waveguide

A waveguide is a physical structure that directs the propagation of electromagnetic waves along a desired path, typically extending along one dimension while confining energy in the transverse directions. Waveguides rely on boundary conditions to minimize radiation loss; the guiding mechanism depends on the wave frequency and the material properties.

There are two broad classes: metallic (hollow) waveguides used at microwave frequencies, and dielectric (optical) waveguides used at optical frequencies. Metallic waveguides are hollow tubes with conducting walls in shapes such as circular or rectangular, supporting transverse electric and transverse magnetic modes. Dielectric waveguides consist of a high-refractive-index core surrounded by a lower-index cladding, using total internal reflection to confine light.

Guidance is characterized by modes with specific field patterns and cutoff frequencies. Optical waveguides can be single-mode or multimode depending on core size and wavelength. Planar and channel waveguides are used in integrated optics; optical fibers form long-distance links. Microwave waveguides have characteristic dimensions tied to the wavelength, and losses depend on material conductivity and surface roughness.

Common materials include copper or aluminum for metal waveguides, and silica, doped glass, or polymers for dielectric waveguides. Applications span telecommunications, radar and microwave systems, sensing, medical imaging, and photonic integrated circuits. Ongoing research addresses dispersion, nonlinear effects, and fabrication tolerances to improve confinement and reduce losses.