Self-polarized RGB device realized by semipolar micro-LEDs and perovskite-in-polymer films for backlight applications

In backlighting systems for liquid crystal displays,conventional red,green,and blue(RGB)light sources that lack polarization properties can result in a significant optical loss of up to 50%when passing through a polarizer.To address this inefficiency and optimize energy utilization,this study presents a high-performance device designed for RGB polarized emissions.The device employs an array of semipolar blueμLEDs with inherent polarization capabilities,coupled with mechanically stretched films of green-emitting CsPbBr3 nanorods and red-emitting CsPbI3-Cs4PbI6 hybrid nanocrystals.The CsPbBr3 nanorods in the polymer film offer intrinsic polarization emission,while the aligned-wire structures formed by the stable CsPbI3-Cs4PbI6 hybrid nanocrystals contribute to substantial anisotropic emissions,due to their high dielectric constant.The resulting device achieved RGB polarization degrees of 0.26,0.48,and 0.38,respectively,and exhibited a broad color gamut,reaching 137.2%of the NTSC standard and 102.5%of the Rec.2020 standard.When compared to a device utilizing c-plane LEDs for excitation,the current approach increased the intensity of light transmitted through the polarizer by 73.6%.This novel fabrication approach for polarized devices containing RGB components holds considerable promise for advancing next-generation display technologies.

An overview on the principle of inkjet printing technique and its application in micro-display for augmented/virtual realities

Augmented reality(AR)and virtual reality(VR)are two novel display technologies that are under updates.The essential feature of AR/VR is the full-color display that requires high pixel densities.To generate three-color pixels,the fluorescent color conversion layer inevitably includes green and red pixels.To fabricate such sort of display kits,inkjet printing is a promising way to position the color conversion layers.In this review article,the progress of AR/VR technologies is first reviewed,and in succession,the state of the art of inkjet printing,as well as two key issues-the optimization of ink and the reduction of coffee-ring effects,are introduced.Finally,some potential problems associated with the color converting layer are highlighted.

Recent developments of quantum dot based micro-LED based on non-radiative energy transfer mechanism

With regard to micro-light-emitting diodes(micro-LEDs),their excellent brightness,low energy consumption,and ultrahigh resolution are significant advantages.However,the large size of traditional inorganic phosphors and the number of side defects have restricted the practical applications of small sized micro-LEDs.Recently,quantum dot(QD)and nonradiative energy transfer(NRET)have been proposed to solve existing problems.QDs possess nanoscale dimensions and high luminous efficiency,and they are suitable for NRET because they are able to nearly contact the micro-LED chip.The NRET between QDs and micro-LED chip further improves the color conversion efficiency(CCE)and effective quantum yield(EQY)of full-color micro-LED devices.In this review,we discuss the NRET mechanism for QD micro-LED devices,and then nano-pillar LED,nano-hole LED,and nano-ring LED are introduced in detail.These structures are beneficial to the NRET between QD and micro-LED,especially nano-ring LED.Finally,the challenges and future envisions have also been described.

High-speed visible light communication based on micro-LED:A technology with wide applications in next generation communication

The evolution of next-generation cellular networks is aimed at creating faster,more reliable solutions.Both the next-generation 6G network and the metaverse require high transmission speeds.Visible light communication(VLC)is deemed an important ancillary technology to wireless communication.It has shown potential for a wide range of applications in next-generation communication.Micro light-emitting diodes(μLEDs)are ideal light sources for high-speed VLC,owing to their high modulation bandwidths.In this review,an overview ofμLEDs for VLC is presented.Methods to improve the modulation bandwidth are discussed in terms of epitaxy optimization,crystal orientation,and active region structure.Moreover,electroluminescent white LEDs,photoluminescent white LEDs based on phosphor or quantum-dot color conversion,andμLED-based detectors for VLC are introduced.Finally,the latest high-speed VLC applications and the application prospects of VLC in 6G are introduced,including underwater VLC and artificial intelligence-based VLC systems.

Fractional Langevin Equation in Quantum Systems with Memory Effect

In this paper, we introduce the fractional generalized Langevin equation (FGLE) in quantum systems with memory effect. For a particular form of memory kernel that characterizes the quantum system, we obtain the analytical solution of the FGLE in terms of the two-parameter Mittag-Leffler function. Based on this solution, we study the time evolution of this system including the qubit excited-state energy, polarization and von Neumann entropy. Memory effect of this system is observed directly through the trapping states of these dynamics.

Glucose detection in a highly scattering medium with diffuse photon-pair density wave

We propose a novel optical method for glucose measurement based on difuse photon-pair density wave(DPPDW)in a multiple scattering medium(MSM)where the light scattering of photon-pair is induced by refractive index mismatch between scatters and phantom solution.Experi-mentally,the DPPDW propagates in MSM via a two frequency laser(TFL)beam wherein highly correlated pairs of linear polarized photons are generated.The reduced scattering coefficientμ2s and absorption coefficientμ2a of DPPDW are measured simultaneously in terms of the amplitude and phase measurements of the detected heterodyne signal under arrangement at different dis-tances between the source and detection fibers in MSM.The results show that the sensitivity of glucose detection via glucose-induced change of reduced scattering coefficient(δμ′2)is 0.049%mM^(-1)in a 1%intralipid solution.In addition,the linear range ofδμ′2s vs glucose concentration implies that this DPPDW method can be used to monitor glucose concentration continuously and noninvasively subcutaneously.

POLARIZATION-SENSITIVE OPTICAL COHERENCE TOMOGRAPHY USING A MODIFIED BALANCE DETECTOR

In conventional polarization sensitive optical coherence tomography(PS-OCT),phase retar-dation is obtained by the amplitude of P and S polarization only,and the fast axis angle is obtained by the phase difference in P and S polarizations via Hilbert transformation.In this paper,we proposed a modifed PS OCT setup in which the phase retardation and fast axis angle are simply expressed as the function of the amplitude ofP and S polarization and their differential signal.Due to the common-path feature between the two channels ofP and S polarization,the fuctuation in the measurement of phase retardation and fast axis angle caused by excess noise and phase noise from the laser source can be reduced by the differential signal of P and S polarization via a modified balance detector.Thus,the signal of phase retardation and fast angle axis in the deep layer of a porcine sample can be improved.

Directly modulated 25 Gbaud/s tunable in-series DFB laser array for WDM systems

In this Letter,we proposed and experimentally demonstrated a directly modulated tunable laser based on the multi-wavelength distributed feedback(DFB)laser array.The lasers are placed in series to avoid the usage of an optical combiner and additional power loss.A three-section design is utilized to reduce the interference from other lasers and improve the electro-optic response bandwidth.Besides,the reconstruction-equivalent-chirp technique is used to simplify the grating fabrication and precisely control the grating phase.We realized 12 channels with 100 GHz spacing with high side mode suppression ratios of above 50 dB.The output power of all the channels is above 14 mW.The 3 dB electro-optic bandwidth is above 20 GHz at a bias current of 100 mA for all four lasers.A 25 Gb/s data transmission over a standard single-mode fiber of up to 10 km is demonstrated for all 12 channels,and 50 Gb/s data per wavelength is obtained through the four-level pulse amplitude modulation.The proposed directly modulated tunable in-series DFB laser array shows the potential for a compact and low-cost light source for wavelength division multiplexing(WDM)systems,such as next-generation front-haul networks and passive optical networks.

Full-color monolithic hybrid quantum dot nanoring micro light-emitting diodes with improved efficiency using atomic layer deposition and nonradiative resonant energy transfer

Full-color displays based on micro light-emitting diodes(μLEDs) can be fabricated on monolithic epitaxial wafers. Nanoring(NR) structures were fabricated on a green LED epitaxial wafer; the color of NR-μLEDs was tuned from green to blue through strain relaxation. An Al_2O_3 layer was deposited on the sidewall of NR-μLEDs,which improved the photoluminescence intensity by 143.7%. Coupling with the exposed multiple quantum wells through nonradiative resonant energy transfer, red quantum dots were printed to NR-μLEDs for a full-color display. To further improve the color purity of the red light, a distributed Bragg reflector is developed to reuse the excitation light.

Optical cross-talk reduction in a quantumdot-based full-color micro-light-emitting-diode display by a lithographic-fabricated photoresist mold

In this study, a full-color emission red–green–blue(RGB) quantum-dot(QD)-based micro-light-emitting-diode(micro-LED) array with the reduced optical cross-talk effect by a photoresist mold has been demonstrated. The UV micro-LED array is used as an efficient excitation source for the QDs. The aerosol jet technique provides a narrow linewidth on the micrometer scale for a precise jet of QDs on the micro-LEDs. To reduce the optical cross-talk effect,a simple lithography method and photoresist are used to fabricate the mold, which consists of a window for QD jetting and a blocking wall for cross-talk reduction. The cross-talk effect of the well-confined QDs in the window is confirmed by a fluorescence microscope, which shows clear separation between QD pixels. A distributed Bragg reflector is covered on the micro-LED array and the QDs' jetted mold to further increase the reuse of UV light.The enhanced light emission of the QDs is 5%, 32%, and 23% for blue, green, and red QDs, respectively.

Full-color micro-LED display with high color stability using semipolar(20-21) InGaN LEDs and quantum-dot photoresist

Red-green-blue(RGB)full-color micro light-emitting diodes(μ-LEDs)fabricated from semipolar(20-21)wafers,with a quantum-dot photoresist color-conversion layer,were demonstrated.The semipolar(20-21)In Ga N/Ga Nμ-LEDs were fabricated on large(4 in.)patterned sapphire substrates by orientation-controlled epitaxy.The semipolarμ-LEDs showed a 3.2 nm peak wavelength shift and a 14.7%efficiency droop under 200 A∕cm2injected current density,indicating significant amelioration of the quantum-confined Stark effect.Because of the semipolarμ-LEDs’emission-wavelength stability,the RGB pixel showed little color shift with current density and achieved a wide color gamut(114.4%NTSC space and 85.4%Rec.2020).

Micro-light-emitting diodes with quantum dots in display technology

Micro-light-emitting diodes(μ-LEDs)are regarded as the cornerstone of next-generation display technology to meet the personalised demands of advanced applications,such as mobile phones,wearable watches,virtual/augmented reality,micro-projectors and ultrahigh-definition TVs.However,as the LED chip size shrinks to below 20μm,conventional phosphor colour conversion cannot present sufficient luminance and yield to support highresolution displays due to the low absorption cross-section.The emergence of quantum dot(QD)materials is expected to fill this gap due to their remarkable photoluminescence,narrow bandwidth emission,colour tuneability,high quantum yield and nanoscale size,providing a powerful full-colour solution for μ-LED displays.Here,we comprehensively review the latest progress concerning the implementation of μ-LEDs and QDs in display technology,including μ-LED design and fabrication,large-scale μ-LED transfer and QD full-colour strategy.Outlooks on QD stability,patterning and deposition and challenges of μ-LED displays are also provided.Finally,we discuss the advanced applications of QD-based μ-LED displays,showing the bright future of this technology.

Increasing the hole energy by grading the alloy composition of the p-type electron blocking layer for very high-performance deep ultraviolet light-emitting diodes

It is well known that the p-type AlGaN electron blocking layer(p-EBL) can block hole injection for deep ultraviolet light-emitting diodes(DUV LEDs). The polarization induced electric field in the p-EBL for [0001] oriented DUV LEDs makes the holes less mobile and thus further decreases the hole injection capability. Fortunately,enhanced hole injection is doable by making holes lose less energy, and this is enabled by a specifically designed p-EBL structure that has a graded AlN composition. The proposed p-EBL can screen the polarization induced electric field in the p-EBL. As a result, holes will lose less energy after going through the proposed p-EBL, which correspondingly leads to the enhanced hole injection. Thus, an external quantum efficiency of 7.6% for the 275 nm DUV LED structure is obtained.

20.231 Gbit/s tricolor red/green/blue laser diode based bidirectional signal remodulation visible-light communication system

We propose and experimentally demonstrate a recorded 1-m bidirectional 20.231-Gbit/s tricolor R/G/B laser diode(LD) based visible-light communication(VLC) system supporting signal remodulation. In the signal remodulation system, an LD source is not needed at the client side. The client reuses the downstream signal sent from the central office(CO) and remodulates it to produce the upstream signal. As the LD sources are located at the CO, the laser wavelength and temperature managements at the cost-sensitive client side are not needed.This is the first demonstration, to our knowledge, of a >20 Gbit∕s data rate tricolor R/G/B VLC signal transmission supporting upstream remodulation.

Highly stable full-color display device with VLC application potential using semipolarμLEDs and all-inorganic encapsulated perovskite nanocrystal

A promising approach for the development of effective full-color displays is to combine blue micro LEDs(μLEDs)with color conversion layers.Perovskite nanocrystals(PNCs)are notable for their tolerance to defects and provide excellent photoluminescence quantum yields and high color purity compared to metal chalcogenide quantum dots.The stability of PNCs in ambient conditions and under exposure to blue light can be improved using a SiO;coating.This study proposes a device that could be used for both display and visible light communication(VLC)applications.The semipolar blueμLED array fabricated in this study shows a negligible wavelength shift,indicating a significant reduction in the quantum confined Stark effect.Owing to its shorter carrier lifetime,the semipolar μLED array exhibits an impressive peak 3 dB bandwidth of 655 MHz and a data transmission rate of1.2 Gb/s corresponding to an injection current of 200 m A.The PNC-μLED device assembled from a semipolarμLED array with PNCs demonstrates high color stability and wide color-gamut features,achieving 127.23% and 95.00%of the National Television Standards Committee standard and Rec.2020 on the CIE 1931 color diagram,respectively.These results suggest that the proposed PNC-μLED device is suitable for both display-related and VLC applications.

Quantum dot vertical-cavity surface-emitting lasers covering the ‘green gap’

Semiconductor vertical-cavity surface-emitting lasers(VCSELs)with wavelengths from 491.8 to 565.7 nm,covering most of the‘green gap’,are demonstrated.For these lasers,the same quantum dot(QD)active region was used,whereas the wavelength was controlled by adjusting the cavity length,which is difficult for edge-emitting lasers.Compared with reports in the literature for green VCSELs,our lasers have set a few world records for the lowest threshold,longest wavelength and continuous-wave(CW)lasing at room temperature.The nanoscale QDs contribute dominantly to the low threshold.The emitting wavelength depends on the electron–photon interaction or the coupling between the active layer and the optical field,which is modulated by the cavity length.The green VCSELs exhibit a low-thermal resistance of 915 kW^(−1),which benefits the CW lasing.Such VCSELs are important for small-size,low power consumption full-color displays and projectors.

50 Gb/s PAM4 underwater wireless optical communication systems across the water–air–water interface [Invited]

A 50 Gb/s four-level pulse amplitude modulation(PAM4)underwater wireless optical communication(UWOC)system across the water-air-water interface is demonstrated in practice.In practical scenarios,laser beam misalignment due to oceanic turbulence degrades performance in UWOC systems.With the adoption of a reflective spatial light modulator(SLM)with an electrical controller,not only can the laser be arbitrarily adjusted to attain a water-air-water scenario,but oceanic engineering problems can also be resolved to establish a reliable UWOC link.Brilliant bit error rate performance and clear PAM4 eye diagrams are attained by adopting a Keplerian beam expander and a reflective SLM with an electrical controller.This proposed PAM4 UWOC system presents a feasible state that outperforms existing UWOC systems due to its feature providing a high-speed water-air-water link.

Dynamic Gain-Clamped Amplifier with Backward-Injection of a Fabry-Perot Laser

We have been experimentally demonstrated an active control technique of dynamic gain-clamped spectra for theerbium-doped fiber amplifiers (EDFA's) by a backward-injected Fabry-Perot (F-P) laser into this EDFA. In addition, employing a short length erbium-doped fiber (EDF) that not cause any gain saturation for preamplification in front of this amplifier module, it can reduce the noise figure degradation and simultaneously achieve gain variation from 11.1 dB to 0.5 dB for 10 dB input power level change.

Low-Loss Fiber De-Multiplexers

Reported are fiber de-multiplexers based on side-polished fibers with a long interaction length and intra-core fiber Bragg gratings. In conjunction with the silicon processing technologies, we demonstrate fiber filters and advantages of our approaches are addressed.