Optical cross-bar switch that provides stable, low-loss, fiber-optic path protection

A bidirectional optical fiber path includes a primary optical fiber path; a secondary optical fiber path coupled to the primary optical fiber path; an optical coupler coupled to both the primary optical fiber path and the secondary optical fiber path; an optical switch coupled to both the primary optical fiber path and the secondary optical fiber path, the optical switch selecting a path of lower optical loses; an optical cross-bar switch coupled to both the primary optical fiber path and the secondary optical fiber path and located between the optical coupler and the optical switch; a primary upstream light detector coupled to the primary optical path between the optical cross bar switch and the optical switch; a secondary upstream light detector coupled to the secondary optical path between the optical cross bar switch and the optical switch; a primary downstream light detector coupled to the primary optical path between the optical cross bar switch and the optical switch; a secondary downstream light detector coupled to the secondary optical path between the optical cross bar switch and the optical switch; and a stabilizing downstream light detector coupled to the primary optical fiber path between the optical coupler and the optical cross bar switch.