Optical Isolator

Abstract

Various optical isolator embodiments are disclosed. Embodiments comprise a waveguide section utilizing materials that induce a propagation constant shift that is propagation-direction-dependent. Embodiments are characterized by a cutoff frequency for forward propagating waves that is different than the cutoff frequency for reverse waves; the dimensions and direction of magnetization of the waveguide can be tailored so that, in a particular embodiment, the cutoff frequency for forward propagating waves is lower than the cutoff frequency for reverse waves. A particular embodiment is constructed as a single-mode waveguide on a substrate. The cross-section of the waveguide is inhomogeneous in terms of materials. At least one part of the cross-section is a non-reciprocal magneto-optic medium, which has nonzero off-diagonal permittivity tensor components. This inhomogeneity induces a propagation constant shift, which is propagation-direction-dependent. This device works as an optical isolator from the cut-off frequency of the lowest forward wave (lower frequency) to one for the lowest reverse wave (higher frequency). Various configurations consistent with the principles of the invention are disclosed.

1 . An optical isolator comprising:
 a waveguide on a substrate, the waveguide being dimensioned to operate in a single mode for a selected frequency range and the waveguide further being structured such that, given magneto-optical properties of the waveguide's material, the waveguide has a cutoff frequency in a forward propagation direction that is different than a cutoff frequency in a reverse propagation direction.   
     
     
         2 . The optical isolator of  claim 1  wherein:
 the waveguide includes first and second portions; 
 one of the first and second waveguide portions comprises a magnetic material and; 
 the other of the first and second waveguide portions comprises a non-magnetic material. 
 
     
     
         3 . The optical isolator of  claim 2  wherein the non-magnetic material is a same material as a material of the substrate. 
     
     
         4 . The optical isolator of  claim 2  wherein the non-magnetic material is a different material than a material of the substrate. 
     
     
         5 . The optical isolator of  claim 2  wherein the first and second waveguide portions are arranged side-by-side on the substrate. 
     
     
         6 . The optical isolator of  claim 2  wherein the first waveguide portion is on the substrate and the second waveguide portion is on the first waveguide portion.