Sergey Samagin

Light modulation in planar aligned short-pitch deformed-helix ferroelectric liquid crystals

We study both experimentally and theoretically modulation of light in a planar aligned deformed-helix ferroelectric liquid crystal (DHFLC) cell with subwavelength helix pitch, which is also known as a short-pitch DHFLC. In our experiments, the azimuthal angle of the in-plane optical axis and electrically controlled parts of the principal in-plane refractive indices are measured as a function of voltage applied across the cell. Theoretical results giving the effective optical tensor of a short-pitch DHFLC expressed in terms of the smectic tilt angle and the refractive indices of the ferroelectric liquid crystal (FLC) are used to fit the experimental data. The optical anisotropy of the FLC material is found to be weakly biaxial. For both the transmissive and reflective modes, the results of fitting are applied to model the phase and amplitude modulation of light in the DHFLC cell. We demonstrate that if the thickness of the DHFLC layer is about 50μm, the detrimental effect of field-induced rotation of the in-plane optical axes on the characteristics of an axicon designed using the DHFLC spatial light modulator in the reflective mode is negligible.

Aberration influenced generation of rotating two-lobe light fields

The influence of aberrations on light fields with a rotating intensity distribution is considered. Light fields were generated with the phase masks developed using the theory of spiral beam optics. The effects of basic aberrations, such as spherical aberration, astigmatism and coma are studied. The experimental implementation of the fields was achieved with the assistance of a liquid crystal spatial light modulator HOLOEYE HEO-1080P, operating in reflection mode. The results of mathematical modelling and experiments have been qualitatively compared.

Light fields generated by LC focusing device in different operational regimes

The types of light fields that can be generated with the use of proposed by the authors 4-channel modulator (LC focusing device) in different modes depending on the value of χl (where χ is the modal parameter, l – the characteristic size of the aperture and the square of χl is the ratio of the resistance of the high resistance layer and the impedance of the LC layer) are analyzed. By means of numerical simulation it was shown that χl value determines reshaping of equipotential lines of voltage from ring/ellipses to square/parallelogram contours or octagon contours. The capability of LC focusing device to generate light fields with intensity distribution in the shape of intersections, sets of points, boundaries of squares, diamonds, parallelograms, octagons is demonstrated. Obtained light fields can be useful in the problems of optical manipulation.

Experimental implementation of the high-sensitivity liquid-crystal lens with optically controlled focal length

Spherical and cylindrical lenses with intensity dependent focal length are investigated experimentally. The lenses were photosensitive enough for incident laser power about 0.5 mW/cm2. Two adaptive systems are implemented to demonstrate feasibility of a) power-in-diaphragm stabilization and b) auto-correction of defocus, in all-optical setups. With very little efforts on optimization, the first system reduced intensity variation of 150% down to less than 5%, and the second one practically removed the optical power variation in the output beam when of the input beam optical power increased up to 0.46 dptr.