Active Optical Cables Research Articles

RIFL: a reliable link layer network protocol for data center communication

More and more latency-sensitive services and applications are being deployed into the data center. Performance can be limited by the high latency of the network interconnect. Because the conventional network stack is designed not only for a local area network, but also for a wide area network, it carries a great amount of redundancy that is not required in a data center network. This paper introduces the concept of a three-layer protocol stack that can fulfill the exact demands of data center network communications. The detailed design and implementation of the first layer of the stack, which we call RIFL, is presented. A novel low latency in-band hop-by-hop re-transmission protocol is proposed and adopted in RIFL, which guarantees lossless transmission in a data center environment. Experimental results show that RIFL achieves 110 ns point-to-point latency on 10 m active optical cables, at a line rate of 112 Gbps. RIFL is a multi-lane protocol with scalable throughput up to multi-hundred gigabits per second. It can be the enabler of low latency, high throughput, flexible, scalable, and lossless data center networks.

Split-enabled 350–630 Gb/s optical interconnect with direct detection NOMA-CAP and 7-core multi-core fiber

The ever-growing data traffic volume inside data centers caused by the popularization of cloud services and edge computing demands scalable and cost-efficient network infrastructures. With this premise, optical interconnects have recently gained more and more research attention as a key building block to ensure end-to-end energy efficient solutions, offering high throughput, low latency and reduced energy consumption compared to current networks based on active optical cables. An efficient way for performing such optical interconnects is to make use of multi-core fibers (MCFs), which enables the multiplexing of several spatial channels, each using a different core inside the same fiber cladding. Moreover, non-orthogonal multiple access combined with multi-band carrierless amplitude and phase modulation (NOMA-CAP) has been recently proposed as a potential candidate to increase the network capacity and an efficiency/flexibility resource management. In this paper, using direct detection we experimentally demonstrate the transmission of NOMA-CAP signals through a 2 km MCF with 7 spatial channels for high capacity optical interconnect applications. The results show negligible transmission penalty for different total aggregated traffics ranging from 350 Gb/s to 630 Gb/s.

Advantages of Active Optical Cables for Industrial Applications

AbstractActive optical cables transmit signals using photons instead of electrons. A couple of advantages arise when using optical fibers instead of copper wires when transmitting high speed data signals over extended reach. When using optical cables with standard electrical interfaces, with protocols such as USB or the Thunderbolt∗) protocol, they can be seamlessly used with existing devices. At the same time, new applications and system architectures will come up, which will benefit from optical fiber communication technologies.

A 10-Meter Active Optical Cable Utilizing POF With 4 × 10-Gb/s CMOS Transceiver Chipsets

This paper presents a 10-m active optical cable (AOC) utilizing a graded-index plastic optical fiber (POF) for HDMI applications, where 4-channel 10-Gb/s/ch transceiver chipsets were implemented in 0.13-μm CMOS process and integrated upon a FR4 PC-board within pluggable connectors. Passive optical alignment comprising optical devices, optical subassembly, and POF was precisely located within the tolerance range of +/-10 μm, leading to successful mass-production. The transmitter (Tx) includes a VCSEL driver exploiting equalization and feedforward pre-emphasis to support 10-Gb/s data modulation. Also, a novel input data detector is proposed to turn on/off VCSEL diodes automatically for longer sustainability and lower power consumption. The receiver (Rx) employs a double-gain feedforward transimpedance amplifier followed by a selectable two-stage equalizer to choose either 6-Gb/s or 10-Gb/s operations, depending upon the specified HDMI applications. Also, a simple dc offset current cancellation and a novel monitor circuit are proposed for stable biasing and to keep tracking the average photocurrent of each photodiode. Measured results of Tx demonstrate 5.6-mA bias currents and 6.0-mAPP modulation currents, consuming 21.25 mA in maximum, whereas Rx provides 56.7-dBΩ transimpedance gain, 6-GHz bandwidth, and -10.4-dBm optical sensitivity for 10 -12 BER with 21.2 mA current consumption. The 10-meter POF AOC demonstrates wide and clean eye-diagrams up to 10 Gb/s, successfully showing 8-Mpixel 60-fps video data stream.

A 25.78-Gbit/s × 4-ch Active Optical Cable with Ultra-Compact Form Factor for High-Density Optical Interconnects

A 25.78-Gbit/s × 4-ch active optical cable (AOC) with an ultra-compact form factor is proposed. The size of the proposed AOC is 5.2 cm3, which is 55% smaller than the standard form factor of Quad Small Form-factor Pluggable (QSFP28), and 45% smaller than that of Micro Quad Small Form-factor Pluggable (μQSFP). As a result of utilizing a high-efficiency heat-dissipation structure and optimizing signal transmission lines and ground vias, the proposed AOC achieves high-heat dissipation and low-crosstalk characteristics. Furthermore, the proposed AOC demonstrated 25.78-Gbit/s error-free optical transmission over a 100-m Optical Multimode 3 (OM3) multimode fiber under all-channels (4-ch) operation and case temperature (Tc) of 70 °C.

A 4-Channel 6.25-Gb/s/ch VCSEL Driver for HDMI 2.0 Active Optical Cables

This paper presents a 4-channel common-cathode VCSEL driver array operating up to 6.25 Gb/s per channel for the applications of HDMI 2.0 active optical cables. The proposed VCSEL driver consists of an input buffer, a modified Cherry-Hooper amplifier as a pre-driver, and a main driver with pre-emphas...

From Chip to Cloud: Optical Interconnects in Engineered Systems

The high-performance server compute landscape is changing. The traditional model of building general-purpose enterprise compute boxes that end-users can configure with storage and networking to assemble their desired compute environments, has evolved to purpose-built systems optimized for specific applications. This tight integration of hardware and software components together with high-density midboard optical modules and an optical backplane allows for unprecedented levels of switching and compute efficiencies and has fueled the penetration of optical interconnects deep “inside the box,” particularly for switch scale-up. We briefly review earlier 40 G/port switching systems based on active optical cables, and present our newest system: An all-optically-interconnected 100 G/port 8.2 Tb/s InfiniBand packet switch ASIC with 41 ports running 100 Gb/s per port interconnected by 12-channel midboard optical transceivers with 25 Gb/s per channel per direction of optical I/O. Using a blind-mate optical backplane, these components enable systems with up to 50 Tb/s bandwidth in a 2U standard rack mount configuration with industry-leading density, efficiency, and latency. For even tighter co-integration of optical interconnects with switch and processor ASICs, we discuss photonic multichip module and interposer packaging technologies that will further improve system energy efficiencies and overcome impending system I/O bottlenecks.

25-Gbps/ch Error-Free Operation over 300-m MMF of Low-Power-Consumption Silicon-Photonics-Based Chip-Scale Optical I/O Cores

Aiming to solve the input/output (I/O) bottleneck concerning next-generation interconnections, 5 × 5-millimeters-squared siliconphotonics-based chip-scale optical transmitters/receivers (TXs/RXs)— called “optical I/O cores”—were developed. In addition to having a compact footprint, by employing low-power-consumption integrated circuits (ICs), as well as providing multimode-fiber (MMF) transmission in the O band and a user-friendly interface, the developed optical I/O cores allow common ease of use with applications such as multi-chip modules (MCMs) and active optical cables (AOCs). The power consumption of their hybrid-integrated ICs is 5mW/Gbps. Their high-density user-friendly optical interface has a spot-size-converter (SSC) function and permits the physical contact against the outer waveguides. As a result, they provide large enough misalignment tolerance to allow use of passive alignment and visual alignment. In a performance test, they demonstrated 25-Gbps/ch error-free operation over 300-m MMF. key words: Si photonics, low-power-consumption, small footprint, high density interface, I/O bottleneck

Focus on silicon photonics

Si photonics has attracted much interest over the last decade as it allows integration of photonic and electronic devices on a small Si chip, providing high-capacity, energy-efficient, and cost-effective optical interconnects. Active optical cables based on Si photonics are now commercially available for rack-to-rack interconnects in supercomputers and data centers. Shorter reach optical interconnects, i.e., inter- and intra-chip optical interconnects, have been studied as the next challenge for higher speed computing. Science and technology of advanced materials is essential for rapid development in this field, and therefore it is very appropriate to publish this focus issue in STAM.This focus issue introduces state-of-the-art material and device technologies in Si photonics. The topics cover not only technologies for the optical interconnects but also optical sensing as a novel application.We are grateful to the authors who contributed to this focus issue, and hope that it will help researchers understand the frontiers of Si photonics, stimulating novel concepts in material and device technologies, as well as novel developments in and applications of Si photonics.

Optical Interconnect Networks for Data Communications

In this invited tutorial paper, we review the changing nature of data center networks and the role played by optoelectronics in future network designs. Conventional network protocols will be reviewed, including Ethernet, Fibre Channel, and InfiniBand, and requirements for WAN connectivity between data centers. The transition to converged networks based on lossless Ethernet will be discussed, including FCoE and RoCE protocols. Industry roadmaps for bandwidth, port density, and scalability of optical links will be presented, and optical transceiver form factors including QSFP, CFP, and active optical cables will be discussed. The role of software defined networking (SDN) in next generation data center networks will also be presented in this context.

Comparison of Modulation Schemes for 10.7 Gb/s Transmission Over Large-Core 1 mm PMMA Polymer Optical Fiber

The authors give an overview of experimental results on 10.7 Gb/s over large-core 1 mm polymethyl-methacrylate (PMMA) polymer optical fiber (POF). The comparison starts with simple non-return-to-zero (NRZ) transmission without equalization. Next, measurement results with feed-forward-, decision -feedback equalization (FFE, DFE) and maximum likelihood sequence estimation (MLSE) are presented. Finally, experimental results with more advanced modulation schemes like pulse amplitude modulation (PAM) and discrete multitone (DMT) modulation are investigated. The experiments were carried out with a Vertical-Cavity Surface-Emitting Laser (VCSEL) at 0 dBm to comply with consumer eye-safety regulation or with a 10 mW laser diode (LD) that could be used in active optical cables.

Petabit Photonic Internet

A review of today's understanding of the ultimately broadband photonic Internet is presented. A simple calculation shows a throughput estimate of a core photonic network. The role of photonics is increasing in the development of a physical layer in the future Internet. Photonics leads to better usage of the available bandwidth measured in b/s/Hz, increase in the transmission rate from Tbps to Pbps, increase in the transmission distance without signal regeneration in distortion compensated active optical cables, as well as increase in energy/power efficiency measured in W/Gbps. Photonics also leads to fully transparent, low-noise, optical networks and to an increase in bandwidth and network reliability. It is expected that photonics will build a new kind of EM cloud interface between humans and the future global network. The following optical signal multiplexing methods were considered, which are possible without the O/E/O conversion: OTDM, CO-OFDM, OCDM-OCDMA, UDWDM. Full text: PDF

Active Optical Cables 2010 Market Report

Active optical cables are those that employ some form of powered amplification in order to overcome deficiencies in more traditional “passive” copper cables. Active optical cable revenue is expected to build significant revenue growth over the next five years.

Micro integration of optical components for the fabrication of active optical cables

Optical interconnects have become very interesting for short reach data transfer. We examine a new concept for integration and miniaturization of such systems based on recent experiments. The application of these designs is an active optical cable. The advantages of the concept and the employed technologies are presented.

Optical lasers in a $100 cable. Really

As homes go high definition, copper will give way to active optical cables.