Dual-wavelength fiber laser operating above 2 μm based on cascaded single-mode-multimode-single-mode fiber structures

A stable dual-wavelength Tm³⁺:Ho³⁺ co-doped fiber laser operating above 2 μm based on cascaded single-mode-multimode-single-mode (SMS) fiber structures is proposed and experimentally demonstrated. Based on the theoretical analysis of the transmission properties of the SMS fiber structure, two cascaded SMS fiber devices with different multimode fiber (MMF) lengths were used in our laser system, where one acted as a long-pass filter to suppress the competitive laser below 2 μm, and the other worked as a band-pass filter to select the specific operating wavelengths of the laser. Dual-wavelength operation of the fiber laser at 2002.8 and 2016.1 nm has been achieved in the experiment with a signal to a noise ratio up to 50 dB.