KEYWORDS: Education and training, Holography, Data storage, Super resolution, Neural networks, Holograms, Tunable filters, Spatial light modulators, Holographic data storage systems, Deep learning
In this paper, we propose a super-resolution holographic data storage system based on deep learning. A low-pass filter was introduced into the Fourier plane to remove the high frequency. This produces a blurred intensity image of the reconstructed beam. A convolutional neural network is used to establish the relationship between the blurred intensity image and the data page. The encoded phase data page can be directly demodulated from a captured intensity image, which is a non-interferometric method without iterations. The function of the filter is to generate the blurred intensity image and to reduce the recording area to improve the recording intensity. Usually, the limit of the aperture is the Nyquist size. Here, by introducing embedded data on the phase data page, the aperture size of the recording can be reduced to smaller than the Nyquist size. A simulation experiment was established to verify the effectiveness of the proposed method.
We report on a numerical study of interaction optical torque between twisted gold nanorods induced by the plasmon
coupling. Our results indicate that interaction optical torque can be generated and enhanced by the plasmon coupling
between twisted nanorods, highly depending on the gap size and twisted angle. This interaction optical torque implements
the rotations to mutually perpendicular and parallel arrangements of nanorods with the light excitations of different
plasmon modes. Thus, the interaction optical torque induced by the plasmon coupling will play an important role to
control the plasmonic characteristics and functions.
Wavelength conversion using plasmonic nanostructures has been attracting attention as a novel nonlinear optical effect occurred in nano-sized regions. In general, the second order nonlinear polarization does not occur in the isotropic metal, while the breaking symmetry on the metal surface is considered to permit the SHG (second harmonic generation). The radiation control of the SHG signal is essential in order to apply plasmonic nanostructures as wave conversion devices. However, its radiation control has been difficult because the second order nonlinear polarization on the metal surface is sensitive to the surface roughness. In this study, we demonstrated the control of the SHG radiation pattern and phase by the unique idea that the second order nonlinear polarization couples to the dipole plasmon mode.
We have demonstrated a linear nanomotor employing lateral optical force exerted on a plasmonic nanoparticle, in which the force direction is determined by the orientation of the nanoparticle rather than a field gradient or propagation direction of the incident light beam. The arrangements of the nanoparticles provide the lateral force distributions with nanoscale precision and resolution, resulting in not only linear but also rotational movement of a micrometer-sized object. Our nanomotors would provide a paradigm shift in optical manipulation as it removes the need for oblique incidence, focusing and steering of the light beam.
We report that localized surface plasmon resonance allows a single-element nanostructure to induce an extrinsic angular momentum of light in its interaction with a propagating plane wave. The recoil of the angular momentum results in an optical torque on the structure along an axis perpendicular to the optical axis, and the characteristics of this transverse torque depend on the incident polarization state, including the spin direction. Our results suggest that the designed dark plasmon mode can provide a new degree of freedom for optical manipulation of nanoparticles smaller than the diffraction limit.
Launching and control of graphene plasmon are crucial for nanodevice applications. To achieve that, previous studies used foreign object and/or angled illumination to provide plasmon launching and directional control. In this study, we considered graphene nanoridges, which is a defect-free natural structure of graphene to launch plasmon, using analytic method and simulation. The result shows that a single graphene nanoridge can launch plasmon, with an interesting relationship between the SPP amplitude and ridge physical curve length. By using two nanoridges with different size, the interference between SPP wave launch from each ridge result in right-left asymmetric plasmon launching. With the proper size and separation, unidirectional, bidirectional, or wavelength-sorted plasmon launching can be achieved.
We investigated the surface plasmon resonance (SPR) of aluminum (Al) thin films with varying refractive index of the environment near the films in the far‒ultraviolet (FUV, ≤ 200 nm) and deep‒ultraviolet (DUV, ≤ 300 nm) regions. By using our original FUV‒DUV spectrometer which adopts an attenuated total reflectance (ATR) system, the measurable wavelength range was down to the 180 nm, and the environment near the Al surface could be controlled. In addition, this spectrometer was equipped with a variable incident angle apparatus, which enabled us to measure the FUV‒DUV reflectance spectra (170–450 nm) with various incident angles ranging from 45° to 85°. Based on the obtained spectra, the dispersion relation of Al‒SPR in the FUV and DUV regions was obtained. In the presence of various liquids (HFIP, water, alcohols etc.) on the Al film, the angle and wavelength of the SPR became larger and longer, respectively, compared with those in the air (i.e., with no materials on the film). These shifts correspond well with the results of simulations performed according to the Fresnel equations, and can be used in the application of SPR sensors. FUV‒DUV‒SPR sensors (in particular, FUV‒SPR sensors) with tunable incident light wavelength have three experimental advantages compared with conventional visible‒SPR sensors, as discussed based on the Fresnel equations, i.e., higher sensitivity, more narrowly limited surface measurement, and better material selectivity.
Despite often illustrated as a perfect two-dimensional sheet, real graphene sample is not always flat. Nanostructures can be occurred on graphene sheet, especially for epitaxial graphene. The nanostructures alter the electrical and mechanical properties of graphene. This is crucial for epitaxial graphene since its main potential is in the electronics and optics application. This study investigates nanostructures on epitaxial graphene by tip-enhanced Raman spectroscopy, which is a technique that can provide Raman spectra with great spatial resolution, exceeding the diffraction limit of light. The results suggest that the compressive strain on nanoridges is weaker compared to neighbor flat area, supporting the ‘ridge as compressive strain relaxation’ mechanism. TERS measurement of nanoridges on epitaxial graphene microisland also indicates that the ‘Si vapor trapping’ mechanism for ridge formation is unlikely to occur.
This study presents the synthesis, SERS properties in three dimensions, and an application of 3D symmetric nanoporous silver microparticles. The particles are synthesized by purely chemical process: controlled precipitation of AgCl to acquire highly symmetric AgCl microparticle, followed by in-place to convert AgCl into nanoporous silver. The particles display highly predictable SERS enhancement pattern in three dimensions, which resembles particle shape and retains symmetry. The highly regular enhancement pattern allows an application in the study of inhomogeneity in two-layer polymer system, by improving spatial resolution in Z axis.
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