We present a 2-mode group, switchable spatial mode erbium doped fiber laser incorporating a spatial light modulator. The laser wavelength can be tuned using an intra-cavity wavelength selective filter and provides >10dB extinction ratio between LP 01 /LP 11 modes.OCIS codes: (060.3510) Lasers, fiber; (060.2410) Fibers, erbium; (060.0060) Fiber optics and optical communications. IntroductionFiber lasers [1] offer excellent beam quality, reliability, compactness and high photon conversion efficiency and have been widely used in diverse fields including optical communications, medicine, spectroscopy and material processing. Typically, fiber lasers are designed to operate on the fundamental spatial mode and the high beam quality enables applications such as fine laser marking. Multimode fiber lasers by contrast are typically used to generate the higher output powers needed for many industrial applications such as cutting, welding and heat treatment of metals. Recently, few-mode fibers have been used for mode division multiplexed (MDM) data transmission [2,3] where information is simultaneously transmitted on several spatial modes within a single optical fiber, and inline few-mode fiber amplifiers have been used to boost the transmission. In MDM optical networks selective excitation and detection of light propagating on the different transverse modes is a critical issue and proper modal characterization of the subsystems and fiber components needed is a key requirement. To this end a transverse mode switchable and wavelength tunable fiber laser offering well defined modal output at relatively high output powers would represent a very useful tool. In ref.[4], a mode selective fiber laser based on a multimode fiber Bragg grating (FBG) has been introduced. However, the operating wavelengths of the lowest two transverse modes (LP 01 and LP 11 ) is achieved at different wavelengths with ~5nm separation due to the very different Bragg resonance conditions for each mode, while the wavelength tuning range of the fiber laser is fixed (or is necessarily narrow) due to the relatively limited tuning range associated with fiber Bragg gratings. In a recent publication in Nat. Comm.[5], a reflective phase-only spatial light modulator (SLM) was used as an intra-cavity holographic mirror in a standard (bulk crystal) solid-state laser resonator and showed the feasibility of electronically controlling the spatial transverse mode of the laser. This represents the first "mode on demand" operation of a solid-state laser and the high resolution of the SLM enables precise and highly flexible intra-cavity laser beam shaping.In this paper, we employ such a high-speed, electronically addressable SLM device as a cavity mirror in an erbium doped fiber laser cavity and demonstrate digital electronic control of the spatial output mode. In this case selection of the transverse spatial mode requires only a change to the phase pattern applied to the SLM and no additional alignment to the fiber laser cavity is required. Furthermore, a tunabl...