This paper demonstrates a thin and transparent reflector film for the near infrared, based on chiral nematic liquid crystal (CLC) polymers. Two films reflect almost 50% of unpolarized incident light from 730 to 820 nm and from 880 to 1030 nm, while remaining completely transparent in the visible region with transmittance > 90 % . An efficient window uses the combination of two reflectors. After exposing two window-cubes for 2 h to direct sunlight, the temperature inside the cube with reflector windows was 4°C lower than in cube with plain windows. This reveals that the infrared (IR) reflectors can effectively control the indoor temperature. These films, which are 8 µm in thickness, can be detached from the glass substrates and used as a free-standing film, or be attached to a flexible optical foil or a solid window. The foils can be applied in buildings, offices, and automobiles to statically reduce the energy consumption required for air conditioning or lighting. The free-standing foils show acceptable resistance to polar protic solvents and are thermally stable up to 100°C.
Surface plasmon resonance (SPR) thermal effects have been the focus of researchers lately and are commonly used in sensors, micro heaters in integrated circuits, and other applications. In this study, a new type of tunable all-optical liquid crystal (LC) lens is fabricated by employing the SPR thermal effects. Due to the absorption of pump light by gold nanoparticles, the generated heat is transferred to the surrounding LC layer, leading a radial gradient distribution of LC molecules. Passing a probe light through the center of the fabricated cell, a lens shaped optical phase retardation observed. The temperature increase with intensification of the pump light power has been numerically calculated. In addition, the focal length of the lens reduces from 157.8 to 13.1 cm during this process. The tunable all-optical LC lens is a fascinating new concept that could open up new horizons and has numerous applications. It has a simpler and cheaper structure compared to electronic lenses, provides greater stability than other all-optical counterparts, and allows for optical control of the focal length.
A thin, waterproof, and stable spatially tunable band reject filter is fabricated based on a chiral nematic liquid crystal polymer. The fabrication method for this filter is new, to the best of our knowledge, and straightforward. The photonic bandgap (PBG) of the proposed filter can be tuned from 350 nm to 760 nm by a mechanical movement of 6.5 mm. The filter reflects almost 50% of unpolarized incident light in the PBG and remains practically transparent for other wavelengths. The filter remains stable for four years and has acceptable resistance to polar protic solvents and thermal stability up to 90°C. The filter can be detached from the glass substrates, to be used as a thin 8-µm free-standing film or to be attached to a flexible substrate. This spatial tunable band reject filter may be used in displays, optical devices, and optical communication.
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