Mode density inside an omnidirectional mirror is heavily directional but not small

We show that ominidirectional reflection is not a sufficient signature of a photonic bandgap. Although dramatic angular redistribution takes place, the mode density of the electromagnetic field is hardly altered within the ominidirectional reflection range but rather has characteristics typical of a waveguide. The strikingly large polarization anisotropy is due to the huge dielectric contrast but not to a photonic bandgap. (C) 2000 Optical Society of America OCIS codes: 230.1480, 230.4170, 230.7390.