Compact and Highly Efficient Faraday Rotators Using Relatively Low Verdet Constant Faraday Materials

Abstract

A compact and highly efficient Faraday rotator which can produce a large amount of Faraday rotation despite using a relatively low Verdet constant Faraday material is described. This Faraday rotator consists of a small thin plate with perfectly reflecting surfaces and a small electromagnet or permanent magnet which applies the magnetic field to the plate in the direction of the thickness. A light beam with small diameter travels through the plate with multiple passes. The condition under which the light beam couples with the plate with the least optical loss is described. The effect of a small wedge angle of the plate on Faraday rotation is studied. A practical Faraday rotator for the He–Ne laser beam (λ=633 nm) is constructed by using an FR5 glass plate of 3 mm thickness and a small electromagnet. Faraday rotation of 45° is obtained when the power consumption of the magnetic coil is 1.5 W (2.8 V–0.56 A). The polarization extinction ratio is larger than 250: 1 and the total optical loss is 10%.