Investigation of the optical properties of ferroelectric oxide thin film photonic crystals

The optical properties of two dimensional photonic crystals were investigated using ferroelectric barium titanate thin films as the optically active medium. Barium titanate has a high electro-optic coefficient and fast response time so it is a promising non-linear optical material for integrated nano-photonics. Highly uniform photonic crystals were fabricated by focused ion beam lithography. The lattice constants of the photonic crystals range from 250 nm to 1 mum. Minimal distortion was observed for the milled circular air hole which has a Gaussian profile. A high aspect ratio larger than 2 was demonstrated in the ion beam milling.;The photonic band structure was calculated by the 2-D finite difference time domain method and subsequently determined by the waveguide transmission measurements. A band gap width greater than 150 nm is observed in which the propagating light is strongly confined in the photonic cavities. The broad bandwidth is attributed to the high refractive index contrast between the barium titanate and the air. By utilizing photonic superlattice a large tunability of -0.18 THz/Volt is theoretically achieved.;The optical resonance effects were analyzed using the fluorescence in the visible region from dyed covered photonic crystals. The scattered light intensities are highly sensitive to the excitation light wavelength and the photonic lattice constant. When the light wavelength shifts by 29 nm the scattered light intensity is reversed. A strong enhancement of fluorescence was observed for photonic arrays with periodicity of 200 nm. The increased light emission is attributed to reduction of the in-plane wave propagation due to a photonic stop band.;Optical diffraction was measured in the visible region. The symmetry of the photonic crystal is determined from optical diffraction patterns. The diffraction pattern along the [1 0] and [1 1] directions reveals that the photonic arrays have square lattice symmetry. The thermo-optical response was measured. A 3 dB modulation of light intensity is demonstrated. This indicates heating leads to a red shift of the photonic band structure. Upon applying an electrical field, a shift by 1.2 nm of the transmission spectra of the photonic lattices was measured. This work on photonic crystal composed of barium titanate thin films indicates it is highly tunable and it has great potential as a nano-optic switch.