Multi-wavelength fiber laser with high-purity LP11 output mode based on a symmetrical fiber mode selective coupler and Sagnac interferometer

In this work, a multi-wavelength fiber laser with a high-purity LP11 output mode was proposed and experimentally demonstrated. More specifically, a novel symmetrical fiber mode selective coupler (MSC) was utilized for mode conversion and a Sagnac interferometer is fabricated as a multi-channel filter for wavelength selection. From the experimental results, it was shown that the laser was able to emit stable single-, dual-, and triple-wavelength outputs both around 1530 nm and 1550 nm, and the purity of the LP11 mode was above 97 % and 98 % at the two bands respectively. In addition, the laser was capable of simultaneous dual-wavelength emission around 1530 nm and 1550 nm, resulting in an overall four-wavelength output with an LP11 mode purity of above 98 %. The proposed high-order mode multi-wavelength fiber laser has potential applications in various fields including optical communications, optical sensing, and materials processing.