  Besides the relation between the wave vector $\bm k$ and the complex
frequency $\omega$, wave polarization is useful for characterizing the
properties of a plasma wave. The polarization of the electromagnetic fields,
$\delta \bm E$ and $\delta \bm B$, have been widely used in plasma physics
research. Here, we derive equations for the density and velocity perturbations,
$\delta n_s$ and $\delta{\bm v}_s$, respectively, of each species in the
electromagnetic kinetic plasma dispersion relation by using their relation to
the species current density perturbation $\delta {\bm J}_s$. Then we compare
results with those of another commonly used plasma dispersion code (WHAMP) and
with those of a multi-fluid plasma dispersion relation. We also summarize a
number of useful polarization quantities, such as magnetic ellipticity,
orientation of the major axis of the magnetic ellipse, various ratios of field
energies and kinetic energies, species compressibility, parallel phase ratio,
Alfv\'en-ratio, etc., which are useful for plasma physics research, especially
for space plasma studies. This work represents an extension of the BO
electromagnetic dispersion code [H.S. Xie, Comput. Phys. Comm. 244 (2019)
343-371] to enhance its calculation of polarization and to include the
capability of solving the electromagnetic magnetized multi-fluid plasma
dispersion relation.
