This page is about waveguides for transmission of optical signals or power. For other types of waveguide, see the disambiguation page Waveguide.

An optical waveguide is a physical structure that guides electromagnetic waves in the optical spectrum. Common types of optical waveguides include optical fiber and rectangular waveguides.

Optical waveguides are used as components in integrated optical circuits or as the transmission medium in local and long haul optical communication systems.

Optical waveguides can be classified according to their geometry (planar, strip, or fiber waveguides), mode structure (single-mode, multi-mode), refractive index distribution (step or gradient index) and material (glass, polymer, semiconductor).

Rectangular optical waveguide

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Optical waveguides with rectangular geometry are produced by a variety of means, usually by a planar process. They are commonly used as the basis of such optical components as Mach-Zehnder interferometers and wavelength division multiplexers. The cavities of laser diodes are frequently constructed as rectangular optical waveguides.

Dielectric slab waveguide

Practical rectangular-geometry optical waveguides are most easily understood as variants of the simple dielectric slab waveguide . The slab waveguide consists of three layers of materials with different dielectric constants, extending infinitely in the directions parallel to their interfaces.

Light may be confined in the middle layer by total internal reflection. This occurs when the angle of incidence between the propogation direction of the light and the normal, or perpendicular direction, to the material interface is greater than the critical angle. The critical angle depends on the index of refraction of the materials, which may vary depending on the wavelength of the light.

This structure confines electromagnetic waves only in one direction, and therefore it has little practical application. Structures that may be approximated as slab waveguides do, however, sometimes occur as incidental structures in other devices.

Rectangular waveguide

Rectangular optical waveguide is formed when the guiding layer of the slab waveguide is restricted in both transverse directions rather than just one. Rectangular waveguides are used in integrated optical circuits, and as the optical cavity in laser diodes. The field distribution in rectangular waveguide cannot be solved analytically, however approximate solution methods, such as Marcatili's method, are known.

Optical fiber

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Optical fiber is typically a circular cross-section dielectric waveguide consisting of a dielectric material surrounded by another dielectric material with a lower refractive index. Optical fibers are most commonly made from silica glass, however other glass materials are used for certain applications and plastic optical fiber can be used for short-distance applications.

See also

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• Cutoff wavelength
• Dielectric constant
• Electromagnetic radiation
• Leaky mode
• List of telecommunications transmission terms
• Transmission medium
• Waveguide
• Waveguide (electromagnetism)

Notes

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1. Ramo, Simon, John R. Whinnery, and Theodore van Duzer, Fields and Waves in Communications Electronics, 2 ed., John Wiley and Sons, New York, 1984.

Optics