lightguide

A lightguide, or light guide, is a transparent medium that directs light from a source to another location with minimal loss. It is a passive optical component used to transport or distribute light in various systems.

Lightguides operate on the principle of total internal reflection. Light is confined inside a higher‑refractive‑index core by surrounding lower‑index cladding; when entering at proper angles, rays are guided along the length, with losses due to absorption, scattering, and bends.

Common forms include optical fibers, which carry light through a cylindrical core and cladding; and light guide plates or light pipes, which spread light across a plane or along a path for illumination or displays. Materials include silica, PMMA, and other polymers.

Applications range from telecommunications and data transmission to illumination, signage, and backlighting for liquid crystal displays. In displays, light guide plates distribute light from compact LEDs to achieve uniform brightness on screens.

Manufacture and integration involve drawing or extruding the core and cladding, polishing end faces for efficient coupling, and attaching the light source. Design parameters include numerical aperture, attenuation, and mode structure (single‑mode or multimode).

Advances include microstructured surfaces and nanophotonic coatings to improve extraction and control.