Multiwavelength fiber laser using a spatial mode beating filter

A multiwavelength comb is obtained from Er(3+) - and Nd(3+)-doped fiber lasers by incorporation of a section of multimode optical fiber into an otherwise single-mode fiber ring cavity. This combination of fiber types acts as a wavelength-dependent filter in the laser through spatial mode beating between the LP(01) and LP(11) modes in the multimode fiber.