Confinement loss, including cladding material loss effects, in Bragg fibers

Abstract

Confinement loss (CL), including cladding material losses, is comprehensively evaluated for TE, TM, and hybrid modes of hollow-core Bragg fibers. We show that the combined fiber loss tends to approach a loss depending only on CL Lconf for a small number N of cladding pairs, while it approaches a material loss limit value Lmat for large N. Transition point Ntr is defined by a crossing point of the asymptotes of Lconf and Lmat. Lmat and Ntr are investigated as a function of cladding material losses, cladding index contrast, and core radius rc, mainly under the quarter-wave stack condition. Lmat decreases in inverse proportion to the third and first powers of rc for TE and the other three modes for sufficiently large rc. An increase in rc more effectively reduces Lmat than an increase in the cladding index contrast. For rc=2.0, 5.0, and 10.0 μm in the TE01 mode transmission, we attain fiber losses less than about 10−2, 10−3, and 10−4 times cladding material losses, respectively.