2020-11-12

Scientists first discovered spatial optical solitons regulated by Mohr angle

By yqqlm yqqlm

Professor Ye Fangwei from the School of Physics and Astronomy of Shanghai Jiaotong University published a new study, which was the first internationally to combine Mohr The research of lattice has been advanced to the category of nonlinear optics, and the spatial optical soliton under the adjustment of the Moiré angle is discovered. Related research results were recently published in”Nature-Photonics”.

Optical soliton refers to a beam of light or a light pulse whose wave shape remains unchanged during the evolution process by balancing the spreading effect of light with nonlinear effects. Optical soliton has particle properties and has important application value in carrying light information and realizing light control. The research of optical soliton has always been closely linked with material development and structural design. With the help of energy band design, people can control the intensity of diffraction and dispersion, thereby reducing the threshold power for forming optical soliton, but even so, the threshold power is still at a high level.

Ye Fangwei’s research group discovered for the first time spatial optical solitons in quasi-periodic lattices such as Moiré lattices. The researchers found that at most of the moiré angle (at this time the moiré lattice presents an”irreducible” phase), the threshold power required to excite the spatial optical soliton in the moiré lattice is almost zero. Therefore, the Moiré lattice provides a unique platform for the excitation of optical soliton under extremely low power conditions, and breaks the limitation on power conditions for the practical application of optical soliton.

Ye Fangwei said that due to the experimental conditions of the research group, in this study, the moiré lattice is”written” on a photorefractive material called barium strontium niobate. It has a high non-linear effect, so the power requirement to excite the soliton is inherently low. However, the existence of ultra-low power threshold optical soliton in the moiré lattice is not due to the high nonlinear effect of the material itself, but the existence of a large number of flat bands in the moiré lattice. Therefore, if the Moiré lattice is”written” into other nonlinear materials, it will not affect the existence of very low power solitons.

At the same time, the moiré lattice produced by the research team in the experiment has highly adjustable characteristics. When the Moiré angle is continuously adjusted, the corresponding moiré lattice undergoes a continuous”phase change” from a quasi-periodic lattice to a periodic lattice, which makes it possible to directly compare the light in the periodic and quasi-periodic systems on the same platform. Soli. The researchers found that for a moiré lattice composed of two square lattices, these special angles are actually Pythagorean angles, while the corresponding moiré lattice returns to a periodic lattice (“reducible” phase). The curvature of the band structure reaches the maximum, so the threshold power required to form the soliton also reaches the maximum. Further research found that the power threshold of the soliton decreases sharply with the increase of the Pythagorean angle (or the generalized Pythagorean angle), which means that the moiré lattice under the high-order Pythagorean angle also supports the light under very low power conditions. Soli. (Reporter Huang Xin)

Source:”China Science News”