查看更多>>摘要：Resonant structure consisting of waveguide layer with metallic strips array is a promising design for various optical effects control and enhancement at the nanoscale due to its strong resonant properties and light localization phenomena. However, different applications require understanding the nature of eigenmodes of the structure, that possess peculiar properties. In this research, the optical properties of the planar waveguide with one-dimensional periodic gold grating on it was examined. Emitting layer of a-Si1-xCx:H was deposited by plasma chemical vapour deposition technique and the gold array was created by the e-beam lithography. Angle-resolved reflection and photoluminescence spectra in s- and p-polarizations were measured by the Fourier-imaging spectroscopy method. The theoretical analysis was performed to reveal the physical nature of the observed spectral features and their effect on the waveguide layer emitting properties was studied.
查看更多>>摘要：Dual-wavelength Q-switched lasers have currently received extensive attention due to their wide applications in nonlinear optoelectronic devices. Their main mechanism can be based on the integration of laser with devices such as dual defective photonic crystals (DPCs). Nonetheless, DPCs with a high modulation depth is still demanding in this field. Toward this goal, in this paper, we have designed a dual DPC with MoS2 monolayers as defects in this structure. Defect modes helped adjust the wavelength by the distance between the two defects, and finally, a tunable wavelength was created by changing the intensity, incident angle, and polarization. Using the dual DPC, modulation depth was increased to 97% and 85% in the dual defect modes and a wide range of light intensities was achieved with over 80% of absorption, which helps accomplish a tunable dual Q-switching operation.
查看更多>>摘要：Graphene and other 2D materials have attracted many scientific communities due to excellent performance in the area of SPR biosensor. In this paper, we propose SPR biosensors for the detection of ssDNA using hybrid structure of different 2D materials in Kretschmann configuration. Further, we compare eight different types of configurations using silver (Ag), graphene, gold (Au) and transition metal dichalcogenides (TMDCs) in terms of various sensing performance parameters such as sensitivity (S), detection accuracy (D. A) and quality factor (Q. F). The schematic study of different configurations indicates that introduction of graphene, WS2 and MoS2 increase the sensing performances as compare to the conventional SPR biosensor. In our proposed structures, maximum sensitivity occurs for monolayer graphene, bilayer WS2 and monolayer MoS2 combination. In this case, maximum obtained sensitivity is 203 deg./RIU with detection accuracy 1.13 and quality factor 28.31 RIU?1. This analysis shows that heterostructure SPR biosensor with sandwiched graphene layer, consisting of bimetallic layers of TMDCs, enhances the sensing performance as compare to the other reported works which comprised of graphene and 2D materials. Therefore, our proposed SPR biosensor may have potential applications in medical diagnostic for biochemical detection and open a new dimension in the field of biosensing.
查看更多>>摘要：We propose an asymmetric distribution of a hexagonal lattice for achieving near-zero group velocity with negative group delay. This study reports the effect of the continuous geometric perturbation on the photonic band diagram and consequently its impact on phase velocity, group velocity, and effective refractive index. We provide a promising method for modifying the photonic band diagram to obtain an exotic dispersion diagram. With this broadband spanning from the E band to the L band, the light pulse envelope travels with almost zero velocity and is promising for application in a wide variety of light-based devices.
查看更多>>摘要：We numerically calculated multi-octave spanning supercontinuum generation (SCG) in two proposed As2Se3 photonic crystal fibers (PCFs) with low input peak powers and highly coherent characteristics with the effects of vacuum noise and pulse-to-pulse relative intensity noise. The first PCF with a lattice constant (Λ) of 1.5 μm and core diameter (dcore) of 5.48 μm has the flat all-normal dispersion in the wavelength range of 2–10 μm. For the input peak power of 5 kW, this fiber generates the all-normal dispersion SCG with a spectral bandwidth of 1.85–5.7 μm with pump wavelength at 3.5 μm, and two octave-spanning of 1.9–7.6 μm with pump wavelength at 5.5 μm. The second PCF with Λ of 1.52 μm and dcore of 7.3 μm has flat dispersion and two zero-dispersion wavelengths at 4.3 μm and 7.8 μm. By launching the input peak power of 7.5 kW, and pump wavelength at 3.5 μm, the second PCF generates the broad SCG with a spectral bandwidth of 2–10 μm. The SCG in two proposed PCFs has high coherence due to the effects of vacuum noise. However, the results of our works point out that pulse-to-pulse relative intensity noise significantly decreases the coherence. The amount of coherence reduction depends on the pulse duration and the physical mechanism for spectral broadening in which a part of the supercontinuum spectrum induced by optical wave breaking and dispersive wave experiences a remarkable reduction of coherence due to the effects of pulse-to-pulse relative intensity noise.
查看更多>>摘要：The need for optically multi-functional micro- and nano-structures is growing in various fields. Designing such structures is impeded by the lack of computationally low-cost algorithms. In this study, we present a hybrid design scheme, which relies on a deep learning model and the local search optimization algorithm, to optimize a diffractive optical element that performs spectral splitting and spatial concentration of broadband light for solar cells. Using generated data set during optimization of a diffractive optical element, which is a one-time effort, we design topography of diffractive optical elements by using a deep learning-based inverse design scheme. We show that further iterative optimization of the reconstructed diffractive optical elements increases amount of spatially concentrated and spectrally split light. Our joint design approach both speeds up optimization of diffractive optical elements as well as providing better performance at least 57% excess light concentration with spectral splitting. The algorithm that we develop here will enable advanced and efficient design of multi-functional phase plates in various fields besides the application that we target in solar energy. The algorithm that we develop is openly available to contribute to other applications that rely on phase plates.
查看更多>>摘要：Ultra-high field MRI head coils present a characteristic B1+ magnetic field distribution resulting in inhomogeneous signal and contrast over the image, affecting relevant regions of interest such as the temporal lobes of the brain and the cerebellum. This is a consequence of the spatially varying flip angle distribution attributed to the reduction of the electromagnetic wavelength inside the human tissues. Without radical changes in the experimental setup, this problem has been effectively targeted by different passive RF shimming approaches such as high permittivity dielectric pads or metamaterials. The latter, however, may potentially decrease the B1+ field in other relevant areas or compromise the patient's comfort. Here, we present a novel approach based on meander dipoles inspired from Hilbert fractals. The structures were designed and studied numerically using finite element simulations. Prototypes of the structures were printed and tested with a 1Tx/32Rx birdcage head coil on a 7 T MR scanner. We demonstrate a new device based on compact, thin and flexible design, able to improve the B1+ field over each temporal lobe without deterioration of the RF performances in other brain areas and with minimal impact on patient comfort.
查看更多>>摘要：In recent years metamaterial-inspired resonators, due to the ability to form desired near field patterns at subwavelength scale, have found application in various practical fields, i.e., magnetic resonance imaging or wireless power transfer. This paper proposes an approach for controlling the near electromagnetic field distribution inside the volumetric metamaterial-inspired structure based on a set of split-ring resonators or materials with high permittivity. We numerically and experimentally demonstrate how to precisely manipulate the near-field pattern's uniformity by changing the number of resonant elements while maintaining the geometric dimensions of the structure. The effectiveness of the concept was also verified via a magnetic resonance imaging study. The optimized volumetric metamaterial-inspired resonator showed an increase in transmit efficiency and receive performance of the large body coil compared to the commercial dedicated radiofrequency coil.
查看更多>>摘要：Highly photoluminescent organic crystals are the cornerstone of organic optoelectronics and photonics. Here we report on rational design of new organic crystal based on 2-amino-4-oxobut-2-enoic acid. An ability to tune the structure of the acid during the synthesis allows obtaining a series of organic crystals with high structural rigidity at ambient conditions. The crystals also demonstrate a chemically driven efficiency and a shape of red photoemission, allowing us to tune their functionalities. Moreover, scaling of the crystals from a single microcrystal to large-scale thin films retains the PL properties, thus makes it possible to utilize them as active nano and macro components in optoelectronics.
查看更多>>摘要：The need for optically multi-functional micro- and nano-structures is growing in various fields. Designing such structures is impeded by the lack of computationally low-cost algorithms. In this study, we present a hybrid design scheme, which relies on a deep learning model and the local search optimization algorithm, to optimize a diffractive optical element that performs spectral splitting and spatial concentration of broadband light for solar cells. Using generated data set during optimization of a diffractive optical element, which is a one-time effort, we design topography of diffractive optical elements by using a deep learning-based inverse design scheme. We show that further iterative optimization of the reconstructed diffractive optical elements increases amount of spatially concentrated and spectrally split light. Our joint design approach both speeds up optimization of diffractive optical elements as well as providing better performance at least 57% excess light concentration with spectral splitting. The algorithm that we develop here will enable advanced and efficient design of multifunctional phase plates in various fields besides the application that we target in solar energy. The algorithm that we develop is openly available to contribute to other applications that rely on phase plates.
NSTL
Elsevier