TIA TIA-455-77

This document describes a method for the qualification of a
higher-order mode filter to be used for making measurements on a
single-mode fiber. This type of mode filter is required when effectively
single-moded operation of short lengths of single-mode fiber is needed
at wavelengths near cutoff wavelength of the first higher-order mode (as
measured by FOTP-80).  It is not meant to be used in the 800 nm region.
Effectively single-moded operation is necessary:

   a.  when making cutback measurements of spectral attenuation (per
       FOTP-78),

   b.  when making mode field diameter measurements (per FOTP-164, 167,
       or 174),

   c.  whenever short lengths of fiber are used.

This test procedure uses a method similar to that of FOTP-80, Method B,
to ensure that the fiber is effectively single-moded at the wavelengths
of interest.