Given that spin and orbital angular momenta of photons have been widely investigated in optical communication and information processing systems, efficient decoding of optical vortex states using a single element is highly anticipated. In this work, a wavelength-independent holographic scheme has been proposed for total angular momentum sorting of both scalar and vector vortex states with a stationary broadband geometric-phase waveplate by means of reference-free shearing interferometry. The entangled spin and orbital angular momentum modes can be distinguished simultaneously based on the spin-orbit optical Hall effect in order to realize single-shot vortex detection. The viability of our scheme has also been demonstrated experimentally.
Given that spin and orbital angular momenta of photons have been widely investigated in optical communication and information processing systems, efficient decoding of optical vortex states using a single element is highly anticipated. In this work, a wavelength-independent holographic scheme has been proposed for total angular momentum sorting of both scalar and vector vortex states with a stationary broadband geometric-phase waveplate by means of reference-free shearing interferometry. The entangled spin and orbital angular momentum modes can be distinguished simultaneously based on the spin-orbit optical Hall effect in order to realize single-shot vortex detection. The viability of our scheme has also been demonstrated experimentally.
Poincaré beams (PBs), characterized by their entanglement between helical wavefronts and vectorial polarization, serve as high-dimensional information carriers in classical and quantum optics. The topological charge (TC) is the fundamental parameter governing their singularity structure; however, characterizing the phase and polarization TCs simultaneously remains a significant challenge. Conventional approaches are often limited to static measurements or decouple these parameters through complex, multi-step processes, failing to capture the real-time dynamics essential for modern optical communications. Here, we demonstrate a robust, single-shot detection system capable of simultaneously resolving phase and polarization TCs for arbitrary states on the hybrid-order Poincaré sphere (HyPS). By leveraging a pair of Pancharatnam-Berry optical elements (PBOEs), we implement a conformal mapping that transforms the full angular momentum eigenstates into spatially separated coordinates. This unique configuration allows for the direct readout of TCs through position encoding, effectively decoupling the spin and orbital angular momentum components. We experimentally validate this method by detecting the dynamic evolution of PBs across eight different HyPSs with component orders up to 20, confirming its capability to distinguish between scalar, vector, and hybrid modes in real-time. This work establishes a versatile framework for the dynamic decoding of structured light, holding profound implications for high-capacity optical communications and information encryption.
Optical vortex beams (OVBs) carrying orbital angular momentum (OAM) offer access to an unbounded set of orthogonal states, enabling a dramatic increase in the information capacity for optical communication systems. However, practical OAM detection in telecommunication platforms remains challenging due to background noise, detector limitations at infrared communication wavelengths, and the destructive nature of conventional sampling methods. Here, we introduce an all-optical, nearly nondestructive OAM detection method based on sum-frequency generation (SFG) that overcomes these limitations by transferring the information on the OAM into a distinct frequency domain. In our scheme, two OVBs─one carrying OAM-encoded information and the other serving as a reference─are coupled within a beta-barium borate (BBO) crystal to generate an SFG signal. Our theoretical and experimental studies demonstrate that SFG efficiency is governed by the spatial overlap of the interacting vortex profiles, providing mode-selective and OAM-resolved detection. Crucially, as only a small fraction of the input photons undergo conversion into the nonlinear signal, the original beams remain functionally intact. Since detection is performed exclusively on the upconverted signal in a spectrally distinct visible wavelength region, the signal-to-noise ratio can be improved. Moreover, the SFG signal is generated only when specific OAM states and temporal overlap conditions are simultaneously satisfied, enabling ultrafast and conditionally gated access to the OAM information. This nonlinear selectivity offers enhanced physical-layer security and high-throughput capabilities. Together, our approach provides a robust and versatile platform for advanced OAM-based optical communications and high-capacity photonics applications.
Optical spin-orbit coupling is an important phenomenon and has fruitful applications. Here, we investigate the spin-orbit total angular momentum entanglement in the optical parametric downconversion process. Four pairs of entangled vector vortex modes are experimentally generated directly using a dispersion- and astigmatism-compensated single optical parametric oscillator, and for the first time, to the best of our knowledge, the spin-orbit quantum states are characterized on the quantum higher-order Poincaré sphere, and the relationship of spin-orbit total angular momentum Stokes entanglement is demonstrated. These states have potential applications in high-dimensional quantum communication and multiparameter measurement.
The desire to increase the amount of information that can be encoded onto a single photon has driven research into many areas of optics. One such area is optical orbital angular momentum (OAM) [1]. These beams have helical phasefronts and carry an orbital angular momentum of mbar per photon, where the integer m is unbounded, giving a large state space in which to encode information. We recently developed a telescope system comprising two bespoke refractive optical elements to transform OAM states into transverse momentum states [2]. This is achieved by mapping the azimuthal position of the input plane to the lateral position in the output [3]. A mapping of this type transforms a set of concentric rings at the input plane into a set of parallel lines in the output plane. A lens can then separate the resulting transverse momentum states into specified lateral positions, allowing for the efficient measurement of multiple OAM states simultaneously. Separating OAM states in this way presents an opportunity for this larger alphabet to improve the data capacity of a free space link and has potential application in both the classical and quantum regimes. We will present our latest design, increasing the bandwidth of measurable states to over 50 OAM modes. In such a system we study the crosstalk introduced by a thin phase turbulence, showing that turbulence similarly degrades the purity of all the modes within this range.
Abstract Atmospheric turbulence disrupts spatial coherence in free-space optical (FSO) systems, fundamentally limiting the reliable extraction of optical information encoded in intensity, phase, or spatial degrees of freedom. While polarization is intrinsically immune to scalar turbulence, its robust detection remains challenging due to the lack of turbulence-invariant observables. Here, we establish a general spin-dependent phase-difference-to-angle (PDA) mapping mechanism that converts polarization states into global angular intensity modulations, forming a class of turbulence-invariant observables accessible via intensity-only detection. This mapping, enabled by spin–orbit coupling in a vortex waveplate, eliminates the need for wavefront reconstruction and preserves information integrity under strong turbulence. We experimentally validate turbulence-invariant polarization readout over an equivalent long-distance FSO link under both weak and strong turbulence, achieving error rates below 2%. Leveraging this invariant readout, we further demonstrate a 100-Gbps-class orbital angular momentum polarization shift keying (OAMPolSK) communication scheme, with a 12.43-dB reduction in the required optical power compared with PAM-6 at a reference SER of 0.1 under the implemented experimental configurations. Our results demonstrate a turbulence-resilient optical information extraction strategy, in which polarization information is mapped onto a robust angular observable, offering a potential approach for optical communication and sensing in complex environments.
Encoding information in high-dimensional degrees of freedom of photons has led to new avenues in various quantum protocols such as communication and information processing. Yet to fully benefit from the increase in dimension requires a deterministic detection system, e.g., to reduce dimension dependent photon loss in quantum key distribution. Recently, there has been a growing interest in using vector vortex modes, spatial modes of light with entangled degrees of freedom, as a basis for encoding information. However, there is at present no method to detect these non-separable states in a deterministic manner, negating the benefit of the larger state space. Here we present a method to deterministically detect single photon states in a four dimensional space spanned by vector vortex modes with entangled polarisation and orbital angular momentum degrees of freedom. We demonstrate our detection system with vector vortex modes from the |[Formula: see text]| = 1 and |[Formula: see text]| = 10 subspaces using classical and weak coherent states and find excellent detection fidelities for both pure and superposition vector states. This work opens the possibility to increase the dimensionality of the state-space used for encoding information while maintaining deterministic detection and will be invaluable for long distance classical and quantum communication.