A low loss 0.8 µm band optical isolator using highly Bi- substituted LPE garnet film

A low loss 0.8 μm band optical isolator was achieved by using highly Bi-substituted LPE garnet film as a 45 deg Faraday rotator. Only Bi
2
O
3
was used as the flux to achieve a low optical absorption and a high specific Faraday rotation at once. Doping of Ca
²⁺
or Mg
²⁺
in the melt combined with annealing in the air after growth has been found effective to reduce optical absorption around 0.8 μm wavelength. For an optical isolator with the maximum Bi content of 1.56 per formula unit, the optical absorption loss L=1.7 dB or the forward transmittance of 68 % was obtained. An optical isolator was evaluated in a magnetooptical disc system. The isolator has proved effective to remove unbalanced component of tracking servo signals and to make the servo system stable.