Investigation of one-way absorption properties in an asymmetric photonic crystal containing a semiconductor defect.

We theoretically study the one-way absorption in two 1D defective asymmetric photonic crystals, air/(DB)NA(BD)M/air and air/(DB)NA(BD)MA(DB)NA(BD)M/air, where A and B are dielectrics, D is the semiconductor, n-InSb, and N, M are stack numbers with N≠M. It is revealed that their absorption spectra exhibit one-way properties. We also find that the number of one-way absorption peaks depends on the symmetry and number of defect layers, which are similar to the defect modes in the transmittance spectra of the usual symmetry photonic crystals. Additionally, effects of the incident angles for both TE and TM waves on the one-way feature are also presented. At a large incident angle, the TE wave is almost reflected, whereas the TM wave can have a partial absorption.

Wave properties in asymmetric single-negative-base photonic crystals.

We theoretically study wave properties for one-dimensional defective asymmetric photonic crystals, air/(AB)MG(BA)N/air, air/(AQ)MG(QA)N/air, and air/(BQ)MG(QB)N/air, where A is a lossy epsilon-negative material, B is a lossy mu-negative material, G and Q are dielectrics with different refractive indexes, and M and N are stack numbers with M≠N. Special attention has been paid to their absorption spectra. It is found that at certain frequencies the absorption can exhibit unidirectional properties. Our calculated results show two kinds of unidirectional absorption peaks. One is a single absorption peak whose frequency depends on the thickness of defect layer G. For the other peaks, its frequency does not change when the defect layer's thickness changes. In addition, in the second kind of peaks, the peak numbers for forward and backward propagation are different, that is, there are (M-1) absorption peaks for forward propagation, while there are (N-1) absorption peaks for backward propagation. When the two kinds of unidirectional absorption peaks are merged, some new peaks appear, and both forward and backward propagation will have (M+N-1) absorption peaks.

Experimental measure of transmission characteristics of low-frequency surface plasmon polaritons in frequency and time domains.

In this work, based on the use of the concept of spoof surface plasmon polaritons (spoof SPPs), we propose a novel kind of microstrips to suppress the interference between bended parallel microstrips. This novel structure is implemented by introducing subwavelength periodic structures onto the sides of a conventional microstrip. We numerically analyze the transmission characteristics of such new microstrips. We also measure the suppression arising from crosstalk between the bended corrugated microstrip and the conventional microstrip in both frequency and time domains. Experimental results show that such transmission line structure has superb interference restraining properties. Additionally, transmission properties have been investigated using circuit model. It is found that the coupling effect between the corrugated microstrip and the conventional microstrip can be efficiently suppressed in high speed digital signal transmission application.

Single-negative metamaterial periodic multilayer doped by magnetized cold plasma.

This study theoretically investigates the properties of the defect mode in a 1D defective single-negative photonic crystal containing a magnetized cold plasma defect layer. The considered photonic crystal structure is made of epsilon-negative and mu-negative metamaterials. We investigate the defect mode as a function of the thickness and the electron density of the defect layer and the magnetic field. The results show that the thickness, electron density, and variations of the magnetic field affect the frequency of the defect mode. In addition, the shift trend in the defect mode is shown to rely on the polarization due to the presence of polarization-dependent magnetized cold plasma. The results lead to some new information concerning the designing of new types of tunable narrowband filters at microwave frequency.

Use of single-negative material as a tunable defect in a dielectric photonic crystal heterostructure.

The defect mode in a photonic crystal heterostructure of (1/2) N (2/1)N tuned by using a single-negative layer as a defect layer; that is, the structure to be considered is (1/2)ND (2/1)N, where 1, 2 are dielectrics, N is the stack number, and D is a defect layer taken to be a single-negative material. The results show that when D is a mu-negative (µ < 0) medium, the defect mode frequency is redshifted as a function of the thickness of D as well as the static permittivity. On the other hand, if D is an epsilon-negative (ε < 0) medium, the defect mode frequency is blueshifted as the defect layer thickness increases, but it is independent of the static permeability. We also investigate the angular dependence of the defect frequency for both two polarizations, transverse electric (TE) wave and transverse magnetic (TM) wave. The defect mode frequency is shown to be blueshifted as a function of the angle of incidence. Additionally, the shift in the TE wave is larger than that in the TM wave.

Magnetic-field tunable multichannel filter in a plasma photonic crystal at microwave frequencies.

The microwave magnetic-field tunable filtering properties in a multichannel filter based on use of a one-dimensional finite magnetized plasma photonic crystal (PPC) are theoretically investigated. The considered PPC has a structure of air/(AB)N/air, where A is a dielectric layer, B is a plasma layer, and N is the stack number. First, in the absence of an externally applied magnetic field, the structure can work as a multichannel filter whose channel number is equal to N-1 for N>1. Next, in the presence of an externally applied field, the filtering properties become tunable, i.e., the channel frequencies can be shifted as a function of the applied magnetic field. We find that the effect of the magnetic field will cause the channel frequencies to be blue-shifted or red-shifted depending on the orientation of the applied magnetic field.

Analysis of multigroup and multichannel filtering properties in a ferroelectric-dielectric periodic multilayer.

In this work, we propose a filter structure using a one-dimensional ferroelectric-dielectric periodic multilayer, air/[(ABA)Ns C]Np(ABA)Ns /air, where Ns and Np are the two numbers of periods. Here, B is a dielectric material of SiO2, C is the same as B with a different thickness, and A is taken to be a ferroelectric material Ba55Sr45TiO3+30%Mg2SiO4, whose dielectric constant is very high (ϵ=439 at 10 GHz). The results show that the transmittance spectra have Ns-channel groups at microwave frequencies and these groups can be classified into two types. The first type has only one channel group with Np narrower channels. The other has Ns-1 groups, each of which has Np+1 broader channels. In this filter structure the group number and channel number of each group can be determined simply by changing Ns and Np.

Design of a terahertz photonic crystal transmission filter containing ferroelectric material.

The ferroelectric material KTaO3 (KTO) has a very high refractive index, which is advantageous to the photonic crystal (PC) design. KTO polycrystalline crystal has a high extinction coefficient. In this work, we perform a theoretical study of the transmission properties of a PC bandpass filter made of polycrystalline KTO at terahertz (THz) frequencies. Our results show that the defect modes of usual PC narrowband filters no longer exist because of the existence of the high loss. We provide a new PC structure for the high-extinction materials and show that it has defect modes in its transmittance spectra, providing a possible bandpass filter design in the THz region.

Analysis of defect mode in a one-dimensional symmetric double-negative photonic crystal containing magnetized cold plasma defect.

In this paper, the characteristic matrix method is employed to theoretically investigate properties of the defect mode in a 1D lossy symmetric defective photonic crystal containing two magnetized cold plasma defect layers. The considered photonic crystal is made of double-negative and double-positive materials. The defect mode, as a function of the magnetic field and the electron density, will be investigated in three different structures. The results show that the defect mode frequency can be tuned by variations of the magnetic field and the electron density as well. Due to the polarization-dependent magnetized cold plasma, the shift trend in the defect mode is shown to also rely on the polarization. The proposed structures could provide another alternative for the design of narrowband filters at microwave.

Analysis of tunable negative refraction in a lossy and extrinsic semiconductor.

In this work, within the framework of an inhomogeneous wave, we study the wave transmission at the boundary between air and a lossy extrinsic semiconductor of n-type indium antimonide. Transmission properties such as negative refraction are specifically investigated. The choice of such a semiconductor enables us to study the tunable features in the negative refraction because its permittivity is a function of the frequency, the temperature, and the doping concentration. It is found that there exist a threshold temperature and a threshold frequency in order to obtain the negative refraction. The dependence of threshold temperature on the doping concentration and the operating frequency will be numerically demonstrated. The analysis of negative refraction can be used to study the electromagnetic response for a lossy and extrinsic semiconductor.

Photonic band gap structure for a ferroelectric photonic crystal at microwave frequencies.

In this work, the photonic band gap (PBG) structure in a one-dimensional ferroelectric photonic crystal (PC) is theoretically investigated. We consider a PC, air/(AB)N/air, in which layer A is a dielectric of MgO and layer B is taken to be a ferroelectric of Ba0.55Sr0.45TiO3 (BSTO). With an extremely high value in the dielectric constant in BSTO, the calculated photonic band structure at microwave frequencies exhibits some interesting features that are significantly different from those in a usual dielectric-dielectric PC. First, the photonic transmission band consists of multiple and nearly discrete transmission peaks. Second, the calculated bandwidth of the PBG is nearly unchanged as the angle of incidence varies in the TE wave. The bandwidth will slightly reduce for the TM mode. Thus, a wide omnidirectional PBG can be obtained. Additionally, the effect of the thickness of the ferroelectric layer on the PBG is much more pronounced compared to the dielectric layer thickness. That is, the increase of ferroelectric thickness can significantly decrease the PBG bandwidth.

Differential microstrip lines with reduced crosstalk and common mode effect based on spoof surface plasmon polaritons.

We apply the concept of spoof surface plasmon polaritons (SPPs) to the design of differential microstrip lines by introducing periodic subwavelength corrugations on their edges. The dispersion relation and field distribution of those lines are analyzed numerically. And then through designing practical coupling circuits, we found that compared with conventional differential microstrip lines, the electromagnetic field can be strongly confined inside the grooves of the corrugated microstrip lines, so the crosstalk between the differential pair and the adjacent microstrip lines is greatly reduced, and the conversion from the differential signal to the common mode signal can also be effectively suppressed. The propagation length of those lines is also very long in a wide band. Moreover, the experimental results in time domain demonstrate those lines perform very well in high-speed circuit. Therefore, those novel kinds of spoof SPPs based differential microstrip lines can be widely utilized in high-density microwave circuits and guarantee signal integrity in high-speed systems.

Design of multichannel filters based on the use of periodic Cantor dielectric multilayers.

A fractal multilayer structure made of two dielectric materials can exhibit photonic bandgap (PBG). In this work, with the use of this PBG, we study the transmission properties of periodic triadic Cantor set structures. The results indicate that the structure can be used to design multichannel filters with channel number equal to N-1 for a given number of periods, N. In addition, the channel frequencies can be designed at will. The considered structure provides another new type of design for a tunable multichannel filter.

Near-infrared photonic band structure in a semiconductor metamaterial photonic crystal.

In this study, we theoretically investigate the near-infrared (NIR) photonic band structure (PBS) in a one-dimensional semiconductor metamaterial (MM) photonic crystal (PC). The considered PC is (AB)N, where N is the stack number, A is a dielectric, and B is a semiconductor MM composed of Al-doped ZnO and ZnO. It is found that the photonic band gaps (PBGs) can be tunable by the variations in filling factor, and thicknesses of A and B. It is of particular interest to see that the PBG will vanish when the thicknesses of A and B satisfy a certain condition. The results provide fundamental information on a NIR PBS that could be of technical use in photonic applications using such a semiconductor MM. The band gap vanishing makes it possible to design a wider band pass filter at NIR based on the use of such a PC.

Use of two-dimensional nanorod arrays with slanted ITO film to enhance optical absorption for photovoltaic applications.

Two-dimensional (2D) Si-nanorod arrays offer a promising architecture that has been widely recognized as attractive devices for photovoltaic applications. To further reduce the Fresnel reflection that occurs at the interface between the air and the 2D Si-nanorod array because of the large difference in their effective refractive indices, we propose and adopt a slanted ITO film as an intermediate layer by using oblique-angle sputtering deposition. The nearly continuous surface of the slanted ITO film is lossless and has high electrical conductivity; therefore, it could serve as an electrode layer for solar cells. As a result, the combination of the above-mentioned nanostructures exhibits high optical absorption over a broad range of wavelengths and incident angles, along with a calculated short-circuit current density of JSC = 32.81 mA/cm2 and a power generation efficiency of η = 22.70%, which corresponds to an improvement of approximately 42% over that of its bare single-crystalline Si counterpart.

Practically acquired and modified cone-beam computed tomography images for accurate dose calculation in head and neck cancer.

BACKGROUND: On-line cone-beam computed tomography (CBCT) may be used to reconstruct the dose for geometric changes of patients and tumors during radiotherapy course. This study is to establish a practical method to modify the CBCT for accurate dose calculation in head and neck cancer. PATIENTS AND METHODS: Fan-beam CT (FBCT) and Elekta's CBCT were used to acquire images. The CT numbers for different materials on CBCT were mathematically modified to match them with FBCT. Three phantoms were scanned by FBCT and CBCT for image uniformity, spatial resolution, and CT numbers, and to compare the dose distribution from orthogonal beams. A Rando phantom was scanned and planned with intensity-modulated radiation therapy (IMRT). Finally, two nasopharyngeal cancer patients treated with IMRT had their CBCT image sets calculated for dose comparison. RESULTS: With 360° acquisition of CBCT and high-resolution reconstruction, the uniformity of CT number distribution was improved and the otherwise large variations for background and high-density materials were reduced significantly. The dose difference between FBCT and CBCT was < 2% in phantoms. In the Rando phantom and the patients, the dose-volume histograms were similar. The corresponding isodose curves covering ≥ 90% of prescribed dose on FBCT and CBCT were close to each other (within 2 mm). Most dosimetric differences were from the setup errors related to the interval changes in body shape and tumor response. CONCLUSION: The specific CBCT acquisition, reconstruction, and CT number modification can generate accurate dose calculation for the potential use in adaptive radiotherapy.

Terahertz multichanneled filter in a superconducting photonic crystal.

Terahertz spectroscopic properties in a one-dimensional superconductor-dielectric photonic crystal are theoretically investigated. Based on the calculated results, a terahertz multichanneled transmission filter can be achieved within the photonic passband. This structure possesses the comb-like resonant peaks in transmission spectrum at low temperature. The number of resonant peaks is directly related to the number of periods. The resonant peak height is lowered and broadened as the temperature increases. The dependence of the filling factor in the superconductor layer is also discussed. This filter containing no defect layer in structure is fundamentally different from the usual multichanneled filter based on a photonic crystal containing a photonic quantum well as a defect layer.

Analysis of photonic band structure in a one-dimensional photonic crystal containing single-negative materials.

A theoretical analysis on the angle- and thickness-dependent photonic band structure in a one-dimensional photonic crystal containing single-negative (SNG) materials is presented. The photonic crystal consists of two alternating SNG materials, including that one has a negative permittivity (ENG) and the other has a negative permeability (MNG). It is found that there are two types of SNG gaps. The first is the low-frequency gap which is very insensitive to the incident angle in the transversal electric (TE) wave. The second gap, which strongly relies on the incident angle for both TE and transversal magnetic (TM) waves, will close at the zero bandgap frequency at which the impedance match as well as the phase match in the constituent ENG and MNG layers must be simultaneously satisfied. This zero bandgap frequency is also strongly dependent on the incident angle. The band edges and the gap maps are investigated rigorously as a function of the incident angle and the ratio of thickness of the two SNG layers. The analyses are made in the lossless and lossy cases for both TE and TM waves. The inclusion of the loss enables us to further clarify two fundamentally distinct second SNG gaps which are separated by a threshold angle of incidence.

Properties of Transmission and Leaky Modes in a Plasmonic Waveguide Constructed by Periodic Subwavelength Metallic Hollow Blocks.

Based on the concept of low-frequency spoof surface plasmon polaritons (spoof SPPs), a kind of leaky mode is proposed in a waveguide made of a subwavelength metal-block array with open slots. Numerical results reveal that a new transmission mode is found in the periodic subwavelength metal open blocks. This modal field is located inside the interior of a hollow block compared with that in a solid metal block array. The dispersion curve shows that such a new SPPs mode has a negative slope, crossing the light line, and then going into a zone of leaky mode at higher frequencies. The leaky mode has a wider frequency bandwidth, and this can lead to a radiation scanning angle of 53° together with high radiation efficiency. Based on the individual characteristics exhibited by a frequency-dependent radiation pattern for the present leaky mode, the waveguide structure can have potential applications such as frequency dividers and demultiplexers. Experimental verification of such a leaky mode at microwave has been performed, and the experimental results are found to be consistent with the theoretical analysis.

Device modeling of ferroelectric memory field-effect transistor for the application of ferroelectric random access memory.

An improved theoretical analysis on the electrical characteristics of ferroelectric memory field-effect transistor (FeMFET) is given. First, we propose a new analytical expression for the polarization versus electric field (P-E) for the ferroelectric material. It is determined by one parameter and explicitly includes both the saturated and nonsaturated hysteresis loops. Using this expression, we then examine the operational properties for two practical devices such as the metal-ferroelectric-insulator-semiconductor field-effect transistor (MFIS-FET) and metal-ferroelectric-metal-insulator-semiconductor field-effect transistor (MFMIS-FET) as well. A double integral also has been used, in order to include the possible effects due to the nonuniform field and charge distribution along the channel of the device, to calculate the drain current of FeMFET. By using the relevant material parameters close to the (Bi, La)4Ti3O12 (BLT) system, accurate analyses on the capacitors and FeMFET's at various applied biases are made. We also address the issues of depolarization field and retention time about such a device.