Evgenii M Dianov

High-temperature stability of long-period fiber gratings produced using an electric arc

We report, for the first time to our knowledge, the excellent optical performance of long-period gratings written in three standard fibers and in two nonstandard fibers, namely, S-doped and N-doped fibers, using the flexible and low-cost electric arc technique. The fundamental mechanism for their formation is proposed. The grating thermal behavior and the effect of fiber preannealing prior to writing have been investigated. We have demonstrated a good stability of these gratings at high temperatures.

Electrostriction mechanism of soliton interaction in optical fibers.

In contrast to the mechanism of interaction determined by the Kerr nolinearity, the electrostrictive interaction between picosecond pulses in optical fibers can occur when the temporal interval between them is much greater than their duration. The width of the interval is determined by the lifetime of the sound wave in the fiber core region, i.e., ~1 nsec. It follows from our calculations that for long propagation distances (L > 1000 km) the relative temporal separation of the interacting pulses can reach hundreds of picoseconds at the temporal interval between them of ~1 nsec.

Self-starting mode-locked laser with a nonlinear ring resonator

A laser with a ring resonator that incorporates a nonlinear antiresonant loop is proposed and analyzed. With computer simulation it is shown that the mode-locking process is self-starting and that, when the laser is properly designed, gain-bandwidth-limited pulses can be obtained. Passive mode-locked, bistable, and chaotic solutions are found to depend on the design parameters of the model.

Passive mode locking of a laser with a nonlinear fiber reflector

A nonlinear mirror in the form of a fiber-loop reflector with nonreciprocity is proposed as a passive mode locker. The mode-locking process occurs as a result of the interference of counterpropagating pulses, when they are properly chirped in the fiber loop. With a computer simulation, we study a simple one-cavity model and find stable solutions.

Hollow-core revolver fibre with a double-capillary reflective cladding

We report the fabrication of the first hollow-core revolver fibre with a core diameter as small as 25 μm and an optical loss no higher than 75 dB km-1 at a wavelength of 1850 nm. The decrease in core diameter, with no significant increase in optical loss, is due to the use of double nested capillaries in the reflective cladding design. A number of technical problems pertaining to the fabrication of such fibres are resolved.

Crystalline and Fiber Raman Lasers

This chapter describes the state of the art of crystalline and fiber Raman lasers based on the simulated Raman scattering (SRS) effect in crystals and silica-based fibers. It includes historical and theoretical background, analysis of properties of known and newly developed high-efficient SRS crystals, such as LiIO3, Ba(NO3)2, NaNO3, PbNO3, CaCO3, KGW, BaWO4, SrWO4,BaMoO4,SrMoO4, PbWO4, and germanosilicate and phosphosilicate fibers. A large set of data on IR Raman shifters and lasers operating in the CW, nanosecond, and picosecond regimes with low and high repetition rates is given. Some applications of Raman lasers in medicine, ecology, fiber optics, and communications are discussed.

Dynamics of ultrashort-pulse generation by Raman fiber lasers: cascade self-mode locking, optical pulsons, and solitons

The dynamics of ultrashort-pulse generation in Raman fiber lasers is numerically investigated. The regime of cascade self-mode locking in the process of generation of higher-order Stokes components as well as formation of ultrashort solitary pulses with a high contrast of radiation are described. The generation of optical solitons at the Stokes frequency is shown to be the result of a cooperative effect of self-phase modulation, negative group-velocity dispersion, and distributed stimulated Raman scattering. In the same way we explain the formation of pulses with regularly pulsating amplitude and frequency modulation; we call these optical pulsons.

All-solid photonic bandgap fiber with large mode area and high order modes suppression

We present all-solid bandgap fiber design with the small ratio of cladding elements diameter to pitch (0.24), with MFD of 36 m at 1 m wavelength and higher order mode suppression caused by the propagation loss difference.

Spectral and polarization selective fiber-optic elements

A pair of coupled step-index waveguides is analyzed. Characteristic equations are obtained and used to evaluate the cutoff frequencies and coupling constants. Mode transformation at tapers is analyzed. The spectral properties of fused couplers and tapered filters for which cutoff frequencies of higher modes were observed are studied. A fiber polarization splitter is realized. A semiconductor laser with an external dispersive cavity based on the spectral selective coupler is designed. >

Dielectric and transport properties of thin films precipitated from sols with silicon nanoparticles

Dielectric properties of thin films precipitated on solid substrates from colloidal solutions containing silicon nanoparticles (average diameter is 10 nm) are studied by optical ellipsometry and impedance-spectroscopy. In the optical region, the values of real ɛ′ and imaginary ɛ″ components of the complex permittivity ɛ vary within 2.1–1.1 and 0.25–0.75, respectively. These values are significantly lower than those of crystalline silicon. Using numerical simulation within the Bruggeman effective medium approximation, we show that the experimental ɛ′ and ɛ″ spectra can be explained with good accuracy, assuming that the silicon film is a porous medium consisting of silicon monoxide (SiO) and air voids at a void ratio of 0.5. Such behavior of films is mainly caused by the effect of outer shells of silicon nanoparticles interacting with atmospheric oxygen on their dielectric properties. In the frequency range of 10–106 Hz, the experimentally measured ɛ′ and ɛ″ spectra of thin nanoscale silicon films are well approximated by the semi-empirical Cole-Cole dielectric dispersion law with the term related to free electric charges. The experimentally determined power-law frequency dependence of the ac conductivity means that the electrical transport in films is controlled by electric charge hopping through localized states in the unordered medium of outer shells of silicon nanoparticles composing films. It is found that the film conductivity at frequencies of ≤2 × 102 Hz is controlled by proton transport through Si-OH groups on the silicon nanoparticle surface.