There is a question in our minds which is the reason of using such complex materials as photonic crystals rather than simply using the reflective properties of metals or the phenomenon of total internal reflection in dielectrics to prevent light from going somewhere.
The answer lies within the energy losses and the scale.
Photonic crystals are much less dissipative than metal mirrors for the control of electromagnetic waves.
Further, as compared to total internal reflection based waveguides such as glass fiber cables, photonic crystals can manipulate the flow of light at a much smaller scale, namely that of the wavelength of the guided light itself .