One-dimensional magnetic photonic crystal structures with wide absolute bandgaps

The photonic absolute bandgaps have many potential applications in specific fields, and some methods to enlarge the absolute bandgaps, such as adjusting the material and the rotational symmetry, constituting a heterostructure have been explored. Recently, with the occurring of metamaterial, the photonic crystal based on metamaterial has also realized the wide absolute bandgaps. However, the metamaterial is an artificially structured material of which the construction is more complicated. In this paper, one-dimensional magnetic photonic crystal structure with wide absolute bandgaps is proposed, which is composed of two kinds of magnetic materials with the same refractive index and physical thickness but different wave impedances. First of all, the transmission properties of one-dimensional magnetic and non-magnetic photonic crystals with the same wave impedance ratio are studied by using transfer matrix method. It is shown that the normalized frequency bandwidth of magnetic photonic crystal, i. e. the ratio of the band of bandgap to its center, is 0.41, while the normalized frequency bandwidth of the non-magnetic photonic crystal is 0.14. From the results, we can conclude that the absolute bandgap of the above magnetic photonic crystal is wider than that of non-magnetic photonic crystal because the former bandgap is not sensitive to the incident angle nor polarization. Secondly, we adjust the wave impedance ratios of the two kinds of magnetic materials and make them respectively reach 2, 4 and 6, with the refractive index and the physical thickness kept unchanged. By analyzing their transmission properties, it is found that the normalized frequency bandwidths of the absolute bandgaps are respectively 0.47, 0.84 and 1.03, and the greater the difference between the two wave impedances, the wider the normalized frequency bandwidth is. Thirdly, we investigate the influence of the per-layer physical thickness of the magnetic material on the bandgap, with the other parameters remaining unchanged. It is shown that the center of the absolute bandgap shifts toward high frequency with the decrease of the per-layer physical thickness. Finally, a kind of heterostructure is constructed by the above two one-dimensional magnetic photonic crystals. The normalized frequency ranges of the first and the second absolute bandgap of one magnetic photonic crystal structure are respectively 1.18-2.85 and 5.37-6.85. The normalized frequency range of the absolute bandgap of the other magnetic photonic crystal is 2.37-5.68. The normalized frequency range of the absolute bandgap of the heterostructure can be enlarged to 1.18-6.85 and the corresponding normalized frequency bandwidth can reach more than 1.41. The wide absolute bandgaps can be applied to integrated optics, optical fiber communication and high-power laser systems, according to which we may design the polarization-independent and omnidirectional devices such as reflectors, optical switchers and optical filters.