  The Stokes V parameter characterizes asymmetry of amplitudes between right-
and left-handed waves, and non-vanishing value of the V parameter yields a
circularly polarized signal. Cosmologically, V parameter may be a direct probe
for parity violation in the universe. In this paper, we theoretically
investigate a measurement of this parameter, particularly focusing on the
gravitational-wave backgrounds observed via ground-based interferometers. In
contrast to the traditional analysis that only considers the total amplitude
(or equivalently $\Omega_{GW}$), the signal analysis including a
circular-polarized mode has a rich structure due to the multi-dimensionality of
target parameters. We show that, by using the network of next-generation
detectors, separation between polarized and unpolarized modes can be performed
with small statistical loss induced by their correlation.
