Chiral metamaterials refer to metamaterials consisting of gyrotropic inclusions that do not
have a superposable mirror image. Because of the extraordinary optical activity (OA) and
circular dichroism (CD) phenomena, it has been suggested that chiral negative index meta-
materials (chiral NIMs) can provide a new route for constructing a superlens that goes
beyond the diffraction limit. The plasmonic-enhanced circular dichroism, on the other hand,
has also been evaluated as a crucial key in bio-chemistry to boost the sensitivity of CD-
spectroscopy to dissect complex biomolecules, such as proteins. In this regard, there has
been an increasing interest in studying chiral metamaterials. In this thesis, we investigated,
designed, and simulated the chiral metamaterials based on the intertwined gold helices, ded-
icating to construct negative index materials and high transmission and large rotary power
devices through finite-difference time domain (FDTD) method. By employing the effective
parameter retrieval technique, a four-intertwined helix combined with metallic wire griddings
that reached NIM was proposed. The NIM exhibited the maximum figure of merit (FOM,
−Re{n}/Im{n}) of 0.5 under normal incidence at 24.72 THz for the LCP wave. Incorporat-
ing the simulations with genetic algorithm (GA), we designed 4 polarization rotators with
maximum rotary power 105.24 (0/λ)and extremely high transmittance (average above 80%)
at the communication wavelength of 1.55 micrometer. These results show that helix-based devices
serve as potential candidates for future optoelectronic applications.

Chiral metamaterials refer to metamaterials consisting of gyrotropic inclusions that do not
have a superposable mirror image. Because of the extraordinary optical activity (OA) and
circular dichroism (CD) phenomena, it has been suggested that chiral negative index meta-
materials (chiral NIMs) can provide a new route for constructing a superlens that goes
beyond the diffraction limit. The plasmonic-enhanced circular dichroism, on the other hand,
has also been evaluated as a crucial key in bio-chemistry to boost the sensitivity of CD-
spectroscopy to dissect complex biomolecules, such as proteins. In this regard, there has
been an increasing interest in studying chiral metamaterials. In this thesis, we investigated,
designed, and simulated the chiral metamaterials based on the intertwined gold helices, ded-
icating to construct negative index materials and high transmission and large rotary power
devices through finite-difference time domain (FDTD) method. By employing the effective
parameter retrieval technique, a four-intertwined helix combined with metallic wire griddings
that reached NIM was proposed. The NIM exhibited the maximum figure of merit (FOM,
−Re{n}/Im{n}) of 0.5 under normal incidence at 24.72 THz for the LCP wave. Incorporat-
ing the simulations with genetic algorithm (GA), we designed 4 polarization rotators with
maximum rotary power 105.24 (0/λ)and extremely high transmittance (average above 80%)
at the communication wavelength of 1.55 micrometer. These results show that helix-based devices
serve as potential candidates for future optoelectronic applications.

Abstract

contents
1. Introduction
1.1 Development of Metamaterials
1.2 Chiral Metamaterials
1.3 Helix Metamaterials
1.4 Motivation

2. Fundamentals and Methods
2.1 Simulation Method and Material Model
2.1.1 Finite-Difference Time Domain method
2.1.2 Optical Properties of Materials
2.2 Negative Index Material
2.2.1 Negative Refractive Phenomenon
2.2.2 Diffraction Limit and NIM Perfect Lens
2.3 Genetic Algorithm
2.4 Bi-isotropic Media and Effective Medium Theory
2.4.1 Bi-isotropic Media
2.4.2 The Significance of Chirality Index κ
2.4.3 Effective Medium Theory
2.4.4 Validity of Effective Medium Theory
2.5 Optical Activity and Circular Dichroism for CMM
2.5.1 Born-Kuhn Model
2.5.2 One Electron Model

3 Parameter Retrieval and Negative Index Based on Helix Metamaterials
3.1 The 4-intertwined Helix and Method
3.2 Results and Discussion

4 Large Optical Activity and High Transmission Based on Helix Metamaterials
4.1 Method
4.2 Results
4.3 Discussion

5 Conclusions

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