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그래핀 플라즈모닉스 기반의 고효율 광소자 연구

A study on highly efficient photonic devices based on graphene plasmonics

초록/요약

Graphene, two-dimensional material comprised of carbon atoms, has attracted great interest in optical devices owing to outstanding electrical and optical properties such as high thermal conductivity, outstanding electrical mobility, flexible, and exceptional mechanical strength. Above all, since the complex permittivity of graphene is easily tunable, it is considered as a promising material for wavelength tunable photonic devices. In spite of the superb properties, graphene-based photonic device applications have been limited by the low light-graphene interaction. In this dissertation, author presents several solutions to mitigate the restriction by using unique properties of graphene. In particular, author designed highly efficient optical modulators by using epsilon-near-zero (ENZ) mode that extremely confines light in a graphene layer: a free space-type graphene-based modulator using surface plasmon resonance and a waveguide-type modulator inserting a graphene layer into a Si waveguide. The designed modulators provide higher modulation depths and lower insertion losses compared with previously reported graphene-based modulators. Author also realized perfect absorption by using graphene ENZ mode in a modified Otto configuration. The wavelength of the perfect absorption is tunable and the perfect absorption can be achieved regardless of graphene quality. Plasmon-induced transparency (PIT) in coupled graphene grating has also been demonstrated. The wavelength tenability of the PIT peak and its modulator application in mid-infrared has been investigated. The theoretical analysis of the proposed photonics devices has been conducted by using various numerical tools, including the finite element method (FEM), the using rigorous coupled wave method (RCWA), and the transfer matrix method (TMM), as well as by using a Maxwell’s equation solver developed by the author. The FEM and the Maxwell’s equation solver were used for the modal analysis of the proposed structures. The RCWA and the TMM were used for the calculation of the transmission, reflection, and absorption spectra of the proposed structures.

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목차

Chapter 1: Introduction 1
1.1 Graphene-based optical devices 1
1.2 Overall objectives 2
1.3 Thesis outline 2

Chapter 2: Properties of graphene and an ENZ mode 4
2.1 Introduction 4
2.2 Band structure of graphene 4
2.2.1 Lattice structure of graphene 4
2.2.2 Tight-binding model for graphene 5
2.3 Optical properties of graphene 8
2.4 Permittivity of graphene 9
2.5 Graphene surface plasmon 11
2.6 An ENZ property and an ENZ mode 13
2.6.1 The ENZ property 13
2.6.2 The ENZ mode 14
Chapter 3: A graphene-based optical modulation using surface plasmon resonance at
optical communication wavelength 18
3.1 Introduction 18
3.2 Structure of the proposed optical modulator 19
3.3 Mechanism of reflection modulation 21
3.4 SPR curves for the proposed optical modulator 24
3.5 Absorption curves for the proposed optical modulator 38
3.6 Summery 30

Chapter 4: Tunable plasmon induced transparency in coupled graphene nano-ribbons 31
4.1 Introduction 31
4.2 Coupled graphene gratings structure 32
4.3 Guided mode resonance for single graphene structure 33
4.4 Direct-coupled PIT in coupled graphene gratings 34
4.5 Phase-coupled PIT in coupled graphene gratings 40
4.6 Tuning property of PIT 44
4.7 Summery 45
Chapter 5: Epsilon-near-zero mode in graphene 47
5.1 Introduction 47
5.2 ENZ mode in a single layer graphene 48
5.3 ENZ mode in two-graphene layer 53
5.4 Modulation properties 54
5.5 Sensitivity of the ENZ mode 56
5.6 Summary 57
Chapter 6: Graphene based tunable perfect absorption by epsilon-near-zero mode 59
6.1 Introduction 59
6.2 Structure of absorber and guided mode 60
6.3 Absorption curves with respect to gap size 61
6.4 Absorption curves with respect to mobility 63
6.5 Tunable property 65
6.6 Summary 66
Chapter 7: Conclusion and Future Work 67
Reference 69
Authors Publications 78

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