Photonic devices that exploit photonic crystal (PhC) principles in a planar environment continue to provide a fertile field of research. 2D PhC based channel waveguides can provide both strong confinement and controlled dispersion behaviour. In conjunction with, for instance, various electro-optic, thermo-optic and other effects, a range of device functionality is accessible in very compact PhC channel-guide devices that offer the potential for high-density integration. Low enough propagation losses are now being obtained with photonic crystal channel-guide structures that their use in real applications has become plausible. Photonic wires (PhWs) can also provide strong confinement and low propagation losses. Bragg-gratings imposed on photonic wires can provide dispersion and frequency selection in device structures that are intrinsically simpler than 2D PhC channel guides--and can compete with them under realistic conditions.
Photonic crystal devices are now being produced for a variety of functions-and the need to provide thermal control of the behaviour suggests the use of thermo-optic effects. It has emerged that thermo-optic effects can provide useful modulation, switching and tuning capability. Future trends indicate fast, low-power, thermo-optically operated photonic crystal and photonic wire devices-and the possibility of simultaneous athermal characteristics.
We have fabricated and measured 2D photonic crystal Mach-Zehnder device structures using W1 channel waveguides oriented along GK directions in AlGaAs/GaAs epitaxial waveguide material and silicon-on-insulator waveguide material, with operation at wavelengths around 1550 nm. 2D FDTD simulations and experimental results will be shown and compared. The structure has been designed using progressive tapering of the hole diameter in the bend regions, while a 'defect' hole with reduced radius has been placed in the centre of the Y-Junction, giving a substantial improvement in the transmission and bandwidth. The overall length of the photonic crystal Mach-Zehnder structure is typically about 32 um and the structure has been fabricated using a combination of direct-write electron-beam lithography (EBL) and dry-etch processing. Devices were measured using a tunable laser with end-fire coupling. We shall describe the application of such structures for switching and sensing, with deliberate exploitation of the thermo-optic effect via the incorporation of heater electrodes.
This paper highlights photonic crystal Mach-Zehnder structures that use W1 channel waveguide in 2D hexagonal photonic crystal structures and have channel orientation along GammaK directions. The FDTD software, Fullwave, from RSoft has been used to simulate photonic crystal channel waveguides, Y-junction and bend in order to design a complete Mach-Zehnder interferometer structure in epitaxial II-V semiconductor material for operation at 1550nm. It is our near-future aim to use these Mach-Zehnder structures as the basis for thermo-optic switching devices. Electro-Beam lithography (EBL) and reactive ion etching (dry-etching) processes have been used to fabricate these devices