For controlling of light photonic crystals have been extensively investigated in the past some decades. Many interesting optical phenomenon, i.e. photonic band gap, super prism effect etc., can be brought to realization by using Bragg diffractions in the periodic structure of different dielectric materials. Contrary to periodic structure, fractals, which consist of self-similar structure, is considered as a promising approach for manipulating electromagnetic waves. Although fractals are originally mathematical concept, they can be observed in real world, i.e. veins of a leaf, capillary blood vessel, etc.
However, only little investigations about the interaction of fractals with electromagnetic waves have been reported so far. If we use fractals as a subwavelength unit cell of metamaterials, they have a great potential to show exotic optical characteristics and consequently, to make useful novel optical devices. Especially, based on the fractal’s characteristic that some kind of ideal fractals has an infinite surface area in a finite volume (or an infinite boundary length in a finite area), the extremely small size of metamaterials with respect to the wavelength at an operation frequency can be possibly constructed.
Based on the above background, the goal of this study is to develop optical devices in terahertz (THz) region with fractal structures. One of targeted devices is a photoconductive fractal antenna, which can radiate a high power THz wave owing to the strong local resonance in the fractal design. In addition, by using fractal structure as a unit cell, I will show a new approach to develop the THz metamaterials which has a unique optical property to fractal structure. |