Building the data rate out of smaller baud rates

In the second article addressing the challenges of increasing the symbol rate of coherent optical transport systems, Professor Andrew Lord, BT’s head of optical network research, argues that the time is fast approaching to consider alternative approaches.

Coherent discourse 2

Coherent optical transport systems have advanced considerably in the last decade to cope with the relentless growth of internet traffic.

Professor Andrew Lord

One-hundred-gigabit wavelengths, long the networking standard, have been replaced by 400-gigabit ones while state-of-the-art networks now use 800 gigabits.

Increasing the data carried by a single wavelength requires advancing the coherent digital signal processor (DSP), electronics and optics.

It also requires faster symbol rates.

Moving from 32 to 64 to 96 gigabaud (GBd) has increased the capacity of coherent transceivers from 100 to 800 gigabits.

Last year, Acacia, now part of Cisco, announced the first 1-terabit-plus wavelength coherent modem that uses a 128GBd symbol rate.

Other vendors will also be detailing their terabit coherent designs, perhaps as soon as the OFC show, to be held in San Diego in March.

The industry consensus is that 240GBd systems will be possible towards the end of this decade although all admit that achieving this target is a huge challenge.

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Huawei sets transmission record with new modulator

Coherent discourse: Part 1

A paper from Huawei and Sun Yat-Sen University in the January issue of the Optica journal describes a thin-film lithium niobate modulator. The modulator enabled a world-record coherent optical transmission, sending nearly 2 terabits of data over a single wavelength.

Maxim Kuschnerov

Much of the industry’s focus in recent years has been to fit coherent optical technology within a pluggable module.

Such pluggables allow 400-gigabit coherent interfaces to be added to IP routers and switches, serving the needs of the data centre operators and telecom operators.

But research labs of the leading optical transport vendors continue to advance high-end coherent systems beyond 800-gigabit-per-wavelength transmissions.

Optical transport systems from Ciena, Infinera and Huawei can send 800-gigabit wavelengths using a symbol rate of 96-100 gigabaud (GBd).

Acacia Communications, part of Cisco, detailed late last year the first 1.2-terabit single-wavelength coherent pluggable transceiver that will operate at 140GBd, twice the symbol rate of 400-gigabit modules such as 400ZR. 

Now Huawei has demonstrated in the lab a thin-film lithium niobate modulator that supports a symbol rate of 220GBd and beyond.

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Nvidia's plans for the data processor unit

When Nvidia’s CEO, Jensen Huang, discussed its latest 400-gigabit BlueField-3 data processing unit (DPU) at the company’s 2021 GTC event, he also detailed its successor.

Companies rarely discuss chip specifications two generations ahead; the BlueField-3 only begins sampling next quarter.

BlueField-3 die. Source: Nvidia

The BlueField-4 will advance Nvidia’s DPU family. It will double again the traffic throughput to 800 gigabits-per-second (Gbps) and almost quadruple the BlueField-3’s integer processing performance.

But one metric cited stood out. The BlueField-4 will increase by nearly 1000x the number of terabit operators-per-second (TOPS) performed: 1,000 TOPS compared to the BlueField-3’s 1.5 TOPS.

Huang said artificial intelligence (AI) technologies will be added to the BlueField-4, implying that the massively parallel hardware used for Nvidia’s graphics processor units (GPUs) are to be grafted onto its next-but-one DPU.

Why add AI acceleration? And will it change the DPU, a relatively new processor class?

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Books read in 2021: Final Part

In the final favoured reads during 2021, the contributors are Daryl Inniss of OFS, Vladimir Kozlov of LightCounting Market Research, and Gazettabyte’s editor.

Daryl Inniss, Director, Business Development at OFS

Four thousand weeks is the average human lifetime.

The book by Oliver Burkeman: Four Thousand Weeks: Time Management For Mortals is a guide to using the finite duration of our lives.

Burkeman argues that by ignoring the reality of our limited lifetime, we fill our lives with busyness and distractions and fail to achieve the very fullness that we seek.

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Intel sets a course for scalable optical input-output

• Intel is working with several universities to create building-block circuits to address its optical input-output (I/O) needs for the next decade-plus.

• By 2024 the company wants to demonstrate the technologies achieving 4 terabits-per-second (Tbps) over a fibre at 0.25 picojoules-per-bit (pJ/b).

Intel has teamed up with seven universities to address the optical I/0 needs for several generations of upcoming products.

The initiative, dubbed the Intel Research Center for Integrated Photonics for Data Centre Interconnects, began six months ago and is a three-year project.

No new location is involved, rather the research centre is virtual with Intel funding the research. By setting up the centre, Intel’s goal is to foster collaboration between the research groups.

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PCI-SIG releases the next PCI Express bus specification

The Peripheral Component Interconnect Express (PCIe) 6.0 specification doubles the data rate to deliver 64 giga-transfers-per-second (GT/s) per lane.

For a 16-lane configuration, the resulting bidirectional data transfer capacity is 256 gigabytes-per-second (GBps).

Al Yanes

“We’ve doubled the I/O bandwidth in two and a half years, and the average pace is now under three years,” says Al Yanes, President of the Peripheral Component Interconnect Special Interest Group (PCI-SIG).

The significance of the specification’s release is that PCI-SIG members can now plan their products.

Users of FPGA-based accelerators, for example, will know that in 12-18 months there will be motherboards running at such rates, says Yanes.

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Books read in 2021: Part 4

In Part IV, two more industry figures pick their reads.

Michael Hochberg, a silicon photonics expert and currently at a start-up in stealth mode, discusses classical Greek history, while Professor Laura Lechuga, a biosensor luminary highlights Michael Lewis's excellent book about the pandemic, among others. 

Leonidas, King of Sparta 

Michael Hochberg, President of a stealth-mode start-up

One of the primary ways that I mis-spent my youth was by crawling through my father's library of social science and history books.  This activity generally occurred when I was supposed to be asleep, resting up for a full day of stark and abject boredom in school. This resulted in some perverse outcomes, like my tendency to fall asleep in class at an unusually young age.

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