Topological-charge-tunable and wavelength- switchable vortex laser enabled by a helically twisted high-absorption few-mode erbium-doped fiber.

Vortex beams carrying orbital angular momentum (OAM) offer a solution for enhancing spatial degrees of freedom, particularly in conjunction with wavelength division multiplexing, which can significantly boost data capacity for optical communication. Addressing the increasing demand for high information-carrying capacity, we present a dynamically tunable OAM laser source in this study. We demonstrate a ring-cavity vortex fiber laser employing intra-cavity mode conversion through a helically twisted high-absorption few-mode erbium-doped fiber (HA-FM-EDF). The constructed vortex fiber laser exhibits wavelength switchability via an integrated Sagnac loop, facilitated by a homemade ring-core fiber. Furthermore, topological-charge tunability is achieved through the utilization of twisted HA-FM-EDF with varying helical pitches. To our knowledge, this marks the first successful implementation of two-dimensional multiplexing of wavelength and OAM in a vortex fiber laser. The OAM laser serves as a versatile vortex source with high tunability and flexibility, holding significant potential for deployment in ultrahigh-speed/ultrahigh-capacity communications, ultrahigh-resolution imaging, and ultrahigh-sensitivity sensing applications.