A novel all fiber magneto-optic on-off switch

Abstract

This paper represents recent results and efforts in developing the concept and the implementation of an all fiber optical on-off switch based on Faraday Effect exhibited by magneto-optic (MO) materials such as rare earth doped iron garnets. The on-off function of the switch is useful for isolation and connection of node/nodes from the network without having to electronically turn off the laser. In this paper Faraday rotation of the polarization of light with a variable bias magnetic field is demonstrated. An extinction ratio of about 19dB is measured. It can be improved further by additional Faraday rotation created by another MO material in the light path. The interferometric configuration of the switch design reduces its dependence on the polarization. The biasing circuit for the magnetic field should be able to change the voltage rapidly in order to obtain fast operating time of the optical switch. The inductance of the coil used for generating the required magnetic field is the bottleneck for rapid switching of the magnetic field in the magneto-optic material. Circuits used to change the voltage across the bias circuit rapidly are discussed. The switching speed of magneto-optic materials depends on the speed of the domain walls. The switching time for the magneto-optic material will be discussed. Thick film ferrimagnetic bismuth-substituted rare-earth iron garnets are used as the Faraday rotators.