The paper presents the results of design, manufacturing and characterization of an hybrid broad band in-line device using a nematic liquid crystal as an active medium which influences light propagating in a biconical optical fibre taper. A liquid crystal mixture denoted 6CHBT*and E7 is designed for electric, as well as temperature control of electromagnetic wave propagation in a broad wavelength range. The main reason of using the taper structure with a waist of 10± 0.5 μm and losses lower than 0.5 dB is possibility of using a liquid crystalline medium as cladding. Such approach enables effective control of its refractive index. Two kinds of initial liquid crustal molecules’ orientation (parallel and orthogonal) in relation to the light beam propagating in a taper were applied. Performance of a tuned cladding was studied at electric field of the range of 0V – 160V in the room temperature equal to 20°C. Influence of induced reorientation of liquid crystal molecules was measured at a broad wavelength range [500-1700 nm].
In this paper a two liquid crystal (LC) modulators for mid-wave infrared radiation (MWIR) are presented. A two electrooptical effects (EOE) in liquid crystalline structures have been utilized for MWIR modulation: electric field induced cholesteric - nematic (Ch-N*) phase transition (ChN mode) and switching of the twisted-nematic (TN) structure (TN mode). At the Ch-N* mode an intensity modulation depth was of order of 15% but there wasn’t a dark state. In case of the modulation induced at TN mode was near full. These modulators are quite slow, switching times are order of a few hundreds of milliseconds for Ch-N* mode electrooptical effect and dozens of minutes in case of TN mode.
It is well known that the Young interference experiment is the fundamental setup to combine two beams and to construct the phase modulated light. Moreover, homodyne phase demodulator is based on signal decoding in back Fourier focal plane using bicell photodetector (B-PD). On the above base, we propose a novel experimental approach to the signals demodulation by using the optical interferometer which operates in homodyne mode, combined with liquid crystal spatial light modulators operating both phase as speckle modulator. Dynamic phase changes between the two beams can be controlled by monopixel liquid crystals cell placed in one branch of the interferometer. A phase modulation effect in a signal arm of interferometer is observed as a dynamic shift of the speckle pattern. Simple arithmetic combination of signals from B-PD placed in speckle pattern plane is only one necessary numerical manipulation to obtain exactly phase difference. Concept of signals demodulation in the Fourier focal plane can be only used for exactly defined geometrical (B-PD as well as Young interferometer) and physical parameters (polarization, wavelength). We optimize the setup geometry to obtain extremely high measurement resolution. In this paper we focus on the principles of operation of each part of the system as well as discussion their requirement in order to increase the signal to noise ratio.
Low viscosity high birefringence nematic liquid crystalline compounds and mixtures are described. They belong to the families of 4'-alkyl-3-fluoro-4-isothiocyanatobiphenyls, 4"-alkyl-3,5-difluoro-4-isothiocyanatoterphenyls, 4'-alkyl-3-fluoro-4-isothiocyanatotolanes and 4'-(4-alkylphenyl)-3,5-difluoro-4-isothiocyanatotolanes.
The optic and electrooptic properties of recently prepared orthoconic antiferroelectrics have been revieved. Relation between their chemical structure and mesogenic properties, smectic layer structure and helical pitch is discussed.
Bi- and multicomponent mixtures consisted of two groups of synclinic chiral esters: first one with a partially fluorinated terminal chain and the second one with hydrogenated terminal chain have been used for investigations. For some systems the induction of the anticlinic smectic C<sub>A</sub>* phase was observed. Enthalpies of the phase transitions for the systems with induced smectic C<sub>A</sub> phase upon compositions and specific heat were measured by DSC method.