Direct observation of beat-frequency switching in a self-sweeping fiber laser using variable space length

Lately, a novel beat-frequency signal doubling In this work, we constructed a SFSSFL, where we phenomenon has been reported based on a self-sweeping fiber introduced a piece of variable space lengths using a collimator laser platform, which is essential for understanding the and mirror. We observed the RF spectra under different space mechanism of the self-sweeping effect and the wavelength lengths, and the RF peak increased as the space length interval in sweeping operation. In this work, we studied the decreased. We developed a simulation of the FSA bandwidth phenomenon using a variable space length. By controlling the to explain the switching of the beat-frequency. cavity length (also known as “the spacing of longitudinal mode”) and using a 1.8 m long fiber saturable absorber (FSA), we achieved the beat-frequency switching from the fundamental to the double frequency. Furthermore, a theoretical analysis was proposed to explain the phenomenon by calculating the reflected spectrum provided by the FSA and the change of the longitudinal mode in the cavity.