  We present two novel hybrid photonic structures made of silica that possess
two well-separated frequency bandgaps. The addition of interstitial air holes
in a precise location and size allows these bandgaps to open up with a ratio of
${\sim3}$ between their central frequencies at the air line ${ck_z/w=1}$, thus
fulfilling the basic guidance condition for third harmonic generation in
hollow-core fibers. In addition, these designs may serve as high-power laser
delivery of two well-separated wavelengths, such as visible and near infrared.
