Nowadays, rare-earth ion-doped fiber lasers and amplifiers are widely used in optical communication, industrial processing, military, and medical applications. Among them, the Er-Yb co-doped fiber amplifiers (EYDFA) with high power, low noise, and small size have a great potential for long-range space communication applications. However, rare-earth-doped fibers produce many color centers when exposed to various types of cosmic radiation such as X-rays, γ-rays, etc. Some of the color centers generated during irradiation originate from co-dopant elements like aluminum and phosphorus in rare-earth-doped fibers, whereas others originate from precursors formed during fiber fabrication. The absorption bands of these color centers are mainly located in the UV and NIR bands, which can cause radiation-induced absorption (RIA) in the pump and signal bands of the Er-Yb-doped fiber (EYDF), resulting in a severe degradation of the performance of the fiber amplifier. Therefore, it is crucial to improve the radiation resistance of the EYDF.

A radiation-resistant Er-Yb co-doped fiber (RREYDF) was prepared via modified chemical vapor deposition (MCVD), and the concentration and ratio of doping components such as erbium, ytterbium, phosphorus, and cerium were adjusted to enhance the radiation tolerance of the fibers. The Er, Yb, and P doping ratio was 1∶22∶536, and the core and cladding dimensions were 10.5 μm and 130 μm, respectively. The irradiation doses for current space missions range from 300 Gy to 1000 Gy, so those values are chosen to test the RIA and radiation-induced gain variation (RIGV) of RREYDF. The RIA and RIGV were tested using Photon Kinetics 2500 and a typical EYDFA, respectively.

Radiation-induced absorption (RIA) was 0.10 dB/m and 0.19 dB/m (300 Gy) at 940 nm, and 0.46 dB/m and 0.37 dB/m (1000 Gy) at 1550 nm. For gain testing, an Er-Yb co-doped fiber amplifier (EYDFA) was built, and the radiation-induced gain variation (RIGV) was 0.2 dB (300 Gy) at 1550 nm and 0.7 dB (1000 Gy) at a pump power of 7.3 W. The mechanisms of the relevant irradiation resistance studies were analyzed. Cerium co-doping was used in Er-Yb fibers to enhance the radiation resistance, taking advantage of the coexistence of Ce³⁺ and Ce⁴⁺ in silicates, where Ce³⁺ can trap the holes created during radiation. Therefore, the latter competes with the precursor P₂O₃ and reduces the formation of P₁ color centers, thus improving the radiation resistance of the fibers.

In summary, the RIA of the radiation-resistant Er-Yb co-doped fibers prepared by MCVD were 0.10 dB/m and 0.19 dB/m (300 Gy), and 0.46 dB/m and 0.37 dB/m (1000 Gy) at 940 nm and 1550 nm, respectively, after irradiation at 300 Gy and 1000 Gy and 0.2 Gy/s average dose rate. The RIGV was tested by a typical EYDFA, and the results showed that the RIGV was 0.2 dB (300 Gy) at 1550 nm and 0.7 dB (1000 Gy) at a pump power of 7.3 W. In addition, the radiation-resistance mechanism of the fibers was analyzed. This Er-Yb co-doped optical fiber has excellent radiation performance and extensive applications in the fields such as long-range space communication, remote sensing, and space navigation.