Japanese Researchers Realize Laser With 3D Photonic Crystals
A Japanese research group announced that it has succeeded in laser oscillation by using a resonator based on 3D-structured photonic crystals.
The research group is led by Yasuhiko Arakawa, professor at the University of Tokyo. The details of the research was published on the Dec 12 edition of the online version of the Nature Photonics magazine.
Photonic crystals are artificial structures that can be described as photic semiconductors. While normal semiconductors consist of an array of atoms measuring about 10nm and electrons flowing on them, photonic crystals consist of artificial cyclical structures arranged at an interval of several hundred nanometers and light. What corresponds to semiconductor bandgap is called "photonic bandgap (PBG)."
Thus far, 2D-structured photonic crystals have mainly been researched. But, this time, the research group made a 3D-structured photonic crystal and confirmed that it confines laser light and brings about laser oscillation.
New photonic crystal made like plastic model
The new 3D-structured photonic crystal is made like a plastic model, Arakawa said. Parts of plastic models are cut off from a frame called "runner," and the 3D-structured photonic crystal is made by stacking 2D-structured parts separated from a runner.
The new photonic crystal is different from normal plastic models in that the parts of the photonic crystal are as small as 10 x 10μm and 150nm thick. By using an electron microscope, 25 parts are manually stacked (micro manipulation).
Because it requires high artisan skills, only one crystal can be made per day. And it can be made only by some members of the research group, Arakawa said. The current margin of error in position adjustment is 50nm.
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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."