Single-frequency switchable-dual-OAM laser in eye-safe band toward rotational Doppler metrology

Single-frequency laser beams, especially when located in eye-safe bands, provide significant insights for Doppler metrology exploiting lidar technology. To extend these prospects further, we push forward the advancement of such lasers into the orbital angular momentum (OAM) manipulation domain. The intra-cavity generation of single-frequency degenerate modes with opposite OAM in eye-safe band is experimentally demonstrated in a unidirectional ring resonator with a spot-defect filter (SDF). By slightly adjusting the position of spot defect, mode matching is changed flexibly, allowing the switch of output dual-OAM modes ranging from |±1⟩ to |±6⟩. The high modes fidelities and the favorable single-frequency spectra emphasize the efficiency of the laser source. For further verification, the switchable-dual-OAM modes are exploited to conduct rotational Doppler metrology with an accuracy deviation less than 2.5%. This work, as a proof of principle, indicates a practical and robust methodology for manipulating multi-degrees-of-freedom and high-dimensional modes, paving the way for extensive future applications especially toward lidar metrology.