minimum-loss window
Of an optical fiber, the transmission window at which the attenuation coefficient is at or near the theoretical (quantum-limited) minimum.
Note 1: If the losses from various mechanisms are plotted on a single graph as a function of wavelength, the minimum-loss window occurs in the vicinity of the wavelength at which the Rayleigh-scattering attenuation curve and the infrared-phonon-absorption curve intersect.
Note 2: For silica-based fibers, the minimum-loss window occurs at approximately
1. 55 
m. [After FAA]