PC-SEL emits blue-violet for first time

17 Jan 2008

A short wavelength surface-emitting laser could help Japanese researchers to develop next-generation information storage devices.

Far-field beam pattern

Researchers in Japan have for the first time produced a photonic crystal surface-emitting laser (PC-SEL) that emits in the blue-violet wavelength range. They claim that their innovative fabrication method is an important step in the development of laser sources that can be focused to a spot much less than the emitted wavelength. (Science Express 10.1126/science.1150413)

"We have succeeded in developing a new method in the GaN system resulting in a current-driven PC-SEL that emits at a peak wavelength of 406.5 nm," Susumu Noda, a researcher from Kyoto University, told optics.org. "PC-SELs operating at blue-violet wavelengths could find uses in a variety of new areas including next-generation information storage and micro- to nano-operation in biological or medical fields."

Noda's team

Noda believes that thanks to the large-area, coherent oscillation produced by PC-SELs, very high-power blue-violet lasers could be achieved. "Over 10 W could be produced while maintaining a single longitudinal and lateral mode," commented Noda. "What's more, PC-SELs could also be used as super-high-resolution light sources that can be focused to a spot much smaller than blue-violet wavelengths. This could be applied to next-generation DVDs."

Until now, no fabrication techniques could form high-quality photonic crystals in the GaN system. The key to the team's success was the development of the air-hole retained over-growth (AROG) method which relies on the unique characteristics of GaN growth.

"GaN growth proceeds much faster in the lateral direction than vertical growth on the crystal plane," explained Noda. ""We integrated air holes within a layer of GaN situated just beneath an active layer of InGaN. We used a combination of nanopatterning and growth techniques to create a 2D GaN/air photonic crystal. The structure exhibits a photonic crystal band-edge effect sufficient for operating a current-injection surface-emitting laser."

The laser currently operates with a large threshold current, however the team believes that the performance could be improved significantly by optimizing the design. "We can improve the crystalline quality of the active layer, optimize growth conditions and semiconductor design," concluded Noda.