  Numerical results are presented for single-mode guidance, which is based on
photonic band gap (PBG) effect, in one-dimensional planar all-dielectric
light-guiding systems. In such systems there may be two kinds of light-speed
point (the intersection of a mode-dispersion curve and the light line of
guiding region ambient medium): one is the intrinsic light-speed point that is
independent of the guiding region width, and the other is the movable
light-speed point that varies with the guiding region width. It is found that
the intrinsic light-speed point plays an important role to form the single-mode
regime by destroying the coexistence of the lowest guided TM and TE modes that
are born with a degeneration point. A sufficient and necessary condition for
intrinsic light-speed points is given. The transverse resonance condition is
derived in the Maxwell optics frame, and it is shown that there is a
significant revision to the traditional one in the ray optics model. A
mode-lost phenomenon is exposed and this phenomenon suggests a way of how to
identify PBG-guided fundamental modes. Quasi-cutoff-free index-guided modes in
the PBG guiding structures, which appear when the higher-index layers are
adjacent to the guiding region and the guiding region width is small, are
exposed and analyzed as well.
