One of the possible future architectural implementations of new computing devices is brain-inspired neuromorphic computers. Artificial synapse is one of the key neuromorphic computing elements. This work is devoted to the search for new bioinspired artificial synapse properties and the demonstration of already known neuromorphic properties on the original photoelectric synapse based on nanocrystalline ZnO film. Photoelectric synapse demonstrated basic neuromorphic properties: spike signals operation, the presence of short-term memory, long-term memory and paired-pulse facilitation. Artificial photoelectric synapse adaptation properties have been demonstrated in a series of experiments with different conductivity cutoff levels.
In a current study, we have developed a cheap and easy-to-use urine analysis method using visible and near-infrared wavelength range optical transmission spectra using artificial intelligence approaches. The manufactured prototype based on an 18-channel spectrometer and LED light sources, was used to measure 431 patients’ urine transmission spectra. 19 parameters clinical urine analysis was performed in a medical laboratory for each patient. Machine learning partial least squares discriminant analysis (PLS-DA) was used to solve the binary multidimensional classification problem. Developed machine learning model could detect urine pathological changes with sensitivity and specificity comparable to laboratory diagnostic methods for most parameters.
The possibility to use one-dimensional magnetoplasmonic crystals as localized and sensitive sensors of the DC magnetic field is shown. The achievable sensitivity of such sensors is estimated to be up to 10-5 Oe at a local area of 1 mm2. The performance of demonstrated sensors strongly depends on the geometry-driven magnetic properties and can be tuned by the change of materials and thicknesses of functional layers. Demonstrated results in details explain the mechanisms of tuning the properties of MPlCs and give a discussion on possible applications.
The work is devoted to the development of magnetic field sensor based on magnetoplasmonic crystal and demonstrates the results of studying spectral and field dependences of reflectivity and transverse magneto-optical Kerr effect (TMOKE) geometry. It is shown, that magneto-optical properties of studied samples non monotonously change due to the different contributions of surface plasmon-polaritons excitation, magnetic and optical properties into the TMOKE enhancement process. Presented samples allow one to achieve the sensitivity of tens μOe to the DC magnetic field magnitude in an area of 1 mm2 and perform a mapping of external uniaxial magnetic field without moving the MPlC.
One of the promising future ways of computing is using principles similar to the human brain work mechanism. Neuromorphic photonics makes it possible to create computational elements with properties similar to the principles of the biological synapse. Neuromorphic computers can overcome the von Neumann bottleneck fundamental limitation of existing computing systems.
In a current study, we demonstrate a neuromorphic properties, observing on photoconductive structures based on nanocrystalline ZnO, WO3, In2O3 triggered by presynaptic light spikes with the 405nm wavelength. Photoconductive structures based on ZnO, WO3, In2O3 were deposited as a 100–200 nm thick film on the surface of the chip.
Excitatory post-synaptic current value was measured for different excitation pulse durations. The excitatory post-synaptic current caused by a pair of presynaptic light spikes was studied for different delay times between pulses. The ability of these structures to act as biological synapses like high-pass temporal filtering function was demonstrated by measuring post-synaptic current when exposed to a series of 30 consecutive presynaptic light spikes.
Our photoconductive semiconductor structures have two different relaxation mechanisms. Due to this, the structures possess short-term and long-term photoconductivity memory. To demonstrate the ability of our samples possesses long-term memory, we studied the semiconductor photoconductivity relaxation values after light exposure during 500 seconds. The memory level after light exposure were stored over an hour.
The studied photoconductive structures showed the presence of a spike reaction properties, the effect of amplitude and frequency filtering, short-term and long-term memory, and they are looking promising for use as elements of neuromorphic photonics.
Here we report on the interplay between the magnetic, optical and magneto-optical properties of magnetoplasmonic crystals (MPC) based on the 1D diffraction gratings. A wide range of the characteristic parameters is examined to be effective for magnetic field sensor application. The gratings with periods of 320 nm and 740 nm with corresponding profile heights of 20 nm and 100 nm were used. Using ion-beam sputtering the diffraction gratings were covered by combination of following functional layers: noble metal - silver or gold with thicknesses of 50 or 100 nm; ferromagnetic metal - iron, silver, permalloy with thicknesses of 5, 20, 50, 100 nm; passivation layer of silica nitride with thicknesses of 20, 30 or 40 nm. The details of fabrication and characterization of magnetoplasmonic crystals will be discussed. We show how the 1D MPC can operate as highly sensitive and local sensor of DC magnetic field by utilizing the magneto-modulation sensor technique combined with the magneto-optical probes. As a result, the design of sensor prototype was optimized and the achieved sensitivity was found to be up to 10 μOe at a local area of 1 mm2. The main contribution to effect of MPC design on sensor parameters is geometry-driven magnetic properties formed during fabrication and depended on characteristic parameters of MPC. The developed sensor has sensitivity suitable for in biomedical applications and can be further improved by optimizing the sensing element and the sensor’s setup overall design.
Plasmonic band gap is a range of frequencies, within which, surface plasmon polaritons cannot propagate for any wavevector. Unfortunately the first plasmonic band gap cannot be observed directly in reflectance spectroscopy [1]. To detect it, biharmonic metal-air surface structuring is conventionally utilized [2,3]. However in this case experimental geometry is strictly limited to normal angle of incidence, which is not compatible with large range of applications.
In current work we introduce biperiodic plasmonic crystals. We experimentally demonstrate, that biperiodic structuring allows to tune band gap spectral-angular position.
Laser interference lithography (LIL) is a well-established technique for creating periodic planar nanostructures over a large surface area. LIL allows to precisely control the modulation period and depth and thus perfectly match diffraction coupling conditions and tune plasmonic band gap properties.
We used LIL experimental setup based on Lloyd interferometer. The radiation from the laser source (He-Cd, wavelength 325 nm, average power 14 mW) was spatially filtered and then formed interference pattern on the silicon wafer, covered with a thin layer of SU-8 2015. The structure period was defined by the incident angle on the interferometer. Modulation depth was defined by exposure time. By applying subsequent second exposure with another angle of incidence, we obtained biperiodic structure. Exposed samples were washed in corresponding developer, dried in air and later sputtered with 100 nm of aluminium.
We fabricated a set of biperiodic plasmonic crystals with different periods and modulation depths. The quality and geometrical parameters of biperiodic plasmonic crystals were monitored by scanning electron microscopy and atomic force microscopy. The appearance of plasmonic band gap was measured by spectral-angular polarisation spectroscopy. We experimentally determined the dependance of plasmonic band gap properties (width and position) on geometrical parameters of biperiodic plasmonic crystals. We also performed FDTD numerical simulations (Lumerical). The experimental results are in good agreement with numerical calculations.
[1] Raether, Heinz. [Surface Plasmons on Smooth and Rough Surfaces and on Gratings.], Springer Berlin Heidelberg, 91-105 (1988).
[2] Barnes, William L., et al. "Physical origin of photonic energy gaps in the propagation of surface plasmons on gratings." Physical Review B 54.9 (1996): 6227.
[3] Kocabas, Askin, S. Seckin Senlik, and Atilla Aydinli. "Plasmonic band gap cavities on biharmonic gratings." Physical Review B 77.19 (2008): 195130.
The results of experimental observation of magneto-optical Kerr effect (MOKE) enhancement caused by surface
plasmon-polaritons (SPP) excitation in 1D and 2D magnetoplasmonic crystals are presented. One-dimensional
nickel magnetoplasmonic crystals have periodic structure formed by periodic nickel grooves made on nickel
surface. The period of the structure is 320 nm and the depth of the grooves is 50 nm. The second group of the
samples represents itself a 2D self-assembled hexagonally ordered monolayer of polystyrene (PS) microspheres
with diameters from 500 to 760 nm and covered by 100- nm - thick nickel film. MOKE measurements performed
in transversal configuration demonstrate that SPP excitation lead to transversal Kerr effect (TKE) enhancement
resulting as a sharp peak in TKE spectrum.
One-dimensional photonic microstructures with optical thicknesses chosen according to the fractal sequence of
the Cantor's ladder are considered. Experimental samples made by electrochemical etching of porous silicon are
studied. Both numerical calculations and experimental results demonstrate self-similarity in reflection spectrum.
Numerical calculations demonstrate self-similarity in space distribution and time-resolved response caused by
self-similarity in morphology.
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