High-Precision and Large-Scale Phase-Based Laser Ranging With High Receiving Sensitivity via Multi-Tone Modulation and Frequency-Shift-Based Coherent Low-Frequency Detection

The phase-based laser ranging (PBLR) technology can achieve high-precision distance measurement. Nevertheless, it is challenging to realize real-time and high-sensitivity measurement with a high precision in a large non-ambiguity range (NAR). Here, a PBLR scheme is proposed and demonstrated to solve the above problems. In the transmitter, a multi-tone microwave signal is modulated onto the optical carrier to configure a synthetic wavelength chain, which is beneficial for extending the NAR. In the receiver, a new frequency-shift-based optical down-conversion architecture is used to achieve coherent low-frequency detection, which not only enhances the receiving sensitivity, but also facilitates real-time measurement. In addition, an optical phase noise cancellation algorithm is proposed to eliminate the phase noise in the photocurrent introduced by optical coherent detection, largely enhancing the measurement precision. In the experiment, the time delay measurement precision for a section of single-mode fiber (SMF) with a length of 30 m reaches 0.46 fs within a measurement time of 3.76 ms, corresponding to a distance measurement precision of 0.09 μm. Besides, the time delay measurement precision for a spool of SMF with a length of 10 km reaches 2.61 fs within a measurement time of 2.92 ms, corresponding to a distance measurement precision of 0.52 μm. Compared to the incoherent method, the measurement precision of the proposed scheme is enhanced by 95 times when the probe light power is −20 dBm.