  The properties of polarization in scattered light by aligned ellipsoidal
grains are investigated with the Fredholm integral equation method (FIM) and
the T-matrix method (Tmat), and the results are applied to the observed
circular polarization in OMC1. We assume that the grains are composed of
silicates and ellipsoidal (oblate, prolate, or tri-axial ellipsoid) in shape
with a typical axial ratio of 2:1. The angular dependence of circular
polarization p_c on directions of incident and scattered light is investigated
with spherical harmonics and associated Legendre polynomials. The degree of
circular polarization p_c also depends on the Rayleigh reduction factor R which
is a measure of imperfect alignment. We find that p_c is approximately
proportional to R for grains with |m|x_{eq} < 3 - 5, where x_{eq} is the
dimensionless size parameter and m is the refractive index of the grain. Models
that include those grains can explain the observed large circular polarization
in the near infrared, ~15%, in the south-east region of the BN object (SEBN) in
OMC1, if the directions of incidence and scattering of light is optimal, and if
grain alignment is strong, i.e. R > 0.5. Such a strong alignment cannot be
explained by the Davis-Greenstein mechanism; we prefer instead an alternative
mechanism driven by radiative torques. If the grains are mixed with silicates
and ice, the degree of circular polarization p_c decreases in the 3 micron ice
feature, while that of linear polarization increases. This wavelength
dependence is different from that predicted in a process of dichroic
extinction.
