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The polarization conversion of electromagnetic waves plays a crucial role in practical application. Here, a tunable multi-mode dual-band high-efficiency and reflection-type polarization converter based on liquid crystal (LC) in the terahertz region is proposed. It is composed of periodic unit structures, each unit of which is constituted by the designed structure, LC mixture and fully reflected gold mirror. It numerically reveals that in the operating bandwidth 1.03–1.53 and 1.27–1.86 THz corresponding to the refractive index of LC mixtureñoandñe, the converter can convert linear-polarized and circular-polarized waves to its corresponding cross-polarizations, whose polarization conversion ratio is larger than 90%. Meanwhile, the proposed converter can realize the conversion from linear-polarized wave to circular-polarized one in dual-band, 1.10–1.25 and 1.92–2.2 THz or 0.93–1.04 and 1.57–1.88 THz corresponding toñoandñewith axis ratio lower than 3 dB. The insensibility of incident angle is analyzed as well. In addition, the physical mechanism of the polarization conversion is disclosed. The ultra-thin and compactness characteristic of this designed polarization converter are very attractive for a variety of applications in EM measurement, sensing, terahertz technology and 6G communication.

A proper excitation wavelength and strong hot-spot effect are of great importance for the application of surface-enhanced Raman spectroscopy (SERS) in the field of biochemistry. As a popular SERS substrate, noble metal nanoparticles dimer is analyzed systematically in this paper. The hot-spot effect and the resonance peak position with varying geometric parameters of metal nanoparticles are investigated. Moreover, the excitation wavelength of bimetallic structure is discussed as well. The conclusions can provide reference for the selection of metal material at different excitation wavelengths.

Here, a novel Au Wedge-enhanced Raman spectroscopy (WERS) substrate is proposed. The electric field enhancement factor and the effective mode field radius with varying geometry parameters are investigated. The proper excitation wavelength 633 nm is obtained. The practical application of WERS substrate is discussed. The Au WERS not only can provide a continuous extremely highly localized electric field as surface-enhanced Raman scattering (SERS) hotspots, but also can offer 10 orders of magnitude of SERS enhancement factor. The corresponding results reveal that WERS substrate will be widely applied in optics, biology, chemistry and other fields.

Polarization measurement has found applications in many fields ranging from quantum science to our daily life. However, traditional polarization measurement systems suffer from large volume and high cost. To keep pace with the continued device miniaturization and system integration, new detection approaches and devices are desirable. The marriage between optical metasurfaces and superposition of optical vortex beams has offered a new idea method for polarization detection. We propose and experimentally demonstrate a single metasurface for polarization measurement based on the superposition of optical vortex beams. The relationship between the three parameters of the polarization state and the interference pattern of vortex beams is deduced theoretically. The major axis, ellipticity and handedness of a polarization state are determined by analyzing the intensity patterns of the superimposed vortex beams. Our method has provided a new approach for the development of compact optical devices for polarization measurement.

An efficient surface-enhanced Raman scattering substrate based on silver nanoparticles/silicon pyramid arrays structure is theoretically investigated and experimentally demonstrated. The electric field distributions using finite-element-method are calculated. The surface-enhanced Raman scattering behaviors of sensitivity, uniformity and stability are emphatically discussed and compared by the detection of crystal violet. These theoretical and experimental results reveal that the silver nanoparticles/silicon pyramid arrays substrate is expected to be an effective surface-enhanced Raman scattering platform for label-free sensitive surfaceenhanced Raman spectroscopy detection in areas of biotechnology, medicine and food safety.

A TM-pass polarizer based on multilayer graphene polymer waveguide is proposed and theoretically analyzed. The mode properties, the extinction ratio, the insertion loss and the bandwidth are also discussed. The results show that a TM-pass polarizer, which only guides the TM mode, can be achieved by multilayer graphene polymer waveguide. With length of 150 μm, the proposed polarizer can achieve extinction ratio of 33 dB and insertion loss of 0.5 dB at optical wavelength of 1.55 μm. This device has an excellent performance, including large extinction ratio and low insertion loss within the spectral range from 1.45 μm to 1.6 μm.

The outstanding ability of optical metasurfaces to tailor light's amplitude, phase, and polarization with a subwavelength resolution has attracted big interest. A multifunctional metasurface device is reported and experimentally demonstrated that integrates an arbitrary polarization profile for image concealment and a computer‐generated hybrid hologram. Herein, a high‐resolution image is hidden in the polarization profile of the light beam, while the holographic images are encoded in its phase profile for the reconstruction of two different types of holographic images. The designed polarization profile is realized based on the superposition of two different phase profiles for circular polarization states with opposite handedness. This method can further extend the design degree of freedom in optical metasurfaces, which may open an alternative avenue for anticounterfeiting, optical image encoding, and optical information security.

The three-dimensional (3D) polarization-dependent optical property is one distinctive characteristic of the anisotropic metal nanoparticles. This has the potential applications in 3D polarization information encryption to detect the polarization information and single particle 3D orientation determination. Previous studies almost focus on the condition that the polarization orientation is in-plane. In the present paper, we systematically investigate the 3D polarization-dependent near- and far-field properties of a kind of fascinating anisotropic nanoparticle, i.e., gold nanostar (AuNS). It shows that the scattering spectra of the AuNS induced by arbitrary incident polarizations can be described as a linear superposition of a set of basic scattering spectra. And we introduce a trigonometric equation to reveal the inherent relationship between the scattering intensity and the 3D polarization orientation, which is universally independent of the size, shape, or surrounding medium of the nanostar. Furthermore, it is facile to synthesize AuNS with two pairs of orthogonal different-length arms, based on the 3D polarization dependence of the scattering trait, and using coordinate transformation, we have demonstrated that such AuNS is useful for designing single particle 3D orientation and rotational tracking sensor and orientation-unlimited polarization information detector. And the self-rotation problem of the gold nanorod, i.e., rotation around the gold nanorod’s long axis cannot be resolved, can be solved by replacing it with AuNS. In addition, the precision of the 3D polarization angles and 3D orientation angles confirmed by our method is only with subdegree uncertainty.

Polarization measurement is crucial for many optical applications in science and technology. Geometric metasurfaces have been used to develop polarization-sensitive holograms, providing a new opportunity for polarization measurement. We propose and experimentally demonstrate a hologram method to measure the polarization state of light. A reflective-type metasurface hologram is used to generate holographic images of graphene pattern. The ellipticity and helicity of the incident light are measured based on the intensities of the neighboring light spots, corresponding to two opposite circular polarization states. Benefiting from the advantages of reflective geometric metasurfaces, this device can operate in broadband.

Two prototypical transducer structures are proposed, including a single-waveguide (SW) and Mach–Zehnder interferometer (MZI), implemented with surface plasmon polariton waveguides. Formulas of the output power with structural parameters are deduced respectively. The sensitivities are found to be proportional to S1 for SW and S2 for MZI, which are dependent on waveguide parameters. Maximizing S1 or S2 maximizes the corresponding sensitivity, leading to optimized waveguide designs and preferred operating wavelengths. Sensitivity parameters S1 and S2 are calculated for fundamental modes of V grooves, triangular wedges, and dielectric-loaded surface plasmon polariton waveguides (DLSPPWs), as a function of measured material refractive index nc (nc = 1.3∼1.6, representative refractive index of biochemical matter), at wavelength λ = 1.55 μm. Finally, the sensitivity S2 is analyzed as a function of work wavelength for DLSPPWs with different ridge thickness and specific fluidic SPP waveguide for biochemical sensing is presented. The results offer foundations for application of surface plasmon polariton waveguides in biochemical sensing.

In allusion to special modes supported by surface plasmon polariton (SPP) waveguides, explicit expression for mode coupling coefficient which plays a central role in coupled mode theory is firstly redefined by adding the longitudinal electric field component. The mode coupling coefficients calculated by the proposed formula improve greatly compared with the coupled mode theory suited to conventional optical waveguides, and reasonable explanations from the point of view of physics and mathematics have been given. Afterwards, the coupling lengths, the transmission lengths, the normalized power exchanges, and the cross talk performances of adjacent parallel SPP waveguides with varying waveguide separation distances D and waveguide lengths L are investigated at telecom wavelength. The results are encouraging as they indicate that the coupled mode theory is developed in a self-consistent manner by retaining the longitudinal electric field component in the derivation and neglecting it only when the waveguides structure satisfies the weakly guiding situations. As a result, the new mode coupling coefficient formula for SPP waveguides considered in this paper is an important complement in the theory of SPP waveguides.

Optical labels are needed for probing specific target molecules in complex biological systems. As a newly emerging category of tags for molecular imaging in live cells, the Raman label attracts much attention because of the rich information obtained from targeted and untargeted molecules by detecting molecular vibrations. Here, we list three types of Raman probes based on different mechanisms: Surface Enhanced Raman Scattering (SERS) probes, bioorthogonal Raman probes, and Resonance Raman (RR) probes. We review how these Raman probes work for detecting and imaging proteins, nucleic acids, lipids, and other biomolecules in vitro, within cells, or in vivo. We also summarize recent noteworthy studies, expound on the construction of every type of Raman probe and operating principle, sum up in tables typically targeting molecules for specific binding, and provide merits, drawbacks, and future prospects for the three Raman probes.

This paper presents a numerical study of the electromagnetic wave propagation in dielectric loaded circular quadruple-ridged waveguide (CQRW) by the edge element method. The variations of the cut-off wavelength and single-mode bandwidth with the ridge dimensions for different values of dielectric constant are studied in detail. The numerical results in this paper provide an extension to the design for the ridge waveguide and are helpful in practical applications for millimeter waves.

Semi-elliptical dielectric-loaded surface plasmon-polariton waveguide (DLSPPW) is proposed. The mode effective index, field confinement, and propagation length of the fundamental mode supported by it are calculated at the telecom wavelength λ = 1.55 μm for different dimensions of a polymer ridge (with the refractive index of 1.535) placed on a gold film surface. The waveguide structure is found to exhibit 23% increase of the propagation length while showing similar confinement as compared to conventional rectangular DLSPPW when ridge thickness t w = 600 nm) and ridge width w t = 600 nm).

A new kind of V-ridge waveguide is presented in this paper. The transmission problem is solved by edge element for the first time. The field patterns of the waveguide with single, double and triple V-ridge for different values of dielectric constant have been presented. Variations of the cutoff wavelength, single-mode bandwidth with the ridge dimensions for different values of dielectric constant are investigated in detail. The results will be of practical significance in designing ridge waveguide components in microwave and millimeter wave engineering.

A new kind of multiple elliptical ridge waveguide is presented. The design data for the air-filled and dielectric-loaded double, quadruple, and sextuple elliptical ridge waveguide are presented by finite element method for the first time. Variations of the cut-off wavelength, single-mode bandwidth with the ridge dimensions for different values of dielectric constant are investigated in detail. The correctness of the numerical results is verified. The results provide an extension to the existing design data for ridge waveguide and considered helpful in practical applications. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 3082–3085, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22909

By using edge element method, the transmission characteristics of the multiple layer dielectric loaded circular ridge waveguide have been studied in this paper. Variations of the cutoff wavelength and single-mode bandwidth with the ridge dimensions for different values of dielectric constant have been investigated in detail. Further more, the field patterns of the waveguide also have been presented. It is shown that the waveguide would gain a higher single mode bandwidth as the distance of the ridges is closer.

A new kind of multiple layer dielectric loaded elliptical ridge waveguide is presented in this paper. Variations of the cutoff wavelength and single-mode bandwidth with the ridge dimensions for different values of dielectric constant have been investigated in detail by using edge element method. The field patterns of the waveguide also have been presented. The results will be of practical significance in designing ridge waveguide components in microwave and millimeter wave engineering.

A kind of asymmetric V ridge waveguide is presented. Variations of the cut-off wavelength, single-mode bandwidth with the ridge dimensions and the ridge position for different values of dielectric constant are investigated in detail. The field patterns of the dominant are presented. The correctness of the numerical results is verified. The results provide an extension to the existing design data for ridge waveguide and considered helpful in practical applications.

A kind of asymmetric elliptical ridge waveguide is presented. Variations of the cut-off wavelength, single-mode bandwidth with the ridge dimensions and the ridge position for different values of dielectric constant are investigated in detail. The field patterns of the dominant and the first higher mode are also presented. The correctness of the numerical results is verified. The results provide an extension to the existing design data for ridge waveguide and considered helpful in practical applications.

La decentralisation en Chine a place les hopitaux municipaux (HM) au cœur du systeme sanitaire en zone rurale. Nous avons collecte des informations dans un echantillon de 21 HM de la province de Shandong et dans les administrations concernees pour analyser par des methodes quantitatives les determinants de leur activite, mesurer leur efficience et en rechercher les facteurs explicatifs pour la periode 1986-2000. Nos resultats suggerent entre autres que le revenu per capita de la zone de desserte des HM et leur attractivite percue ont un effet positif sur leur activite, que les tarifs pratiques en sont un frein et que les dispositifs de couverture maladie n’ont pas d’impact significatif sur leur frequentation. L’integration verticale partielle des HM avec les centres de sante villageois a relativement freine l’activite de ces hopitaux. Leur efficience s’est globalement amelioree, selon une dynamique relativement heterogene, durant la periode etudiee, mais on observe une certaine convergence des performances. Cette evolution s’est faite en partie sous l’influence de facteurs institutionnels qui tiennent a des modalites de regulation sectorielle et a des questions de gouvernance liees aux relations entre les HM et la tutelle.Classification JEL : I12 – I18 – I19 – H51.

The scattering of target in dispersive soil is simulated under Gaussian pulse excitation. 2D PML perfectly matched layer (PML) absorbing boundary condition is proposed to truncate computation space for finite-element time-domain (FETD) in dispersive media. Numerical examples show that the proposed PML-FETD approach has small reflection errors and no late-time instability for simulations. The PML formulations for Debye dispersive are derived. The scattering results excited by Gaussian pulse are calculated. The numerical results of vector and nodal based finite-element time-domain with PML are compared with finite-difference time-domain. Good agreement is observed.