  This paper reports a practical method of generating circularly polarized
terahertz (THz) waves from intrinsic Josephson junctions (IJJs) and controlling
their polarization states by external local heating. We theoretically find that
a mesa-structure IJJ whose geometry is almost square can emit circularly
polarized THz waves by local heating of the mesa. Moreover, we demonstrate that
the polarization states of the THz waves change dramatically with the local
heating position. Our results indicate that the use of local heating can
provide a high level of controllability of the THz emissions and significantly
extend the range of applications of IJJ-based THz emitters.
