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Photonic crystals are composed of periodic dielectric, metallo-dielectric or even superconductor microstructures or nanostructures that affect the propagation of electromagnetic waves (EM) in the same way as the periodic potential in a semiconductor crystal affects the electron motion by defining allowed and forbidden electronic energy bands.

Photonic crystals contain regularly repeating regions of high and low dielectric constant. Photons (behaving as waves) propagate through this structure – or not – depending on their wavelength. Wavelengths that are allowed to travel are known as modes; groups of allowed modes form bands. Disallowed bands of wavelengths are called photonic band gaps. This gives rise to distinct optical phenomena such as inhibition of spontaneous emission, high-reflecting omni-directional mirrors and low-loss-waveguiding.

The periodicity of the photonic crystal structure must be around half the wavelength of the electromagnetic waves that are to be diffracted. This is ~200 nm (blue) to 350 nm (red) for photonic crystals operating in the visible part of the spectrum

a property of the electromagnetic fields known as scale invariance – in essence, the electromagnetic fields, as the solutions to Maxwell’s equations, has no natural length scale,solutions for centimeter scale structure at microwave frequencies are the same as for nanometer scale structures at optical frequencies. Continue reading →