We present a compact intensity interferometer designed to synthesize the second-order complex correlation function through intensity correlation measurements. By leveraging the diffraction-multiplexed vortex generation capability of a Dammann vortex grating alongside a holographic intensity correlation technique, our system generates tunable one- and two-dimensional correlation vortex array patterns. This advancement enables applications in optical communication and orbital angular momentum encryption, offering robust stability and propagation adaptability in diverse environments.
We present a compact intensity interferometer designed to synthesize the second-order complex correlation function through intensity correlation measurements. By leveraging the diffraction-multiplexed vortex generation capability of a Dammann vortex grating alongside a holographic intensity correlation technique, our system generates tunable one- and two-dimensional correlation vortex array patterns. This advancement enables applications in optical communication and orbital angular momentum encryption, offering robust stability and propagation adaptability in diverse environments.
Quantum dot molecules (QDMs), with their unique optoelectronic properties derived from quantum confinement and tunneling effects, are not only promising for advanced photonic applications but also provide the intrinsic advantage of nanoscale dimensions, which is critical for integrated miniaturized devices. In this work, we propose a scheme to realize a high-intensity two-dimensional asymmetric electromagnetically induced diffraction grating in a QDMs system by incorporating spontaneously generated coherence (SGC) and dual tunneling channels. Our theoretical analysis shows that the presence of SGC markedly enhances the intensity and efficiency of higher-order diffractions. Furthermore, by adjusting the orbital angular momentum and beam waist of vortex beams, we not only amplify the disparity in asymmetric diffraction and enhance the efficiency of the third-order diffraction peak, but also enable a lossless spatial interchange between the diffraction peak positions and those at symmetric positions solely by reversing the orbital angular momentum direction. Additionally, tuning the interdot tunneling strength increases the maximum third-order diffraction intensity by three orders of magnitude, reaching an intensity that is more than ten times higher than the third-order diffraction intensity observed at symmetric positions. These results, which fully leverage the nanoscale advantage and tunable characteristics of QDMs, offer a solid foundation for the implementation of compact photonic devices and pave the way for potential applications in optical diffractive neural networks and electromagnetically induced quantum holography.
Multichannel vortex beams serve as an essential physical source for enabling multi-spot laser processing and high-dimensional spatial multiplexing communications. We demonstrate a compact, flexibly tunable multichannel vortex beam generator using spatially structured bidirectional two-color pump vortex four-wave mixing in a single 133Cs vapor cell. To enhance spatial multiplexing, both sides of the cell are utilized. By engineering the propagation directions and frequencies of five input beams, we establish a nonlinear interaction region that supports 16 concurrent phase-matching conditions, thereby enabling the parallel generation of up to eight vortex channels. The orbital angular momentum of the output beams follows deterministic algebraic rules, allowing for programmable control via tailored input orbital angular momentum combinations. Moreover, the channel count can be linearly tuned by selectively deactivating pumps—each switched-off pump reduces the number of output channels by two. This flexible control over orbital angular momentum states, together with channel count and spatial arrangement, establishes a highly integrated platform for on-demand vortex generation. This work highlights the potential of spatially bidirectional structured pumping in atomic vapor to expand optical dimensionality and enhance multiplexing capacity, paving the way toward multidimensional communications, quantum networks, and integrated photonics.
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.
A beam of single-photon vortex has been detected with near-field diffraction. Our single-photon beam is generated with a weak coherent pulse method and subsequently imprinted with the orbital angular momentum of the vortex using a zeroth-order vortex half-wave retarder. The detection is employed with a two-grating Talbot near-field effect. Instead of using expensive single-photon image detection, we use a mask grating and an avalanche photodiode for the detection. This technique can identify the order and charge of the vortex from different count rates. Our technique can be utilized in the field of quantum information technology such as quantum cryptography using orthogonal states of an optical vortex beam.
A novel encoding method based on the orbital angular momentum (OAM) mode and radial mode of composite vortex beams is proposed. The superposition of two vortex beams generates 32 different types of composite vortex beams: one of them is a Laguerre–Gaussian (LG) beam with a fixed OAM mode and radial mode, and the other is a LG beam containing four radial modes (p = 0, 1, 2, 3) and eight OAM modes with the same interval (l = ±3, ±5, ±7, ±9). A specially designed composite fork-shaped grating (CFG) is utilized to generate the intensity array pattern, and the received composite vortex beam is diffracted into a Gaussian beam with the relevant coordinates. Based on the coordinates and the number of bright rings in the intensity pattern, the OAM modes and radial modes of the two vortex beams composing the superposition state are determined, and finally the received composite vortex beam is decoded into the initially propagated information sequence. The correctness and effectiveness of the proposed encoding are confirmed through the comparative analysis of the correlation of the optical fields at both the transmitter and receiver in the two scenarios of interval and non-interval encoding. The proposed encoding method can significantly improve the efficiency of information transmission and its resistance to interference, holding great potential for future applications in free-space optical communication.
Orbital angular momentum (OAM), a new dimension of photons, has potentials in lots of domains as high-dimensional data coding/decoding. Here we experimentally demonstrate a free-space data transmission system based on 8 bits multi-state OAM shift keying, where multiplexed optical vortices containing 8 various OAM states are employed to constitute 8 bits binary symbols. In the transmitter, the data coding of OAM shift keying is realized by switching a series of special-designed holograms. And in the receiver, the decoding is done by a single Dammann vortex grating along with image processing. We experimentally transmit data, including a gray-scale image, in free-space for 10 meters, showing zero bit-error-rate. The demonstrated results indicate a wide prospect for the future high-dimensional large data rate optical security communications.