Chiral liquid crystals for photonic components

Chiral liquid crystals tend to spontaneously introduce twist in a 3D director configuration. For chiral liquid crystal with intrinsic pitch in the same range as the thickness of the cell, patterns with internal twist can be spontaneously created, and bistability can be achieved. For chiral liquid crystal with intrinsic pitch in the range of the wavelength of light, an optical band gap is created and high reflectivity is obtained when the Bragg condition is satisfied. Such mirrors can be used to achieve cavity modes with high q-factor and low lasing threshold. Patterned photoalignment based on photosensitive azodye materials has been achieved using either a spatial light modulator or interference illumination. The first approach offers flexibility to independently pattern the azimuthal angle in two million pixels. The second approach can achieve patterns with high resolution. When chiral liquid crystal is combined with patterned photoalignment, complex 3D director patterns can be achieved. This approach has been used with long pitch liquid crystal to achieve multistable diffraction gratings that can be switched with a hysteresis behavior between them. In combination with short pitch chiral liquid crystal, gratings with high efficiency and large diffraction angles can be realized. Single component spectrometers in which a grating achieves at the same time focusing and diffraction has been used, either on a flat or on a curved substrate.