By analyzing the principle of dual-pump parametric amplification and the polarization dependent gain of fiber optical parametric amplifier (FOPA), a polarization-insensitive FOPA based on polarization-diversity technique with dual parallel pumps is presented. The performances of polarization-insensitivity, gain and BER are theoretically analyzed and numerically simulated by comparing the proposed scheme with parallel pump solution and orthogonal pump solution. The presented solution can reduce the complexity of state of polarization (SoP) of pumps.
We report the enhanced performance of organic solar cells (OSCs) based on regioregular poly(3-hexylthiophene) (P3HT) and methanofullerene [6,6]-phenyl C61-butyric acid methyl ester (PCBM) blend by using dihydroxybenzene as additive in the active layer. The effect of the content of the additives on electrical characteristics of the device is studied. The device with 0.2 wt% dihydroxybenzene additive achieves the best power conversion efficiency (PCE) of 4.58% with Jsc of 12.5 mA/cm2, Voc of 0.65 V, and FF of 66.6% under simulated solar illumination of AM 1.5G (100 mW/cm2), compared with the control device with PCE of 3.39% (35% improvement compared with the control device). The XRD measurement reveals that the addition of additives induces the crystallization of P3HT and establishes good inter-network to increase the contact area of donor and acceptor, and then helps charge to be effectively transferred to the electrode to reduce the chance of recombination. All evidences indicate that the dihydroxybenzene is likely to be a promising new type additive that can enhance the performance of organic bulk heterojunction solar cells.
Thin alloy films of palladium (Pd) and silver (Ag) are deposited onto glass substrates via the direct current (DC) magnetron technique. The hydrogen sensor probe consists of optical fiber bundle and Pd/Ag optical thin film. When the sensor is exposed to hydrogen, the refractive index of Pd/Ag optical thin layer will diminish and cause attenuation changes of the reflective light. It is observed that the thickness of Pd/Ag alloy layer can affect the hydrogen sensor signal. Under different substrate temperatures, several Pd/Ag samples are coated with different thicknesses of Pd/Ag alloy, and the results of a hydrogen sensor based on reflective light from the Pd/Ag alloy thin film are discussed.
We propose a novel optical polarizer based on an asymmetric dual-core photonic crystal fiber (PCF) with triangular lattice air-holes. The fiber is designed as that the effective indices of modes in the two cores are matched at one polarized state but mismatched at another polarized state. As a result, one of the polarization states is coupled to the other core and transferred into a high-order mode. The transmission properties of the polarizer are investigated by the semi-vectorial beam propagation method (SV-BPM). Numerical results demonstrate that a device length of 11.3 mm shows extinction ratio as low as −20 dB with bandwidth as great as 80 nm ranging from 1.51 m to 1.59 m.
The performance of broadband polarizing beam splitters (PBSs) is sensitive to the incident angle. By taking account of the spectrum of the laser source and using the needle optimization method, a large acceptance angle PBS for laser-based displays is designed. The average degrees of polarization in transmission and reflection can reach 0.989 and 0.980 for an acceptance angle of 13.6° in air using two materials, while better results of 0.993 and 0.989 for an acceptance angle of 14.8° in air are attained when three common materials are used. Both designs consist of 40 layers.
In order to study the dark current characteristics in a quantum wire infrared photodetector (QRIP), the average number of electrons in quantum wires (QRs) must be got, which is mostly too complicated. In this paper we give a simple formula to calculate the average number of carriers in a quantum wire (QR) that can be easily evaluated by mathematical softwares, and then we use this formula to study dark current characteristics of a quantum wire infrared photodetector (QRIP).
The proton implantation is one of key procedures to confine the current diffusion in vertical cavity surface emitting lasers (VCSELs), in which the proton implanted depth and profile are main parameters. Threshold characteristics of VCSELs with various proton implanted depths are studied after optical, electrical and thermal fields have been simulated self-consistently in three dimensions. It is found that for VCSELs with confinement radius of 2 μm, increasing proton implanted depth can reduce the injected current threshold power and enhance the laser temperature in active region. Numerical results also indicate that there are optimal values for current aperture in proton implanted VCSELs. The minimum injected current threshold can be achieved in VCSELs with proton implantation near the active region and confinement radius of 1.5 μm, while the VCSELs with proton implantation in the middle of p-type distributed Bragg reflectors (DBRs) and confinement radius of 2.5 μm can realize the minimum temperature.
We demonstrate a novel SOI-based photonic crystal (PC) double-heterostructure slot waveguide microcavity constructed by cascading three PC slot waveguides with different slot widths, and simulate the luminescence enhancement of sol-gel Erdoped SiO2 filled in the microcavity by finite-difference time-domain (FDTD) method. The calculated results indicate that a unique sharp resonant peak dominates in the spectrum at the expected telecommunication wavelength of 1.5509 μm, with very high normalized peak intensity of ∼108. The electromagnetic field of the resonant mode exhibits the strongest in the microcavity, and decays rapidly to zero along both sides, which means that the resonant mode field is well confined in the microcavity. The simulation results fully verify the enhancement of luminescence by PC double-heterostructure slot waveguide microcavity theoretically, which is a promising way to realize the high-efficiency luminescence of Si-based materials.
The influence of thermal stress on the temperature sensitivity of fiber Bragg grating-glass fiber reinforce polymer (FBGGFRP) bars is studied by three methods, namely, direct experimental calibration method, stress analysis (finite element analysis) method and the method of apparent temperature sensitivity coefficient. In comparison with the other two methods, fewer parameters are required and the calculation is simple in the method of apparent temperature sensitivity coefficient, while the analytical error is limited within 2%. It is concluded that the results of the method of apparent temperature sensitivity coefficient could be good reference for engineering applications.
AlN films with preferred c-axis orientation are deposited on Si substrates using the radio frequency (RF) magnetron sputtering method. The post-processing is carried out under the cooling conditions including high vacuum, low vacuum under deposition gas ambient and low vacuum under dynamic N2 ambient. Structures and morphologies of the films are analyzed by X-ray diffraction (XRD) and atomic force microscopy (AFM). The hardness and Young’s modulus are investigated by the nanoindenter. The experimental results indicate that the (100) and (110) peak intensities decrease in the XRD spectra and the root-mean-square of roughness (Rrms) of the film decreases gradually with the increase of the cooling rate. The maximum values of the hardness and Young’s modulus are obtained by cooling in low vacuum under deposition gas ambient. The reason for orientation variation of the films is explained from the perspective of the Al-N bond formation.
When the electromagnetic wave propagates through a slab superconducting material in microwave ranges, tunneling properties of the electromagnetic wave at critical temperature are investigated theoretically. The transmittance and the reflectance of the slab superconducting material vary with the thickness of material as well as the refractive index of substrates. The high transmittance is found for thin superconductor at low wavelength region. However, optical properties are strongly dependent upon temperature and incidence wavelength. The electromagnetic wave is totally transmitted without loss for incidence wavelength (λ = 5000 nm) due to the zero refractive index and infinite penetration depth of the superconductor at the critical temperature.
The band characteristics of two-dimensional (2D) lead lanthanum zirconate titanate (PLZT) photonic crystals are analyzed by finite element method. The electro-optic effect of PLZT can cause the refractive index change when it is imposed by the applied electric field, and the band structure of 2D photonic crystals based on PLZT varies accordingly. The effect of the applied electric field on the structural characteristics of the first and second band gaps in 2D PLZT photonic crystals is analyzed in detail. And the results show that for each band gap, the variations of start wavelength, cut-off wavelength and bandwidth are proportional to quadratic of the electric field.
By citrate sol-gel auto-combustion method, the nanophase M-type planar hexagonal ferrite is prepared. The transmission electron microscopy (TEM), X-ray diffraction (XRD) and thermal analysis are used to study the grain size, phase composition, microstructure and crystallization process. The results show that the nanophase M-type Sr-ferrite prepared by this method is single, and its grain size is smaller than 100 nm. Moreover, most of the grains present hexagonal sheet shape. Tests are carried out for its attenuation to 1.06 μm laser. It is found that the extinction capability of the nanophase M-type Sr-ferrite smoke is good, and its mass extinction coefficient is 1.628 m2/g.
In order to reduce the noises affixed to the signals when testing high frequency devices, a single-port test mode (S11) is used to test frequency response of high frequency (GHz) and dual-port surface acoustic wave devices (SAWDs) in this paper. The feasibility of the test is proved by simulating the Fabry-Perot model. The frequency response of the high-frequency dual-port resonant-type diamond SAWD is measured by S11 and the dual-port test mode (S21), respectively. The results show that the quality factor of the device is 51.29 and the 3 dB bandwidth is 27.8 MHz by S11-mode measurement, which is better than the S21 mode, and is consistent with the frequency response curve by simulation.
A precise measurement of the applanated diameter of the ocular cornea with the optical probe is very important in applanation tonometry. A novel optical probe with a common path configuration is presented. The optical probe mainly consists of a cone-shaped prism and a photodetector. The former serves as a measuring body touching the ocular cornea to shape the area to be measured, and the latter converts the quantity of the luminous flux returning from the cone-shaped prism into one electronic current signal. Laboratory experiments are carried out on a simulated eyeball, followed by an enucleated porcine eyeball specimen. Experimental results show that there is a significant rise of the normalized variational current with increasing the applanation diameter of the ocular cornea, and the sensitivity is 0.2111/mm with an error of 0.00263/mm. Measurements of the normalized variational current on the porcine eyeball have good agreement with those on the simulated eyeball.
To shun the vortex hazard, the airport wake vortex monitoring system based on 1.5-μm pulsed coherent Doppler lidar is designed successfully in this paper. Based on the realistic analytical model, the wake vortex generated by airbus A340 under typical flight condition is simulated. Then the principle of airport wake vortex monitoring is introduced, and the work flow of the monitoring system is also presented. Moreover, based on the mechanism of vortex coherent detection and typical system parameters, both detection SNR and detection precision are obtained through numerical simulations. When the system outputs 2 J energy, the coherent detection SNR at 10 km distance is up to 23.452, and detection precision can reach 0.328 m/s. With the wake vortex monitoring experiment of A340, some vortex parameters are estimated. Due to these results comparatively coinciding with the previous simulation conclusions, the ability of Doppler lidar for full-scale wake vortex characterization and real time measurement is demonstrated. The study shows that the wake vortex detection based on 1.5-μm pulsed coherent Doppler lidar has the advantages of high accuracy and far distance, and the designed airport wake vortex monitoring system has proved to be effective and feasible, which has significant development and application prospect in the aspect of assuring flight security and increasing airport capacity.
A scheme is presented to realize the controlled teleportation of an unknown three dimensional (3D) two-particle state by using a non-maximally entangled two-particle state and a non-maximally entangled three-particle state in the 3D space as the quantum channels, and one of the particles in the channels is used as the controlled particle. Analysis shows that when the quantum channels are of maximal entanglement, namely the channels are composed of a 3D Bell state and a 3D GHZ state, the total success probability of the controlled teleportation can reach 1. And this scheme can be expanded to control the teleportation of an unknown D-dimensional two-particle state.
Based on the coherence theory of diffracted optical field and the model for partially coherent beams, analytical expressions for the cross-spectral density and the irradiance spectral density in the far zone are derived, respectively. Utilizing the theoretical model of radiation from secondary planar sources, the physical conditions for sources generating a cosh-Gaussian (CHG) beam are investigated. Analytical results demonstrate that the parametric conditions strongly depend on the coherence property of sources. When almost coherence property is satisfied in the source plane, the conditions are the same as those for fundamental Gaussian beams; when partial coherence or almost incoherence property is satisfied in the spatial source plane, the conditions are the same as those for Gaussian-Schell model beams. The results also indicate that the variance of cosine parameters has no influence on the conditions. Our results may provide potential applications for some investigations such as the modulations of cosh-Gaussian beams and the designs of source beam parameters.
Under classical mechanics, the general equation of particle motion in the periodic field is derived. In the dampless case, the existence possibility of the higher-order harmonic radiation is explored by using Bessel function expansion of a generalized trigonometrical function and the multi-scale method. In the damping case, the critical properties and a chaotic behavior are discussed by the Melnikov method. The results show that the use of a higher-order harmonic radiation of non-relativistic particles as a short-wavelength laser source is perfectly possible, and the system’s critical condition is related to its parameters. Only by adjusting parameters suitablely, the stable higher-order harmonic radiation with bigger intensity can be obtained.
We investigate theoretically the temperature effects on the evolutions of both bright and dark screening spatial solitons in biased two-photon photorefractive crystals. For a stable bright or dark two-photon screening spatial soliton originally formed in a crystal at a given temperature, when the crystal temperature changes, it will evolve into another stable screening soliton if the temperature change is quite small, while it will become unstable or break down if the temperature change is large enough. The spatial shape of a stable two-photon screening spatial soliton can be changed by appropriately adjusting the crystal temperature.