Waveguide Grating Router Research Articles

Direct Optical Convolution Computing Based on Arrayed Waveguide Grating Router

AbstractOptical convolution computing is gaining traction owing to its inherent parallelism, multi‐dimensional processing, and energy efficiency. To handle input dimensions of N, conventional implementations necessitate N2 optical elements, such as Mach–Zehnder interferometers or micro‐ring resonators, to process multiply‐accumulate (MAC) operations, limiting scalability and resulting in elevated power consumption. Here, a direct convolution computing method based on wavelength routing, utilizing the unique sliding property of an arrayed waveguide grating router (AWGR) to perform the sliding window operation of the convolution in the wavelength–space domains is proposed. With two input vectors directly loaded onto two modulator arrays, the convolution result is instantaneously produced at a photodetector array. The entire convolution computation is executed within a single clock cycle without the need for preprocessing or decomposition into elementary MAC operations. The number of active elements is minimal, only needed for input/output. The proposed optical convolution unit has striking advantages of high scalability, high speed, and processing simplicity compared to those based on optical matrix‐vector multipliers. In the first experimental demonstration, a remarkable classification accuracy of up to 98.2% in handwritten digit recognition tasks using a LeNet‐5 neural network is achieved.

ODRAD: An optical wireless DCN dynamic-bandwidth reconfiguration with AWGR and deep reinforcement learning

The rapid growth of Data Center Network (DCN) traffic has brought new challenges, such as limited bandwidth, high latency, and packet loss to existing DCNs based on electrical switches. Because of its theoretically unlimited bandwidth and faster data transmission speeds, optical switching can overcome the problems of electrically switched DCNs. Additionally, numerous research works have been devoted to optical wired DCNs. However, static and fixed-topology DCNs based on optical interconnects significantly limit their flexibility, scalability, and reconfigurability to provide adaptive bandwidth for traffic with heterogeneous characteristics. In this study, we propose and conduct performance evaluations on a reconfigurable optical wireless DCN architecture based on distributed Software-Defined Networking (SDN), Deep Reinforcement Learning (DRL), Semiconductor Optical Amplifier (SOA), and Arrayed Waveguide Grating Router (AWGR). Our architecture is called ODRAD (which stands for Optical Wireless DCN Dynamic-bandwidth Reconfiguration with AWGR and Deep Reinforcement Learning). A Mininet simulation model is established to further verify the reconfigurability of the ODRAD network for various server scales. Based on experimental verification, ODRAD achieves an average end-to-end server latency of 5.2μs under a load of 99%. Compression results demonstrate a 17.36% improvement in packet rate latency performance compared to RotorNet and a 15.21% improvement compared to OPSquare at a load of 99% as the ODRAD network scales from 2,560 to 40,960 servers. Furthermore, ODRAD exhibits effective throughput across different routing protocols, DCN scales and loads.

Re-routable and Low-latency All Optical Switching Algorithm for Next Generation DCN

Digital infrastructure is now indispensable to the function of society and quality of life of the citizen. All over the world there is leveraging of digital infrastructure that comprises use of data, computerized devices, methods and systems. During COVID-19 pandemic it comes more prominently in front. India being the most popular and populated country in the world, comprises nearly half billion internet users expected to transform the digital ecosystem. With the increasing demand of smartphone application, online activities gigantic amount of data has been generated, so evolution and development of data centers be the high importance not only for India but as well as for the world. Thus, it is the need to promote and create robust data center network infrastructure that supports emerging technologies such as 5G, IoT, AI, machine learning, adaptive manufacturing, smart agriculture, and automation and so on. In this paper we propose an all Optical re-routable, low latency Data Center Network (DCN) architecture using Passive Optical Datacenter Switch (PODS). The PODS consists of an Arrayed Waveguide Grating Router (AWGR) in association with a controller unit. An efficient wavelength assignment algorithm is integrated in PODS, to reroute the packet for congestion avoidance and packet loss.. This feature makes the DCN architecture more scalable, proficient with high throughput, low latency, power efficient under high traffic and bursty traffic conditions. The performance of the proposed PODS-based DCN is compared with existing passive optical DCN architectures PODCA and finds improved characteristics in terms of delay, throughput and blocking probability. Simulation of the framework is done in Python platform and executed on google COLAB in the Windows environment and the result shows 46.3% improvement in latency and throughput in terms of 90% network load compared with PODCA architecture.

A 51 Gb/s Reconfigurable mmWave Fiber-Wireless C-RAN Supporting 5G/6G MNO Network Sharing

The growing demand for ubiquitous broadband connectivity in 5G/6G Radio Access Networks (RANs) has turned Centralized RAN (C-RAN) and reconfigurable Point-to-MultiPoint (PtMP) network topologies into the mainstream approach for keeping pace with the vastly increasing traffic capacities and connection densities. Relying on an all-passive Arrayed Waveguide Grating Router (AWGR), we propose and demonstrate reconfigurable allocation of multiple parallel Fiber-Wireless (FiWi) millimeter wave (mmWave) analog (Intermediate Frequency over Fiber) IFoF interfaces. The proposed technology provides a framework for the implementation of reconfigurable multiple FiWi backhaul /midhaul/fronthaul (X-haul) connections. The use of AWGR enables wavelength slicing and the co-existence of multiple transport links over the same X-haul network infrastructure. The proposed concept is experimentally validated by two sets of experimental measurements. More specifically a 4λ- Wavelength-Division Multiplexed (WDM) signals modulated by IFoF signals are routed through the AWGR and wirelessly transmitted over the air across a 1m V-band distance by two different pairs of mmWave 60 GHz antennas. In the first experiment, a Phased Array Antenna (PAA) operating at 60 GHz is utilized achieving a 2.5 Gb/s data rate per wavelength and beam pair with an Error Vector Magnitude (EVM) of less than 12.5% and an aggregate 10 Gb/s traffic capacity. The achieved performance meets for the first time the respective 5G Key Performance Indicator (KPI) requirements for EVM quality and peak data traffic while supporting the link reconfiguration wavelength routing and mmWave beam direction. In the second experiment, the PAA is replaced by a point-to-point 60 GHz link utilizing a high-end mm-wave transmitter, thus achieving a data rate of 12.75 Gb/s per wavelength-beam with an EVM of less than 6.5% and an aggregate capacity of 51 Gb/s. To this end, the proposed solution is shown to form a promising roadmap toward flexible and reconfigurable 5G/6G mmWave C-RAN architectures where multiple Mobile Network Operators (MNOs) can share the same network infrastructure and dynamically allocate fiber, antenna beams and wavelengths.

Effective switchless inter-FPGA memory networks

FPGA network bandwidth increases to 400 Gbps or higher by high-density optical integration, e.g., Co-Packaged Optics (CPO) and onboard Si-photonics transceivers. This study presents its lightweight switchless network architecture by exploiting an indirect path, consisting of up to k one-hop paths for a diameter-k network topology. It integrates interconnection network and memory channels into a lightweight memory-to-memory inter-FPGA network. It has a uni-directional network topology for connecting the largest number of FPGAs. A newly introduced indirect flow control enables lossless uni-directional networks. We present multi-path point-to-point communications, multi-port message-combine collective communications, and efficient WDM (Wavelength Division Multiplexing) cabling method for the uni-directional networks. We implement and evaluate the uni-directional switchless network on an FPGA cluster consisting of six custom Stratix10 MX2100 FPGA cards connected with a 16-wavelength Arrayed Waveguide Grating (AWG) router. Simulation results show that the multi-port message-combine collective communication achieves 7× faster than conventional communication with 272 FPGAs. Effective WDM cabling using 16 wavelengths decreases the number of cables by 88% compared with parallel optical cabling for 272 FPGAs.

Monolithically Integrated 8 × 8 Transmitter-Router Based on Tunable V-Cavity Laser Array and Cyclic Arrayed Waveguide Grating Router

A monolithic 8 × 8 transmitter-router chip fabricated on InGaAlAs-InP multi-quantum well wafer for distributed wavelength routing network in the O-band with a channel spacing of 400 GHz is experimentally demonstrated. A tunable V-cavity laser (VCL) array, a cyclic-arrayed waveguide grating router (AWGR) and a semiconductor amplifier (SOA) array are integrated using the quantum-well intermixing (QWI) technique for its fabrication simplicity and cost effectiveness. A 200 GHz-spaced compact-size VCL is demonstrated with a 27 nm tuning range and a side-mode suppression ratio (SMSR) around 40 dB using a single-electrode controlled tuning. The chip output power is 24.6 mW. Measurement results of the transmitter-router chip show that all 64 input-output combinations have cyclic response spectra. After passing through the SOA with 80 mA bias current, an output power of about 9.6 mW and optical signal-to-noise ratio (OSNR) up to 39 dB have been measured. The demonstrated transmitter-router chip is fabricated on the same quantum well structure without requiring multiple epitaxial growth and complex grating fabrication. The characteristics of multi-wavelength and multi-port transmissions enable the distributed optical routing networks with flexible bandwidth allocation, which can find wide application in datacenters and high-performance computers.

Low-Latency Optical Wireless Data-Center Networks Using Nanoseconds Semiconductor-Based Wavelength Selectors and Arrayed Waveguide Grating Router

In order to meet the massively increasing requirements of big-data applications, data centers (DCs) are key infrastructures to cope with the associated demands, such as high performance, easy scalability, low cabling complexity and low power consumption. Many research efforts have been dedicated to traditional wired data center networks (DCNs). However, DCNs’ static and rigid topology based on optical cables significantly limits their flexibility, scalability, and even reconfigurability. The limitations of this wired connection can be addressed with optical wireless technology, which avoids cable complexity problems while allowing dynamic adaption and fast reconfiguration. Here, we propose and investigate a novel optical wireless data-center network (OW-DCN) architecture based on nanoseconds semiconductor optical amplifier (SOA)-based wavelength selectors and arrayed waveguide grating router (AWGR) controlled by fast field-programmable gate array (FPGA)-based switch schedulers. The full architecture, including the design, packet-switching strategy, contention solving methodology, and reconfiguration capability, is presented and demonstrated. Dynamic switch scheduling with a FPGA-based switch scheduler processing optical label and software-defined network (SDN)-based reconfiguration were experimentally confirmed. The proposed OW-DCN was also achieved with a power penalty of less than 2 dB power penalty at BER < 1 × 10−9 for a 50 Gb/s OOK transmission and packet-switching transmission.

Multimedia Encrypted Experiment of Reconfigurable Wavelength Hopping Protection against Eavesdroppers over a Wireless Wavelength Division Multiplexing Network

To enhance the video transmission security of a physical layer over wireless optical communication, an optical switch configured in front of an arrayed waveguide grating (AWG) router is proposed for implementing reconfigurable wavelength hopping configuration over a wavelength division multiplexing network for protection against eavesdropping. In the practical experiment of an AWG/optical-switch-based random wavelength hopping scheme, a simulated pseudorandom noise generator algorithm was designed and embedded into a master‐slave microprocessor (e.g., Arduino chips) to generate a time series of electrical signals for triggering an optical switch. The path of the optical switch was randomly varied to change the space transmission of the AWG router. Therefore, varying wavelengths were assigned as the carriers of authorized users to realize the AWG/optical-switch-based wavelength hopping scheme. An optical spectrum analyzer and an oscilloscope were used for monitoring measurement. The experimental results indicated that eavesdroppers cannot accurately interpret analog, digital, audio, and uncompressed high-definition multimedia interface signals of 10 MHz, 1 MHz, 3.125 MHz (encoded into 6.25 MHz), and 1.485 GHz, respectively. According to the experimental results, authorized and unauthorized users are characterized by a large difference in the retrieved energy signal, which ensures the safety and privacy of the proposed AWG/optical-switch-based reconfigurable wavelength hopping scheme over a wireless optical communication network.

25.6 Tbps Capacity and Sub-µsec Latency Switching for DataCenters Using >1000-Port Optical Packet Switch Architectures

We discuss the challenges and limitations of current electrical DataCenter switches towards scaling beyond the 25.6 Tb/s capacity-era while meeting a low-latency and high-radix envelope. With the high-power SerDes and required DSP interfaces forming critical scaling factors, we discuss the perspectives and challenges of migrating to Optical Packet Switch (OPS) technologies for avoiding the electronically-induced bottlenecks, while exploiting reliable and practical techniques for overcoming well-known OPS problems, like buffering and high-port connectivity. We demonstrate the feasibility of OPS schemes by reporting experimental results of our Hipoλaos architecture towards extending its line-rate to 25 Gb/s per port and enabling 25.6 Tb/s switch capacities through a 1024-radix layout, while still preserving sub-μs latency metrics. Experimental results are presented for both unicast and multicast packets, employing the 1024-radix Hipoλaos architecture in a fully-fledged FPGA-controlled switching Plane, along with a 32 × 32 Arrayed Waveguide Grating Router (AWGR) device. The unicast performance is validated through BER measurements, while optical multicasting to 5 nodes is also experimentally evaluated at 25 Gb/s, along with an evaluation of the broadband multicast capabilities of the switch. Moreover, a mixed-traffic scenario involving both unicast and multicast traffic is demonstrated. Finally, a discussion about the perspectives and challenges of bringing OPS in DC networks is presented.

WDM-Based Silicon Photonic Multi-Socket Interconnect Architecture With Automated Wavelength and Thermal Drift Compensation

A silicon photonic circuit comprising all the building blocks necessary to demonstrate optical communication between two sockets interconnected through an Arrayed Waveguide Grating Router (AWGR) is reported. The article focuses on the robustness of the interconnection scheme to the unavoidable wavelength and thermal fluctuations observed in real datacenter environments. To improve the reliability of the system, a feedback control mechanism, based on contactless integrated photonic probes (CLIPP) and heater actuators, is added to the interconnection to monitor in parallel the working point of each sensitive device and keep it locked in real-time. Experimental results demonstrate successful operations in a 30 Gbit/s data routing scenario at $\text{5}\cdot \text{10}^{-11}$ bit error rate, irrespective of sudden wavelength shifts of up to 200 pm or of iterated thermal variations in a 10 $^\circ$ C temperature range, with a recovery time of around 30 ms. These results prove that AWGR-based interconnections equipped with real-time drift compensation systems can be a viable option in multi-socket layouts even in highly demanding environments.

400 Gb/s Silicon Photonic Transmitter and Routing WDM Technologies for Glueless 8-Socket Chip-to-Chip Interconnects

Arrayed Waveguide Grating Router (AWGR)-based interconnections for Multi-Socket Server Boards (MSBs) have been identified as a promising solution to replace the electrical interconnects in glueless MSBs towards boosting processing performance. In this article, we present an 8-socket glueless optical flat-topology Wavelength Division Multiplexing (WDM)-based point-to-point (P2P) interconnect pursued within the H2020 ICT project ICT-STREAMS and we report on our latest achievements in the deployment of the constituent silicon (Si)-photonic transmitter and routing building blocks, exploiting experimentally obtained performance metrics for analyzing the 8-socket chip-to-chip (C2C) connectivity in terms of throughput and energy efficiency. We demonstrate an 8-channel WDM Si-photonic microring-based transmitter (Tx) capable of providing 400 (8 × 50) Gb/s non-return-to-zero (NRZ) Tx capacity and an 8 × 8 Coarse-WDM (CWDM) Si-AWGR with verified cyclic data routing capability in O-band. Following an overview of our recently demonstrated crosstalk (XT)-aware wavelength allocation scheme, that enables fully-loaded AWGR-based interconnects even for typical sub-optimal XT values of silicon integrated CWDM AWGRs, we validate the performance of a full-scale 8-socket interconnect architecture through physical layer simulations exploiting experimentally-verified simulation models for the underlying Si-photonic Tx and routing circuits. This analysis reveals a total aggregate capacity of 1.4 Tb/s for an 8-socket interconnect when operating with 25 Gb/s line-rates, which can scale to 2.8 Tb/s at an energy efficiency of just 5.02 pJ/bit by exploiting the experimentally verified building block performance at 50 Gb/s line. This highlights the perspectives for up to 69% energy savings compared to the standard QuickPath Interconnect (QPI) typically employed in electronic glueless MSB interconnects, while scaling the single-hop flat connectivity from 4- to 8-socket interconnection systems.

提高损耗均匀性的氮氧化硅阵列波导光栅路由器

提高损耗均匀性的氮氧化硅阵列波导光栅路由器

Silicon photonic 8 × 8 cyclic Arrayed Waveguide Grating Router for O-band on-chip communication.

We report an 8 × 8 silicon photonic integrated Arrayed Waveguide Grating Router (AWGR) targeted for WDM routing applications in O-band. The AWGR was designed for cyclic-frequency operation with a channel spacing of 10 nm. The fabricated AWGR exhibits a compact footprint of 700 × 270 μm2. Static device characterization revealed 3.545 dB maximum channel loss non-uniformity with 2.5 dB best-case channel insertion losses and 11 dB channel crosstalk, in good agreement with the simulated results. Successful data routing operation is demonstrated with 25 Gb/s signals for all 8 × 8 AWGR port combinations with a maximum power penalty of 2.45 dB.

Performance improvement for silicon-based arrayed waveguide grating router

We analyze the impact of aberration on spectral performance of silicon-based arrayed waveguide grating (AWG) router with the conventional design using a constant pitch along the grating circle for the array waveguides near the free propagation region (FPR), and simulation results show that due to existence of large aberration, side lobes occur in spectral responses of peripheral output channels for the center input light while more serious side lobes appear in most output channels within a free spectral range (FSR) for the edge channel input. Therefore, there is a high crosstalk in conventional N × N silicon AWG, which is very detrimental for router applications. In order to address it, a simple design with a constant projected period on a line tangent to the grating at its pole for the array waveguides near the FPR is proposed, and aberrations of all output wavelengths within a FSR are kept at a rather low level both for the center and edge input. Then we fabricate two kinds of AWG routers with the conventional and proposed design respectively on a SOI wafer, and experimental results show that spectral responses of the AWG router with the proposed design are significantly improved compared to those obtained in the conventional design, especially for the edge channel input.

Sub-GHz Resolution Photonic Spectral Processor and Its System Applications

A record performance metric waveguide grating router (WGR) design with a 200 GHz free spectral range (FSR) capable of resolving sub-GHz resolution spectral features is developed for a fine resolution photonic spectral processor (PSP). The WGR's FSR was designed to support subchannel add/drop from a superchannel of 1 Tb/s capacity. Due to fabrication imperfections, we introduce phase corrections to the light beams emerging from the 250 waveguides of the WGR output using a liquid crystal on silicon (LCoS) phase spatial light modulator (SLM) placed in an imaging configuration. A second LCoS SLM is located at the Fourier plane, for arbitrary spectral amplitude and phase manipulations. The PSP is utilized in multiple system transmission experiments, such as flexible spectral shaping and subcarrier drop demultiplexing with sub-GHz spectral resolution.

Fine Resolution Photonic Spectral Processor Using a Waveguide Grating Router With Permanent Phase Trimming

Spectrally dispersed light from a fine resolution waveguide grating router (WGR) of 25-GHz free spectral range that radiates to free space is spatially filtered at ~1 GHz optical resolution and 50 MHz spectral addressability using a liquid crystal on Silicon (LCoS) spatial light modulator (SLM). Fabrication imperfections leading to phase errors on the 32 waveguide arms of the WGR are corrected using a UV pulsed laser to inscribe permanent optical path changes to the waveguides. WGR phase errors are permanently trimmed waveguide-by-waveguide with an excimer laser by inducing stress in the glass cladding above the waveguide for coarse setting and using the photosensitivity effect for fine setting. The WGR was then mated with an LCoS SLM located at the Fourier plane to form a photonic spectral processor, for arbitrary spectral amplitude and phase manipulations.

ADON: a scalable AWG-based topology for datacenter optical network

With the development of cloud computing and other online applications, data centers holding hundreds of thousands of servers need to handle massive amounts of data and the network traffic has increased significantly. These services have driven a new design of data center networks to improve network capacity. In this paper, we propose ADON, an Arrayed Waveguide Grating Router (AWGR) based scalable data center network architecture. There are two ways to extend the ADON include adding more clusters in the same layer and adding more layers. ADON alleviates the problem of scalability. It can support more servers than Fat Tree. Moreover ADON exploits the wavelength routing characteristic of the AWGR fabric and resolves contention in the optical domain. An experimental platform based on OPNET is built to test the performance of ADON. The simulation results show that not only ADON guarantees such merits as high throughput and low latency than Fat Tree, it also improves the availability rate of the equipment and reduces the construction cost of the network appreciably compared with Petax.

A Scalable, Low-Latency, High-Throughput, Optical Interconnect Architecture Based on Arrayed Waveguide Grating Routers

This paper proposes, simulates, and experimentally demonstrates an optical interconnect architecture for large-scale computing systems. The proposed architecture, Hierarchical Lightwave Optical Interconnect Network (H-LION), leverages wavelength routing in arrayed waveguide grating routers (AWGRs), and computing nodes (or servers) with embedded routers and wavelength-specific optical I/Os. Within the racks and clusters, the interconnect topology is hierarchical all-to-all exploiting passive AWGRs. For the intercluster communication, the proposed architecture exploits a flat and distributed Thin-CLOS topology based on AWGR-based optical switches. H-LION can scale beyond 100 000 nodes while guaranteeing up to 1.83×saving in number of inter-rack cables, and up to 1.5×saving in number of inter-rack switches, when compared with a legacy three-tier Fat Tree network. Network simulation results show a system-wide network throughput reaching as high as 90% of the total possible capacity in case of synthetic traffic with uniform random distribution. Experiments show 97% intracluster throughput for uniform random traffic, and error-free intercluster communication at 10 Gb/s.

Low-loss and low-crosstalk 8 × 8 silicon nanowire AWG routers fabricated with CMOS technology.

Low-loss and low-crosstalk 8 × 8 arrayed waveguide grating (AWG) routers based on silicon nanowire waveguides are reported. A comparative study of the measurement results of the 3.2 nm-channel-spacing AWGs with three different designs is performed to evaluate the effect of each optimal technique, showing that a comprehensive optimization technique is more effective to improve the device performance than a single optimization. Based on the comprehensive optimal design, we further design and experimentally demonstrate a new 8-channel 0.8 nm-channel-spacing silicon AWG router for dense wavelength division multiplexing (DWDM) application with 130 nm CMOS technology. The AWG router with a channel spacing of 3.2 nm (resp. 0.8 nm) exhibits low insertion loss of 2.32 dB (resp. 2.92 dB) and low crosstalk of -20.5~-24.5 dB (resp. -16.9~-17.8 dB). In addition, sophisticated measurements are presented including all-input transmission testing and high-speed WDM system demonstrations for these routers. The functionality of the Si nanowire AWG as a router is characterized and a good cyclic rotation property is demonstrated. Moreover, we test the optical eye diagrams and bit-error-rates (BER) of the de-multiplexed signal when the multi-wavelength high-speed signals are launched into the AWG routers in a system experiment. Clear optical eye diagrams and low power penalty from the system point of view are achieved thanks to the low crosstalk of the AWG devices.

A scalable silicon photonic chip-scale optical switch for high performance computing systems

This paper discusses the architecture and provides performance studies of a silicon photonic chip-scale optical switch for scalable interconnect network in high performance computing systems. The proposed switch exploits optical wavelength parallelism and wavelength routing characteristics of an Arrayed Waveguide Grating Router (AWGR) to allow contention resolution in the wavelength domain. Simulation results from a cycle-accurate network simulator indicate that, even with only two transmitter/receiver pairs per node, the switch exhibits lower end-to-end latency and higher throughput at high (>90%) input loads compared with electronic switches. On the device integration level, we propose to integrate all the components (ring modulators, photodetectors and AWGR) on a CMOS-compatible silicon photonic platform to ensure a compact, energy efficient and cost-effective device. We successfully demonstrate proof-of-concept routing functions on an 8 × 8 prototype fabricated using foundry services provided by OpSIS-IME.