Structural colors can be generated by metasurfaces with the capability of spectrum manipulation at subwavelength. In general, the optimization of specific color designs and iterative geometric parameters is computationally time-consuming, so obtaining thousands of different structural colors can be challenging. Deep learning methods offer a new approach to the efficient design of nanophotonic devices, as it revolutionizes the way nanophotonic devices are designed. Here, we trained a deep learning method, which can predict the colors by random geometries in the forward modeling process. The forward design model is good at processing data, which is an effective way to design nanophotonic devices.
Recently, deep learning methods have revolutionized the design of nanophotonic devices, which provides a new
way to efficiently design nanophotonic devices. Here, we demonstrated a deep learning method using attention
mechanisms to inverse design nanophotonic devices, the mean relative error of the predicted value can be as low
as 4.1% or less. Using the encoder part of Transformer, the long sequence of spectral data can be mapped to the
structural parameters of the nanorod hyperbolic metamaterial. The inverse design model based on the attention
mechanisms is good at processing sequence data and can be calculated in parallel, which is an effective way to
design nanophotonic devices.
We propose polarization control system based on graphene-dielectric multilayer stacking arrays and numerically investigate the characteristics of transmission spectrum and phase shift. The results show a high extinction ratio polarizer, and the operating frequency of which can be designed via changing the geometric parameters and Fermi level. In addition, a large phase difference is generated in the x and y directions, and polarization control can be achieved by the superposition of the two modes along the orthogonal directions. The proposed structure demonstrates excellent polarization manipulation capability, ultrathin thickness and flexible control of the operating frequency, providing a good avenue for integration of device in the infrared.
In this paper, we propose dynamically tunable plasmon induced transparency (PIT) in a graphene-based nanoribbon waveguide structure by changing the chemical potential of graphene. It is the direct destructive interference between the propagating plasmonic edge mode in the graphene nanoribbon waveguide and the rectangular resonators gives rise to the PIT effect. Our numerical results reveal that high tunability in the PIT transparency window can be obtained by altering the chemical potential of the graphene rectangular resonators. Moreover, a novel plasmonic refractive index sensor (RIS) has been proposed and investigated numerically based on the PIT effect in the mid-IR range. Our calculated results exhibit that large wavelength sensitivity as high as 2500 nm/RIU and a high figure of merit (FOM) of 10.50 can be achieved in this ultra-compact structure (<0.05 μm2 ). This work not only paves a new way towards the realization of graphene-based integrated nanophotonic devices, but also has important applications in multi-channel-selective filters, sensors, and slow light.
We used bright and dark nanocavities coupled to a metal-insulator-metal waveguide to realize a plasmonic analogue of electromagnetically induced transparency (EIT) in integrated plasmonics. The bright nanocavity is directly coupled to the waveguide, while the dark nanocavity is achieved with the help of evanescent coupling. The numerical simulation shows a typical EIT-like line in the transmission spectrum. Using the model of EIT effect in a three-level atomic system, this phenomenon is well explained. Adding the number of dark nanocavities, we get multiple transparent peaks in the transmission spectrum of plasmon-induced transparency (PIT) effect, and we can realize control of the PIT effect by changing the geometric parameters of the plasmonic structure.
New procedure of designing slotted photonic crystal waveguides (SPCW) is proposed to achieve slow light with improved normalized delay-bandwidth product (NDBP) and low group velocity dispersion, which is suitable for both the W1 defect mode and the slot mode. The lateral symmetry of the waveguide in our study is broken by shifting the air holes periodically along the slot axis . The conversion of the “flat band” from band-up slow light to band-down slow light is achieved for W1 defect mode. The group index curves of W1 mode change from U-like to step-like and the group index of 47, 67 and 130 are obtained with the bandwidth over 7.2, 4.8, and 2.3nm around 1550nm, respectively. We also obtain the group index of 42, 55, and 108 for the slot mode with the bandwidth over 6.2, 5.6, and 2.2nm. Then the low dispersion slow light propagation is numerically demonstrated by the finite-difference time-domain method.
In this paper, we focus on three issues: 1) proposing a novel photonic crystal waveguide based Symmetric-Mach-
Zehnder-type ultrafast all-optical switch using Quantum Dot Semiconductor Optical Amplifier (QD-SOA) and the basic
parameters of the photonic crystal waveguide, 2) simulating the general features of the QD-SOA, 3)performance analysis
of the all-optical switch. We find that the switching contrast ratio of this kind of all-optical switch has been enhanced due
to the superior optical confinement of the photonic crystal waveguide.
Exciton saturation and optical nonlinearities in multiple quantum wells due to many body interactions consisting of phase-space filling and Coulomb screening are investigated. We have made a theoretical model to compare the different effects induced by the two many-body interactions. We focus our calculations on the shift of the exciton absorption resonance at highly excited carrier densities in MQW which can be obtained through femtosecond pump-probe technique. We find that the blue shift of the exciton absorption resonance wavelength caused by the phase-space filling effects is about equivalent to the red shift of Coulomb screening effects in same circular polarization, while in contrary the red shift is much lager than the blue shift in opposite circular polarization. This phenomenon happens within optical switching timescale.
A reconfigurable optical add-drop multiplexer (OADM) based on F-P cavity and piezoelectric translator is proposed. In this structure, the displacement of F-P cavity can be controlled by piezoelectric translator. The OADM can add/drop one of the multi input channels or pass the channel directly by adjusting the electric voltage of the piezoelectric translator. The channel isolation is more than 30dB. Crosstalk, including inter-band crosstalk and intra-band crosstalk, in F-P filter based OADM are analyzed and calculated in this paper.
Exciton saturation and optical nonlinearities caused by phase-space filling(PSF) in InGaAs(P) MQWs are investigated. In-well carrier population under pump beam is calculated as a function of time. Changes in absorption of the two circularly polarized component of the linear polarized test beam resulting from PSF are calculated by the semiconductor nonlinear absorption formula, respectively. The refractive indices of the two circularly polarized component are obtained from the K-K relations. Transient rotation angle of the major axis of the probe polarization is then deduced.
A novel technique is presented in obtaining the performance characteristics of traveling-wave semiconductor optical amplifier (TWA) with tensile-strained-barrier multiple-quantum-well structure. In-out fiber ends of TWA are used to construct an external cavity resonator to produce big ripple on amplified spontaneous emission (ASE) spectrum. By this means, Hakki-Paoli method is adopted to obtain gain and differential gain spectra over a wide spectral range. From measured longitudinal mode spacing and peak wavelength shift due to increased bias current, we further calculate the effective refractive index, carrier-induced refractive index change and linewidth enhancement factor. Some special features about ASE mode spectrum shift and refractive index change above lasing threshold are revealed and explained.
Effective management of computer networks has become a more and more difficult job because of the rapid development of the network systems. Fault identification is to find where is the problem of the network and what is it. Data mining generally refers to the process of extracting models from large stores of data. We can use data mining techniques to help us in the fault identification task. Existing approaches of fault identification are introduced and a new approach of fault identification is proposed. This approach improves MSDD algorithm but it need more computation. So some new techniques are used to increase the efficiency.
Based oii quantum theory and combined with the nonlinear effects of both Stimulated Raman Scattering (SRS) and Simulated FoLirth-photon Mixing (SFPM), the correlation among the pump, the input signal and the output in the Raman amplified fiber-optic transmission systems, is calculated and analyzed. Synthesize the correlation function group and program the corresponding software package. And when the ratio of the pump to the Stocks waves is in a certain field, the correlation is comparatively high, the corresponding input signal amplification multiple ? gets to the extreme field. And when the ratio of the pump to the Stocks waves is oversize or undersize, the correlation is decreasing correspondingly. The conclusion of this letter is benefit to optimize the design and experimental research of Fiber Raman Amplifier (FRA).
In this letter we introduce three typical cw, singly resonant OPO configurations based on PPLN and the different advantages and disadvantages of them. And we also show three different kinds of PPLN's and describe the differences between them.
Thermal lens effect is a very important factor in designing stable resonators for high-power solid-state laser pumped by laser diodes. In a symmetric plane-parallel resonator , if the thermal lens of the laser crystal is close to a thin lens, according to the theory of transfer matrix we can get that there is a critical hollow point where the resonator changes from stable region to unstable state, then back to stable region. So we can measure the ultrashort thermal focal length of high-power solid-state laser based on this fact. We used this method to measure the ultrashort thermal focal length of a 100W magnitude Nd:YAG laser. The experimental results have shown this is a simple and effective technique.
In order to improve the coupling efficiency of semiconductor optical amplifiers to single-mode fibers, a model of tapered-rib semiconductor optical amplifier is presented in this papers. The effects of the refractive index of the waveguide region and the structure of tapered-rib waveguide on the expanded output-mode of tapered-rib waveguide are studied and calculated by using the finite element method. A coupling efficiency of 95% is obtained by optimizing the parameters and the structure of the tapered-rib semiconductor optical amplifier.
Investigation into the behavior characteristics of particle phases in laser cladding WC-TiC-TaC/Co based ceramic-metal composite coating suggested that TiC particles had exhibited a continuous increase in amount from the bottom to the top of clad layer, and partial TiC particles gathered and became large. Partial WC and TaC particles exhibited smashing phenomenon (heat damage), and the degree of heat damage of both WC and TaC particles was much more serious than that of TiC particles. Experimental results also showed that there existed obviously a surrounding structure (Ti, W, Ta) C at edge of carbonitride phase TiC in clad coating. In addition, ledeburite with shape of fish-bone was generated in the toppest region of clad coating, coarser eutectic microstructures was generated in boding zone of clad coating in the liquid state solidifying process, and both of these microstructures contained W, Ti, Ta etc. elements.
Investigation has been carried out into the solidification features and formation law of microstructure for laser cladding Co-base Cr-W Alloy Laser on Stainless Steel Valve. It is shown that the microstructure at the cladding layer bottom belongs to typical epitaxial growth on basis of plane, and the dendrite crystal is coarser. The microstructure at the top is the regular pine-tree eutectic crystal, and at the middle is small cell crystal and columnar crystal. The crystalline anisotropy influences the crystal growth form. Grain nucleation has obvious features of heterogeneous nucleation in microstructure of cladding. The results also show that the compositions in microzone of cladding layer are non-uniform, different elements segregate along crystalline axis or interdendritic, and these have resulted in the non-uniform microstructure.
The transmitting efficiency and light intensity of the hollow waveguide with two curved surfaces was analyzed with a ray optics approach. The eigenmode of the waveguide was analyzed with Helmholtz equation. The hollow waveguide was fabricated and the experiment of laser propagation in it was carried out. The CO2 laser power of 1123 W was delivered through the waveguide.
The oxide ceramic powders have been sintered with a high power CW CO2 laser. The products of Al2(WO3)2 as a new compound which can not be found in 2D equilibrium phase diagrams. The hardness of laser synthesized materials are shown to be higher than that produced with the general sintering method in furnace. The microstructure and character is of oxide ceramics synthesis using CW CO2 laser have investigated. We found that the products of laser sintering Al2O3-50mol percent WO3 have the electrical resistance characters varied linearly of negative temperature coefficient from the room temperature to 220 degrees C.
The most important problems to be solved lie in the generation of thermal stresses and the subsequent spalling of the coating. Now the method for improving the coating quality is to remelt the coating using a laser beam. This method can reduce the porosity and stresses and achieve proper microstructure and homogeneity. The Ni-Cr alloys were plasma sprayed onto A3 steel substrates as bond coat with a layer of 50 approximately 100 micrometers thick. Alumina and/or zircoia powders were plasma sprayed onto the bond coat led to a 100 approximately 150 micrometers thick surface layer. The surfaces of the laser-treated coatings and prepared cross-sections were observed by optical microscopy and scanning electron microscopy. The relation between surface status of ceramic and laser process was discussed. The element permeability in ceramic coating and in bond coatings were discussed also.
Non-equilibrium sintering of ZrO2 solid electrolyte, a kind of high temperature superionic conductor, was realized using high-power CO2 laser beam. The theory and technology of non-equilibrium sintering were introduced. The microstructure of the laser sintered specimens were analyzed by SEM and XRD. The conductivity of laser sintered CSZ and MSZ samples were measured, which were the order of 2 X 10-2(Omega) -1CM-1 at the temperature of 1000 degree(s)C.
This paper reports rapidly solidified amorphous by 10 kW cw CO2 laser glazing Fe40Ni36Cr2Si8B14 and Fe40Ni40P16B4 alloys, previously prepared by melting the above alloys onto mild carbon steel substrates in a vacuum furnace. The process variables of laser glazing were investigated. The surface layers of laser glazing have been examined by scanning electron microscope (SEM), transmission electron microscope (TEM), and x-ray diffraction (XRD). An amorphization layer was achieved by laser glazing. A large-area amorphous layer has also been obtained by laser overlapping glazing, but a recrystallization was produced in the overlapped area.
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