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Moving the fiber laser emission to the region below one micron may provide a cheaper, more compact and robust alternatives to the existing solid state lasers. Here, for the first time we report a neodymium mode-locked fiber laser emitting at 905 nm in the all-fiber polarization maintaining configuration. We obtain a self-starting pulse generation in nonlinear amplifying loop mirror (NALM) cavity configuration. To suppress a dominant emission at 1064 nm corresponding to a 4-level laser scheme, we use an active fiber - 920/1064 division multiplexer - active fiber sandwich-like sequence in the NALM loop. A rectangular shape dissipative soliton had nJ energy, 30 pm spectral width and 80 - 430 ps width linearly depending on the pump power. Excellent agreement with numerical simulation allowed us to recover pulse shape and width for the pulses out of autocorrelation window., Comment: 7 pages, 4 figures

This paper reports on transient processes and cross talk (cross modulation) in an O-band (1260 – 1360 nm) bismuth-doped phosphosilicate fibre amplifier. Times characterising dynamic parameters of the amplifier at a pump wavelength of 1.23 μm have been determined experimentally. Data have been obtained on the effect of the modulation frequency Ω of one of the channels in the range 10 Hz to 1 MHz on the cross-talk intensity in another channel. The data, in combination with numerical calculation results, show that the cross talk in the Bi-doped fibre amplifier is insignificant at modulation frequencies Ω above 100 kHz. Our results demonstrate that O-band Bi-doped fibre amplifiers are potentially attractive for practical application in multichannel high-speed data transmission systems.

Bismuth-doped fibers (BDFs) are considered nowadays as an essential part of the development of novel optical amplifiers, which can provide a significant upgrade to existing fiber optic telecommunication systems, securing multiband data transmission. In this paper, a series of BDF amplifiers (BDFAs) for O-, E-, and S-telecom bands based on a cladding pumping scheme using low-cost multimode semiconductor laser diodes at a wavelength of 0.7–0.8 µm were demonstrated for, it is understood, the first time. The developed BDFAs are characterized by a high peak gain of >25–30 dB in the corresponding telecom bands and a relatively low noise figure of 5–6 dB. Comparative analysis shows that most of the parameters of cladding pumped BDFAs are close to those of the best core pumped ones. This research opens up new opportunities for utilizing Bi-doped fibers as a key element of cost-effective and ready-to-work BDFAs for various practical applications.

In this article, we describe the technology for manufacturing of the phosphosilicate bismuth-doped optical fibers providing optical amplification near 1.32 $\mu$ m. The effect of preforming sintering process and fiber drawing on the optical properties of the fabricated fibers were studied. We showed that an increase in the vitrification temperature of the P-doped silica glass soot layers deposed on the inner surface of a fused silica tube from 1850 to $\mathbf {\sim \text{2000}}$ °C (while keeping other parameters unchanged) provides a noticeable reduction of the unsaturable losses. We also found that the fiber drawing speed significantly affects the optical properties of bismuth-doped fibers. In particular, an increase in the drawing speed from $\sim$ 1 to $\sim$ 80 m/min led to a decrease of both active absorption and unsaturable losses, while the ratio of active absorption to unsaturable losses became greater. As a result, the laser efficiency of the bismuth-doped fibers grew two-fold from 19.5% to 37%.

The effect of drawing conditions on the optical properties of the bismuth-doped high-germania-glass core fibers has been studied. It was found that the gain characteristics of these fibers become better with the increase of the drawing speed from 10 to 100 m/min. The small-signal absorption spectra of the Bi-doped fibers obtained at drawing speeds lower than 1 m/min are characterized by a high level of the unsaturable loss and the presence of an unstructured band situated within a wavelength region of 1100 - 1250 nm. The variation of drawing temperature ranging from 1770 to 1830 °C almost did not affect the optical properties of the fibers studied. It was shown that an optimization of the drawing parameters can significantly increase the performance of the developed bismuth-doped fiber lasers.

We have studied polarised luminescence of bismuth active centres in germanosilicate glasses. The 1.4-μm luminescence components with orthogonal polarisation states under excitation with linearly polarised light at λ = 1.26 μm have been shown to differ in intensity. The degree of polarisation reaches ∼0.12. Increasing the concentration of bismuth active centres leads to a decrease in the degree of polarisation of luminescence in the range studied.

For the first time, to the best of the authors’ knowledge, a cladding-pumped bismuth-doped fiber laser (BDFL) is demonstrated. A “home-made” Bi-doped germanosilicate fiber with a 125 µm circular outer cladding made of fused silica and coated by a low refractive index polymer is used as an active medium pumped by commercial multimode laser diodes with a total output power of 25 W at 808 nm. We find that the BDFL with a free-running cavity (when feedback is provided by ≈4% back reflection from two bare right-angle cleaved fiber ends) composed of a 100-m-long bismuth-doped fiber is capable of emitting at a wavelength of 1440 nm. A slope efficiency of 0.5% with respect to the absorbed pump power with a maximum output power of ≈50 mW is obtained in a BDFL with a cavity formed by a highly reflective Bragg grating at 1461 nm and a right-angle cleaved fiber end. The beam quality factors (M2) of the output BDFL in the horizontal and vertical directions are measured to be 1.18 and 1.13, respectively. The processes affecting the efficiency of the BDFLs are also discussed. The possible improvements for the output power scaling and increasing the efficiency of the cladding-pumped BDFLs are proposed.

We report the 1.3/1.4 µm dual-wave band dissipative soliton resonance (DSR) in a passively mode-locked bismuth-doped phosphosilicate fiber (Bi-PSF) laser. The low-water-peak Bi-PSF with two bismuth active centers associated with silicon and phosphorus supports the O+E-band gain. Using a 1239 nm home-made Raman fiber laser as pump source and nonlinear amplifying loop mirror for initiating mode-locking, stable DSR operation at 1343 and 1406 nm is achieved with the spectral bandwidth of 12 and 16 nm. The pulse duration with the pump power increases from 62 to 270 ps with a repetition frequency of 4.069 MHz. The average power is 11.05 mW corresponding to the maximum energy of 2.7 nJ. This is, to the best of our knowledge, the first demonstration of a mode-locked fiber laser in the ∼1.38 µm water absorption band and the O+E dual-wave band operation for applications in all-spectral-band communications, bio-medical imaging, and terahertz difference frequency generation.

Moving the fiber laser emission to the region below one micron may provide a cheaper, more compact and robust alternatives to the existing solid state lasers considering an ideal source for two-photon microscopy (TPM), optical coherent tomography, laser spectroscopy, precision metrology, LIDAR, quantum communications and also for generation of blue light through frequency doubling [1] - [4] . Here we report, for the first time to the best of our knowledge, a neodymium mode-locked fiber laser emitting at 905 nm in the all-fiber polarization maintaining configuration.

This paper presents a study of the properties of erbium-doped optical fibres with enhanced gamma-ray resistance at a high dose rate. The fibres have a silica core containing different dopants. The gamma-ray resistance of the fibres is due to additional doping of their core with cerium and germanium ions, as well as to aluminium concentration optimisation. We assess the effect of fibre composition on the radiation-induced loss at a wavelength of 1310 nm and the output power and weighted average wavelength of superluminescent fibre sources based on erbium-doped fibre under pulsed gamma irradiation (dose per pulse, ∼ 20 Gy). The fibre doped with aluminium, germanium and cerium oxides is shown to be optimal for use in gamma-ray-resistant broadband superluminescent fibre sources.

We report on, to the best of our knowledge, the first Q-switched bismuth-doped fiber laser operating at ${\sim }1.3~\mu \mathrm {m}$ . An acousto-optic modulator (AOM)-based active Q-switching was realized in a ring cavity with a bismuth-doped phosphosilicate fiber as an active medium. Stable pulsing in the range from 1310 to 1350 nm was achieved using various fiber Bragg gratings. The dependence of the laser operation on the unsaturable loss of the active fiber was studied. Optimization of the scheme and selection of an appropriate bismuth-doped fiber provided maximum pulse energy of ${\sim }11.5~\mu \mathrm {J}$ at the output of the laser. Using the data obtained, the evaluation of the extractable energy and the concentration of the bismuth active centers in the fiber samples under investigation was performed.

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.

We present highly efficient b ismuth-doped fi ber am plifier cov ering almost all O- and E-bands. Using 250 mW single wavelength pumping at 1256 nm and low OH bismuth-doped fiber, we managed to achieve 26dB peak gain with -3dB bandwidth of 116 nm.

Bismuth-doped fibre amplifiers offer an attractive solution for expanding the bandwidth of fibre-optic telecommunication systems beyond the current C-band (1530-1565 nm). We report a bismuth-doped fibre amplifier in the spectral range from 1370 to 1490 nm, with a maximum gain exceeding 31 dB, and a noise figure as low as 4.75 dB. The developed system is studied for forward, backward, and bi-directional pumping schemes and three different signal power levels. The forward pumping scheme demonstrates the best performance in terms of the achieved noise figure. The developed amplifier can be potentially used as an in-line amplifier with >20dB gain in the spectral band from 1405 to 1460 nm.

We present a wideband fiber amplifier with a flat gain spectrum ranging from 1306 to 1441 nm at a 3 dB level from maximum of 26 dB based on bismuth-doped active fibers with phosphosilicate and germanosilicate glass core. Combination of pumping at 1180 nm and gain clamping at 1280 nm was used to achieve a wider gain spectrum.

We report experimental results and numerical calculations regarding the stability of laser-active bismuth-related centers in Bi-doped GeO 2 –SiO 2 glass fibers to laser radiation at 1550 nm (at different temperatures).

For the first time, we fabricated and studied optical characteristics of a bend-insensitive bismuth-doped P 2 O 5 – SiO 2 glass core fiber operating in a spectral region of 1.3 – 1.4 µm having a depressed cladding design.

The alteration of the laser properties of bismuth-doped high-GeO 2 fibers brought about by thermal treatment was investigated experimentally and simulated numerically. We have demonstrated that thermal treatment can be beneficial for the shortening of the active fiber length due to an increased concentration of the laser-active centers.

We present results on the lasing properties of the Bi-doped high-germania glass fibers thermally treated at different heating and cooling conditions. The absorption and luminescence spectra, the luminescence lifetime of bismuth-related active centers (BACs) formed in the Bi-doped fibers before and after treatment were measured. Analyzing the results, it was shown that the concentration of the BACs could be increased by approximately two times after treatment at certain conditions. A series of experiments regarding laser action at 1730 nm using pristine and treated Bi-doped fibers was performed. From the dependencies of the slope efficiencies of the Bi-doped fiber lasers on the length of the active fibers obtained at various cooling conditions, it was found that the optimal length $${L}\approx 20$$ m of the treated active fibers required for the realization of the Bi-doped fiber lasers is two times shorter than that of the pristine fibers. In addition, the efficiency of the developed lasers being $$\approx 18\, \%$$ with respect to the absorbed pump power is greater than that of the lasers based on the pristine fibers ($$\approx 10\%$$ at $${L} = 20$$ m), but it is lower than their maximum efficiency ($$\approx 25 \,\%$$ at the optimum lengths of 45 m). From the numerical simulation of the Bi-doped fiber laser, a number of parameters needed for estimation of the native and thermally induced BAC concentrations were determined.

In this paper, we performed numerical and experimental study of the stability of bismuth-doped high-GeO2 glass core fiber used as an active medium in lasers operating in the wavelength region 1600 - 1800 nm. Mainly, we focus on the investigation of the joint effects of temperature and pumping radiation on the spectroscopic and laser characteristics of the fibers. Temporal evolution of the degradation of bismuth-related active centers (BACs) under pumping at 1550 nm, as well as the annealing of the fibers at temperature ranging from 300 to 550 °C was experimentally revealed and studied. A model describing the photochemical processes of the transformation of the BACs at different ambient conditions was proposed and used to make a long-term prediction of the dynamics of the process. The ability to simulate the long-term behavior of the medium might be instrumental since direct measurements are time consuming and therefore impractical. In addition, we performed numerical simulation to find out how the effect of photoinduced degradation of BACs affects the performance of a laser based on this type of fibers.

During last decades there has been considerable interest in developing a fiber amplifier for the 1.3-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\upmu $$\end{document}μm spectral region that is comparable in performance to the Er-doped fiber amplifier operating near 1.55 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\upmu $$\end{document}μm. It is due to the fact that most of the existing fiber-optic communication systems that dominate terrestrial networks could be used for the data transmission in O-band (1260–1360 nm), where dispersion compensation is not required, providing a low-cost increase of the capacity. In this regard, significant efforts of the research laboratories were initially directed towards the study of the praseodymium-doped fluoride fiber amplifier having high gain and output powers at the desired wavelengths. However, despite the fact that this type of amplifiers had rapidly appeared as a commercial amplifier prototype it did not receive widespread demand in the telecom industry because of its low efficiency. It stimulated the search of novel optical materials for this purpose. About 10 years ago, a new type of bismuth-doped active fibers was developed, which turned out to be a promising medium for amplification at 1.3 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\upmu $$\end{document}μm. Here, we report on the development of a compact and efficient 20-dB (achieved for signal powers between \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$-40$$\end{document}-40 and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$-10$$\end{document}-10 dBm) bismuth-doped fiber amplifier for a wavelength region of 1300–1350 nm in the forward, backward and bi-directional configurations, which can be pumped by a commercially available laser diode at 1230 nm with an output power of 250 mW. The compactness of the tested amplifier was provided by using a depressed cladding active fiber with low bending loss, which was coiled on a reel with a radius of 1.5 cm. We studied the gain and noise figure characteristics at different pump and signal powers. A record gain coefficient of 0.18 dB/mW (at the pump-to-signal power conversion efficiency of above 27\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\%$$\end{document}%) has been achieved.

We investigated the optical properties of a depressed-cladding bismuth-doped phosphosilicate fiber. The performance characteristics of CW laser and optical amplifier operating within the O-band based on this fiber were studied.

We present the absorption spectra of bismuth active centers associated with phosphorus obtained experimentally. The results showed that the peak values are ~2.5 ±0.4 pm2 and weakly depend on the active centers concentration.

In present paper we demonstrate a carbon nanotube saturable absorber with variable nonlinear optical response controlled by electrochemical gating. Implemented into all-PM fiber laser scheme this device allows switching between mode-locked and Q-switched generation regimes.

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.

An all-vapor phase modified chemical vapor deposition (MCVD) process has been proposed for the fabrication of active-fiber preforms with a fluorine-rich F–Yb2O3–GeO2–Al2O3–SiO2 glass core. The composition of the glass has been shown to differ significantly from that of the vapor–gas mixture because of the formation of GeF4, AlF3, and YbF3, which are volatile at typical MCVD temperatures. We have identified F–Yb2O3–GeO2–Al2O3–SiO2 glass deposition conditions that ensure uniform distributions of the dopants along the length of the preform.

We report on a new record in the field of broadband BDFA in the O+E spectral range. Using only 250 mW single wavelength pump at 1256 nm and a low-OH bismuth-doped fiber containing two types of bismuth active centers, we achieved >23 dB gain from 1325 nm to 1441 nm with flatness

We investigate the fluorescence characteristics of a purely Ce-doped silica fiber and demonstrate broad-bandwidth fluorescence across the visible and near-infrared. The Ce-doped fiber is fabricated using standard modified chemical vapor deposition technology. Trace metal analysis by inductively coupled plasma mass spectrometry confirmed the purity of Ce-doping. The Ce valence state of 3+ was revealed by X-ray photoelectron spectroscopy. The optimum pump wavelength for the broadest luminescence from a fiber is scanned between 405 nm to 440 nm wavelength of diode lasers operating under continuous-wave regime. The strongest pump absorption is observed at the wavelength of 405 nm. Variation of pump power and fiber length results in the demonstration of broad-bandwidth fluorescence with spectral widths up to 301 nm (at -10 dB). The measured fluorescence spectra cover the wavelength range from ∼458 nm to ∼819 nm with spectral power densities of up to 2.4 nW/nm. publishedVersion

Performance characteristics of superluminescent fiber source (SFS) operating at 1.73 μ m under different temperature conditions and gamma-irradiation of active fiber were studied. The SFS in a single-pass and backward pumping configuration was constructed using a bismuth-doped high-germania silicate fiber. The output parameters of the SFS including output power, spectral shape, mean wavelength, full width at half maximum, and peak position were measured in the temperature range from –60 to +60 °C. The simulation of the bismuth SFS at room temperature was performed for the first time to our knowledge. The simulation was also used for theoretical study of the SFS performance under gamma-irradiation. The obtained results of calculation are in good agreement with the experimental data. The effect of gamma-radiation exposure (60Co source) of active fiber on the SFS output power was investigated at different temperatures. The output power as a function of radiation dose is presented. No photobleaching of radiation induced absorption in bismuth doped fibers by pump light at 1550 nm was observed.

Photobleaching of IR luminescence in bismuth-doped fibers was studied using laser radiation with different wavelengths: 407, 532, 639, 975, 1460 nm. For each wavelength the bleaching time was determined by fitting a stretched-exponential function to the data measured. It was revealed that the bleaching time increases with the decrease of the photon energy. The measured dependence of the bleaching rate on the launched power at 532 nm is also presented. The effect of temperature on the bleaching rate was also investigated. The role of the oxygen-deficient centers in the bleaching process is discussed.