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Three poly(organosiloxanes) (hydromethyl-, dimethyl-, and epoxymethylsiloxane) of different chain lengths and pendant groups and their mixtures of dimethyl (DMC) or diethyl carbonates (DEC) were applied in the modification of fumed silica nanoparticles (FSNs). The resulting modified silicas were studied in depth using 29Si, 1H, and 13C solid-state NMR spectroscopy, elemental analysis, and nitrogen adsorption-desorption (BET) analysis. The obtained results reveal that the type of grafting, grafting density, and structure of the grafted species at the silica surface depend strongly on the length of organosiloxane polymer and on the nature of the “green” additive, DMC or DEC. The spectral changes observed by solid-state NMR spectroscopy suggest that the major products of the reaction of various organosiloxanes and their DMC or DEC mixtures with the surface are D (RR’Si(O0.5)2) and T (RSi(O0.5)3) organosiloxane units. It was found that shorter methylhydro (PMHS) and dimethylsiloxane (PDMS) and their mixtures with DMC or DEC form a denser coverage at the silica surface since S BET diminution is larger and grafting density is higher than the longest epoxymethylsiloxane (CPDMS) used for FSNs modification. Additionally, for FSNs modified with short organosiloxane PMHS/DEC and also medium organosiloxane PDMS/DMC, the dense coverage formation is accompanied by a greater reduction of isolated silanols, as shown by solid-state 29Si NMR spectroscopy, in contrast to reactions with neat organosiloxanes. The surface coverage at FSNs with the longest siloxane (CPDMS) greatly improves with the addition of DMC or DEC. The data on grafting density suggest that molecules in the attached layers of FSNs modified with short PMHS and its mixture of DMC or DEC and medium PDMS and its mixture of DMC form a “vertical” orientation of the grafted methylhydrosiloxane and dimethylsiloxane chains, in contrast to the reaction with PDMS/DEC and epoxide methylsiloxane in the presence of DMC or DEC, which indicates a “horizontal” chain orientation of the grafted methyl and epoxysiloxane molecules. This study highlights the major role of solid-state NMR spectroscopy for comprehensive characterization of solid surfaces. Graphical abstract

In this paper, we propose a modified platform for on-chip integrated photonics. The platform allows one to efficiently connect a tapered optical fiber or fiber lens to an on-chip waveguide with high alignment precision and to mechanically fix the fiber on the chip to prevent defocusing, lateral shift, and angular detuning during device operation. The metal screen of the connector-made of gold-prevents any penetration of the background radiation into the optical circuit, something which is not possible to achieve in all the cases using tapers or grating couplers. We performed impedance-matching analysis based on transmission line theory and numerically optimized the platform, allowing us to achieve a tapered fiber mode to on-chip waveguide mode transformation efficiency as high as 96% (-0.177 dB) at wavelengths of 785 and 1550 nm. The platform bandwidth (transformation efficiency ≥80%) is 151 nm. At the same time, transformation efficiency is stable (reduction less than 1%) in an offset range of ±2 nm-enough for modern on-chip and off-chip coherent light sources. The horizontal and vertical lateral alignment tolerances for the platform are 700 and 600 nm, respectively, at a transformation efficiency ≥80% while the longitudinal alignment tolerance is approximately 70 nm. Due to the relatively high lateral and longitudinal tolerances, it is possible to produce the platform at high efficiency using existing fabrication nanotechnologies. We believe that this platform accelerates the realization of fully on-chip Raman spectroscopes and may be of practical importance in other on-chip integrated photonic devices.

In this paper, we analyze the ultrafast temporal and spectral responses of optical fields in tapered and metalized optical fibers (MOFs) and optical plasmon nanostrip probes (NPs). Computational experiment shows that output pulses of the NPs are virtually unchanged in shape and duration for input pulses with a duration of >1 fs and are not sensitive to changes in the parameters of the probe (such as convergence angle and taper length), while local enhancement of the electric field intensity reaches 300 times at the NP apex. Compared with the NPs, MOFs lead to significant output pulse distortions, even for input pulses with a duration of 10 fs. In addition, the temporal response at the MOF apex is critically sensitive to changes in MOF parameters and cannot provide any significant local enhancement of the electric field. These findings reveal the high potential of optical plasmon nanostrip probes as an ultrashort pulse delivery system to nanometer-size areas and indicate that its usage can be promising for a wide variety of techniques studying ultrafast processes in nanoscopic volumes.

The improved scheme of data recording process on an optical disc based on a substrate made of high-stable materials has been proposed. Information layer with depth of 115nm and width of 600nm has been obtained on sapphire substrate by ion-beam etching using improved scheme. These experimental results allow to create the sapphire optical discs for long-term data storage.

An analytical model of interference between an electromagnetic field of fundamental quasi-TM(EH)00-mode and an electromagnetic field of background radiation at the apex of a near-field probe based on an optical plasmon microstrip line (microstrip probe) has been proposed. The condition of the occurrence of electromagnetic energy reverse flux at the apex of the microstrip probe was obtained. It has been shown that the nature of the interference depends on the length of the probe. Numerical simulation of the sample scanning process was conducted in illumination-reflection and illumination-collection modes. Results of numerical simulation have shown that interference affects the scanning signal in both modes. However, in illumination-collection mode (pure near-field mode), the signal shape and its polarity are practically insensible to probe length change; only signal amplitude (contrast) is slightly changed. However, changing the probe length strongly affects the signal amplitude and shape in the illumination-reflection mode (the signal formed in the far-field zone). Thus, we can conclude that even small background radiation can significantly influence the signal in the far-field zone and has practically no influence on a pure near-field signal.

We propose a design for efficient end-fire coupling of surface plasmon polaritons in a metal-insulator-metal (MIM) waveguide with an optical fiber as part of a simple photoplastic connector. The design was analyzed and optimized using the three-dimensional finite-difference time-domain method. The calculated excitation efficiency coefficient of the waveguide is 83.7% (−0.77 dB) at a wavelength of 405 nm. This design enables simple connection of an optical fiber to a MIM waveguide and highly efficient local excitation of the waveguide. Moreover, the length of the metallic elements of the waveguide, and thus the dissipative losses, can be reduced. The proposed design may be useful in plasmonic-type waveguide applications such as near-field investigation of live cells and other objects with super-resolution.