  Light polarization can conveniently encode information. Yet, the ability to
steer polarized optical fields is notably demanding but crucial to develop
practical methods for data encryption and to gather fundamental insights into
light-matter interactions. Here we demonstrate the dynamic manipulation of the
chirality of light in the telecom wavelength regime. This unique possibility is
enrooted in the multivalley nature of the conduction band of a conventional
semiconductor, namely Ge. In particular, we demonstrate that optical pumping
suffices to govern the kinetics of spin-polarized carriers and eventually the
chirality of the radiative recombination. We found that the polarization of the
optical transitions can be remarkably swept through orthogonal eigenstates
without magnetic field control or phase shifter coupling. Our results
anticipate spin-enhanced optoelectronic functionalities in materials backed by
the mainstream microelectronics industry and provide guiding information for
the selection and design of functionalized emitters based on novel group IV
compounds.
