Optical super-resonance in a customized P T-symmetric system of hybrid interaction.

We investigate the optical resonances in coupled meta-atoms with hybrid interaction pathways. One interaction pathway is the directly near-field coupling between the two meta-atoms. The other interaction pathway is via the continuum in a waveguide functioned as a common bus connecting them. We show that by properly introducing gain or loss into the meta-atoms, the hybrid optical system becomes parity-time (P T) symmetric, in which the effective coupling rate can be customized by manipulating the length of the waveguide. At the exact phase of the customized P T symmetry, the coupled meta-atoms support discrete super-resonant modes that can be observed from the transmission spectra as extremely sharp peaks. At an exception point where the eigenmodes coalesce, albeit the transmission curve is flat, a high-Q factor of the localized field in the meta-atoms can be obtained. Similarities of the super-resonance with the bound states in the continuum (BICs) are discussed. This investigation promotes our understanding about the ways in realizing high-Q optical resonance especially by manipulating the distributions of loss and gain via the concepts of P T and BICs. Many attractive applications are expected.

Kerr-nonlinearity induced bistable-like parity-time phase transition in coupled waveguides.

We analyze the parity-time (PT) symmetric phase in coupled two waveguides with a Kerr-type medium in between. Paying attention to the emitted field from a dipole source inside, we show that when the strength of the dipole increases, the optical Kerr effect can render a phase transition from the exact PT phase to the broken PT phase. Furthermore, a salient phenomenon of bistable-like PT phase is observed, in which the emitted field possesses a paradox between the two kinds of PT phases. We show that the physical mechanism of this bistable-like phenomenon is a globally inhomogeneous PT phase, in which different spatial regions of the whole structure can possess different PT phases (broken or exact). This study highlights the potential to manipulate the PT phase transition by using optical nonlinearity for many interesting applications.

Hybrid parity-time modulation phase and geometric phase in metasurfaces.

We analyze the similarity between the geometric phase and the phase from parity-time symmetric modulation and argue that they can be integrated together in nanostructures. We provide a simple hybrid metasurface design to demonstrate the simultaneous utilization of these phases in manipulating the diffraction of optical field. Polarization-sensitivity of the hybrid phase is also discussed. This study provides a more advanced method of achieving polarization-dependent optical manipulation in artificial nanostructures.

Nonreciprocal parity-time phase in magnetized waveguides.

In a single magneto-optical (MO) waveguide, the dispersion of guided bulk wave is reciprocal in the Voigt configuration. Here we show that the parity-time (P T) phase in two coupled MO waveguides can be nonreciprocal if the waveguides are properly biased. The nonreciprocal P T phase is closely related to the asymmetric field profile induced by the MO effect that modifies the coupling strength between adjacent waveguides. We show that it is feasible to switch between broken and conserved P T phases by simply reversing the magnetic bias or the propagating direction of wave. Theoretical analysis and numerical calculation prove our theory. This investigation highlights a flexible method in manipulating the field dynamics of waveguide arrays by using the novel properties of P T phase especially the exceptional points.

[Geographical variation and the response to hydrothermal factor of stable carbon isotope (δ13C) in Pinus massoniana.] / é©¬å°¾æ¾ç¨³å®šç¢³åŒä½ç´ (δ13C)çš„åœ°ç†å˜å¼‚åŠå ¶å¯¹æ°´çƒ­å› å­çš„å“åº”.

We used 10 representative provenances at different latitudes in two 33-year-old Pinus massoniana provenance test stands (Chun'an Laoshan in Zhejiang and Taizi Mountain Shilong in Hubei) to measure the differences among provenances, study the geographical variation, and identify its responses to hydrothermal factors. The results showed that the δ13C of the average annual rings was significantly different among the provenances of P. massoniana, being higher in trees from high latitude than from low latitude. The δ13C of average annual rings showed a zonal variation trend, indicating an adaptation to the original environment. The δ13C of annual rings was negatively correlated with mean annual temperature (MAT), mean temperature in January (T1), annual precipitation (MAP), precipitation from May to September (P5-9) and cumulative temperature above 10 ℃ (CT). It was positively correlated with the aridity index (AI). The response function of AI toδδ13C annual rings in Chun'an and Taizi Mountain explained 37.5% and 42.5% of the variation, respectively, indicating that AI was the most important limiting factor. The Taizi Mountain test site in Hubei Province located in the central and western region with relatively dry soil and high aridity. Therefore, the δ13C of the average annual ring was 1.8% higher than that in the Chun'an test site. The δ13C rings of P. massoniana at the Taizi Mountain and Chun'an were sensitive to the temperature in July and August, respectively. Summer precipitation was the main factor for carbon isotope fractionation with stable rings. The sensitivity of different provenances to future climate changes was different.