  Vortex lattice structures to occur in Rashba non-centrosymmetric
superconductors under a magnetic field parallel to the basal plane are studied
by assuming a singlet Cooper pairing and taking account of both the
paramagnetic and orbital depairings. A vortex lattice of
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) type with modulation perpendicular to
the field is expected to occur in the limit of vanishing ${\tilde \eta}$, where
${\tilde \eta}$ is the spin-orbit coupling {\it normalized} by Fermi energy. As
${\tilde \eta}$ increases, however, this state tends to be replaced by another
new vortex lattice with a modulation of the gap amplitude parallel to the
helical phase modulation induced by the absence of inversion symmetry.
Differences of the present results from those in the Pauli limit and a
correlation of a structural transition with the $H_{c2}(T)$-curve are discussed
in relation to possible experimental realization.
