Professor Hong Gyu Park's team captures transforming light in an extremely narrow space
Optical device adopts nano-cylinder structure that changes the color of light, could have quantum cryptography applications
Experimental observation of a third way to control light, results published in Science
▲ Professor Hong Gyu Park, Department of Physics, Korea University College of Science
Light has existed since the birth of the universe. Experimental evidence on new ways to control light is emerging as mankind's efforts to control light are paying off in industries and products such as optical communications, GPS, medical endoscopes, solar cells, optical sensors, and optical switches.
A research team headed by Professor Hong Gyu Park, Department of Physics, Korea University and Professor Kivishar, Australian National University, developed an optical device that can trap light in a nanocylinder structure and change the color of the light as desired. Previously, total internal reflection at the interface of an optic fiber or light reflection at a particular wavelength of a photonic crystal were the only two methods of controlling light. A third method of controlling light and changing the wavelength of light by focusing light on tiny nanostructures had been theoretically proposed, but there were no experimental results to prove it.
The team directly observed light emitted in the visible region by trapping light in the infrared region in a nanocylinder that is 100 times thinner than a strand of hair. When red light is trapped in an extremely narrow space, it reinforces the nonlinearity of the emitted blue light. The possibility of converting the incident light into light of various colors (wavelengths) was confirmed through experiments. Experimental observation was made possible by optimizing the structure and size of the nanocylinder and forcing the incident light into a donut shape so that the wavelength conversion appeared clearly. Even with the introduction of weak incident light, the nanocylinder is designed to interact with the compound semiconductor (AlGaAs) that forms the nanocylinder and to increase the wavelength conversion efficiency of the light.
As a result, the wavelength conversion efficiency of light can be increased more than 100 times compared to existing nanostructures. As the optical device and laser operate in the same way in terms of confining light in a small space, the research team plans to carry out nanolaser research using nano-cylinder structures in the future.
The results of this global joint research are expected to be very important in the future because of their potential as quantum cryptography applications through the ability to change the color of even grains of light. The results, supported by the Basic Research Support Program (Research Leader), a research project led by the Ministry of Science and ICT and the National Research Foundation of Korea, were published on January 17 in the international journal, Science.
* Paper title: Subwavelength dielectric resonators for nonlinear nanophotonics
* Corresponding authors: Professor Hong Gyu Park (Korea University), Professor Kivshar (Australian National University)
Professor Park said, "It was difficult to fabricate large numbers of nanocylinder structures on ITO substrates. In order to observe the BIC phenomena, a very accurate size of the nanocylinder structure must be used. Considering the experimental error, many samples had to be made before experimentation. The team made samples by making 300 nanocylinders of slightly different sizes, tearing them off and moving them onto an ITO substrate.” He said it was the first time such a large number of nanostructures had been fabricated, but he added that his team was able to make samples successfully by tearing off graphene monolayers with transparent tape.
(Figure 1) Generation mechanism of a second harmonic wave
The process of transforming azimuthally polarized light at 1,570 nm wavelength (marked as w, in red) incident on a nanocylinder (cylindrical part in gold) with a diameter of about 1 micrometer in the center into a second harmonic wave at 785 nm (marked as 2w, in blue)
(Figure 2) Second harmonic wave measurement result
The graph shows the intensity of a second harmonic wave measured according to incident wavelength and diameter of the nanocylinder structure