LabH6: Optical fibers for amplifiers and lasers

KEY COMPONENTS FOR SPACE MISSIONS

Rare earth ion doped fibers (Er³⁺, Yb³⁺ or Er/Yb) are crucial elements in the design of optical amplifiers or fiber lasers. These components are then used in more complex systems such as fiber optic gyroscopes or high-speed free-space optical communications. Radiation tests show that commercial active optical fibers, components and associated systems are highly vulnerable to space radiations [S. Girard et al., J. Optics, 2018].

Deeper fundamental studies showed that their high sensitivity is rather explained by the nature of the aluminosilicate or phosphosilicate host glass matrices used to incorporate the ions than by the rare-earth ions themselves. Several techniques have been identified allowing to improve the radiation responses of these fibers and components.

Indeed, by co-doping the active fiber with ceriumor by loading it with hydrogen [B. Cadier et al., US20130101261A1, 2012 / S. Girard et al., Opt. Express, 2012], it is possible to passivate the radiation induced defects relative to P or Al and thus improve the device radiation tolerance. Simultaneously, simulation tools have been developed to optimize the architecture of hardened systems with respect to the system profile of use in harsh environments [A. Ladaci et al., J. Appl. Phys., 2017]. These hardening approaches by component or system do not affect the optical performances of the amplifiers as illustrated in Fig(1) that compares the characteristics of two amplifiers: one standard and one radiation-hardened.

TOWARD THE VERY HIGH POWERS …

Fig.2 and Fig.3 compare the performance of Er and Er/Yb amplifiers based on standard and hardened optical fibers. With the hardening solutions implemented by LabH6, it is today possible to design radiation-resistant systems up to doses of the order of 3 kGy(SiO₂) (300 krad) covering the most demanding space missions. Today one of the main challenges concerns the development of systems delivering signals of very high power (> 10 W to 1550 nm). For these, it is necessary to study the radiation effects as well as the thermal contributions due to these high powers.

Studies combining simulations and experiments are under way (UJM / iXblue / CNES / Bari PhD thesis) to validate these computational codes before using them to design high power systems hardened to very high doses of radiation.

• Optical amplifiers with gain losses of less than 10% at 1 kGy are available: Rad Hard Space Grade Doped Fibers