Focusing Grating Couplers for Integrated Optics

摘要

Focusing grating couplers (FGCs) are designed to outcouple a guided wave from anintegrated optical circuit and to focus it onto a point above the waveguide. The authors aim at a design of an FGC in which a guided diverging wave is outcoupled as a spherical wave converging to a point above the waveguide. The incident guided wave (collimated in the experiments) is generated by prism-incoupling into the waveguide. The field distribution at the FGC and at the focal plane are investigated theoretically. FGCs are produced by holographic recording and are etched into the waveguide surface by wet chemical etching. The field distribution around the focus of the diffracted beam is studied by recording the intensity. Chapter 2 presents a model including the vectorial treatment of the electromagnetic field, in order to calculate the field distributions at the FGC and around the focal point for estimating the image quality. Chapter 3 gives a comparison of the results of the author's model and those from earlier theories. Chapter 4 describes the method to design a holographic setup for recording FGCs. Chapter 5 presents the experimental work. Chapter 6 summarizes the main results and presents some suggestions for future investigation.