Effect of pitch angle on modal propagation characteristics of an annular circular dielectric waveguide having helical windings on the inner and outer boundaries as claddings

Using a fairly rigorous analysis, a general characteristic equation for an annular step‐index fiber with helical windings on the core‐cladding boundaries was derived. We present the modal dispersion characteristics for some lower‐order modes of this dielectric waveguide. We also use the variation of helix pitch angles of the windings and discuss their effect on the dispersion curves of the proposed waveguide. An important property, the presence of band gap, was found for some particular combinations of pitch angles. This may be attributed to the periodicity of the helical structure. We can say that pitch angle acts as a controlling factor for the propagation modes. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 33: 338–344, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10315