Single-mode all-silica photonic bandgap fiber with 20-microm mode-field diameter.

An all-silica photonic bandgap fiber with a cladding index difference of approximately 2 % and diameter-to-pitch ratio (d/wedge) of 0.12 was fabricated and studied. To our knowledge, this is the first report on the properties of photonic bandgap fiber with such a small d/wedge. The fiber is single-mode in the fundamental bandgap. The mode field diameter in the 1000-1200 nm wavelength range is 19-20 microm. The minimum loss in the same range is 20 dB/km for a 30-cm bending diameter. In our opinion, all-silica photonic bandgap fiber can serve as a potential candidate for achieving single-mode propagation with a large mode area.