Abstract
It is well known that high refractive index contrast is essential to the formation of an omnidirectional Photonic Band Gap (PBG). It is generally cited also that the width of the omnidirectional PBG of a dielectric mirror is determined by the refractive-index contrast. But in this work, we show that this condition is not really general criteria. Dielectric mirror with higher refractive index contrast does not necessarily mean that it has the largest omnidirectional photonic band gap. So, we investigate the necessary conditions on the high and low refractive indices of the quarter wave layers to have the largest omnidirectional bandwidth in the visible range. We present a profound study of the omnidirectional band center wavelength and the bandwidth behaviors versus the layers refraction indices. It is shown therefore that one can modulate omnidirectional photonic band gap center by modulating the optical phase of the mirror.