Provided is a bidirectional wavelength division multiplexed passive optical network (WDM-PON) which includes a central office (CO) that transmits and receives multiplexed optical signals, a remote node (RN) that communicates with the CO, receives a multiplexed optical signal to demultiplex, and receives a demultiplexed optical signal to multiplex, an optical network unit (ONU) that transmits and receives demultiplexed optical signals to and from the RN, operational and protective backbone optical fibers that connect the CO to the RN, and operational and protective distribution optical fibers that connect the RN to the ONU. The ONU transmits and receives optical signals through the operational distribution optical fiber and the operational backbone optical fiber, and, where a failure occurs in the operational distribution optical fiber or the operational backbone optical fiber, the ONU transmits and receives optical signals through the protective distribution optical fiber and the protective backbone optical fiber.