Flexible generation of broadly wavelength- and OAM-tunable Laguerre-Gaussian (LG) modes from a random fiber laser.

Broadband wavelength tunable Laguerre-Gaussian (LG) mode with flexibly manipulated topological charge is greatly desired for large-capacity optical communication. However, the operating wavelengths achieved for the current LG modes are significantly restricted either by the emission spectrum of the intracavity gain medium or by the operation wavelengths of mode-conversion or modulation components. Here, broadband wavelength-tunable LG modes with a controllable topological charge are generated based on a random fiber laser (RFL) and a digital micromirror device (DMD). The RFL can produce broadly wavelength-tunable laser emissions spanning from 1044 to 1403 nm with a high spectral purity and an excellent beam quality, benefiting from the cascaded random Raman gain starting from a ytterbium fiber based active gain. A commercially available broadband DMD is then utilized to excite the LG modes with a flexibly tunable topological charge of up to 100 order through the super-pixel wavefront shaping technique. The combination of the RFL and the DMD greatly broadens the operating wavelength region of the LG modes to be achieved, which facilitates the capacity scaling-up in the orbital angular momentum multiplexed optical communication application.

20 watt-level single transverse mode narrow linewidth and tunable random fiber laser at 1.5 µm band.

High power 1.5 µm band fiber lasers are of great importance for many practical applications. Generally, the technical targets including high average output power, narrow linewidth, temporally suppressed intensity dynamics, high spectral purity, single transverse mode lasing, and excellent robustness are the major concerns when constructing a high-performance laser source. Here, we demonstrate the highest output power of a wavelength tunable 1.5 µm band random fiber laser based on the active fiber gain mechanism to the best of our knowledge. A master oscillator power-amplifier (MOPA) configuration is employed to greatly boost the output power to 20 watt-level with a single transverse mode lasing and the same linewidth as the seed, benefiting from the spectral broadening free feature when employing the random fiber laser as the seed. This work not only enriches the progress of random fiber laser, but also provides an attractive alternative in realizing high performance lasing light source at 1.5 µm band.