Orbital angular momentum (OAM), as nature of optical field, has attracted considerable attention, due to its
academic interest and potential applications such as quantum information, atomic manipulation, micromanipulation
and the biosciences. The well-known OAM carried by an optical field originates from the azimuthal phase
gradient of an optical vortex field with a helical phase structure. Here we predict a novel optical OAM, which
is induced by curl of polarization. To demonstrate experimentally the above prediction, we present an idea for
creating a kind of radial-variant vector fields, which could have all local linear polarization and hybrid states of polarization (SoPs). By specifically arranging the SoPs of the vector fields, new effects and phenomena can be anticipated that can expand the functionality and enhance the capability of optical system. The generated vector fields with the radial-variant hybrid SoPs can carry such a novel OAM. Optical trapping experiments validate that the focused vector fields without any additional phase vortex, as the ring optical tweezers, exert torques to drive the orbital motion of the trapped isotropic microspheres.
We describe a convenient way to generate arbitrary vector beams by using a spatial light modulator, based on
interferometric superposition of two orthogonally polarized beams. In our constructed optical setup, the SLM is used to
produce a computer-generated holographic grating that diffracts a linearly polarized incident light into the +1st and -1st
diffraction orders with desired wavefronts. After the two diffraction beams pass through two quarter wave-plates, the
left- and right-handed circularly polarizations are yielded, respectively. Then a Rochi grating is utilized to recombine the
two beams into single one such that any desired polarization configuration is achieved. We demonstrate the versatility of
our method through optical experiment, in which a variety of polarization beams are realized. By making use of the
incident wave with helical phase, our technique can produce both cylindrically symmetric and asymmetric polarizations.
To the best of our knowledge, the experimental realization of cylindrically asymmetric polarization is reported for first
time. We also study the focal properties of vector beam through a high numerical aperture lens. Starting from
Richards-Wolf vectorial diffraction theory we calculate the focal field distribution and obtain some interesting focal
volume structures, such as flat-topped focus, doughnut focus with special dark volume structure.