Japanese researchers at NTT's Basic Research Laboratory in Kanagawa claim to have come up with a simple and cost effective method to fabricate photonic-crystal lasers. The researchers say that their direct nanoprinting approach not only saves time but could slash production costs by a factor of 100.

Photonic crystals are conventionally fabricated by electron beam lithography, an expensive and time-consuming technique. In comparison, NTT's direct nanoprinting technique involves simply pressing a patterned silicon carbide (SiC) mould into an organic thin-film layer. The resulting microstructural organic layer forms the basis of a photonic-crystal laser.

In the first step of the production process, a nickel mask is used to fabricate the SiC mould. "The pattern is transferred to the SiC substrate using a dry etching process," NTT researcher Atsushi Yokoo told Optics.org.

This leaves circular protrusions on the mould. The pitch, which can be varied between 60 and 500 nm, dictates both the height and diameter of the protrusions. By changing the pitch, Yokoo and colleagues can alter the emission wavelength of the laser.

Yokoo says that the height of the protrusions can range from 200 to 1000 nm whilst the diameter can be 40 to 80% of the pitch. Pressing the mould into an organic thin-film layer transfers the pattern. "It takes less than one minute to transfer the pattern," he said.

A pitch of 400 nm yields a laser with an emission wavelength of around 600 nm. To stimulate lasing, the researchers optically pump the photonic crystal with light from a nitrogen laser operating at 337 nm.

The researchers have also fabricated photonic crystals by pressing the mould into aluminium.

"The next stage is to fabricate other functional photonic-crystal devices using the direct nanoprinting approach," said Yokoo. "Organic materials can provide many functions such as nonlinear optics and electron transfer."