This article reviews recent progress leading to the generation of optical vortex beams. After introducing the basics of optical vortex beams and their promising applications, we summarized different approaches for optical vortex generation by discrete components and laser cavities. We place particular emphasis on the recent development of vortex generation by the planar phase plates, which are able to engineer a spiral phasefront via dynamic or geometric phase in nanoscale, and highlight the independent operation of these two different phases which leads to a multifunctional optical vortex beam generation and independent spin‐orbit interaction. We also introduced the recent progress on vortex lasing, including vortex beam generation from the output of bulk lasers by modification of conventional laser cavities with phase elements and from integrated on‐chip microlasers. Similar approaches are also applied to generate fractional vortex beams carrying fractional topological charge. The advanced technology and approaches on design and nanofabrications enable multiple vortex beams generation from a single device via multiplexing, multicasting, and vortex array, open up opportunities for applications on data processing, information encoding/decoding, communication and parallel data processing, and micromanipulations.

The physics of bound states in the continuum (BICs) allows the design and demonstration of optical resonant structures with large values of the quality factor ($Q$ factor) by employing dielectric structures with low losses. However, BIC is a general wave phenomenon that should be observed in many systems, including the metal-dielectric structures supporting surface plasmon polaritons where optical resonances are hindered by losses. Here we suggest and develop a comprehensive strategy to achieve high-$Q$ resonances in plasmonic metasurfaces by effectively tailoring the resonant modes from local to nonlocal regimes, thus transitioning from quasi-isolated localized resonances to extended resonant modes involving strong interaction among neighboring structure metaunits.

Bound states in the continuum (BICs) offer novel mechanisms to boost the quality factor (Q‐factor) of resonances. Unfortunately, current studies on chiral BICs metasurfaces suffer from a fundamental trade‐off between Q‐factor and circular dichroism (CD), presenting a significant hurdle that severely limits the independent control between CD and Q‐factors. Here, 3D plasmonic metasurfaces are numerically demonstrated that overcome the trade‐off and offer high‐Q quasi‐BIC resonances (Q ≈ 938) with strong CD (≈0.67) in the mid‐infrared. These metasurfaces are made of integrated‐resonance units consisting of a twisted vertical split‐ring resonator (VSRR) and a wall. Importantly, this dissimilar dimer configuration unlocks a new degree of freedom to decouple the Q‐factor and CD, that is, the Q‐factor and CD can be relatively independently manipulated by the height of the wall and the twisted angle of the VSRR, respectively. These results provide novel paradigms to manipulate advanced chiroptical responses, with various applications that require strong CD with enhanced light–matter interaction.

We demonstrate enhanced four-wave mixing (FWM) in doped silica waveguides integrated with graphene oxide (GO) layers. Owing to strong mode overlap between the integrated waveguides and GO films that have a high Kerr nonlinearity and low loss, the FWM efficiency of the hybrid integrated waveguides is significantly improved. We perform FWM measurements for different pump powers, wavelength detuning, GO coating lengths, and number of GO layers. Our experimental results show good agreement with theory, achieving up to ∼9.5-dB enhancement in the FWM conversion efficiency for a 1.5-cm-long waveguide integrated with 2 layers of GO. We show theoretically that for different waveguide geometries an enhancement in FWM efficiency of ∼20 dB can be obtained in the doped silica waveguides and more than 30 dB in silicon nanowires and slot waveguides. This demonstrates the effectiveness of introducing GO films into integrated photonic devices in order to enhance the performance of nonlinear optical processes.