Optical Properties of Liquid Crystals and LCD Displays - Research Paper Example

Optical properties of Liquid crystals and LCD displays Optical properties of Liquid crystals and LCD displays Liquid crystals and LCDs have become significantly popular with producers of the products enjoying an immense commercial advantage over its wide application. The use and application of the liquid crystals span from nearly 25 years ago and have a wide array of applications. The LCDs have dominated the display market progressively replacing the once cathode ray tubes-dominated market. With the surge in the adoption of the liquid crystals and LCDs technology, understanding of the various important components of the technology is important. In particular, LCD technology is influenced by the unique optical properties of the liquid crystal molecules. Optical properties The liquid crystals are used in various consumer audiovisual devices among other office gadgets such as calculators, cell phones, digital cameras, watches, stereos, clocks, laptop computers and other personal organizers. The LCDs are also applied as technical instruments information display in automobiles speedometers, clocks and navigation aids. Nevertheless, there are a number of competing display technologies such as the light emitting diodes (LEDs), the plasma displays (PDs), and the organic light-emitting diodes. Liquid crystal displays incorporate the unique properties of certain materials, nematic, selected smectic and cholesteric liquids. In certain liquid phases, the materials exhibit some electro-optic effects attributed to crystals. A typical liquid crystal display contains two electrodes or polarizer. A liquid crystal film material plugs the space between the two electrodes (Gu 2010, p. 6). Glass fibers are used as spacers that keep the thickness of the liquid crystals uniform within a range of 5µ to 10µ (Koide 2014, p. 86). The plates are also known as the polarizers, which are usually orientated at 900 to one another. The twisted phase commonly serves to reorient light that passes through the first plate, which consequently allows the transmission of the light through the second polarizer. When an electric field is applied to the liquid crystal layer, the molecular axes align parallel to the electric field and untwist. In such a state, light is not oriented making the polarized light from the first polarizer, which leads to loss of transparency with a further increase in voltage. This electric field property can be applied in making a pixel switch between the opaque and the transparent on command. According to Afa (2013), the liquid crystal display works in accordance with the Kerr’s effect. In the liquid crystal, there is normally a very fast response time for the shuttering of light estimated at less than 1µs. The fast shuttering utilizes an organic material’s orientation in an electric field perpendicularly applied to an incident beam of light. The occurrence of the Kerr effect mainly relies on the alignment of the polarizable molecules in an electric effect to produce he birefringence from the isotropic liquid. The birefringence magnitude depends on the strength of the electric field strength applied. The Kerr effect is a form of quadratic electro-optic effect commonly as a result of an electric-field-initiated command of polar molecules in an optically isotropic medium. The effect exists in crystals with centro-symmetric group points. From Kerr effect, when no voltage is applied, the liquid crystal is isoptropic but becomes anisotropic in the presence of an electric field. Kelly and O’Neill (2000, p. 5) explores on the optical anisotropy property of the liquid crystal. They point out that the optical anisotropy makes the liquid crystals uniaxial, and therefore, birefringent. They enhance that the free rotation in liquids renders them optically isotropic. This can be described using the following equation; Where; is the induced birefringence or refractive index change is the wavelength of the incident light B is the Kerr constant E is the strength of the applied field. Pallana (2009, p. 206) describes that to reproduce an image, the electrode plates enclosing a thin layer of liquid crystals between them receive a current that is produced when light strikes a metal. The voltage hitting the electrode plate generates an electric field that subsequently controls the orientation of the electric dipole moment of the liquid crystals molecules. This eventually causes them to turn. Different orientations of the liquid crystal molecules will alter the polarization state of the light that had been linearly polarized (Chen, 2013, p. 6). The alteration will be done in accord with birefringence degree of the liquid crystals (Chen 2011, p3). Gu (2010, p. 8) confirms that the liquid crystal cell can be controlled electrically to modify the polarization state and the intensity of transmitted beam of light. In particular, Gu (2010, p. 10) illustrated that when the voltage is on, the liquid crystal molecules are aligned in a perpendicular manner to the glass plates as shown in the diagram below. On the hand, Gu (2010, p. 10) further points out that when the voltage is turned on, the liquid crystals are aligned in a parallel fashion to the glass plates as illustrated below. Liquid crystal displays are, therefore, based on optical phenomena of electrically controlled birefringence and polarization. That liquid crystals are usually birefringent implies that the liquid crystals have two refraction indices, which is as a result of their anisotropic nature as shown below; Liquid crystal cells in LCD systems can function as light valves that control the light transmission via application of an electric voltage. According to Gu (2010, p. 8), this optical property of liquid crystals makes the LCDs application in monochrome displays that use dark and bright picture or image elements to display information (Gu 2010, p. 8). Optical devices known as color filters are usually placed after the light valves array to change the spectral distribution of a beam of light incident on the inner surface of the upper glass plate. LCD devices also have another unique property in that the characteristic of the light emitted from the monitor surface is commonly asymmetrical. These characteristics include the polarity and the intensity. For example, when measured from different angles from the central axis of the monitor surface, the light intensity markedly differs. The asymmetry is associated with the optical anisotropy of the liquid crystal cell that hinges on the elements of the liquid crystal pixel, as well as the voltage applied. Subsequently, the asymmetry is also attributed to the effect of polarized light being viewed in a co-linearly with the polarizing filter direction (Ray, 2012). In conclusion, Liquid crystals and LCD devices are mainly made up of two glass plates that sandwich a liquid crystal film. The two plates polarize the light that passes through them in a series of processes. Some of the important optic properties of the liquid crystals that enhance the functioning of the liquid crystals include birefringence and anisotropy. These optical properties mainly deal with the orientation of the crystals depending on the presence or absence of voltage. References Afa, I. J. (2013). A Study on Liquid Crystal Display (LCD) in Optoelectronics. GRIN Verlag. Chen, R. H. (2013). Liquid Crystal Displays: Fundamental Physics and Technology. New York: John Wiley and Sons. Gu, C. (2010). Optics of Liquid Crystal Displays. Hoboken, NJ: John Wiley & Sons. Kelly, S. M., & ONeill, M. O. (2000). Liquid Crystals for Electro-optic Applications. In H. S. Nalwa, Handbook of Advanced Electronic and Photonic Materials and Devices, (pp. 1-66). Academic Press. Koide, N. (2014). The Liquid Crystal Display Story: 50 Years of Liquid Crystal R&D that Lead the way to the future. Tokyo, Japan: Springer. Pallana, O. G. (2009). Engineering Chemistry. New York: Tata McGraw-Hill Education. Ray, A. (2012). Liquid Crystal- A Review. Asian Journal Research of Chemistry, 5(4), 563-569. Read More