Dual-bandgap hollow-core photonic crystal fibers for third harmonic generation

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 with a ratio of ∼3 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 for high-power laser delivery of two well-separated wavelengths, such as visible and near infrared.