Four-spot light-intensity based demodulation method for orbital-angular-momentum interferometer

Recently, orbital-angular-momentum (OAM) beams-based interferometers (OAMIs) have been demonstrated significant potential in achieving ultra-high accuracy. However, the demodulation speed of traditional interferograms-based demodulation methods for OAMIs has always been limited by the interferogram acquisition devices and demodulation algorithms. To address these challenges, a demodulation method for OAMI using the four-spot light-intensity (FSLI) signals was firstly put forward and demonstrated in experiment. By using a 1-to-7 fan-out bundles, these FSLI signals at the fixed azimuthal positions on petal-like interference patterns (interferograms) were detected and precisely sampled using photodetectors-based acquisition devices. Then, a random four-step azimuthal phase-shifting algorithm was firstly proposed to quickly demodulate the measured phases from these signals. As a result, linear motions and periodic vibrations were precisely reconstructed. ‌This method greatly improves the demodulation speed of OAMIs, which opens a new way in the field of dynamic measurement using OAMIs.