Can multimode fiber transmit visible light

Multimode fiber does not use visible light; it transmits infrared light, typically at wavelengths of 850 nm and 1300 nm.

Multimode optical fiber (MMF) is designed to carry multiple light propagation paths simultaneously through a relatively large core, usually 50 or 62.5 microns in diameter, which allows multiple modes of light to travel at once . The light sources used in MMF systems are typically LEDs or vertical-cavity surface-emitting lasers (VCSELs), which emit light in the infrared spectrum, not the visible spectrum . The standard operating wavelengths for multimode fiber are 850 nm and 1300 nm, both of which are longer than the visible light range (approximately 400–700 nm) and therefore invisible to the human eye . Infrared light is chosen because it experiences lower attenuation and scattering in glass fibers, allowing more efficient data transmission over short to medium distances, such as within buildings, data centers, or campus networks . While multimode fiber can carry high data rates—up to 100 Gbps over distances of 300–550 meters depending on fiber type (OM3, OM4, OM5)—the light itself is not visible, so it is unsafe to attempt to see the signal directly without proper equipment . Specialized detectors or fiber optic power meters are required to measure or test the light in these fibers. In summary, multimode fiber transmits infrared light, not visible light, which is why the signals cannot be seen with the naked eye, and this design choice optimizes performance for short-distance high-speed communication.