Photonic-crystal fibers (PCFs) with high numerical aperture (NA) and small mode-field diameter are used in many nonlinear applications such as supercontinuum generation (see www.laserfocusworld.com/articles/338737). However, suspended-core fibers (SCFs)–first reported in 2002–consist of a simpler, easier-to-fabricate design with potentially higher NA values, smaller mode-field diameters, and shorter zero-dispersion wavelengths. Building on earlier lead-silicate SCF designs, researchers at IMRA America (Ann Arbor, MI) have now developed small-core, low-loss SCFs from silica that provide a pathway towards compact, all-fiber nonlinear devices.
Analysis of SCF designs, fabricated by stacking six silica capillaries around a silica core and expanding the air holes while drawing, showed that confinement losses could be reduced by increasing the air-cladding dimension. With a core diameter of only 1.27 µm, measured loss at 1550 nm was only 0.078 dB/m–a record for such a small core diameter. A 1.3 m length of a similar SCF with an oval core of 2.3 x 2.8 µm and only a 0.25 dB splice loss to Hi1060 fiber (a specialty fiber made by Corning of Corning, NY) generated a supercontinuum from 1300 to 1600 nm using an ytterbium-fiber laser (1045 nm, 350 fs at 200 kHz repetition rate) at a peak power of only 2 kW, eliminating the need for amplification in frequency-stabilized ytterbium-fiber oscillators using a self-reference scheme. Contact Liang Dong at [email protected].