By making use of the unique properties of Liquid Crystal (LC) materials, Liquid Crystal Displays (LCDs) as well as many other liquid crystal photonic devices have been playing an important role in serving our daily lives. The key of controlling the optical properties of liquid crystal devices is the controlling of liquid crystal molecular alignment, which is commonly achieved by a specially treated liquid crystal alignment layer. For some applications, spatially varying liquid crystal alignment is required so that the liquid crystal alignment layer needs to be patterned precisely with desired domain structures. In this thesis, an advanced method of producing spatially varying liquid crystal patterned alignment called photocopy photoalignment (PCPA) has been studied both theoretically an...[ Read more ]

By making use of the unique properties of Liquid Crystal (LC) materials, Liquid Crystal Displays (LCDs) as well as many other liquid crystal photonic devices have been playing an important role in serving our daily lives. The key of controlling the optical properties of liquid crystal devices is the controlling of liquid crystal molecular alignment, which is commonly achieved by a specially treated liquid crystal alignment layer. For some applications, spatially varying liquid crystal alignment is required so that the liquid crystal alignment layer needs to be patterned precisely with desired domain structures. In this thesis, an advanced method of producing spatially varying liquid crystal patterned alignment called photocopy photoalignment (PCPA) has been studied both theoretically and experimentally. Furthermore, with the help of photocopy photoalignment technology, a photo patterned thin film polarizer with close to 100% efficiency has been proposed which is capable of converting input non-polarized light to output linear or circular polarized light with close to 100% efficiency.

The photo patterned thin film polarizer with close to 100% efficiency consists of two polymer layers, wherein the front layer is a specially engineered thin film LC polymer which splits incident non-polarized light into left hand circular and right hand circular polarized beams and then separate them spatially. To achieve the splitting and separating functions, the specially engineered LC polymer film is designed with highly complex micro and nano scale alignment structures which is fabricated with photocopy photoalignment technology. The rear polymer layer is a patterned wave plate which converts the spatially separated circular polarized beams to desired polarization states.

The thin film polarizer with close to 100% efficiency normally operates at a narrow wavelength band due to its diffraction mechanism, which is acceptable for applications like polarized LED. However; taking into consideration that white LEDs are more attractive for many applications like LCD backlight system, we also proposed a solution for polarized while LED with a thin film polarizer with close to 100% efficiency and a LC polymer film mixed with aligned quantum rods.

The thin film polarizer with close to 100% efficiency could be used together with a thin film of lens array to expend its acceptance angle. Lens array diffusers light, and take into account the diffraction of the specially engineered LC polymer film increases the divergence angle of incident light; the package of a lens array, a thin film polarizer with close to 100% efficiency and a thin film of aligned quantum rods would serve as a highly efficient polarizer and a diffuser which can be used in LCD backlight systems to replace all the Brightness Enhancement Film (BEF) and diffuser layers. Moreover, the aligned quantum rods would contribute to additional enhancement of optical efficiency and color performance after the color filter. As a result, more than 3 times optical efficiency of backlight units could be achieved with improved colors comparing to conventional LED backlight units.

Several important patents have been filed along with my research on this project, including thin film polarizer with close to 100% efficiency, alignment of quantum rods and highly efficient LCD backlight system. The technology disclosed in the above would have great potential to start a revolution in LCD backlight systems as we can make it more compact, more efficient and better colored.