  We investigate theoretically the polarization properties of the quantum dot's
optical emission from chiral photonic crystal structures made of achiral
materials in the absence of external magnetic field at room temperature. The
mirror symmetry of the local electromagnetic field is broken in this system due
to the decreased symmetry of the chiral modulated layer. As a result, the
radiation of randomly polarized quantum dots normal to the structure becomes
partially circularly polarized. The sign and degree of circular polarization
are determined by the geometry of the chiral modulated structure and depend on
the radiation frequency. A degree of circular polarization up to 99% can be
achieved for randomly distributed quantum dots, and can be close to 100% for
some single quantum dots.
