Integrated Optical Polarizer

Abstract

In the following a polarizer will be described whose dielectric multilayer is not incorporated as a discontinuity in the planar waveguide as in /1/ but is deposited as a superstrate. A polarizer in the form of a dielectric multilayer and a glass plate (refractive index nG) is deposited as a superstrate on a planar waveguide (refractive index nF, film thickness tF) which is deposited in turn on a substrate (refractive index nS) (Fig. 1). The sides of the polarizer are normal to the direction of propagation. The dielectric multilayer has a periodic structure with a basic period composed of two layers with different refractive indices (refractive indices nH and nL, thicknesses tH and tL). If the refractive indices are suitably chosen the multilayer will transform the waveguide into a leaky waveguide. The light which is consequently coupled into the dielectric multilayer will be very diversely affected at the interfaces between the layers of the multilayer as a function of the direction of polarization due to the satisfaction of the Brewster-angle condition and to interference effects. In consequence, TM modes will be transmitted and refracted out through the glass plate at the side, whereas TE modes will be reflected back into the waveguide. Thus TE modes will be dominant in the light which continues to propagate behind the polarizer. The advantages of this polarizer are that it can be deposited at practically any point of an integrated optical system, that the desired modes are not attenuated by absorption and that no birefringent materials are used.