TIA TIA-455-46A

This test method describes a procedure for measuring the spectral
attentuation of long-length (greater than or equal to 1 km),
graded-index multimode optical fibers.

Definition of Spectral Attenuation

The attenuation A(lambda) expressed in dB at wavelength lambda between
two cross sections 1 and 2 separated by distance L of fiber is defined
as:

                    A(lambda) = -10 log P2/P1

where: P1 is the optical power traversing the cross section 1.
       P2 is power traversing cross section 2.

For a uniform fiber under equilibrium conditions, it is possible to
define an attenuation per unit length, or an attenuation coefficient
alpha(lambda) = A(lambda)/L which is independent of the chosen length of
the fiber.