关键词: 零折射率/
类狄拉克点/
光子晶体/
磁流体
English Abstract
Tunable near-zero index of self-assembled photonic crystal using magnetic fluid
Geng Tao1,Wu Na1,
Dong Xiang-Mei1,
Gao Xiu-Min2
1.Shanghai Key Lab of Modern Optical System, Engineering Research Center of Optical Instrument and System, Ministry of Education, School of Optical-Electrical and Computer Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China;
2.Electronics and Information College, Hangzhou Dianzi University, Hangzhou 310018, China
Fund Project:Project supported by the National Basic Research Program of China (Grant No. 2015CB352001), the Special-Funded Program on National Key Scientific Instruments and Equipment Development of China (Grant No. 2012YQ17000408), the National Nature Science Foundation of China (Grant No. 61378035), the Basic Research Program of Shanghai, China (Grant No. 14ZR1428500), and the 151 Talent Project of Zhejiang Province, China (Grant No. 12-2-008).Received Date:06 July 2015
Accepted Date:26 August 2015
Published Online:05 January 2016
Abstract:In a zero index material, the phase velocity of light is much greater than the speed of light in vacuum and can even approach to infinity. Thus, the phase of light throughout a piece of zero-index material is essentially a constant. The zero index material has recently been used in many areas due to its extraordinary optical properties, including beam collimation, cloaking and phase matching in nonlinear optics. However, most of zero index materials usually have narrow operating bandwidths and the operating frequencies are not tunable. In this work, the model of tunable near-zero index photonic crystal is established by using colloidal magnetic fluid. Magnetic fluid, as a kind of easy-made mature nanoscale magnetic material, has proved to be an excellent candidate for fabricating self-assembled photonic crystal, especially the band-tunable photonic crystal with fast and reversible response to external magnetic field. The band structure can be calculated using the plane wave expansion method. For TE mode, it can be seen that a triply-degenerate point (normalized frequency f=0.734) at point under external magnetic field H=147 Oe, forms a Dirac-like point in the band structure, which is called an accidental-degeneracy-induced Dirac-like point. The effective permittivity eff and permeability eff are calculated using an expanded effective medium theory based on the Mie scattering theory. The calculated results show that both eff and eff are equal to zero at Dirac-like point, which means that the effective index neff is zero and the effective impedance Zeff is 1. The lattice structure of such a self-assembled photonic crystal will change with the external magnetic field, leading to the disappearance of Dirac-like point. However, when 143.6 OeH 152.4 Oe (1 Oe=79.5775 A/m), |neff | can keep less than 0.05 under the condition of Zeff = 1. Correspondingly, the operating frequency will change from 0.75 to 0.716. The model is verified by the numerical simulations (COMSOL Multiphysics) and the theoretical results agree well with the numerical ones.
Keywords: zero index/
Dirac-like point/
photonic crystal/
magnetic fluids
