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.

Ten-channel mode-division-multiplexed silicon photonic integrated circuit with sharp bends

A multimode silicon photonic integrated circuit(PIC) comprising a pair of on-chip mode(de)multiplexers with 10-mode channels and a multimode bus waveguide with sharp bends is demonstrated to enable multi-channel on-chip transmissions. The core width of the multimode bus waveguide is chosen such that it can support 10 guided modes, of which there are four transverse-magnetic polarization modes and six transverse-electric polarization modes. This multimode bus waveguide comprises sharp bends based on modified Euler curves. Experimental results demonstrate that the present silicon PIC enables the 10-channel on-chip transmission with a low inter-mode crosstalk of approximately-20 dB over a broad bandwidth of 1520–1610 nm even when the bending radius of the S-bend is as small as 40 μm. Compared with a silicon PIC using a conventional arc-bend with the same bending radius, our proposed PIC demonstrates a significant improvement.

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.

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.

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.

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.

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.