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Opto-Electronics Plus

Simultaneous dynamic detection of phase and polarization topological charges of Poincaré beams

Xiangle Li, Junna Yao, Shuimei Wu, Qiwen Zhan, Anting Wang

Published Jan 1, 2026• 1 citation
Publisher

Abstract

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.

DOI
10.67704/oep.2026.260005

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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.
Featuring a nontrivial coupling between the orbital angular momentum of light and spatially inhomogeneous polarization, hybrid-order Poincaré sphere (HyOPS) beams have recently triggered numerous curiosities, especially in classical and quantum informatics. Despite much effort devoted to creating single HyOPS beam, it is still a formidable challenge to simultaneously harness multichannel and diverse HyOPS beams in a simple and efficient manner. Here, we propose a digitalized geometric phase optical element via photo-induced liquid crystal microstructures and demonstrate flexible and spin-controlled massive channels of HyOPS beams. By tuning the incident polarization, any state on up to 24 diverse HyOPSs is simultaneously mapped from common Poincaré sphere in high efficiency and good energy uniformity. All experimental results match well with the theoretical predictions of such a planar multifunctional device. This adds an extra spatial degree of freedom to advanced light tailoring and may facilitate parallel optical trapping, high-capacity communication, and high-dimensional quantum entanglement.
A single projective measurement on a superposition state does not provide the full information about the state. Therefore, multiple projections of the state onto a multitude of eigenstates are necessary. In this paper, we have demonstrated that generic Poincaré beams can be uniquely identified through a single projective measurement, although they are superposition states. Polarization optics utilizes different orders of Poincaré spheres as topological models to describe both uniform and spatially varying polarization states. These topological constructs quantify the underlying singularities and symmetries. Any measurement performed using a polarizer collapses the superposition state into one of its eigenstates. The additional features introduced by the orbital angular momentum basis, which vary across different orders of Poincaré spheres, make such projection measurements particularly interesting. In particular, a generic Poincaré beam exhibits the unique property that every possible superposition state produces a distinct signature intensity pattern when passed through a polarizer, a phenomenon explored in this paper.
We propose a geometric hybrid Poincaré sphere (GHPS) as a unified geometrical framework for describing structured photon states with independently controllable spin angular momentum (SAM) and orbital angular momentum (OAM). Unlike the conventional higher-order Poincaré sphere, in which the SAM and OAM are intrinsically coupled through fixed basis states, the GHPS is constructed by defining its poles as direct products of arbitrary orthogonal bases on the Poincaré sphere (PS) and orbital Poincaré sphere (OPS) and by superposing these pole states. Using numerical simulations, we analyze representative GHPS states and show that the GHPS spherical coordinates govern the amplitude ratio and relative phase between the pole bases. This framework enables spatially inhomogeneous polarization distributions and intensity patterns, including nonseparable structures in which polarization and intensity are intrinsically intertwined, and provides a systematic state-space description for the coherent geometrical control of advanced structured light fields.
In the present dissertation we describe the generation of a Gaussian bipartite entangled state in which the two subsystems are multi-distinguishable thanks to the fact that they have different polarizations and carry an opposite amount of orbital angular momentum along the propagation direction. Polarization entangled states are produced by using an optical parametric oscillator as spontaneous parametric down conversion source. This is able to produce a bipartite state consisting of collinear thermal crossed polarized modes exhibiting entanglement. These two modes have the same frequency and constitute a continuous variable bipartite entangled system in which each of the modes can be labeled by the polarization degree of freedom. Once these two polarization entangled states are produced, the bipartite state is endowed with an additional degree of freedom constituted by orbital angular momentum, that makes possible to further distinguish between these two co-propagating modes. The two-dimensional Hilbert polarization space is mapped into the orbital angular momentum one by means of Gaussian operations i.e. physical trasformations that preserve Gaussianity. In order to achieve this task we used a liquid crystal optical device called q-plate. This device is able to couple polarization and orbital angular momentum degrees of freedom by making the passing through beam acquire orbital angular momentum that depends on the topological charge q of the device and on the polarization of the incoming beam. Moreover, the setup enginereed to achieve this task is also capable of generating squeezed vortex beams i.e. single mode states for which the quadrature noise is below the standard quantum limit. After producing the bipartite entangled state it enters the characterizaton stage. Its quantumness is investigated by witnessing both squeezing and non classical correlations via balanced optical homodyne, a phase sensitive detection method that permits, by measuring the electromagnetic field quadratures statistics, to reconstruct the state of the system. In order to retrieve the quantum state with a high fidelity, homodyne detector needs to be optimized. This, besides imposing stringent conditions on the optical components involved in the setup, forces to improve the mode matching between the signal and the local oscillator that plays a central role in determining the overall detector efficiency. Although homodyne is a consolidated detection scheme, herein it is proposed an innovative extension of this technique to structured modes that opens the doors for homodyning directly in the orbital angular momentum space. The very central role, in this detection method, is played by interference between the signal under investigation and a strong coherent reference beam called local oscillator. Besides behaving as an amplifier for the quadrature under scrutiny, local oscillator also acts as a spatial and frequency filter, selecting for the measure the part of the signal that shares with it the same spatio-temporal properties. Hence, in order to ensure interference, in case of a signal carrying orbital angular momentum a further effort is required. Indeed, also the local oscillator has to be in the same helical mode, in particular the two beams have to transport the same amount of orbital angular momentum along the propagation direction. So by suitably designing the overall experimental setup it is possible to homodyne the bipartite entangled state carrying orbital angular momentum directly in this degree of freedom Hilbert space. Once the covariance matrix of the bipartite Gaussian state has been reconstructed, thanks to Gaussianity, it is possible to assess entanglement between the vortex modes by means of entanglement criteria based on covariance matrix elements such as the Peres-Horodecki-Simon (PHS) and the Duan ones.
Structured light provides high-dimensional Hilbert spaces holding tremendous potential for fundamental quantum optics and quantum technologies. However, existing characterization methods, like Hong-Ou-Mandel (HOM) interference, typically assume perfectly tuned conditions, overlooking the geometric physics governing spatial mode evolution. Here, we establish topological quantum interferometry driven by an interaction-based geometric phase, the exchange Berry phase (BPX). Our formalism generalizes qqq-plate state generation and characterization to arbitrary topological charges and (de)tuning conditions, demonstrating that BPX acts as a geometric marker governing spatial interference. We show BPX serves as a deterministic control parameter, decomposing two-photon spatial patterns into geometry-dictated fundamental modes. This mapping reveals topological invariants and phase singularities that function as a non-tomographic witness for state dimensionality estimation, circumventing full-state reconstruction. Being device-independent and highly scalable, this approach enables scalable high-dimensional characterization and topologically protected state selection, with direct applicability to quantum metrology and high-capacity quantum networks.
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.