Borogermanate glasses for Faraday isolators at high average power

• Characteristics of terbium doped borogermanate glass (TBG) were investigated.
• Verdet constant of TBG is only 10% lower that for the traditional TGG medium.
• The isolation ratio of Faraday isolator on TBG is 30 dB for the laser power of 350 W.
• TBG may be used for FI in the “eye-safe” wavelength range unaccessible for TGG.

The temperature dependence of Verdet constant and thermo-optical characteristics of a new magneto-optical borogermanate glass has been investigated. The performed analysis confirmed a possibility of developing a Faraday isolator and a cryogenic Faraday isolator based on the studied medium, providing a 25 dB isolation ratio of laser radiation in the “eye-safe” wavelength range (1530–1620 nm) at the power of 0.4 kW and 1.3 kW, respectively, which is a leading-edge result for magneto-optical glasses.