Highly stable and wavelength-switchable single-longitudinal-mode Tm3+-doped fiber laser with a specially-designed tri-coupler dual-ring filter

Abstract

A single-longitudinal-mode (SLM) Tm3+-doped fiber laser (TDFL) with a narrow linewidth, less than 8 kHz, is proposed and demonstrated. A superimposed polarization-maintaining fiber Bragg grating (SI-PM-FBG), a specially-designed tri-coupler dual-ring (TCDR) cavity filter, and a section of unpumped Tm3+-doped fiber are combined to realize output lasing with SLM operation for each wavelength channel in 2 µm band. The design, fabrication, and characterization of the TCDR filter are demonstrated in detail. The proposed four-wavelength-switchable TDFL can be switched among fifteen lasing states, including four single-wavelength, six dual-wavelength, four triple-wavelength, and one quadruple-wavelength operations by adjusting the drop-in polarization controller. The experimental results show that the four SLM single-wavelength lasings are all with a relative intensity noise below − 113.06 dB/Hz at frequencies above 2 MHz, and the wavelength and output power fluctuation below 0.02 nm and 0.40 dB whihin 60 min, respectively. Four lasing wavelengths at 2048.28, 2048.71, 2049.05, and 2049.52 nm exhibit good wavelength and power stability and can maintain SLM operation.