POLICRYPS: a liquid crystal composed nano/microstructure with a wide range of optical and electro-optical applications

Abstract

POLICRYPS (an acronym of polymer liquid crystal polymer slices) is a nano/microcomposite structure made of slices of almost pure polymer alternated with films of well aligned nematic liquid crystal (NLC). The structure is obtained by irradiating a homogeneous syrup of NLC, monomer and curing agent molecules with an interference pattern of UV/visible light under suitable experimental and geometrical conditions; the spatial periodicity can be easily varied from an almost nanometric (200 nm) to a micrometric (15 µm) scale. Where the effect on an impinging reading light beam is concerned, the POLICRYPS can be utilized either in a transmission or a reflection configuration (depending on the geometry and substrate used) with negligible scattering losses, while the effect of spatial modulation of the refractive index (from polymer to NLC values) can be switched on and off by applying an external electric field of the order of few V µm−1. In this paper, we start by reviewing the general features of the POLICRYPS structure, that is the 'recipe' to fabricate it, along with a chemical–diffusive model that indicates the right physical and chemical conditions to make samples exhibiting good morphological, optical and electro-optical properties. We then show some possible utilizations of POLICRYPS with a light beam impinging almost perpendicularly to the structure: a switchable diffraction grating and a switchable optical phase modulator. Furthermore, we put into evidence that POLICRYPS channels can become an array of mirrorless optical micro-resonators for lasing effects. Finally, we report about utilization of POLICRYPS with a light beam impinging parallel to the structure and perpendicular to the channels, demonstrating that, in this case, the structure becomes a tuneable Bragg filter. Performances exhibited in all above applications put the POLICRYPS structure at the top level of the state of art of application oriented research in optics of liquid crystalline composite materials.