We report the evaluation of one long period grating (LPG) and one fiber Bragg grating (FBG) under gamma irradiation. The LPG was produced by the melting-drawing method based on CO2 laser assisted by a micro-flame and was engraved in a commercial single mode fiber SMF28 from Corning, grating length 25 mm, grating pitch of 720 μm. After the manufacturing of the grating, the fiber was re-coated with Acrylate and the grating was inserted into special ceramic case transparent to gamma radiation. The FBG is commercialized by Technica SA, and it is written in SMF-28 optical fiber (λ= 1546 nm; grating length of 12 mm; reflectivity > 80 %; bandwidth – BW @3 dB < 0.3 nm; side lobe suppress ratio – SLSR >15 dB; Acrylate recoating). By on-line monitoring of the LPG wavelength deep with an optical fiber interrogator during the irradiation exposure and pauses, both the irradiation induced shift (maximum 1.45 nm) and the recovery (in the range of 200 pm) phenomena were observed. Temperature sensitivity of the LPS was not affected by gamma irradiation.
We study the effect of hydrogen gas diffusion in silica optical fibers on Brillouin and Rayleigh scatterings. By modeling hydrogen diffusion kinetics as a function of temperature and pressure and by measuring simultaneously Rayleigh and Brillouin scattering on G652 single-mode fiber samples during H<sub>2</sub> desorption (previously exposed to 175 bars H<sub>2</sub> at 80°C), we have demonstrated experimentally that acoustic velocity increases linearly with H2 concentration with a ratio of about (4.8 m/s) / (%mol H<sub>2</sub>).
This paper reviews and extends the work done on photodarkening by our project consortium and present our latest results
on bleaching and photodarkening mitigation in fiber lasers. We shows the need for a standard set-up to avoid
underestimation of photodarkening equilibrium losses and we suggest photodarkening losses scale with the square of Yb
doping level. Investigation on visible light emission suggest an interplay of visible light with the Yb excited level.
Finally we present an extensive investigation of photobleaching, both as post-irradiation and as simultaneous bleaching.
We show evidence photobleaching can effectively mitigate the impact of photodarkening on laser performance when
highly-doped Al-silicate fibers are used.
Distributed optical fiber sensors are a clue technology for the monitoring of geological repository for long-lived nuclear
wastes. Environment includes hydrogen whose influence on Rayleigh and Brillouin scatterings is experimentally
evaluated. Induced propagation losses are quantified, as a function of wavelength and fiber dopants. 1310nm resulted the
most favorable working wavelength. Distance range would anyway be reduced down to a hundred meter. We show
hydrogen also induces Brillouin frequency shifts, up to 21MHz which corresponds to large temperature and strain
measuring errors if not corrected. Fluorine fibers appeared more sensitive for short hydrogen exposure than other tested
Flat gain EDFA are key devices in long haul DWDM systems. A flat gain is needed to ensure an adequate signal to noise ratio evolution between channels during transmission. The dissipative filter introduced between two sections of doped fiber inside the amplifier can have a small residual reflective contribution at a particular wavelength. We have investigated the impact of such a back reflection and shown it is negligible for EDFA operation.