Seminar: “METASURFACE MICROLENS FOCAL PLANE ARRAYS AND MIRRORS” BY ONUR AKIN, Ph.D. Defence in Electrical and Electronics Engineering
Supervisor: Prof. Dr. H. Volkan Demir
The seminar will be on Wednesday, January 18 at 13:30 @EE-314
Lenses, mirrors and focal plane arrays (FPAs) are among the key components affecting the functionality, performance and cost of electro-optical (EO) systems. Conventional lenses rely on phase accumulation mechanism for bending wavefront of light. This mechanism and the scarcity of transparent materials result in high-complexity, high-cost and bulky EO systems. Conventional mirrors, on the other hand, are limited by the electromagnetic properties of metals and cannot be used in certain EO systems. Also, conventional FPAs suffer the fundamental tradeoff between the optical resolution and optical crosstalk. Metasurfaces, relying on the concept of abrupt phase shifts, can be used to built a new class of optical components. However, for realizing metasurfaces, optical resonators should cover a full 0-to-2π phase shift response with close to uniform amplitude response. In this thesis, to develop these metasurface optical components, nanoantennas that act as unit cell optical resonators were designed and modeled. A design methodology for building and optimizing these metasurfaces using the designed nanoantennas was developed. After obtaining the metasurfaces, we successfully addressed the problems of optical crosstalk in mid-wavelength infrared (MWIR) FPAs and weak field localization in mirror contacts. Full-wave simulations confirmed major crosstalk suppression of the microlens arrays to achieve ≤ 1% optical crosstalk in the proposed metasurface FPAs, which outperforms all other types of MWIR FPAs reported to date. However, due to intrinsic absorption losses in metals, the resulting device efficiency was low (≤ 10%). To solve this problem, metallic nanoantennas were replaced by dielectric nanodisks and the focusing efficiency was dramatically increased to 80%. This is the first account of high-efficiency low-crosstalk MWIR FPAs. Full-wave simulations also confirmed the strong field localization of metasurface mirrors that can impose a phase shift response close to 0˚. The findings of this thesis indicate that metasurface FPAs and mirrors are highly promising for future EO systems.
Keywords: Metasurfaces, Microlenses, Magnetic mirrors.