A Switchable Figure Eight Erbium-Doped Fiber Laser Based on Inter-Modal Beating By Means of Non-Adiabatic Microfiber

A switchable multiwavelength figure eight fiber laser effect of multimode interference is proposed and experimentally demonstrated. A narrow bandpass filter of multiple specific wavelengths was created by incorporating a tapered non-adiabatic microfiber of 70 mm length and 2 μm diameter in a Sagnac loop mirror. Spatial mode beating arose due to the modal interference in the non-adiabatic microfiber, and resulted in a comb filter able to suppress mode competition. The proposed laser generated single longitudinal modes having a 3-dB linewidth of less than 0.16 pm, which represents an upper limit measurement imposed by the restrictions of the optical analyzer resolution, and possessed an optical signal-to-noise ratio of 58 dB at 82 mW pumping power. Moreover, nonlinear polarization rotation and strain switching mechanisms are demonstrated for generating single, dual, and triple wavelength over more than 20 nm span. In addition, a description is provided on a new technique of packaging non-adiabatic microfiber that diminishes issues relating to degradation of the microfiber over time and external perturbation.