Switchable multi-wavelength LP 11 mode fiber laser based on symmetric mode-selective coupler and dual-Sagnac comb filter

Abstract In this work, a switchable multi-wavelength higher-order transverse mode fiber laser based on a symmetric fiber mode-selective coupler (MSC) and a dual-Sagnac comb filter is proposed and experimentally demonstrated. More specifically, two identical segments of two-mode fibers are used to make the symmetrical fiber MSC to avoid exciting the LP 21 and LP 02 modes and eliminate the influence of other higher-order modes on the purity of the LP 11 mode. In addition, the proposed symmetrical fiber MSC is confirmed to exhibit higher purity output of the LP 11 mode and simpler operations. The proposed laser achieves a maximum number of seven output wavelengths. Experimental results reveal that the laser can generate stable and switchable single-, dual-, triple-, quadruple-, quintuple-, sextuple-, and septuple-wavelength outputs near 1550 nm at room-temperature conditions. All output wavelengths exhibit a side-mode suppression ratio exceeding 31.8 dB, while the LP 11 mode purity in this band exceeds 98.5%, which can up to 99.14%. This proposed multi-wavelength higher-order transverse mode fiber laser has potential applications in optical communication, optical sensing, etc.