About the author
Jon Cartwright is a reporter for physicsworld.com
Jon Cartwright is a reporter for physicsworld.com
----------------
A photonic crystal contains regularly alternating regions with high and low refractive indices. This structure creates a “photonic bandgap”, holding back light of certain frequencies while letting light of other frequencies through.
An offshoot of this property is that photonic crystals can confine light to travel along predetermined paths inside waveguides. Such waveguides could be used to process optical signals in telecommunications, or to serve as small laser cavities that only require a low power to start lasing. Unfortunately, nearly all waveguides made so far have been 2D, and until now no-one has come up with a method that can create 3D waveguides at any place within a photonic crystal and with any dimensions so that useful devices can be created.
Scanning-electron-microscope image of a 3D photonic-crystal feature, created by Braun’s group. (Credit: S. Rinne et al.)
Marking out
Paul Braun and colleagues at the University of Illinois at Urbana Champaign have pioneered a flexible process for a fabricating 3D photonic-crystal waveguide by using a focused laser to mark it out (Nature Photonics advance online publication).
The researchers begin by crystallizing a colloid of silica spheres either 725 or 925 nm in diameter onto a substrate to create a structure similar to an opal — a well known natural photonic crystal comprising high-refractive-index silicon interspersed with pockets of low-refractive-index air. To this structure they then add a monomer solution, and sweep the focal point of the focused laser beam over the desired waveguide region to make the monomers bond together to form a polymer. With this region now cordoned off, the researchers fill the rest of the structure with silicon and etch away the original silica spheres with acid. (See figure: Method.)
The researchers begin by crystallizing a colloid of silica spheres either 725 or 925 nm in diameter onto a substrate to create a structure similar to an opal — a well known natural photonic crystal comprising high-refractive-index silicon interspersed with pockets of low-refractive-index air. To this structure they then add a monomer solution, and sweep the focal point of the focused laser beam over the desired waveguide region to make the monomers bond together to form a polymer. With this region now cordoned off, the researchers fill the rest of the structure with silicon and etch away the original silica spheres with acid. (See figure: Method.)
(a) Once the opal photonic-crystal structure has been created, (b) Braun’s group sweep the focal point of a laser over the waveguide region to polymerize a monomer solution. (c) They then fill the rest of the space in the structure with silicon, (d) finally removing the original structure using acid. (Credit: S. Rinne et al.)
沒有留言:
張貼留言