Structured light beams have rapidly advanced over the past few years, from specific spatial-transverse/longitudinal structure to tailored spatiotemporal structure. Such beams with diverse spatial structures or spatiotemporal structures have brought various breakthroughs to many fields, including optical communications, optical sensing, micromanipulation, quantum information processing, and super-resolution imaging. Thus, plenty of methods have been proposed, and lots of devices have been manufactured to generate structured light beams by tailoring the structures of beams in the space domain and the space–time domain. In this paper, we firstly give a brief introduction of different types of structured light. Then, we review the recent research progress in the generation and detection of structured light on different platforms, such as free space, optical fiber, and integrated devices. Finally, challenges and perspectives are also discussed.

Spin-orbit photonics, involving the interaction between the spin angular momentum (SAM) and orbital angular momentum (OAM) of light, plays an important role in modern optics. Here, we present the spin-orbit mapping of light in a few-mode fiber that originates from the mode degeneracy lifting (${\mathrm{TM}}_{01}$ and ${\mathrm{TE}}_{01}$) property. We demonstrate two kinds of spin-orbit mapping phenomena, i.e., mapping from intrinsic SAM to OAM and mapping from polarization direction rotation to field pattern rotation. The demonstrated spin-orbit mapping shows high efficiency, large bandwidth, availability for short pulses, and scalability to high-order OAM states.

Increasing data transmission capacity is a persistent demand for optical interconnects. Recently, different physical dimensions of light waves, including time,¹ amplitude,² phase,³ wavelength,⁴ and polarization,⁵ have been fully utilized to scale the data traffic. Even though various multiplexing techniques exploiting these physical dimensions have been developed, it is becoming rather difficult to follow the demand of a global network that is growing by 40% annually.⁶ To keep pace with the ever-increasing demand, a new physical dimension of light is urgently needed. Fortunately, space-division multiplexing technology that transmits orthogonal spatial modes loaded with different signals in an optical interconnect system has further improved the transmission capacity, providing a new degree of freedom for capacity scaling of optical interconnects^{7 – 9} [Fig. 1(a)]. The utilization of the spatial modes in optical interconnects systems requires the development of key optical devices, including spatial mode generators, (de)multiplexers, and exchangers. Traditional optical devices manipulating the spatial modes rely on bulky optics, such as phase plates^10,11 or spatial light modulators,^12,13 which take up too much space and are unscalable. To meet the requirement of a compact solution, the miniaturization of these key optical devices is of great importance.

Free-space point-to-point optical communication often suffers from atmospheric turbulence and device vibration where the environment is harsh. In this paper, by introducing an adaptive system composed of turbulence compensation and fast auto-alignment installation, we propose and experimentally demonstrate an optical communication system that is effective against turbulence and vibration. Turbulence compensation can increase the coupling efficiency by at least 3dB, while fast auto-alignment can reduce the spatial range of beam vibration caused by device vibration by 72.22%. Since the photodiode detector (PD) is sensitive to optical power, reducing the loss of the link improves the communication quality of the system. Bit-error rate (BER) of 10-Gbaud 16-ary quadrature amplitude modulation (16-QAM) signal transmission in the link is also measured under different transmitted power, having ∼8dB power penalty improvement with the adaptive system. In addition, turbulence compensation for higher-order modes such as optical vortex (OV) beams is also implemented, showing a promising prospect in space-division multiplexing (SDM) applications.

We design, fabricate and characterize two types of low-loss weakly guiding ring-core fibers (RCFs) supporting orbital angular momentum (OAM) modes. The ring core and cladding have a relative refractive index difference of 1%. The RCFs feature largely separated OAM mode groups (MGs), where the first MG only contains two fundamental modes and the other MGs each have four OAM modes. The effective refractive index difference (neff) between all MGs in the type-1 RCF is larger than 1.510-3. For the type-2 RCF, except the first two MGs, the neff between the other MGs is also larger than 1.110-3. These enable relatively low-level inter-group crosstalk and facilitate multiple-input multiple-output (MIMO) simplified OAM multiplexing transmission systems, where small-scale MIMO assisted intra-group OAM multiplexing and MIMO-free inter-group OAM multiplexing can be considered to take full use of all OAM modes in RCFs. The transmission loss of the fabricated RCFs is approximately 0.2 to 0.3 dB/km. The effective refractive index, group velocity dispersion, differential group delay, crosstalk and stability of RCFs are all characterized showing favorable performance. Moreover, using fabricated two types of low-loss RCFs and adopting 8-ary quadrature amplitude modulation (8-QAM) signals, we also demonstrate data-carrying two OAM mode group multiplexing transmission over 25.32 km type-1 RCF and 50 km type-2 RCF free of MIMO. The demonstrations show a great potential to use low-loss RCFs in long-distance fiber-optic OAM multiplexing communications.