Lasers usually require mirrors at each end of the laser cavity, but this is not possible for some material systems. Now, a group of US scientists has developed a silicon-based waveguide that can act as a mirrorless laser. Galen Stucky of the University of California at Santa Barbara and colleagues found that by patterning waveguides onto a soft-gel situated on a silicon wafer, they could amplify light pumped into the waveguide. The technique could have potential for making integrated optical circuits (Science 287 465).
The waveguide structure was created by pouring a mixture of copolymer solution and molecular laser dye into a mould situated on top of a silicon wafer. The solution was allowed to solidify over 12 hours. The mold was imprinted with a set of thin lines by a soft lithography stamp. The sol-gel copolymer used by the group is suitable for waveguide applications because its refractive index is lower than that of standard silicon wafers. The mould was then peeled off leaving the waveguide pattern on top of the wafer. The waveguide was pumped with laser radiation and a charge-coupled device (CCD) camera was used to record the output.
Stucky believes that parts of their technique could be used commercially within a year or two, but it will take longer to develop the lasing waveguides. “The first application for these lasing waveguides will be in lab-on-chip applications for microanalysis or sensing purposes,” he says.
