Optical power confinement factor in a Bragg fiber: 1 Formulation and general properties

The optical power confinement factor Γ is evaluated for TE, TM, and hybrid modes in a Bragg fiber. Results are also formulated for ΓQWS, the optical power confinement factor under the quarter-wave stack (QWS) condition. The ΓQWS nearly agrees with a maximum optical power confinement factor when fiber parameters are varied. For a sufficiently large core radius, expressions of ΓQWS have simplified forms and are represented in terms of the normalized core radius and fiber refractive indices. The ΓQWS is inversely proportional to the third power of the normalized core radius and to the normalized core radius, respectively, for the TE mode and for the TM and hybrid modes. The TE01 mode exhibits the highest optical power confinement factor among all the modes, as in the case of the circular metallic waveguide. The optimum value of the cladding lower index, for which the ΓQWS is maximized, is explicitly represented as a function of indices of the core and cladding higher-index layer.