Crystal Finds a Home in Lasers

Michael D. Wheeler

Researchers at the University of Würzburg have employed a two-dimensional photonic crystal as a mirror in a ridge waveguide laser, an advance that they say could usher in the development of on-chip lasers for integrated optical circuits.

Researchers have replaced one mirror of asemiconductor ridge waveguide laser with a photonic crystal, seen here in a scanning electron microscope image. The technique may enable the development of other optoelectronic devices based on photoniccrystals. Courtesy of Jürgen Moosburger.

Since the late 1980s, a growing circle of scientists have become enamored with photonic crystals. These periodic structures are unique in that they prevent the propagation of light at particular wavelengths, enabling them to control light to a degree far greater than conventional optics.

To fabricate their photonic crystal mirror at one end of a laser ridge, the researchers used Cl₂-Ar plasma etching to transfer holes from a mask into the semiconductor material. The Al₂O₃ mask was produced through the wet chemical oxidation of a 60-nm-thick layer of AlAs in the cladding of the laser, and the holes were first defined in the mask with electron-beam lithography through another resist.

The InGaAs/AlGaAs laser demonstrates a higher efficiency than conventional semiconductor lasers with cleaved facets for mirrors. The researchers are planning further investigations with the technique.

"The next step is to combine such lasers with photonic crystal waveguides," said Jürgen Moosburger, who reported the results of the tests with his team in the May 5 IEEE Photonics Technology Letters. He suggested that photonic crystal filters and completely integrated optical systems could be developed.