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The distributions in different particle sizes of municipal solid waste incinerator (MSWI) fly ash in spring and autumn were studied by sieve method, and the heavy metal contents of Cu, Zn, Mn, Pb, Cd, Ni, Cr and Hg in different size particles were measured, and the heavy metal leaching amount in the different particle size were also studied under the GB5085.3-2007 and USEPA-TCLP leaching procedure, respectively. The results showed that the particle size of fly ash in autumn was relatively smaller than that of in spring, more than 90% of particle size of fly ash in spring and autumn were less than 250 μm, and the particle size in 83-105 μm of fly ash in spring distributes in most with about 40% of the total, but 105-149 μm in autumn distributes in most, accounted for about 45% of the total. The content of heavy metals decreased first and then increased with the decreasing particle sizes except for Ni, and the content of heavy metals in the spring is higher than that of in autumn except for Fe and Zn. Under the GB5085.3-2007 leaching procedure, the leaching content of Cu, Zn and Ni in MSWI fly ash in both spring and autumn and Cr in spring were not beyond limited standard, but Pb and Cd in both spring and autumn and Cr in autumn were beyond limited standard. However, under TCLP leaching procedure, the leaching content of Pb, Cr and Cd in both spring and autumn were beyond the standard limits.

The effect of different tillage systems on the size distribution of aggregates and organic carbon distribution and storage in different size aggregates in a Hydragric Anthrosol were studied in a long-term experiment in Chongqing, China. The experiment included five tillage treatments, which are conventional tillage with rice only system (DP), conventional tillage with rotation of rice and rape system (SH), no-till and ridge culture with rotation of rice and rape system (LM), no-till and plain culture with rotation of rice and rape system (XM) and tillage and ridge culture with rotation of rice and rape system (LF), respectively. The results showed that the aggregates 0.25-0.05 mm in diameter accounted for the largest proportion in each soil layer under all treatments. The organic carbon mainly exist in aggregates in the 0.25-2 mm and 0.05-0.25 mm diameter in the plough layer, which mainly exist in the 0.25-2 mm in diameter in the bottom layer. Distribution of organic carbon in aggregates in the 0.05-0.25 mm diameter class was highest, followed by the aggregates in the 0.25-2mm diameter class. The organic carbon in aggregates under different tillage systems was in a decreasing order of LM (21.05 g·kg-1)> DP (14.13 g·kg-1)> XM (13.29 g·kg-1)> LF (12.54 g·kg-1) > SH (11.41 g·kg-1). The total organic carbon content showed a significant correlation with the amount of aggregates with diameter >0.005 mm. The results showed that the accumulation of soil organic carbon was mainly affected by aggregates in the >0.005mm diameter class.

Blue-shifted spectra of supercontinuum generation in photonic crystal fibers are studied theoretically and experimentally.The influences of input power on supercontinuum spectra generation are analyzed.The research results show that when the power of the laser is low,the theoretical results obtained by the nonlinear Schrodinger equation including self-phase modulation,self-steeping and intrapulse Raman scattering agree with the experimental results.However,when the power of the laser is high,the theoretical and experimental blue-shifted spectra are different.Therefore,the influences of the cross phase modulation and four-wave mixing effects on the supercontinuum generation are discussed,which provide the mechanism for the bule-shifted spectra of supercontinuum generation.

A nonamer metamaterial composed of nine split ring resonators with different orientations was experimentally and numerically researched in terahertz band. The nine split rings were arranged spirally. From the first split ring, the subsequent split rings were rotated anti-clockwise by 40. Generally, the split ring resonator was polarization-dependent. It was found that split rings oligomer, which can produce multiple resonance modes, was polarization-independent owing to the near-field energy coupling. The split rings oligomer composed of polarization-dependent resonators exhibited a polarization-independent effect, which enriched the design idea of traditionally uncoupled metamaterial composed of disperse resonators, and induced a new path for terahertz functional devices, like optical switch, modulator, filter and so on.

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 photonic crystal waveguide can serve as a switch and continuously tunable band-pass filter with controlling of the magnetic field.

Polarization is one of the basic properties of electromagnetic wave conveying valuable information about signal transmission and sensitive measurements. Manipulations of polarization state and amplitude have aroused a lot of research interest in many different fields, especially in the terahertz (THz) regime. Although many researches on THz polarization controller have been carried out, their transmission losses are still difficult to lower in a broad bandwidth. And there are few reports on THz polarization controller which can rotate the polarization state and split beams at the same time. Multifunctional THz devices are required to meet the needs of the progress of THz technology and its applications. In order to overcome this constraint, semiconductor silicon is integrated into the proposed structure to manipulate the polarization state and the amplitude, because of its optical properties with the external pump light. Here, according to the electromagnetic resonance between split rings and silicon rings in Fabry-Prot-like cavity, we propose a metasurfaces-based terahertz polarization controller. The unite cell structure is composed of metal grids-split ring/Si ring-metal grids spaced by silica layers. By using the finite element method in CST Microwave Studio, we simulate the transport and polarization properties under different conditions. The results show that a linear polarization state can be nearly perfectly converted into its orthogonal one from 0.39 to 1.11 THz with a transmission loss of 1 dB, which fits well to the one of multiple-beam interference theory. Then we study the properties of the proposed metasurface structure for oblique incidence. The property of rotating polarization basically keeps stable even at an incident angle of 60 from 0.52 to 1.05 THz. At the end of the paper, the polarization splitting feature of the device is discussed in the THz regime. The results demonstrate that the transmitted and reflected beam power of the device can be tuned by changing the pump light power. The modulation depths of two beams reach more than 90% at 0.5 THz. It is worth noting that the proposed structure can not only rotate the polarization state of transmitted light in a broad bandwidth of 0.72 THz, but also modulate the transmitted and reflected beam power with a wide modulation depth. It can be used as a broad-band, low-loss and tunable terahertz polarization controller which is also insensitive to the incident angle. So it meets the requirements in THz communication, spectrum detection and imaging systems.

With the continuous development of terahertz (THz) technology in recent years, many kinds of THz functional devices including switchers, filters, modulators, isolator and polarizers have been demonstrated. However, researches of the focusing devices in the terahertz frequency range are rarely reported. In this paper, we propose a subwavelength metal-air-InSb-metal periodic array structure to perform terahertz wave focusing. The dependence of permittivity of InSb in the THz regime on external magnetic field and temperature is calculated theoretically. Based on the magneto-optical effect of the semiconductor material InSb and asymmetrical waveguide structure, the influences of external magnetic field and temperature on the focusing and transmittance characteristics of the device are studied in detail. Numerically simulated results show that the structure proposed above can not only improve the transmittance greatly but also perform focusing perfectly. Calculations on the transmission properties show that in a certain range of temperature, the power flow transmittance at the focus point increases with the increase of temperature. In the meantime, for a certain temperature, with increasing the external magnetic field, the power flow continuously increases as well and reaches a maximum value at a certain magnetic field. For example, for a temperature of 172 K and a magnetic field of 0.6 T, the maximum power flow transmitted at the focus point is 10200 W/m2 at 0.8 THz, which is about 28 times larger than that without magnetic field at the same temperature. In addition, the simulation results also show that when the temperature and external magnetic field are fixed at 172 K and 0.5 T, respectively, the power flow transmittances for the incident waves at different frequencies are different. There is a peak value of the transmittance appearing at a specific frequency of 0.8 THz. Moreover, when the incident wave frequency is far from 0.8 THz, the transmittance decreases dramatically. It is worth noting that by choosing different temperatures and external magnetic fields, the structure proposed can not only enhance the transmittance over 20 times at the focus point, but also manipulate effectively the THz wave in a broad operating bandwidth of 400 GHz from 0.4 THz to 0.8 THz. These properties indicate that the proposed structure can act as an ideal tunable, broadband, and high transmittance focusing device in the terahertz regime.

We propose a vector beam generation method based on the spatial light modulator composed of twisted nematic liquid crystal. According to the relation between the rotation angle and the applied voltage on the spatial light modulator, a common optical system for generating a variety of vector beams is designed in experiments. By using this common optical system, a variety of vector beams in axisymmetric phases as well as the complex vector beams are generated, and their polarization characteristics are observed and measured experimentally, where a tight focusing field is obtained, and this may be applied in optical tweezers and lithography. In addition, the device structure is simple and easy to operate, its efficiency of producing vector beam is very high and the laser spectral characteristics are not changed in the proposed generation of vector beams. Therefore, the method we proposed can find important potential applications in strong laser of vector beams interacting with matter, and laser acceleration, etc.

In this paper, an interlacing layered infiltration method is proposed, using some liquid material as the common porous fiber with triangular air-hole array in the core region, which can achieve the characteristic of ultrahigh modal birefringence in this circumstance. Förstly, the basic properties of the porous fiber with a porosity of 43.08% are thoroughly analyzed by using a full-vector finite element method, as wellas the dispersion curves of the fiber, modal birefringence, fraction of the fundamental modal power for x and y polarizations, loss characteristics, etc. Secondly, to enhance the asymmetry of the proposed structure, some liquid material with a refractive index of 1.4 is infiltrated into the air holes in the fiber core region, by using interlacing filling method. It is found that the modal birefringence of the fiber dramatically increases. At an operation frequency of 1.1 THz, the peak value of modal birefringence rises from 1.05×10-3 to 1.36×10-2 after the infiltration operation. The fundamental model effective material absorption loss coefficients for x and y polarization modes increase from 0.16 dB/cm to 0.25 dB/cm and 0.28 dB/cm, respectively. And the operation frequency band increases from 1.1 to 1.9 THz. Simulation results indicate that the modal birefringence of the fiber can be remarkably improved by increasing the refractive index of the infiltrated liquid material. With an operation frequency of 2.2 THz and a refractive index of 2, this fiber can realize an ultrahigh modal birefringence of 8.03×10-2. Moreover, to achieve the gradient distribution of the refractive index, an interlacing layered infiltration method to infiltrate the liquid material with different refractive indices in different layers is employed. Results show that the confinement capability to the guided modes has been greatly enhanced. Results also show that the peak value of the modal birefringence for the fundamental modes does not exist in the operation band. It represents a monotonically increasing trend. At an operation frequency of 2.2 THz, the fiber modal birefringence can reach as high as 7.19×10-2. This scheme presents an ultrahigh modal birefringence, and it presents the tunable characteristic as well. This study may be of significance in the practical applications in the field of THz functional devices.

A low loss broadband THz polarization splitter made from suspended dual-core porous fiber is proposed. The property of low loss is due to the porous structure of the fiber, and the match of single polarization mode is achieved by the orthogonal relationship of the microstructure in the two fiber cores. Structure of the fiber is designed by using index converse matching coupling method. Numerical simulation is carried out by employing full vector finite element method. The background material is cyclo olefin polymer COC with low loss property in THz region. Firstly, the properties of a suspended porous fiber with a single core has been analyzed in detail, including the effective refractive index, birefringence, fraction of modal power in air, and material absorption loss in the fundamental mode. Moreover, the properties of THz polarization splitter made from suspended dual-core porous fibers have been investigated theoretically. Numerical simulation results show that the operation bandwidth is 1.5 THz (from 0.8 THz to 2.3 THz). At 1 THz, the splitting length is only 0.66 cm. The extinction ratios for x and y polarization modes can reach -14.64 dB and -14.84 dB, respectively. The practical material absorption loss is less than 0.12 dB for both x and y polarization modes. Compared with other dual-core-PCF-based polarization splitters, the dual-core porous fiber has several advantages such as simplicity for structure designing, ease of fabrication, better feasibility in practical applications, low transmission loss, and wide operation frequency bandwidth.

Utilizing insulator-metal phase transition of vanadium dioxide thin film, we propose a thermally controlled terahertz modulator based on metamaterial, and research the transmission characteristics and temperature tunable characteristics of phase transition in metamaterials in THz wave band. While the incident THz wave is of horizontal polarization or vertical polarization, two independent pass bands are generated near 1 THz. The center frequencies of the two pass bands are 1.3 THz and 1.7 THz, the bandwidths of them are 0.2 THz and 0.35 THz. In addition, when temperature rises from 40℃ to 80℃, the transmissions of the two pass bands drop apparently, especially at phase transition temperature of 68℃. For the two polarization states, the modulation depths achieve 60% or more, which is the great function of a modulator.

A novel low-loss dual-core fiber directional coupler for terahertz raditional is proposed, Coupling properties, loss and group velocity dispersion of the fibers are investigated by the full-vector finite-element method (FEM). The simulation results demonstrate that the coupling length of this coupler is less than 1.8 cm between 1.55 and 1.80 THz, and the coupling broadband of 0.07THz can be realized. And the loss coefficient of the coupler is less than 0.02 cm-1. The directional coupler has potential applications in narrowband filtering, wavelength-division multiplexing, switching, polarization splitter and so on.

We propose a novel tunable photonic crystal (PC) waveguide Mach-Zehnder interferometer (MZI) based on nematic liquid crystals (LCs) 5CB and investigate its interference properties numerically by using the finite-difference time-domain method. We can change the refractive index of LC by rotating the directors of the LC molecules. The line defect modes of the PC waveguide with different liquid crystal refractive indices are analyzed by using the plane wave expansion method. Owing to the slow group velocity region of the line defect mode, when the index of 5CB changes from 1.53 to 1.63, the variation of the effective index of the line defect mode arrives at 0.168. This property helps to significantly control the phase of light propagation in a PC waveguide MZI. The novel interferometer can be used as either an optically controlled on-off switch or an amplitude modulator in optical circuits.

A low-loss and broadband terahertz twin-core photonic band-gap fiber directional coupler is proposed, which consists of a cladding with a triangular lattice array of sub-wavelength air rods and two cores formed respectively by omitting seven nearby air rods. The group velocity dispersion, the coupling and the loss of the fibers are investigated by using a full-vector finite element method. The numerical simulations show that the loss coefficient of the coupler is less than 0.021 cm-1, and the coupling broadband of 0.14 THz can be realized. The directional coupler has potential applications in terahertz communication systems, such as filtering, wavelength-division multiplexing, polarization isolation, switching and so on.

A multifunctional terahertz polarization controller is designed based on the two-dimensional photonic crystal structure and the ferrite material. The different working devices including a controllable polarizer, a polarization beam splitter and a tunable phase retarder with continuous phase retardations of - at 1 THz are controlled by the shift of photonic band gap with different external magnetic fields. By using the plane wave expansion method and the rigorous coupled wave analysis, we calculate the band gap positions and transmittances of device with the variation of magnetic field. The field distribution and phase are simulated by the finite difference time domain method.

A novel magnetically tunable liquid crystal terahertz switch is designed to reduce the coupling loss. The main structure of the switch is the hollow-core Bragg fiber with its cladding constructed by periodically setting of high density polyethylene and nematic liquid crystal E7 The refractive index of the E7 can be changed by the application of outside magnetic field and thus alter the loss property of the Bragg fiber dramatically to achieve its function as a switch. The main advantage of this switch is that it can eliminate the loss of coupling with fibers,and what is more,this switch can select the basic mode and is easy to be controlled. This article uses the finite element method to obtain the parameter of the switch and the simulated value of the extinction ratio reaches 2634 dB.