We report on an extensive investigation of photodarkening in Yb-doped silica fibers. A set of similar fibers, covering a large Yb concentration range, was made so as to compare the photodarkening induced losses. Careful measurements were made to ensure equal and uniform inversion for all the tested fibers. The results show that, with the specific set-up, the stretching parameter obtained through fitting has a very limited variation. This gives more meaning to the fitting parameters. Results tend to indicate a square law dependence of the concentration of excited ions on the final saturated loss. We also demonstrate self-similarity of loss evolution when experimental curves are simply normalized to fitting parameters. This evidence of self-similarity also supports the possibility of introducing a preliminary figure of merit for Yb-doped fiber. This will allow the impact of photodarkening on laser/amplifier devices to be evaluated.

Al-silicate fibers have excellent manufacturing quality. Unfortunately, high-Yb doping concentration may be limited by severe losses induced by photodarkening phenomenon. In this paper we demonstrate for the first time that Al-silicate Yb-doped fibers with high-inversion and doping concentration above 1 wt% can be successfully used by implementing a simple optical bleaching scheme. A co-injection into the active fiber of a few mW of light at around 550 nm wavelength successfully eliminates almost all photodarkening induced losses. We demonstrate operation at above 90% of the pristine output power level in several lasers with up to 30% Yb ions in the excited state. These results may allow using Yb-doped Al-silicate fibers with doping level increased by one order of magnitude. Finally, we provide a comprehensive picture of main parameters affecting photobleaching performance and, to the best of our knowledge, we report the first quantitative measurement of the Ytterbium excited state absorption cross-section in the visible range.

In this letter, we investigate the impact of a 405 nm radiation on photodarkening generation in Yb-doped fiber laser. Simultaneous photodarkening and photobleaching effects induced by 976 and 405 nm radiations, respectively, were investigated in a 1070 nm laser and compared with the loss induced in an irradiated active fiber. We observed a significant photobleaching effect due to 405 nm radiation but not a complete recovery. A strong absorption of the 405 nm radiation by the excited ions was also observed and could be the limiting factor for the bleaching performance. We also observed for the first time, to the best of our knowledge, ground-state absorption induced photodarkening in pristine fiber irradiated at 405 nm. This effect could generate additional residual losses in the laser system.

Glass photonics are widespread, from everyday objects around us to high-tech specialized devices. Among different technologies, sol–gel synthesis allows for nanoscale materials engineering by exploiting its unique structures, such as transparent glass-ceramics, to tailor optical and electromagnetic properties and to boost photon-management yield. Here, we briefly discuss the state of the technology and show that the choice of the sol–gel as a synthesis method brings the advantage of process versatility regarding materials composition and ease of implementation. In this context, we present tin-dioxide–silica (SnO₂–SiO₂) glass-ceramic waveguides activated by europium ions (Eu³⁺). The focus is on the photorefractive properties of this system because its photoluminescence properties have already been discussed in the papers presented in the bibliography. The main findings include the high photosensitivity of sol–gel 25SnO₂:75SiO₂ glass-ceramic waveguides; the ultraviolet (UV)-induced refractive index change (Δn ~ −1.6 × 10⁻³), the easy fabrication process, and the low propagation losses (0.5 ± 0.2 dB/cm), that make this glass-ceramic an interesting photonic material for smart optical applications.

Third-order harmonic mode locking of a diode-laser pumped bulk Er:Yb:glass laser by frequency modulation with a lithium niobate modulator is reported. Stable pulses at a repetition rate of 2.5 and 5 GHz with a pulse duration down to 9.6 ps are obtained. The average output power is 3 mW, the pulse peak power is 120 mW at 2.5 GHz repetition rate, and the pulses are approximately 1.4 times transform limited. The pulse duration can be increased up to 30 ps by decreasing the mode-locker drive power.