Laguerre-Gaussian (LG) modes, carrying the orbital angular momentum of light, are critical for important applications, such as high-capacity optical communications, superresolution imaging, and multidimensional quantum entanglement. Advanced developments in these applications demand reliable and tunable LG mode laser sources, which, however, do not yet exist. Here, we experimentally demonstrate highly efficient, highly pure, broadly tunable, and topological-charge-controllable LG modes from a Janus optical parametric oscillator (OPO). The Janus OPO featuring a two-faced cavity mode is designed to guarantee an efficient evolution from a Gaussian-shaped fundamental pump mode to a desired LG parametric mode. The output LG mode has a tunable wavelength between 1.5 and 1.6 μm with a conversion efficiency >15 % , a controllable topological charge up to 4, and a mode purity as high as 97%, which provides a high-performance solid-state light source for high-end demands in multidimensional multiplexing/demultiplexing, control of spin-orbital coupling between light and atoms, and so on.

In this work, we propose a new scheme to generate frequency-doubled vortex beams from a radially poled LiNbO₃ micro-ring resonator based on nonlinear Cherenkov radiation. The near-infrared fundamental wave is resonant in the micro-ring, while the second harmonic is emitted from the resonator along the Cherenkov phase-matching direction. The topological charge of the emitted second-harmonic vortex beam is determined by both the azimuthal order of the whispering galley modes and the number of nonlinear grating elements. The field distribution and the conversion efficiency of the emitted vortex beam are investigated.

We demonstrate an efficiency-enhanced picosecond (ps) mid-infrared radiation via optical parametric downconversion. Based on a cascaded periodically poled MgO-doped stoichiometric lithium tantalate crystal (MgO:sPPLT), a tandem optical parametric oscillation-optical parametric amplification (OPO-OPA) process is achieved. Compared with a single OPO process, the conversion efficiency obtains an enhancement of 71%.