Tailoring the dispersion behavior of optical nanowires with intercore-cladding lithium niobate thin film Hairong He, Lili Miao, Guobao Jiang, Chujun Zhao,* and Shuangchun Wen Key Laboratory for Micro-/Nano- Optoelectronic Devices of Ministry of Education, School of Physics and Electronics, Hunan University, Changsha 410082, China *
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Abstract: The dispersion properties of silica and silicon subwavelengthdiameter wires with intercore-cladding uniaxial dielectric lithium niobate thin film has been studied numerically in detail. The waveguide dispersion shifts centered around 1550-nm wavelength have been investigated. It shows that the dispersion of optical nanowires with intercore-cladding lithium niobate thin film is highly sensitive to fiber geometry. Moreover, with applied electric field, considerable dispersion shifts without changing its geometric structure can be obtained. Our work may provide an inroad for developing miniaturized functional optoelectronic devices. ©2015 Optical Society of America OCIS codes: (000.4430) Numerical approximation and analysis; (060.2400) Fiber properties; (260.2030) Dispersion.
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Received 28 Jul 2015; revised 20 Sep 2015; accepted 21 Sep 2015; published 6 Oct 2015 19 Oct 2015 | Vol. 23, No. 21 | DOI:10.1364/OE.23.027085 | OPTICS EXPRESS 27085
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1. Introduction Waveguide dispersion engineering is very important for linear and nonlinear pulse transmission processes in different fields, such as optical communication, optical sensing and nonlinear optics [1–3]. By tailoring the waveguide geometry, different waveguide dispersion profiles can be obtained and the performance of the optical devices, such as optical modulators, switches, super-continuum sources, and wavelength converters, can be improved [4–8]. Among the various waveguides, micro-nano wires have been received increasing attentions for their giant waveguide dispersion, small size, low optical loss, and high tensile strength [9–11]. With the decreasing waveguide dimension, the waveguide characteristics will be different from their conventional counterpart. As a typical representative of one dimensional dielectric micro/nano optical waveguide, silica and silicon nanowires provide a simple and effective way for manufacturing nano-photonic devices, which has a natural compatibility with the existing optical waveguides. Moreover, the emerging semiconductor, polymer, hybrid photon-plasmon nanowires provide a versatile platform for manipulating light at the nanoscale [12–15]. The waveguide dispersion is associated with refractive index of material, the structure size, and the wavelength of the travelling light. Previous works focused on size-dependent waveguide dispersion [16–19]. However, it is difficult to change the structure and the waveguide dispersion once the waveguide geometry is determined. Lithium niobate (LiNbO3) crystal, an excellent electro-optical and nonlinear optical material, can be used in optical switches, electro-optical modulators and nonlinear optical devices [20,21]. By combing the silica/silicon and LiNbO3, the hybrid waveguide can present excellent electro-optical modulation performance [22]. If the dimension of the hybrid waveguides decreases, the waveguide will show totally different waveguide characteristics. Meanwhile, the fieldinduced change of the refractive index of LiNbO3 provides a flexible method to tailor the dispersion of nanowires waveguide device. In this paper, the waveguide characteristics of the optical nanowires with intercorecladding lithium niobate thin film were studied numerically. Considerable dispersion shift of the guided light can be obtained with different fiber geometry or different applied electric field for the same fiber geometry. The results cannot only provide design guidelines for dispersion components, but also shed light on the design of modulator at the nanoscale.
#246714 © 2015 OSA
Received 28 Jul 2015; revised 20 Sep 2015; accepted 21 Sep 2015; published 6 Oct 2015 19 Oct 2015 | Vol. 23, No. 21 | DOI:10.1364/OE.23.027085 | OPTICS EXPRESS 27086
2. Mathematical model We consider intercore-cladding uniaxial dielectric thin film optical nanowires with rotational symmetry about the z-axis, as shown in Fig. 1. A circular dielectric core (e.g. silica nanowire) with radius a and a uniaxial cylinder dielectric coat (e.g. LiNbO3) with thickness d (d = b-a) are embedded in the infinite air cladding. Refractive indices of the core and air-cladding are assumed to be ns and nc, respectively, whereas the film is uniaxial dielectric material with ordinary and extraordinary refractive indices no and ne, respectively. Solving Maxwell’s equations in cylindrical coordinates (r, φ , z) leads to the following expressions for the components of the electromagnetic field for the m th mode [23]: Am ℑm ( ur ) fc , m () n = Am J m e m no A( ) K ( wr ) f , c m m m (1)
Ez
2
0
