The viewing angle characteristics of an LCM (Liquid Crystal Module) directly affect its display performance at multiple angles, especially in high-end displays, automotive instrument clusters, and medical imaging, where color consistency, contrast stability, and brightness uniformity at wide viewing angles are core requirements. Optical design, as a key element in improving the viewing angle characteristics of LCMs, requires a comprehensive approach encompassing multiple dimensions, including optimizing liquid crystal molecule arrangement, compensation film technology, multi-domain structure design, backlight system improvement, and simulation verification, to achieve a systematic improvement in viewing angle characteristics.
The arrangement of liquid crystal molecules is fundamental to determining the viewing angle characteristics of an LCM. In the traditional TN (Twisted Nematic) mode, liquid crystal molecules are arranged in a twisted pattern, leading to significant changes in optical path difference at wide viewing angles, causing a decrease in contrast and even grayscale inversion. By optimizing the liquid crystal molecule arrangement, such as using the VA (Vertical Alignment) mode, where liquid crystal molecules are aligned perpendicular to the substrate at zero field, viewing angle characteristics can be significantly improved. Furthermore, by employing MVA (Multi-Domain Vertical Alignment) or PVA (Patterned Vertical Alignment) technology, a single pixel is divided into multiple domains, each with liquid crystal molecules tilted in a different direction. This complementary effect offsets the optical path difference caused by changes in viewing angle, thereby widening the viewing angle range.
Compensation film technology is one of the core methods for improving the viewing angle characteristics of LCMs. Phase difference compensation films compensate for the birefringence effect of liquid crystal molecules at different viewing angles by adjusting the phase retardation of light. For example, negative birefringence compensation films can offset the viewing angle dependence in the dark state of TN mode, significantly improving contrast; while wide-viewing-angle compensation films, through a multi-layer film structure, simultaneously compensate for phase differences in the horizontal and vertical directions, achieving color consistency across all viewing angles. In addition, quarter-wave plate compensation technology, by introducing circularly polarized light, can effectively improve the viewing angle asymmetry problem of TN mode, making the vertical viewing angle characteristics more consistent.
Multi-domain structure design is another important direction for improving the viewing angle characteristics of LCMs. By dividing a single pixel into multiple sub-pixels, each sub-pixel has liquid crystal molecules arranged in a different direction, creating a complementary viewing angle effect. For example, in a dual-domain structure, one sub-pixel has a wide upper viewing angle, and the other has a wide lower viewing angle, resulting in a significantly expanded overall viewing angle range after synthesis. A quadruple-domain structure further achieves complementary viewing angles in both the horizontal and vertical directions, improving viewing angle characteristics in all directions. The realization of multi-domain structures requires a combination of processes such as photolithography, rubbing alignment, or photo-alignment. Photo-alignment technology, by controlling the pretilt angle of liquid crystal molecules through ultraviolet light irradiation, can achieve high-precision, low-defect multi-domain structures.
Backlight system design also significantly affects the viewing angle characteristics of LCMs. In traditional backlight systems, light enters from the bottom or sides, leading to significant brightness attenuation at large viewing angles. By using a collimated backlight source, the light direction is concentrated near the normal direction, reducing brightness loss at large viewing angles. Simultaneously, placing a diffuser screen on the viewing surface can eliminate azimuth inhomogeneity, further widening the viewing angle range. Furthermore, quantum dot backlight technology, through spectral conversion of nanomaterials, can improve color gamut coverage, resulting in more accurate color reproduction at large viewing angles.
Optical simulation and experimental verification are essential steps in optimizing the viewing angle characteristics of LCMs. By establishing the partial differential equation for the equilibrium free energy density of the liquid crystal system, and using the finite difference iterative method to solve for the director distribution of liquid crystal molecules, combined with Berreman's 4×4 matrix method to simulate the intensity distribution of light passing through the liquid crystal cell, the transmittance characteristics at different viewing angles can be accurately predicted. In the experimental phase, the viewing angle characteristic curves of actual samples are measured using spectrometers, luminance meters, and other equipment. Comparison with simulation results allows for rapid identification of design flaws and optimization of parameters. For example, by adjusting the thickness of the compensation film or the pretilt angle of the liquid crystal molecules, the viewing angle characteristics can be iteratively optimized until the design requirements are met.
