Optical Interconnect Technology Research Articles

Higher-speed PONs based on data center technology and optics [Invited

Data center interconnects are currently the fastest growing market for optical interconnect technology and innovations. Data centers must upgrade their infrastructure regularly to keep up with increasing bandwidth demand from digital services. Successive Ethernet generations based on intensity-modulated direct-detection progressed to 50 GBd per lane and will reach 100 GBd per lane before the end of this decade. Also, the continued reduction in complexity, power consumption, and cost of coherent technologies will eventually lead to adoption of it in short-reach coherent in the intra-data center, which will further drive volumes of low-cost coherent technologies. Passive optical networks (PONs) depend mostly on the availability of high-volume, low-cost components. In this paper we will review the benefits as well as challenges to overcome in adoption of the Ethernet data center ecosystem as a low-power, cost-effective technology for next-generation time-division-multiplexed PONs.

Analysis of the Principle and State-of-art Applications of Si-Based Chip on Lidar

In recent years, as the feature size of transistors continues to decrease, Moore's Law is also approaching its limits. On this basis, In the post-Moore era, optical interconnect technologies with inherent attributes such as low latency, low power consumption, and low crosstalk have gained widespread attention in the industry. Silicon photonics technology has emerged, leveraging the accumulated knowledge from the silicon-based microelectronics industry over half a century. Optical phased arrays, unlike traditional mechanical-based lidar systems, offer advantages such as small size, low cost, and high accuracy. When combined with mature CMOS processes, they hold significant research value and market prospects. With this in mind, this study will discuss the principle as well as the state-of-art applications for Si-based chip on Lidar. According to the analysis, the current limitations are also demonstrated and suggestions are proposed based on the evaluations. Overall, these results shed light on guiding further exploration of chip developments on Lidar.

Routing and Wavelength Assignment for Multiple Multicasts in Optical Network-on-Chip (ONoC)

Optical Network-on-Chip (ONoC) is an emerging chip-scale optical interconnection technology to realize high-performance and power-efficient inter-core communication for many-core processors. Multicast communication is popularly used in parallel applications on chip. However, existing researches for multicast in ONoC mainly focus on the optimization of one multicast. This limits the practical applications of the research outcomes because we often face the dynamic formation of multiple multicast groups in real network systems. In this paper, we define the problem of routing and wavelength assignment for multiple multicasts in ONoC with the objective of minimizing the number of wavelengths required. To solve the problem, we first formulate it as an integer programming model for general topologies. Then we design routing policies for special instances that optimally use only one wavelength on mesh topology. For general instances, we design a Group-Partitioning Routing algorithm for Multiple Multicasts (GPRMM). GPRMM decouples a group of multicasts into a number of sub-groups, each of which matching one of the special instances. Theoretical results show that the number of wavelengths required by GPRMM is no more than the Destination Density σd, i.e., the maximum number of multicasts with destinations in the same row or column. Moreover, we find the upper bound and the lower bound on the number of wavelengths required for GPRMM. The wavelength requirement is also upper bounded by the network size n for an n×n mesh network. Simulation results show that GPRMM can reduce the number of wavelengths by 26.7% compared with previous methods. GPRMM has the advantages of low routing complexity, low wavelength requirement, low power consumption, and good scalability.

Direct ink writing 3D-printed optical waveguides for multi-layer interconnect.

Low-cost, short-range optical interconnect technology plays an indispensable role in high-speed board-level data communications. In general, 3D printing technology can easily and quickly produce optical components with free-form shapes, while the traditional manufacturing process is complicated and time-consuming. Here, we present a direct ink writing 3D-printing technology to fabricate optical waveguides for optical interconnects. The waveguide core is 3D printed optical polymethylmethacrylate (PMMA) polymer, with propagation loss of 0.21 dB/cm at 980 nm, 0.42 dB/cm at 1310 nm, and 1.08 dB/cm at 1550 nm, respectively. Furthermore, a high-density multilayer waveguide arrays, including a four-layer waveguide arrays with a total of 144 waveguide channels, is demonstrated. Error-free data transmission at 30 Gb/s is achieved for each waveguide channel, indicating that the printing method can produce optical waveguides with excellent optical transmission performance. We believe this simple, low-cost, highly flexible, and environmentally friendly method has great potential for high-speed short-range optical interconnects.

On Chip Polarization Beam Splitter Based on Inverse Design

With the gradual improvement of optical interconnection technology’s requirements for high-speed broadband transmission of data, multidimensional multiplexing technology must be used to meet the application scenarios. Among them, polarization multiplexing technology has opened up a higher multiplexing dimension, and the application prospects are very broad. Polarization beam splitters have received a lot of attention as a key device in polarization multiplexing technology. The polarization multiplexer designed by traditional design methods with the help of classical theory and empirical calculation generally has deficiencies such as excessive volume and complex design, which is not conducive to large-scale integration, and the introduction of inverse design can effectively solve this problem and improve design efficiency. In this paper, the polarization beam splitter is implemented by using the inverse design, which can realize the output of the modes TE0 and TM0 in the bus waveguide from the respective regional waveguides, and the integration of TE0 and TM0 in the respective branch waveguides into the fusion transmission in the bus waveguide, with a size of only 2.4μm × 2μm. At the same time, simulation experiments show that the insertion loss of the device in the operating wavelength range of 1520nm to 1580nm is less than 1.4dB, and the crosstalk value between channels is almost negligible because the core layer of 220nm is difficult to achieve polarization rotation.

Research progress of intelligent design of on-chip optical interconnection devices

<sec>Compared with traditional communication technologies such as electrical interconnection, optical interconnection technology has the advantages of large bandwidth, low energy consumption, anti-interference, etc. Therefore, optical interconnection is becoming an important approach and development trend of short distance and very short distance data terminal communication. As the chip level optical interconnection is implemented, silicon on insulator (SOI) based on-chip optical interconnection has been widely utilized with the support of a series of multiplexing technologies. In recent decades, many on-chip optical interconnection devices have been developed by using conventional design methods such as coupled-mode, multimode interference, and transmission line theories. However, when used in device design, these conventional methods often face the problems such as complex theoretical calculations and high labor costs. Many of the designed devices also encounter the problems of insufficient compactness and integration, and single function.</sec><sec>Intelligent design method has the advantages such as pellucid principle, high freedom of optimization, and good material compatibility, which can solve the problems of conventional design methods to a large extent. With the widespread use of intelligent design methods in the design of on-chip optical interconnection devices, three main trends have emerged. Firstly, the size of on-chip optical interconnect device is gradually developing towards ultra compact size. Secondly, the number of intelligently designed controllable on-chip optical interconnect devices is increasing. Thirdly, on-chip optical interconnect devices are gradually developing towards integration and systematization. This paper summarizes the most commonly used intelligent design methods of photonic devices, including intelligent algorithms based intelligent design methods and neural networks based intelligent design methods. Then, the above three important research advances and trends of intelligently designed on-chip optical interconnection devices are analyzed in detail. At the same time, the applications of phase change materials in the design of controllable photonic devices are also reviewed. Finally, the future development of intelligently designed on-chip optical interconnection devices is discussed.</sec>

Advanced photonic integrated circuit building blocks for reconfigurability in hyperscale data centres - INVITED

In this talk we introduce two new European projects DYNAMOS and ADOPTION, which will develop advanced integrated photonic technologies for WDM hyperscale data centre architectures including a novel stamped metallic micro-mirror array for advanced PIC-to-fibre coupling with the potential to dramatically reduce PIC design and assembly costs. We also discuss international standardization efforts for these corresponding optical interconnect technologies for future hyperscale data centre, HPC and 6G and Quantum environments.

Recent Progress and Prospect of Optical Interconnect Technologies

Recent Progress and Prospect of Optical Interconnect Technologies

Design, Manufacture and Assembly of 3D Integrated Optical Transceiver Module Based on an Active Photonic Interposer

The new generation of data centers is further evolving towards the direction of high speed and intelligence, which puts forward a great demand for the iteration of optical interconnection technology. Three-dimensional integration based on active photonic interposers can achieve the advantages of high integration, high bandwidth and low power consumption, which has become the main direction for next generation optical module technology. The fabrication and assembly of 3D optical modules based on active interposer-integrated edge couplers and TSV are realized in this paper. Different active interposer processes with integrated edge couplers and RDL-TSV-RDL structures are discussed, manufactured, analyzed and evaluated. The problem of the co-fabrication of the TSV and edge coupler was solved, and perfect electrical and optical characteristics were also achieved. Finally, the fabrication of the substrate and the assembly of the 3D optical module were completed. This paper lays a solid foundation for the further research and large-scale application of 3D optical modules in the future.

Scaling Optical Interconnects for Hyperscale Data Center Networks

Due to widespread applications and rapid development of cloud computing and Internet services, hyperscale data centers have experienced an unprecedented demand for networking. Data center networks are required not only to handle fast-growing traffic, which doubles almost every one to two years, but also to provide high flexibility and availability to support rapidly changing businesses as well. Therefore, hyperscale data center networks have become one of the main drivers for optical interconnect technologies in recent years. In this article, technologies for scaling optical interconnects for inter-data center interconnects (DCIs) are presented. We first describe hyperscale data center network architectures and requirements, as well as the differences between carrier’s optical transport networks and DCI optical networks, with the main focus on metro-DCI and campus-DCI networks. The scale and fast growth rates of DCI networks require innovations not only in data plane technologies but also in control and management planes as well. In data planes, high-capacity flexible coherent technology, pluggable wavelength-division-multiplexing (WDM) optical transponders, including 100G direct-detection four-level pulse-amplitude modulation (PAM4) and coherent 400ZR/800ZR, and flex-grid and disaggregated reconfigurable optical add-drop multiplexer (ROADM) optical networks are described. Control and management planes are an integral part of optical transport networks and crucial for effectively operating DCI networks. We show that standard protocols, data models, and modular design of a software platform are essential to building a scalable open and disaggregated optical network, which is fundamental to enabling high automation and intelligence in an optical network. An example control and management platform is discussed in detail. With current fiber capacity approaching the nonlinear Shannon limit, challenges to further scale DCI networks and some potential technologies to support ever-increasing traffic growth are discussed at the end.

Emerging Light-Emitting Materials for Photonic Integration.

The arrival of the information explosion era is urging the development of large-bandwidth high-data-rate optical interconnection technology. Up to now, the biggest stumbling block in optical interconnections has been the lack of efficient light sources despite significant progress that has been made in germanium-on-silicon (Ge-on-Si) and III-V-on-silicon (III-V-on-Si) lasers. 2D materials and metal halide perovskites have attracted much attention in recent years, and exhibit distinctive advantages in the application of on-chip light emitters. Herein, this Progress Report reviews the recent progress made in light-emitting materials with a focus on new materials, i.e., 2D materials and metal halide perovskites. The report briefly introduces the current status of Ge-on-Si and III-V-on-Si lasers and discusses the advances of 2D and perovskite light-emitting materials for photonic integration, including their optical properties, preparation methods, as well as the light sources based on these materials. Finally, challenges and perspectives of these emerging materials on the way to the efficient light sources are discussed.

Research of Optical Interconnection Technology in Datacenter Networks

In recent years, with rapid development of cloud computing, the business volume of datacenter has increased unprecedentedly and the development of datacenter is facing great challenges. At this point, more efficient interconnection schemes are needed to maintain the increasing demand for communication bandwidth. With its great bandwidth advantage, optical fiber provides low-loss and low-cost solutions for telecom networks. At the same time, compared with the electric interconnection based on copper wire, optical switching technology greatly improves the transmission rate of the communication network. In this paper, the interconnection structure of the datacenter network is studied. Aiming at the interconnection for different top-of-racks (ToR), the c-Through and Helios structures based on photoelectric hybrid technology are reported. Moreover, some structures based on all-optical interconnection such as Proteus, OSMOSIS and IRIS are mentioned. For the interconnection in ToR, arrayed waveguide grating (AWG) based passive optical interconnection and the passive optical couplers-based interconnection schemes are described. Meantime, the main principles, advantages and disadvantages of various structures are analyzed. Finally, the future development of optical interconnection applications is stated.

Recent Progress and Prospect of Optical Interconnect Technologies

Recent Progress and Prospect of Optical Interconnect Technologies

MNDM: MEMS-based N-dimensional modular hybrid data center network

The rapid development of virtualization technology and cloud computing technology for the data center has brought the explosive growth of business volume and scale. The data center network is facing new challenges, such as ultra-high bandwidth requirements and energy-efficiency. The introduction of optical interconnect technology improves the performance of data center networks by virtue of less cost of devices, complexity, power consumption. However, there are still three major problems when adopting optical switching, which are constraint of centralized control system, non-modularity and poor scalability. Aiming at these problems, this letter proposes a MEMS-based N-dimensional modular hybrid data center network (MNDM) and corresponding MEMS scheduling strategy. We evaluate the performance of MNDM via OPNET simulation and results demonstrate that the MNDM architecture is stable in saturation point of latency and saturation point of throughput when the network size changes or network traffic changes.

Cost-effective parallel optical interconnection module based on fully passive-alignment process

In optical interconnection technology, high-speed and large data transitions with low error rate and cost reduction are key issues for the upcoming 8K media era. The researchers present notable types of optical manufacturing structures of a four-channel parallel optical module by fully passive alignment, which are able to reduce manufacturing time and cost. Each of the components, such as vertical-cavity surface laser/positive-intrinsic negative-photodiode array, microlens array, fiber array, and receiver (RX)/transmitter (TX) integrated circuit, is integrated successfully using flip-chip bonding, die bonding, and passive alignment with a microscope. Clear eye diagrams are obtained by 25.78-Gb/s (for TX) and 25.7-Gb/s (for RX) nonreturn-to-zero signals of pseudorandom binary sequence with a pattern length of 231 to 1. The measured responsivity and minimum sensitivity of the RX are about 0.5 A/W and ≤−6.5 dBm at a bit error rate (BER) of 10−12, respectively. The optical power margin at a BER of 10−12 is 7.5 dB, and cross talk by the adjacent channel is ≤1 dB.

Thunderbolt Interconnect—Opitcal and Copper

Thunderbolt interconnect technology has adopted copper and optical cables. Single cable can support 2 × 20 Gb/s data rate, which is driven by 4K video. Future 8K video and virtual reality will push the bandwidth requirement even higher. Key technologies developed to enable this high data rate for consumer electronics are discussed, such as robust copper and optical cables, miniature optical engine, and 2 × 25.625 Gb/s low power integrated circuits for vertical cavity surface emitting laser based optical link. Copper and optical interconnect technologies are compared on the basis of cost, power, form factor, and scalability. Same circuit with four channels (4 × 25.625 Gb/s) can be used in 100G data center optical interconnect. Total power consumption is 146 mW for each 25.625 Gb/s optical link, which gives 5.69 mW/Gb/s. Among the commercially available optical ICs we evaluated at 25 Gb/s, this work has lowest power consumption and smallest die area in industry.

ハイパフォーマンスコンピュータにおける光インターコネクションの将来展望

ハイパフォーマンスコンピュータにおける光インターコネクションの将来展望

光インターコネクション技術の現状と将来展望

光インターコネクション技術の現状と将来展望

All-optical guided resonance tuning in hybrid GaN/Si microring induced by non-radiatively trapped injected hot electrons.

Advanced Si/III-V nanophotonics that emerged in the last decade has already founded the on-chip optical interconnect technology for future integrated systems on chip. New possibilities of light-on-chip applications beside signal transmissions, such as, all-optical sensing, have been given but small attention. Here, all-optical ultraviolet (UV)-sensitive guided resonance tuning in a hybrid GaN/Si microring resonator (HMR) was studied. Resonance redshifting by free-space UV pumping resulted in a 12 dB guided-mode modulation at the 1560 nm telecommunication wavelength. Investigations by experiments, theory, and simulations indicated the origin of the tuning mechanism from hot-electron heat extraction via defects-assisted non-radiative recombinations and electron-phonon interactions. A photothermal tuning efficiency of 73 pm/mW was attained at a pump power of 850 μW, thank to photothermal energy directly generated in the HMR. The UV-sensitive visible-blind all-optical tuning in the HMR may benefit all-optical UV sensing for the optical data era to come.

Low-Loss Passive Si$_{3}$N $_{4}$ Serial-to-WDM Interface for Energy-Efficient Optical Interconnects

The increasing number of computational servers in data centers is imposing tighter constraints on the networking infrastructure. Scalable power efficient optical interconnect network becomes necessary to leverage the bandwidth capacity of current electronic switches or opto-electronic components. Hence, novel optical interconnect technology can enhance the network capacity by harnessing the feasibility of simultaneous processing of optical signal in the wavelength and time domains. In this paper, we present a four channel optical passive wavelength-striped mapping (PWSM) device, which passively time compresses/expands serial packets through optical wavelength multiplexing/demultiplexing. The PWSM device, which has a 1 $\times$ 4 channel optical wavelength demultiplexer with integrated optical delay lines, is designed in a low-loss Si $_{3}$ N $_{4}$ (propagation loss $\sim$ 3.1 dB/m) waveguide platform. The PWSM device multiplexes/demultiplexes four WDM channels and offsets in time the adjacent channels to optically serialize/de-serialize data packets. In this demonstration, a 64 ns long data packet is formed at the output of the device by combining four 16 ns data segments of the packet in time domain. Incremental optical insertion loss between adjacent channels is $\sim$ 9.7 dB due to the integrated passive optical delay waveguides. The data rate of the four segmented packets and the combined packet is 25 Gb/sec. We have measured a bit error rate performance below 1 $\times 10^{-9}$ for the 64 ns serial data packet regenerated by the PWSM device for a received optical power of 6.7dBm.