Hole-assisted lightguide fiber for large anomalous dispersion and low optical loss

Hole-assisted lightguide fiber (HALF) is a microstructured fiber comprising a material index profile for waveguiding and air holes for modifying optical properties. Anomalous dispersion larger than those of the conventional fibers can be realized without severe degradation in optical loss, because of low power fraction in the holes and structural simplicity. We investigate into the causes of the loss of the fabricated HALFs, and show that a GeO2-doped core, in addition to the low power fraction, is desirable for low loss. The fabricated HALF exhibits a loss as low as 0.41 dB/km and a large anomalous dispersion of +35 ps/nm/km at 1550 nm.