具有纳米导模共振结构的偶氮染料薄膜偏振片研究(特邀)

高性能薄膜偏振片一直是液晶显示(Liquid Crystal Display,LCD)技术领域的研究热点之一，相比于市面上常见的线栅偏振片，它在保持高二向色性的同时实现了小于微米级的厚度，是高对比度超薄LCD显示器的重要组成部分。偶氮染料(Azo Dye,AD)类各向异性材料因其光致转向和强各向异性吸收的特点，拥有制备简单、厚度薄、大二向色性比(Dichroic Ratio,DR)等优势，被看作是用于超薄LCD显示器的高性能薄膜偏振片的理想材料。然而，AD在强线偏振光照射下，分子排列易被破坏导致性能下降，分子结构调控可以使其稳定性提升，但同时也使DR性能急剧下滑，因此，对其进行结构化调控以提升性能亟需突破。通过在AD薄膜层上引入纳米导模共振周期性结构，将分子级各向异性吸收和结构级强共振吸收相结合，实现了AD薄膜偏振片的双重吸收增强。通过针对纳米导模共振单元和薄膜层厚度的优化，与150 nm单一AD薄膜偏振片相比，实现平均DR提升83.3%，最小和最大值分别达到40.5%和149.5%，而偏振片总体厚度仅为220 nm。这项研究为AD高性能薄膜偏振片的设计制备提供了思路，在高对比度超薄LCD显示设备的研制中具有重要意义。<br/> Objective High performance thin film polarizer has become one of the research hotspots in the research of LCD display technology. Compared with wire grid polarizer on the market, it achieves a thickness of less than μm while maintaining high birefringence and being an important component of high contrast ultra-thin LCD displays. Azo dye (AD) anisotropic materials are considered ideal materials for high-performance thin film polarizers used in ultra-thin LCD displays due to their photoinduced steering and strong anisotropic absorption characteristics, which have advantages like simple preparation, thin thickness, and large dichroism ratio (DR). Methods This article builds an FDTD model of AD thin film polarizer for comparing experimental absorption spectrum and simulated absorption spectrum (Fig.3). Four possible models were constructed based on the different alignments of AD molecules in the thin film layer and the GMR unit, and their DR differences were compared in Fig.4. Then, we explore the effect on DR performance with the different heights of GMR unit and different thicknesses on thin film layer (Fig.6 and Fig.7). Results and Discussions This paper introduces a nano-GMR structure upon the AD film layer, combining molecular-level anisotropic absorption and structural-level strong resonant absorption to achieve dual absorption enhancement of the AD thin film polarizer. By optimizing the nano-GMR unit and thin film layer thickness, an average DR improvement of 83.3% was achieved compared to a single 150 nm AD film polarizer, where the minimum and maximum values reached 40.5% and 149.5%, respectively, while the overall thickness of the polarizer was only 220 nm. This study provides ideas for the design and preparation of high-performance AD thin film polarizer, which is of great significance in the development of high contrast ultra-thin LCDs. Conclusions This paper introduces the nano-GMR unit into the AD4455 thin film polarizer, which generates molecular anisotropic absorption of linearly polarized light and enhanced absorption of GMR structure. The results showed that by placing nano-GMR unit upon an AD thin film polarizer, DR performance has an average improvement of 54.4% in the wavelength range of 400-550 nm compared to a single AD4455 thin film polarizer, where the minimum and maximum value reach 38.5% and 74.4%, respectively. After further optimization for the thickness of the thin film layer, the final average DR improvement reached 83.3%, where the minimum and maximum values reached 40.5% and 149.5%, respectively. The introduction of this structure significantly enhances the performance of AD-based thin film polarizer, which is of great significance for the integration of high-performance thin film polarizers in ultra-thin LCD displays.