Polarization-dependent gain in bismuth-doped phospho- and germanosilicate fiber amplifiers.

Polarization-dependent gain (PDG) effect was studied in a conventional core-pumping configuration of bismuth-doped fiber amplifiers (BDFAs) based on PANDA-type phospho- and germanosilicate core fibers. The PDG value was determined as the gain difference between the orthogonal signal polarizations, which was found to be in range of 2.5-3 dB at total gain of >20 dB in such BDFAs. This effect is more pronounced for BDFA with a germanosilicate fiber. The experimental results are in a good agreement with the calculated data derived from the simulation model, relying on the anisotropy parameter of bismuth active centers (BACs) obtained from the degree of luminescence polarization, which ranges between 9 and 12% for BACs-Si and 18 and 22% for BACs-P. The obtained data can be useful for the optimization of performance of BDFAs and studying structural peculiarities of BACs.

Cladding pumped bismuth-doped fiber amplifiers operating in O-, E-, and S-telecom bands.

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.

Compact and efficient O-band bismuth-doped phosphosilicate fiber amplifier for fiber-optic communications.

During last decades there has been considerable interest in developing a fiber amplifier for the 1.3-[Formula: see text]m spectral region that is comparable in performance to the Er-doped fiber amplifier operating near 1.55 [Formula: see text]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 [Formula: see text]m. Here, we report on the development of a compact and efficient 20-dB (achieved for signal powers between [Formula: see text] and [Formula: see text] 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[Formula: see text]) has been achieved.

Photostability of laser-active centers in bismuth-doped GeO2-SiO2 glass fibers under pumping at 1550 nm.

We report experimental measurements and numerical calculations regarding the photostability of laser-active centers associated with bismuth (BACs) in Bi-doped GeO2-SiO2 glass fibers under pumping at 1550 nm at different temperatures. It was discovered that BACs are unstable under 1550-nm pumping when the temperature is elevated to hundreds of degrees centigrade. A simple numerical model was proposed to account for the discovered instability which turned out to be in good agreement with the experimental data.

Formation of laser-active centers in bismuth-doped high-germania silica fibers by thermal treatment.

The effect of thermal annealing on the luminescent and laser properties of high-germania-core silicate fibers doped with bismuth was investigated. We studied the behavior of optical absorption assigned to the bismuth-related active centers associated with germanium as well as the behavior of unsaturable absorption in annealed fibers with respect to the Bi content. The dependence of the increment of the active center content on the Bi concentration in the annealed fibers was obtained. We achieved laser oscillations near a wavelength of 1700 nm with a slope efficiency of 18% using a 8.5 m long Bi-doped fiber. The comparison of the output parameters of the laser based on an annealed Bi-doped fiber with the ones of a pristine Bi-doped fiber laser is given. The performance of the obtained bismuth-doped fiber lasers was modeled using the propagation and rate equations of a homogeneous quasi-two-level laser medium. Theoretical results are compared with experimental ones.