Theodor Doll

Design and fabrication of silicon photonic crystal optical waveguides

We have designed and fabricated waveguides that incorporate two-dimensional (2-D) photonic crystal geometry for lateral confinement of light, and total internal reflection for vertical confinement. Both square and triangular photonic crystal lattices were analyzed. A three-dimensional (3-D) finite-difference time-domain (FDTD) analysis was used to find design parameters of the photonic crystal and to calculate dispersion relations for the guided modes in the waveguide structure. We have developed a new fabrication technique to define these waveguides into silicon-on-insulator material. The waveguides are suspended in air in order to improve confinement in the vertical direction and symmetry properties of the structure. High-resolution fabrication allowed us to include different types of bends and optical cavities within the waveguides.

Organic field-effect transistors with nonlithographically defined submicrometer channel length

We developed an underetching technique to define submicrometer channel length polymer field-effect transistors. Short-channel effects are avoided by using thin silicon dioxide as gate insulator. The transistors with 1 and 0.74 mum channel length operate at a voltage as low as 5 V with a low inverse subthreshold slope of 0.4-0.5 V/dec, on-off ratio of 10(4), and without short-channel effects. The poly(3-alcylthiophene)s still suffer from a low mobility and hysteresis does occur, but it is negligible for the drain voltage variation. With our underetching technique also device structures with self-aligned buried gate and channel length below 0.4 mum are fabricated on polymer substrates.

Realistic monomode air-core honeycomb photonic bandgap fiber with pockets

We present a photonic bandgap calculation of monomode air-core fibers with a realistic treatment of pocket interstitials that are formed in a honeycomb cladding. The analytic Fourier transformations of different honeycomb-lattice unit cells are used for plane-wave calculations. The consideration of the true pocket geometry within the cladding shifts the fundamental bandgap to higher frequencies and leads to a hollow-core fiber. The core radius necessary for a monomode fiber is approximated and then proved via the full-vectorial solution. The field distribution and polarization state of the fundamental mode for a real honeycomb photonic-crystal fiber (PCF) are given.

Waveguiding at 1500 nm using photonic crystal structures in silicon on insulator wafers

Summary form only given. Planar photonic crystal waveguides and devices may offer the possibility to build photonic circuits with greater density and new functionality compared to existing waveguide devices that are based on the control of light by refraction. The primary vehicles for this research are the study of microcavity lasers as a path to understanding new functionality, and the propagation of light around sharp bends as the path to increasing the packing density of planar optical circuits. We report our results on the successful demonstration of coupling and guiding of light in a planar photonic circuit incorporating sharp bends. Photonic crystal structures were designed to confine light in a silicon waveguide at 1500 nm, by drilling air holes at periodic intervals around the waveguide region. Both square and hexagonal structures have been studied. The pattern design was transferred to a silicon-on-insulator wafer using direct-write e-beam lithography. The pattern was etched into the silicon layer by chemically assisted ion beam etching (CAIBE).

Waveguiding in planar photonic crystals

Photonic crystal planar circuits designed and fabricated in silicon on silicon dioxide are demonstrated. Our structures are based on two-dimensional confinement by photonic crystals in the plane of propagation, and total internal reflection to achieve confinement in the third dimension. These circuits are shown to guide light at 1550 nm around sharp corners where the radius of curvature is similar to the wavelength of light.