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1. Non-diffracting states at exceptional points

   https://doi.org/10.1364/OL.411999  

   Yuce, Cem ; Ramezani, Hamidreza ( February 2021 , Optics Letters)

   We propose to use exceptional points (EPs) to construct diffraction-free beam propagation and localized power oscillation in lattices. We specifically consider two systems to utilize EPs for diffraction-free beam propagation, one in synthetic gauge lattices and the other in unidirectionally coupled resonators where each resonator individually is capable of creating orbital angular momentum (OAM) beams. In the second system, we introduce the concept of robust and tunable OAM beam propagation in discrete lattices. We show that one can create robust OAM beams in an arbitrary number of sites of a photonic lattice. Furthermore, we report power oscillation at the EP of a non-Hermitian lattice. Our research widens the study and application of EPs in different photonic systems including OAM beams and their associated dynamics in discrete lattices.

    

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2. Tunable topological charge vortex microlaser

   https://doi.org/10.1126/science.aba8996  

   Zhang, Zhifeng ; Qiao, Xingdu ; Midya, Bikashkali ; Liu, Kevin ; Sun, Jingbo ; Wu, Tianwei ; Liu, Wenjing ; Agarwal, Ritesh ; Jornet, Josep Miquel ; Longhi, Stefano ; et al ( May 2020 , Science)

   The orbital angular momentum (OAM) intrinsically carried by vortex light beams holds a promise for multidimensional high-capacity data multiplexing, meeting the ever-increasing demands for information. Development of a dynamically tunable OAM light source is a critical step in the realization of OAM modulation and multiplexing. By harnessing the properties of total momentum conservation, spin-orbit interaction, and optical non-Hermitian symmetry breaking, we demonstrate an OAM-tunable vortex microlaser, providing chiral light states of variable topological charges at a single telecommunication wavelength. The scheme of the non–Hermitian-controlled chiral light emission at room temperature can be further scaled up for simultaneous multivortex emissions in a flexible manner. Our work provides a route for the development of the next generation of multidimensional OAM-spin-wavelength division multiplexing technology. 

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3. Efficient generation and amplification of intense vortex and vector laser pulses via strongly-coupled stimulated Brillouin scattering in plasmas

   https://doi.org/10.1038/s42005-023-01493-6  

   Wu, Yipeng ; Zhang, Chaojie ; Nie, Zan ; Sinclair, Mitchell ; Farrell, Audrey ; Marsh, Kenneth A. ; Alves, E. Paulo ; Tsung, Frank ; Mori, Warren B. ; Joshi, Chan ( January 2024 , Communications Physics)

   The past decade has seen tremendous progress in the production and utilization of vortex and vector laser pulses. Although both are considered as structured light beams, the vortex lasers have helical phase fronts and phase singularities, while the vector lasers have spatially variable polarization states and polarization singularities. In contrast to the vortex pulses that carry orbital angular momentum (OAM), the vector laser pulses have a complex spin angular momentum (SAM) and OAM coupling. Despite many potential applications enabled by such pulses, the generation of high-power/-intensity vortex and vector beams remains challenging. Here, we demonstrate using theory and three-dimensional simulations that the strongly-coupled stimulated Brillouin scattering (SC-SBS) process in plasmas can be used as a promising amplification technique with up to 65% energy transfer efficiency from the pump beam to the seed beam for both vortex and vector pulses. We also show that SC-SBS is strongly polarization-dependent in plasmas, enabling an all-optical polarization control of the amplified seed beam. Additionally, the interaction of such structured lasers with plasmas leads to various angular momentum couplings and decouplings that produce intense new light structures with controllable OAM and SAM. This scheme paves the way for novel optical devices such as plasma-based amplifiers and light field manipulators.

    

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4. On-chip spin-orbit locking of quantum emitters in 2D materials for chiral emission

   https://doi.org/10.1364/OPTICA.463481  

   Ma, Yichen ; Zhao, Haoqi ; Liu, Na ; Gao, Zihe ; Mohajerani, Seyed Sepehr ; Xiao, Licheng ; Hone, James ; Feng, Liang ; Strauf, Stefan ( August 2022 , Optica)

   Light carries both spin angular momentum (SAM) and orbital angular momentum (OAM), which can be used as potential degrees of freedom for quantum information processing. Quantum emitters are ideal candidates towards on-chip control and manipulation of the full SAM–OAM state space. Here, we show coupling of a spin-polarized quantum emitter in a monolayer${\mathrm{W}\mathrm{S}\mathrm{e}}_2$with the whispering gallery mode of a${\mathrm{S}\mathrm{i}}_3{\mathrm{N}}_4$ring resonator. The cavity mode carries a transverse SAM of$\mathrm{\sigma <\#comment/>}=\pm <\#comment/>1$in the evanescent regions, with the sign depending on the orbital power flow direction of the light. By tailoring the cavity–emitter interaction, we couple the intrinsic spin state of the quantum emitter to the SAM and propagation direction of the cavity mode, which leads to spin–orbit locking and subsequent chiral single-photon emission. Furthermore, by engineering how light is scattered from the WGM, we create a high-order Bessel beam which opens up the possibility to generate optical vortex carrying OAM states.

    

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5. Efficient Generation of Microwave Plasmonic Vortices via a Single Deep‐Subwavelength Meta‐Particle

   https://doi.org/10.1002/lpor.201800010  

   Su, Hai ; Shen, Xiaopeng ; Su, Guangxu ; Li, Lin ; Ding, Jianping ; Liu, Fanxin ; Zhan, Peng ; Liu, Yongmin ; Wang, Zhenlin ( June 2018 , Laser & Photonics Reviews)

   Light beams carrying orbital angular momentum (OAM) in the form of optical vortices have attracted great interest due to their capability for providing a new dimension and approach to manipulate light–matter interactions. Recently, plasmonics has offered efficient ways to focus vortex beams beyond the diffraction limit. However, unlike in the visible and near‐infrared regime, it is still a big challenge to realize plasmonic vortices at far‐infrared and even longer wavelengths. An effective strategy to create deep‐subwavelength near‐field electromagnetic (EM) vortices operating in the low frequency region is proposed. Taking advantage of the asymmetric spatial distribution of EM field supported by a metallic comb‐shaped waveguide, plasmonic vortex modes that are strongly confined in a well‐designed deep‐subwavelength meta‐particle with desired topological charges can be excited. Such unique phenomena are confirmed by the microwave experiments. An equivalent physical model backed up by the numerical simulations is performed to reveal the underlying mechanism of the plasmonic vortex generation. This spoof‐plasmon assisted focusing of EM waves with OAM may find potentials for functional integrated elements and devices operating in the microwave, terahertz, and even far‐infrared regions.

    

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