Study On The Optical Circular Polarizers With Metallic Helical Metamaterials

Optical circular polarizations of light are attractive for applications in reflective colourdisplays, life science microscopies, and photographies. Generally, the most common methodto get the circularly polarized light in optical applications is using a linear polarizer and aquarter-wave plate, However, this method have been restricted to narrow frequency rangesand the division components, which is a major drawback for many potential applications.In September of2009, J. K. Gansel succeeded in developing a broadband circularpolarizer by using gold helix metamaterials. But their research is limited to the followingthree aspects:1. The device is only for the single-helical structure.2. The material of thehelix is gold.3. The device only works in the region of3~6μm. Base on the research resultsof J. K. Gansel, we carried out the following two part of the research.For the first part of this thesis, the single-helical circular polarizers in differentfrequency range were studied. Since Maxwell’s equations are scale invariant, weappropriately scaled the structures to other frequency range. We also analyzed its bandwidthand extinction performance in detail. Then, the circular polarizers in terahertz frequencyrange polarizers were studied to show the the relation ship between the optical properties andthe parameters of the helical structures.In the second part, the double-helical circular polarizers in the visible frequency rangewere studied. Based on the previous research of the single-helical circular polarizers in thevisible bands, we proposed the double-helical circular polarizers of the visible bands, andcompared their optical performances, such as operation bandwidth and extinction ratio. Then,we proposed a circular polarizer with hetero-structured double-helical metamaterials, whichcould get a higher extinction ratio. This hetero-structure broke the balance state of theinteraction between the two helixes in one unit. Thus, the transmittance of the left circularpolarized light was decreased much, but for the right circular polarized light it was not.