Helical wavefront and beam shape modulated by advanced liquid crystal q-plate fabricated via photoalignment and analyzed by Michelson’s interference

Abstract

In this study, electrically tunable advanced liquid crystal q-plates (ALCQPs) that combine two q values in one device to generate optical vortex beams were fabricated using a photoalignment method that involves the use of azo dye, a surfactant alignment material. The electrically tunable ALCQP device could be modulated to control the shape and polarization of a circularly polarized Gaussian laser beam that propagated through the device. A Gaussian beam modulated by an ALCQP under suitable applied voltage showed a variation beam shape with helical wavefront, as demonstrated by Michelson's interference. This helical wavefront beam carries an orbital angular momentum and can be used in an optical tweezers system to trap, move, and rotate particles simultaneously.

Meta-q-plate for complex beam shaping

“…The output polarization is sign-inverted 37 . By means of traditional fabrication methods, only single q and α 0 , and simple azimuthally changing q could be achieved 32 33 . If the q and α 0 could be arbitrarily changed along r and φ , the capability of beam shaping would be drastically enhanced and the manipulation of optical beams in a point-to-point manner is possible.…”

“…The corresponding experimental results are in agreement with the simulations. To further characterize the wavefront generated by the meta-q-plate ( n = 10, q = 2~6.5), the Michelson interferogram between the output beam and a spherical reference wave is simulated, and experimentally verified 33 . As revealed in Fig.…”

“…Owing to the pronounced optical birefringence and controllable director distribution, liquid crystals (LCs) become the first choice for q-plate fabrication. The objective LC orientations can be obtained via self-assembled 26 27 or extra-field induced 28 29 LC topological defects, and circular rubbing 30 or photoalignment technique 31 32 33 34 35 . Till now, the reported q-plates are restricted to azimuthally variant optical axes.…”

Azimuthal Anchoring Strength in Photopatterned Alignment of a Nematic

“…There have been many different implementations of azobenzene-based photoalignment. For example, McConney et al [20] used a laser beam with a controllable direction of polarization to irradiate a rotating substrate with a photosensitive azobenzene layer, thus producing axially-symmetric patterns, also known as q-plates [21][22][23][24]. Culbreath et al [25] introduced a maskless digital micromirror photopatterning technique that allows one to create an array of disclinations.…”

Manipulating orbital angular momentum of light with tailored in-plane polarization states

“…A great success has been achieved in the creation and manipulation of optical OAM and a varierty of practical applications were developed such as imaging and metrology8910, atom optics111213, nonlinear optics141516, optical spanner1718, quantum optics and information19202122, optical communications2324252627282930, and others. The conventional ways to manipulate the optical OAM rely on the phase components/devices, e.g., spiral phase plates31323334, q -plates35, computer-generated holograms3637, sub-wavelength gratings38 and plasmonic metasurfaces394041. These devices can effectively control the outputting phase to generate beams with desired OAM modes.…”