Frequency-modulated continuous-wave laser ranging using low-duty-cycle signals for the applications of real-time...

A frequency-modulated continuous-wave laser ranging method using low-duty-cycle linear-frequency-modulated (LFM) signals is proposed. A spectrum consisting of a dense Kronecker comb is obtained so that the frequency of the beat signal can be measured with finer resolution. Since the dense comb is provided, super-resolved laser ranging can be achieved using a single-parametric frequency estimation method. Therefore, the run times of the estimation are reduced which promises real-time applications. A proof-of-concept experiment is carried out, in which an LFM signal with a bandwidth of 5 GHz and a duration of 1 µs is used. The duty-cycle of the LFM signal is 10%. The time delay of a scanning variable optical delay line is obtained in real time from the frequency of the highest comb tooth, of which the measurement resolution is 20 ps. Moreover, a single-parametric nonlinear least squares method is used to fit the envelope so that the time delay can be estimated with super-resolution. The standard deviation of the estimation displacements is 2.3 ps, which is 87 times finer than the bandwidth-limited resolution (200 ps). Therefore, the variation of the time delay can be precisely monitored. The proposed method may be used to achieve real-time high-resolution laser ranging with low-speed electronic devices.