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Research on Magneto/Phonon Polaritons and Optical Properties of Antiferromagnetic Photonic Crystals

Author: TaJinXing
Tutor: WangXuanZhang
School: Harbin Institute of Technology
Course: Optics
Keywords: magnetic photonic crystals antiferromagnets ionic crystals polaritons optical propertities
CLC: O73
Type: PhD thesis
Year: 2012
Downloads: 41
Quote: 0
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Abstract


Magnetic photonic crystals refer to that photonic crystals contain one or moremagnetic ordering components and they have currently been a very important issue.The main reasons are as follows. First, controllable structures of magnetic photoniccrystals are easy to obtain. Concretely speaking, design and control of the opticalproperties can be accomplished with variation of components, components states andcomponents ratio, etc. Second, some novel behaviors of magnetic photonic crystalsmay be achieved, which can not be found in single component. For instance, theemergence of band gap, left-handedness and so on. Additionally, optical properties ofthe system can be conveniently tuned by the external magnetic field. All thecharacteristics contribute to the exploitation of novel photonic devices. Responsefrequencies of antiferromagnets are mostly located at millimeter wave and far-infrared frequency regimes, which are to be exactly exploited in THz technology. Wefind matched antiferromagnets and ionic crystals with close resonance frequency. Itis expected that some novel properties can be accomplished in magnetic photoniccrystals made of matched materials. Employing transfer matrix method and effectivemedium method, we study magneto/phonon polaritons and optical properties of one-dimension antiferromagnetic/ion-crystal photonic crystals as well as magneto/phononpolaritons of two-dimension antiferromagnetic/ion-crystal photonic crystals.Magneto/phonon polaritons of one-dimension antiferromagnetic/ion-crystalphotonic crystals are examined via transfer matrix method and effective mediummethod. The concept of magneto/phonon polaritons is proposed. The reason is that themagnetic moment in magnets can directly couple with the magnetic field, which isthe origin of magnetic polaritons. However, the transverse optical phonon modes ofionic layers can directly couple with the electric field in an electromagnetic wave andthis coupling generates the phonon polaritons. Therefore, collective excitations arereferred to as magneto/phonon polaritons in magnetic photonic crystals consisting ofmatched materials.Two bulk mini-bands are observed in term of the magneto/phonon polaritonsspectrum near resonance frequency of antiferromagnets. The group velocities of twomini-bands are both negative. Surface modes with various features scatter near mini-bands, which are completely different from the behaviors of single component.Optical properties of one-dimension antiferromagnetic/ion-crystal photoniccrystals are discussed via transfer matrix method, including transmission, refractionand absorption. Based on careful observation on the transmission spectrum, two transmission guided modes are found, which corresponds to mini-bands. Therefraction spectrum suggest the angle between the energy flow and wave vectorof forward-going wave are greater than90o, but less than180onear the frequenciesof two transmission guided modes, meaning the system possess quasi-left-handedness. What is more interesting is the angles are negative at certain left-handedness frequency regimes, indicating the system possess negative refraction.Negative refraction or quasi-left-handedness, and even both of them can be obtainedwhen polarization and incidence direction are appropriate, as well as effectivepermeability and effective permittivity are both negative. Thus, the refractive indexof this antiferromagnetic/ion-crystal superlattice is negative. Absorption spectra suggestabsorption corresponding to guided modes is noticeable, which is due toantiferromagnetic resonance effect.Additionally, we compare distinction and likeness of numerical results obtainedby transfer matrix method and effective medium method, showing the results are thesame in short period limit as well as the similarity is qualitatively in substantialagreement and the difference is quantitatively apparent. Subsequently we extend onedimensional system to two-dimensional structure, and then two-dimensional effectivemedium method of magnetic composite structure is established.

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CLC: > Mathematical sciences and chemical > Crystallography > Crystal physics
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