Method of integral equation in the theory of weak-guiding inhomogeneous optical waveguides

A method of integral equation is stated and applied in the analysis of the characteristic and noncharacteristic modes in 3D weak-guiding inhomogeneous optical waveguides. The dispersion curves for the modes of diffused channel waveguides are studied near the critical conditions in absorbing media. The accuracy of recovering the permittivity profile in a channel waveguide from the far-field radiation of the fundamental mode is estimated.     

Kinetics of the reduction of molecular oxygen from water by ultrafine copper in an ion-exchange matrix

The rate of the reduction of molecular oxygen from water with a low-capacity copper-containing electron-ion exchanger at various initial ionic forms, grain radii, and sizes of metal particles dispersed into pores. The applicability of the mixed-diffusion and diffusional-kinetic models incorporating a first-order irreversible reaction to describing the system under study was examined. The kinetic parameters of the system were determined within the framework of these models. It was found that the limiting stage of the process in the stationary mode is the internal diffusion of oxygen molecules to the redox sorbent particle. The increase in the rate of the absorption of oxygen by samples containing copper of higher dispersity was observed at the initial stage of the process and was likely associated with an increase in the surface area of the reactive interface.     

Kinetics of the formation of solid phase in electrolyte for electroless nickel deposition

The effect of 1-(3-methyl-4-phenylpyrazolyl)-3-phenylthiourea (PPTU) on the kinetics of formation of particles of the solid phase in the bulk of electrolyte for nickel plating is investigated by photocolorimetry and photon correlation spectroscopy. It is established that PPTU favors the formation of larger particles as compared to the solution containing no additive and, depending on the concentration, can accelerate or slow down the formation and growth of metal particles and affect the location of the process.     

The effect of composition of electrodeposited Ni-P alloys on the hydrogen evolution rate

The effect of composition and structure of electrodeposited nickel-phosphorus coatings on their catalytic properties in the hydrogen evolution reaction is studied. It is found that an increase in the content of phosphorus in the alloy from 0.1 to 12.6 wt % leads to an increase in the hydrogen evolution rate. The coatings, which were deposited under the galvanostatic conditions, exhibit higher activity than those plated under the potentiodynamic conditions. It is shown that the nature of acceleration of hydrogen evolution rate on the alloys depends on the alloy composition: only Ni-P alloys containing up to 6.5 wt % phosphorus possess true catalytic activity, whereas the coatings enriched in phosphorus promote the hydrogen evolution due to significant development of their surface area.     

Modes of capillary photonic-crystal fibers with hollow core

A rigorous method of integral equations has been used to calculate the dispersion characteristics, fields, and radiation patterns of the leaky modes of photonic-crystal fibers with a shell in the form of a bounded 2D photonic crystal composed of parallel quartz capillaries contacting each other and a core in the form of a defect of a photonic crystal with one capillary removed. It is shown that, when thick-walled capillaries (with an air content in the shell of about 28%) are used, these fibers can be single mode and have an overlap integral of the fundamental-mode field with the dielectric medium that is smaller by a factor of more than two (in comparison with similar fibers formed by air channels of circular cross section). The significant dispersion of the group velocity of the fundamental modes of fibers near the edge of the photonic crystal band gap has been found.     

Reconstruction of parameters of an adlayer on the surface of a channel optical waveguide

A simple solution of an inverse problem of reconstruction of thickness, permittivity and surface coverage of an adlayer disposed on the surface of a channel optical waveguide is proposed and substantiated theoretically. It is shown that the reconstruction errors for the parameters of the adlayer can be minimized by a choice of the channel waveguide parameters. The application of the procedure to biochemical sensors is considered.     

Calculation of optical properties of hollow-core photonic crystal fibers

We propose a method for calculation of the bandgaps in the cladding of hollow-core photonic crystal fibers, based on the Floquet theorem. The effectiveness of the approach is confirmed by estimates of the effect of the number of air channels in the cladding on attenuation of the fiber modes due to mode energy leakage from the core. We have studied the conditions for the existence of eigenmodes in the indicated fibers. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 2, pp. 311–320, March–April, 2009.     

Leakage in LiNbO3 channel H-waveguides

Attenuation of leaky modes in LiNbO₃ channel H-waveguides is studied theoretically. It is shown that leakage significantly affects the parameters of waveguides made of X-and Y-cut crystals. An approximate expression for attenuation coefficients is obtained from the solution to the scalar eigenvalue problem.