Design of micro-antenna optical metasurfaces

• Main Author: Sun, Zhuohan
• Other Authors: Wang Qijie
• Format: Thesis-Master by Coursework
• Language: English
• Published: Nanyang Technological University 2023
• Subjects: Engineering::Electrical and electronic engineering
• Online Access: https://hdl.handle.net/10356/164467
• Institution: Nanyang Technological University

Metasurface devices usually exhibit certain properties which are not common or cannot be found in natural materials within certain frequency ranges. One type of optical metasurface contain periodic unit cells whose reflection or transmission phase shift can be manipulated through structure parameters. Based on Huygens’ principle, if the unit cells can maintain a constant phase shift difference, the wavefront of reflection or transmission wave can be manipulated. This in effect controls the propagation direction of the reflection/transmission wave. Thus phenomenon is known as anomalous reflection or anomalous refraction. In this paper, two optical metasurfaces with micro-antenna unit cells operating in near-infrared region (wavelength of 1 micrometer) are proposed and simulated with ANSYS HFSS electromagnetic solver. One of the metasurface device exhibits anomalous reflection and the other with anomalous refraction. When a light beam is perpendicularly incident, the metasurface devices can generate an oblique reflection or refraction light beam which is not perpendicular to the metasurface plane. Additionally, two metasurface unit cells with similar structures are proposed as optical band-stop filters working in reflection and transmission modes. In this thesis, the proposed reflective metasurface achieves an anomalous reflection directed at 40° with a relatively good efficiency of -2.52dB, and the transmitting device has an anomalous transmission at approximately 45° but with a lower efficiency. For the optical filters, the reflective filter device has a center frequency attenuation of 30dB and a bandwidth of 150nm, while the transmitting one possesses a lower attenuation of 15dB and a narrower bandwidth of 90nm.