直立式裂環共振器之非線性增加

Nonlinear enhancement of vertical split ring resonator

鍾宗霖(Tsung-Lin Chung)

指導教授 ： 蔡定平

國立臺灣大學/理學院/物理學研究所/碩士(2018年)

https://doi.org/10.6342/NTU201801734

摘要

自非線性光學發展以來，人們便致力於了解在強場下物質內的非線性光學效應。至今已經有許多實際的非線性光學應用，包含了超快雷射、可調式非線性光學震盪器或是非線性光學影像用於超解析成像等等。除了這些應用以外，隨著奈米科技的日新月異，近年來在奈米結構－超穎材料領域中也開始著重於非線性方面的應用。超穎材料，為一種尺寸在波長等級以下的人造結構，在這種次波長尺寸下，材料可以展現出優越的光學性質，便使得人們得以操縱光的相位、偏振、場強等等。在傳統的非線性光學中，光透過材料本身的非線性特性來產生非線性轉換，是利用光在材料中的能量以及動量守恆過程，而在超穎介面中，由於其本身超薄的特性，取而代之地，是使用其內部特殊結構的擺放來達到空間對稱破壞性質或多種結互相構耦合等性質，來產生非線性效果。
在本研究中，我們比較了裂環共振器以及直立式裂環共振器的非線性（二倍頻）的現象，探討在相同結構尺寸下，其空間擺放形式對非線性效果的影響。藉由模擬分析後，由於直立式裂環共振器其特殊的擺放方式，使得正向入射光的電場以及磁場能夠同時與結構耦合，比起只能由電場激發的平面式裂環共振器，直立式裂環共振器可以擁有較大的侷域場強，也因此能夠將二倍頻訊號提升數倍，除此之外，直立式裂環共振器在正向入射激發下會產生兩種不同的二倍頻偏振態，並且可以被用來操縱二倍頻光的輻射方向，這些結果使得直立式裂環共振器在非線性超穎材料領域中，有著極佳的潛力。

關鍵字

非線性光學 ； 二倍頻 ； 裂環共振器 ； 超穎表面 ； 三維超穎表面

並列摘要

Nonlinear optics has been developed for several decades to understand the responses from interaction between electrons and strong incident light. So far, there are many practical applications by using the concept of nonlinear optics, such as ultrafast pulse laser, tunable light source (optical parametric oscillator), super resolution imaging.
Recently, with the development of nanophotonics, metamaterial gradually attracts wide attentions. Metamaterial is an artificial structure in sub-wavelength scale. Because of its unique optical properties, it can be used for light manipulation, including the phase, polarization and electromagnetic field of light. In ordinary nonlinear optics, when a light impinges onto a nonlinear crystal, the nonlinear effects are from the intrinsic properties of the material. The whole nonlinear process must follow the conservation law of energy and momentum. However, in the sub-wavelength region, metamaterial offers a unique platform to interact with incident light. By arranging nano-structures in a specific orientation or introducing multi-resonant system, metamaterial is able to generate nonlinear light.
In this work, we compare the second harmonic generation (SHG) response between vertical split ring resonator (VSRR) and planar split ring resonator (SRR). The finite element method (FEM) simulation is used to analyze both fundamental and nonlinear optical properties of VSRR and SRR. From simulation results, we found VSRR can simultaneously couple with incident electric and magnetic field, so it has a stronger fundamental field confinement compared to SRR. We assume this property leading VSRR has stronger SHG signal than SRR. On the other hand, VSRR has a dual SHG polarization states while SRR only has one, which is additional advantage of VSRR. From experiment results, the SHG signal of VSRR is about 3 times as stronger than those of planar SRR. The result proves VSRR has a potential in generating and manipulating SHG in the future.

並列關鍵字

Nonlinear optics ； nonlinear plasmon ； split ring resonator ； three-dimensional structure ； nonlinear metasurface

參考文獻

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