When circularly polarized light is reflected, its propagation direction reverses, changing left-circular polarization to right-circular polarization and vice versa. Therefore, the same polarizer that produces circular polarization of the incident beam will block the return beam with an isolation of at least 99.8 percent.
Achieving optical isolation using Meadowlark's circular polarizers requires that a given reflection be specular and that there is no medium intervening between the reflector and optical isolator to cause significant depolarization or polarization modification.
Fiber optics signal processing 
