  We report an optical method of generating arbitrary polarization states by
manipulating the thicknesses of a pair of uniaxial birefringent plates, the
optical axes of which are set at a crossing angle of {\pi}/4. The method has
the remarkable feature of being able to generate a distribution of arbitrary
polarization states in a group of highly discrete spectra without spatially
separating the individual spectral components. The target polarization-state
distribution is obtained as an optimal solution through an exploration. Within
a realistic exploration range, a sufficient number of near-optimal solutions
are found. This property is also reproduced well by a concise model based on a
distribution of exploration points on a Poincar\'e sphere, showing that the
number of near-optimal solutions behaves according to a power law with respect
to the number of spectral components of concern. As a typical example of an
application, by applying this method to a set of phase-locked highly discrete
spectra, we numerically demonstrate the continuous generation of a vector-like
optical electric field waveform, the helicity of which is alternated within a
single optical cycle in the time domain.
