Recent Progress of Quantum Dot Lasers Monolithically Integrated on Si Platform

With continuously growing global data traffic, silicon (Si)-based photonic integrated circuits have emerged as a promising solution for high-performance Intra-/Inter-chip optical communication. However, a lack of a Si-based light source remains to be solved due to the inefficient light-emitting property of Si. To tackle the absence of a native light source, integrating III-V lasers, which provide superior optical and electrical properties, has been extensively investigated. Remarkably, the use of quantum dots as an active medium in III-V lasers has attracted considerable interest because of various advantages, such as tolerance to crystalline defects, temperature insensitivity, low threshold current density and reduced reflection sensitivity. This paper reviews the recent progress of III-V quantum dot lasers monolithically integrated on the Si platform in terms of the different cavity types and sizes and discusses the future scope and application

Room-temperature continuous-wave Dirac-vortex topological lasers on silicon

Robust laser sources are a fundamental building block for contemporary information technologies. Originating from condensed-matter physics, the concept of topology has recently entered the realm of optics, offering fundamentally new design principles for lasers with enhanced robustness. In analogy to the well-known Majorana fermions in topological superconductors, Dirac-vortex states have recently been investigated in passive photonic systems and are now considered as a promising candidate for single-mode large-area lasers. Here, we experimentally realize the first Dirac-vortex topological lasers in InAs/InGaAs quantum-dot materials monolithically grown on a silicon substrate. We observe room-temperature continuous-wave single-mode linearly polarized vertical laser emission at a telecom wavelength. Most importantly, we confirm that the wavelength of the Dirac-vortex laser is topologically robust against variations in the cavity size, and its free spectral range defies the universal inverse scaling law with the cavity size. These lasers will play an important role in CMOS-compatible photonic and optoelectronic systems on a chip

Room-temperature continuous-wave topological Dirac-vortex microcavity lasers on silicon

Robust laser sources are a fundamental building block for contemporary information technologies. Originating from condensed-matter physics, the concept of topology has recently entered the realm of optics, offering fundamentally new design principles for lasers with enhanced robustness. In analogy to the well-known Majorana fermions in topological superconductors, Dirac-vortex states have recently been investigated in passive photonic systems and are now considered as a promising candidate for robust lasers. Here, we experimentally realize the topological Dirac-vortex microcavity lasers in InAs/InGaAs quantum-dot materials monolithically grown on a silicon substrate. We observe room-temperature continuous-wave linearly polarized vertical laser emission at a telecom wavelength. We confirm that the wavelength of the Dirac-vortex laser is topologically robust against variations in the cavity size, and its free spectral range defies the universal inverse scaling law with the cavity size. These lasers will play an important role in CMOS-compatible photonic and optoelectronic systems on a chip

The Epitaxial Growth and Unique Morphology of InAs Quantum Dots Embedded in a Ge Matrix

In this work, we investigated the epitaxial growth of InAs quantum dots (QDs) on Ge substrates. By varying the growth parameters of growth temperature, deposition thickness and growth rate of InAs, a high density of 1.2 ×1011 cm-2 self-assembled InAs QDs were successfully epitaxially grown on Ge substrates by solid-source molecular beam epitaxy (MBE) and capped by Ge layers. Pyramidal- and polyhedral-shaped InAs QDs embedded in Ge matrices were revealed, which are distinct from the lens- or truncated pyramid-shape dots in InAs/GaAs or InAs/Si systems. Moreover, with 200 nm Ge capping layer, one third of the embedded QDs are found with ellipse and hexagonal nanovoids with sizes of 7 – 9 nm, which is observed for the first time for InAs QDs embedded in a Ge matrix to the best of our knowledge. These results provide a new possibility of integrating InAs QD devices on Group-IV platforms for Si photonics

Mining heuristic evidence sentences for more interpretable document-level relation extraction

Current research on evidence sentences is aimed at developing document-level relational extraction models with improved interpretability. Evidence sentences extracted using existing methods are often incomplete, leading to poor relationship prediction accuracy. To address this problem, we developed a novel efficient heuristic rule and entity representation method. First, a heuristic rule is constructed according to the interactions between different mentions of the head and tail entities of the target entity pair, and evidence sentences are subsequently extracted. Second, pseudo documents, constructed according to the original document order, are used as input text to remove noisy statements. Finally, different representations of the same entity in different entity pairs are learned to represent it more accurately through the interactive mention of head and tail entities. Experiments on the document-level general domain dataset DocRED indicated that our heuristic rules improved sentence extraction by 6.01% compared to that achieved by the baseline model Paths-BiLSTM. In terms of relation prediction, the accuracy of the proposed method was comparable to those of existing models that use the entire document as input text; however, the input text used by the proposed method was shorter and more interpretable

Improved Method for Measuring the Permeability of Nanoporous Material and Its Application to Shale Matrix with Ultra-Low Permeability

Nanoporous materials have a wide range of applications in clean energy and environmental research. The permeability of nanoporous materials is low, which affects the fluid transport behavior inside the nanopores and thus also affects the performance of technologies based on such materials. For example, during the development of shale gas resources, the permeability of the shale matrix is normally lower than 10−3 mD and has an important influence on rock parameters. It is challenging to measure small pressure changes accurately under high pressure. Although the pressure decay method provides an effective means for the measurement of low permeability, most apparatuses and experiments have difficulty measuring permeability in high pressure conditions over 1.38 MPa. Here, we propose an improved experimental method for the measurement of low permeability. To overcome the challenge of measuring small changes in pressure at high pressure, a pressure difference sensor is used. By improving the constant temperature accuracy and reducing the helium leakage rate, we measure shale matrix permeabilities ranging from 0.05 to 2 nD at pore pressures of up to 8 MPa, with good repeatability and sample mass irrelevance. The results show that porosity, pore pressure, and moisture conditions influence the matrix permeability. The permeability of moist shale is lower than that of dry shale, since water blocks some of the nanopores

Cantilever-based microring lasers embedded in a deformable substrate for local strain gauges

A cantilever-based microring laser structure was proposed for easily integrating III-V active layer into mechanically stretchable substrates. Local strain gauges were demonstrated by embedding cantilever-based microring lasers in a deformable polymer substrate. The characterizations of microscale local strain gauges had been studied from both simulated and experimental results. The lasing wavelength of strain gauges was blue-shift and linear tuned by stretching the flexible substrate. Gauge factor being ∼11.5 nm per stretching unit was obtained for a cantilever-based microring laser with structural parameters R=1.25 μm, W1=450 nm and W2=240 nm. Such microring lasers embedded in a flexible substrate are supposed to function not only as strain gauges for monitoring the micro- or nano-structured deformation, but also tunable light sources for photonic integrated circuits

Highly integrated photonic crystal bandedge lasers monolithically grown on Si substrates

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Single-Mode Photonic Crystal Nanobeam Lasers Monolithically Grown on Si for Dense Integration

International audienc

Monolithically integrated photonic crystal surface emitters on silicon with a vortex beam by using bound states in the continuum

Optical resonant cavities with high quality factor ( Q -factor) are widely used in science and technology for their capabilities of strong confinement of light and enhanced light–matter interaction. The 2D photonic crystal structure with bound states in the continuum (BICs) is a novel concept for resonators with ultra-compact device size, which can be used to generate surface emitting vortex beams based on symmetry-protected BICs at the Γ point. Here, to the best of our knowledge, we demonstrate the first photonic crystal surface emitter with a vortex beam by using BICs monolithically grown on CMOS-compatible silicon substrate. The fabricated quantum-dot BICs-based surface emitter operates at 1.3 µm under room temperature (RT) with a low continuous wave (CW) optically pumped condition. We also reveal the BIC's amplified spontaneous emission with the property of a polarization vortex beam, which is promising to provide a novel degree of freedom in classical and quantum realms