  We compute the optical conductivity of 2D f-wave superconductors and also of
the multigap model proposed recently by Zhitomirsky and Rice at T=0K in the
Born limit. The presence of interband impurity scattering was found to play an
important role: the contributions from the two bands mix up, and new structures
are seen in the tunneling density of states and in the optical spectrum as
well, corresponding to interband transitions.
  This will provide a sensitive test in selecting the competing models for the
triplet superconductivity in Sr_2RuO_4.
