Commercial non-tunable q-plates have become popular optical elements to generate vector beams at the design wavelength where the device exhibits half-wave (HW) retardance. However, their use is restricted since both the topological charge and the operating wavelength are set in fabrication. In this work, we report how to make such commercial q-plates more versatile for generating vector beams of higher topological charge and in different wavelength ranges. First, we show how to add, subtract or change the sign of the charge, by combining q-plates with HW plates. Second, we perform a broadband spectral characterization of the q-plate retardance, and identify the wavelengths with retardance values relevant for vector beam generation π, ±π/2). The wavelength is then used as a tuning parameter to change the device performance from a HW q-plate to a QW q-plate. The vector beams expected at these QW wavelengths are obtained as a superposition of the input polarization state and the output state of a HW q-plate. Experimental results are shown using the red and blue lines of an Ar-Kr laser. For input linearly polarized light of 488 nm the device generates hybrid vector beams (where the ellipticity varies with the azimuthal angle), while for 647 nm pure radial vector beams with constant ellipticity are obtained. These results could extend the use of commercial q-plates for multicolor vector beam applications.
In this work we report on our achievements in generating switchable and arbitrary vector beams by means of q-plates. Two kind of q-plates are considered: i) a physical prototype from Citizen Co. and ii) a virtual device that is encoded onto a spatial light modulator (SLM). In both cases experimental and analytical results within the Jones formalism are shown. The performance of a segmented and tunable liquid crystal q-plate prototype is characterized at visible and telecommunications wavelengths, and the generation of first-order vector beams is probed. By using a reflective geometry and tuning the q-plate at half-wave or at quarter-wave retardance, it is shown how the device can operate either as a q-plate with double order. Finally, we show the generation of arbitrary programmable integer and fractional vector beams by encoding a q-plate onto a SLM based system. The system is based on a double-pass configuration that consecutively modulates the vertical and the horizontal polarization components of light using a transmissive LCoS display. Therefore, new and exotic q-plate designs can be analyzed prior to their fabrication.
We present the use of a q-plate device operating at the 1550 nm telecommunications wavelength. A prototype liquid-crystal device from Citizen Holdings Co. is demonstrated to be useful for the generation of vector beams and orbital angular momentum transfer at this important wavelength.
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