Bi-substituted rare-earth iron garnet composite film with temperature independent Faraday rotation for optical isolators

(BiLuGd)IG/(BiGd)(FeGa)G composite films of which the temperature derivatives of Faraday rotation angle at 45 degree (≡β) are nearly zero, were grown by a two-step liquid phase epitaxial (LPE) method. The relative intensity noise (RIN) of the 1.3 μm laser diode (LD) with an optical isolator using the β=0.00 deg/°C garnet composite film were measured in comparison with an isolator using the garnet crystal with β of 0.05 deg/ °C. The relation between the RIN and the feedback light power and the relation between the RIN and β value were clarified. It was found that the increase of the RIN by periodic noise caused by feedback light to the LD from the fiber-far-end was observed when the feedback light power increases more than -62dB. In the practical temperature range of-20~+60 garnet composite films with β=0.00 deg/°C are required in order to prevent the periodic noise.