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1.
We introduce a new model of one-dimensional (1D) photonic crystal composed of alternately arranged RHM and LHM layers with positive and negative refractive indices respectively, for which the transmission spectra of the model are calculated numerically with the transfer matrix method, and the bandgap structure and the polarization properties are analyzed. We found that the introduction of negative refractive index layers (i.e. LHM medium layers) gives rise to some peculiar band-gap structure and polarization properties as follows. Firstly, the forbidden bands are extremely wide and the transmission bands are very sharp without oscillation;and secondly, the change of incident angle has different influences on the forbidden bands of TE and TM modes. For the TM mode, the forbidden band width decreases substantially and finally vanishes, and for the TE mode with central wavelength, the total reflection happens at anv incident anale.  相似文献   

2.
In this paper, we propose a silicon-based high-speed plasmonic modulator. The modulator has a double-layer structure with a 16 μm long metal-dielectric-metal plasmonic waveguide at the upper layer and two silicon single-mode waveguides at the bottom layer. The upper-layer plasmonic waveguide acts as a phase shifter and has a dielectric slot that is 30 nm wide. Two taper structures that have gradually varied widths are introduced at the bottom layer to convert the photonic mode into plasmonic-slot mode with improved coupling efficiency. For a modulator with two 1 μm-long mode couplers, simulation shows that there is an insertion loss of less than 11 dB and a half-wave voltage of 3.65 V. The modulation bandwidth of the proposed modulator can be more than 100 GHz without the carrier effect being a limiting factor in silicon. The fabrication process is also discussed, and the proposed design is shown to be feasible with a hybrid of CMOS and polymer technology.  相似文献   

3.
A large-scale antenna system(LSAS) with digital beamforming is expected to significantly increase energy efficiency(EE) and spectral efficiency(SE) in a wireless communication system. However, there are many challenging issues related to calibration, energy consumption, and cost in implementing a digital beamforming structure in an LSAS. In a practical LSAS deployment, hybrid digital-analog beamforming structures with active antennas can be used. In this paper, we investigate the optimal antenna configuration in an N × M beamforming structure, where N is the number of transceivers, M is the number of active antennas per transceiver, where analog beamforming is introduced for individual transceivers and digital beamforming is introduced across all N transceivers. We analyze the green point, which is the point of maximum EE on the EE-SE curve, and show that the log-scale EE scales linearly with SE along a slope of-lg2/N. We investigate the effect of M on EE for a given SE value in the case of fixed NM and independent N and M. In both cases, there is a unique optimal M that results in optimal EE. In the case of independent N and M, there is no optimal(N, M) combination for optimizing EE. The results of numerical simulations are provided, and these results support our analysis.  相似文献   

4.
In order to compensate the dispersion accumulated in a single mode fiber (SMF) for higher communication capacity, a simplified dispersion-compensation microstructure fiber (DC-MSF) with seven cores is proposed in this paper. The fiber’s cladding is made of pure silica without air holes, and its outer cores are composed of six germanium up-doped cylinders, which has the advantage of simple structure. The finite element method (FEM) and beam propagation method (BPM) are used to study the properties of the fiber, and the relationship between the structural parameters of the fiber and the dispersion, as well as the phase matching wavelength, is obtained. By optimizing the structural parameters of the fiber, the dispersion of the fiber can reach −5 291.47 ps.nm-1.km-1 at 1 550 nm, and the coupling loss to the conventional single-mode fiber is only 0.137 dB. Compared with the conventional dispersion-compensation fiber, the fiber has lots of advantages, such as single mode transmission, easy to fabricate and low coupling loss with traditional SMF, etc.  相似文献   

5.
Two kinds of compact electromagnetic band gap (EBG) structures are designed. A two layer compact EBG structure configured with cross spiral shape line inductors and interdigital capacitors is first presented. Because of its significantly enlarged equivalent inductor and capacitance, the period of the lattice is approximately 4.5% of the free space wavelength. By insetting several narrow slits in the ground plane, the bandwidth of the main bandgap is enhanced by nearly 19%. Further effort has been made for designing a three layer compact EBG structure. Simulation results show that its period is reduced by about 26% compared to that of proposed two layer EBG structure, and the bandwidth of the main bandgap is about 3 times as that of the proposed two layer EBG structure. The detailed designs including a two layer compact 3×7 EBG array with and without defect ground plane and the three layer EBG array are given and simulation results are presented.  相似文献   

6.
ZnTe/ZnTe:Cu layer is used as a complex back contact.The parmeters of CdTe solar cells with and without the complex back contacts are compared.The effects of un-doped layer thickness,doped concentration and post-deposition annealing temperature of the complex layer on solar cells preformance are investigated.The results show that ZnTe/ZnTe:Cu layer can improve back contacts and largely increase the conversion efficiency of CdTe solar cells.Un-doped layer and post-deposition annealing of high temperature can increase open voltage.Using the complex back contact,a small CdTe cell with fill factor of 73.14% and conversion efficiency of 12.93% is obtained.  相似文献   

7.
The various mode effective indices of the doped photonic crystal fibers (PCFs) are compared, the mode field distributions of the fundamental mode and the second-order mode are analyzed, and the single-mode condition is presented. The mode effective indices of large-core doped PCFs with different core indices and structure parameters are simulated by the finite element method (FEM). The relations of the core index with the fiber structure parameters of pitch, hole-to-pitch ratio and core diameter are obtained for single-mode propagation. In the design and fabrication of the doped PCF, we can adjust the core index and fiber structure parameters to achieve large mode area and single-mode propagation.  相似文献   

8.
戈勤  刘新宇  郑英奎  叶川 《半导体学报》2014,35(12):125004-5
A flat gain two-stage MMIC power amplifier with a 2.8 GHz bandwidth is successfully developed for X band frequency application based on a fully integrated micro-strip Al Ga N/Ga N HEMT technology on a semiinsulating Si C substrate. Designed with a binary-cluster matching structure integrated with RC networks and LRC networks, the developed power MMIC gets a very flat small signal gain of 15 d B with a gain ripple of 0.35 d B over 9.1–11.9 GHz at the drain bias of 20 V. These RC networks are very easy to improve the stability of used Ga N HEMTs with tolerance to the MMIC technology. Inside the frequency range of 9–11.2 GHz where the measurement system calibrated, the amplifier delivers a pulsed output power of 39 d Bm and an associated power added efficiency of about 20% at 28 V without saturation, as the available RF power is limited.  相似文献   

9.
Room-temperature spectral characteristics of light-emitting diodes that are based on double InAsSbP/InAs heterostructures with an active InAs layer and a cavity formed by a wide anode contact and the structure surface and that emit near 3.3 μm are considered. The far-field pattern and the mode structure of light-emitting diodes 7.5–45 μm thick are reported, as well as the dependences of the mode position on the pump current. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 38, No. 10, 2004, pp. 1270–1274. Original Russian Text Copyright ? 2004 by Zotova, Il’inskaya, Karandashev, Matveev, Remennyi, Stus’, Shustov.  相似文献   

10.
The paper proposed an improved Ordered Successive Interference Cancellation (OSIC) detection scheme for V-BLAST systems with square/rectangular Quadrature Amplitude Modulation (QAM) modulation. It utilizes an equivalent real-valued vector expression of relationship between transmit signals and received signals, exploits the constellation's product-form structure and can eventually make the order, in which components of the transmit signals vector are extracted, more "optimal" in some sense. Thereby, it can offer an improved error probability as compared to the conventional OSIC detection scheme. In addition, the paper also proposes an efficient projection algorithm to calculate nulling vectors in a simple recursive fashion in order to avoid the vast increase of complexity, which is due to the fact that the original complex N- dimensional data vector and M × N channel matrix are transformed into a real 2N- dimensional data vector and a real 2M × 2N channel matrix respectively. A scrutinous complexity analysis shows that the complexity increases by only 33% as compared to the conventional scheme.  相似文献   

11.
一个含有M×N个细胞的反馈型细胞神经网络可以等效成一个非反馈连接网络;这一非反馈连接网络含有2M×N个细胞、具有似镜象结构邻域和空间可变权重模板、输入权重模板为零。本文给出了反馈型细胞神经网络的稳定性定理,以及在似镜象结构邻域下的变换形式。  相似文献   

12.
In 2D resistive sensor arrays, the interconnections are reduced considerably by sharing rows and columns among various sensor elements in such a way that one end of each sensor is connected to a row node and other end connected to a column node. This scheme results in total N?+?M interconnections for N?×?M array of sensors. Thus, it simplifies the interconnect complexity but suffers from the crosstalk problem among its elements. We experimentally demonstrate that this problem can be overcome by putting all the row nodes at virtually equal potential using virtual ground of high gain operational amplifiers in negative feedback. Although it requires large number of opamps, it solves the crosstalk problem to a large extent. Additionally, we get the response of all the sensors lying in a column simultaneously, resulting in a faster scanning capability. By performing lock-in-amplifier based measurements on a light dependent resistor at a randomly selected location in a 4?×?4 array of otherwise fixed valued resistors, we have shown that the technique can provide 86?dB crosstalk suppression even with a simple opamp. Finally, we demonstrate the circuit implementation of this technique for a 16?×?16 imaging array of light dependent resistors.  相似文献   

13.
This paper proposes a method for estimating the direction of arrival (DOA) of multiple source signals for an underdetermined situation, where the number of sources N exceeds the number of sensors M (M < N). Some DOA estimation methods have already been proposed for underdetermined cases. However, since most of them restrict their microphone array arrangements, their DOA estimation ability is limited to a 2-dimensional plane. To deal with an underdetermined case where sources are distributed arbitrarily, we propose a method that can employ a 2- or 3-dimensional sensor array. Our new method employs the source sparseness assumption to handle an underdetermined case. Our formulation with the sensor coordinate vectors allows us to employ arbitrarily arranged sensors easily. We obtained promising experimental results for 2-dimensionally distributed sensors and sources 3×4, 3×5 (#sensors × #speech sources), and for 3-dimensional case with 4×5 in a room (reverberation time (RT) of 120 ms). We also investigate the DOA estimation performance under several reverberant conditions.  相似文献   

14.
Film detectors on the edge of a Ti or Mo/Cu (T c ≈ 0.4 K) superconductor transition are included in an N × M 2D array of planar polarization-separated antennas. The detectors are simultaneously sensors and absorbers of the total electric power from an antenna and bias circuits. The detectors are heat-insulated because of weak electron-phonon interaction with the substrate and because of the effect of the Andreev reflection of electrons in Nb electrodes. Readout based on the projection method necessitates only N + M channels in the case when the signal is continuously accumulated for all N × M detectors. Simulation of a 3 × 3 2D array at a frequency of 600 GHz shows that the matching band is ~30%.  相似文献   

15.
A low-cost method with high yield and good performance is presented by pHEMTs (pseudomorphic high electron mobility transistors) to be used in phase shifter switches. In this method, the capacitor in “off” mode (Coff) of transistor is reduced, without variation of the transistor structure. The transistor structure in switch mode can be optimised. This method increases the transistor isolation in turn “off” mode, while there is no change in resistance of the transistor in “on” mode (Ron). Transistor dimension is determined in turn “off” mode (Vg = ?4.5 V) and standard form of 4 × 75 μm. So, in this method, insertion loss will be reduced without a perceptible change in transistor dimension. Thus, design and fabrication capability of some circuits such as phase shifters, antenna switches, SPDT (single port double throw) – without any change in technology – are increasing. In this paper, post layout and measurement result for a sample block of phase shifter are shown.  相似文献   

16.
The photovoltaic performance and optoelectronic properties of a donor–acceptor copolymer are reported based on indacenodithienothiophene (IDTT) and 2,3‐bis(3‐(octyloxy)phenyl)quinoxaline moieties (PIDTTQ) as a function of the number‐average molecular weight (Mn). Current–voltage measurements and photoinduced charge carrier extraction by linear increasing voltage (photo‐CELIV) reveal improved charge generation and charge transport properties in these high band gap systems with increasing Mn, while polymers with low molecular weight suffer from diminished charge carrier extraction because of low mobility–lifetime (μτ) product. By combining Fourier‐transform photocurrent spectroscopy (FTPS) with electroluminscence spectroscopy, it is demonstrate that increasing Mn reduces the nonradiative recombination losses. Solar cells based on PIDTTQ with Mn = 58 kD feature a power conversion efficiency of 6.0% and a charge carrier mobility of 2.1 × 10?4 cm2 V?1 s?1 when doctor bladed in air, without the need for thermal treatment. This study exhibits the strong correlations between polymer fractionation and its optoelectronics characteristics, which informs the polymer design rules toward highly efficient organic solar cells.  相似文献   

17.
Based on the framework of Colpitts oscillator, a four-dimensional multi-scroll hyperchaotic system is proposed, which generates (2M+1)×(2N+1)-scroll chaotic and hyperchaotic attractors. The key strategy is to increase the number of index-2 equilibrium points by introducing two unit saw-tooth functions to extend and modify the Colpitts oscillator model. By using bifurcation diagram and phase portrait, the dynamical characteristics of the multi-scroll hyperchaotic system are briefly studied. Moreover, micro-controller based circuit realization is introduced and the experimental results demonstrate that 7×5-scroll chaotic and hyperchaotic attractors can be obtained in the digital circuit.  相似文献   

18.
We present new stilbazolium salt DSTMS (4‐N,N‐dimethylamino‐4′‐N′‐methyl‐stilbazolium 2,4,6‐trimethylbenzenesulfonate) with both high second‐order nonlinear optical properties and very favorable crystal growth characteristics. We are able to obtain very large area bulk single crystals of more than 3 × 3 × 0.2 cm3 with a high optical quality without using seed crystals by using low‐temperature solution growth. We also demonstrate the growth of single crystalline thin films of DSTMS with an area of up to 6 × 5 mm2 and a thickness between 5–30 μm. Nonlinear optical measurements reveal that DSTMS possesses large nonlinear optical susceptibilities with χ111(2) = (430 ± 40) pm V–1 at 1.9 μm. Highly efficient generation of broadband THz waves with THz electric field strengths of more than 4 kV cm–1 using 160 fs laser pump pulses at a wavelength λ = 1.45 μm and DSTMS crystals has been demonstrated.  相似文献   

19.
The surface modification of divinylbenzene (DVB)‐based microspheres is performed via a combination of reversible addition fragmentation chain transfer (RAFT) polymerization and rapid hetero‐Diels–Alder (HDA) chemistry with the aim of quantifying the grafting densities achieved using this “grafting‐to” method. Two variants of the RAFT‐HDA concept are employed to achieve the functionalization of the microspheres. In the first approach, the microspheres are functionalized with a highly reactive diene, i.e., cyclopentadiene, and are subsequently reacted with polystyrene chains (number‐averaged molecular weight, Mn = 4200 g mol?1; polydispersity index, PDI = 1.12.) that carry a thiocarbonyl moiety functioning as a dienophile. The functionalization of the microspheres is achieved rapidly under ambient conditions, without the aid of an external catalyst. The surface grafting densities obtained are close to 1.2 × 1020 chains per gram of microspheres. In the second approach, the functionalization proceeds via the double bonds inherently available on the microspheres, which are reacted with poly(isobornyl acrylate) chains carrying a highly dienophilic thiocarbonyl functionality; two molecular weights (Mn = 6000 g mol?1, PDI = 1.25; Mn = 26 000 g mol?1, PDI = 1.26) are used. Due to the less reactive nature of the dienes in the second approach, functionalization is carried out at elevated temperatures (T = 60 °C) yet in the absence of a catalyst. In this case the surface grafting density is close to 7 chains nm?2 for Mn = 6000 g mol?1 and 4 chains nm?2 for Mn = 26 000 g mol?1, or 2.82 × 1019 and 1.38 × 1019 chains g?1, respectively. The characterization of the microspheres at various functionalization stages is performed via elemental analysis for the quantification of the grafting densities and attenuated total reflectance (ATR) IR spectroscopy as well as confocal microscopy for the analysis of the surface chemistry.  相似文献   

20.
Molecularly imprinted polymers (MIPs) are generic alternatives to antibodies in sensors, diagnostics, and separations. To displace biomolecules without radical changes in infrastructure in device manufacture, MIPs should share their characteristics (solubility, size, specificity and affinity, localized binding domain) whilst maintaining the advantages of MIPs (low‐cost, short development time, and high stability) hence the interest in MIP nanoparticles. Herein, a reusable solid‐phase template approach is reported (fully compatible with automation) for the synthesis of MIP nanoparticles and their precise manufacture using a prototype automated UV photochemical reactor. Batches of nanoparticles (30–400 nm) with narrow size distributions imprinted with: melamine (d = 60 nm, Kd = 6.3 × 10?8 M ), vancomycin (d = 250 nm, Kd = 3.4 × 10?9 M ), a peptide (d = 350 nm, Kd = 4.8 × 10?8 M ) and proteins have been produced. The instrument uses a column packed with glass beads, bearing the template. Process parameters are under computer control, requiring minimal manual intervention. For the first time, the reliable re‐use of molecular templates is demonstrated in the synthesis of MIPs (≥30 batches of nanoMIPs without loss of performance). NanoMIPs are produced template‐free and the solid‐phase acts both as template and affinity separation medium.  相似文献   

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