Jingping Xu

Polarization conversion of reflected electromagnetic wave from topological insulator

Based on the special electromagnetic properties of a 3D strong topological insulator (TI), we discuss, theoretically, the reflection of electromagnetic wave at the interface between a dielectric and a TI, and focus on the polarization conversion between the incident field and reflected field. Two cases, linear polarization and elliptical polarization at oblique incidence are considered. We derive the conditions required for the complete polarization conversion from incident s polarization into reflected p polarization, and vice versa. Furthermore, elliptical polarization incidence also can be modulated to linear or circular polarization after reflection, under special conditions, and the corresponding reflectivity can approach 1. All these special polarization behaviors originate from the intrinsic topological magnetoelectric coupling response in TI. This work provides promising applications of TIs on polarized devices and the polarization splitters.

Goos–Hänchen and Imbert–Fedorov shifts at the interface of ordinary dielectric and topological insulator

Using Yasumoto and Oishi’s energy flux method, we evaluated the Goos–Hanchen (GH) and Imbert–Fedorov (IF) shifts of beam incident from the ordinary dielectric upon the topological insulator (TI) with totally internal reflection. Comparing with the case of two ordinary isotropic dielectrics, it is found that the topological parameter Θ of TI can affect two shifts. More important, IF shift appears even for a linear polarized TE or TM beam and achieves the maximum with elliptical polarization, which completely originates from the TI’s intrinsic magnetoelectric coupling effect. This observation provides an optical experimental approach to determine the topological parameters Θ and provide a new way to control the GH shift and IF shift.

Quantum interference between two orthogonal transitions of an atom in one-dimensional photonic crystals

We find that the V-type three-level Zeeman atom has the complete quantum interference when it is embedded in one-dimensional photonic crystals (1D PCs) possessing the TM-polarized complete gap. To avoid the nonradiative decay related to dissipation and the decay through surface exciton, we add two phase compensators made of ideal left-handed materials on two sides of atom, and then the total structure is equivalent to a 1D PC supporting only the radiative modes. The parameter regions (epsilon, mu) leading to the TM-polarized complete gap have been sketched out, and the influence of absorption on the quantum interference is discussed.

Waveguide transport mediated by strong coupling with atoms

We investigate single photon scattering properties in one-dimensional waveguide coupled to quantum emitters chain with dipole-dipole interaction (DDI). The photon transport is extremely sensitive to the location of the evanescently coupled emitters. The analytical expressions of reflection and transmission amplitudes for the chain containing two emitters with DDI are deduced by using real-space Hamiltonian. Two cases, where the two emitters symmetrically and asymmetrically couple to the waveguide, are discussed in detail. It shows that the reflection and transmission typical spectra split into two peaks due to the DDI. The Fano minimum in the spectra can also be used to estimate the strength of the DDI. Furthermore, the DDI makes spectra strongly asymmetric and create a transmission window in the region where there was zero transmission. The scattering spectra for the chain consisting of multi-emitters are also given. Our key finding is that DDI can broaden the frequency band width for high reflection when the chain consists of many emitters.

Spectral properties and highly efficient continuous-wave laser operation in Nd-doped Sr(1-x)Y(x)F(2+x) crystals.

Spectral properties of Nd:Sr(1-x)Y(x)F(2+x) crystals were investigated. Compared with Nd:SrF2, the spectral parameters of Nd:Sr(1-x)Y(x)F(2+x) (x=0.05,0.1) were altered in a large scale. LD-pumped true CW laser has been demonstrated in the crystals. The slope efficiency up to 43.5% in 0.43% Nd:Sr0.95Y0.05F2.05 was achieved. The system is a promising candidate for highly efficient lasers.

Optical nonreciprocity of a single two-level atom in a cavity

We analyze the transmission character of a single-mode cavity containing a resonant two-level atom. Such a simple structure exhibits optical nonlinearity and spatial symmetry breaking, as well as time-reversal symmetry breaking. We perform a detailed analysis in the Purcell regime and find out that there is giant optical nonreciprocity in proper parameter space. Therefore, it is feasible to assemble such a simple atom–cavity structure to realize an acceptable optical nonreciprocal device after carefully designing.

Growth and lasing performance of a Tm,Y:CaF 2 crystal

A Tm3+ ion and Y3+ ion co-doped CaF2 crystal was grown and characterized, in which spectral and lasing performance was presented for the first time, to the best of our knowledge. Under diode end-pumping, in a continuous-wave regime, maximum output power of 453 mW was delivered under an absorption pump power of 2.5 W, corresponding to an optical-to-optical conversion efficiency of 17.9% and a slope efficiency of 21%. With a birefringent quartz plate, wavelength-tunable operation with a tunable range of more than 190 nm was realized. The results show that Tm,Y:CaF2 is a promising laser crystal operating in a spectral region ranging from 1850 nm to 2050 nm.

Enhanced displacements in reflected beams at hyperbolic metamaterials.

We examine the Goos-Hänchen (G-H) shift of a Gaussian beam reflected on a thin slab of Ag/TiO2 hyperbolic multilayer metamaterial (HMM). The HMM is modeled using the effective medium theory which yields the anisotropic dielectric functions of the HMM. The G-H shifts can be very large on the surface of the HMM. It can be about 40 µm which are far bigger than the G-H shifts on the usual materials like metals and dielectrics. The enhancement is due to the excitation of the Brewster modes in HMM. Such Brewster modes in HMM have a well-defined frequency-dependent line shape. We relate the the half width at half maximum of the G-H shift to the imaginary part of the complex frequency of the Brewster mode. Moreover, we also present results for the Imbert-Fedorov shifts as well as the spin Hall effect of light on the surface of a thin HMM slab. We show that the spin Hall effect on the HMM slab is much more pronounced than that on the surface of metal. Thus a thin HMM slab can be used to enhance the lateral displacements, which can have many interesting applications for optical devices.

High contrast all-optical diode based on direction-dependent optical bistability within asymmetric ring cavity

We propose a simple all-optical diode which is comprised of an asymmetric ring cavity containing a two-level atomic ensemble. Attributed to spatial symmetry breaking of the ring cavity, direction-dependent optical bistability is obtained in a classical bistable system. Therefore, a giant optical non-reciprocity is generated, which guarantees an all-optical diode with a high contrast up to 22 dB. Furthermore, its application as an all-optical logic AND gate is also discussed.

Normal mode splitting of transmission spectrum for Fabry-Pérot cavity containing metamaterials

Metamaterials are artificial structures that display properties beyond those available in naturally occurring materials, for instance, it can show negative permeability or negative refractive index made of ordinary materials. On the other hand, metamaterials are resonant materials in general and can be seen as the combination of the electric resonator and the magnetic resonator. Based on this background, the coupling of the cavity mode with the metamaterials in the linear region has been theoretically investigated. We find that magnetic resonators can induce normal mode splitting as the electric resonator does, and the normal mode splitting induced by the metamaterials containing both electric and magnetic resonators is larger than that by only electric resonator. When the resonant frequencies of the electric and the magnetic resonators have the opposite deviations from the cavity frequency, transmission spectrum shows a three-peak shape in which two normal mode-splitting peaks and one revived cavity mode. Of most interest is that the full width at half-maximum (FWAM) of the revived cavity mode is much narrower than that of the empty cavity under certain conditions. This provides a new way to improve the quality factor of the cavity without increasing the reflectivity of the cavity walls.