We demonstrate an optical fiber fault location method based on the frequency response of the modulated fiber optical backscattered signal in a steady state low-frequency step regime. Careful calibration and measurement allows for the reconstruction of the fiber transfer function, which, associated to its mathematical model, is capable of extracting the fiber characteristics. The technique is capable of identifying non-reflective fault events in an optical fiber link and is perfectly compatible with previous methods that focus on the reflective events. The fact that the recuperation of the complex signal is performed in the frequency domain and not via a Fourier Transform enables the measurements to overcome the spatial resolution limitation of Fourier Transform incoherent-OFDR measurements even with frequency sweep ranges down to 100-100000 Hz. This result is backed up by a less than 10 meters difference in fault location when compared to standard OTDR measurements.
We report on the simultaneous monitoring of both fiber and copper links in the context of analog radio signal transmission over fiber-extended copper mobile fronthaul networks. The same monitoring signal is used to determine both the fiber's and copper's characteristics, which translates into a low-complexity monitoring structure readily embeddable in the transmitter. A copper-tofiber converter unit is devised so that both monitoring and data signals can coexist even when the control is centralized at the central office. In-service fiber monitoring is achieved with a spatial resolution of 10 m and ≥7 dB dynamic range, while in-service copper monitoring is achieved with a maximum reach of 100 m and an error in fault location smaller than 1 m. Low-cost centralized monitoring of hybrid networks represents a step toward the deployment of fiber-extended copper lines, which is a promising candidate for next-generation communication architectures.
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