Multiplexing multiple orbital angular momentum (OAM) channels enables high-capacity optical communication. However, optical scattering from ambient microparticles in the atmosphere or mode coupling in optical fibers significantly decreases the orthogonality between OAM channels for demultiplexing and eventually increases crosstalk in communication. Here, we propose a novel scattering-matrix-assisted retrieval technique (SMART) to demultiplex OAM channels from highly scattered optical fields and achieve an experimental crosstalk of –13.8 dB in the parallel sorting of 24 OAM channels after passing through a scattering medium. The SMART is implemented in a self-built data transmission system that employs a digital micromirror device to encode OAM channels and realize reference-free calibration simultaneously, thereby enabling a high tolerance to misalignment. We successfully demonstrate high-fidelity transmission of both gray and color images under scattering conditions at an error rate of <0.08%. This technique might open the door to high-performance optical communication in turbulent environments.

Optical spin-orbit interaction has gained much interest recently due to its universality and importance in modern photonics. In this Letter, we theoretically demonstrate that orbit-induced localized spin angular momentum (SAM) conversion can occur in the tight focusing of spin-free linearly polarized vortex beams (LPVBs). By analysis of the polarization states that are associated with the SAM density, we attribute the occurrence of such a conversion to the helical-phase-induced change of local polarization states in the focused field. In the local SAM, density can be further regulated by altering the sign and value of the orbital angular momentum in the incident LPVBs, as well as their polarization orientations. This Letter is expected to advance our understanding of optical spin-orbit coupling and benefit applications of optical microscopy and trapping.

We present a single-pixel imaging technique that enables phase extraction from objects by complex Fourier spectrum sampling. The technique exploits a digital micromirror device to scan a wavevector-varying plane wave, which interferes with a stationary reference beam to produce time-varying spatial frequencies on the object. Synchronized intensity measurements are made using a single-pixel detector, and four-step phase-shifting is adopted in spectrum acquisition. Applying inverse Fourier transform to the obtained spectrum yields the desired image. The proposed technique is demonstrated by imaging two digital phase objects. Furthermore, we show that the image can be reconstructed from sub-Nyquist measurements via compressive sensing, considerably accelerating the acquisition process. As a particular application, we use the technique to characterize the orbital angular momentum of vortex beams, which could benefit multiplexing techniques in classical and quantum communications. This technique is readily integrated into commercial microscopes for quantitative phase microscopy.

Shaping complex fields with a digital micromirror device (DMD) has attracted much attention recently due to its potential application in optical communication and microscopy. In this paper, we present an optimized Lee method to achieve dynamic shaping of orbital-angular-momentum (OAM) beams using a binary DMD. An error diffusion algorithm is introduced to enhance the accuracy for binary-amplitude hologram design, making it possible to achieve high fidelity wavefront shaping while retaining a high resolution. As a proof of concept, we apply this method to create different classes of OAM beams. The numerical simulations verify that a fidelity of F > 0.985 can be achieved for all the test OAM fields with fully independent phase and amplitude modulation. Moreover, we experimentally demonstrate the dynamic shaping of different OAM beams including pure modes and mixed modes with a switching rate of up to 17.8 kHz. On this basis, accurate information encoding into the generated multiplexed OAM beams is accomplished, which provides access to high speed classical and quantum communications that employ spatial mode encoding.

Multimode fibers (MMFs) can support a large number of spatial modes, increasing the amount of transmitted information, a feature that benefits fields such as endoscopic imaging or optical communications. However, the transport of information encoded in the phase through a standard MMF has not been achieved due to strong mode coupling, hindering direct data transfer using light beams endowed with orbital angular momentum (OAM). Here, we present a computational light field imaging technique to achieve OAM-multiplexed transmission through a commercial MMF. Such a technique enables the retrieval of the incident field from the speckle intensity at the distant end of the fiber. Based on the recovered field, the extraction of the transferred data by addressing all the OAM channels can be achieved. Experimentally, light field imaging through a MMF is demonstrated by recovering a structured light field and a phase picture. For optical transmission, the crosstalk between OAM channels is tested first, and then we demonstrate high-fidelity image data transfer via 24 multiplexed OAM channels through a commercial MMF.

The spin angular momentum (SAM) of an elliptically or circularly polarized light beam can be transferred to matter to drive a spinning motion. It is counterintuitive to find that a light beam without SAM can also cause the spinning of microparticles. Here, we demonstrate controllable spinning of birefringent microparticles via a tightly focused radially polarized vortex beam that has no SAM prior to focusing. To this end, the orbital Hall effect is proposed to control the radial separation of two spin components in the focused field, and tunable transfer of local SAM to microparticles is achieved by manipulating the twisted wavefront of the source light. Our work broadens the perspectives for controllable exertion of optical torques via the spin-orbit interactions.