Photonic Crystals

Researchers: Anu Huttunen and Päivi Törmä* *Department of Physics, Nanoscience Center, University of Jyväskylä.

Photonic crystals are periodic dielectric structures for which the period is of the order of the wavelength of light. Photonic crystals exhibit band gaps for light as a result of interference. Light with a frequency inside the band gap cannot exist in the photonic crystal.

We study waveguides in thin slabs of two-dimensional photonic crystals. Conventionally, waveguides in two dimensional photonic crystals are made by introducing a line defect (see Fig.31(a)). We have shown that the material on top/below the slab changes the band gap of the photonic crystal slab and we suggest to use this phenomenom to make a new type of waveguide by patterning the photonic crystal slab (see Fig.31(b) and (c)).

Figure 31

Figure 31: (a) Conventional defect waveguide. (b) and (c) New type of waveguide: photonic crystal slab with no defects is patterned with a material that changes the band gap of the photonic crystal.

We also study photonic crystal fibers, which have a periodic cladding. We found that when there is a defect ring in the cladding, the fiber has extremely high dispersion, but still a large mode area (see Fig.32). This type of fiber can be used for dispersion compensation of high power pulses.

Figure 32

Figure 32: Geometry and dispersion parameter (D) as a function of the core refractive index () the photonic crystal dispersion compensating fiber.