Silicon-based optoelectronic heterogeneous integration for optical interconnection

The performance of optical interconnection has improved dramatically in recent years.Silicon-based optoelectronic heterogeneous integration is the key enabler to achieve high performance optical interconnection,which not only provides the optical gain which is absent from native Si substrates and enables complete photonic functionalities on chip,but also improves the system performance through advanced heterogeneous integrated packaging.This paper reviews recent progress of silicon-based optoelectronic heterogeneous integration in high performance optical interconnection.The research status,development trend and application of ultra-low loss optical waveguides,high-speed detectors,high-speed modulators,lasers and 2D,2.5D,3D and monolithic integration are focused on.

Sixteen-element Ge-on-SOI PIN photo-detector arrays for parallel optical interconnects

We describe the structure and testing of one-dimensional array parallel-optics photo-detectors with 16 photodiodes of which each diode operates up to 8 Gb/s. The single element is vertical and top illuminated 30μm-diameter silicon on insulator （Ge-on-SOI） PIN photodetector. High-quality Ge absorption layer is epitaxially grown on SO1 substrate by the ultra-high vacuum chemical vapor deposition （UHV-CVD）. The photodiode exhibits a good responsivity of 0.20 A/W at a wavelength of 1550 nm. The dark current is as low as 0.36/aA at a reverse bias of 1 V, and the corresponding current density is about 51 mA/cm2. The detector with a diameter of 30 t.trn is measured at an incident light of 1.55 μm and 0.5 mW, and the 3-dB bandwidth is 7.39 GHz without bias and 13.9 GHz at a reverse bias of 3 V. The 16 devices show a good consistency.

Short-Range Optical Wireless Communications for Indoor and Interconnects Applications

Optical wireless communications have been widely studied during the past decade in short-range applications, such as indoor highspeed wireless networks and interconnects in data centers and high-performance computing. In this paper, recent developments in high-speed short-range optical wireless communications are reviewed, including visible light communications （VLCs）, infrared indoor communication systems, and reconfigurable optical interconnects. The general architecture of indoor high-speed optical wireless communications is described, and the advantages and limitations of both visible and infrared based solutions are discussed. The concept of reconfigurable optical interconnects is presented, and key results are summarized. In addition, the challenges and potential future directions of short-range optical wireless communications are discussed.

DESIGN AND IMPLEMENTATION OF A GIGABIT PER SECOND OPTICAL INTERCONNECTION DATA LINK

The interconnection network is one of the key elements of distributed computing systems such as MPP (massively parallel processing) or NOWs (network of workstations).In this paper,a high speed optical interconnection data link which has been designed and implemented is presented.Using TDM (time division multiplexing),virtual parallel synchronous data transmission between the PCI buses of two computers has been achieved.The maximum data rate of the link is 1 250 Mbit/s,and the communication distance of link is more than 600 m using multi mode fibers.The design method of the high frequency electrical signals on the network interface card has been analyzed,and the efficient data transmission bandwidth of the link in different transmission modes has been tested and analyzed.

USING WAVELENGTH ROUTING IN THE OPTICAL INTERCONNECTION COMPUTER NETWORK

The wavelength routing technology applied to computer interconnection networks is introduced in this paper.By analyzing the relation between wavelength and network routing,we describe a concept of wavelength used as network IP address,and propose a wavelength routing topology to extend the scale of a network and realize the scalability of the network.Moreover,a twin wavelength ring network that is being developed in our laboratory to implement and test the function of wavelength routing is presented,and the main units of the twin wavelength ring network are presented also.According to the testing results based on a single wavelength ring network,it proves that the optical interconnection technology is a perfect technology to provide enough communication bandwidth for computer network.

The 8×10 GHz Receiver Optical Subassembly Based on Silica Hybrid Integration Technology for Data Center Interconnection

An 8×10 GHz receiver optical sub-assembly （ROSA） consisting of an 8-channel arrayed waveguide grating （AWG） and an 8-channel PIN photodetector （PD） array is designed and fabricated based on silica hybrid integration technology. Multimode output waveguides in the silica AWG with 2% refractive index difference are used to obtain fiat-top spectra. The output waveguide facet is polished to 45° bevel to change the light propagation direction into the mesa-type PIN PD, which simplifies the packaging process. The experimentM results show that the single channel I dB bandwidth of AWG ranges from 2.12nm to 3.06nm, the ROSA responsivity ranges from 0.097 A/W to 0.158A/W, and the 3dB bandwidth is up to 11 GHz. It is promising to be applied in the eight-lane WDM transmission system in data center interconnection.

Parallel Optical Interconnect Technology: Combination of Higher Performance and Lower Energy Consumption

This paper analyzes the physical potential, computing performance benefi t and power consumption of optical interconnects. Compared with electrical interconnections, optical ones show undoubted advantages based on physical factor analysis. At the same time, since the recent developments drive us to think about whether these optical interconnect technologies with higher bandwidth but higher cost are worthy to be deployed, the computing performance comparison is performed. To meet the increasing demand of large-scale parallel or multi-processor computing tasks, an analytic method to evaluate parallel computing performance ofinterconnect systems is proposed in this paper. Both bandwidth-limit model and full-bandwidth model are under our investigation. Speedup and effi ciency are selected to represent the parallel performance of an interconnect system. Deploying the proposed models, we depict the performance gap between the optical and electrically interconnected systems. Another investigation on power consumption of commercial products showed that if the parallel interconnections are deployed, the unit power consumption will be reduced. Therefore, from the analysis of computing influence and power dissipation, we found that parallel optical interconnect is valuable combination of high performance and low energy consumption. Considering the possible data center under construction, huge power could be saved if parallel optical interconnects technologies are used.

Review of the Low-Latency Optical Interconnect Technologies for Peta-Scale Computing

This paper reviews the recently developed optical interconnect technologies designed for scalable, low latency and high-throughput comunications within datacenters or high perforrmnce computers. The three typical architectures including the broadcast-and-select based Optical Shared Memory Supercomputer Interconnect System （OSMOSIS） switch, the defection routing based Data Vortex switch and the arrayed waveguide grating based Low-latency Interconnect Optical Network Switch （LIONS） switch are discussed in detail. In particular, we investigate the various Ioopback buffering technologies in LIONS and present a proof of principle testbed demonstration showing feasibility of LIONS architecture. Moreover, the performance of LIONS, Data Vortex and OSMOSIS with traditional state-of-the-art electrical switching network based on the Flattened-ButterFly （FBF） architecture in terms of throughput and latency are compared. The sinmlation based perfortmnce study shows that the latency of LIONS is almost independent of the number of input ports and does not saturate even at very high input load.

A Single Mode Hybrid Ⅲ-Ⅴ/Silicon On-Chip Laser Based on Flip-Chip Bonding Technology for Optical Interconnection

A single mode hybrid Ⅲ-Ⅴ/silicon on-chip laser based on the flip-chip bonding technology for on-chip optical interconnection is demonstrated. A single mode Fabry-Perot laser structure with micro-structures on an InP ridge waveguide is designed and fabricated on an InP/AIGaInAs multiple quantum well epitaxial layer structure wafer by using i-line lithography. Then, a silicon waveguide platform including a laser mounting stage is designed and fabricated on a silicon-on-insulator substrate. The single mode laser is flip-chip bonded on the laser mounting stage. The lasing light is butt-coupling to the silicon waveguide. The laser power output from a silicon waveguide is 1.3roW, and the threshold is 37mA at room temperature and continuous wave operation.

MSONoC: a non-blocking optical interconnection network for inter cluster communication

Electric router is widely used for multi-core system to interconnect each other. However, with the increasing number of processor cores, the probability of communication conflict between processor cores increases, and the data delay increases dramatically. With the advent of optical router, the traditional electrical interconnection mode has changed to optical interconnection mode. In the packet switched optical interconnection network, the data communication mechanism consists of 3 processes: link establishment, data transmission and link termination, but the circuit-switched data transmission method greatly limits the utilization of resources. The number of micro-ring resonators in the on-chip large-scale optical interconnect network is an important parameter affecting the insertion loss. The proposed λ-route, GWOR, Crossbar structure has a large overall network insertion loss due to the use of many micro-ring resonators. How to use the least micro-ring resonator to realize non-blocking communication between multiple cores has been a research hotspot. In order to improve bandwidth and reduce access latency, an optical interconnection structure called multilevel switching optical network on chip(MSONoC) is proposed in this paper. The broadband micro-ring resonators(BMRs) are employed to reduce the number of micro-ring resonators(MRs) in the network, and the structure can provide the service of non-blocking point to point communication with the wavelength division multiplexing(WDM) technology. The results show that compared to λ-route, GWOR, Crossbar and the new topology structure, the number of micro-ring resonators of MSONoC are reduced by 95.5%, 95.5%, 87.5%, and 60% respectively. The insertion loss of the minimum link of new topology, mesh and MSONoC structure is 0.73 dB, 0.725 dB and 0.38 dB.

Adaptive and Intelligent Digital Signal Processing for Improved Optical Interconnection

In recent years, explosively increasing data traffic has been boosting the con?tinuous demand of high speed optical interconnection inside or among data centers, high performance computers and even consumer electronics. To pursue the improved intercon?nection performance of capacity, energy efficiency and simplicity, effective approaches are demonstrated including particularly advanced digital signal processing (DSP) meth?ods. In this paper, we present a review about the enabling adaptive DSP methods for opti?cal interconnection applications, and a detailed summary of our recent and ongoing works in this field. In brief, our works focus on dealing with the specific issues for short-reach interconnection scenarios with adaptive operation, including signal-to-noise-ratio (SNR) limitation, level nonlinearity distortion, energy efficiency consideration and the de?cision precision.

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.

Tailoring light on three-dimensional photonic chips: a platform for versatile OAM mode optical interconnects

Explosive growth in demand for data traffic has prompted exploration of the spatial dimension of lightwaves, which provides a degree of freedom to expand data transmission capacity. Various techniques basedon bulky optical devices have been proposed to tailor light waves in the spatial dimension. However, theirinherent large size, extra loss, and precise alignment requirements make these techniques relativelydifficult to implement in a compact and flexible way. In contrast, three-dimensional (3D) photonic chips withcompact size and low loss provide a promising miniaturized candidate for tailoring light in the spatialdimension. Significantly, they are attractive for chip-assisted short-distance spatial mode optical interconnectsthat are challenging to bulky optics. Here, we propose and fabricate femtosecond laser-inscribed 3D photonicchips to tailor orbital angular momentum (OAM) modes in the spatial dimension. Various functions on theplatform of 3D photonic chips are experimentally demonstrated, including the generation, (de)multiplexing,and exchange of OAM modes. Moreover, chip-chip and chip–fiber–chip short-distance optical interconnectsusing OAM modes are demonstrated in the experiment with favorable performance. This work paves the wayto flexibly tailor light waves on 3D photonic chips and offers a compact solution for versatile opticalinterconnects and other emerging applications with spatial modes.

Strict non-blocking four-port optical router for mesh photonic network-on-chip

We report a strict non-blocking four-port optical router that is used for a mesh photonic network-on-chip on a silicon-on-insulator platform.The router consists of eight silicon microring switches that are tuned by the thermo-optic effect.For each tested rousting state,the signal-to-noise ratio of the optical router is larger than 13.8 dB at the working wavelength.The routing functionality of the device is verified.We perform 40 Gbps nonreturn to zero code data transmission on its 12 optical links.Meanwhile,data transmission using wavelength division multiplexing on eight channels in the C band(from 1525 to 1565 nm)has been adopted to increase the communication capacity.The optical router’s average energy efficiency is 25.52 fJ/bit.The rising times(10%to 90%)of the eight optical switch elements are less than 10μs and the falling times(90%-10%)are less than 20μs.

Influence on Multimode Rectangular Optical Waveguide Propagation Loss by Surface Roughness

Optical scattering loss coefficient of muhimode rectangular waveguide is analyzed in this work. First, the effective refrac tive index and the mode field distribution of waveguide modes are obtained using the Marcatili method. The influence on scattering loss coefficient by waveguide surface roughness is then analyzed. Finally, the mode coupling efficiency for the SMFOpticalWaveguide （SOW） structure and MMFOptical Waveguide （MOW） structure are presented. The total scatter ing loss coefficient depends on modes scattering loss coeffi cients and the mode coupling efficiency between fiber and waveguide. The simulation results show that the total scatter ing loss coefficient for the MOW structure is affected more strongly by surface roughness than that for the SOW struc ture. The total scattering loss coefficient of waveguide decreas es from 3.97 x 10^-2 dB/cm to 2.96 x 10^-4 dB/cm for the SOW structure and from 5.24 - 10^-2 dB/cm to 4.7 x 10^-4 dB/ cm for the MOW structure when surface roughness is from 300nm to 20nm and waveguide length is 100cm.

Ferroelectric Liquid Crystal Gates and Optical Computing

The surface stabilized ferroelectric liquid crystal device configuration and ferroelectric liquid crystal gates are described.The liquid crystal electrooptical gates have numerous applications,including optical computation,optodigital circuits,and optical communication networks.

基于深度神经网络的数据中心光互连网络资源分配方法

在人工智能环境下为了提高数据中心光互联网络组件和软件的安全性,需要构建优化的资源分配模型,提出基于深度神经网络的数据中心光互连网络资源分配方法。采用用户关联和功率谱分配联合优化方法构建数据中心光互连网络资源调度模型,结合对网络资源粒度的服务请求QoS资源配置实现对不同种类资源的融合和聚类处理,提取数据中心光互连网络资源的空间、时间、频谱等多维网格抽象模型参数,通过深度神经网络学习方法实现对网络资源分配过程中的多种资源粒度融合和收敛性寻优控制,建立用户之间分配数据中心光互连网络资源的信道模型,通过传输链路均衡配置方案实现对网络资源的优化分配和均衡配置。仿真结果表明,本方法的资源分配传输比特率为18 bit/s,延时较小,资源分配阻塞率低,为0.05%,且资源持有度较高,可始终维持在100%,说明本方法具有对较强的资源均衡配置能力。

多维光互连柔性光背板压力分布优化实验研究

【目的】文章旨在改进多层光纤布线结构,提高其抗压性能,进行压力分布优化实验研究,并提出一种多维光交叉互连柔性光背板压力分布优化结构和设计方法。【方法】文章通过改进多层光纤布线结构,利用实验分析不同光纤交叉方式,研究在相同压力下光纤排布、光纤交叉点的密度和光纤交叠层数等因素对光纤损耗的影响,由此提出一种优化光背板压力分布的双层背板理想光纤布线结构。【结果】由实验结果提出的理想双层布线结构采用双层背板和每个背板中的多层光纤优化布线,将两层柔性光背板进行上下叠加,光纤的布线方案采用光纤端口均匀分布在背板的4个边缘,且同一层级光纤紧密排布,交叠两层光纤于交叉点处。通过多层光纤交叉及错位叠加的布局,可实现多层光纤交叉互连布线优化分布,以提高光背板的抗压性能,从而提高其光传输交换的整体性能。【结论】文章所提方案光背板具有更小的体积、更好的抗压性能和更好的光信号传输损耗性能,能够实现更大面积、高密度和大容量柔性n×n光背板,具有良好的可拓展性,并使光纤布线工作更加简单和方便。

面向数据中心的超高速光模块板级信号完整性研究

【目的】人工智能的高速发展对数据中心算力提出了更高的要求。光模块作为数据中心光/电互连的核心器件,其设计也将迎来巨大挑战。随着光模块速率的不断提升,信号完整性问题成为制约光模块性能不可忽视的瓶颈。因此为了设计出满足数据中心光互连,特别是高性能计算场景速率要求的超高速光模块,需要对光模块内部高速链路进行优化设计。【方法】文章以一款双密度4通道小型可插拔(QSFP-DD)光模块设计方案为例,对光模块中影响信号完整性的因素进行了仿真优化。具体工作为,从理论角度分析了链路上引起信号完整性问题的部分,如过孔和球栅阵列(BGA)焊球,并讨论了优化这些性能的改进方法。特别是分析了针对50 GHz以上频段信号传输的优化方法,使高速链路能实现超高速4阶电平脉冲幅度调制(PAM4)信号低损耗传输。另外,还研究了整体高速通道的传输性能,并利用4端口矢量网络分析仪进行了测试。【结果】研究结果表明,该设计方案能够达到所需的传输带宽并且能有效削弱谐振。全通道仿真结果显示所有通道传输带宽内回波损耗低于-15 dB,插入损耗低于3 dB,可实现224 Gbit/s PAM4信号低损耗传输,同时测试结果与仿真结果基本相符,证明文章所提设计方案能满足数据中心高速光互连对光模块速率的需求。【结论】文章所提光模块信号完整性设计方法对今后超高速光模块设计具有重要的指导意义,同时也可以为其他各类高速电路设计提供参考。

光互连数据中心网络架构与业务路由技术研究

【目的】目前已提出的数据中心光互连网络结构中,大多将光网络用于交换机间的机架间通信,而机架内服务器之间的通信则通过电以太网交换机实现。由于电以太网交换机功率较大且数量众多,目前所提出的数据中心光互连网络存在能耗高、带宽低和分组时延大等问题。为了进一步改善数据中心光互连网络的性能,文章提出了一种基于可重排无阻塞三级Clos网络的机架内光互连网络结构。【方法】在此结构中,机架内服务器通过1个三级Clos网络实现相互连接,同时结合文章所提的多波长路由算法可实现机架内服务器间的无阻塞通信。【结果】文章使用OMNET++软件进行了仿真验证,结果显示,文章所提结构的吞吐量在同等条件下比传统机架内电交换提高20%,端到端平均时延减少90%,能耗减少67%。【结论】通过仿真对比可知,文章所提结构可以改善数据中心光互连网络的带宽利用、分组时延及能耗等性能。