All-fiber high-order mode laser using a metal-clad transverse mode filter.

We propose and demonstrate an all-fiber laser with LP mode output. A transverse mode filter is designed and fabricated to suppress the fundamental mode and enable the fiber laser to oscillate in the second-order (LP) transverse mode. The mechanism is to introduce relatively low ohmic loss for the TE mode and much higher ohmic losses for other modes through the loss of evanescent waves in the metal clad. The fiber laser operates at the center wavelength of 1053.9 nm with a narrow 3 dB linewidth of 0.019 nm. Four states of cylindrical vector mode with high modal purity are obtained through adjusting the intra-cavity polarization controller. This approach has great potentiality and scalability of realizing single high-order mode fiber laser, from which a wide range of applications could benefit.