The invention relates to an optical device for polarizing light by changing its Faraday rotation angle, such as optical attenuators, optical switches or polarization controllers; and its object is to provide such an optical device which can be driven even by small-sized and power-saving magnetic circuits and in which the insertion loss in the Faraday rotator may be reduced. This is accomplished by a filtering server on the network that at least knows which terminals require network based retrieval and only gives these terminals network based data object retrieval. Thus, the terminal fittings are prevented from shaking.