Absolute distance measurement without dead zone based on dual-channel dispersive interferometry using the femtosecond laser

In this paper, a dual-channel dispersive interferometer using femtosecond laser is developed with a reference long optical fiber. The width spectrum of the femtosecond laser is divided into a ranging channel and a monitor channel using a coarse wavelength division multiplexer. The ranging channel uses long fiber to construct an unbalanced interferometer to eliminate measurement dead zone by changing the repetition frequency. The monitor channel can measure the fluctuation of long optical fiber in real-time. The dual-channel interference signal then can be received by one single spectrometer. The optical path drift of the long fiber-based reference path can be synchronously compensated to achieve high-precision ranging. In experiments, a 116 m long optical fiber was compensated to 3 × 10⁻⁸ stability for one hour. Compared with a commercial interferometer, the ranging accuracy is better than ±4 μm within a range of 300 mm.