  Spin-momentum locking of evanescent waves describes the relationship between
the propagation constant of an evanescent mode and the polarization of its
electromagnetic field, giving rise to applications in light nano-routing and
polarimetry among many others. The use of complex numbers in physics is a
powerful representation in areas such as quantum mechanics or electromagnetism;
it is well known that a lossy waveguide can be modelled with the addition of an
imaginary part to the propagation constant. Here we explore how these losses
are entangled with the polarization of the associated evanescent tails for the
waveguide, revealing a well-defined mapping between waveguide losses and the
Poincar\'e sphere of polarizations, in what could be understood as a
"polarization-loss locking" of evanescent waves. We analyse the implications
for near-field directional coupling of sources to waveguides, as optimized
dipoles must take into account the losses for a perfectly unidirectional
excitation. We also reveal the potential advantage of calculating the angular
spectrum of a source defined in a complex, rather than the traditionally purely
real, transverse wavevector space formalism.
