G. V. Sinitsyn

Entropic analysis of the information rate density of broadband active fiber-optic communication links

The maximum transfer rate characteristics of broadband active fiber-optic communication links are considered within the model of filling numbers. It is established that, for active information transmission systems, in contrast to passive ones, not only the parameters of the line itself are significant but also the input signal-to-noise ratio. It is shown that the classical approach underestimates considerably the value of the maximum information rate density of erbium fiber amplifiers. In lengthy communication links with erbium amplifiers, the value of the information rate density may reach ∼12–15 (bit/s)/Hz, which is more than one order of magnitude higher than the values achieved currently.

Spectral luminescence and information characteristics of transparent lead fluoride nano-glass-ceramics doped with erbium ions

Spectral luminescence properties of synthesized transparent nano-glass-ceramics doped with erbium ions are studied. It is shown that, as a result of the secondary heat treatment of nano-glass-ceramics, the width of the luminescence spectrum at half maximum increases more than by 15 nm. Luminescence life-time dependences of erbium ions in studied samples are measured, their absorption cross-sections are determined, and their emission cross-sections are calculated by the McCumber method. Spectral and ultimate information characteristics of erbium-doped fiber amplifiers based on synthesized nano-glass-ceramics are numerically simulated. It is shown that, in the unsaturated gain regime, a substantial ripple of the absorption and emission cross-section spectra and shorter lifetime of the metastable level of the erbium ion reduce the pumping radiation power that is required for obtaining the given peak gain, narrow the gain spectra, and lower the transmission capacity of devices based on nano-glass-ceramics compared to the initial glass. Conversely, fiber amplifiers based on calcium fluoride glass-ceramics, for which the lifetime of the metastable level increases with increasing annealing temperature, have an advantage in the transmission capacity over devices based on the primary glass.

Glasses for erbium-doped fiber amplifiers : A comparison based on the ultimate spectral efficiency of information transmission

A new figure of merit—the ultimate spectral efficiency of information transmission in the regime of unsaturated gain in the case of a quasi-two-level scheme of pumping—is proposed to compare host glasses for erbium-doped fiber amplifiers (EDFAs) that are considered as a constituent of an optical communication system. It is shown that the amplifiers based on silicate glasses possess the best characteristics, whereas the amplifiers based on phosphate and tellurite glasses have somewhat worse and substantially worse characteristics, respectively.

Output characteristics of strongly excited LiF:F/sup -//sub 2/ crystal lasers

An investigation was made of the dependences of the energy characteristics of lasing and of the efficiency of conversion of pump radiation on the pump power density up to 200 MW/cm/sup 2/ supplied to LiF:F/sup -//sub 2/ lasers. It was established that the dependences in question had maxima. This made it possible to optimize the lasers in respect of their output parameters. The output energy of an LiF:F/sup -//sub 2/ laser with a nonselective resonator reached 0.225 J and the efficiency of conversion of the pump energy was 38%. Preliminary experiments were also made on tuning of high-energy (in excess of 0.1 J) radiation from an LiF:F/sup -//sub 2/ laser and of conversion of this radiation to the second harmonic.

Application of projection on latent structures for determining temperature of erbium-doped lead fluoride nano-glass-ceramics from upconversion fluorescence spectra

The temperature of erbium-doped lead fluoride nano-glass-ceramics in the range from 44 to 150°C is determined by constructing a projection on latent structures of upconversion fluorescence spectra in violet, green, and red bands. It is shown that the four-dimensional space of latent structures provides the best accuracy of temperature measurements. This space allows one to determine (using a training set of fluorescence spectra with a step of 10°C) temperatures above 70°C with a relative error not larger than 0.5%.

Parametric field excitation in a cavity with oscillating mirrors

The dynamics of the parametric excitation of an electromagnetic field in a cavity that is composed of two plane mirrors has been analyzed. One of the mirrors is immobile and has a finite reflectance spectral band, while the other mirror is oscillating with a wider spectral band. The field energy in the cavity may increase due to a transfer from the kinetic energy of the mirrors. Estimates and calculation results for a Lorentz profile of the spectral band of the reflectance show that, under conditions of a parametric resonance, the initial exponential increase in the field energy in the cavity is stopped and the stable pulse-periodic mode is formed.

Simulation of the ultimate characteristics of thulium-doped fiber amplifiers

A completely spatially and spectrally resolved model of a thulium-doped fiber amplifier that, unlike existing models, takes into account the radiation mode structure is proposed. A genetic algorithm is used to optimize the pump scheme parameters in order to achieve the maximum gain or the minimum non-uniformity of the gain spectrum. The ultimate information characteristics of the amplifier are determined.

On focusing of terahertz radiation beams and pulses

We show that, for terahertz (THz) radiation, the effective focal length of a lens differs significantly from its geometrical-optics (nominal) focal length. As a pulse of THz radiation with a bell-shaped (Gaussian) transverse profile is incident on a lens, the field-amplitude distribution in the nominally focal plane of the lens may radically change, up to the formation of dips in the paraxial region. These changes in the spatiotemporal shape of the beam (pulse) may considerably distort the results of pulsed THz spectroscopy. These distortions can be minimized by using media with anomalous dispersion, including metamaterials.

On reflection of terahertz radiation from a rough surface

We computationally analyze the influence of random inhomogeneities of the interface surface between two media that are diagnosed by the pulsed THz spectroscopy method. The statistics of inhomogeneities is characterized by the rms dispersion and correlation radius. The medium to be diagnosed is modeled by a Lorentz contour, the position and the width of which can serve as recognizable indicators. For monochromatic radiation and for a radiation pulse with a wide spectrum (close to the video pulse), a signal at a “point” detector is calculated in the absence and in the presence of inhomogeneities. The results yield conditions under which inhomogeneities significantly affect the recognition of different substances.

Temperature dependence of the ratio of intensities of up-conversion fluorescence bands of YVO4 and YGdVO4 crystals and lead fluoride nano glass ceramics activated with erbium ions

Up-conversion fluorescence spectra of YVO4 and YGdVO4 crystals and lead fluoride nano glass ceramics coactivated with erbium and ytterbium ions have been studied in the wavelength range of 520–560 nm under 967-nm pumping. The ratio of intensities of fluorescence bands in the ranges of 520–530 and 540–550 nm has been measured in the temperature range of from room temperature to 150°C. It is shown that the considered materials can be used for preparing a sensing element of optical fluorescent temperature sensors; the sensitivity of measuring the temperature of nano glass-ceramics can be close to that of crystal samples.