Weak localization of polaritons and the generation of phase-conjugated light waves

The microscopic mechanism of generation of phase-conjugated light waves is presented in terms of weak localization of polaritons. Phase-conjugated waves, which are the time-reversal propagation of probe light, are shown to be enhanced by constructive interference between elastic multiple scattering of polaritons at impurities and time-reversed processes. This is characteristic of the time-reversal invariance of the system. We list several characteristics of generation of phase-conjugated waves due to the weak localization of polaritons. These observations will be applied to check the present theory.