The high refractive index (2.4 to 3.0) of chalcogenide glass makes it ideal for use in 2-D photonic crystals (PCs), which more easily achieve complete bandgaps at higher index (the material also has high nonlinearity, desirable for 2-D photonic devices such as optical switches). But this very property makes it hard to couple light into chalcogenide glass PC devices. Researchers at the Centre for Ultrahigh-bandwidth Devices for Optical Systems at the University of Sydney (Sydney, Australia) are coupling 1550-nm light into such devices at a remarkable 98% efficiency using silica “nanowire” optical fibers.
A 300-nm-thick film of AMTIR-1 chalcogenide glass having a refractive index of 2.7 at 1.55 µm was fabricated by ultrafast-pulsed-laser deposition on a silicon nitride (Si3N4) membrane, which was supported by a silicon substrate that was subsequently etched away. The Si3N4 membrane was then thinned to 50 nm via reactive-ion etching. The open aperture of the resulting freestanding chalcogenide-coated film was 130 µm. A triangular PC lattice of 200-nm-radius holes spaced 550 nm apart was fabricated in the structure with a focused ion beam; a line of missing holes formed a waveguide.
To create the nanowire, a silica fiber with an 800-nm-diameter tapered section was drawn and mounted on a glass slide, with its ends spliced losslessly to ordinary fiber. The tapered fiber was forced into a curve for better coupling and brought in proximity to the PC until its modes overlapped with that of the PC, resulting in insertion efficiencies for TE0 and TE1 modes of 98% and 97%, respectively. Efficient coupling of the TE1 was especially dependent on lateral alignment of the taper to the PC. Contact Christian Grillet at [email protected].
