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Topological defects and defect phases of rigid and flexibly bent-shaped liquid crystals are reviewed with emphasis on how they are affected by the departure of molecular shapes from a simple rod. The review discusses defects in bent-core uniaxial and hypothetical biaxial nematics, twist-bend nematic, and various frustrated layered bent-core liquid crystals, such as twist-grain boundary phase, nanoscale helical nanofilament phase, and the so-called B7 textures with helical ribbons. 

We show here that light polarization of a beam propagating through a heliconical cholesteric cell can be controlled by tuning the Bragg resonance of the structure. We demonstrate that this control is achieved by varying either the low-frequency electric field or the intensity of a pump beam impinging on the sample. The study confirms the recently reported phenomenon of optical tuning of the heliconical cholesterics and opens the door for the development of simple and efficient polarization modulators controlled electrically or optically. 

Cholesteric liquid crystals form a right-angle helicoidal structure with the pitch in the submicrometer and micrometer range. Because of the periodic modulation of the refractive index, the structure is capable of Bragg and Raman-Nath diffraction and mirrorless lasing. An attractive feature of cholesterics for optical applications is that the pitch and thus the wavelength of diffraction respond to temperature or chemical composition changes. However, the most desired mode of pitch control, by electromagnetic fields, has so far been elusive. Synthesis of bent-shape flexible dimer molecules resulted in an experimental realization of a new cholesteric state with an oblique helicoidal structure, abbreviated as Ch_OH. The Ch_OHstate forms when the material is acted upon by the electric or magnetic field and aligns its axis parallel to the field. The principal advantage of Ch_OHis that the field changes the pitch but preserves the single-harmonic heliconical structure. As a result, the material shows an extraordinarily broad range of electrically or magnetically tunable robust selective reflection of light, from ultraviolet to visible and infrared, and efficient tunable lasing. The Ch_OHstructure also responds to molecular reorientation at bounding plates and optical torques. This brief review discusses the recently established features of Ch_OHelectro-optics and problems to solve.