T.J. Karle

Superprism phenomena in planar photonic crystals

We utilize the anomalous dispersion of planar photonic crystals near the dielectric band edge to control the wavelength-dependent propagation of light. We typically observe an angular swing of up to 10/spl deg/ as the input wavelength is changed from 1290 nm to 1310 nm, which signifies an angular dispersion of 0.5 degree/nm. Such a strong angular dispersion is of the order required for wavelength-division multiplexing systems. This is the first demonstration of the superprism effect in a planar configuration with a small lattice.

Coupled photonic crystal heterostructure nanocavities

We show the first experimental demonstration of multiple heterostructure photonic crystal cavities being coupled together to form a chain of coupled resonators with up to ten cavities. This system allows us to engineer the group velocity of light over a wide range. Devices were fabricated using 193 nm deep UV lithography and standard silicon processing technology. Structures were analysed using both coupled resonator and photonic bandstructure theory, and we highlight the discrepancies arising from subtle imperfections of the fabricated structure.

Low-loss photonic crystal defect waveguides in InP

We have fabricated high-quality planar photonic crystal defect waveguides in InP/InGaAsP material. Using Fourier analysis of the Fabry-Perot fringes obtained in transmission, we derive the propagation losses. Values as small as 1.8 dB/mm for waveguides consisting of three rows of missing holes (W3) were measured. We believe that the reduction in losses is due to the high quality of etching carried out using a high beam voltage–current ratio regime of chemically assisted ion-beam etching.

Planar photonic crystal coupled cavity waveguides

We present absolute transmission measurements of coupled cavity waveguides defined within planar photonic crystals. We investigate a range of cavity types and also vary the spacing between cavities. Modal analysis of the individual cavities reveals the symmetries that determine the coupling between adjacent cavities. Enhanced transmission is demonstrated by modifying the photonic crystal lattice. We highlight the need for correct impedance matching at the waveguide input in order to improve the transmission.

Efficient photonic crystal Y-junctions

A highly efficient Y-junction based on a planar photonic crystal (PhC) platform is presented. The PhC consists of a triangular array of holes etched into a GaAs/AlGaAs heterostructure, with a typical period of 322 nm and ~35% fill factor. The Y-junction has smaller holes positioned at the centre of the junction, giving rise to very uniform splitting and high transmission. The performance is very encouraging, with experimental transmission of approximately 40% for each arm of the Y-splitter relative to a comparable single-defect PhC waveguide.

Local probing of Bloch mode dispersion in a photonic crystal waveguide

The local dispersion relation of a photonic crystal waveguide is directly determined by phase-sensitive near-field microscopy. We readily demonstrate the propagation of Bloch waves by probing the band diagram also beyond the first Brillouin zone. Both TE and TM polarized modes were distinguished in the experimental band diagram. Only the TE polarized defect mode has a distinctive Bloch wave character. The anomalous dispersion of this defect guided mode is demonstrated by local measurements of the group velocity. The measured dispersion relation and measured group velocities are both in good agreement with theoretical calculations.

Experimental verification of numerically optimized photonic crystal injector, Y-splitter, and bend

We present the experimental measurement of a photonic crystal (PhC) device comprising an injector, Y-splitter, and 60/spl deg/ bend. The complete device consists of a 9-/spl mu/m-long injector tapering down from 5 /spl mu/m into a triangular-lattice-of-holes single-line defect waveguide with period a=430 nm and 36.2% air filling factor (corresponding to a radius over period (r/a) ratio of 0.30), an optimized Y-junction, 60/spl deg/ bend and output injectors, with a total device footprint of 30 /spl mu/m. This is etched into a GaAs/AlGaAs heterostructure using chlorine/argon chemically assisted ion beam etching (CAIBE). An erbium-doped fiber amplifier (EDFA)-based source and Fabry-Perot technique are used to characterize the device. The device displays a bandwidth of approximately 110 nm in the 1.55 /spl mu/m window, and a transmission of 70% relative to the same length of 5-/spl mu/m-wide waveguide. This is compared with three-dimensional finite-difference time-domain (3-D FDTD) results, which have a bandwidth and transmission of 120 nm and 75%, respectively. The highlight of this paper is the close agreement of the numerically optimized complete microcircuit with its experimental equivalent, and the significant improvement in bandwidth over previous work on Y-junctions.

Dispersion engineering in photonic crystal waveguides

Photonic crystal integrated circuits offer a range of possibilities for manipulating the propagation of light. Here, we demonstrate two different systems, i.e. superprisms and coupled cavity waveguides, that allow dispersion engineering in space and time, respectively.

High resolution, dispersion measurement of photonic waveguides

We demonstrate a high-resolution dispersion characterization technique for photonic waveguide structures. Direct measurement of 120 mum long photonic crystal waveguides, at a band edge of 1.55 mum, demonstrates group delay dispersion of 0.4 ps2.

Flatband Slow Light in Photonic Crystal Waveguides

A photonic crystal waveguide that features slow light without noticeable dispersion is demonstrated using a higher order even mode in a W2 waveguide on a SOI platform.