Multi-valued property of phase conjugation and control of its threshold condition

Summary form only given. Four-wave mixing with photorefractive crystals has been an active area, and cross-polarized four-wave mixing (CPFWM) has attracted much attention due to its advantage of efficient utilization of the phase conjugate beam. Recently, multi-valued phase conjugate reflectivity has been studied and its availability for optical applications such as optical memories and switches has been suggested, however the studies have been restricted to the case of parallel-polarized four-wave mixing, or even the existence of the multi-valued property of CPFWM has not been found so far. We prove the existence of multi-valued property of the phase conjugate reflectivity in CPFWM and reveal a threshold value of the coupling strength of beam interaction to turn it up. As a result, we show a method to control the threshold value and suggest the utilities of multi-valued property for optical applications.