Information encryption with optical technologies has become increasingly important due to remarkable multidimensional capabilities of light fields. However, the optical encryption protocols proposed to date have been primarily based on the first-order field characteristics, which are strongly affected by interference effects and make the systems become quite unstable during light–matter interaction. Here, we introduce an alternative optical encryption protocol whereby the information is encoded into the second-order spatial coherence distribution of a structured random light beam via a generalized van Cittert–Zernike theorem. We show that the proposed approach has two key advantages over its conventional counterparts. First, the complexity of measuring the spatial coherence distribution of light enhances the encryption protocol security. Second, the relative insensitivity of the second-order statistical characteristics of light to environmental noise makes the protocol robust against the environmental fluctuations, e.g, the atmospheric turbulence. We carry out experiments to demonstrate the feasibility of the coherence-based encryption method with the aid of a fractional Fourier transform. Our results open up a promising avenue for further research into optical encryption in complex environments.

We introduce a general optical system for synthesis of partially coherent vector beams with a variety of correlation functions. In particular we employ it for generation of the family of beams, termed the specially correlated radially polarized (SCRP) beams and examine their free-space propagation both theoretically and experimentally. Our results clearly show that a SCRP beam exhibits unique features on propagation in comparison with those of beams with conventional correlation functions. The technique for modulation of the correlation functions and, hence, the coherence state of a SCRP beam in the source plane leads to efficient control of its intensity distribution and its degree of polarization on propagation, which is of importance in particle trapping and material thermal processing applications.

We carry out experimental measurement of the scintillation index of a partially coherent beam-carrying vortex phase (i.e., Gaussian–Schell model vortex beam) propagating through thermally induced turbulence. It is demonstrated that a Gaussian–Schell model vortex beam has appreciably smaller scintillation than a Gaussian–Schell model beam, which will be useful in free-space optical communication.

The degree of coherence (DOC) function that characterizes the second-order correlations at any two points in a light field is shown to provide a new degree of freedom for carrying information. As a rule, the DOC varies along the beam propagation path, preventing from the efficient information recovery. In this paper, we report that when a partially coherent beam carrying a cross phase propagates in free space, in a paraxial optical system or in a turbulent medium, the modulus of the far-field (focal plane) DOC acquires the same value as it has in the source plane. This unique propagation feature is employed in a novel protocol for far-field imaging via the DOC, applicable to transmission in both free-space and turbulence. The advantages of the proposed approach are the confidentiality and resistance to turbulence, as well as the weaker requirement for the beam alignment accuracy. We demonstrate the feasibility and the robustness of the far-field imaging via the DOC in the turbulent media through both the experiment and the numerical simulations. Our findings have potential applications in optical imaging and remote sensing in natural environments, in the presence of optical turbulence.

We report experimental generation of a radially polarized Bessel-Gauss (RPBG) beam of order 1 with the help of a spatial light modulator, a spiral phase plate, and a radial polarization converter. Furthermore, we carry out a comparative study of the self-healing properties of a RPBG beam and a linearly polarized Bessel-Gauss (LPBG) beam which are blocked by a sector-shaped opaque obstacle both experimentally and numerically. Our results clearly show that the self-healing ability of a RPBG beam indeed is superior to that of a LPBG beam, and some physical interpretations are given. Our results will be useful for particle trapping and microscopy.

The techniques of optical beam shaping have enabled progress in a broad range of interdisciplinary science and engineering, owing to the unique properties and promising applications of their created structured light. However, the conventional methods, which are based on fully coherent optics approaches, introduce several adverse effects such as speckles noise in the generated beams and susceptible to be disturbed in complex environment (e.g. turbulent atmospheres), because of the sensitive coherent light-matter interaction. To overcome those side effects, a new protocol relied on the partially coherent beam shaping has been developed. By elaborately tailoring the complex spatial coherence structure of a partially coherent beam, the desired beam profile and trajectory with high beam quality and robust propagation feature in complex environment can be generated. In this review, we present an overview of such unconventional partially coherent beam shaping with a focus on the important role of the complex spatial coherence structure engineering. Partially coherent beam shaping not only provides an efficient means for resisting the disadvantages in coherent optics methods but also enables new applications in novel optical imaging and tweezers. Graphical abstract