Which wavelengths are appropriate for use with multimode fiber?

Which wavelengths are appropriate for use with multimode fiber?

• A. 650 and 850 nm
• B. 850 and 1310 nm
• C. 850 and 1300 nm
• D. 1310 and 1550 nm

Answer: (C)

Multimode fiber is designed to carry many light paths, so you want wavelengths that pair with the fiber’s optimized windows and with common light sources. The practical windows for multimode systems are around 850 nm and around 1300 nm. At 850 nm, LED and VCSEL sources couple efficiently and the fiber supports many modes with good bandwidth over short distances. At 1300 nm, attenuation stays low and dispersion is manageable, enabling longer links with the same fiber. That combination—850 nm for the short-range, high-bandwidth side and 1300 nm for the longer-range side—matches typical MMF use and transmitter technology. Wavelengths around 650 nm are not favored for MMF because blue light experiences higher attenuation in optical glass and isn’t efficiently supported by standard MMF designs. The 1550 nm window is ideal for long-haul single-mode systems; multimode fibers aren’t optimized for that long-wavelength window, so it’s not the standard choice for MMF. While 1310 nm sits in the same general region as 1300 nm, the conventional multimode practice emphasizes 1300 nm as the representative long-wavelength window.

Multimode fiber is designed to carry many light paths, so you want wavelengths that pair with the fiber’s optimized windows and with common light sources. The practical windows for multimode systems are around 850 nm and around 1300 nm. At 850 nm, LED and VCSEL sources couple efficiently and the fiber supports many modes with good bandwidth over short distances. At 1300 nm, attenuation stays low and dispersion is manageable, enabling longer links with the same fiber. That combination—850 nm for the short-range, high-bandwidth side and 1300 nm for the longer-range side—matches typical MMF use and transmitter technology.

Wavelengths around 650 nm are not favored for MMF because blue light experiences higher attenuation in optical glass and isn’t efficiently supported by standard MMF designs. The 1550 nm window is ideal for long-haul single-mode systems; multimode fibers aren’t optimized for that long-wavelength window, so it’s not the standard choice for MMF. While 1310 nm sits in the same general region as 1300 nm, the conventional multimode practice emphasizes 1300 nm as the representative long-wavelength window.