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- 摘要
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Polymer Based PCF with High Nonlinearity and Low Bend Loss: A New Modeling
摘要： The effect of ellipticity ratio on low bend loss, high nonlinearity, wideband high birefringence and low confinement loss in a hexagonal spiral thermoplastic polymer based PCF having air holes with Kerr nonlinearity is investigated. Moreover, the above all property are simulated initially with wide range of wavelength (for different value ellipticity ratio) and secondly with ellipticity ratio at an operating wavelength of 1.55 μm. Through the optimization of arrangement and diameter of elliptical air holes, the designed spiral PCF offers low bend loss, high nonlinearity depends on mode field area (As small as mode field area, increase the nonlinearity), high birefringence and nonzero dispersion for X/Y polarization within the wavelength range of 0.5 to 1.75 μm. These results seem to be most useful in optical communication.
关键词： Bend loss,High nonlinearity,Spiral PCF
更新于2025-09-23 15:21:01
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Unveiling Complex Plasmonic Resonances in Archimedean Nanospirals through Cathodoluminescence in a Scanning Transmission Electron Microscope
摘要： Metallic nanostructures with a complex plasmonic response, such as the Archimedean nanospiral (ANS) present novel ways to utilize plasmonics in modern technology [1,2]. The nanospiral can support several resonant modes, with distinct electric field profiles as shown by finite-difference time-domain (FDTD) simulations such as the hourglass (500-650nm) and focusing (650-980nm) modes [2]. In addition to the linear plasmonic response, the ANS exhibits a stronger second-order nonlinearity than seen in other metallic nanostructured systems. A high spatial-resolution picture of the plasmonic modes is critical to understanding the interactions between plasmonic modes that drive the high non-linear efficiencies [3]. Purely optical experiments struggle to observe the near field behavior of the structure due to being diffraction limited. However cathodoluminescence (CL) experiments in a scanning transmission electron microscope (STEM) create a unique opportunity for characterizing plasmonic systems with both the spatial sensitivity of electron optics and the spectral sensitivity of photonics. A significant benefit to the use of STEM-CL, as opposed to other high-resolution spectroscopy techniques such as electron energy loss spectroscopy (EELS), is that the photons generated from radiative decays in the sample are collected for signal instead of the electrons from the probe. As a result, the signal can be manipulated and filtered using standard optical techniques, allowing us to map difficult to observe plasmon modes and even give insight into the polarization of their radiative decay. To experimentally observe the plasmon modes, an Au ANS array is fabricated using electron-beam lithography on a 50 nm silicon nitride film supported by a silicon substrate. A 500μm x500 μm window is then backside-etched beneath the array. STEM-CL is done in a VG-HB601 STEM operated at 60 kV with a home-built CL spectrometer system. Radiative emission is collected with a parabolic mirror and reflected out of a port in the side of the microscope, allowing the signal to be filtered and polarized using standard optical equipment, and ultimately collected in a photomultiplier tube (PMT). First, the focusing mode (650-980nm) is examined. Fig 1a shows a FDTD simulation of the plasmon mode. Fig 1b shows a high angle annular dark field (HAADF) image of the fabricated ANS on the SiN window. The raw CL intensity is shown in Fig 1c with no spectral filtering. Emission from all plasmonic modes, interband transitions, and any other radiative decay pathways are all simultaneously detected. However, by spectrally filtering the CL signal, individual modes can be isolated. The focusing mode is predicted to be strongest in the 650-980 nm region, so by using a 600 nm long-pass spectral filter, the radiative decay from other optical features can be eliminated, and a map of the focusing mode (Figure 1d) can be obtained. For the hourglass mode, however, spectral filters cannot be used to observe the spatial profile of the plasmonic resonance, because unlike the focusing mode, the hourglass mode has a distinct polarization axis that is parallel to the axis of the exciting optical pulse, as shown in the FDTD simulation in Fig 1e. With no polarization selectivity on electron-optics, the hourglass plasmon modes can be excited in all in-plane axes of the ANS simultaneously within the STEM, and no individual plasmon can be isolated and detected. However, since the hourglass mode has a strong polarization dependence on the exciting pulse, it is likely that the resulting emission is similarly polarized. In Fig 1f the HAADF image of an ANS is shown, and Fig 1g shows the unfiltered CL image. Fig 1h shows CL image filtered with a linear polarizer and exhibits a similar spatial profile to the simulation in Fig 1e, demonstrating that the modes that have a have a strong dependence on the polarization of the exciting optical source also exhibit a polarization dependence on their radiative decay. Nanostructures with complex, nonlinear plasmonic responses, such as the ANS, have unique optical attributes not present in simpler geometries. As a result, high spatial-resolution techniques to investigate the near-field profiles are an important avenue of plasmonic investigation. STEM-CL presents a particularly unique opportunity to combine photon and electron optics in order to characterize and map plasmonic modes, such as the hourglass and focusing modes of the ANS, with nanoscale precision.
关键词： nonlinearity,cathodoluminescence,scanning transmission electron microscope,Archimedean nanospiral,plasmonics
更新于2025-09-23 15:19:57
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2D Layered Graphene Oxide Films Integrated with Microa??Ring Resonators for Enhanced Nonlinear Optics
摘要： Layered 2D graphene oxide (GO) films are integrated with micro-ring resonators (MRRs) to experimentally demonstrate enhanced nonlinear optics. Both uniformly coated (1?5 layers) and patterned (10?50 layers) GO films are integrated on complementary-metal-oxide-semiconductor (CMOS)-compatible doped silica MRRs using a large-area, transfer-free, layer-by-layer GO coating method with precise control of the film thickness. The patterned devices further employ photolithography and lift-off processes to enable precise control of the film placement and coating length. Four-wave-mixing (FWM) measurements for different pump powers and resonant wavelengths show a significant improvement in efficiency of ≈7.6 dB for a uniformly coated device with 1 GO layer and ≈10.3 dB for a patterned device with 50 GO layers. The measurements agree well with theory, with the enhancement in FWM efficiency resulting from the high Kerr nonlinearity and low loss of the GO films combined with the strong light–matter interaction within the MRRs. The dependence of GO’s third-order nonlinearity on layer number and pump power is also extracted from the FWM measurements, revealing interesting physical insights about the evolution of the GO films from 2D monolayers to quasi bulk-like behavior. These results confirm the high nonlinear optical performance of integrated photonic resonators incorporated with 2D layered GO films.
关键词： four-wave mixing,graphene oxide,micro-ring resonators,integrated optics,Kerr nonlinearity,2D materials
更新于2025-09-23 15:19:57
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Progress toward third-order parametric down-conversion in optical fibers
摘要： Optical ?bers have been considered an optimal platform for third-order parametric down-conversion since they can potentially overcome the weak third-order nonlinearity by their long interaction length. Here we present, in the ?rst part, a theoretical derivation for the conversion rate both in the case of spontaneous generation and in the presence of a seed beam. Then we review three types of optical ?bers and we examine their properties in terms of conversion ef?ciency and practical feasibility.
关键词： optical ?bers,phase matching,nonlinearity,photon triplet states,third-order parametric down-conversion
更新于2025-09-23 15:19:57
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Functional-Link Neural Network for Nonlinear Equalizer in Coherent Optical Fiber Communications
摘要： We propose and experimentally demonstrate a simple nonlinear equalizer based on functional-link neural network (FLNN). The nonlinear stochastic mapping enables FLNN to serve as a nonlinear network, so we construct an FLNN with the signals from the two polarizations and the mapped features as input to combat the fiber nonlinearity in coherent optical transmission systems. The FLNN can use the Moore-Penrose generalized inverse or the ridge regression to solve the weights, which can speed up the training process, and avoid the iterative and time-consuming training process that exist universally in most of the deep neural networks. We also extend the FLNN to the multi-channel transmissions. All of the received signals from different channels are stretched as the input and then we use a joint FLNN to extract features and equalize the nonlinear distortions. We conduct simulations and experiments to verify the proposed scheme. In the simulation and experiment, we transmit a 128 Gb/s polarization division multiplexed 16-QAM (PDM-16-QAM) signal over 1000-km and 600-km standard single mode fiber (SSMF), respectively. Both the simulation and experimental results show that the FLNN has similar performance as deep neural network (DNN), which can improve the transmission performance in the nonlinear region. Moreover, the FLNN can avoid the gradient dissipation and local minimum problems in DNN, which simplify the training process. We also extend the proposed scheme in a five-channel (5 × 160 Gb/s) multiplexed transmission system. In simulation, we use joint FLNN and joint DNN to compensate the nonlinear distortions, respectively. We find that the BERs of the five channels can be below 7% HD-FEC with nonlinear equalizer.
关键词： enhancement node,functional-link neural network,Optical communication,deep neural network,fiber nonlinearity
更新于2025-09-23 15:19:57
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Nonlinear Optics in Microspherical Resonators
摘要： Nonlinear frequency generation requires high intensity density which is usually achieved with pulsed laser sources, anomalous dispersion, high nonlinear coefficients or long interaction lengths. Whispering gallery mode microresonators (WGMRs) are photonic devices that enhance nonlinear interactions and can be exploited for continuous wave (CW) nonlinear frequency conversion, due to their capability of confine light for long time periods in a very small volume, even though in the normal dispersion regime. All signals must be resonant with the cavity. Here, we present a review of nonlinear optical processes in glass microspherical cavities, hollow and solid.
关键词： kerr nonlinearity,optomechanical oscillations,stimulated brillouin scattering,optical resonators,whispering gallery mode
更新于2025-09-23 15:19:57
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Role of magnetic field on self focusing of super-Gaussian laser beam under relativistic effect
摘要： Considering an external magnetic field along the direction of propagation of laser, the self focusing of a super-Gaussian laser beam is studied when it propagates through the plasma at relativistic intensities. We consider the cyclotron motion of the electrons and use the tensor form of the plasma dielectric constant obtained based on the direction of the external magnetic field. For completeness, relativistic mass effect is incorporated in both the plasma frequency and electron cyclotron frequency. Using appropriate conditions, an equation for the beam width parameter is derived and solved. The equilibrium beam radius for a self trapped laser beam is also derived. Self focusing is better when cyclotron effects are taken into account. At higher intensity and higher spot size of the laser beam, self focusing becomes better.
关键词： Super-Gaussian laser,Moment theory,Beam width parameter,Self focusing,Relativistic nonlinearity
更新于2025-09-23 15:19:57
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Influence of the Fifth-Order Nonlinearity of Gold Nanorods on the Performance of Random Lasers
摘要： We present the first experimental evidence for the influence of the fifth-order nonlinearity on the characteristics of Random Lasers with plasmonic nanoparticles as scatterers. The experiments were performed with gold nanorods suspended in an ethanolic solution of Rhodamine 6G, pumped by a picosecond laser. It is shown that by varying the nanorods aspect-ratio, it is possible to control the cooperative influence of both transverse and longitudinal localized surface plasmons on the fifth-order nonlinear light scattering, a phenomenon that allows to manage the optical feedback causing significant changes in the threshold intensity and emission power of Random Lasers.
关键词： fifth-order nonlinearity,gold nanorods,Random Lasers,optical feedback,plasmonic nanoparticles
更新于2025-09-23 15:19:57
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Observation of edge solitons in photonic graphene
摘要： Edge states emerge in diverse areas of science, offering promising opportunities for the development of future electronic or optoelectronic devices, sound and light propagation control in acoustics and photonics. Previous experiments on edge states in photonics were carried out mostly in linear regimes, but the current belief is that nonlinearity introduces more striking features into physics of edge states, leading to the formation of edge solitons, optical isolation, making possible stable lasing in such states, to name a few. Here we report the observation of edge solitons at the zigzag edge of a reconfigurable photonic graphene lattice created via the effect of electromagnetically induced transparency in an atomic vapor cell with controllable nonlinearity. To obtain edge solitons, Raman gain is introduced to compensate strong absorption experienced by the edge state during propagation. Our observations may open the way for future experimental exploration of topological photonics on this nonlinear, reconfigurable platform.
关键词： topological photonics,nonlinearity,Raman gain,edge solitons,photonic graphene
更新于2025-09-23 15:19:57
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Prediction of MCO [M = S, (Cl <sub/>2</sub> B) <sub/>3</sub> B] Systems with Giant Optical Birefringence and Nonlinearity in the Deep-Ultraviolet Region
摘要： Deep-ultraviolet (DUV) materials with giant optical birefringence and nonlinearity are scarce, and their discovery is very challenging. In this Communication, we predict that the MCO [M = S, (Cl2B)3B] compounds containing the polar C?O motif, which have been synthesized in the experiments, could be the ?rst material systems to achieve this rare capability. First-principles calculations demonstrate that (Cl2B)3BCO and SCO exhibit the largest second-harmonic-generation e?ect (～4.4 pm/V) and the largest birefringence (～0.6) in all known DUV nonlinear-optical (NLO) crystals. In addition, SCO might be a DUV NLO material for the practical 193.7 nm laser output. Our discovery could enrich the structural chemistry of NLO crystals and advance the development of functional DUV optical materials.
关键词： Deep-ultraviolet,nonlinearity,polar C?O motif,DUV nonlinear-optical crystals,first-principles calculations,MCO compounds,second-harmonic-generation,optical birefringence
更新于2025-09-23 15:19:57