1 Department of Photonics Engineering, Technical University of Denmark2 Nanophotonics Theory and Signal Processing, Department of Photonics Engineering, Technical University of Denmark3 Nanophotonic Devices, Department of Photonics Engineering, Technical University of Denmark
This thesis deals with the modeling, design, fabrication and characterization of integrated ultrasonic-photonic devices, with particular focus on the use of standard semiconductor materials such as GaAs and silicon. The devices are based on the use of guided acoustic waves to modulate the light in channel waveguides and Mach-Zehnder interferometers. Numerical models are developed based on the finite element method, and applied to several scenarios, such as optimization of the geometrical parameters of waveguides, use of slow light in photonic crystal waveguides and use of Lamb waves in membranized systems, all in search for paths to improve acousto-optic interaction. Some of the solutions proposed lead to enhancements of up to two orders of magnitude in the eciency of the device. The main aspects related to the design of the devices are discussed, including single-mode guidance, optical coupling to the ber, bending losses, power splitting, phase delays and coupling between adjacent waveguides. The use of different numerical methods for the design of the different components are also discussed in terms of accuracy and speed. The devices are fabricated and characterized. Three material platforms were investigated. Comparisons are made with the numerical and experimental results, and they validate the obtained response of the acoustic and photonic components of the device. Finally, a new design for an optical frequency shifter is proposed, posing several advantages over existing devices in terms of size, integration and cost. The design proves to be robust towards fabrication and design tolerances. Several uses for this device are proposed, opening up a whole new group of applications for this class of integrated ultrasonic-photonic devices.
Main Research Area:
Poel, Mike van der, Hvam, Jørn Märcher, Yvind, Kresten