Annular beam with segmented phase gradients

Abstract

An annular beam with a single uniform-intensity ring and multiple segments of phase gradients is proposed in this paper. Different from the conventional superposed vortices, such as the modulated optical vortices and the collinear superposition of multiple orbital angular momentum modes, the designed annular beam has a doughnut intensity distribution whose radius is independent of the phase distribution of the beam in the imaging plane. The phase distribution along the circumference of the doughnut beam can be segmented with different phase gradients. Similar to a vortex beam, the annular beam can also exert torques and rotate a trapped particle owing to the orbital angular momentum of the beam. As the beam possesses different phase gradients, the rotation velocity of the trapped particle can be varied along the circumference. The simulation and experimental results show that an annular beam with three segments of different phase gradients can rotate particles with controlled velocities. The beam has potential applications in optical trapping and optical information processing.

Modified Bessel–Gaussian Vortex Beam with an Adjustable Broken Opening

“…[34][35][36][37] Phase gradients significantly affect optical forces, [38] and vortex beams with different phase gradients can rotate microparticles with controlled velocities. [39,40] Power-exponent-phase vortex beams are characterized by spiral intensities that are regulated by the exponent phase term, which can generate helical phases with non-uniform gradients. [41][42][43][44] Although these beams are useful in the field of optical trapping for uneven intensity or phase distributions, the annular or small broken intensities generated by them limit the broad applications in optical manipulation.…”

An annular beam with segmented phase gradients generated by a modified spiral zone plate

“…The phase distribution y q ( ) with the segmented phase gradients can be obtained by equation (1) [34] y q q q q q q q q q q q p…”

“…Nevertheless, the shifting parameter is redundant, this zone plate cannot remove the inner redundant spiral zones, and the generated vortex does not have multiple OAM states. The optical vortices with superimposing OAM states can be produced with some methods [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37]. There are some modified spiral phase plates which can be used to generate superimposing OAM states, i.e.…”

“…Nevertheless, these methods producing the superimposing OAM states cannot be applied to generate the annulus with the tailored radius and multiple segments of phase gradients. Tao et al [34] proposed the annular beam produced by the proposed complex amplitude shaping algorithms [35][36][37] which generate an output beam with the arbitrary complex amplitude with a spatial light modulator (SLM) conveniently, which has a single ring of the tailored radius independent of the topological charge and multiple segments of phase gradients, and found that the rotation velocity of the trapped particle can be varied along the circumference as the beam possesses different phase gradients. However, the computer-generated hologram with the complicated multi-stage phases cannot be fabricated simply and cost-effectively.…”

Three tailorable optical vortices generated by a modified fractal spiral forked plate

“…Radial spiral phase plates produce optical vortices of large spectrum width [22]. Furthermore, holograms generated by the proposed complex amplitude shaping algorithms have optical vortices at the focal plane of the lens, which provide annular beams with segmented phase gradients and tailorable radii [23]. In addition, optical vortices can be produced by the zone plates.…”