Range extension for optical fiber sensing systems

In an optical fiber sensing system of embodiments of the present invention one or more optical fiber amplifiers are provided in series with the sensing fiber in order to increase the power of any sensing pulses being sent in a forward direction along the fiber. Optical circulators are provided either side of the optical amplifier, to allow backscattered light to be routed around the forward path optical amplifier. In some embodiments an optical amplifier may also be provided in the backscatter and/or reflections feedback path, to increase the power of the backscatter. In further embodiments signal conditioning circuitry may be used, such that the forward optical pulse signal is filtered and/or reconstructed so as to be more like the original pulse (i.e. typically with less time spreading) when output by the amplifier. In some embodiments this may be done within the optical domain by the provision of appropriate bandpass filters, or in other embodiments electronically, with an incoming pulse being electronically sampled and then fed to a controller, which then electronically controls an optical amplifier to reproduce a re-conditioned (with respect to amplitude, wavelength and time) pulse for onward transmission along the next length of fiber.