A Hybrid Optical Fiber and FSO System for Bidirectional Communications Used in Bridges

In this paper, a 10-Gb/s hybrid optical fiber (OF) and free-space optics (FSO) link as part of a bidirectional long-haul OF transmission for application in outdoor environments such as bridges is proposed. A fiber-Bragg-grating (FBG) sensor head is used for monitoring the condition of a bridge, and in the case of the bridge being damaged, the transmission path is changed over from OF to the FSO link to ensure link connectivity. An Erbium-doped fiber amplifier is used to compensate for losses due to the fiber cable and the free-space channel. At a bit error rate (BER) of 10e-9, the power penalty between the OF and FSO paths is <; 1 dB, and the power variations for both paths are ±0.07 and ±0.12 dB, respectively.