Abstract
During last decades there has been considerable interest in developing a fiber amplifier for the 1.3-
$$\upmu $$
μ
m spectral region that is comparable in performance to the Er-doped fiber ...amplifier operating near 1.55
$$\upmu $$
μ
m. 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
$$\upmu $$
μ
m. Here, we report on the development of a compact and efficient 20-dB (achieved for signal powers between
$$-40$$
-
40
and
$$-10$$
-
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
$$\%$$
%
) has been achieved.
It is now almost twenty-five years since the first Erbium-Doped Fiber Amplifier (EDFA) was demonstrated. Currently, the EDFA is one of the most important elements widely used in different kinds of ...fiber-optic communication systems. However, driven by a constantly increasing demand, the network traffic, growing exponentially over decades, will lead to the overload of these systems ("capacity crunch") because the operation of the EDFA is limited to a spectral region of 1530-1610 nm. It will require a search for new technologies and, in this respect, the development of optical amplifiers for new spectral regions can be a promising approach. Most of fiber-optic amplifiers are created using rare-earth-doped materials. As a result, wide bands in shorter (1150-1530 nm) and longer wavelength (1600-1750 nm) regions with respect to the gain band of Er-doped fibers are still uncovered. Here we report on the development of a novel fiber amplifier operating in a spectral region of 1640-1770 nm pumped by commercially available laser diodes at 1550 nm. This amplifier was realized using bismuth-doped high-germania silicate fibers fabricated by MCVD technique.
In this paper, we report the detailed study of photobleaching and recovery in bismuth-doped fibers that proved to be a unique laser media for the near IR spectral regions unreachable for ...rare-earth-doped lasers. The laser-induced bleaching and recovery dynamics of the characteristic absorption and emission bands assigned to different types of the bismuth-related active centers were obtained. By analyzing the Raman-scattering spectra of the bleached bismuth-doped fibers, the intensity-dependence of the photobleaching rate and the experimentally determined activation energy of the recovery process and underlying mechanisms of these phenomena are discussed. Furthermore, a bleaching–recovery cycling and “memory effect” are demonstrated.
A novel Yb-doped fiber design for improved lasing near 976 nm based on spectral filtering of the amplified spontaneous emission near 1030 nm was realized and investigated. A very sharp short-pass ...filter was implemented by adding appropriately chosen high-index absorbing rods into the silica cladding. In this case, the resonant interaction of the core mode with the high-index rod mode could be controlled by fiber bending, which allows for the precise adjustment of the stop-band position. It was shown that the utilization of Sm-doped absorbing rods allows one to achieve very high absorption of emission at unwanted wavelengths, but it also adds background losses for the pump near 915 nm and for the signal at 976 nm. Despite this fact, the improvement of efficiency in the 976 nm fiber amplifier, after shifting the stop-band to 1000 nm, was clearly demonstrated. Based on theoretical calculations, it was shown that, after optimizing the fiber parameters, a further twofold improvement in efficiency was possible despite the excess losses at the pump and signal wavelengths.
The polarization properties of bismuth active centers (BACs) are important for many applications of bismuth-doped fibers, but they are still lacking in study. In this paper, we present the ...measurements of polarized luminescence (PL) of the BACs formed in a Bi-doped phosphosilicate glass matrix. This research was performed on phosphosilicate fiber preforms used for the drawing of active bismuth-doped fibers for efficient optical amplifiers and lasers. The degree of polarization (DOP) of luminescence of the BACs associated with phosphorus and silica (BAC-P and BAC-Si) is provided and discussed. The DOP of luminescence at the 1320 nm wavelength appeared to be around 19%, 0% and 7.5% for pumps at 1240 nm, 762 nm and 425 nm, respectively. The DOP of PL caused by resonant excitation may be described in terms of a model of a partially anisotropic oscillator with the parameters represented by the principal axes of an ellipsoid. For the resonant excitation at 1240 nm, the ratio of the major principal axis to the minor one turned out to be 5.1 and 3.0 for BAC-P and BAC-Si, respectively.
Performance characteristics of superluminescent fiber source (SFS) operating at 1.73 μm 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 ( 60 Co 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.
The light sources operating in the spectral range 1600-1800 nm are of great interest because of a number of potential scientific and practical applications. This stimulates a search for effective ...laser media for this wavelength region. Recent progress in the studying of bismuth (Bi)-doped fibers is related to the development of Bi-doped high-germania-core fibers for the mentioned wavelength region. This paper is concerned with the current state of the art in the research field of this kind of the laser-active fibers. The fabrication and spectroscopic properties of the Bi-doped high-germania-core fibers are described. The photo-induced bleaching and recovery stimulated by thermal treatment of luminescent centers in these fibers are presented. The review also includes the description of the basic parameters of the optical devices (continuous wave (CW) and pulsed lasers, amplifiers, superluminescent sources) developed using Bi-doped high-germania-core fibers.
The spectral range between 1650 and 1700 nm is an interesting region due to its potential applications in optical telecommunication and optical-based methane sensing. Unfortunately, the availability ...of compact and simple optical amplifiers with output powers exceeding tens of milliwatts in this spectral region is still limited. In this paper, a single-frequency continuous-wave bismuth-doped fiber amplifier (BDFA) operating at 1651 and 1687 nm is presented. With the improved signal/pump coupling and modified pump source design, the output powers of 163 mW (at 1651 nm) and 197 mW (at 1687 nm) were obtained. Application of the BDFA to the optical spectroscopy of methane near 1651 nm is also described. We demonstrate that the BDFA can be effectively used for signal amplitude enhancement in photothermal interferometry.
We present experimental results on the effects of isothermal and isochronal heat treatments, cooling and heating rates in the temperature range 400–600 °C on the optical properties of the ...bismuth-related active centers (BACs) formed in glass with high GeO2 content. The results reported here provide evidence that a luminescence intensity increment is caused by an increase in the amount of the BACs, but is not related to the modification of the structure of the BACs itself. Analyzing the experimental data, it was determined that the cooling rate has no noticeable effect on the ratio between the number of the BACs and that of the non-laser-active ones responsible for the unsaturable loss. Finally, some discussion of the annealing behavior of the BACs is provided.
Photobleaching of IR luminescence in bismuth-doped fibers was studied using laser radiation with different wavelengths: 407, 532, 639, 975, 1460nm. 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 532nm 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.
•Photobleaching time increases with the decrease of the photon energy of laser radiation and fiber temperature.•Bismuth-doped high-germania silicate fibers have high resistance to the near IR irradiation.•Photoionization of the GeODC is one of the underlying mechanisms of the photobleaching process.
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