Waveguide for propagating radiation

A device comprising a waveguide structure for propagating electromagnetic radiation, for example optical, millimeter-wave or microwave electromagnetic radiation having a wavelength in the range embracing ultra-violet, visible, near infra-red, mid infra-red, far infra-red, millimeter-waves and microwaves, the device comprising:

• a slab (10) of dielectric material, for example silicon nitride;
• a first pair of metal plates (12L) and a second pair of metal plates (12R) each pair comprising a first and a second metal plate extending in a propagation direction on opposite faces of the slab, said metal plates comprising, for example, gold, silver or other highly-conductive metal, preferably with a thickness (t) in the range from about 3 nm to about 1000 nm;
• the plates on each face of the slab (10) being spaced apart laterally with respect to the propagation direction, preferably such that a lateral spacing (w) between said plates is in the range from about 0.05 microns to about 10 microns;
• dielectric cladding material (D) disposed along each of the opposite faces of the slab (10) and having a refractive index (n2) less than the refractive index (n1) of the slab, said dielectric cladding material comprising, for example, silicon dioxide, the slab (10) preferably having a thickness (s) in the range from about 0.05 microns to about 10 microns, and
• input means, such as an optical fiber (160) or other dielectric waveguide, or a light source, for injecting electromagnetic radiation into the slab to propagate in said propagation direction in a zone defined by and between the four metal plates,
• wherein the lateral spacing (w) between said plates on the same face of the slab (10) is in the range from about 0.05 microns to about 10 microns, the thickness (s) of the slab (10) is in the range from about 0.05 microns to about 10 microns, and the thickness (t) of each of the metal plates (12L, 12R) is in the range from about 3 nm to about 1000 nm.