Rangeability extension of fiber-optic low-coherence measurement based on cascaded multistage fiber delay line

We demonstrate a simple method to extend the measurable fiber length with a fiber-optic low-coherence technique. This method is based on a cascaded structure of multistage fiber delay line laid in one arm of the low-coherence technique. By choosing different individual stages in the cascaded fiber delay line, the length of the fiber under test can be continuously measured with a different measurement range. The measurement range of 0.81 km and spatial resolution of 60 μm are successfully realized.