Surface plasmon resonance in a bent single-mode fiber with a metallized cladding experimental research

The processes of surface plasmon resonance excitation in a bent single-mode optical fiber with a metallized cladding have been studied experimentally. It is shown that, for a certain combination of the bending radius of an optical fiber and the thickness of a metal film, a strong coupling between the fundamental and plasmon–polariton mode is achieved through a whispering gallery mode supported by the fiber cladding, which leads to the formation of a resonance dip with a depth of ~30 dB or more in the transmission spectrum of an optical fiber loop. The position of the dip depends strongly on the ambient refractive index, which provides the possibility of refractometric measurements with a spectral sensitivity of ~5 μm/RIU and a resolution of ~4 × 10^–6. Limits of measurement of the refractive index are determined by the operating spectral range and the bending radius of the optical fiber and are 1.42–1.44 for the setup used.     

Reconstruction of distributed physical fields in integrating measuring systems and systems of direct measuring in rare points of field

The theoretical analysis of reconstruction problem of distributed physical fields in integrating measuring systems has been carried out. The integrating measuring systems are compared with the systems of direct measuring in rare points of the field. And the application prospects have been revealed. The text was submitted by the authors in English.     

Measuring the deformity of dentofacial bone tissues using a speckle correlation method

A noninvasive method for investigating the deformity of dentofacial bone tissues is proposed. The method is based on speckle field correlation analysis. The optimal conditions for the method are found. It is shown that the threshold sensitivity of the method may reach 10 μm.     

Artifacts suppression in limited data problem for parallel fiber optical measuring systems

The paper discusses tomography reconstruction of distributed physical fields by means of fiber optical measuring systems (FOMN) [1] for parallel schemes of measuring lines stacking with a small number of scanning directions. This work considers the sampling theory for a case with sampling sets which are unions of two co-sets. The case of non-equidistant sampling requires application of new approaches, namely the generalized sampling theorems with group-theory basis. An explicit reconstruction formula for extracting additional (missing or distorted) projection data values are provided, using approximating of a projection function on a non regular grid. Furthermore, standard restoration algorithms are applied to this function. Two restoration methods are proposed, UQC 1 (union of quotient classes), and UQC 2. Comparative analysis of the operating efficiency of UQC 1 and UQC 2 methods versus standard analytical FBP method for fiber-optical tomography reconstruction is reported.     

A model of nonlinear optical transmittance for insulator nanocomposites

A theoretical model of the laser radiation transmittance of insulator nanocomposites containing low concentrations of nanoparticles is proposed. It is shown that the basic mechanisms of low-threshold effects of nonlinear absorption and scattering of laser radiation are, first, the induction of electric dipole moments of nanoparticles in the external field and, second, the orientation of nanoparticles along the polarization direction of this field. The behavior of the transmittance in the vicinity of the central region of a separate absorption band and the dependence of the depth of this band in the transmittance spectrum on the external radiation intensity are considered.     

Luminescent Sensing via Photonic Nanojets

Semiconductors - A new optical sensor system based on an array of dielectric aluminum oxide microspheres covered with a layer of chitosan polymer with molecules of a luminescent chemosensitive...     

Optical transmittance spectra of insulator nanoparticles in bulk heterocomposites

A theoretical model is presented of the visible, near-infrared, and near-ultraviolet transmittance spectra of arbitrarily-shaped small-sized insulator particles embedded in an insulator in relation to the particle dimensions and the radiation frequency. The model is based on a number of assumptions. In the band gap of the nanoparticles, there are allowed energy bands produced by surface defects. Two-particle states (electron-hole pairs) are only slightly confined, and the size-quantized states of charge carriers are formed in the conduction band; the states depend on the shape and dimensions of the nanoparticles. By the example of Al₂O₃ nanoparticles introduced into a liquid matrix of a transparent insulator, the results of experimental studies are compared with the theoretical model.     

A multichannel correlation filter based on a photorefractive crystal for the processing of varying speckle fields

A method for the simultaneous processing of speckle fields generated by several single-fiber multimode interferometers is developed. The method uses a multichannel correlation filter based on a single photorefractive crystal. Mutual influence of the neighboring channels is analyzed, and it is shown that the simultaneous processing of several channels can be performed with the help of a single photorefractive crystal, provided that the interchannel spacing is not smaller than half of the size of the optical field pattern formed in the crystal plane.     

An interrogation technique for fiber Bragg grating sensors based on optical time-domain reflectometry

A method for fiber Bragg grating (FBG) interrogation is proposed. The method rests on measuring the light intensity reflected from FBG sensors by means of a standard optical time-domain reflectometer. Multiple FBGs along the fiber optic line are interrogated through time division multiplexing. Specifications of FBGs enabling linear response of the sensors to strain and temperature are determined. The threshold sensitivity to strain is 0.8 · 10^?4; the threshold sensitivity to temperature is 5°C.