Leakage and bend losses in solid-core Bragg fibers

An analytical approach describing the modes of solid-core Bragg fibers is presented. Our method does not assume the periodic structure of a fiber cladding; therefore, it is applicable to a wide class of solid-core Bragg fibers, including bent ones. To check derived formulas, six Bragg fibers with a core diameter from 8.4 to 42 mu m and a number of cladding rings from 5 to 15 were fabricated. The measured loss spectra of the straight and bent Bragg fibers agree well with theoretical ones. Based on these results, we show that bending affects leakage losses by two mechanisms: decreasing the reflection of light from interfaces and destroying the constructive interference of reflected waves in the cladding. The role of these mechanisms at low and large (near critical) fiber curvature is discussed.