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Electrically Tunable Liquid-Crystala??Polymer Composite Laser with Symmetric Sandwich Structure
摘要： This study investigates and develops for the first time an electrically tunable liquid-crystal?polymer composite laser with a symmetric sandwich structure. This structure includes two identical polymer-stablized cholesteric liquid-crystal (PSCLC) layers, and a dye-doped nematic LC (DDNLC) layer is sandwiched between them. The PSCLC and DDNLC layers act as distributed Bragg reflectors and half-wave plate with a gain medium, respectively. The entire cell behaves as an optical cavity, where the resonant modes occur at the maxima of the cell’s transmission spectrum. Through the competition among the resonant modes by considering the gain and loss, the resonant mode with the lowest lasing threshold can be sieved out for lasing occurrence. When the same voltage is applied to the two PSCLC layers, the pitch gradients are simultaneously formed through the two layers because of the electrically induced ion-concentration gradients. When the voltage increases, the pitch gradients increase, thereby leading to the expansion of the cell photonic band gap (PBG) and blue shift of the lasing wavelength. The sandwich cell PBG can expand from 55 nm to over 170 nm, and the tuning range of the lasing wavelength is as high as 70 nm, which is the widest ever achieved in LC-related sandwich systems. The proposed configuration of the sandwich sample presents new insights into tunable LC PBG and laser devices, thereby providing potential applications in the form of sensors, medical imaging, displays and lighting, among others.
关键词： distributed Bragg reflectors,electrically tunable,dye-doped nematic LC,photonic band gap,liquid-crystal?polymer composite laser,optical cavity,symmetric sandwich structure,half-wave plate,lasing wavelength,polymer-stablized cholesteric liquid-crystal
更新于2025-09-19 17:13:59
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High Refractive Index Inverse Vulcanized Polymers for Organic Photonic Crystals
摘要： Photonic technologies are nowadays dominated by highly performing inorganic structures that are commonly fabricated via lithography or epitaxial growths. Unfortunately, the fabrication of these systems is costly, time consuming, and does not allow for the growth of large photonic structures. All-polymer photonic crystals could overcome this limitation thanks to easy solubility and melt processing. On the other hand, macromolecules often do not offer a dielectric contrast large enough to approach the performances of their inorganic counterparts. In this work, we demonstrate a new approach to achieve high dielectric contrast distributed Bragg reflectors with a photonic band gap that is tunable in a very broad spectral region. A highly transparent medium was developed through a blend of a commercial polymer with a high refractive index inverse vulcanized polymer that is rich in sulfur, where the large polarizability of the S–S bond provides refractive index values that are unconceivable with common non-conjugated polymers. This approach paves the way to the recycling of sulfur byproducts for new high added-value nano-structures.
关键词： distributed Bragg reflectors,inverse vulcanization,refractive index,polymer photonic crystals
更新于2025-09-16 10:30:52
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Strategy toward ultra-high-resolution micro-LED displays by bonding interface-engineered vertical stacking and surface passivation
摘要： In this paper, we have proposed the strategy to fulfill the vertically stacked subpixel (VSS) micro-light-emitting diodes (μ-LEDs) for future ultra-high resolution microdisplays. At first, to vertically stack the LED with different colors, we have successfully adopted the bonding interface engineered monolithic integration method by using SiO2/SiNx distributed Bragg reflectors (DBRs). It was found that an intermediate DBR structure can be performed as the bonding layer and the color filter, which can reflect and transmit desired wavelengths the bonding interface. Furthermore, the optically pumped μ-LEDs array with 0.4 μm pitch corresponding to ultra-high-resolution of 63500 PPI was successfully fabricated by using typical semiconductor processing, including electron-beam lithography. Compared with pick-and-place with the limitation of the machine alignment accuracy, there is a significant improvement for fabricating the high-density μ-LEDs. Finally, we have systematically investigated the effects of surface traps by using time-resolved photoluminescence (TRPL) and two-dimensional simulation. These results clearly demonstrated that performance improvements could be possible by employing the optimal passivation techniques according to diminishing the pixel size for low power and highly-efficient microdisplays.
关键词： ultra-high-resolution,micro-LEDs,wafer bonding,distributed Bragg reflectors,surface passivation
更新于2025-09-11 14:15:04
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Graphene quantum dot vertical cavity surface emitting lasers
摘要： Nonzero-bandgap graphene quantum dots (GQDs) are novel optical gain materials promising for solution-processed light sources with high cost efficiency and device performance. To date, there have only been a few reports on the realization of GQDs-based lasers. Herein, we demonstrate for the first time room-temperature lasing emission with green gamut from GQDs in a vertical optical cavity composed of Ta2O5/SiO2 dielectric distributed Bragg reflectors (DBRs). The lasing is enabled by the unique design of the DBR which not only provides a wide stopband spectrally overlapping with the emission of the GQDs but also allows high transmittance of optical excitation in the UV-light region. This demonstration is a clear evidence of the use of GQDs as optical gain materials and represents an important step forward toward their potential applications in wide-gamut laser displays and projectors.
关键词： Vertical Cavity Surface Emitting Laser,Graphene Quantum Dots,Green Gap,Microwave-Assisted Hydrothermal Method,Distributed Bragg Reflectors (DBRs)
更新于2025-09-11 14:15:04