Pu Zhang

Based on the transfer-matrix method, we theoretically explore the transmission and reflection properties of light waves in a one-dimensional defective photonic crystal composed of superconductor (HgBa₂Ca₂Cu₃O_8+δ) and semiconductor (GaAs) layers. The whole system is centrosymmetric and can generate a defect transmission peak in the photonic band gap. We study the effect of the temperature on the defect mode. Results obtained show that the defect mode shifts to the lower frequency regions as the value of the environmental temperature increases, and the resonance of the defect mode can be strengthened further as the number of periods increases. In addition, our findings reveal that the central wavelength of the defect mode increases with the increase in the environmental temperature and it presents a nearly linear relationship between the central wavelength of the defect mode and the temperature in cryogenic environments. Therefore, we can use the temperature response of the defect mode to detect the temperature. It is hoped that this study has potential applications for the development of cryogenic sensors with high sensitivity.

We theoretically investigate the tunable dual- and multi-channel filter in one-dimensional aperiodic photonic crystals (PCs) embedded with graphene. The dielectrics slabs arrayed alternately submit to the Cantor sequence rule and graphene sheets are local at the interfaces of dielectrics layers. Cantor PCs are fractal structures and support a series of discrete resonant channels in transmission spectra, viz . fractal states. Consequently, dual- and multi-filtering channels could be achieved in the compound systems. The central wavelength of each channel and its value of transmission could be modulating by the chemical potential of graphene and the incident angle as well. It shows that the dual-channel amplitude of transmission can be varied by over 100% and the multiple channels could be switched on and off by the chemical potential of graphene. This study will be very helpful in designing tunable optical filters.

In this study, we explore the anisotropic reflection of light waves around the exceptional points (EPs) in anti-parity-time−symmetric (APT−symmetric) Cantor dielectric multilayers. This one-dimensional fractal structure governed by the Cantor substitution law is modulated to satisfy APT symmetry. The Cantor multilayers are aperiodic and support optical fractal resonances. The optical fractal effect combined with APT symmetry can induce multiple exceptional points (EPs) in the parameter space by modulating the loss coefficient of materials and optical frequency. Reflection anisotropy for light waves incident from two opposite directions presents unidirectional suppression and enhancement around EPs. This study can be utilized for multiple wavelengths of photonic suppressors and reflectors.

We investigate the splitting and incorporation of optical fractal states in one-dimensional photonic quasi-crystals. The aperiodic crystals which are composed of two different dielectrics submit to Cantor sequence. Defects in Cantor crystals can greatly enhance the localization of electric field, which induces the optical fractal effect. The number of optical fractal states increases exponentially with the generation number of Cantor sequence. Moreover, the optical fractal characteristics depend on the incident angle of light, of which the fractal states may split/incorporate by modulating the value of incident angle. This study could be utilized for band-pass filters and reflectors.

We investigate the topological bound modes of surface plasmon polaritons (SPPs) in a graphene pair waveguide array. The arrays are with uniform inter-layer and intra-layer spacings but the chemical potential of two graphene in each pair are different. The topological bound modes emerge when two arrays with opposite sequences of chemical potential are interfaced, which are analogous to Jackiw-Rebbi modes with opposite mass. We show the topological bound modes can be dynamically controlled by tuning the chemical potential, and the propagation loss of topological bound modes can be remarkably reduced by decreasing the chemical potential. Thanks to the strong confinement of graphene SPPs, the modal wavelength of topological bound modes can be squeezed as small as 1/70 of incident wavelength. The study provides a promising approach to realizing robust light transport beyond diffraction limit.

We investigate the coherent perfect absorption laser points (CPA-LPs) in anti-parity–time-symmetric photonic crystals. CPA-LPs, which correspond to the poles of reflection and transmission, can be found in the parameter space composed of gain–loss factor and angular frequency. Discrete exceptional points (EPs) split as the gain–loss factor increases. The CPA-LPs sandwiched between the EPs are proved to be defective modes. The localization of light field and the bulk effect of gain/loss in materials induce a sharp change in phase of the reflection coefficient near the CPA-LPs. Consequently, a large spatial Goos–Hänchen shift, which is proportional to the slope of phase, can be achieved around the CPA-LPs. The study may find great applications in highly sensitive sensors.