Recently there is an increasing interest in tailored optical fields with complex amplitude, phase and polarization spatial distributions, as well as specifically designed temporal waveforms. Scalar optical vortices carrying orbital angular momentum and vectorial vortices such as radially and azimuthally polarized beams are among the most intensively studied examples. Comprehensive summaries of earlier developments can be found in several recent articles and edited books, e.g., by Zhan (Adv. Opt. Photon.1, 1, 20091943-8206), Padgett (Adv. Opt. Photon.3, 161, 20111943-8206 ), Forbes (Adv. Opt. Photon.8, 200, 20161943-8206), Zhan (Vectorial Optical Fields, World Scientific Publishing, 2013), and Forbes (Laser Beam Propagation, CRC Press, 2014), while applications of these complex optical fields in promising areas continue to emerge. To capture the latest developments in this important emerging field of optics, it is our pleasure to introduce the Chinese Optics Letters Special Issue on the Complex Optical Fields with contributions from scientists around the world who are active in this field.

It is known that one can determine the mode orders (i.e., the azimuthal order and radial order) of a partially coherent LGpl beam (i.e., a partially coherent vortex beam) based on the measurement of the cross-correlation function (CCF) and the double correlation function (DCF) together. The technique for measuring the CCF is known. In this Letter, we propose a method for measuring the DCF. Based on the proposed method, the determination of the mode orders of a partially coherent LGpl beam is demonstrated experimentally.

We investigate the linear momentum density of light, which can be decomposed into spin and orbital parts, in the complex three-dimensional field distributions of tightly focused vortex segmented beams. The chosen angular spectrum exhibits two spatially separated vortices of opposite charge and orthogonal circular polarization to generate phase vortices in a meridional plane of observation. In the vicinity of those vortices, regions of negative orbital linear momentum occur. Besides these phase vortices, the occurrence of transverse orbital angular momentum manifests in a vortex charge-dependent relative shift of the energy density and linear momentum density.

In this Letter, a refractive index measurement of a dielectric sample using highly focused radially polarized light is reported. Through imaging analysis of the optical field at the pupil plane of a high numerical aperture (NA) objective lens reflected by the sample under study, the Brewster angle is found. Employing a high NA objective lens allows the measurement of multiple angles of incidence from 0° to 64° in a single shot. The refractive index of the sample is estimated using the measured Brewster angle. The experimental results are compared with the theoretical images computed with the Fresnel theory, and a good agreement is obtained.

Tailored complex optical fields, may find applications in optical manipulation, imaging, microscopy, quantum information processing, and optical communications. Here, we focus on data information transfer for optical communications using complex optical fields. We review recent research progress in complex optical field modulation, multiplexing, and multicasting for data information transfer on different platforms of waveguides, free space, and fiber. Challenges and perspectives are also discussed.

We investigate the stimulated Brillouin scattering (SBS) properties of light beams carrying orbit angular momentum (OAM). The phase conjugation of light beams carrying OAM is experimentally achieved in an SBS mirror with a random phase plate. The spectrum and the pulse width compression of SBS light are measured. It is shown that the phenomena of pulse compression is observed and OAM conservation is confirmed in the SBS process. The OAM transfer from photons to phonons may find potential applications in photon-phonon conversion-based signal-processing schemes by using OAM multiplexing.

Femtosecond (fs) cylindrical vector beams (CVBs) have found use in many applications in recent years. However, the existing rigid generation methods seriously limit its development. Here, we propose a flexible method for generating fs-CVBs with arbitrary polarization order by employing half wave plates and vortex retarders. The polarization state, autocorrelation width, pulse width, and spectrum features of the input and generated CVB pulses are measured and compared. The results verify that the generated CVBs remain in the fs regime with no appreciable temporal distortion, and the energy conversion efficiency can reach as high as 96.5%, even for a third-order beam. As a flexible way to generate fs-CVBs, this method will have great significance for many applications.

In this Letter, an effective method using a mode selective coupler (MSC), which is composed of a three-core fiber is presented to generate optical vortices (OVs). The conversions of OVs with different topological charges, 0→±1 and 0→±3, are simulated in detail. We also prove that a higher-order topological charge can be obtained simply by changing the parameters of the fiber to increase the number of modes in the fiber. The polarization of OVs can be controlled as well.

We generate and measure the versatile vortex linear light bullet, which combines a high-order Bessel beam and an Airy pulse. This three-dimensional optical wave packet propagates without distortion in any medium, while carrying an orbital angular momentum. Its non-varying feature in linear propagation is verified by a three-dimensional measurement. Such a novel versatile linear light bullet can be useful in various applications such as micromachining.

We design and demonstrate new types of optical tweezers with lateral pulling forces that allow full control of biological samples with complex geometric shapes. With appropriate beam shaping, the dual tug-of-war tweezers effectively hold and stretch elongated biological objects of different sizes, and the triangular tug-of-war tweezers with threefold rotational symmetry steadily hold asymmetric objects in the plane of observation and exert stretching forces along three directions. We successfully apply these tweezers to manipulate microparticles and bacterial cells in aqueous media.

Light fields with extraordinary propagation behaviors, such as nondiffracting and self-bending, are useful in the optical delivery of energy, information, and even objects. A kind of helical beam is constructed here based on the caustic method. With the appropriate design, the main lobe of these helical beams can be both well-confined and almost nondiffracting, while moving along a helix with its radius, period, number of rotations, and main lobes highly adjustable. In addition, the peak intensity of the main lobe fluctuates below 15% during propagation. These promising characteristics may enable a variety of potential applications based on these beams.

Remotely sensing an object with light is essential for burgeoning technologies, such as autonomous vehicles. Here, an object’s rotational orientation is remotely sensed using light’s orbital angular momentum. An object is illuminated by and partially obstructs a Gaussian light beam. Using an SLM, the phase differences between the partially obstructed Gaussian light beam’s constituent OAM modes are measured analogous to Stokes polarimetry. It is shown that the phase differences are directly proportional to the object’s rotational orientation. Comparison to the use of a pixelated camera and implementation in the millimeter wave regime are discussed.

We show the power of spirally polarized doughnut beams as a tool for tuning the field distribution in the focus of a high numerical aperture (NA) lens. Different and relevant states of polarization as well as field distributions can be created by the simple turning of a λ/2 retardation wave plate placed in the excitation path of a microscope. The realization of such a versatile excitation source can provide an essential tool for nanotechnology investigations and biomedical experiments.