Compared to horizontally emitting lasers, vertically emitting devices—where light is emitted from an upper surface rather than side wall facets—offer significant advantages for technological applications including the easier collection of emitted light and a much smaller area per laser compared to laser structures that emit in the horizontal plane.

A recent implementation of surface–emitting lasers relies on the optical properties of photonic crystals to enable oscillation of light within the structure and to guide this laser light to the surface of the device. A technologically important advantage of PCSEL (photonic-crystal surface-emitting lasers) is that they emit broad–area laser beams with perfect optical properties. However, such PCSEL have been realised only for wavelengths in the near–infrared region.

Here, Hideki Matsubara and colleagues at Kyoto University, Kyoto, Japan report on PCSEL structures that emit light in the blue–violet wavelength region1. Their devices incorporate an InGaN active layer that converts electrical current into blue laser light. In order to extract the light in the vertical direction, a photonic crystal layer—consisting of a regular array of holes—is embedded within the structure close to the InGaN layer.

A fundamental obstacle to this development was producing holes within a structure that eventually required the deposition of more layers on top of it. This problem solved by using the unique property of GaN-based materials to grow much faster horizontally than vertically. Therefore, holes small enough will be ‘roofed’ quickly without being filled up by other materials.

Fig 1: Blue laser emission from a PCSEL. (a) Close-up of the laser emission in the near field. The rectangular square is 100 x 100 µm, and represents the electrode used to contact the device. (b) The laser pattern at larger distances assumes an intentionally designed doughnut shape with the very small divergence angle of less than one degree. Such a beam can be focused to diameters much smaller than the wavelength, but could also be used as an ‘optical tweezer’ to manipulate and guide small particles.

The successful demonstration of this PCSEL at the blue-violet wavelength of about 406 nm (Fig. 1) is an important advance. In fact, vertical lasing at such short wavelengths with such efficiencies has not been demonstrated for any prior design.

“This achievement will have a very high impact on a variety of research fields ranging from information storage and processing to biology,” says Susumu Noda, leader of the team.

Indeed, the flexibility in the design of the photonic crystal structure offers the means to achieve efficient and powerful laser emission with unprecedented control over its beam parameters (Fig. 1b).