• Special Issue
  • Theme Issue on Orbital Angular Momentum
  • 13 Article (s)
Editorials
News and Commentaries
Reviews
Torsion pendulum driven by the angular momentum of light: Beth’s legacy continues
Etienne Brasselet
The optical angular momentum is ubiquitous to the science of light, especially whenever the polarization state and the spatial distribution of the phase are involved, which are most often associated with the spin and orbital parts of the total angular momentum, respectively. Notably, the independent introduction of these two contributions to the total optical angular momentum was accompanied by suggestions regarding the possible detection of their mechanical effects using a torsion pendulum. Today, the classical and quantum mechanical aspects of spin and orbital angular momentum of light and their mutual coupling remain active research topics offering exciting perspectives for photonic technologies. Our brief historical overview shows how the torsion pendulum has accompanied scientific advances on mechanical effects based on the angular degrees of freedom of light since Beth’s pioneering contribution published in 1935.
Advanced Photonics
  • Publication Date: Jun. 30, 2023
  • Vol. 5, Issue 3, 034003 (2023)
Research Articles
Generation of time-varying orbital angular momentum beams with space-time-coding digital metasurface
Jingxin Zhang, Peixing Li, Ray C. C. Cheung, Alex M. H. Wong, and Jensen Li
The recently proposed extreme-ultraviolet beams with time-varying orbital angular momentum (OAM) realized by high-harmonic generation provide extraordinary tools for quantum excitation control and particle manipulation. However, such an approach is not easily scalable to other frequency regimes. We design a space-time-coding digital metasurface operating in the microwave regime to experimentally generate time-varying OAM beams. Due to the flexible programmability of the metasurface, a higher-order twist in the envelope wavefront structure of time-varying OAM beams can be further designed as an additional degree of freedom. The time-varying OAM field patterns are dynamically mapped by developing a two-probe measurement technique. Our approach in combining the programmability of space-time-coding digital metasurfaces and the two-probe measurement technique provides a versatile platform for generating and observing time-varying OAM and other spatiotemporal excitations in general. The proposed time-varying OAM beams have application potentials in particle manipulation, time-division multiplexing, and information encryption.
Advanced Photonics
  • Publication Date: Apr. 17, 2023
  • Vol. 5, Issue 3, 036001 (2023)
Propagation of transverse photonic orbital angular momentum through few-mode fiber|On the Cover
Qian Cao, Zhuo Chen, Chong Zhang, Andy Chong, and Qiwen Zhan
Spatiotemporal optical vortex (STOV) pulses can carry transverse orbital angular momentum (OAM) that is perpendicular to the direction of pulse propagation. For a STOV pulse, its spatiotemporal profile can be significantly distorted due to unbalanced dispersive and diffractive phases. This may limit its use in many research applications, where a long interaction length and a tight confinement of the pulse are needed. The first demonstration of STOV pulse propagation through a few-mode optical fiber is presented. Both numerical and experimental analysis on the propagation of STOV pulse through a commercially available SMF-28 standard telecommunication fiber is performed. The spatiotemporal phase feature of the pulse can be well kept after the pulse propagates a few-meter length through the fiber even with bending. Further propagation of the pulse will result in a breakup of its spatiotemporal spiral phase structure due to an excessive amount of modal group delay dispersion. The stable and robust transmission of transverse photonic OAM through optical fiber may open new opportunities for transverse photonic OAM studies in telecommunications, OAM lasers, and nonlinear fiber-optical research.
Advanced Photonics
  • Publication Date: Apr. 17, 2023
  • Vol. 5, Issue 3, 036002 (2023)
Tailoring light on three-dimensional photonic chips: a platform for versatile OAM mode optical interconnects
Jue Wang, Chengkun Cai, Feng Cui, Min Yang, Yize Liang, and Jian Wang
Explosive growth in demand for data traffic has prompted exploration of the spatial dimension of light waves, which provides a degree of freedom to expand data transmission capacity. Various techniques based on bulky optical devices have been proposed to tailor light waves in the spatial dimension. However, their inherent large size, extra loss, and precise alignment requirements make these techniques relatively difficult to implement in a compact and flexible way. In contrast, three-dimensional (3D) photonic chips with compact size and low loss provide a promising miniaturized candidate for tailoring light in the spatial dimension. Significantly, they are attractive for chip-assisted short-distance spatial mode optical interconnects that are challenging to bulky optics. Here, we propose and fabricate femtosecond laser-inscribed 3D photonic chips to tailor orbital angular momentum (OAM) modes in the spatial dimension. Various functions on the platform of 3D photonic chips are experimentally demonstrated, including the generation, (de)multiplexing, and exchange of OAM modes. Moreover, chip-chip and chip–fiber–chip short-distance optical interconnects using OAM modes are demonstrated in the experiment with favorable performance. This work paves the way to flexibly tailor light waves on 3D photonic chips and offers a compact solution for versatile optical interconnects and other emerging applications with spatial modes.
Advanced Photonics
  • Publication Date: May. 24, 2023
  • Vol. 5, Issue 3, 036004 (2023)
Single-shot Kramers–Kronig complex orbital angular momentum spectrum retrieval
Zhongzheng Lin, Jianqi Hu, Yujie Chen, Camille-Sophie Brès, and Siyuan Yu
Orbital angular momentum (OAM) spectrum diagnosis is a fundamental building block for diverse OAM-based systems. Among others, the simple on-axis interferometric measurement can retrieve the amplitude and phase information of complex OAM spectra in a few shots. Yet, its single-shot retrieval remains elusive, due to the signal–signal beat interference inherent in the measurement. Here, we introduce the concept of Kramers–Kronig (KK) receiver in coherent communications to the OAM domain, enabling rigorous, single-shot OAM spectrum measurement. We explain in detail the working principle and the requirement of the KK method and then apply the technique to precisely measure various characteristic OAM states. In addition, we discuss the effects of the carrier-to-signal power ratio and the number of sampling points essential for rigorous retrieval and evaluate the performance on a large set of random OAM spectra and high-dimensional spaces. Single-shot KK interferometry shows enormous potential for characterizing complex OAM states in real time.
Advanced Photonics
  • Publication Date: Jun. 12, 2023
  • Vol. 5, Issue 3, 036006 (2023)
Orbital angular momentum based intra- and interparticle entangled states generated via a quantum dot source
Alessia Suprano, Danilo Zia, Mathias Pont, Taira Giordani, Giovanni Rodari, Mauro Valeri, Bruno Piccirillo, Gonzalo Carvacho, Nicolò Spagnolo, Pascale Senellart, Lorenzo Marrucci, and Fabio Sciarrino
Engineering single-photon states endowed with orbital angular momentum (OAM) is a powerful tool for quantum information photonic implementations. Indeed, due to its unbounded nature, OAM is suitable for encoding qudits, allowing a single carrier to transport a large amount of information. Most of the experimental platforms employ spontaneous parametric down-conversion processes to generate single photons, even if this approach is intrinsically probabilistic, leading to scalability issues for an increasing number of qudits. Semiconductor quantum dots (QDs) have been used to get over these limitations by producing on-demand pure and indistinguishable single-photon states, although only recently they have been exploited to create OAM modes. Our work employs a bright QD single-photon source to generate a complete set of quantum states for information processing with OAM-endowed photons. We first study hybrid intraparticle entanglement between OAM and polarization degrees of freedom of a single photon whose preparation was certified by means of Hong–Ou–Mandel visibility. Then, we investigate hybrid interparticle OAM-based entanglement by exploiting a probabilistic entangling gate. The performance of our approach is assessed by performing quantum state tomography and violating Bell inequalities. Our results pave the way for the use of deterministic sources for the on-demand generation of photonic high-dimensional quantum states.
Advanced Photonics
  • Publication Date: Aug. 30, 2023
  • Vol. 5, Issue 4, 046008 (2023)
Self-seeded free-electron lasers with orbital angular momentum
Jiawei Yan, and Gianluca Geloni
X-ray beams carrying orbital angular momentum (OAM) are an emerging tool for probing matter. Optical elements, such as spiral phase plates and zone plates, have been widely used to generate OAM light. However, due to the high impinging intensities, these optics are challenging to use at X-ray free-electron lasers (XFELs). Here, we propose a self-seeded free-electron laser (FEL) method to produce intense X-ray vortices. Unlike passive filtering after amplification, an optical element will be used to introduce the helical phase to the radiation pulse in the linear regime, significantly reducing thermal load on the optical element. The generated OAM pulse is then used as a seed and significantly amplified. Theoretical analysis and numerical simulations demonstrate that the power of the OAM seed pulse can be amplified by more than two orders of magnitude, reaching peak powers of several tens of gigawatts. The proposed method paves the way for high-power and high-repetition-rate OAM pulses of XFEL light.
Advanced Photonics Nexus
  • Publication Date: Mar. 30, 2023
  • Vol. 2, Issue 3, 036001 (2023)
Generation of high-efficiency, high-purity, and broadband Laguerre-Gaussian modes from a Janus optical parametric oscillator
Dunzhao Wei, Pengcheng Chen, Yipeng Zhang, Wenzhe Yao, Rui Ni, Xiaopeng Hu, Xinjie Lv, Shining Zhu, Min Xiao, and Yong Zhang
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.
Advanced Photonics Nexus
  • Publication Date: Apr. 21, 2023
  • Vol. 2, Issue 3, 036007 (2023)

Advanced Photonics and its sibling journal Advanced Photonics Nexus welcome submissions to a joint theme issue on orbital angular momentum (OAM) and its association with optical science and applications. The theme issue is dedicated to the 30th anniversary of Professor Allen’s paper published in Physical Review A in 1992, where laser light with a Laguerre-Gaussian amplitude distribution was found to have an OAM. Since then, conceptual studies on OAM have attracted great attention in physics and optics communities for many years. In recent years, the world has witnessed birth and development of novel and break-through technologies originally driven by the OAM, from novel light manipulation to significant applications in super resolved microscopy, lithography, optical communication, and others. In this connection, we are honored to organize the theme issue to pay our respect to Professor Allen for his pioneering study on OAM, as well as great achievements by other scientists and scholars in this field.