查看更多>>摘要：Symmetric and asymmetric quantum wells of ZnCdO structures grown on ZnO in non-polar orientations are investigated for their potential in THz emission due to the intersubband transitions between the subbands in the conduction band. The Schro?dinger and Poisson equations are solved self-consistently for the square and step barrier quantum wells of the Zn1-xCdxO layers for x up to 0.25. The results are represented as functions of the Cd concentration in the well and step-barrier layers and their dimensions. The role of the many-body effects on the intersubband transitions is discussed. It is found that emission wavelengths between 4.5 and 8.55 THz in the step-barrier quantum wells are possible in the case of an optical pumping at a wavelength in the range of 8.27-15.7 mu m. The depolarization and excitonic shifts are found to contribute to the bare intersubband transition energies as much as their 15% at maximum.
Kotlyar, Victor V.Stafeev, Sergey S.Nalimov, Anton G.Kotlyar, Maria, V...
9页
查看更多>>摘要：Using e-beam lithography and reactive ion beam etching of a 120 nm amorphous silicon film, we fabricate a 30?m spiral metalens that has a very short focal length that is equal to the incident 633 nm wavelength (numerical aperture about 1) and is composed of 16-sectored subwavelength binary gratings with a 220 nm period. Its unique feature is that the metalens generates a left-hand circularly polarized optical vortex with topological charge 2 when illuminated by a left-hand circularly polarized light but generates a cylindrical second-order vector beam when illuminated by linearly polarized light. Both for linearly and circularly polarized light, an inverse energy flow occurs near the strong focus of the metalens. Transverse near-focus intensity distributions measured with a scanning near-field optical microscope are found to be in qualitative agreement with those obtained via the FDTD-aided numerical simulation. Thus, the near-focus reverse energy flow is experimentally confirmed to occur.
查看更多>>摘要：A three-dimensional electromagnetic field model has been developed to study the photon capture properties of gradient band-gap AlxGa1-xN nanomaterials with built-in electric field using COMSOL Multiphysics commercial software based on finite element numerical simulation. Based on the phototrapping mechanism and the concept of radial mode resonance absorption, we studied AlxGa1-xN nanomaterials with different cross-section shapes and Al component distributions to obtain broad-band and omnidirectional light absorption in the ultraviolet band. In this process, based hexagonal periodic arrangement, we simulated and analyzed the optical responses of cones, hexagonal pyramids and hexagonal prisms structure, including optical absorption, quantum efficiency, electric field distribution and generation rate distribution. The results show that the non-uniform pyramid structure can effectively enhance the optical absorption efficiency at FR = 0.9. The photon generation rate of the pyramid nanostructure is mainly distributed in the cathode nanostructure part, which is significant for improving the emission efficiency of cathode electrons. In addition, we investigated the optical properties of AlxGa1-xN nanostructures by changing the distribution of Al component and the thickness of different sublayers. As a result, the prism structure achieves optimal optical absorption and quantum efficiency when the Al component ranges from 0 to 0.75. Although a strict three-dimensional AlGaN NWAs array model has been established in this work, it is still necessary to demonstrate the experimental results. In the future research, we will experimentally study the effect of different geometric shapes on UV photocathode.
查看更多>>摘要：This work investigates the effect of titanium dioxide (TiO2) nanostructures on the overall optical performance of gallium arsenide (GaAs) solar cells. The optical properties of three different TiO2 nanostructures shapes namely, cubic, spherical, and pyramidal are studied to minimize the reflectivity of GaAs substrates. The dimensions of these three nanoparticle-shapes are varied in the simulations, and the effects of this parameter-variation on the reflectance is investigated. The simulation was carried using the wave optics module in COMSOL Multiphysics (R). The results indicate that the spherical nanoparticle with a radius of 25 nm gives a reduction of the reflectance down to 9.2 % (compared to the 37.2 % of uncoated GaAs). Furthermore, the pyramidal nanoparticle with both width and length of 50 nm has a nearly similar performance achieving a 9.8 % reflectance. However, the cubic nanoparticles with a width of 100 nm achieved the worst optical performance with a reflectance of 28 %.
查看更多>>摘要：In this work we report on a light analysis system based on narrowband colloidal PbS quantum dot photodetectors. The proposed system is able to identify both the peak wavelength of a quasi-monochromatic radiation and the emission spectrum of an arbitrary light source, in the visible and near infrared spectral range, starting from photocurrent measurements of several photoconductive devices with different spectral responses. We demonstrate the feasibility of our approach, optimizing several system parameters and obtaining a mean error of 5 nm and a maximum resolution of 40 nm as regards the peak wavelength identification and the spectral reconstruction, respectively.
查看更多>>摘要：To realize wavelength division multiplexing for high-capacity optical communications, we theoretically investigate the properties of a photonic crystal waveguide structure in which a row of air holes is displaced by a/2 (a is the lattice constant). We calculate transmission loss and coupling efficiency to circular defect cavities of this waveguide structure, which we call an orthogonal lattice waveguide (OLW). The communication bandwidth of the OLW is estimated to be about 20 nm, which is twice that of the conventional line-defect (W1) waveguide. This result indicates that improvements in characteristics of the wavelength division multiplexing are expected by using the OLW instead of W1.
查看更多>>摘要：In this paper, the modified SIMP topology optimization (TO) method was used, to introduce diverse auxetic unit cells with different volume fractions, composing of the symmetric, chiral and re-entrant unit cells. The output results suggested that the geometry of the 2D auxetic structures were extremely dependent on the values of SIMP method parameters, including initial designs and volume fractions. The brilliant modes of deformation in the auxetic structures, whose unit cells are symmetric, are based on either buckling or bending. To validate the TO results, four structures containing symmetric unit cells were chosen, called structure 1, 2, 3 and 4. The auxetic structures were produced by using 3D printing, with TPU as a hyperelastic material as well. Under Compression, the dominating mode of deformation in structures 1 and 2 is based on bending, caused by the movement of the oblique struts between the unit cells. There is also a linear relationship between the vertical and horizontal displacements in structure 1, the structure with 50 % volume fraction and-0.55 Poisson?s ratio value. However, the deformation mechanisms in structures 3 and 4 are based on buckling, called shearing deformation, which is the result of the buckling of the vertical struts between the unit cells.
查看更多>>摘要：A temperature sensor with a wide measurement range and high sensitivity is proposed and analyzed. It is based on a microstructured fiber (MSF) Sagnac interferometer. The air holes were filled with ethanol by a full filling method. Increase of the birefringence and the sensitivity of the proposed sensor can be achieved by moving the two air holes on the left and right sides of the core. For an MSF with air hole diameters D-1 = 0.8 mu m, D-2 = 0.6 mu m, and D-3 = 0.4 mu m, pitch A = 2 mu m, and distance R = 8.2 mu m, when the length of the MSF is 0.274 cm, the simulation results show that the sensitivity of the proposed sensor can reach 14.7 nm/degrees C in the temperature range from 15 to 75 degrees C. This means that the length and sensing range of the MSF have a great influence on the sensitivity of our designed MSF temperature sensor. Because of the advantages of simple structure, high sensitivity, and wide temperature measurement range, the proposed temperature sensor has great application prospects in environmental temperature measurement.
Munshid, Mohammed A.Hassan, HibaAL-Janabi, Abdulhadi
7页
查看更多>>摘要：We report on tellurium nanorods as a new type of saturable absorber (SA)-induced four-wave-mixing to construct an all-fiber multi-wavelength passively Q-switched erbium-doped-fiber laser. This proposed material is prepared via a green method of nanorod synthesis. The results show that the SA device simultaneously generates seven wavelengths within 1592.4?1599.6 nm waveband and mode spacing of 1.2 nm. Meanwhile, the Q-switched operation is attained with the minimum pulse width of 2.85 ?s, maximum repetition rate is 44 kHz and maximum pulse energy of 50 nJ at 275 mW pump power. The number of the generated multi-wavelength lasing lines and the performance of Q-switched pulse fiber lasers have significant value for understanding the dynamics of laser physics and also have potential applications in different fields of photonics such as sensing, optical communication, optical metrology and spectroscopy.
查看更多>>摘要：The design, analysis, and simulation of a 1 x 2 decoder based on self-collimated beams was the aim of this work. The proposed structure consists of two-dimensional (2D) photonic crystals with their silicon rods in air. The device, of a relatively simple structure with a footprint of 228.71 mu m(2), comprises two inputs (I and I-ref) and three outputs (Q1, Q2, and QI). It, furthermore, contains two beam splitters, produced by point defects. 2D Finite Difference Time Domain (FDTD) and Plane Wave Expansion (PWE) codes have been used for the simulation. Contrast ratio of 2.02 dB and a bit rate of 2.8 Tb/s were obtained for this device potential candidate for all-optical digital integrated circuits.
NSTL
Elsevier