Magneto-optical properties of (TbBi)3Fe5O12 and its application to a 1.5 μm wideband optical isolator

A new composition of Bi-substituted terbium iron garnet (Tb3−xBixFe5O12) for a wideband optical isolator was investigated. The Faraday rotation of Tb3−xBixFe5O12 (x=0.25) at 1.5 μm band proved to be independent of wavelength λ. The value of the Faraday rotation of the crystal with x=0.25 was about −205 deg/cm at λ=1.5 μm. We have also found empirically that there is a simple relationship between the Faraday rotation coefficient θF(x) and Bi content x, given by θF(x)=−1540x+180 deg/cm. By using these crystals as a Faraday rotator, we have developed wideband optical isolators for a 1.5 μm band. Forward loss of 0.4 dB and backward loss of 34 dB were obtained in the wavelength region from 1.5 to 1.7 μm. The size of the isolator is 5 mm diameter×5 mm long and its weight is 0.4 g. Through an optical fiber transmission system with the isolator, we could transmit a stable and clear picture for the lights of 1.53 and 1.57 μm wavelength.