Towards integrated mode-division demultiplexing spectrometer by deep learning

Miniaturized spectrometers have been widely researched in recent years,but few studies are conducted with on-chip multimode schemes for mode-division multiplexing(MDM)systems.Here we propose an ultracompact mode-division demultiplexing spectrometer that includes branched waveguide structures and graphene-based photodetectors,which realizes simultaneously spectral dispersing and light fields detecting.In the bandwidth of 1500-1600 nm,the designed spectrometer achieves the single-mode spectral resolution of 7 nm for each mode of TE_(1)-TE_(4) by Tikhonov regularization optimization.Empowered by deep learning algorithms,the 15-nm resolution of parallel reconstruction for TE_(1)-TE_(4) is achieved by a single-shot measurement.Moreover,by stacking the multimode response in TE_(1)-TE_(4) to the single spectra,the 3-nm spectral resolution is realized.This design reveals an effective solution for on-chip MDM spectroscopy,and may find applications in multimode sensing,interconnecting and processing.

Finding the superior mode basis for mode-division multiplexing:a comparison of spatial modes in air-core fiber

Diverse spatial mode bases can be exploited in mode-division multiplexing(MDM)to sustain the capacity growth in fiber-optic communications,such as linearly polarized(LP)modes,vector modes,LP orbital angular momentum(LP-OAM)modes,and circularly polarized OAM(CP-OAM)modes.Nevertheless,which kind of mode bases is more appropriate to be utilized in fiber still remains unclear.Here,we aim to find the superior mode basis in MDM fiber-optic communications via a system-level comparison in air-core fiber(ACF).We first investigate the walk-off effect of four spatial mode bases over 1-km ACF,where LP and LP-OAM modes show intrinsic mode walk-off,while it is negligible for vector and CP-OAM modes.We then study the mode coupling effect of degenerate vector and CP-OAM modes over 1-km ACF under fiber perturbations,where degenerate even and odd vector modes suffer severe mode cross talk,while negligible for highorder degenerate CP-OAM modes based on the laws of angular momentum conservation.Moreover,we comprehensively evaluate the system-level performance for data-carrying single-channel and two-channel MDM transmission with different spatial mode bases under various kinds of fiber perturbations(bending,twisting,pressing,winding,and out-of-plane moving).The obtained results indicate that the CP-OAM mode basis shows superiority compared to other mode bases in MDM fiber-optic communications without using multiple-input multiple-output digital signal processing.Our findings may pave the way for robust shortreach MDM optical interconnects for data centers and high-performance computing.

On-chip metamaterial-enabled high-order mode-division multiplexing

Mode-division multiplexing(MDM)technology enables high-bandwidth data transmission using orthogonal waveguide modes to construct parallel data streams.However,few demonstrations have been realized for generating and supporting high-order modes,mainly due to the intrinsic large material groupvelocity dispersion(GVD),which make it challenging to selectively couple different-order spatial modes.We show the feasibility of on-chip GVD engineering by introducing a gradient-index metamaterial structure,which enables a robust and fully scalable MDM process.We demonstrate a record-high-order MDM device that supports TE_(0)–TE_(15)modes simultaneously.40-GBaud 16-ary quadrature amplitude modulation signals encoded on 16 mode channels contribute to a 2.162 Tbit∕s net data rate,which is the highest data rate ever reported for an on-chip single-wavelength transmission.Our method can effectively expand the number of channels provided by MDM technology and promote the emerging research fields with great demand for parallelism,such as high-capacity optical interconnects,high-dimensional quantum communications,and large-scale neural networks.

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.

中美地方治理比较研究

在经济全球化的时代,中国地方治理面临着新的机遇和挑战。治理理论在西方的成功实践引起了我国政治学界的高度关注。在市场经济不断完善和全球化冲击的环境下,中国地方政府如何借鉴西方地方政府治理的成功经验,创新和完善地方治理的模式,重塑政府形象,对于构建社会主义和谐社会具有重要的现实意义。

Fiber-based mode converter for generating optical vortex beams

In this work, an all-fiber-based mode converter for generating orbital angular momentum （OAM） beams is proposed and numerically investigated. Its structure is constructed by cascading a mode selective coupler （MSC） and an inner elliptical cladding fiber （IECF）. OAM modes refer to a combination of two orthogonal LPlm modes with a phase difference of ±π/2. By adjusting the parameters and controlling the splicing angle of MSC and IECF appropriately, higher-order OAM modes with topological charges of l = ±1, ±2, ±3 can be obtained with the injection of the fundamental mode LP01, resulting in a mode-conversion efficiency of almost 100%. This achievement may pave the way towards the realization of a compact, all-fiber, and high-efficiency device for increasing the transmission capacity and spectral efficiency in optical communication systems with OAM mode multiplexing.

大麦叶绿体分裂的研究

报道了大麦叶绿体分裂的全过程。发现叶绿体是在长轴的中部或近中部产生缢痕、逐渐紧缩并断裂为两个子叶绿体的。并对遗传性黄化大麦叶绿体的结构特征、叶绿体分裂机制、同步性及子叶绿体的大小等进行讨论。

民事执行分权改革的理性检视

民事执行分权改革艰难推进,相继出现执行局内分权和法院内分权两种典型的分权模式。然而执行案件的执结率却未出现期许中的上升,反而有逐年下降的趋势,改革效果不尽人意。改革目标定位的差误、改革方法的失当、对执行权本质的认识错觉共同致成了改革的偏失。上海模式的出现为民事执行分权改革提供了思路,执行裁判权的独立运行与“执行警务化”改革或可成为砸碎民事执行难、执行乱问题的“重锤”。

人民法庭负责执行的实践与模式选择

无论是在立法层面抑或是实践层面,人民法庭负责执行工作向来有规可循。在执行体制改革的浪潮中,各地人民法院在探索人民法庭负责执行工作中推陈出新。实践中人民法庭与执行局各自的执案守备范围不同,根据分案标准的不同,执行工作呈现出两种模式,固定分案执行模式及随机分案执行模式。在我国人民法庭负责执行工作制度化构建方面,固定分案执行模式应当成为基本走向。但是在理论和制度构建上则不应局限于人民法庭负责执行工作的改进,而应纵观全局,继续深化执行改革,健全解决执行难长效机制,组建专业化执行团队,依托现代信息技术,以执行指挥中心综合管理平台为核心,推进案件科学合理的繁简分流,以彰显执行的效率价值。

LP modes exchange based on multiplane light conversion

Data exchange between different mode channels is essential in the optical communication network with mode-division multiplexing(MDM).However,there are challenges in realizing mode exchange with low insert loss,low mode crosstalk,and high integration.Here,we designed and fabricated a mode exchange device based on multiplane light conversion(MPLC),which supports the transmission of LP01,LP11a,LP11b,and LP21 modes in the C-band and L-band.The simulated exchanged mode purities are greater than 85%.The phase masks were fabricated on a silicon substrate to facilitate the integration with optical systems,with an insert loss of less than 2.2 dB and mode crosstalk below-21 dB due primarily to machining inaccuracies and alignment errors.We carried out an optical communication experiment with 10 Gbit/s OOK and QPSK data transmission at the wavelength of 1550 nm and obtained excellent performance with the device.It paves the way for flexible data exchange as a building block in MDM optical communication networks.

Flexible orbital angular momentum mode switching in multimode fibre using an optical neural network chip

Mode-division multiplexing technology has been proposed as a crucial technique for enhancing communication capacity and alleviating growing communication demands.Optical switching,which is an essential component of optical communication systems,enables information exchange between channels.However,existing optical switching solutions are inadequate for addressing flexible information exchange among the mode channels.In this study,we introduced a flexible mode switching system in a multimode fibre based on an optical neural network chip.This system utilised the flexibility of on-chip optical neural networks along with an all-fibre orbital angular momentum(OAM)mode multiplexer-demultiplexer to achieve mode switching among the three OAM modes within a multimode fibre.The system adopted an improved gradient descent algorithm to achieve training for arbitrary 3×3 exchange matrices and ensured maximum crosstalk of less than-18.7 dB,thus enabling arbitrary inter-mode channel information exchange.The proposed optical-neural-network-based mode-switching system was experimentally validated by successfully transmitting different modulation formats across various modes.This innovative solution holds promise for providing effective optical switching in practical multimode communication networks.

Differential mode-gain equalization via femtosecond laser micromachining-induced refractive index tailoring

The mode-division multiplexing technique combined with a few-mode erbium-doped fiber amplifier(FM-EDFA)demonstrates significant potential for solving the capacity limitation of standard single-mode fiber(SSMF)transmission systems.However,the differential mode gain(DMG)arising in the FM-EDFA fundamentally limits its transmission capacity and length.Herein,an innovative DMG equalization strategy using femtosecond laser micromachining to adjust the refractive index(RI)is presented.Variable mode-dependent attenuations can be achieved according to the DMG profile of the FM-EDFA,enabling DMG equalization.To validate the proposed strategy,DMG equalization of the commonly used FM-EDFA configuration was investigated.Simulation results revealed that by optimizing both the length and RI modulation depth of the femtosecond laser-tailoring area,the maximum DMG(DMGmax)among the 3 linear-polarized(LP)mode-group was mitigated from 10 dB to 1.52 dB,whereas the average DMG(DMGave)over the C-band was reduced from 8.95 dB to 0.78 dB.Finally,a 2-LP mode-group DMG equalizer was experimentally demonstrated,resulting in a reduction of the DMGmax from 2.09 dB to 0.46 dB,and a reduction of DMGave over the C band from 1.64 dB to 0.26 dB,with only a 1.8 dB insertion loss.Moreover,a maximum range of variable DMG equalization was achieved with 5.4 dB,satisfying the requirements of the most commonly used 2-LP mode-group amplification scenarios.

A review of multiple optical vortices generation: methods and applications

Optical vortices carrying orbital angular momentum(OAM)have attracted increasing interest in recent years.Optical vortices have seen a variety of emerging applications in optical manipulation,optical trapping,optical tweezers,optical vortex knots,imaging,microscopy,sensing,metrology,quantum information processing,and optical communications.In various optical vortices enabled applications,the generation of multiple optical vortices is of great importance.In this review article,we focus on the methods of multiple optical vortices generation and its applications.We review the methods for generating multiple optical vortices in three cases,i.e.,1-to-N collinear OAM modes,1-to-N OAM mode array and N-to-N collinear OAM modes.Diverse applications of multiple OAM modes in optical communications and non-communication areas are presented.Future trends,perspectives and opportunities are also discussed.

Asymmetric directional couplers based on silicon nanophotonic waveguides and applications

Directional couplers （DCs） have been playing an important role as a basic element for realizing power exchange. Previously most work was focused on symmetric DCs and little work was reported for asymmetric directional couplers （ADCs）. In recently years, silicon nanophotonie waveguides with ultra-high index contrast and ultra-small cross section have been developed very well and it has been shown that ADCs based on silicon-oninsulator （SOI） nanophotonic waveguides have some unique ability for polarization-selective coupling as well as mode-selective coupling, which are respectively very important for polarization-related systems and mode-division-mulitplexing systems. In this paper, a review is given for the recent progresses on silicon-based ADCs and the applications for power splitting, polarization beam splitting, as well as mode conversion/（de）multiplexing.