one degenerate mode is the average of 60- and 120-degree rotations of the other
mode. We will not go into more detail here but will simply note that the existence
of these doubly degenerate modes means that PMD and birefringence occur
when the symmetry of a PCF is broken; indeed, these effects occur much more
strongly because the index contrast is so much larger than in traditional doped-
silica fiber. Most experimental PCF work has relied on such doubly degenerate
modes, because they are the fundamental modes of the fiber. Alternatively, it
may be possible to employ a higher order nondegenerate operating mode analo-
gous to the TE
01
mode of Bragg fibers or metal waveguides.
10.3 APPLICATIONS OF HOLLOW-CORE FIBERS
10.3.1 Hollow-Core Fibers for Medical ...