Engineering the band gap of a two-dimensional photonic with hybrid structure

• Main Authors: Wen-Long Liu, 劉文龍
• Other Authors: Tzong-Jer Yang
• Format: Others
• Language: en_US
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/16697729803327227659

博士 === 國立交通大學 === 電子物理系所 === 95 === Photonic crystals (PCs) are artificial materials having the periodical modulation of dielectric structures in space and there exhibit photonic band gaps (PBGs) in which the propagation of electromagnetic (EM) waves in any propagating direction and polarization state is inhibited. This feature leads to various peculiar physical phenomena and provides potential applications. Most proposed applications of PCs rely on large PBGs of PCs, therefore, the design and construction of PCs with large PBGs are a major goal in the PC field. Much attention has been devoted two-dimensional (2D) photonic crystals (i.e., structures with periodic dielectric patterns on a plane and translational symmetry in the perpendicular direction), since they are easier to fabricate (particularly in the optical region) and may be employed in waveguide configuations. In this thesis, we developed several procedures to systematically engineer the 2D PCs with large PBGs, which were scribed into the crystal structure by removing partial composited materials or introducing additional scatterers into unit cell of the prototype lattices. For the first time, we have fabricated a PC with tunable PBGs. The proposed 2D tunable PC structure is realized by inserting a movable circular dielectric rod into a square lattice of square dielectric cylinders in air. The PBGs can be tunable by shifting the position of the circular dielectric rod. In the present work, we mainly concentrate on the subject of sensitivity of the PBGs to the variations of structural parameters of system, especially paying the attention on the effects of the shift s of the position of the circular dielectric rod. We find that there is a region of parameters in which the ratio of the gap width to the midgap is insensitive to the shift of the position of the circular dielectric rod. This property provides the large benefit of relaxing the fabrication tolerance of the tunable PCs. Then, we propose 2D square lattices of square cross-section dielectric rods in air, designed with an air hole drilled into each square rod. By adjusting the shift of the hole position in the square rod in each unit cell, the dielectric distribution of the square rod will be modified. The PC structure proposed here has a sizable complete PBG and exhibits very gently sloped bands near such gap edge, which resulting in a sharp peak of density of state. In addition, the zero or small group velocities are observed in a broad region of k-space. This structure can be fabricated with materials widely used today and opens a facinating area for applications in optoelectric devices.