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0The generation of vortex light fields using a sector spiral plate based on ferroelectric and ferrielectric liquid crystals
S. Kotova1*, E. Pozhidaev2, S. Samagin1, T. Tkachenko2
1- Lebedev Physical Institute, Samara Branch, 221, Novo-Sadovaya, Samara, 443011, Russian Federation 2- Lebedev Physical Institute, 53, Leninskiy Prospekt, Moscow, 119991, Russian Federation
* kotova@fian.smr.ru
Increasing the conversion rate of spatial light field distributions is an important goal in modern photonics. The modulation frequency in modern phase space light modulators (SLM) based on nematic liquid crystals (LC) is in the range of several tens of hertz. This speed can be increased through orientation effects in liquid crystal ferroelectric materials (LCFs) and ferrielectrics with subwavelength spiral structures, particularly the Kerr effect [1-3]. The paper presents the results of research on the electro-optical properties of these materials for use in phase modulation applications, using the example of generating light fields with a sectorial spiral plate (SSP). A feature of the Kerr effect in these liquid crystals is the biaxial transformation of the ellipsoid of refractive indices and the rotation of its main optical axis when an electric field is applied. This prevents the implementation of pure phase modulation in cells with a planar orientation of the axis of the helix to the substrate.
We studied the modulation characteristics of several mixed LC ferroelectric materials synthesized at LPI [1], as well as the ferrielectric crystal FerriLCM-1 [3], whose spiral pitch is less than 100 nanometers. Using the experimental data obtained, we calculated the characteristics of vortex light fields that can be generated using a 12-segment spiral plate based on the studied ferroelectric liquid crystal mixture FLC-587-F-7 and FerriLCM-1 [4]. It was shown that the effect of amplitude modulation due to changes in the ellipticity state on the formation of vortex light fields using the SLM based on these materials is not significant.
An experimental sample of a 12-sector spiral plate was made using FLC-587-F-7 [5]. The SSP was controlled by an alternating supply voltage, with the signal frequency varying from 100 to 4000 Hz. The formation of ring-shaped light fields with topological charges ranging from 1 to 4, as well as a set of symmetric light spots, has been demonstrated. The value of the topological charge has been determined using the compensation method with a phase element created by a multi-pixel liquid crystal SLM.
Thus, ferroelectric and ferrielectric liquid crystals are compared as electro-optical media for phase modulation, using the example of the formation of vortex light fields. It has been shown that both types of LC provide comparable values for changes in the ellipticity of the modulated light field. The loss of light when cutting off the unwanted polarization component is less than 10%, which is more than sufficient for a number of practical applications. The control voltage required to achieve a 2n phase shift is 2.6 times lower in the case of ferrielectric LC than in ferroelectric LC, when considering the same LCD layer thickness.
The study was supported by the RSF under grant number 24-22-00239.
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[2] S.P. Kotova, S.A. Samagin, E.P. Pozhidaev, A.D. Kiselev, Light modulation in planar aligned short-pitch deformed-helix ferroelectric liquid crystals, Phys. Rev. E, vol. 92, 062502, (2015).
[3] E.P. Pozhidaev, M.V. Minchenko, A.V. Kuznetsov, et al, Broad temperature range ferrielectric liquid crystal as a highly sensitive quadratic electro-optical material, Optics Letters. vol.47, pp. 1598-1601, (2022).
[4] E.P. Pozhidaev, S.P. Kotova, S.A. Samagin, Ferrielectric Liquid Crystal with a Subwavelength Helix Pitch As an Electro-Optic Medium for Phase Spatial Light Modulators, Bulletin of the Lebedev Physics Institute, vol. 50(Suppl 1), pp. S85-S95, (2023).
[5] S.P. Kotova, E.P. Pozhidaev, S.A. Samagin, et al, Ferroelectric liquid crystal with sub-wavelength helix pitch as an electro-optical medium for high-speed phase spatial light modulators, Optics & Laser Technology, vol.135, 106711, (2021).
