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Radiation-induced absorption (RIA) of light in five isotropic optic fibers (OFs) with a core of undoped silica glass (SiO2) and a fluorosilicate cladding and one birefringent OF of the “PANDA” type of the same chemical composition was measured at a wavelength λ = 1.55 μm under γ-irradiation to a dose of 1 kGy (∼ 1 Gy/s), 15–45 min after completion of irradiation, and in a few months at temperatures +25 and –60°C. An extrapolation of the RIA after irradiation in the framework of the kinetic model of the nth order, which gave a forecast of the RIA for isotropic OFs of ∼1.1 and ∼ 0.3 ± 0.1 dB/km at –60 and +25°C, respectively, was made to assess the RIA at the end of a 15-year mission in space. It has been concluded that it is possible to use at least 4–5 km of OF in space under conditions of temperature variation within ±60°C at a maximum dose of 1 kGy and a mission duration of 15 years. It has also been established that the RIA will not have been higher in the birefringent OF than in the isotropic ones by the end of such a mission.

This paper presents a study of anti-Stokes luminescence in optical fibres with a bismuth-doped ~50%GeO2 – 50%SiO2 glass core under IR excitation. The anti-Stokes luminescence intensity has been measured as a function of temperature in the range 77 – 300 K. From these data, we have evaluated the activation energy for the thermal quenching of anti-Stokes luminescence in the visible and IR spectral regions. A mechanism of anti-Stokes luminescence in this type of optical fibre has been proposed.

Radiation-induced attenuation (RIA) at λ = 1.55 μm is studied in polarization-maintaining (PM) pure-silica-core optical fibers of the Panda-type under γ-irradiation and upon pulsed-X-ray-irradiation. For the first time, the RIA spectrum is compared under γ-irradiation in a Panda and in a non-PM fiber drawn from the same preform before embedding the stress-applying rods. It is found out that the chief RIA origins in the near-IR range in both fibers are an extremely short-lived band centered at ~1 eV and the tails of the classical bands due to strain-assisted self-trapped holes (STHs) at 1.63 and 1.88 eV. The former band is found to be many times more intense in the Panda; the latter bands, somewhat more intense in the non-PM fiber. The ~1-eV band proved to be composed of two Gaussian sub-bands centered at 0.95 and 1.12 eV. Under γ-irradiation, the composite ~1-eV band is found to be photobleached virtually fully by 1.55-μm light of 5-mW power, which results in manifold reduction of the total RIA. Upon pulsed irradiation, RIA in Pandas at large post-pulse times (>1 ms–1 s) is found to fall off below the record low level demonstrated elsewhere by a non-PM pure-silica-core fiber. This fact is explained as being due to a smaller concentration of strain-assisted STHs in Pandas than in non-PM fibers. The concentration of strain-assisted STHs in Pandas is shown to increase with increasing the value of birefringence.

Using a bismuth-doped aluminosilicate fibre laser tunable in the range 1130–1210 nm, we have examined the effect of pump wavelength on the gain spectrum of bismuth-doped phosphosilicate fibres in the range 1220–1400 nm. At a pump wavelength of 1195 nm, we obtained a peak gain wavelength of 1300 nm, which is near the centre of the standard range for O-band transmission (1270–1320 nm) in fibre-optic communication links, in particular between data centres. Using a bismuth-doped phosphosilicate fibre amplifier pumped at 1195 nm, we have demonstrated that the transmission distance for a signal from a semiconductor laser diode directly modulated at 25 Gb s−1 [on – off keying (OOK) modulation] can be increased for G.652 fibre from the standard 10 to 80 km or even more.

Short-lived radiation-induced absorption (RIA) of light peaking at wavelengths >1700 nm has been revealed in a γ-irradiated (≤1 kGy) heavily (50 mol% GeO2) Ge-doped silica optical fiber (Ge-doped fiber) at low temperatures (≤−30 °C). This RIA is found to closely resemble in properties the known RIA due to inherent self-trapped holes (STHs) in undoped-silica-core optical fibers (same spectral range, low thermostability, non-monotonic evolution with dose, shift of the peak wavelength with temperature, Arrhenius dependence on temperature, growth of the activation energy in the course of irradiation and recovery). The STH-like RIA is found not to occur in more lightly Ge-doped fibers and in a Bi-codoped Ge-doped fiber with the same (50 mol%) GeO2 concentration. A possible microscopic structure of the STH in heavily Ge-doped fibers is discussed.

A Raman laser with a wavelength exceeding 4 μm is designed for the first time. Using a revolver silica fibre with a hollow core filled with molecular hydrogen (1H2) as an active medium, we have obtained SRS lasing at a wavelength of 4.4 μm under pumping by a pulsed erbium fibre laser (λ = 1.56 μm, τ = 2 ns). The SRS conversion quantum efficiency reaches 15 %, and the maximum output peak power at a wavelength of 4.4 μm is 0.6 kW.

We developed a simple silica-based BDFA with 80nm 6-dB gain-bandwidth flexibly centred within 1305–1325nm, and parameters comparable to EDFAs. The amplifier can extend 400GBASE-LR8 transmission (8×26.6 Gbaud/s PAM-4 channels) beyond 50 km of G.652 fiber.

A single-mode fibre based on bismuth-doped germanosilicate glass with a high germanium concentration is considered as an active medium of a laser continuously tunable within the range 1.65 – 1.8 μm. The laser scheme included a broadband ring cavity, and the laser wavelength was controlled by an external plane diffraction grating in the Littrow configuration. For a pump power of 300 mW at a wavelength of 1.564 μm, the maximum output laser power was 15 mW in the zero diffraction order and 6 mW at the fibre output.

Operation of single-stage, single-pump E-band bismuth-doped fibre amplifier with gain, noise figure and efficiency comparable to the state-of-the-art erbium-doped fibre amplifier of the same complexity and the gain bandwidth of 50 nm is demonstrated. The amplification of 10 Gbit/s intensity modulation/direct detection signal with power penalty below 1.5 dB is reported.

We have studied second-harmonic generation (SHG) of a cw single-frequency ytterbium-doped fibre laser, using a periodically poled silica fibre as a nonlinear medium for frequency conversion. All-fibre external cavity SHG has been investigated for the first time. A twofold increase in second-harmonic power in a fibre ring cavity has been demonstrated and possibilities of further optimising the fibre scheme have been analysed.

Absorption, luminescence and luminescence excitation spectra of MCVD-prepared SiO2:Pb glasses with Pb content up to 0.35 wt% were studied. UV and visible luminescence was observed in the 0.3–0.45 and 0.5–0.6 μm ranges. IR luminescence was found in the 0.85–0.95, 1.1–1.2 and 1.3–1.4 μm ranges. Computer modeling of SiO2:Pb glass was performed. The main possible forms of Pb in the SiO2 glass network were found to be threefold coordinated Pb atom, diatomic Pb center, twofold coordinated Pb atom, and possibly fourfold coordinated Pb atom. Structure, electronic properties, absorption and luminescence of the centers corresponding to these forms and of possible lead-related centers responsible for the IR luminescence were calculated. The results of the experiments and modeling suggest that (1) the 0.3–0.45 μm luminescence band is caused mainly by twofold coordinated Pb atoms and partly by threefold coordinated Pb atoms, (2) the 0.5–0.6 μm luminescence band is caused by twofold coordinated Pb atoms, (3) 1.1–1.2 μm IR luminescence band is caused by Pb+ interstitial ions, and (4) 0.85–0.95 and 1.3–1.4 μm IR luminescence bands are caused by complexes formed by interstitial Pb0 atom and a pair of ≡ SiSi ≡ oxygen vacancies.

We have studied the luminescence properties of optical fibres with a bismuth-doped alumino- and phosphosilicate glass core under two-step excitation and obtained new experimental data on the properties of luminescence centres in such fibres.

We have studied the influence of cross-sectional structure and bends on optical cross-talk in a multicore fibre. A reduced refractive index layer produced between the cores of such fibre with a small centre-to-centre spacing between neighbouring cores (27 μm) reduces optical cross-talk by 20 dB. The cross-talk level achieved, 30 dB per kilometre of the length of the multicore fibre, is acceptable for a number of applications where relatively small lengths of fibre are needed. Moreover, a significant decrease in optical cross-talk has been ensured by reducing the winding diameter of multicore fibres with identical cores.

The effect of laser and thermal annealing on the gain characteristics of bismuth-doped optical fibers was studied. Net gain enhancement in a wavelength region of $1.6-1.8\ \mu m$ in Bi-doped germanosilicate fibers after laser or/and thermal treatment was revealed.

We report the results on lasing features in annealed bismuth-doped optical fibers. It was found that the annealed fibers present better lasing properties than the pristine ones which contain similar amount of the bismuth active centers associated with germanium.

Three single-mode fibers have been drawn from each of four MCVD-made pure-silica-core F-doped-silica-cladding preforms, the drawing parameters (temperature, speed, and tension) being varied among the fibers in a controlled fashion. The initial optical loss spectra in the range 200-1700 nm as well as radiation-induced attenuation (RIA) spectra in the near-IR range under γ-irradiation to 82 kGy (7.6 Gy/s) are measured in the fibers. RIA is found to increase significantly with increasing the drawing temperature and to increase much less with increasing the speed and tension. The mechanism of the strong drawing temperature effect on RIA is argued to be associated with a rise in the fiber silica fictive temperature, which, in turn, enhances the concentration of strain-assisted radiation-induced self-trapped holes.

Radiation-induced absorption spectra are analyzed in germanosilicate fibers with different GeO2-content (3.5–50 mol%) under gamma-irradiation at different temperatures. GeY-center peaking at ~1.38 eV is resolved for the first time. GeY- and GeX-center properties are compared.

The laser performance at the wavelength 1700 nm with a slope efficiency of 18% has been demonstrated using a 8.5-m long bismuth-doped fiber containing thermally induced active centers.

Efficient Raman generation in a molecular hydrogenfilled hollow-core fibre having a cladding in the form of a single ring of capillaries has been demonstrated for the first time. The pump source used was a Q-switched Nd:YAG laser with a pulse duration of 125 ns, and a single-pass (cavity-free) configuration was employed. The maximum average output power at 1.9 μm was 300 mW, and the differential quantum efficiency was 87%, a record level for such experiments.

We have studied UV excitation spectra of IR luminescence in bismuth-doped glasses of various compositions and obtained energy level diagrams of IR-emitting bismuth-related active centres (BACs) associated with silicon and germanium atoms up to ~5.2 eV over the ground level. A possible energy level diagram of the BACs in phosphosilicate glass has been proposed. The UV excitation peaks for the IR luminescence of the BACs in the glasses have been shown to considerably overlap with absorption bands of the Bi3+ ion, suggesting that Bi3+ may participate in BAC formation.

We have studied photodarkening in ytterbium-doped fibre preforms with an aluminosilicate glass core. Analysis of their absorption and luminescence spectra indicates the formation of stable Yb{sup 2+} ions in the glass network under IR laser pumping at a wavelength λ = 915 nm and under UV irradiation with an excimer laser (λ = 193 nm). We have performed comparative studies of the luminescence spectra of the preforms and crystals under excitation at a wavelength of 193 nm. The mechanism behind the formation of Yb{sup 2+} ions and aluminium – oxygen hole centres (Al-OHCs), common to ytterbium-doped YAG crystals and aluminosilicate glass, has been identified: photoinduced Yb{sup 3+} charge-transfer state excitation. (optical fibres)

The study of detonation-like mode of laser induced damage propagation was considered. Velocity of this propagation is two orders of magnitude faster than known published data on burning fiber glass. The condition of optical fiber and enough long laser pulse let us obtain laser induced damage propagation passing near hundred own core diameters during pulse. The using as target the core of silica-based optical fiber has some diagnostic advantages. It allows spatially splits “start” and “stop” points and to supply the same form of energy deposition in every cross section of optical fiber. Tested regime demonstrates near constant velocities during 250 ns in the range of laser intensity 2-4.5 GW/cm2.

Using bismuth/erbium-doped optical fibre, we have fabricated the first optical amplifier with a gain of in a wide spectral range , which covers the C-, L- and U-bands.

We have demonstrated the first superluminescent IR source based on bismuth-doped high-germania fibre. Its main output characteristics are as follows: centre wavelength, ; emission bandwidth, at an output power of ; optical efficiency, .

Aleksandr Mikhailovich Prokhorov was a Russian physicist, academician, one of the originators of quantum electronics, laser physics and laser technologies, winner of the 1964 Nobel Prize in Physics 'for fundamental work in the field of quantum electronics, which has led to the construction of oscillators and amplifiers based on the maser – laser principle' (shared with N.G. Basov and Ch.H. Townes), Lenin Prize and State Prize winner and twice Hero of Socialist Labour.

We report the first bismuth-doped fibre amplifier operating between 1600 and 1800 nm, which utilises bidirectional pumping (co-propagating and counter-propagating pump beams) by laser diodes at a wavelength of 1550 nm. The largest gain coefficient of the amplifier is 23 dB, at a wavelength of 1710 nm. It has a noise figure of 7 dB, 3-dB gain bandwidth of 40 nm and gain efficiency of 0.1 dB mW-1.

The temperature dependencies of the characteristics of a bismuth-doped fiber amplifier (BDFA) for a 1725-nm band have been studied. The amplifier was backward-pumped with an Er-Yb-codoped fiber laser at 1568 nm. A peak gain of 24 dB, a 3-dB gain bandwidth of 55 nm, a noise figure of 5 dB and slope gain efficiency of 0.17 dB/mW at room temperature have been obtained. It has been shown that peak gain of the BDFA varies by 25 % in the temperature range from −60 to +60 °C while the noise figure remains almost unchanged. Some possible mechanisms responsible for the thermal behavior of the characteristics of the BDFA are considered.

An all-fiber ultrafast dissipative soliton laser at 1.3 microns based on phoshosilicate fiber doped with bismuth is presented. A nonlinear optical loop mirror containing high-germanium fiber with high nonlinearity and large positive dispersion was used. The scheme yields 11.3 ps pulses with energy of 1.7 nJ at repetition rate of 3.5 MHz. By means of bismuth-doped fiber amplifier and diffraction gratings compressor, the pulses were amplified up to 8.5nJ and compressed down to 530 fs. To achieve best results the optimal bismuth active fiber was chosen according to the investigated dependence of the gain coefficient on bismuth active centers concentration in phosphosilicate fibers.

4.4 μm Raman laser based on silica fiber is realized for the first time. H 2 -filled hollow-core silica fiber is used as an active medium. Pumped by high-power 1.56 μm Er-doped fiber laser, the Raman laser generates up to 0.6 kW of peak power at 4.4 μm with quantum conversion efficiency up to 15%.

We report the first demonstration of optical amplifier based on bismuth- and erbium-codoped germanosilicate fibers. The 15-dB small-signal gain window covers a 260-nm band by using a single-wavelength pumping at 1460 nm.

The spectral-luminescent properties of the synthesized bismuth-containing quartz-like glass exposed to heat treatment have been studied. The appearance of the thermoinduced bismuth centers of luminescence, which are the result of the reduction of Bi3+ ions, has been observed. It has been shown that the reduction of Bi3+ ions into Bi2+ proceeds at 870°C. It has been determined that the activation of bismuth centers of IR luminescence in quartz-like glass appears at the temperatures above the glass transition temperature of quartz-like glass Tg ∼ 1400°C.

Divalent tin-containing silicate glass has shown infrared photoluminescence with the properties, similar to those of bismuth-activated glasses and laser fibers. Relatively long lifetime, wide emission bands within the fiber telecommunication window and good overlapping of the excitation spectra with the wavelengths of the most common laser diodes make it a promising novel material for fiber lasers and amplifiers.

We have studied the photodarkening in active fibres with an ytterbium-doped phosphosilicate glass core under IR irradiation with a pump source (920 nm) and UV irradiation (193 nm). Analysis of absorption and luminescence spectra suggests that such irradiations produce phosphorus – oxygen – hole centres (P-OHCs) in the core glass network and lead to the reduction of the ytterbium ions to a divalent state (Yb{sup 2+}). The photoinduced optical loss in the fibres in the visible range (400 – 700 nm) is mainly due to absorption by the P-OHCs. A quantum-mechanical model is proposed for P-OHC and Yb{sup 2+} formation. (nonlinear optical phenomena)

We report an all-fibre ultrashort pulse erbium-doped ring laser passively mode-locked by single-wall carbon nanotubes dispersed in carboxymethylcellulose-based polymer films. Owing to intracavity dispersion management and controlled absorption in the polymer films, the laser is capable of generating both femto- and picosecond pulses of various shapes in the spectral range 1.53 – 1.56 μm. We have demonstrated and investigated the generation of almost transform- limited, inversely modified solitons at a high normal cavity dispersion.

We have studied novel materials promising for fiber-optic applications: composites in the form of As2S3 glass containing Cr2+-doped zinc chalcogenide particles. Their dispersion characteristics and optical properties have been investigated in relation to preparation conditions. Process parameters have been found that enable the fabrication of optical fibers possessing luminescence properties.

Bismuth-doped optical glasses emit NIR luminescence in an ultrabroad spectral region of 1000-2000 nm. It makes Bi-doped glasses and glass optical fibers a promising active medium for the creation of Bi-doped fiber lasers and broadband optical amplifiers for this spectral region. Since the first fabrication of Bi-doped fibers in 2005 a large number of papers devoted to the development of Bi-doped fiber lasers and optical amplifiers have been published. It has been shown that Bi-doped fibers are a new breakthrough in active laser materials.

Divalent tin-containing germanate glasses have demonstrated wide photoluminescence similar to that of tin silicate glasses discovered recently. In comparison with silicate glasses, the germanate glasses are characterized by longer emission lifetimes (145 ÷ 440 µs), emission peaking at 1.59 ÷ 1.64 µm and the absence of SnO disproportionation into SnO2 and Sn during glass synthesis. The potential fabrication of optical fiber via the SnC2O4 + GeO2 powder in silica tube method was demonstrated.

We show both experimentally and theoretically a method to increase the stimulated Brillouin scattering (SBS) threshold and output power of narrow linewidth fiber Raman amplifiers. This method employs two or more fibers with varying concentrations of the Raman gain material dopant such as GeOsub2/subor Psub2/subOsub5/subin silicate-based glasses. These fibers are then cascaded to form an amplifier gain stage, disrupting the buildup of SBS that normally occurs in single continuous fibers. The numerical model shown is applicable to arbitrary amplifier systems for gain stage optimization and increased power scaling. We give experimental results for phosphosilicate fibers that agree well with simulation predictions that support the numerical model used.

1907 nm generation by pure vibrational stimulated Raman scattering in hydrogen-filled hollow-core fiber is demonstrated. Due to special design of hollow-core revolver fiber with nested capillaries, the Raman threshold as low as 270 W of peak power is achieved.

Review on recent results on lasers and amplifiers operating in four bands between 1.1 and 1.8 μm using Bi-doped active fibers with different compositions will be given. Future prospects of the Bi-doped fibers and devices will be discussed.