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Jianjun Liu

Publications and source records attributed to Jianjun Liu.

44 records · Page 3Linked to original sources
arXiv2021

Coupled cavity-waveguide system based on topological corner state and edge state

Topological corner state (TCS) and topological edge state (TES) have provided new approaches to control the propagation of light. The construction of topological coupled cavity-waveguide system (TCCWS) based on TCS and TES is worth looking forward to, due to its research prospects in realizing high-performance micro-nano integrated photonic devices. In this Letter, TCCWS is proposed in two-dimensional (2D) photonic crystal (PC), which possesses strong optical localization, high quality factor and excellent robustness compared with the conventional coupled cavity-waveguide system (CCCWS). This work will provide the possibility to design high-performance logic gates, lasers, filters and other micro-nano integrated photonics devices and expand their applications.

physics.optics↗
arXiv2020

Near-zero-sidelobe optical subwavelength asymmetric focusing lens with dual-layer metasurfaces

The existing metasurfaces with ultrathin volume for asymmetric transmission were often constructed by metal with low efficiency in optical frequency, and could not realize the optical asymmetric transmission and focusing simultaneously. Although the acoustic asymmetric focusing in asymmetric focusing lens (AFL) was realized, the obtained focal point was accompanied by large sidelobe. To solve those problems, an AFL with dual-layer metasurfaces designed by using dielectric materials can realize optical asymmetric transmission and focusing simultaneously in this paper. Furtherly, through optimizing the design theory of AFL, the near-zero-sidelobe (NZS) focusing can be realized on the subwavelength scale. The NZS asymmetric focusing of the optimized AFL is effective in broadband, which is expected to possess tremendous potential in the optical micro-nano processing, quantum communication, optical micromanipulation, etc.

physics.optics↗
arXiv2019

Frequency tunable topological edge states of two-dimensional honeycomb lattice photonic crystals

In this paper, the photonic quantum spin Hall effect (PQSHE) is realized in dielectric two-dimensional (2D) honeycomb lattice photonic crystal (PC) by stretching and shrinking the honeycomb unit cell. Combining two honeycomb lattice PCs with a common photonic band gap (PBG) but different band topologies can generate a topologically protected edge state at the combined junction. The topological edge states and their unidirectional transmission as the scatterers with triangular, pentagonal, and heptagonal shapes are researched. Meanwhile, the unidirectional transmission in an inverted Ω-shaped waveguide with large bending angle is realized, and verifies the characteristics of the topological protection by adding different kind of defects. Moreover, the frequency varies significantly when changing the scatterers shape, which shows that the PC with various scatterers shape can tune the frequency range of the topological edge state significantly. In other words, it can adjust the frequency of unidirectional transmission and increase the adjustability of the topological edge state.

physics.optics↗
arXiv2019

Non-Hermitian two-dimensional photonic crystal flat lens

In this paper, a non-Hermitian two-dimensional photonic crystal flat lens is proposed. The negative refraction of the second band of photonic crystal is utilized to realize super-resolution imaging of the point source. Based on the principles of non-Hermitian systems, a negative imaginary part is introduced into the imaging frequency, in which case the imaging intensity and resolution are improved. The results indicate that the non-Hermitian system provides a new method to improve the imaging performance of the photonic crystal lens.

physics.optics↗
arXiv2018

Invariant Cantor manifolds of quasi-periodic solutions for the derivative nonlinear Schrodinger equation

This paper is concerned with the derivative nonlinear Schrodinger equation with periodic boundary conditions $$\mathbf{i}u_t+u_{xx}+\mathbf{i}\Big(f(x,u,\bar{u})\Big)_x=0,\quad x\in\mathbb{T}:=\mathbb{R}/2π\mathbb{Z},$$ where $f$ is an analytic function of the form $$f(x,u,\bar{u})=μ|u|^2u+f_{\geq4}(x,u,\bar{u}),\quad 0\neqμ\in\mathbb{R},$$ and $f_{\geq4}(x,u,\bar{u})$ denotes terms of order at least four in $u,\bar{u}$. We show the above equation possesses Cantor families of smooth quasi-periodic solutions of small amplitude. The proof is based on an infinite dimensional KAM theorem for unbounded perturbation vector fields.

math.DS↗
arXiv2007

A Low-Temperature Specific Heat Study of the Giant Dielectric Constant Materials

Low-temperature specific-heat study has been performed on the insulating giant dielectric constant material CaCu3Ti4O12 and two related compounds, Bi2/3Cu3Ti4O12 and La0.5Na0.5Cu3Ti4O12, from 0.6 to 10 K. From analyzing the specific heat data at very low-temperature range, 0.6 to 1.5 K, and moderately low-temperature range, 1.5 to 5 K, in addition to the expected Debye terms, we noticed significant contributions originated from the linear and Einstein terms, which we attributed as the manifestation of low-lying elementary excitations due to lattice vibrations occurred at the grain boundaries and induced by local defects. Together with the findings on electronic and mechanical properties, a phenomenological model is proposed to explain the high dielectric constant behaviors at both low and high frequency regions.

cond-mat.mtrl-sci↗