| dc.description.abstract | The main topic reported in this study is waveguide liquid crystal (LC)
devices with asymmetrical light scattering property and their applications. The
key points we discuss herein include the asymmetrical light scattering optical
characteristics when an edge light source is coupled into the proposed three
different LC devices applied with suitable electric fields, and then scattered out of
the LC devices. They are (i) polymer network LC (PNLC) cell coated with a low
refractive index thin film (MgF2), (ii) PNLC cell with cholesteric LC polymer
(CLCP) layers, and (iii) twisted hybrid aligned PNLC (TH-PNLC) cell with a
linear polarizer. We are going to explain the principle and the functional
characteristics of the structures of each LC device.
First of all, we discuss the properties of a homogeneous aligned PNLC (HAPNLC) cell whose one substrate is coated with a thin film having low refractive
index. Such a low refractive index magnesium fluoride (MgF2) film is deposited
on the top of the indium-tin-oxide film of one of the substrates of the LC cell by
evaporation method. The main mechanisms adopted here are the properties of LC
waveguide and total internal reflection (TIR). Based on the different times of TIR
of the incident light source, occurred on the boundaries of different films, the
asymmetrical output light in its scattering state can be obtained. The second part
is the asymmetrical light scattering properties demonstrated by the proposed HAPNLC cell with a CLCP layer. Due to the limitation of the CLCP layer, the edge
light source selected herein is a He-Ne laser with its wavelength of 632.8 nm,
which is within the reflection band of the used CLCP layer. Briefly, the powers of
light scattered out of the LC device from the sides with and without the CLCP
layer are different, indicating that the asymmetrical light scattering property can
also be realized. The last part of the research about asymmetrical light scattering
property is based on the proposed TH-PNLC cell with a linear polarizer. The
surface treatments of the two substrates of the TH-PNLC cell are different, one is
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homogeneous alignment, and the other one is homeotropic alignment. Moreover,
the twisted and hybrid aligned PNLC structures provide light scattering with
different degrees of polarization from two sides of TH-PNLC cell applied with
suitable electric fields. Therefore, we can realize asymmetrical light scattering
property with one polarizer stuck on the side of the TH-PNLC cell treated with a
homeotropic alignment layer.
Finally, the three LC devices mentioned above can be applied to various
practical applications in daily life. In this thesis, the applications of the proposed
waveguide LC devices, including electrically switchable one-way transparent
light sources, switchable LC privacy smart windows, and LCDs with privacy
protection, have also been demonstrated. However, lots of challenges, such as
contrast, operation voltage, uniformity, etc., still need to be overcome | en_US |