Broad Comparison between Au Nanospheres, Nanorods and Nanorings as an S-Bend Plasmon Waveguide at Optical C-band Spectrum
УДК 543.429; 681.785
BROAD COMPARISON BETWEEN AU NANOSPHERES, NANORODS AND NANORINGS AS AN S-BEND PLASMON WAVEGUIDE AT OPTICAL C-BAND SPECTRUM
СРАВНЕНИЕ AU НАНОСФЕР, НАНОТРУБОК И НАНОКОЛЕЦ, ИСПОЛЬЗУЕМЫХ В КАЧЕСТВЕ ПЛАЗМОННЫХ ВОЛНОВОДОВ S-ФОРМЫ В ОПТИЧЕСКОМ C-BAND СПЕКТРАЛЬНОМ ДИАПАЗОНЕ
© 2013 г.
Arash Ahmadivand*; Saeed Golmohammadi**; Ali Rostami** ** Department of Electrical Engineering, Ahar Branch, Islamic Azad University, Ahar, Iran ** School of Engineering-Emerging Technologies, University of Tabriz, Tabriz, Iran ** Е-mail: a_ahmadivand@iau-ahar.ac.ir, sgolmohammadi@tabrizu.ac.ir, arostami@tabrizu.ac.ir
The integration of optical devices demands the fabrication of waveguides for electromagnetic energy below the diffraction limit of light. In this work, we have investigated the possibility of utilizing specific chains of closely spaced noble metal nanoparticles for waveguides beyond diffraction limit. Accordingly, we have employed Au and Ag nanorings in order to transport the optical energy through the Plasmon waveguide at optical C-band spectrum (l ≈ 1550 nm). In proposed waveguides, we try to select the best structure via comparison between their transmission losses and group velocities of propagated energy. Three-dimensional simulations based on FiniteDifference Time-Domain algorithm (FDTD) are used to determine the related geometrical values. It is shown that nanoring’s geometrical tunability and extra degree of freedom (DoFs) in its geometry can cause the optical energy to transport at 1550 nm with higher efficiency and lower losses in comparison with those of the other shapes of nanoparticles such as nanospheres and nanorods.
Keywords: S-Bend, Transmitted Power, Transmission loss, Nanoparticle, Optical energy, Optical communication band.
OCIS Codes: 130.3130, 190.3970, 300.6490.
Submitted 18.06.2012.
1. Introduction
The principal theoretical and physical properties of sub-wavelength metal nanoparticles have been investigated and studied by most of researchers, in recent years [1–3]. It has been of the most consideration when light has strongly interacted with noble metal nanoparticle; this interaction then causes an excitation inside the metal nanoparticle. Thus a collective electron motion occurs at an specific frequency (Plasmon Frequency) in which these coherent oscillations are named surface Plasmon (SP) [1–3]. For most of noble metals (gold, silver and copper), the excitation frequency is in the visible and near-infrared domain of the spectrum [4, 5]. When the excitation takes place at the surface Plasmon frequency of metal, the energy flux is disturbed and this optical energy is directed toward the metal nanoparticle [5]. To determine the resonance fre-
quency of particular metal nanoparticle, we must consider the effect of some fundamental components such as, 1) the shape and dimensions of the nanoparticle and 2) the refractive index of the host or surrounded material [5, 6].
Nevertheless, operation of Plasmon waveguides and similar structures at optical communication band urges that localized surface Plasmon resonance (LSPR) to be red-shifted [6]. Applying the Quasi-static approximation in previous works has demonstrated that to provide LSPR close to 1550 nm, any shape of metal nanoparticles (nanosphere, nanodisks) must be surrounded by a substrate with relative permittivity more than 55, which is not applicable in these structures [6]. Hence, we have to apply different shapes of nanoparticles with extra degree of freedom (DoF) in order to red-shift the LSPR. Nanoring can be a potential candidate. Comparing to nanospheres and nanorods, nanoring dimensions
“Оптический журнал”, 80, 2, 2013
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permit for a better size reduction and fine tunability [6].
On the other hand, there are significant limitations in utilizing metal-dielectric components to transport the optical energy through the waveguide. One of these fundamental limitations is the relation between metal nanoparticle dimensions and the wavelength of the incident light. If the dimension of the nanoparticle is much smaller than the wavelength of the light (d
BROAD COMPARISON BETWEEN AU NANOSPHERES, NANORODS AND NANORINGS AS AN S-BEND PLASMON WAVEGUIDE AT OPTICAL C-BAND SPECTRUM
СРАВНЕНИЕ AU НАНОСФЕР, НАНОТРУБОК И НАНОКОЛЕЦ, ИСПОЛЬЗУЕМЫХ В КАЧЕСТВЕ ПЛАЗМОННЫХ ВОЛНОВОДОВ S-ФОРМЫ В ОПТИЧЕСКОМ C-BAND СПЕКТРАЛЬНОМ ДИАПАЗОНЕ
© 2013 г.
Arash Ahmadivand*; Saeed Golmohammadi**; Ali Rostami** ** Department of Electrical Engineering, Ahar Branch, Islamic Azad University, Ahar, Iran ** School of Engineering-Emerging Technologies, University of Tabriz, Tabriz, Iran ** Е-mail: a_ahmadivand@iau-ahar.ac.ir, sgolmohammadi@tabrizu.ac.ir, arostami@tabrizu.ac.ir
The integration of optical devices demands the fabrication of waveguides for electromagnetic energy below the diffraction limit of light. In this work, we have investigated the possibility of utilizing specific chains of closely spaced noble metal nanoparticles for waveguides beyond diffraction limit. Accordingly, we have employed Au and Ag nanorings in order to transport the optical energy through the Plasmon waveguide at optical C-band spectrum (l ≈ 1550 nm). In proposed waveguides, we try to select the best structure via comparison between their transmission losses and group velocities of propagated energy. Three-dimensional simulations based on FiniteDifference Time-Domain algorithm (FDTD) are used to determine the related geometrical values. It is shown that nanoring’s geometrical tunability and extra degree of freedom (DoFs) in its geometry can cause the optical energy to transport at 1550 nm with higher efficiency and lower losses in comparison with those of the other shapes of nanoparticles such as nanospheres and nanorods.
Keywords: S-Bend, Transmitted Power, Transmission loss, Nanoparticle, Optical energy, Optical communication band.
OCIS Codes: 130.3130, 190.3970, 300.6490.
Submitted 18.06.2012.
1. Introduction
The principal theoretical and physical properties of sub-wavelength metal nanoparticles have been investigated and studied by most of researchers, in recent years [1–3]. It has been of the most consideration when light has strongly interacted with noble metal nanoparticle; this interaction then causes an excitation inside the metal nanoparticle. Thus a collective electron motion occurs at an specific frequency (Plasmon Frequency) in which these coherent oscillations are named surface Plasmon (SP) [1–3]. For most of noble metals (gold, silver and copper), the excitation frequency is in the visible and near-infrared domain of the spectrum [4, 5]. When the excitation takes place at the surface Plasmon frequency of metal, the energy flux is disturbed and this optical energy is directed toward the metal nanoparticle [5]. To determine the resonance fre-
quency of particular metal nanoparticle, we must consider the effect of some fundamental components such as, 1) the shape and dimensions of the nanoparticle and 2) the refractive index of the host or surrounded material [5, 6].
Nevertheless, operation of Plasmon waveguides and similar structures at optical communication band urges that localized surface Plasmon resonance (LSPR) to be red-shifted [6]. Applying the Quasi-static approximation in previous works has demonstrated that to provide LSPR close to 1550 nm, any shape of metal nanoparticles (nanosphere, nanodisks) must be surrounded by a substrate with relative permittivity more than 55, which is not applicable in these structures [6]. Hence, we have to apply different shapes of nanoparticles with extra degree of freedom (DoF) in order to red-shift the LSPR. Nanoring can be a potential candidate. Comparing to nanospheres and nanorods, nanoring dimensions
“Оптический журнал”, 80, 2, 2013
15
permit for a better size reduction and fine tunability [6].
On the other hand, there are significant limitations in utilizing metal-dielectric components to transport the optical energy through the waveguide. One of these fundamental limitations is the relation between metal nanoparticle dimensions and the wavelength of the incident light. If the dimension of the nanoparticle is much smaller than the wavelength of the light (d