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Frontiers of Physics

Inter-modal interference of arbitrary orbital angular momentum modes in nonlinear frequency conversion

Biao Xing, Xuewen Wang, Lirong Wang Lirong Wang, Jinpeng Yuan, Liantuan Xiao, Suotang Jia

Published Jan 1, 2026• 2 citations
Publisher

Abstract

Nonlinear interaction between orbital angular momentum (OAM) modes provides an enticing promise for realizing high-dimensional quantum states and multimodal communications. Here, we demonstrate the inter-modal interference of OAM modes based on the nonlinear frequency conversion of perfect vortex beams, permitting the arbitrary spatial intensity and phase information to be transformed and manipulated from 778 nm input beam to 420 nm output beam. The conversion of single OAM state obeys the typical arithmetic operation. In contrast, the conversion of superposition state is predicted and revealed as the inter-modal interference of full spatial complex amplitude. For the allowed OAM modes, the probability amplitude is quantitatively analyzed by the intensity overlap of input OAM modes, which determines the degree of degradation in the intensity and phase. As a result, the output beam exhibits the nonuniform petal-shaped intensity and phase distributions under the conditions of phase matching and OAM conservation. Furthermore, the inherent transverse structure invariance of perfect vortex beams enables them to accommodate and support larger OAM values and more superposition states.

DOI
10.15302/frontphys.2026.092201

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Nonlinear interaction between orbital angular momentum (OAM) modes provides an enticing promise for realizing high-dimensional quantum states and multimodal communications. Here, we demonstrate the inter-modal interference of OAM modes based on the nonlinear frequency conversion of perfect vortex beams, permitting the arbitrary spatial intensity and phase information to be transformed and manipulated from 778 nm input beam to 420 nm output beam. The conversion of single OAM state obeys the typical arithmetic operation. In contrast, the conversion of superposition state is predicted and revealed as the inter-modal interference of full spatial complex amplitude. For the allowed OAM modes, the probability amplitude is quantitatively analyzed by the intensity overlap of input OAM modes, which determines the degree of degradation in the intensity and phase. As a result, the output beam exhibits the nonuniform petal-shaped intensity and phase distributions under the conditions of phase matching and OAM conservation. Furthermore, the inherent transverse structure invariance of perfect vortex beams enables them to accommodate and support larger OAM values and more superposition states.
The efficient transport and engineering of photonic orbital angular momentum (OAM) lie at the heart of various related classical and quantum applications. Here, by leveraging the spatial-mode-engineered frequency conversion, we realize the remote transport of high-dimensional orbital angular momentum (OAM) states between two distant parties without direct transmission of information carriers. We exploit perfect vortices for preparing high-dimensional yet maximal O AM entanglement. Based on nonlinear sum-frequency generation working with a strong coherent wave packet and a single photon, we conduct the Bell-like state measurements for high-dimensional perfect vortices. We experimentally achieve an average transport fidelity 0.879 ± 0.048 and 0.796 ± 0.066 for a complete set of 3-dimensional and 5-dimensional OAM mutually unbiased bases, respectively. Furthermore, by exploring the full transverse entanglement, we construct another strategy of quantum imaging with interaction-free light. It is expected that, with the future advances in nonlinear frequency conversion, our scheme will pave the way for realizing truly secure high-dimensional quantum teleportation in the upcoming quantum network.
Nonlinear interaction between orbital angular momentum (OAM) modes has interesting effects and tremendous applications in both classical and quantum realms. Here we propose a strategy of using perfect vortices, which not only overcomes the spatial mode matching problem of nondegenerate OAM modes, but also reveals the OAM-only influence on the momentum matching by tuning the OAMs of the fundamental wave. We use perfect vortices of degenerate and nondegenerate OAM modes to clearly demonstrate the flexible control of OAM modes on nonlinear interaction by carefully exploring second-harmonic generation (SHG) in periodically poled crystal. We generate second-harmonic perfect vortices with the OAM order up to 40. Based on the observed phase-matching temperature shift caused by OAMs, we also use the SHG nonlinear process to distinctly confirm the OAM-only-induced subluminal effect. Our results pave the way toward unveiling the underlying physics behind nonlinear process of OAM modes and building high-capacity quantum links between systems operating at various wavelengths. The inverse process of SHG we developed, perfect-vortex-based spontaneous parametric down-conversion, may provide a promising solution for high-dimensional OAM entangled source.
Utilizing the phase-matching conditions of inter-modal four-wave mixing in an elliptical-core few-mode fiber supporting three non-degenerate modes, we experimentally demonstrate schemes for generating orbital-angular-momentum (OAM)-entangled photon pairs with high mode purity and for achieving highly mode-selective frequency conversion of beams in OAM-compatible (LP11a, LP11b) mode basis. These techniques expand the toolbox for using OAM modes in both classical and quantum communications and information processing.
Orbital-angular-momentum- (OAM) based photonic nonlinear interfaces, such as the nonlinear manipulation of a single-photon OAM state between the communication wavelength for entanglement distribution and the near-visible wavelength for quantum memories. Here, we experimentally demonstrate this kind of quantum state transformation for simultaneously adjusting the weight of the spatial OAM modes and operating the wavelength of single photons by effectively cascading the frequency conversion and electro-optical (EO) polarization coupling in a periodically poled lithium niobate crystal. The fidelity of the OAM state is measured to be higher than 95% before and after the frequency conversion. The results show that the OAM state of single photons can be modulated on demand by applying a transverse electric field across the nonlinear crystal. Our work demonstrates the integration and high performance of our proposed transformation interface, and paves a route toward connecting different remote nodes based on quantum memories in a large-scale OAM-encoded quantum network.
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.
Frequency interface, namely, converting the colors of photons while retaining their other features, is indispensable for numerous applications ranging from up-conversion imaging to the multimode quantum network. However, limited by the nonuniform nonlinear frequency-conversion efficiency, constructing the frequency interface for high-dimensional spatial modes is still challenging. Here, to break this fundamental barrier, we construct a high-dimensional (HD) orbital-angular-momentum (OAM) frequency interface via conducting sum-frequency generation between HD OAM states to be converted and a radial structured pump. Specifically, by replacing the conventional Gaussian pump with an optimized coherent superposition of HD Laguerre-Gaussian radial modes (i.e., its azimuthal number is zero), we experimentally achieve the OAM frequency interface in nine dimensions with a record fidelity up to 90.38 %. Additionally, by increasing the number of radial modes, our scheme can be flexibly extended to higher dimension. Such a high-dimensional frequency interface could find potential applications in the high-capacity free-space optical communication and would also pave the way for constructing high-dimensional quantum networks.