14.3.3 Photonic Band Gaps
Full 2D PBGs exist in the black finger-shaped regions in Figure 14.3. Some of
these extend into the region <k, where light is free to propagate in vacuum,
confirming the feasibility of trapping light within a hollow core.
14.4 CHARACTERISTICS OF GUIDANCE
In single-mode fiber (SMF), guided modes form within the range of axial
refractive indices n
cl
< n
z
< n
co
, when light is evanescent in the cladding
(n
z
= /k; core a nd cladding indices are n
co
and n
cl
). In PCF, three distinct
guidance mechanisms exist: a modified form of TIR [14, 15], PBG guidance
[11, 16], and a leaky mechanism based on a low density of photonic states in the
cladding [17]. In the following subsections, we explore the role of resonance and
antiresonance, and ...