Defect Modes In One-Dimensional Photonic Crystals Consisting Of Ta₂O₅ And MgF₂

In 1987, Yablonovitch and John first showed that photonic crystals (PCs) may display a range of frequencies where the propagation of an electromagnetic wave in the PCs is completely forbidden. PCs are of great of novel properties result from photons movement can be modulated in PCs, which has extensive application in fabrication of new conception or advanced optical devices that can not make previously. PCs have been obtained in infrared, microwave, and millimeter-wave region. For wavelength shorter than infrared, especially short wavelength in visible region or UV region only a few experimental and theoretical systems have recently been demonstrated to exhibit the signature of photonic bandgaps. This is because most materials have high absorption coefficients and unstable dielectric constants under prolonged irradiation with VIS/UV light. On the other hand, tremendous trouble exists in the preparation of two-dimensional and three-dimensional PCs with several nanometres for present technology. However, for the simple structure and preparation of one-dimensional PCs, moreover, 1D PCs can replace some higher dimensional PCs in applications, it is becoming hot point recently.Ta₂O₅ is a ceramic material with high refractive index and low absorption which has high reflection in visible and near infrared region thus is applied in more and more extensive fields. And MgF₂ is that one of potential optical materials in VIS/UV region which has high transmissivity and low refractivity and well resistance to damage. Therefore, this paper chooses both Ta₂O₅ and MgF₂ fabricated 1D PCs in visible range. Because of the thickness of films just have some nanometers in visible region, thus a layer with various refractivity appears due to atoms diffusion on the surface between two materials. As a result, the paper also considers the influence of atoms diffusion on Ta₂O₅/MgF₂ surface to the properties of gap.Using transfer matrix method, this paper designed theoretically the multilayer 1D PC and the structure with defect layer. The detail of the study can be introduced as follows.In the first place, we designed Ta₂O₅/MgF₂ multilayer which photonic band gap (PBG) covered the whole blue-green range from 439nm to 559nm. The gap in TE and TM mode completely overlapped each other when the incident angle varing from 0? to 20? but incompletely overlapped each other when the incident angle more than 20?, then the gaps move towards to more short wavelength and became narrow in TE mode but broad in TM mode.In the second place, Ta₂O₅ defect layer is introduced into Ta₂O₅/MgF₂ multilayer and single defect mode or double defect modes appear in PBG when varying the thickness of the defect layer. One defect mode presents at 495.3nm and two defect modes lie in 471nm and 528nm, respectively.Last but not least important, the structure of atoms diffusion on the surface between Ta₂O₅ and MgF₂ is designed and the influence of diffusion layers with different refractivity between Ta₂O₅ and MgF₂ is considered for studying the properties of PBG and defect modes.