A full-duplex self-recovery optical fibre transport system is proposed on the basis of a novel passive single-line bidirectional optical add/drop multiplexer (SBOADM). This system aims to achieve an access network with low complexity and network protection capability. Polarisation division multiplexing technique, optical double-frequency application and wavelength reuse method are also employed in the transport system to improve wavelength utilisation efficiency and achieve colourless optical network unit. When the network comprises a hybrid tree-ring topology, the downstream signals can be bidirectionally transmitted and the upstream signals can continuously be sent back to the central office in the reverse pathways due to the remarkable routing function of the SBOADM. Thus, no complicated optical multiplexer/de-multiplexer components or massive optical switches are required in the transport system. If a fibre link failure occurs in the ring topology, then the blocked network connections can be recovered by switching only a single optical switch preinstalled in the remote node. Simulation results show that the proposed architecture can recover the network function effectively and provide identical transmission performance to overcome the impact of a breakpoint in the network. The proposed transport system presents remarkable flexibility and convenience in expandability and breakpoint self-recovery.

An all-passive optical fiber sensor network is proposed based on a novel singleline bidirectional optical add-drop multiplexer (SBOADM). By reasonably employing fiber Bragg gratings and optical circulators to compose the self-developed SBOADM, single-line bidirectional transmission can be easily achieved by the SBOADM without the assistance of a power supply or optical switch. Experimental results prove that when optical signals are fed into the proposed SBOADM in clockwise or counterclockwise direction, the insertion loss of the dropped optical signals is roughly 3.7 dB or 4.5 dB, respectively, and the attenuation of each added signal is about 3.6 dB. When the SBOADM is employed to bridge a hybrid tree-based and ring-based optical fiber sensor network, self-healing functionality can be easily embedded into the network. Once an interruption occurs in the network, the only thing that the system maintainer needs to do is to adjust one optical switch pre-installed in the remote node of the sensor network. Simulation results show that the maximum power penalty caused by the self-healing function is roughly 6 dB. That is to say, the proposal can easily overcome any one fiber-link failure without adjusting the network deploying setting or employing complex control management.

A two-ring-based radio over fiber (RoF) transport system with a two-step fiber link failure detection and self-healing algorithm is proposed to ensure quality of service (QoS) by automatically monitoring the health of each fiber link in the transport system and by resourcefully detecting, locating, and bypassing the blocked fiber links. With the assistance of the fiber Bragg grating remote sensing technique, preinstalled optical switches, and novel single-line bidirectional optical add/drop multiplexers, the optical routing pathways in the RoF transport system can be dynamically adjusted by the proposed algorithm when some fiber links are broken. Simulation results show that except in some extreme situations, the proposed algorithm can find the blocked fiber links in the RoF transport system and animatedly adjust the status of preinstalled optical switches to restore all blocked network connections, thereby ensuring QoS in the proposed RoF transport system.

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