In this paper, we present a new approach for the exact calculation of band
structure in one-dimensional periodic media, such as photonic crystals and
superlattices, based on the recently reported differential transfer matrix
method (DTMM). The media analyzed in this paper can have arbitrary profile of
refractive index. We derive a closed form dispersion equation using
differential transfer matrix formalism, and simplify it under the assumptions
of even symmetry and real-valued wavenumber. We also show that under normal
incidence both TE and TM modes must have the same band structure. Several
numerical test cases are also studied and discussed.