Abstract
Spiral polarization rotators, rotating polarization ellipse axes clockwise or counterclockwise, depending on the azimuth angle in the transverse plane, are considered. It is shown that spiral polarization rotators lead to a change in the order of optical vortices with circular polarization. A comparative analysis of spiral rotators of two types (polar and non-polar) is carried out, using a mirror that allows light to pass in the opposite direction through the rotator. The effect of spiral rotators on optical vortices in a resonator is studied. It is shown that spiral rotators can preserve or accumulate changes of the vortex order during the passage of the beam in both directions. The properties of the spiral rotator and the cube-corner reflector with a special phase-correcting coating, as a diffractive polarization-optical element, are compared.
Highlights
Study of polarization-inhomogeneous beams allows to conclude that, despite the complex structure, such beams have certain types of polarization symmetry [1]-[6]
If the sign of the optical vortex is opposite to the sign of circular polarization, after passing twice the positive Faraday spiral rotator in the direct and reverse direction, the order of the optical vortex increases by 2: rL ⇔ 3lR and lR ⇔ r3L
The counter-propagating waves acquire a phase shift where w is the parameter of the Gaussian mode distribution; ρ—curvature of the wave front; d—the distance between two spiral Faraday rotators, whose thickness is neglected; s1,2 —polarization orders of the counter-propagating optical vortices. Note that this device can be used to identify the sign of an optical vortex, because the change of the waves sign leads to the absence of a phase shift
Summary
Study of polarization-inhomogeneous beams allows to conclude that, despite the complex structure, such beams have certain types of polarization symmetry [1]-[6]. Polarization structures with axial symmetry are characterized by the following: in the cross-sectional plane a certain orientation of the polarization ellipse (polarization azimuth ψ ) is a constant along the radius vector, outgoing from the beam axis, but changes in proportion to coordinate azimuth φ. The beams with axisymmetric polarization structure have two modifications, depending on rotation direction of the polarization ellipse axis and are closely related to optical vortices. In [16] new polarization convertor, based on diffractive optical elements, is proposed. The corner-cube reflector with special faces coating as new diffraction polarization-optical devices is considered in [17] [19]. This article is a continuation of [19], where, along with polarization-symmetric structures of optical vortices, spiral polarization elements were considered, except for spiral rotators. The difference between the properties of polar and non-polar spiral polarization rotators is analyzed
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