A reconfigurable optical network on chip for streaming applications

We are delighted to introduce a Special Issue on Optical Interconnects for the IET Optoelectronics magazine. This issue presents the current status as well as some of the outstanding progress that has been witnessed in the rapidly evolving area of optical interconnects. Today, data centres (DC) and high-performance computers are struggling with limited interconnect capacity and increased power consumption while trying to meet overwhelming bandwidth demands. As photonics technologies have been rapidly maturing, optical interconnects have come into the spotlight as the means to cope with the emerging bandwidth, energy, and capacity needs. As such, a wealth of photonic interconnect solutions across the DC hierarchy has unfolded, covering from electro-optic boards to transceiver development, on-chip and on-board switches and interconnects as well as novel noninvasive monitoring methods for light controlling for compensating thermal crosstalk, fabrication tolerances and unstable environmental conditions. At the same time, the increased penetration of optical interconnects in short-reach communications, such as board and chip levels, has triggered new challenges in photonics technologies calling for new innovations with respect to integration techniques and packaging methods. This Special Issue of IET includes integrated circuits, assembly techniques, systems-level architectures, and controlling methods related to short reach ‘chip-to-chip’, ‘in-the-box’, and ‘box-to-box’ communications. Specific areas covered by this special issue include: Silicon photonic transceiver technologies and flat DC topologies; High-speed electro-optic hosting boards and fast, energy-efficient electronics; DC switches and co-packaged optic (CPO) technologies; and Noninvasive controlling techniques for complex photonic integrated circuits. The four papers in this special section promote high-performance optical interconnect architectures and key technologies to tackle the rising bandwidth demands of DCs. They cover (a) co-packaged DC optics, (b) silicon technology transceiver modules and high-speed hosting boards for multisocket server board (MSB) interconnects and (c) automated controlling architecture for complex photonic systems; Items (b) and (c) draw from impressive achievements accomplished through the recently completed European H2020 Project ICT-STREAMS. This report written by C. Mickenberg tries to shed light on motivating factors behind co-packaged optics (CPO), the trade-offs involved and their potential impact on data centre network architectures. The article reviews the evolution of DC switch application-specific integrated circuit (ASICs) and DC optics, provides a future road map and finally discusses the potential impact of CPO on the network architecture. This topic is covered by two articles. The first, written by M. Morallis-Pegios, proposes using silicon photonics to advance interconnect throughput, socket connectivity and energy efficiency in MSB layouts by enabling a flat-topology wavelength division multiplexing (WDM) point-to-point optical MSB interconnect scheme. WDM silicon photonic transceivers coassembled with their electronic circuits achieving a 50-Gb/s line rate and 400-Gb/s aggregate data transmission are demonstrated. The article also proposes silicon photonic Arrayed Waveguide Grating Router (AWGRs) that can offer collision-less time-of-flight connectivity for up to 16 nodes. The second article covering that area is written by T. Lamprecht and reports on the development of electro-optic hosting boards for on-board transceiver subassemblies which is required to eventually form the Tb/s multi-socket onboard communication. The article also discusses the electrical interface as well as photonic board requirements, including the manufacturing technique and the assembly concept that was followed to deliver terabyte per second multichip optical communication. This article, written by F. Zanetto, introduces a novel dithering technique for real-time control of multiple cascaded photonic integrated devices, proposing a calibration-free strategy to support the development and real-life diffusion of increasingly complex photonic systems. The article elaborates on the implementation of a calibration-free automated control loop exploiting integral controllers to close a real-time feedback and stabilise the optimum working point of the employed photonic devices. The effectiveness of the proposed architectural approach is experimentally validated with the error-free routing and transmission of a 30-Gbit/s optical signal traversing a cascade of micro-ring resonator filters. All of the articles selected for this Special Issue present a wide variety of key topics and significant results addressing optical interconnects in high-performance data communication systems, including new progress on architectures, systems and packaging techniques as well as novel optimised controlling methods. As guest editors, we would like to thank all of the authors for their high-quality submissions that significantly contribute to the optical interconnect field. We would also like to thank the reviewers for their valuable and constructive technical comments that greatly enhance the Special Issue, because their feedback and comments ensure the high quality of the IET Optoelectronics Journal. We hope that this IET Special Issue will provide a useful reference of the state-of-the-art in optical interconnects to readers, and we anticipate such technological perspectives will stimulate new advancements and technological outcomes that will in turn enrich the growing field of optical interconnects. This work was supported by the E.C. through the H2020-ICT-STREAMS research project (688172).

Effect of high-pressure grinding rolls pretreatment on the preparation of vanadium-titanium magnetite pellets

The rapid scaling of microprocessor technologies has led to unprecedented advancements in processing speed and transistor density. However, as device dimensions shrink below the nanometre scale, traditional electrical on-chip interconnects face critical limitations including increased signal delay, power consumption, and reduced bandwidth. These challenges have emerged as major bottlenecks in the performance and energy efficiency of modern microprocessors, especially in multi-core and many-core architectures. To overcome these limitations, optical interconnects have gained significant attention as a high-performance alternative for on-chip and chip-to-chip communication. Optical interconnects offer key advantages such as higher data rates, lower latency, reduced power dissipation, and immunity to electromagnetic interference. The integration of optical components like waveguides, modulators, photodetectors, and silicon photonics within the chip architecture has the potential to revolutionize interconnect design by addressing the shortcomings of conventional electrical wiring. This paper explores the evolution of on-chip interconnects, comparing the performance, scalability, and integration challenges of electrical and optical solutions in scaled microprocessors. It also discusses emerging hybrid interconnect architectures that combine the strengths of both technologies. A comparison is made between electrical and optical interconnects for different design criteria, based on projections about the future of optical devices. Around a tenth of the length of the chip's edge is the crucial dimension beyond which optical connectivity becomes preferable to electrical interconnect at the 22 nm technological node.

Wavelength multiplexing and tuning capabilities are highly important for applications in optical interconnects and optical communications using wavelength division multiplexing (WDM). We review novel methods and experimental results to achieve these functions in vertical cavity surface-emitting lasers (VCSEL), we believe for the first time. By implementing spatially chirped layers in the laser cavities and obliquely aligning the array axes to the thickness chirp direction, we obtained 7 × 20 VCSEL array emitting 140 unique, non-redundant, controllable, uniformly separated single-mode wavelengths. A large total wavelength span of 43 nm is obtained without compromising the performance of the lasers. Moreover, our techniques are generic and can be readily extended to other wavelength regimes. In addition, we describe our work on wavelength-tunable VCSELs with a 1.8-nm (~540 GHz) continuous tuning and no mode hopping. The laser output power remains nearly constant throughout the tuning range. The wavelength tuning speed is ~400 ns. The multiple wavelength tunable laser arrays are promising for achieving ultrahigh bandwidth (hundreds Gbit/sec to Tbit/sec), high redundancy and reliability, reconfigurable optical networks.

As the infrastructure of cloud computing and big data, data centers have been deployed widely. Then, how to make full use of the computing and storage resources in data centers will be the focus. Data center networks are considered important solution for the problem above, which include intra-data center and inter-data center networks. Both of them will depend on the optical networking due to its advantages, such as high bandwidth, low latency, and low energy consumption. Data center interconnected by flexi-grid optical networks is a promising scenario to allocate spectral resources for applications in a dynamic, tunable and efficient control manner. Compared with inter-data center, optical interconnect in intra-data center networks is a more pressing need and promising scenario to accommodate these applications in a dynamic, flexible and efficient manner. OpenFlow based Software Defined Networking (SDN) is considered as a good technology, which is very suitable for data center networks. This paper mainly focuses on the data center optical networks based on software defined networking (SDN), which can control the heterogeneous networks with unified resource interface. Architecture and experimental demonstration of OpenFlow-based optical interconnects in intra-data center Networks and OpenFlow-based flexi-grid optical networks for inter-data center are presented in the paper respectively. Some future works are listed finally.

The switching and routing is essential for an advanced and reconfigurable optical network, and great efforts have been done for traditional single-mode system. We propose and demonstrate an on-chip switch compatible with mode-division multiplexing system. By controlling the induced phase difference, the functionalities of dynamically routing data channels can be achieved. The proposed switch is experimentally demonstrated with low insertion loss of ~1 dB and high extinction ratio of ~20 dB over the C-band for OFF-ON switchover. For further demonstration, the non-return-to-zero on-off keying signals at 10 Gb/s carried on the two spatial modes are successfully processed. Open and clear eye diagrams can be observed and the bit error rate measurements indicate a good data routing performance.

In this paper, we discuss TCP (transport control protocol data transfers over a reconfigurable optical network. We find the throughput to be diminished by false detection of congestion by TCP congestion control and avoidance mechanisms.

Multi-core systems-on-chip are becoming state-of-the-art. Therefore, there is a need for a fast and energy-efficient interconnect to take full advantage of the computational capabilities. Integration of silicon photonics with a traditional electrical interconnect in a Network-on-Chip (NoC) proposes a promising solution for overcoming the scalability issues of electrical interconnect. In this article, we derive and evaluate prediction modeling techniques for the design space exploration (DSE) of application-specific communication architectures for an Optical Network-on-Chip (ONoC). Our proposed model accurately predicts network packet latency, contention delay, and the static and dynamic energy consumption of the network. This work specifically addresses the challenge of accurately estimating performance metrics of the entire design space without having to perform time-consuming and computationally intensive exhaustive simulations. The proposed technique, based on machine learning (ML), can build accurate prediction models using only 10% to 50% (best case and worst case) of the entire design space. The accuracy, expressed as R 2 (Coefficient of Determination) is 0.99901, 0.99967, 0.99996, and 0.99999 for network packet latency, contention delay, static energy consumption, and dynamic energy consumption, respectively, in six different benchmarks from the Splash-2 benchmark suite, chosen among 6 different machine learning prediction models.

Vertical-cavity surface-emitting lasers (VCSELs) have been widely used in short-reach optical communication links and interconnects because of their high modulation speed and low energy consumption. In this paper, the effect of heat dissipation on the modulation bandwidth of high-speed 850-nm VCSELs has been investigated. With increasing bottom distributed Bragg reflector (DBR) diameter from 34 μm to 46 μm, optical output power increased as well as the −3 dB modulation bandwidth. The maximum small-signal modulation bandwidth of 16.2 GHz was achieved with an aperture of 5 μm. Thermal analysis showed that the heat dissipation of the bottom DBR diameter, which determined the differential gain of the quantum wells, has a strong effect on the modulation bandwidth.

Apache Hadoop has evolved significantly over the last years, with more than 60 releases bringing new features. By implementing the MapReduce programming paradigm and leveraging HDFS, its distributed file system, Hadoop has become a reliable and fault tolerant middleware for parallel and distributed computing over large datasets. Nevertheless, Hadoop may struggle under certain workloads, resulting in poor performance and high energy consumption. Users increasingly demand that high performance computing solutions address sustainability and limit energy consumption. In this paper, we introduce HDFSH, a hybrid storage mechanism for HDFS, which uses a combination of Hard Disks and Solid-State Disks to achieve higher performance while saving power in Hadoop computations. HDFSH brings to the middleware the best from HDs (affordable cost per GB and high storage capacity) and SSDs (high throughput and low energy consumption) in a configurable fashion, using dedicated storage zones for each storage device type. We implemented our mechanism as a block placement policy for HDFS, and assessed it over six recent releases of Hadoop with different architectural properties. Results indicate that our approach increases overall job performance while decreasing the energy consumption under most hybrid configurations evaluated. Our results also showed that, in many cases, storing only part of the data in SSDs results in significant energy savings and execution speedups.

Direct aqueous mineral carbonation of carbide slag in a bubble column reactor under ambient conditions

This primary purpose of this study is to investigate the impact of energy intensity (EI), total primary energy consumption per capita (EC), renewable energy consumption (REW) and CO2 emissions, which are among the energy security elements, on GDP in Turkiye. Additionally, population (POP) and trade openness (TO) rates are control variables in the model. The analysis of the study consists of annual data from 1980 to 2022. The fully modified ordinary least squares (FMOLS) and dynamic ordinary least squares (DOLS) approaches were used in this study to estimate long-term models. The study also employed the canonical cointegrating regression (CCR) method as a robust estimator. The estimated results of the study indicate that energy security has strongly affects on GDP in Turkiye. Accordingly, primary energy consumption, renewable energy consumption, and CO2 emissions have positive effects on GDP. In addition, energy intensity affects GDP negatively, as expected. An energy policy that supports low energy intensity and high renewable energy consumption can be a pioneer of sustainable growth. However, the positive impact of primary energy consumption and CO2 on GDP indicates that environmental degradation may increase in Turkiye's economic growth process. In other words, economic growth also depends on factors that cause energy insecurity. Therefore, it is important to develop policies that support energy security (high renewable energy consumption, low carbon emissions, low energy intensity, and low primary energy consumption). Moreover, as expected, trade openness and population support economic growth in Turkiye.

We present an array of electro-optic Bragg gratings for on-chip optical waveguide interconnect applications. These electro-optical gratings can serve as switchable couplers to couple high-speed optical signals from a vertical cavity surface emitting lasers (VCSEL) to on-chip polymeric waveguides and from waveguides to photodetectors. The unique switching feature provides a promising solution to facilitate dynamically reconfigurable on-chip optical interconnects architecture for intra-chip, chip-to-chip and board-to-board data communications. We demonstrate on-chip switched optical waveguide interconnect using electro-optic grating and polymeric channel waveguides on a silicon substrate.

As CMOS technology is scaled, it has become increasingly difficult for conventional copper interconnect to satisfy different design requirements. On-chip optical interconnect has been considered as a potential substitute for electrical interconnect. In this paper, predictions of the performance of CMOS compatible optical devices are made based on current state-of-art optical technologies. Based on these predictions, electrical and optical interconnects are compared for delay uncertainty, latency, power, and bandwidth density

The present and the potential performances of opto-electronic elements such as a laser diode (LD), a photo diodes (PD) and an optical waveguide for optical interconnects are described. The fabrication and the integration technologies of the opto-electronic chips are also mentioned. The topics to be highlighted include: (1) the state of the art of vertical cavity surface emitting laser diodes for optical interconnects, (2) the performance analysis of the optical interconnects with integrated optical waveguides and free space optics, and (3) opto-electronic integration technology: hybrid-integration technique, receiver and transmitter design for on-chip and intra-chip optical interconnects.