A novel hybrid TOF/phase-shift method for absolute distance measurement using a falling-edge RF-modulated pulsed laser

We propose a hybrid time-of-flight/phase-shift (TOF/phase-shift) method using a falling-edge radio-frequency-modulated (RF-modulated) pulsed laser for absolute distance measurement. The principle of the new hybrid TOF/phase-shift technique is based on the use of an RF-modulated pulse to benefit from both the long unambiguous distance of the pulsed TOF method and the accuracy of the RF phase-shift measurement. The RF-modulated pulse is obtained using a pulsed frequency-shifted amplifying loop coupled to a single-frequency laser. The RF modulation depth and pulse waveform properties of the optical fiber loop are investigated. Then, the fully fibered RF-modulated source is applied to a laboratory distance measurement. We show experimentally that the hybrid TOF/phase-shift method is a promising technique that achieves 3 mm precision in the 1.5 km measurement range (in fiber), corresponding to a relative precision of 2 × 10 ⁻⁶ .