This can allow the low propagation loss constraint for NLO materials to be relaxed significantly. Polymers with high electro-optic activity that might be rejected because of high propagation loss, could potentially be utilized for ZGDC switches. In addition, by using these devices as stand alone switches for the present (i.e., not integrating them with electronic circuits) the de-poling temperature constraint can also be significantly relaxed since neither solder baths nor high density interconnect (HDI) processes will be needed. These relaxed constraints should improve the chances for introduction of viable NLO polymer devices that can compete in the market place today, without being forced to wait for a material in which all properties have been optimized.

Thermally stable nonlinear optical polyimides: synthesis and electro-optic properties

A facile synthetic method has been developed to incorporate efficient nonlinear optical chromophores as side-chains into high temperature polyimides resulting in high electro-optic activity and long-term thermal stability at 90 °C for over one month.

Design and synthesis of thermally stable side-chain polyimides for second-order nonlinear optical applications

Novel Mitsunobu and tricyanovinylation reactions have been employed to incorporate efficient nonlinear optical chromophores as side-chains into aromatic polyimides resulting in high electro-optic activity and long-term alignment stability at 100 °C for more than 500 h.