  We suggest a novel conceptual approach for describing the properties of
waveguides and circuits in photonic crystals, based on the effective discrete
equations that include the long-range interaction effects. We demonstrate, on
the example of sharp waveguide bends, that our approach is very effective and
accurate for the study of bound states and transmission spectra of the
photonic-crystal circuits, and disclose the importance of evanescent modes in
their properties.
