On the strengthening and slip activity of Mg-3Al-1Zn alloy with pre-induced{1012¯}twins

{1012¯}twins were introduced into the magnesium(Mg)plate AZ31 via pre-rolling along its transverse direction.The plates,both with and without the pre-induced{1012¯}twins,were subjected to uniaxial tension along different directions.Using crystal plasticity modeling,we found that the strengthening effect of the pre-induced{1012¯}twins on the macroscopic flow stress primarily arised from the increased slip resistance caused by the boundaries,rather than the orientation hardening due to the twinning reorientation(although the latter did make its contribution in some specific loading directions).Besides,the pre-existing{1012¯}twins were found,by both experiments and simulation,to promote the activity of prismatic and pyramidal<c+a>in the parent matrix of the material.Further analysis showed that the enhanced non-basal slip activity is related to the{1012¯}twin boundaries’low micro Hall-Petch slope ratios of non-basal slips to basal slip.With the critical resolved shear stress(CRSS)obtained from crystal plasticity modeling and the orientation data from EBSD,a probability-based slip transfer model was proposed.The model predicts higher slip transfer probabilities and thus lower strain concentration tendencies at{1012¯}twin boundaries than that at grain boundaries,which agrees with the experimental observation that the strain localization was primarily associated with the latter.The present findings are helpful scientifically,in deepening our understanding of how the pre-induced{1012¯}twins affect the strength and slip activity of Mg alloys,and technologically,in guiding the design of the pre-strain protocol of Mg alloys.

小芯径硫系玻璃光纤的制备及其非线性光学应用

通过动态蒸馏提纯技术制备了高纯Ge-As-Se和Ge-As-S硫系玻璃。采用两步棒管法拉制了以Ge-As-Se玻璃为纤芯、Ge-As-S玻璃为包层的小芯径阶跃折射率光纤,并使用飞秒激光抽运光纤测试了超连续谱的产生。以Al和GaCl_3分别作为除氧剂和C/H纯化剂可以有效消除玻璃中的C、H和O杂质。制备的Ge As Se/Ge As S光纤在2~9μm波段表现出优异的传输性能,光纤数值孔径约为1.3;采用重复频率为10.5 MHz、脉冲宽度为320 fs、中心波长为4.0μm、峰值功率为4.6 k W激光抽运长度为22 cm、芯径为6μm的光纤,获得了覆盖1.9~8.2μm、光谱平坦度为±10 d B、平均功率为4.5 m W的超连续谱。

Prospects and challenges in augmented reality displays

Augmented reality(AR)displays are attracting significant attention and efforts.In this paper,we review the adopted device configurations of see-through displays,summarize the current development status and highlight future challenges in micro-displays.A brief introduction to optical gratings is presented to help understand the challenging design of grating-based waveguide for AR displays.Finally,we discuss the most recent progress in diffraction grating and its implications.

Applications of weakly-coupled few-mode fibers[Invited]

Space-division multiplexing(SDM)has attracted significant attention in recent years because larger transmission capacity is enabled by more degrees of freedom(DOFs)in few-mode fibers(FMFs)compared with singlemode fibers(SMFs).To transmit independent information on spatial modes without or with minor digital signal processing(DSP),weakly-coupled FMFs are preferred in various applications.Several cases with different use of spatial DOFs in weakly-coupled FMFs are demonstrated in this work,including single-mode or mode-groupmultiplexed transmission,and spatial DOFs combined with time or frequency DOF to improve the system performance.

Monolithically integrated stretchable photonics

Mechanically stretchable photonics provides a new geometric degree of freedom for photonic system design and foresees applications ranging from artificial skins to soft wearable electronics.Here we describe the design and experimental realization of the first single-mode stretchable photonic devices.These devices,made of chalcogenide glass and epoxy polymer materials,are monolithically integrated on elastomer substrates.To impart mechanical stretching capability to devices built using these intrinsically brittle materials,our design strategy involves local substrate stiffening to minimize shape deformation of critical photonic components,and interconnecting optical waveguides assuming a meandering Euler spiral geometry to mitigate radiative optical loss.Devices fabricated following such design can sustain 41%nominal tensile strain and 3000 stretching cycles without measurable degradation in optical performance.In addition,we present a rigorous analytical model to quantitatively predict stressoptical coupling behavior in waveguide devices of arbitrary geometry without using a single fitting parameter.

3D integrated photonics platform with deterministic geometry control

3D photonics promises to expand the reach of photonics by enabling the extension of traditional applications to nonplanar geometries and adding novel functionalities that cannot be attained with planar devices.Available material options and device geometries are,however,limited by current fabrication methods.In this work,we pioneer a method that allows for placement of integrated photonic device arrays at arbitrary predefined locations in 3D using a fabrication process that capitalizes on the buckling of a 2D pattern.We present theoretical and experimental validation of the deterministic buckling process,thus demonstrating implementation of the technique to realize what we believe to be the first fully packaged 3D integrated photonics platform.Application of the platform for mechanical strain sensing is further demonstrated.

Electrical programmable multilevel nonvolatile photonic random-access memory

Photonic Random-Access Memories(P-RAM)are an essential component for the on-chip non-von Neumann photonic computing by eliminating optoelectronic conversion losses in data links.Emerging Phase-Change Materials(PCMs)have been showed multilevel memory capability,but demonstrations still yield relatively high optical loss and require cumbersome WRITE-ERASE approaches increasing power consumption and system package challenges.Here we demonstrate a multistate electrically programmed low-loss nonvolatile photonic memory based on a broadband transparent phase-change material(Ge2Sb2Se5,GSSe)with ultralow absorption in the amorphous state.A zero-staticpower and electrically programmed multi-bit P-RAM is demonstrated on a silicon-on-insulator platform,featuring efficient amplitude modulation up to 0.2 dB/μm and an ultralow insertion loss of total 0.12 dB for a 4-bit memory showing a 100×improved signal to loss ratio compared to other phase-change-materials based photonic memories.We further optimize the positioning of dual microheaters validating performance tradeoffs.Experimentally we demonstrate a half-a-million cyclability test showcasing the robust approach of this material and device.Low-loss photonic retention-of-state adds a key feature for photonic functional and programmable circuits impacting many applications including neural networks,LiDAR,and sensors for example.

Mode demultiplexing hybrids for mode-division multiplexing coherent receivers

We propose a mode demultiplexing hybrid(MDH) that integrates mode demultiplexing, local oscillator power splitting, and optical 90-deg mixing using multi-plane light conversion(MPLC). We demonstrate the realization of a three-mode MDH using four phase plates, one more than what is required for an MPLC-based mode demultiplexer, via numerical simulations. The performance of the three-mode MDH is comparable to that of commercial single-mode 90-deg hybrids. This multiple-functionality device enables simplification of the coherent optical front end of mode-division multiplexing receivers.

Scalable non-mode selective Hermite–Gaussian mode multiplexer based on multi-plane light conversion

Non-mode-selective(NMS) multiplexers(muxes) are highly desirable for coherent power combining to produce a high-power beam with a shaped profile(wavefront synthesis) from discrete, phase-locked emitters. We propose a design for a multi-plane light conversion(MPLC)-based NMS mux, which requires only a few phase masks for coherently combining hundreds of discrete input beams into an output beam consisting of hundreds of Hermite–Gaussian(HG) modes. The combination of HG modes as a base can further construct a beam with arbitrary wavefront. The low number of phase masks is attributed to the identical zero-crossing structure of the Hadamard-coded input arrays and of the output HG modes, enabling the practicality of such devices. An NMS mux supporting 256 HG modes is designed using only seven phase masks, and achieves an insertion loss of-1.6 d B, mode-dependent loss of 4.7 d B, and average total mode crosstalk of-4.4 d B. Additionally, this design,featuring equal power for all input beams, enables phase-only control in coherent power combining, resulting in significant simplifications and fast convergence compared with phase-and-amplitude control.

Optical fiber amplifiers for space-division multiplexing

Recently, space-division multiplexing （SDM） techniques using multi-core fiber （MCF） and few-mode fiber （FMF） have been introduced into optical fiber communication to increase transmission capacity. Two main types of optical fiber amplifiers based on the Erbium- doped fiber （EDF） and the Raman effect have been developed to amplify signals in the MCF and FMF. In this paper, we reviewed the principles and configurations of these amplifiers.

Complex skin modes in non-Hermitian coupled laser arrays

From biological ecosystems to spin glasses,connectivity plays a crucial role in determining the function,dynamics,and resiliency of a network.In the realm of non-Hermitian physics,the possibility of complex and asymmetric exchange interactions(|κ_(ij)|≠|κ_(ji)|)between a network of oscillators has been theoretically shown to lead to novel behaviors like delocalization,skin effect,and bulk-boundary correspondence.An archetypical lattice exhibiting the aforementioned properties is that proposed by Hatano and Nelson in a series of papers in late 1990s.While the ramifications of these theoretical works in optics have been recently pursued in synthetic dimensions,the Hatano-Nelson model has yet to be realized in real space.What makes the implementation of these lattices challenging is the difficulty in establishing the required asymmetric exchange interactions in optical platforms.In this work,by using active optical oscillators featuring non-Hermiticity and nonlinearity,we introduce an anisotropic exchange between the resonant elements in a lattice,an aspect that enables us to observe the non-Hermitian skin effect,phase locking,and near-field beam steering in a Hatano-Nelson laser array.Our work opens up new regimes of phase-locking in lasers while shedding light on the fundamental physics of non-Hermitian systems.