Which wavelength has the lowest attenuation?

Which wavelength has the lowest attenuation?

• A. 850 nm
• B. 1310 nm
• C. 1550 nm
• D. 980 nm

Answer: (C)

Attenuation in optical fiber varies with wavelength, and silica fibers have two deep low-loss windows in the infrared, around 1.3 and 1.55 micrometers. In this region, intrinsic absorption is minimized and Rayleigh scattering is reduced as wavelength increases, so the loss per kilometer is smallest. Among the given wavelengths, the one at 1550 nm sits in the deeper low-loss window, giving the lowest attenuation (often around 0.2 dB/km in good fibers). The other wavelengths are higher because they lie outside that deepest minimum: 850 nm experiences more scattering and absorption, while 980 nm and 1310 nm do not reach the same minimum as 1550 nm.

Attenuation in optical fiber varies with wavelength, and silica fibers have two deep low-loss windows in the infrared, around 1.3 and 1.55 micrometers. In this region, intrinsic absorption is minimized and Rayleigh scattering is reduced as wavelength increases, so the loss per kilometer is smallest. Among the given wavelengths, the one at 1550 nm sits in the deeper low-loss window, giving the lowest attenuation (often around 0.2 dB/km in good fibers). The other wavelengths are higher because they lie outside that deepest minimum: 850 nm experiences more scattering and absorption, while 980 nm and 1310 nm do not reach the same minimum as 1550 nm.