PhotonicCrystalResonatoren

Photonic crystals are materials with periodic variations in refractive index on length scales comparable to the wavelength of light, creating photonic band gaps in which certain frequencies cannot propagate. The periodicity can be one-, two-, or three-dimensional, yielding 1D Bragg stacks, 2D lattices such as air holes in a dielectric slab, and 3D lattices like woodpile structures.

The concept parallels electronic band gaps in solids. By introducing defects, localized modes or waveguides can be formed, enabling confinement and routing of light without conventional metal wires. Applications include distributed Bragg reflectors, high-efficiency LEDs, low-threshold lasers, photonic crystal fibers, and planar optical circuits. Defect engineering allows creation of resonant cavities, waveguides, and optical filters with engineered dispersion.

History: the idea was developed in the 1980s by Eli Yablonovitch and Sajeev John, who predicted complete photonic band gaps in periodic dielectrics. Advances in nanofabrication have enabled 2D and 3D crystals compatible with CMOS processing.

Fabrication and characterization: fabrication methods include lithography (electron-beam, optical) and etching, as well as self-assembly for 3D crystals. Characterization relies on transmission and reflection spectroscopy and near-field techniques. Challenges include fabrication imperfections and material losses that can degrade band gaps. Nonetheless, photonic crystals underpin ongoing research in integrated photonics, optical communications, and sensing.