Source: School of Physics
Written by: School of Physics
Edited by: Wang Dongmei

A research team led by Prof. Jianwen Dong, in School of Physics/State Key Laboratory of Optoelectronic Materials and Technologies, Sun Yat-sen University, proposed a second-order topological photonic crystal slab and realized the microwave near-field measurement of topologically protected corner state. This work titled with "Direct observation of corner states in the second-order topological photonic crystal slabs", has been published online June 14th, 2019 in the journal Physical Review Letters.
Photonic crystal slab is an important platform to realize new kinds of light manipulation such as negative refraction, slow light and lasing. The requirement of high depth-diameter ratio increases the difficulty of fabricating photonic crystal samples. The TE-like and TM-like mode crosstalk problems in the structure also bring difficulties to the experimental measurement.

Inspired by the phenomenon of lake reflection, the research team designed a new kind of photonic crystal slab with perfect electric conductor as the substrate. The introduction of the perfect electric conductor can not only decrease the difficulty of the experimental sample fabrication by doubling the equivalent height of dielectric rods, but also inhibit TE-like mode to eliminate crosstalk effects on experimental measurement. This design ably overcomes the above problems.

Based on this new photonic crystal slab structure, the team experimentally demonstrated the zero-dimensional corner state. The zero-dimensional corner state is an eigen-mode supported by the corner formed between second-order topological photonic crystals and topologically trivial photonic crystals. Because of the experimental difficulty, the zero-dimensional corner state constructed from one-dimensional edge states with dipolar polarization has not been experimentally demonstrated yet. The team used a high-precision microwave near-field scanning platform to directly image the zero-dimensional corner state. The experimental results are highly consistent with the numerical simulation results, providing strong experimental evidence. The zero-dimensional corner state provides a new design idea for novel light manipulation, such as high-Q cavity mode, and has potential application in optical nonlinear effects enhancement, on-chip laser light source and optical sensing.

The work was completed independently by the team of Prof. Jianwen Dong. The first author is associate professor Xiaodong Chen, and doctoral student Weimin Deng and Fulong Shi are co-first authors. This work is supported by Cheung Kong Young Scholarship, NSFC Excellent Young Scientists, Natural Science Foundation of Guangdong Province, Science and Technology Program of Guangzhou, State Key Laboratory of Optoelectronic Materials and Technologies and School of Physics.

Paper link: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.233902