0.8 μm Range Optical Isolator Using LPE Garnet Film

(BiGd)
₃
(FeAlGa)
₅
O
₁₂
and Ca-doped (BiGd)
₃
(FeAlGa)
₅
O
₁₂
garnet thin films were subjected to reducing treatment to decrease the optical absorption loss and increase the figure of merit. These materials were investigated for use as the media in 0.8 μm isolators. The absorption loss α decreased after reduction irrespective of whether Ca doping was used or not, but the film with the lowest (220 dB/cm) was doped with Ca and grown at a low supercooling temperature. The figure of merit |θ
_F
|/α reached a maximum of 30 deg/dB, and that is an excellent result. Corresponding thick films were subjected to reduction processing at 300°C, but the film absorption loss did not change, and after processing at a temperature of over 345°C, cracks appeared on the film surfaces and Fe was deposited.