Frequency-swept feedback interferometry for non-cooperative-target ranging with the stand-off distance of hundred meters

Abstract

Frequency-swept interferometry (FSI) is a powerful ranging method with high precision and immunity to ambient light. However, the stand-off distance of the current FSI-based ranging system for non-cooperative targets is relatively short, because the weak echo power cannot provide the needed signal-to-noise ratio (SNR). Here, we report a ranging method combining FSI and the laser feedback technique. Compared with the conventional FSI, the interference between the weak echo signal and the local oscillator occurs in the laser cavity, which makes the signal enhanced spontaneously and then provides a satisfying SNR. In experiments, the detection limit of the echo power is less than 0.1fW, with 230µW output in total. Based on the enhancement from the laser feedback technique, the system achieves a non-cooperative target ranging hundreds of meters away in space without extra optical amplifiers. On the other hand, a large stand-off distance makes the system sensitive to environmental disturbance, which degrades the ranging precision. To correct it, a compensation device is proposed to correct the unwanted optical-path-length drifts. Owing to the high sensitivity and the validity of the compensation, the standard deviation in 10 measurements is better than 0.07mm, targeting an aluminum sheet at about 152m. Generally, hundred-meter range, high relative precision, and low photon consumption predict a novel technical scheme for laser ranging, and demonstrate new capabilities that promise to enable a wide range of scientific and industrial applications.