טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentGal Lior
SubjectAnnular Optical Microcavities and Their Coupling
DepartmentDepartment of Electrical Engineering
Supervisor Professor Meir Orenstein


Abstract

Microring and microdisk optical resonators and lasers are dielectric structures of the dimension of the order of not more than several wavelengths. These structures - equivalent to the low-dimensional quantum structures of electronics - can modify fundamentally the nature of light-matter interaction, and can be applied for miniature integrated optoelectronic devices. Experimental results of such microcavities revealed a narrow band single mode lasing, sub‑milliampere threshold currents, quality factors of the order of thousands and high spontaneous emission coupling factor.

In this research, three main families of annular microcavities of interest were studied : circular, elliptical and ellipto-hyperbolic. The electromagnetic modes evolving in a solitary ring or disk optical microcavity were analyzed by solving the three-dimensional vectorial Maxwell’s equations under a   conformal transformation, obtaining closed form solutions and a significant physical insight regarding the nature of modes and their characteristics. The significant effect of the axial propagation constant on the nature of the modes was emphasized, indicating the feasibility of complete confinement of the optical field within the dielectric micro-cavity.

Systems of two or more concentric microring cavities were then studied in detail, and the concentric coupling issue was treated in full. I have shown that within the frame of a two-dimensional model the coupling is largely prohibited, while when a three-dimensional model is employed it becomes feasible. In addition to closed form analytic solutions, the analysis gives a physical insight to the feasibility, necessary conditions and limitations of this coupling. Concentrically-coupled micro-ring lasers were studied experimentally, demonstrating such coupled operation for the first time.

Elliptical micro-cavities add a dimension to the circular structures, namely the interfocal distance, by which the cavity can be deformed continuously. The optical fields and modes in these structures, including qualitative and quantitative understanding of characteristic properties like mode densities, modal shapes and distributions, directionality, limiting parameters, etc., were derived from a complete three-dimensional modeling and ray-optics approximation.