Displacement Sensing by Repetition Rate Pulling in a Passively Mode Locked Laser Under Feedback

We propose and experimentally validate a simple displacement sensing technique, which relies on the optical feedback-induced pulling of the repetition rate in a passively mode-locked semiconductor laser. Depending on the setup parameters, different realizations of the technique permit displacement and vibration sensing of the reflecting object. Other physical parameters that modify the optical length of the external cavity could also be measured. The technique is particularly well adapted for fast phenomena and offers a subwavelength theoretical displacement resolution, which is limited only by the RF linewidth of the laser and resolution of the repetition frequency measurement.