Single- and dual-wavelength fiber laser with multi-transverse modes

A single- and dual-wavelength fiber laser with multi-transverse modes is proposed. Mode interference is realized in the core of an optical fiber by writing a long period fiber grating on a few-mode fiber to obtain the LP₀₁ mode and the LP₁₁ mode simultaneously. A mode interferometer based on a few-mode long period fiber grating (FM-LPFG) is used as a comb filter in the ring-cavity fiber laser. Single- and dual-wavelength outputs can be achieved in the fiber laser by adjusting a polarization controller (PC). A mode-selective photonic lantern is used to realize mode conversion, and six LP modes, LP₀₁, LP_11a, LP_11b, LP_21a, LP_21b, and LP₀₂, can be generated. A single- and dual-wavelength fiber laser with multi-transverse modes can be achieved by combining a mode interferometer with a mode-selective photonic lantern. This work has potential applications in mode division multiplexing (MDM) systems to enlarge the capacity of optical communications.