Hybrid waveguide tightly confines light, has long-range transmission

A hybrid optical-plasmonic waveguide developed by researchers at the University of California, Berkeley, confines 1550 nm light to dimensions far below a wavelength in two dimensions (λ2/40 to λ2/400) while allowing it to transmit over distances (40 to 150 µm) far larger than can be transmitted by a purely plasmonic waveguide—at least in theory, anyway. A cylindrical high-permittivity dielectric waveguide surrounded by a low-permittivity dielectric is placed parallel to and a short distance away from a metallic plane. If the dimensions are right, the waveguide and plasmonic modes couple, enabling a “capacitor-like” storage of energy.

For a 200-nm-diameter waveguide of gallium arsenide (permittivity of 12.25), a surrounding dielectric of silicon dioxide (permittivity of 2.25), and a plane of silver (permittivity of –129 + 3.3i), the optimum gap between waveguide and plane was around 100 nm. While the results are so far only theoretical, the researchers believe the simultaneous high confinement and long-range transmission of this new geometry could allow fabrication of subwavelength devices such as nanolasers, as well as provide a new approach to designing optical integrated circuits. Contact Xiang Zhang at [email protected].