Compact phase-conjugate mirror utilizing four-wave mixing in a loop configuration

TLDR: In this paper, a compact loop four-wave mixing phase conjugator that can be used in practical optical applications comprises a reflective nonlinear cell (12), relay optics (2, 4, 6, 8), an optical gain medium (26), and an optical diode (24) that together form a circumference ring laser resonator.

Abstract: A compact loop four-wave mixing phase conjugator that can be used in practical optical applications comprises a reflective nonlinear cell (12), relay optics (2, 4, 6, 8), an optical gain medium (26), and an optical diode (24) that together form a unidirectional ring laser resonator. In operation, a signal beam (e 1 ) is directed to the nonlinear cell (12), where it passes through a nonlinear medium (14) contained within the cell and is reflected out of the cell as loop beam (e 2 ). The relay optics direct loop beam (e 2 ) through the optical diode (24), optical gain medium (38), and back to the nonlinear cell (12), where it intersects and optically interferes with the signal beam (e 1 ) to form a refractive index grating (22) in the nonlinear medium (14). The optical diode (24) and gain medium (38) are positioned in the loop so that an oscillation beam (e 3 ) builds up from optical noise in the resonator and oscillates in a direction counter to the propagation direction of loop beam (e 2 ). A portion of oscillation beam (e 3 ) is transmitted by the refractive index grating, reflects off the reflective portion (16) of the nonlinear cell (12) and emerges from the cell as phase conjugate output beam (e 4 ).