Parts located around the center of the 3D photonic crystal are defective resonators that do not have a cyclical structure, and three layers of quantum dots composed of InAs (indium arsenide) are embedded in each part.

The research group confirmed that, when a laser light for excitation is directed at those parts, only the light with a wavelength of 1.2μm is confined. The Q value was about 40,000, and the half bandwidth was 0.031nm. The confinement time was several tens of picoseconds. Arakawa said that the Q value is higher than the Q values of any other 3D-structured photonic crystals.

When the laser light for excitation was further intensified, the photonic crystal caused laser oscillation with a wavelength of 1.2μm.

Theoretically higher performance than 2D photonic crystals

A Q-value of higher than one million has already been reported for a 2D photonic crystal. But 2D photonic crystals can completely confine only the transverse electric (TE) polarized wave of light, and only total reflection can be used for the transverse magnetic (TM) polarized wave, Arakawa said.

On the other than, with 3D photonic crystals, it is theoretically possible to confine every mode of light, enabling to achieve a confinement capability much higher than that of 2D photonic crystals, such as a Q vale of 10 million.

"The new photonic crystal is expected to be applied to, for example, 3D-structured waveguides," Arakawa said. "It might be possible to realize laser oscillation using current excitation if the assembly accuracy is improved. But, in reality, it will not be anytime soon."