Novel Low-Loss Bandgaps in All-Silica Bragg Fibers

We demonstrate that higher order bandgaps in all-silica Bragg fibers can have modes with four orders of magnitude lower confinement loss than those using the fundamental bandgap. A scheme for exploiting the higher order gaps for any specific wavelength via a global scaling of the fiber geometry is proposed. This approach provides lower losses than by reducing the confinement loss of the fundamental gap by scaling the core. Using a variety of modeling techniques, we have examined the band structure and guidance of idealized air-core all-silica Bragg fibers. It is demonstrated that the higher order, low loss, bandgaps analyzed here are uniquely accessible to single-material Bragg fibers, and are fundamentally different from the higher order gaps typically associated with depressed-index Bragg fibers such as the ldquoOmniguiderdquo fibers. Further analysis suggests that some of the key features of the guided modes of Bragg fibers can be understood by considering the properties of single hollow-core homogeneous dielectric waveguides (ldquoboreholesrdquo).