Transmission Properties Of Terahertz Wave In One-dimensional Antiferromagnetic/dielectric Fractal Photonic Crystals

Antiferromagnet is a special kind of magnetic material whose magnetic moment isalso orderly arranged in microcosmic view, i.e. adjacent atomic magnetic moments areof equal size but in opposite directions and do not show magnetic. When frequency isclose to resonance frequency, magnetic susceptibility increasing much rapidly, there aremany new properties appearing. What’s more, one can control the properties of themagnetic system by changing the external magnetic field. In another hand，theresonance frequency of antiferromagnet lies in the terahertz range, which is beingwidely studied. To discover the interaction between terahertz wave and materials hasbeen a major concern recently. So this paper studies the transmission properties ofterahertz wave through antiferromagnetic/dielectric Cantor fractal magnetic photoniccrystals （PCs） in detail.Firstly, we report the research progress of the quasicrystals and quasi periodicstructure, fractal structure, antiferromagnetic and THz technology in the introduction.The main research methods for optical properties of photonic crystal are introduced inthe second chapter. In Chapter3and4, using the transfer matrix method, the transfermatrix, the transmission and reflection of terahertz wave transmitted through andreflected by antiferromagnetic Cantor fractal PCs under Voigt and Faradayconfiguration respectively. By making use of the parameters of MnF₂in numericalcalculation, we get the following conclusions:（1） In the frequency region far away fromthe resonance of MnF2, the properties of the transmission spectrum of the systems underVoigt and Faraday configuration are the same: the spectrum has a periodic characteristicfor perpendicular incident, the number of the transmission peaks in one cycle are equalto G^N, the number of the layers in the fractal; the spectrum shows sequential splittingand self-similarity properties. Together with the increasing of the incident angel of thewave, the photonics band gap moves to the high frequency, transmission peaks becomenarrow and sharp and some imcomplete photonic band gaps become complete photonicband gaps.（2） In the frequency region close to the resonance of MnF₂, the transmissionspectra of the two configurations are not the same any longer. For Voigt configuration,there are two band gaps appearing at the two resonance frequencies, and thetransmission peaks between the two gaps become low with the increasing of the incident angle; For Faraday configuration, the band gaps form at the two resonancefrequencies only when the generation of the fractal is big enough. The external magneticfield can only affect the spectrum in the vicinity of the resonance. When the externalmagnetic field increases from zero, the number of the resonance frequency of MnF₂becomes from one （ω_r）to two（ω_r+ω₀and ω_r-ω₀）, the band gap located at ω_r becomespassband and two new band gaps appearing at ω_r+ω₀and ω_r-ω₀.（3） When choosingCantor fractal as a single cell to produce PCs, the transmission spectrum showsswitching properties together the changing of the number of period.（4） When we put anantiferromagnetic defect layer in the dielectric cantor fractal, the band gap can bebroaden and a narrow perfect defect mode can be introduced at the center of the gap,which can be used as narrow band filter.