Destruction and enhancement of photonic band gap and coherent localization of optical fields in functional photonic crystals

We use electromagnetically induced transparency combined with coherent enhancement of refractive index in the conduction intersubband transitions of a n-doped quantum well structure to study one-dimensional functional (active) photonic band gap structures. In the absence of a control laser field, such structures act as conventional photonic band gaps created by off-resonant (background) refractive index perturbations. In the presence of the control field, they are transformed into resonant structures with transitions around the Bragg wavelength. We show that this process can be used to (i) destroy the band gap, making the structure fully transparent around the Bragg wavelength, or (ii) coherently tune the band gap while enhancing its width by nearly a factor of 2. Using these phenomena we then study coherent localization of electromagnetic modes in photonic band gap structures without having any structural defects. Such a localization process here happens via partial illumination of such structures by the control field, generating electromagnetically induced optical defects. We show that the phase associated with such defects can be adjusted by the control field, allowing us to generate tunable electromagnetically induced transmission resonances (or photonic electromagnetically induced transparency) within the band gap.