Sergey S. Kosolobov

Nonlinear integrated optical devices that can realize threshold filtration of signals are in demand in photonics and optical computing. However, a list of requirements exists for such devices to make them practical. Here, to design a thresholder with the desired behavior, we suggest a mechanism that implements the property of resonators to provide extremely sharp (with respect to the wavelength) π phase shifts near the critical coupling regime. By combining this feature with a nonlinear switching mechanism, one may obtain highly sensitive devices. Notably, the sharpness of the phase step in the considered case is independent of the quality factor of the resonators and the corresponding width of the resonances in transmittance. Instead, it is defined by the proximity to the critical coupling regime. Balancing near the critical coupling allows one to vary the sensitivity and achieve controllable smearing of the step function. The described effect is quite robust and can be realized for different materials and types of nonlinearity. The possibility of using sharp steps and low-quality resonators simultaneously provides multiple advantages for the resulting device. These include compact size, low manufacturing requirements, high operation speed, and low switching intensities. These sensitive and tunable phase thresholders may have multiple applications in optical computing. Few examples are provided, including a minimally invasive logic gate and a signal intensity classifier. In particular, the considered thresholders are useful in neuromorphic chips since they may act as optical neurons. In this paper, we provide an example of a photonic scheme that represents the behavior of a neuron and discuss its characteristics. Both the amplitude and phase of light are actively used in the scheme to store and update the state of a neuron.

В данной работе продемонстрировано сужение спектральной линии лазера с распределенной обратной связью 210 кГц до 150 Гц в режиме самозахвата частоты внешнего кремниевого резонатора на основе фотонной интегральной схемы, что открывает перспективы создания компактных узкополосных лазеров для генерации малошумных микроволновых сигналов.

An integrated plasmonic indium-tin-oxide (ITO)-based silicon electro-optical modulator has been designed, fabricated, and characterized. A sandwich structure shows a 40 GHz bandwidth at the $-2$ dB level and an extinction ratio of about 1.8 dB. The device is fabricated on a silicon-on-insulator wafer. A silicon waveguide is excluded from the electric circuit. Instead, an ITO layer is used both as a bottom electrical contact and as an electric field-sensitive medium. As a gate oxide, we used a silicon dioxide layer capped with a gold top electrode to form a capacitor. The dielectric rib inside the ITO-Au capacitor forms a coupling interface between the TE photonic and plasmonic modes.

Microdiamonds with color centers have unique photophysical properties. We discover extremely narrow spectral lines with full width at half maximum down to 0.5 nm (≈390 GHz at wavelength 630.15 nm) at room temperature in photoluminescence of numerous high-pressure–high-temperature microdiamonds. Correlation spectroscopy proves that these lines originate from single photon emitters. Comprehensive experimental characterization of the emitters is performed by means of complementary scanning electron and fluorescence microscopy that allows morphological characterization and in time monitoring of the same labeled emitters. Study of photoluminescence and photoluminescence excitation spectra of single emitters showed negligible phonon sideband and narrowband excitation. Temperature sensitivity, stable photoluminescence, brightness, linear polarization, and fluorescence lifetime ≈1.5–2.5 ns are demonstrated. The results show great potential of the discovered “enigmatic” emitters for applications in quantum optics, fluorescence labeling, and high-resolution thermometry.

Alcohol intoxication has a dangerous effect on human health and is often associated with a risk of catastrophic injuries and alcohol-related crimes. A demand to address this problem adheres to the design of new sensor systems for the real-time monitoring of exhaled breath. We introduce a new sensor system based on a porous hydrophilic layer of submicron silica particles (SiO₂ SMPs) placed on a one-dimensional photonic crystal made of Ta₂O₅/SiO₂ dielectric layers whose operation relies on detecting changes in the position of surface wave resonance during capillary condensation in pores. To make the active layer of SiO₂ SMPs, we examine the influence of electrostatic interactions of media, particles, and the surface of the crystal influenced by buoyancy, gravity force, and Stokes drag force in the frame of the dip-coating preparation method. We evaluate the sensing performance toward biomarkers such as acetone, ammonia, ethanol, and isopropanol and test sensor system capabilities for alcohol intoxication assessment. We have found this sensor to respond to all tested analytes in a broad range of concentrations. By processing the sensor signals by principal component analysis, we selectively determined the analytes. We demonstrated the excellent performance of our device for alcohol intoxication assessment in real-time.

We present a targeted drug delivery system for therapy and diagnostics that is based on a combination of contrasting, cytotoxic, and cancer-cell-targeting properties of multifunctional carriers. The system uses multilayered polymer microcapsules loaded with magnetite and doxorubicin. Loading of magnetite nanoparticles into the polymer shell by freezing-induced loading (FIL) allowed the loading efficiency to be increased 5-fold, compared with the widely used layer-by-layer (LBL) assembly. FIL also improved the photoacoustic signal and particle mobility in a magnetic field gradient, a result unachievable by the LBL alone. For targeted delivery of the carriers to cancer cells, the carrier surface was modified with a designed ankyrin repeat protein (DARPin) directed toward the epithelial cell adhesion molecule (EpCAM). Flow cytometry measurements showed that the DARPin-coated capsules specifically interacted with the surface of EpCAM-overexpressing human cancer cells such as MCF7. In vivo and ex vivo biodistribution studies in FvB mice showed that the carrier surface modification with DARPin changed the biodistribution of the capsules toward epithelial cells. In particular, the capsules accumulated substantially in the lungs─a result that can be effectively used in targeted lung cancer therapy. The results of this work may aid in the further development of the "magic bullet" concept and may bring the quality of personalized medicine to another level.

We analyze point defect bulk and surface diffusion near the crystal–vacuum interface and show that bulk diffusion is coupled with surface diffusion via the atomic processes in the intermediate subsurface layer. A set of self-contained differential equations describing the interaction of self-interstitials and bulk vacancies with the surface of crystal is proposed. The results show the existence of the fundamental relation between the equilibrium concentrations of the point defects in bulk and at the surface of the crystal. For the case of silicon, the energy barrier differences that restrict the point defect fluxes between the bulk and surface of the crystal are estimated.

Electron beam-induced current in the temperature range from 304 to 404 K was employed to measure the minority carrier diffusion length in metal–organic chemical vapor deposition-grown p-Ga₂O₃ thin films with two different concentrations of majority carriers. The diffusion length of electrons exhibited a decrease with increasing temperature. In addition, the cathodoluminescence emission spectrum identified optical signatures of the acceptor levels associated with the V_Ga⁻–V_O⁺⁺ complex. The activation energies for the diffusion length decrease and quenching of cathodoluminescence emission with increasing temperature were ascribed to the thermal de-trapping of electrons from V_Ga⁻–V_O⁺⁺ defect complexes.

Surface-enhanced Raman spectroscopy (SERS) is a powerful technique for biosensing. However, SERS analysis has several concerns: the signal is limited by a number of molecules and the area of the plasmonic substrate in the laser hotspot, and quantitative analysis in a low-volume droplet is confusing due to the change of concentration during quick drying. The usage of hollow-core microstructured optical fibers (HC-MOFs) is thought to be an effective way to improve SERS sensitivity and limit of detection through the effective irradiation of a small sample volume filling the fiber capillaries. In this paper, we used layer-by-layer assembly as a simple method for the functionalization of fiber capillaries by gold nanoparticles (seeds) with a mean diameter of 8 nm followed by UV-induced chloroauric acid reduction. We also demonstrated a simple and quick technique used for the analysis of the SERS platform formation at every stage through the detection of spectral shifts in the optical transmission of HC-MOFs. The enhancement of the Raman signal of a model analyte Rhodamine 6G was obtained using such type of SERS platform. Thus, a combination of nanostructured gold coating as a SERS-active surface and a hollow-core fiber as a microfluidic channel and a waveguide is perspective for point-of-care medical diagnosis based on liquid biopsy and exhaled air analysis.