Dynamic vortex mode-switchable erbium-doped Brillouin laser pumped by high-order mode

Optical vortex lasers [Invited]

The manipulation of light fields has become pivotal in advancing various domains of optics, including classical and quantum communications, optical trapping, optical metrology and high-resolution imaging. Among various techniques for creating optical vortices, the optical vortex lasers, distinguished by directly emitting customized beams with phase or polarization singularities, have emerged as a burgeoning tool in modern optics. This paper summarizes the recent progress of optical vortex lasers including their primary types, designing methods and diverse applications. We begin by introducing the underlying principles of optical vortices and then explore numerous methods for designing optical vortex lasers, including bulk laser, fiber laser and on-chip laser. We also highlight the optical vortex laser towards higher dimensions for shaping structured beams with more complex spatial and topological patterns. Furthermore, we outline the wide applications of optical vortex lasers and address their challenges and potential future developments. This paper serves as a thorough overview for the physics, optics and engineering communities looking to harness potential of optical vortex lasers in cutting-edge applications.

Sub-kHz high-order mode Brillouin random fiber laser based on long-period fiber grating and distributed Rayleigh scattering in a half-open linear cavity

We demonstrate a narrow-linewidth high-order-mode (HOM) Brillouin random fiber laser (BRFL) based on a long-period fiber grating (LPFG) and distributed Rayleigh random feedback in a half-open linear cavity. The single-mode operation of the laser radiation with sub-kilohertz linewidth is achieved thanks to distributed Brillouin amplification and Rayleigh scattering along kilometer-long single mode fibers whilst a few mode fiber-based LPFGs enable the transverse mode conversion among a broadband wavelength range. Meanwhile, a dynamic fiber grating (DFG) is embedded and incorporated to manipulate and purify the random modes, which hence suppresses the frequency drift resulting from random mode hopping. Consequently, the random laser emission with either high-order scalar or vector modes can be generated with a high laser efficiency of 25.5% and an ultra-narrow 3-dB linewidth of 230 Hz. Furthermore, the dependence of the laser efficiency and frequency stability on the gain fiber length are also experimentally investigated. It is believed that our approach could provide a promising platform for a wide range of applications such as coherent optical communication, high-resolution imaging, highly sensitive sensing, etc.

Dynamic mode-switchable and wavelength-tunable Brillouin random fiber laser by a high-order mode pump

We experimentally investigate two schemes of Brillouin random fiber laser (RFL) by using high-order-mode (HOM) pump in a few-mode fiber (FMF). The core-mode conversion between LP₀₁ and LP₁₁ modes is obtained in the FMF by cascading long period fiber gratings (LPFG) working at the same wavelength region. Different transversal modes of stimulated Brillouin scattering (SBS) can be implemented based on broadband long period fiber gratings (LPFG) and acoustically induced fiber gratings (AIFG). The RFL base on two broadband LPFGs can obtain high purity LP₁₁ mode operating in the range of 1543 nm to 1565 nm. Moreover, the output mode can be dynamically switched between LP₀₁ mode, LP_11a mode and LP_11b mode by modulating frequency shift keying (FSK) signal of the AIFG. This work has potential application prospects in the fields of mode division multiplexing systems, speckle-free imaging, free-space optical communication, laser material processing.