  In this paper, the forward and backward propagating modes in an optical
waveguide structure namely the fiber Bragg filter also considered as a one
dimensional photonic crystal, are analytically computed as a function of
grating length for coupled optical modes. AlxGa1-xN/GaN material composition is
considered as a unit block of the periodic organization, and refractive index
of AlxGa1-xN/GaN is taken to be dependent on material composition, bandgap and
operating wavelength following Adachi's model. Expressions of propagating wave
are derived using coupled mode theory. Simulated results help us to study the
propagation of forward and backward wave propagating modes inside fiber and
waveguide devices.
