Space-division multiple access for CDMA multiuser underwater acoustic communications

Time reversal mirror （TRM） can use the physical characteristics of the underwater acoustic （UWA） channel to focus on the desired user in multi-user UWA communication. The active average sound intensity （AASI） detector can estimate all azimuths of users with the same frequency band at the same time in order to achieve directional communication by vector combination. Space-division multiple access （SDMA） based on TRM combined with the AASI detector is proposed in this paper, which can make the capacity of the code division multiple access （CDMA） UWA system significantly increase. The simulation and lake test results show that the 7-user UWA multi-user system can achieve low bit error communication.

Wide-field ophthalmic space-division multiplexing optical coherence tomography

High-speed ophthalmic optical coherence tomography(OCT)systems are of interest because they allow rapid,motion-free,and wide-field retinal imaging.Space-division multiplexing optical coherence tomography(SDMOCT)is a high-speed imaging technology that takes advantage of the long coherence length of micro electro mechanical vertical cavity surface emitting laser sources to multiplex multiple images along a single imaging depth.We demonstrate wide-field retinal OCT imaging,acquired at an effective A-scan rate of 800,000 A-scans/s with volumetric images covering up to 12.5 mm×7.4 mm on the retina and captured in less than 1 s.A clinical feasibility study was conducted to compare the ophthalmic SDM-OCT with commercial OCT systems,illustrating the high-speed capability of SDM-OCT in a clinical setting.

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.

Few-mode vertical-cavity surface-emitting lasers for space-division multiplexing

In order to choose the proper radius of oxide aperture for few-mode vertical-cavity surface-emitting lasers （VCSELs）, the influences of oxide aperture size on the multi-transverse-mode behaviors are investigated in detail. By establishing the effective refractive index model to simulate VCSELs with different radii of oxide apertures, the wavelength and corresponding order of different modes are obtained. VCSELs with three kinds of oxide apertures are manufactured. Then the multi-transverse-mode spectra and near-field are measured. It is found that when the radius is between 1.5 and 4.5μm, few-mode VCSELs can be implemented. The 2.5μm VCSEL manufactured in this paper only emits LP01 mode and LP21 mode. Since the space distance between the two modes is 2μm, it is expected to realize direct-modulation few-mode VCSELs by channel etching or ion implantation between the two modes.

Novel applications of space-division multiplexing

Space-division multiplexing （SDM） using multi-core fibers （MCFs） and few-mode fibers （FMFs） was proposed as a solution to increase capacity and/or reduce the cost per bit of fiber-optic transmission. Advances in passive and active SDM devices as well as digital signal processing have led to impressive SDM transmission demonstrations in the laboratory. Although the perceived advantages in terms of capacity and cost per bit that SDM offers over parallel SMF bundles are not universally accepted, SDM is beginning to emerge as an indispensable solution in major network segments. The introduction of the spatial degree of freedom allows optical networks to overcome fundamental limitations such as fiber nonlinearity as well practical limitations such as power delivery. We describe these application scenarios that the optical communications industry has already began to explore. From a fundamental science point of view, concepts such as the principal modes, generalized Stokes space, and multi-component solitons discovered in SDM research will likely have a broad impact in other areas of science and engineering.

Visible light communication based on space-division multiple access optical beamforming

We propose and demonstrate a visible light communication （VLC） scheme based on space-division multiple access （SDMA） optical beamforming to accommodate multiple user devices in the VLC based on optical beamforming. SDMA optical bealnforming is a technique which separates light-emitting diode light spa- tially and focuses each part on different target devices simultaneously. We show the experimental results of the VLC signal amplitudes, the optical power densities, and the bit-error rate performance as a function of transmission distance before and after the SDMA optical beamforming. The results show that the VLC signal amplitudes and optical power densities are improved by 8-2 and 3.8- 5 dB, respectively, with the help of SDMA optical beamforming.

Secure optical interconnects using orbital angular momentum beams multiplexing/multicasting

Orbital angular momentum(OAM),described by an azimuthal phase term expej lθT,has unbound orthogonal states with different topological charges l.Therefore,with the explosive growth of global communication capacity,especially for short-distance optical interconnects,light-carrying OAM has proved its great potential to improve transmission capacity and spectral efficiency in the space-division multiplexing system due to its orthogonality,security,and compatibility with other techniques.Meanwhile,100-m freespace optical interconnects become an alternative solution for the“last mile”problem and provide interbuilding communication.We experimentally demonstrate a 260-m secure optical interconnect using OAM multiplexing and 16-ary quadrature amplitude modulation(16-QAM)signals.We study the beam wandering,power fluctuation,channel cross talk,bit-error-rate performance,and link security.Additionally,we also investigate the link performance for 1-to-9 multicasting at the range of 260 m.Considering that the power distribution may be affected by atmospheric turbulence,we introduce an offline feedback process to make it flexibly controllable.

Ultra-low-loss all-fiber orbital angular momentum mode-division multiplexer based on cascaded fused-biconical mode selective couplers

Mode-division multiplexers(MDMUXs)play a pivotal role in enabling the manipulation of an arbitrary optical state within few-mode fibers,offering extensive utility in the fields of mode-division multiplexing and structured optical field engineering.The exploration of MDMUXs employing cascaded resonant couplers has garnered significant attention owing to their scalability,exceptional integration capabilities,and the anticipated low insertion loss.In this work,we present the successful realization of high-quality orbital angular momentum MDMUX corresponding to topological charges 0,±1,and±2,achieved through the utilization of cascaded fused-biconical tapered couplers.Notably,the measured insertion losses at 1550 nm exhibit remarkable minimal values:0.31,0.10,and 0.64 dB,respectively.Furthermore,the 80%efficiency bandwidths exceed 106,174,and 174 nm for these respective modes.The MDMUX is composed of precisionmanufactured high-quality mode selective couplers(MSCs).Utilizing a proposed supermode propagation method based on mode composition analysis,we precisely describe the operational characteristics of MSCs.Building upon this comprehensive understanding,we embark on a pioneering analysis elucidating the influence of MSC cascading order on the performance of MDMUXs.Our theoretical investigation substantiates that when constructing MDMUXs,MSCs should adhere to a specific cascading sequence.

基于非线性序转换的层次分析模型

为了解决复杂层次结构中方案排序问题,将排序度量映射到高维状态空间,挖掘隐藏在指标隶属度中的分类信息,利用区分权滤波算法将一维空间上无法实现的非线性序关系转换转化为高维空间上隶属度向量间的非线性转换,通过计算底层方案对目标的影响度,实现底层指标排序,建立基于非线性序转换的层次分析模型。以某矿出现渗漏的污水坝为例,根据拟采用的4种防渗加固方案以及6种衡量方案优、劣的指标构建三层递阶层次结构,并进行验证分析,结果表明本模型能够实现非线性序转换,可以作为解决复杂层次结构中方案排序的一种实用方法。

Optical multiplexing techniques and their marriage for on-chip and optical fiber communication:a review

Herein,an attention-grabbing and up-to-date review related to major multiplexing techniques is presented which in-cludes wavelength division multiplexing(WDM),polarization division multiplexing(PDM),space division multiplexing(SDM),mode division multiplexing(MDM)and orbital angular momentum multiplexing(OAMM).Multiplexing is a mech-anism by which multiple signals are combined into a shared channel used to showcase the maximum capacity of the op-tical links.However,it is critical to develop hybrid multiplexing methods to allow enhanced channel numbers.In this re-view,we have also included hybrid multiplexing techniques such as WDM-PDM,WDM-MDM and PDM-MDM.It is prob-able to attain N×M channels by utilizing N wavelengths and M guided-modes by simply utilizing hybrid WDM-MDM(de)multiplexers.To the best of our knowledge,this review paper is one of its kind which has highlighted the most prom-inent and recent signs of progress in multiplexing techniques in one place.

光交换的原理与实现

本文详细介绍了空分、时分、波分以及各种复合形式光交换的概念和所需关键器件的原理，给出了在目前技术条件下各种光交换单元的实现方案，并比较了它们的难易程度和优缺点．

Femtosecond laser additive and subtractive micro-processing:enabling a high-channeldensity silica interposer for multicore fibre to silicon-photonic packaging

Great strides have been made over the past decade to establish femtosecond lasers in advanced manufacturing systems for enabling new forms of non-contact processing of transparent materials.Research advances have shown that a myriad of additive and subtractive techniques is now possible for flexible 2D and 3D structuring of such materials with micro-and nano-scale precision.In this paper,these techniques have been refined and scaled up to demonstrate the potential for 3D writing of high-density optical packaging components,specifically addressing the major bottleneck for efficiently connecting optical fibres to silicon photonic(SiP)processors for use in telecom and data centres.An 84-channel fused silica interposer was introduced for high-density edge coupling of multicore fibres(MCFs)to a SiP chip.Femtosecond laser irradiation followed by chemical etching was further harnessed to open alignment sockets,permitting rapid assembly with precise locking of MCF positions for efficient coupling to laser written optical waveguides in the interposer.A 3D waveguide fanout design provided an attractive balancing of low losses,modematching,high channel density,compact footprint,and low crosstalk.The 3D additive and subtractive processes thus demonstrated the potential for higher scale integration and rapid photonic assembly and packaging of micro-optic components for telecom interconnects,with possible broader applications in integrated biophotonic chips or micro-displays.

Downlink MBER Transmit Beamforming Design Based on Uplink MBER Receive Beamforming for TDD-SDMA Induced MIMO Systems

The downlink minimum bit error rate (MBER) transmit beamforming is directly designed based on the uplink MBER receive beamforming solution for time division duplex (TDD) space-division multiple-access (SDMA) induced multiple-input multiple-output (MIMO) systems, where the base station (BS) is equipped with multiple antennas to support multiple single-antenna mobile terminals (MTs). It is shown that the dual relationship between multiuser detection and multiuser transmission can be extended to the rank-deficient system where the number of users supported is more than the number of transmit antennas available at the BS, if the MBER design is adopted. The proposed MBER transmit beamforming scheme is capable of achieving better performance over the standard minimum mean square error transmit beamforming solution with the support of low-complexity and high power-efficient MTs, particularly for rank-deficient TDD-SDMA MIMO systems. The robustness of the proposed MBER transmit beamforming design to the downlink and uplink noise or channel mismatch is investigated using simulation.

Distributed multicore fiber sensors

Multicore fiber(MCF)which contains more than one core in a single fiber cladding has attracted ever increasing attention for application in optical sensing systems owing to its unique capability of independent light transmission in multiple spatial channels.Different from the situation in standard single mode fiber(SMF),the fiber bending gives rise to tangential strain in off-center cores,and this unique feature has been employed for directional bending and shape sensing,where strain measurement is achieved by using either fiber Bragg gratings(FBGs),optical frequency-domain reflectometry(OFDR)or Brillouin distributed sensing technique.On the other hand,the parallel spatial cores enable space-division multiplexed(SDM)system configuration that allows for the multiplexing of multiple distributed sensing techniques.As a result,multi-parameter sensing or performance enhanced sensing can be achieved by using MCF.In this paper,we review the research progress in MCF based distributed fiber sensors.Brief introductions of MCF and the multiplexing/de-multiplexing methods are presented.The bending sensitivity of off-center cores is analyzed.Curvature and shape sensing,as well as various SDM distributed sensing using MCF are summarized,and the working principles of diverse MCF sensors are discussed.Finally,we present the challenges and prospects of MCF for distributed sensing applications.

论小区车位、车库权属规则的完善

虽然《物权法》第74条对小区车位、车库的权属进行了规定,但该条规定没有对不同种类的车位、车库进行区别规定,造成不同程度的困惑,而且,该条规定还存在其他一些弊端,需要加以改进和完善。

岩土破损演化理论(Ⅱ):物理状态指标与分区破损理论

指出当前利用CT数研究岩土力学的所有方法仅为观察研究,浪费了宝贵的CT定量化信息。利用集合论和测度论知识,基于CT数定义了岩土材料的λ水平破损比与λ水平破损率、(λ1-λ2)水平截理比及其截理率的概念,研究了λ水平破损率与CT数及密度的关系;研究了破损产生的位置和破损判据。基于破损空间截理的概念将岩土材料区分为安全区、损伤进行区和破损区,定义了损伤进行区下、上限边界面,给出了强化-弱化准则的定义,建立了岩土体分区破损本构关系,并进一步推导了岩土破损空间理论的基本方程。

Low-insertion-loss femtosecond laser-inscribed three-dimensional high-density mux/demux devices

Recently,transmitting diverse signals in different cores of a multicore fiber(MCF)has greatly improved the communication capacity of a single fiber.In such an MCF-based communication system,mux/demux devices with broad bandwidth are of great significance.In this work,we design and fabricate a 19-channel mux/demux device based on femtosecond laser direct writing.The fabricated mux/demux device possesses an average insertion loss of 0.88 dB and intercore crosstalk of no more than−29.1 dB.Moreover,the fabricated mux/demux device features a broad bandwidth across the C+L band.Such a mux/demux device enables low-loss 19-core fiber(de)multiplexing over the whole C+L band,showing a convincing potential value in wavelength-space division multiplexing applications.In addition,a 19-core fiber fan-in/fan-out system is also established based on a pair of mux/demux devices in this work.

Toward the Energy Efficiency of Resource Allocation Algorithms for OFDMA Downlink MIMO Systems

The problem of the simultaneous multi-user resource allocation algorithm in orthogonal frequency division multiple access(OFDMA)based systems has recently attracted significant interest.However,most studies focus on maximizing the system throughput and spectral efficiency.As the green radio is essential in 5G and future networks,the energy efficiency becomes the major concern.In this paper,we develop four resource allocation schemes in the downlink OFDMA network and the main focus is on analyzing the energy efficiency of these schemes.Specifically,we employ the advanced multi-antenna technology in a multiple input-multiple output(MIMO)system.The first scheme is based on transmit spatial diversity(TSD),in which the vector channel with the highest gain between the base station(BTS)and specific antenna at the remote terminal(RT)is chosen for transmission.The second scheme further employs spatial multiplexing on the MIMO system to enhance the throughput.The space-division multiple-access(SDMA)scheme assigns single subcarrier simultaneously to RTs with pairwise“nearly orthogonal”spatial signatures.In the fourth scheme,we propose to design the transmit beamformers based on the zero-forcing(ZF)criterion such that the multi-user interference(MUI)is completely removed.We analyze the tradeoff between the throughput and power consumption and compare the performance of these schemes in terms of the energy efficiency.

城市化的历史趋势与我国城镇化新政

城市化的历史必然性不仅在于配第-克拉克定理、库兹涅茨的劳动力和国民收入在产业间分布结构变动理论所揭示的农业的小部门化趋势,还在于"发展极"理论、"增长点"理论、产业集群理论、区位理论和主导产业联系效应理论等所揭示的城市强大的经济功能。现阶段,我国正处于城镇化加速期,中共中央十八届三中全会提出了走中国特色的城镇化道路、以人为核心的城镇化、城镇化与新农村建设协调推进等一系列城镇化新政,这对于我国城镇化的建设具有重大意义。

Ultra-wide dual-band Rydberg atomic receiver based on space division multiplexing radio-frequency chip modules

Detecting microwave signals over a wide frequency range is endowed with numerous advantages as it enables simultaneous transmission of a large amount of information and access to more spectrum resources.This capability is crucial for applications such as microwave communication,remote sensing and radar.However,conventional microwave receiving systems are limited by amplifiers and band-pass filters that can only operate efficiently in a specific frequency range.Typically,these systems can only process signals within a three-fold frequency range,which limits the data transfer bandwidth of the microwave communication systems.Developing novel atom-integrated microwave sensors,for example,radio-frequency(RF)chip–coupled Rydberg atomic receiver,provides opportunities for a large working bandwidth of microwave sensing at the atomic level.In the current work,an ultrawide dual-band RF sensing scheme was demonstrated by spacedivision multiplexing two RF-chip-integrated atomic receiver modules.The system can simultaneously receive dual-band microwave signals that span a frequency range exceeding 6 octaves(300 MHz and 24 GHz).This work paves the way for multi-band microwave reception applications within an ultra-wide range by RF-chip-integrated Rydberg atomic sensor.