Ferroelectric thin film photonic crystal waveguide and its electro-optic properties

Barium titanate at the nanoscale: controlled synthesis and dielectric and ferroelectric properties

The current trend in the miniaturization of electronic devices has driven the investigation into many nanostructured materials. The ferroelectric material barium titanate (BaTiO3) has garnered considerable attention over the past decade owing to its excellent dielectric and ferroelectric properties. This has led to significant progress in synthetic techniques that yield high quality BaTiO3 nanocrystals (NCs) with well-defined morphologies (e.g., nanoparticles, nanorods, nanocubes and nanowires) and controlled crystal phases (e.g., cubic, tetragonal and multi-phase). The ability to produce nanoscale BaTiO3 with controlled properties enables theoretical and experimental studies on the intriguing yet complex dielectric properties of individual BaTiO3 NCs as well as BaTiO3/polymer nanocomposites. Compared with polymer-free individual BaTiO3 NCs, BaTiO3/polymer nanocomposites possess several advantages. The polymeric component enables simple solution processibility, high breakdown strength and light weight for device scalability. The BaTiO3 component enables a high dielectric constant. In this review, we highlight recent advances in the synthesis of high-quality BaTiO3 NCs via a variety of chemical approaches including organometallic, solvothermal/hydrothermal, templating, molten salt, and sol-gel methods. We also summarize the dielectric and ferroelectric properties of individual BaTiO3 NCs and devices based on BaTiO3 NCs via theoretical modeling and experimental piezoresponse force microscopy (PFM) studies. In addition, viable synthetic strategies for novel BaTiO3/polymer nanocomposites and their structure-composition-performance relationship are discussed. Lastly, a perspective on the future direction of nanostructured BaTiO3-based materials is presented.

Enhancement of the pockels effect in photonic crystal modulators through slow light

We report a photonic crystal (PhC) optical modulator operating in the optical C band (1530-1565 nm) using barium titanate epitaxial thin films as the electro-optic (EO) medium. The PhC has hexagonal lattice symmetry and an extinction ratio of 9 dB. Due to the slow light enhancement of the EO coefficient near the PhC band edge, the driving electrode can be as short as a one millimeter. We report for the first time, to the best of our knowledge, at microwave frequencies from 10 to 45 GHz the effective EO coefficient and its enhancement through slow light effects. A monotonic increase of the effective EO coefficient from 60 to 110 pm/V across the stopband edge is obtained, resulting in an enhancement as high as 1.8.

Effect of incident angle and polarization on electrically-tunable defect mode in anisotropic photonic crystals

In this study, the effects of incident angle and state of wave polarization on electrically-tunable defect mode in a one-dimensional photonic crystal (1DPC) structure with an anisotropic defect layer is theoretically investigated. A 4×4 transfer matrix method is employed to calculate the transmittance spectrum of the structure with biased defect layer at different incident angles for TE and TM polarizations. The results indicate that at both polarizations, the peak wavelength of the defect mode shifts toward blue as the angle of incidence increases. Also, blue and red shifts can be observed in the defect mode for positive and negative biases, respectively. In addition, the defect mode compresses at TE (TM) polarization at negative (positive) biases and broadens for positive (negative) biases. A tunability defect mode may have potential application in the design of controllable optical filters in all optoelectronic devices.

Active silicon integrated nanophotonics: ferroelectric BaTiO₃ devices

The integration of complex oxides on silicon presents opportunities to extend and enhance silicon technology with novel electronic, magnetic, and photonic properties. Among these materials, barium titanate (BaTiO3) is a particularly strong ferroelectric perovskite oxide with attractive dielectric and electro-optic properties. Here we demonstrate nanophotonic circuits incorporating ferroelectric BaTiO3 thin films on the ubiquitous silicon-on-insulator (SOI) platform. We grow epitaxial, single-crystalline BaTiO3 directly on SOI and engineer integrated waveguide structures that simultaneously confine light and an RF electric field in the BaTiO3 layer. Using on-chip photonic interferometers, we extract a large effective Pockels coefficient of 213 ± 49 pm/V, a value more than six times larger than found in commercial optical modulators based on lithium niobate. The monolithically integrated BaTiO3 optical modulators show modulation bandwidth in the gigahertz regime, which is promising for broadband applications.