Study On Nonreciprocal Transmission Of Photonic Crystal Based On Magneto-Optical Effect

Photonic crystal is a artificial metamaterial with photonic band gap. The defect mode that allow the light pass through the band gap can be made by inserting the magnetic material. The time reversal symmetry of the system is broken by the effect of magneto-optic effect. At the same time, the space inversion symmetry is broken by the nonsymmetry of the structure, so the light in photonic crystal realize a nonreciprocal transmission or absorption.In this paper, the transmission properties of the photonic crystal is analysed by the transfer matrix method. Due to the permittivity of magnetic material in the Voigt effect is a tensor, the traditional transfer matrix method does not apply to it, so we derive the transfer matrix based on the Maxwell equations and calculate the transmission properties of photonic crystal inserting by the magnetic material.In order to realize the nonreciprocal transmission, a simple structure of one-dimensional photonic crystal optical isolator based on the two nonsymmetric magnetic-optical matel defects is designed. After using the improved transfer matrix method to calculate the structure, we research the transmission spectrum based on the MATLAB software. Then we analysis the transmission characteristics of optical isolator with the incident angle, and the external magnetic field and the thickness of the magnetic-optical matel defects. The results show that when the incident angle is small, the nonreciprocal effect of the optical isolator is not obvious, but the nonreciprocal effect grow with the increase of incident angle, and it has a maximum value. When changing the magnetic field and the thickness of defect layers, the nonreciprocal effect also have similar changes. In addition, the position of the non reciprocal channel can be adjusted by changing the structure parameters and rxternal conditions.On the basis, we design a one-way electromagnetic wave absorber by inserting magnetic materials and metal materials in photonic crystal. The magneto-optical effect realizes the one-way absorb, while enhancing the absorption effect of the metal layer. Then we calculate the absorption spectra of the symmetric and nonsymmetric structure, and analysis the reason of the one-way absorption characteristics of the nonsymmetric structure. The relationship between the absorption characteristics of absorber and the metal defect layer shows that the metal layer is thicker, absorption efficiency is higher, and the in the position of absorption wavelength has been changed with the metal layer thickness.