Study Of Design And Properties Of One-dimensional Photonic Crystal Omnidirectional Reflectors And Filters

Photonic crystals (PCs) are a class of artificial materials with periodic variation of refractive index or wave impedance. Compared with two and three dimensional PCs, one dimensional (1D) PCs have attracted considerable attention theoretically and experimentally because of the simple structures, easy fabrication and omnidirectional reflection (ODR) bands analogous to complete photonic band gaps (PBGs). Most researchers are dedicated themselves to studies on 1D dielectric PC omnidirectional reflectors and filters. Nowadays, more kinds of materials other than dielectric ones are used in PCs, and some novel properties are discovered accordingly, which provides new ideas and methods for researchers to further investigate 1D PC omnidirectional reflectors and filters. The main subject of this paper is focused on the investigation of the design and properties of 1D dielectric and magnetic PC omnidirectional refletors and filters with the purpose of simplifying the whole structures while improving the performance. The research contents and results can be summarized as follows:(1) It is reported that the ODR bands of 1D quasi-periodic dielectric PC omnidirectional reflector are much wider than those of traditional 1D periodic ones, while the structures are much more complicated. Hence, with the purpose of obtaining both broad ODR bands and simple structures, we designed a simple and broadband 1D low-order quasi-periodic dielectric PC omnidirectional reflector (S1)6 (S2)6 (S1')10 constructed by low-order Thus-Morse quasi-periodic PC(S1)pi(i=1,2) using demcimal genetic algorithm (DGA) to optimize the structure. The ODR bandwidth of the reflector is 1.508?0, the total thickness is 5.2704?0, and the total layer number is 56. Compared with the reported high-order quasi-periodic dielectric PC omnidirectional reflector constructed by high-order quasi-periodic sequences, the new one owns a wider ODR band while the layer number, total thickness and disorder degree are largely reduced. To verify the design, we fabricated the structure via electron-beam evaporation technique. The measured ODR band is wide, which can cover all of the working wavelength points of optical fiber communication. The experimental results show a good agreement with the theoretical results.(2) In order to further enlarge ODR bands and simplify structures, based on the combination of alternating high permeability and high permittivity materials, which increases the wave impedance ratio between materials, we designed a simple and broadband 1D dielectric-magnetic PC omnidiretional reflector (0.255A,0.255B)5 (0.169A,0.066B)8 and a simple and broadband 1D dielectric-magnetic PC high-precision spatial filter (0.191A,0.201B)14(0.2878B',0.2955A')14 using DGA to optimize the heterostructures constructed by two different 1D dielectric and magnetic PCs. The ODR bandwidth of the optimal reflector is 1.34?0, the total layer number is 26, and the total thickness is 1.8634?0. The reflector has a much simpler structure and a much wider ODR band as compared with the reported dielectric-magnetic reflector constructed by quarter-wave stacks, and it also provides a comparable ODR band while its structure is simplified largely as compared with the abovementioned quasi-periodic dielectric reflector. The ODR bandwidth (including the filtering frequency) of the optimal spatial filter is 1.496?0, the total layer number is 56, and the total thickness is 5.8435?0. The filter provides a simpler structure, a wider ODR band and a high-precision filtering quality as compared with the reporterd dielectric spatial filter. Besides, we designed a broadband high-precision spatial filter (0.199A,0.28B)15(0.2893B',0.2269A')15with an ODR bandwidth of 0.657GHz, total layer number of 60 and total thickness of 0.4244m for microwave application using a reported organic polymer magnetic material with low dispersion, low absorption and light weight.(3) We analysed the properties of the PBG edges of a special kind of 1D PCs constructed by materials with identical refractive indices, and studied the enlargement of ODR bands based on heterostrucures constructed using incident angle domain method. The results indicate that, the PBGs expand as the incident angle increases, which benefits the enlargement of ODR bands; the enlargement of ODR bands is essentially a proper combination of high relection regions without any superposition and abruption due to the special properties of the PBG edges; the requirement of ODR band of each substructure is unnecessary; the more the substructures there are, the lower indices of materials are needed, which extends the range of materials. This kind of 1D PCs can be used to design some novel photoelectric devices which are difficult to be achieved using 1D pure dielectric PCs.(4) Based on the abundant properties of the PBG edges of 1D PCs with different refractive indices and those with identical refractive indices, we deigned four different kinds of non-spatial filters with narrow-frequency pass bands and wide non-transmission bands by crossing the PBG edges of two different 1D PCs. The results indicate that the introduction of magnetic materials makes the properties of PBG edges more diversiform, and the construction of heterostructures enhances the non-tramsmission bands; hence 1D PCs containing magnetic materials can accomplish some simple, broadband and special filter designs instead of 1D pure dielectric PCs.The designs above have potential applications in optical fiber commnucation and microwave communication. The research results are worthful for further investigations and applications of simple and broadband devices and broadband filters with special filtering abilities.