Ultrafast frequency tuning in fiber laser based on recirculating optical phase modulation

Ultrafast frequency tuning of the probe laser is indispensable in optical coherence tomography (OCT) and light detection and ranging (LiDAR). Up to now, the sweep rate of the laser frequency is smaller than 1GHz by using the existing techniques, which is the main factor that hinders the further development of OCT and LiDAR systems. Here, we propose and demonstrate a new approach to generating a frequency-agile laser in a fiber laser. The realization is based on the recirculating electro-optic phase modulation of the self-oscillating optical field in the fiber laser, where the repetition frequency of the driving signal slightly deviates from the resonant frequency of the fiber laser. Consequently, a linear voltage-to-frequency mapping is achieved, which offers a simple way to ultrafast manipulate the laser frequency. In the experiment, the maximum sweep rate of the laser frequency is equal to 2.2GHz. In addition, the frequency-swept range can be tuned by varying two parameters of the fiber laser. The proposed approach can significantly enhance the sweep rate of the laser frequency, which has the potential to be used as a fast frequency-swept optical source in advanced OCT and LiDAR systems.