Dynamic Sideband-Calibrated Frequency-Sweeping Interferometry for Absolute Distance Measurement

A novel frequency-sweeping interferometric method with dynamic sideband calibration for absolute distance measurement is proposed in this paper. The beam of a reference laser is modulated using a high-frequency electro-optical phase modulator (HEOPM) to generate the laser sidebands, and a frequency-sweeping laser (ECDL<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>) is locked to a specific highorder sideband. By sweeping the modulation frequency of the HEOPM while keeping ECDL<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> locked to the high-order dynamic sideband, the frequency of ECDL<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> synchronously follows the modulation frequency. Consequently, its swept-frequency range is inherently calibrated through the sideband frequency shift. Additionally, a monitoring interferometer is constructed using the reference laser to compensate for the target drift. The frequency-division-multiplexing sinusoidal phase modulation technique is employed to simultaneously detect the phases of both the frequency-sweeping interferometer and the monitoring interferometer. Performance test of laser frequency dynamic locking demonstrates that ECDL<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> can track the rapidly sweeping dynamic sideband over a wide range, enabling accurate determination of the swept-frequency range. Experimental results show that the proposed method can effectively compensate for the target drift and achieve absolute distance measurement with standard deviations of 13.90 μm, 17.95 μm, and 22.85 μm at the distances of 1.094 m, 4.444 m, and 7.617 m, respectively. Thus, the proposed scheme achieves relative accuracies of 3.0 × 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> to 1.3 × 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> within a 7.6-meter measurement range.