Light-Propagation Characteristics of Photonic Crystal Waveguide Based on SOI Materials at Different Polarized States

Straight single-line defect optical waveguides in photonic crystal slabs are designed by the plane wave expansion method and fabricated into silicon-on-insulator （SOI） wafer by 248-nm deep UV lithography. We present an emcient way to measure the light transmission spectrum of the photonic crystal waveguide （PhC WG） at given polarization states. By employing the Mueller/Stokes method, we measure and analyse the light propagation properties of the PhC WG at different polarized states. It is shown that experimental results are in agreement with the simulation results of the three-dimensional finite-difference-time-domain method.     

Optical Tamm States in Dielectric Photonic Crystal Heterostructure

We investigate one-dimensional dielectric photonic crystal and optical Tamm modes formed by superposition of two band gaps and find that this kind of mode can be explained by the single negative materials tunnelling effect. A finite-size dielectric photonic band gap can mimic one kind of effective single negative material and this property sensitively depends on the frequency location in stop-band regions and surface termination and so on. The effective impedance match and effective phase match give the precise position of the optical Tamm mode. Complete transparency via tunnelling is achieved by two opaque media and demonstrates the validity of our approach.     

Focusing Properties in Photonic Crystal Structure Formed by Air Holes in Dielectric Background with Concave Interface

We investigate the focusing properties of photonic crystal structures with a concavo-concave as the photonic crystal boundary. The photonic crystal is constituted by air holes parallelly distributed in a uniform dielectric. A good-quality focus of a plane wave can appear out of the photonic crystal structure, and a strong far field focus is also formed from the photonic crystal interface. A negative-refractive beam at the frequency 0.195 （2πc/α） for the excited Bloch wave mode near the Brillouin zone edges under all incident angles are obtained by simulation.     

A novel method of rapidly modeling optical properties of actual photonic crystal fibres

<正>The flexible structure of photonic crystal fibre not only offers novel optical properties but also brings some difficulties in keeping the fibre structure in the fabrication process which inevitably cause the optical properties of the resulting fibre to deviate from the designed properties.Therefore,a method of evaluating the optical properties of the actual fibre is necessary for the purpose of application.Up to now,the methods employed to measure the properties of the actual photonic crystal fibre often require long fibre samples or complex expensive equipments.To our knowledge, there are few studies of modeling an actual photonic crystal fibre and evaluating its properties rapidly.In this paper,a novel method,based on the combination model of digital image processing and the finite element method,is proposed to rapidly model the optical properties of the actual photonic crystal fibre.Two kinds of photonic crystal fibres made by Crystal Fiber A/S are modeled.It is confirmed from numerical results that the proposed method is simple,rapid and accurate for evaluating the optical properties of the actual photonic crystal fibre without requiring complex equipment.     

Near-field imaging of a square-lattice metallic photonic-crystal slab at the second band

Imaging properties of a two-dimensional photonic crystal slab lens are investigated through the finite-difference time-domain method. In this paper, we consider the photonic crystal slab consisting of a square lattice of square metallic rods immersed in a dielectric background. Through the analysis of the equifrequency-surface contours and the field patterns of a point source placed in the vicinity of the photonic crystal slab, we find that a good-quality image can form at the frequencies in the second TM-polarized photonic band. Comparing the images formed at different frequencies, we can clearly see that an excellent-quality image is formed by the mechanisms of simultaneous action of the self-collimation effect and the negative-refraction effect.     

The Second Order Guided Modes Based on Photonic Bandgap Effects in Air/Glass Photonic Crystal Fibers

We introduce a defect site in the periodic structure of a photonic bandgap fiber, to confine and guide the second order mode by photonic bandgap effects. Based on a high air-filling fraction photonic crystal cladding structure, a simplified model with an equivalent air cladding was proposed to explore and analyze the properties of this second order guided mode.     

Photonic crystal structures:Beam deflector and beam router

We investigate the optical characteristic,transverse magnetic(TM) and transverse electric(TE) band of twodimensional(2 D) square lattice photonic crystal structure,which is composed of cylindrical air regions positioned at the corners of the square shaped dielectric rods.We obtain the wide photonic bandwidths between TM1–TM2 and TM3–TM4 bands.According to the results,we demonstrate the band gaps close to each other in the TM and TE frequencies for proposed structures.The resulting photonic gaps are formed to be about 8% at the higher frequencies of TE modes(TE4–TE5)and TM modes(TM7–TM8 and TM9–TM10).In addition,we examine isotropically generated structures for light guiding properties and observe that the light is directed in a particular route without using any deflection.We also investigate the self-collimation effect with the designed structure.The obtained results reveal the influences of the radius of cylindrical air holes and the angle between these air holes on absolute and partial photonic band gaps.Moreover,we observe the TM and TE band gaps that overlap.It is thought that the obtained band overlap will provide an easy way to produce the photonic crystals in practical applications like photonic insensitive waveguide.It is also believed that these results can provide the photonic crystal structures to work as a beam deflecting and beam router in integrated optical circuit applications.     

Graphene Tamm plasmon-induced giant Goos–H?nchen shift at terahertz frequencies

In this Letter, we have shown that a giant Goos–H?nchen shift of a light beam reflected at terahertz frequencies can be achieved by using a composite structure, where monolayer graphene is coated on one-dimensional photonic crystals separated by a dielectric slab. This giant Goos–H?nchen shift originates from the enhancement of the electrical field, owing to the excitation of optical Tamm states at the interface between the graphene and onedimensional photonic crystal. It is shown that the Goos–H?nchen shift in this structure can be significantly enlarged negatively and can be switched from negative to positive due to the tunability of graphene's conductivity. Moreover, the Goos–H?nchen shift of the proposed structure is sensitive to the relaxation time of graphene and the thickness of the top layer, making this structure a good candidate for a dynamic tunable optical shift device in the terahertz regime.     

Magnetically Tunable Terahertz Switch and Band-Pass Filter

A novel design of a tunable terahertz switch and band-pass filter using liquid-crystal-filled photonic crystal waveguide is demonstrated. The effects of magnetic field on the photonic bandgaps and transmitting properties of a THz wave are investigated by using the plane wave expansion method and finite difference time domain method. The efficient photonic bandgap tuning is predicted such that the two-dimensional liquid-crystal-filled photonie crystal waveguide can serve as a switch and continuously tunable band-pass filter with controlling of the magnetic field.     

Influence on photonic crystal fiber dispersion of the size of air holes in different rings within the cladding

The influence on photonic crystal fiber dispersion of the size of air holes in different rings within the cladding is investigated using a semivectorial finite difference method. Numerical results reveal that the photonic crystal fiber dispersion is more sensitive to the variation of the air hole size in the first and second rings, indicating that design of photonic crystal fibers with desirable dispersion properties requires more precise control of the parameters of the air holes in the vicinity of the fiber core.     

Omnidirectional Gaps of One-Dimensional Photonic Crystals Containing Single-Negative Materials

We show that a one-dimensional photonic crystal containing two kinds of single-negative materials can possess an omnidirectional gap whose edges are insensitive to incident angle and polarization, owing to the unusual field configuration in the structure. In contrast to an omnidirectional gap based on a photonic gap that corresponds to zero averaged refractive index, it can be made very wide by varying the ratio of the thicknesses of two media.Moreover, it is independent of polarization under special parameters. These properties may provide a mechanism to design a broadband omnidirectional reflector with fixed bandwidth.     

Fabrication of High Quality Three-Dimensional Photonic Crystals

High quality colloidal photonic crystals made from polystyrene spheres with diameter 24Ohm are fabricated by the vertical deposition method. The scanning electron microscopy (SEM) and the transmittance spectrum are used to characterize the properties of the photonic crystal. The SEM images show that there are few lattice defects. The transmittance of the photonic crystal is above 75% in the pass band at 700nm and is lower than 5% at the centre of the band gap, respectively. It is found that proper concentration is a very important factor to fabricate the photonic crystal when the diameter of the spheres is lower than 30Onm.     

Photonic band gap from periodic structures containing anisotropic nonmagnetic left-handed metamaterial

<正>We demonstrate a photonic band gap(PBG) from one-dimensional(1D) periodic structures created by a double-layer unit cell with an air layer and an anisotropic nonmagnetic left-handed metamaterial(LHM) layer whose permittivity elements are partially negative.The requirements imposed on the materials and structures to realize a PBG are derived when the frequency is above or below the cutoff frequency,and the transmission properties of the PBG are discussed by utilizing 4×4 transfer-matrix method with dispersive semiconductor metamaterial.     

Two-dimensional ring-type photonic crystals in the near-infrared region

We propose a ring photonic crystal working in the near infrared region, where the air holes in the background material GaAs are arranged to form a series of rings. We find that the band gaps do not depend on the incident direction, and only a small number of rows are needed to create a frequency gap in the transmission spectrum. The transmission spectra of both P and S polarizations show that there is a complete bandgap in the hexagonal ring photonic crystals and the ratio of gap width to mid-gap frequency is as high as 11%.     

Influence on photonic crystal fiber dispersion of the size of air holes in different rings within the cladding

The influence on photonic crystal fiber dispersion of the size of air holes in different rings within thecladding is investigated using a semivectorial finite difference method.Numerical results reveal that thephotonic crystal fiber dispersion is more sensitive to the variation of the air hole size in the first and secondrings,indicating that design of photonic crystal fibers with desirable dispersion properties requires moreprecise control of the paxameters of the air holes in the vicinity of the fiber core.     

Engineering Photonic Crystal Impurity Bands for Multiple Channelled Optical Switches

We report theoretically on the engineering of photonic crystal impurity bands to realize multiple channelled optical switches. The mechanism is based on the confinement of the impurity band in a photonic quantum-well structure, leading to N-quantized confined states coming from N-coupled defects. Due to the strong localization of electromagnetic wave at defect regions, the transmission of confined states are greatly dependent on the defects and then multiple channelled optical switches can be realized by slightly changing the defects by a control light. The dependence of the threshold of such a switch on the layer number of photonic barriers is also given.     

Optical fiber sensor based on the short-range surface plasmon polariton mode简

The dispersion compensation properties of dual-concentric core photonic crystal fibers are theoretically investigated in this letter. The effects of geometric structure on the dispersion properties of dual-concentric core photonic crystal fibers are carefully studied by finite element method. The first layer of holes around the core area is enlarged in a new manner with the near-core point fixed. Considering the tradeoff among several parameters, results show that the dispersion compensation wavelength and strength can be tuned to desired values by constructing an appropriate design of the geometric structure of photonic crystal fibers.     

Tunable negative-index photonic crystals using colloidal magnetic fluids

The model of using colloidal magnetic fluid to build tunable negative-index photonic crystal is established. The effective permittivity εe and permeability μe of the two-dimensional photonic crystal are investigated in detail. For transverse magnetic polarization, both εe and μe exhibit a Lorentz-type anomalous dispersion, leading to a region where εe and μe are simultaneously negative. Then, considering a practical case, in which the thickness of photonic crystal is finite, the band structures for odd modes are calculated by the plane wave expansion method and the finite-difference time-domain method. The results suggest that reducing the external magnetic field strength or slab thickness will weaken the periodic modulation strength of the photonic crystal. Simulation results prove that the negative-index can be tuned by varying the external magnetic field strength or the slab thickness. The work presented in this paper gives a guideline for realizing the flat photonic crystal lens with tunable properties at optical frequencies, which may have potential applications in tunable near-field imaging systems.     

Large-scale photonic crystals with inserted defects and their optical properties

Deliberately introducing defects into photonic crystals is an important way to functionalize the photonic crystals. We prepare a special large-scale three-dimensional(3D) photonic crystal(PC) with designed defects by an easy and low-cost method. The defect layer consists of photoresist strips or air-core strips. Field emission scanning electron microscopy(FESEM) shows that the 3D PC is of good quality and the defect layer is uniform. Different defect states shown in the ultraviolet-visible spectra are induced by the photoresist strip layer and air-core strip layer. The special large-scale 3D PC can be tested for integrated optical circuits, and the defects can act as optical waveguides.     

Single Crystal Growth and Physical Property Characterization of Non-centrosymmetric Superconductor PbTaSe_2

We report on the single crystal growth and superconducting properties of PbTaSe_2 with the non-centrosymmetric crystal structure.By using the chemical vapor transport technique,centimeter-size single crystals are successfully obtained.The measurement of temperature dependence of electrical resistivity p(T) in both normal and superconducting states indicates a quasi-two-dimensional electronic state in contrast to that of polycrystalline samples.Specific heat C(T) measurement reveals a bulk superconductivity with T_c≌3.75 K and a specific heat jump ratio of 1.42.All these results are in agreement with a moderately electron-phonon coupled,type-ⅡBardeen-Cooper-Schrieffer superconductor.