Optical fibers with bismuth-doped silicate and germanate glass cores were fabricated by the modified chemical vapor deposition technique (solution and vapor-phase Bi incorporation). The fibers revealed an efficient luminescence with a maximum in the 1050–$1200\mathrm{nm}$ spectral range, FWHM up to $200\mathrm{nm}$, and a lifetime of the order of $1\mathrm{ms}$.

Bismuth (Bi) doped fibers have shown promising potential for lasers and amplifiers in the 1150-1500 nm and 1600-1800nm wavelength region. Bi-doped aluminosilicate, phosphosilicate and germanosilicate fibers provide luminescence around 1150 nm, 1300 nm and 1450 nm, respectively. Recent results have demonstrated the possibility to extend the Bi luminescence window beyond 1600 nm using Bi-doped high (≥ 50 mol %) germanosilicate fibers. These spectral regions can serve a wide range of applications in medicine, astronomy, defense and to extend the optical fiber communication. However, Bi-doped fiber lasers and amplifiers are still far from their optimum performance owing to the unclear nature of the near-infrared emitting Bi active centers. In this paper, we review the current state of the art of Bi-doped silica fiber lasers (CW and pulsed) and amplifiers in different wavelength bands. Also, we present our work on the development of Bi-doped aluminosilicate and phosphosilicate fiber lasers and amplifiers in the 1180 nm and 1330 nm bands. These lasers and amplifiers find applications in generating visible light sources and to access the second telecommunication window. The fibers used here were fabricated by modified chemical vapor deposition-solution doping technique and characterized for their unsaturable loss. Moreover, we present the influence of pump wavelengths on the gain, noise figure and laser efficiency of these Bi-doped fiber amplifiers and lasers. We also discuss Bi-doped fibers for pulsed laser application and demonstrate a mode-locked Bi-doped fiber laser operating at 1340 nm.

Bismuth (Bi)-doped phosphosilicate fibers have been fabricated by the modified chemical vapor deposition (MCVD)-solution doping technique under different process conditions. The influence of fabrication conditions on unsaturable loss in fibers has been investigated. Pump wavelength dependent Bi gain has been studied to obtain a flat gain over a wide bandwidth. A diode pumped all-fiber Bi-doped amplifier with a flat gain of $25\pm 1\mathrm{dB}$ from 1320–1360 nm (40 nm) has been demonstrated for $-10\mathrm{dBm}$ of input signal power with a noise figure (NF) ranging from 4–6 dB. Moreover, a small signal gain of 29 dB and a NF of 4.5 dB at 1340 nm has been achieved for an input signal power of $-30\mathrm{dBm}$.

In this Letter, we investigate and compare the gain and noise figure characteristics of bismuth (Bi)-doped fiber amplifiers configured in both single and double signal pass implementations. A maximum gain of 25 dB and a noise figure of 4 dB is measured at 1360 nm in the single pass configuration for $-23\mathrm{dBm}$ input signal power, whereas in the double pass configuration the gain of the amplifier is improved significantly by 14 dB allowing us to achieve a gain of 39 dB with a noise figure of 5 dB. To the best of our knowledge, this is the highest gain reported to date using Bi-doped fiber as a gain medium. Furthermore, we also study the gain and noise figure dependency on pump power, signal power, and pump wavelength for the double pass amplifier configuration. We observed similar gain and noise figure performance in the double pass configuration to that of the single pass configuration but with the benefit of less pump power and a shorter length of the Bi-doped fiber.

We report a hybrid process by combining both vapor-phase and solution-doping techniques of rare-earth doped preform fabrication in conjunction with the MCVD technique, in order to fabricate highly efficient Tm-doped laser fibers. The proposed fabrication route takes advantage of co-doping silica with high alumina content through the vapor-phase doping process, which is otherwise difficult to achieve using conventional solution doping technique. In addition, by employing the solution doping method, high-purity thulium halide precursors that have low vapor pressures up to several hundred degree Celsius. These high-purity thulium halide precursors can be used to dope the fiber core region with a high thulium concentration that is optimized for an efficient two-for-one cross-relaxation process for 79xnm diode pumped thulium-doped fiber laser. Fibers fabricated using the hybrid approach show more homogeneous and flat-top dopant profiles, compared with the conventional approach, where both aluminum and thulium are incorporated in the core through solution doping. This will ensure that more doped region will take part in the cross-relaxation process. Superior laser performance with a slope efficiency of >70% in the two-micron band has been demonstrated when diode pumped at ~790nm.