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April 17, 2024

Coherent Transceivers at a Low Latency

Latency, the time it takes for data to travel from its source to its destination,…

Latency, the time it takes for data to travel from its source to its destination, is a critical metric in modern networks. Reducing latency is paramount in the context of 5G and emerging technologies like edge computing.

Smaller data centers placed locally (also called edge data centers) have the potential to minimize latency, overcome inconsistent connections, and store and compute data closer to the end-user. Various trends are driving the rise of the edge cloud:

5G technology and the Internet of Things (IoT): These mobile networks and sensor networks need low-cost computing resources closer to the user to reduce latency and better manage the higher density of connections and data.
Content delivery networks (CDNs): The popularity of CDN services continues to grow, and most web traffic today is served through CDNs, especially for major sites like Facebook, Netflix, and Amazon. By using content delivery servers that are more geographically distributed and closer to the edge and the end user, websites can reduce latency, load times, and bandwidth costs as well as increasing content availability and redundancy.
Software-defined networks (SDN) and Network function virtualization (NFV): The increased use of SDNs and NFV requires more cloud software processing.
Augment and virtual reality applications (AR/VR): Edge data centers can reduce streaming latency and improve the performance of AR/VR applications. Cloud-native applications are driving the construction of edge infrastructure and services. However, they cannot distribute their processing capabilities without considerable investments in real estate, infrastructure deployment, and management.

Several of these applications require lower latencies than before, and centralized cloud computing cannot deliver those data packets quickly enough. Let’s explore what changes are happening in edge networks to meet these latency demands and what impact will that have on transceivers.

The Different Latency Demands of the Cloud Edge

As shown in Table 1, a data center on a town or suburb aggregation point could halve the latency compared to a centralized hyperscale data center. Enterprises with their own data center on-premises can reduce latencies by 12 to 30 times compared to hyperscale data centers.

Types of Edge Data Centres

Types of Edge	Data center	Location	Number of DCs per 10M people	Average Latency	Size
On-premises edge	Enterprise site	Businesses	NA	2-5 ms	1 rack max
Network (Mobile)	Tower edge	Tower	Nationwide	3000	10 ms	2 racks max
Outer edge	Aggregation points	Town	150	30 ms	2-6 racks
Inner edge	Core	Major city	10	40 ms	10+ racks
Regional edge	Regional edge	Regional	Major city	100	50 ms	100+ racks
Not edge	Not edge	Hyperscale	State/national	1	60+ ms	5000+ racks

Types of Edge

Data center

Location

Number of DCs per 10M people

Average Latency

Size

On-premises edge

Enterprise site

Businesses

NA

2-5 ms

1 rack max

Network (Mobile)

Tower edge

Tower

Nationwide

3000

10 ms

2 racks max

Outer edge

Aggregation points

Town

150

30 ms

2-6 racks

Inner edge

Core

Major city

10

40 ms

10+ racks

Regional edge

Regional

Major city

100

50 ms

100+ racks

Not edge

Hyperscale

State/national

1

60+ ms

5000+ racks

Types of edge data centers and their characteristics. Source: STL Partners

Cisco estimates that 85 zettabytes of useful raw data were created in 2021, but only 21 zettabytes were stored and processed in data centers. Edge data centers can help close this gap. For example, industries or cities can use edge data centers to aggregate all the data from their sensors. Instead of sending all this raw sensor data to the core cloud, the edge cloud can process it locally and turn it into a handful of performance indicators. The edge cloud can then relay these indicators to the core, which requires a much lower bandwidth than sending the raw data.

Using Coherent Technology in the Edge Cloud

As edge data center interconnects became more common, the issue of interconnecting them became more prominent. Direct detect technology had been the standard in data center interconnects. However, reaching distances greater than 50km and bandwidths over 100Gbps required for modern edge data center interconnects required external amplifiers and dispersion compensators that increased the complexity of network operations.

At the same time, advances in electronic and photonic integration allowed longer-reach coherent technology to be miniaturized into QSFP-DD and OSFP form factors. This progress allowed the Optical Internetworking Forum (OIF) to create the 400ZR and ZR+ standards for 400G DWDM pluggable modules. With modules that are small enough to pack a router faceplate densely, the datacom sector could profit from a 400ZR solution for high-capacity data center interconnects of up to 80km. The rise of 100G ZR technology takes this philosophy a step further, with a product aimed at spreading coherent technology further into edge and access networks.

How Does Latency in the Edge Affect DSP Requirements?

The traditional disadvantage of coherent technology vs direct detection is that coherent signal processing takes more time and computational resources and, therefore, introduces more latency in the network. Adapting to the latency requirements of the network edge might, especially in shorter link distances, might require digital signal processors (DSPs) to adopt a “lighter” version of the signal processing normally used in coherent technology.

Let’s give an example of how DSPs could behave differently in these cases. The quality of the light signal degrades when traveling through an optical fiber by a process called dispersion. The same phenomenon happens when a prism splits white light into several colors. The fiber also adds other distortions due to nonlinear optical effects.

These effects get worse as the input power of the light signal increases, leading to a trade-off. You might want more power to transmit over longer distances, but the nonlinear distortions also become larger, which beats the point of using more power. The DSP performs several operations on the light signal to try to offset these dispersion and nonlinear distortions.

Asset 7 dispersion in optical fibers — Figure 1: Explaining dispersion compensation in optical fibers. A pulse of light will spread out and distort due to dispersion effects.

However, shorter-reach connections require less dispersion compensation, presenting an opportunity to streamline the processing done by a DSP. A lighter coherent implementation could reduce the use of dispersion compensation blocks. This significantly lowers system power consumption and latency too.

Another way to reduce processing and latency in shorter-reach data center links is to use less powerful forward error correction (FEC) in DSPs. You can learn more about FEC in one of our previous articles.

Takeaways

The shift towards edge data centers tries to address the low latency requirements in modern telecom networks. By decentralizing data storage and processing, closer to the point of use, edge computing reduces latency but also enhances the efficiency and reliability of network services across various applications, from IoT and 5G to content delivery and AR/VR experiences.

The use of coherent transceiver technology helps edge networks span longer reaches with higher capacity, but it also comes with the trade-off of increased latency due to more signal processing from the DSP. This scenario means that DSPs will have to reduce the use of certain processing blocks, such as dispersion compensation and FEC, to meet the specific latency requirements of edge computing.

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Tags: 5G, applications, AR/VR, CDNs, cloud, data, data centers, demands, DSPs, Edge computing, EFFECT Photonics, infrastructure, latency, Networks, NFV, processing, SDN, services, technology, Transceivers, trends

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November 9, 2023

What DSPs Do Optics in Space Need?

The space sector is experiencing rapid growth, driven by numerous privately-owned initiatives aiming to reduce…

The space sector is experiencing rapid growth, driven by numerous privately-owned initiatives aiming to reduce the cost of space flight. As this sector expands, it presents new opportunities for developing optical components in space and satellite communications.

Graph-cost-space-flight — *Figure 1: The cost of a kilogram of payload into space since 2000. Source: Visual Capitalist (data from the Center for Strategic and International Studies)*

However, the challenges associated with the space environment required digital signal processors (DSPs) optimized for optical communications in space. Unlike traditional fiber transmission systems, DSPs for space need to be optimized for receiver sensitivity and signal-to-noise ratio, adapt to signal recovery in the presence of frequent signal losses, and comply with stringent space certification standards.

Signal to Noise Ratio Over Dispersion

In traditional optical fiber communications, the presence of dispersion often leads to signal distortions that require extensive dispersion compensation techniques. However, space is a vacuum medium devoid of most dispersion-related challenges. Consequently, DSPs developed for space-based optical communications do not require the same level of dispersion compensation as their fiber counterparts. Instead, the primary focus shifts toward optimizing receiver sensitivity and improving the signal-to-noise ratio (SNR) to ensure reliable data transmission in space.

Optical signals travel enormous distances in space and will be extremely weak when they reach a receiver. Focusing DSP performance on enhancing the receiver’s sensitivity enables more accurate detection of these weak optical signals.

To achieve this goal, DSPs for space-based optical communications need forward error correction (FEC) methods that are even more robust than FEC used for ground links. These methods employ sophisticated coding techniques that introduce redundancy in the transmitted data, allowing for efficient error detection and correction.

network link with FEC — Figure 2: Simplified diagram of a network link with forward error correction (FEC). The FEC encoder adds a series of redundant bits (called overhead) to the transmitted data stream. The receiver can use this overhead to check for errors without asking the transmitter to resend the data.

Handling Signal Losses in Space

In contrast to optical fiber communications, where signal losses are typically infrequent but often fatal, space-based optical communications experience more frequent but non-fatal signal losses. Therefore, DSPs designed for space must be optimized to handle these intermittent signal losses and ensure efficient signal recovery.

While DSPs for fiber optical links on the ground often rely solely on their error correction methods, DSPs for space-based optical communications might ask more frequently for the signal to be retransmitted. This retransmission can increase the link latency significantly, which can be compensated in part by using satellite networks to provide more redundancy. You can read more about these satellite networks in one of our previous articles.

Space Certification and Standards

While industrial or commercial temperature certifications are typically sufficient for optical fiber transceivers and their components, DSPs designed for space-based optical communications must adhere to more stringent space certification standards. Space certification ensures that DSPs can withstand the extreme temperatures, vacuum conditions, and radiation exposure prevalent in space environments.

*Figure 3: The James Webb Telescope. Space Observatory for the Study of the Universe and exploration of deep space*

Our testing facilities and partners include capabilities for the temperature cycling and reliability testing needed to match Telcordia standards, such as temperature cycling ovens and chambers with humidity control.

Takeaways

The testing process for photonic integrated circuits ensures their reliability and performance. Device-level testing focuses on individual components, allowing for precise characterization and identification of faulty elements. Functional testing evaluates the overall performance of the PIC, ensuring adherence to design specifications. Reliability testing assesses the robustness and lifespan of the PIC under various operating conditions.

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Tags: 5G, certification, Coherent Optical Systems, Data center architecture, dispersion, DSP, DSPs, DVT, Electrical Power, free space optics, Networks, noise ratio, noise ratiom, Optical System-On-Chip (SoC), optics in space, Photonic Integrated Circuit, Photonics, PICs, Pluggable Transceivers, signal, signal loss, space, standard

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November 1, 2023

How to Test a Photonic Integrated Circuit

As photonic integrated circuits (PICs) continue to play an increasingly vital role in modern communication…

As photonic integrated circuits (PICs) continue to play an increasingly vital role in modern communication systems, understanding their testing process is crucial to ensure their reliability and performance. Chip fabrication is a process with many sources of variability, and therefore, much testing is required to ensure that the fabricated chip agrees with what was originally designed and simulated.

As with most hardware, PIC testing can follow the steps of the DVT/EVT/PVT validation framework to scale the device from a mere prototype to a stage of mass production.

EVT (Engineering Validation Test): This is the initial phase of hardware testing, where the focus is on validating that the engineering design meets the specifications and requirements.
DVT (Design Validation Test): This phase aims to ensure that the hardware design is mature and stable, ready for production.
PVT (Production Validation Test): PVT is conducted using production-intent materials and processes to verify that the final product will meet quality and performance expectations in mass production.

*Figure 1*: *Diagram of the EVT/DVT/PVT hardware testing framework.*

This article aims to provide an overview of some testing processes for photonic integrated circuits, covering device-level testing, functional testing, and reliability testing.

Device Level Testing

Device-level testing involves evaluating individual components within the PIC and assessing their characteristics, performance, and reliability to ensure proper functionality and integration. This testing is typically performed at the chip level or wafer level.

Ideally, testing should happen not only on the final, packaged device but in the earlier stages of PIC fabrication, such as measuring after the wafer fabrication process is completed or after cutting the wafer into smaller dies.

Figure-Sustainability-set — Figure 2: Package level (top row) vs. die level (bottom row) testing. Manufacturers can find faults earlier by testing at the die level, which avoids wasting packaging materials.

Greater integration of the PICs enables earlier optical testing on the semiconductor wafer and dies. By testing the dies and wafers directly before packaging, manufacturers need only discard the bad die rather than the whole package, which saves valuable energy and materials.

Functional Testing

After the individual device testing, the next step of the EVT testing phase is functional testing. These tests evaluate the key functionalities of the PIC to ensure they meet design specifications and goals. Different applications will have different functionalities to be evaluated, of course. For example, some key functions evaluated in a PIC for telecommunications can be:

Signal Transmission: To ensure reliable transmission, evaluate signal quality, bit error rate, and signal-to-noise ratio.
Modulation: Assessing the modulators’ accuracy, bandwidth, and linearity to ensure accurate signal encoding and decoding.
Switching: Evaluate the switch response time, crosstalk, and extinction ratio to ensure proper signal routing and minimal signal degradation.

Reliability Testing of the Packaged PIC

After the EVT round of characterization and validation of the chip and its package, the packed chip must be made ready for production, requiring a series of reliability tests in several environmental conditions. For example, different applications need different certifications of the temperatures in which the chip must operate.

For example, the packaged PICs made by EFFECT Photonics for telecommunications must comply with the Telcordia GR-468 qualification, which describes how to test optoelectronic devices for reliability under extreme conditions. Qualification depends upon maintaining optical integrity throughout an appropriate test regimen. Accelerated environmental tests are described in the diagram below.

*Figure 3: Examples of necessary verification tests for transceivers that will operate in harsh temperatures*

Our testing facilities and partners include capabilities for the temperature cycling and reliability testing needed to match Telcordia standards, such as temperature cycling ovens and chambers with humidity control.

Takeaways

The testing process for photonic integrated circuits ensures their reliability and performance. Device-level testing focuses on individual components, allowing for precise characterization and identification of faulty elements. Functional testing evaluates the overall performance of the PIC, ensuring adherence to design specifications. Reliability testing assesses the robustness and lifespan of the PIC under various operating conditions.

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Tags: 5G, Coherent Optical Systems, Data center architecture, Design Validation Test, DVT, Electrical Power, Electronic Equipment, Engineering Validation Test, EVT, Networks, Optical System-On-Chip (SoC), Photonic Integrated Circuit, Photonics, PIC, PICs, Pluggable Transceivers, Production Validation Test, PVT, Semiconductor Industry, testing, Wafer Scale Processes, Wireless Transmission

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July 11, 2023

Where is 100ZR Needed?

Simply relying on traditional direct detect technologies will not meet the growing bandwidth and service…

Simply relying on traditional direct detect technologies will not meet the growing bandwidth and service requirements of mobile, cable, and business access networks, particularly regarding long-distance transmission. In many instances, deploying 100G coherent dense wavelength division multiplexing (DWDM) technology becomes essential to transmit larger volumes of data over extended distances.

Several applications in the optical network edge could benefit from upgrading from 10G DWDM or 100G grey aggregation uplinks to 100G DWDM optics:

Mobile Mid-haul: Seamless upgrade of existing uplinks from 10G to 100G DWDM.
Mobile Backhaul: Upgrading links to 100G IPoDWDM.
Cable Access: Upgrading uplinks of termination devices like optical line terminals (OLTs) and Converged Cable Access Platforms (CCAPs) from 10G to 100G DWDM.
Business Services: Scaling enterprise bandwidth beyond single-channel 100G grey links.

However, network providers have often been reluctant to abandon their 10G DWDM or 100G grey links because existing 100G DWDM solutions did not fulfill all the requirements. Although “scaled-down” coherent 400ZR solutions offered the desired reach and tunability, they proved too expensive and power-intensive for many access network applications. Moreover, the ports in small to medium IP routers used in most edge deployments do not support the commonly used QSFP-DD form factor of 400ZR modules but rather the QSFP28 form factor.

How Coherent 100ZR Can Move into Mobile X-haul

Figure-5gc-dwdm-midhaul — Figure 1: Simplified diagram of a DWDM link in the midhaul and backhaul of a mobile network.

The transition from 4G to 5G has transformed the radio access network (RAN) structure, evolving it from a two-level system (backhaul and fronthaul) in 4G to a three-level system (backhaul, midhaul, and fronthaul) in 5G:

Fronthaul: The segment between the active antenna unit (AAU) and the distributed unit (DU).
Midhaul: The segment from DU to the centralized unit (CU).
Backhaul: The segment from CU to the core network.

Figure-backhaul-fronthaul — Figure 2: Simplified diagram that shows and compares the building blocks of 4G (left) and 5G (right) access networks and the links between these blocks.

Most developed countries have already initiated the rollout of 5G, with many operators upgrading their 1G SFP transceivers to 10G SFP+ devices. Some of these 10G solutions incorporated DWDM technology, but many were single-channel grey transceivers. However, to advance to the next phase of 5G deployments, mobile networks must install and aggregate a greater number of smaller base stations to accommodate the exponential increase in connected devices.

These advanced stages of 5G deployment will necessitate operators to cost-effectively scale fiber capacity using more prevalent 10G DWDM SFP+ solutions and 25G SFP28 transceivers. This upgrade will pressure the aggregation segments of mobile backhaul and midhaul, which typically rely on link aggregation of multiple 10G DWDM links into a higher bandwidth group (e.g., 4x10G).

Figure 4x10G link aggregation — Figure 3: Comparison between 4x10G link aggregation and using a single coherent 100ZR link.

However, this type of link aggregation involves splitting larger traffic streams and can be intricate to integrate within an access ring. Adopting a single 100G uplink diminishes the need for such link aggregation, simplifying network configuration and operations. To gain further insight into the potential market and reach of this link aggregation upgrade, it is recommended to consult the recent Cignal AI report on 100ZR technologies.

Coherent 100ZR Uplinks Driven by Cable Migration to 10G PON

Figure-Fixed-Access-Uplinks-DWDM — Figure 4: Simplified diagram of a DWDM link between the coherent termination device (CTD) and the hub in a cable access network.

Cignal AI’s 100ZR report also states that the primary catalyst for 100ZR adoption will be the multiplexing of fixed access network links transitioning from 1G to 10G. This trend will be evident in the long-awaited shift of cable networks from Gigabit Passive Optical Networks (GPON) to 10G PON, driven by the new DOCSIS 4.0 standard. This standard promises 10Gbps download speeds for customers and necessitates several hardware upgrades in cable networks.

To multiplex these larger 10Gbps customer links, cable providers and network operators must upgrade their optical line terminals (OLTs) and Converged Cable Access Platforms (CCAPs) with 100G DWDM uplinks. Additionally, many of these new optical hubs will support up to 40 or 80 optical distribution networks (ODNs), making the previous approach of aggregating multiple 10G DWDM uplinks insufficient for handling the increased capacity and higher number of channels.

Anticipating these needs, the non-profit R&D organization CableLabs has recently spearheaded the development of a 100G Coherent PON (C-PON) standard. This proposal offers 100 Gbps per wavelength with a maximum reach of 80 km and a split ratio of up to 1:512. CableLabs envisions that C-PON, with its 100G capabilities, will play a significant role not only in cable optical network aggregation but also in other scenarios such as mobile x-haul, fiber-to-the-building (FTTB), long-reach rural areas, and distributed access networks.

Advancements in Business Services with 100ZR Coherent and QSFP28

Figure-cloud-DWDM — Figure 5: Simplified diagram of a DWDM link between a business and a cloud provider.

Nearly every organization utilizes the cloud in some capacity, whether for resource development and testing or software-as-a-service applications. However, leveraging the cloud effectively requires fast, high-bandwidth wide-area connectivity to ensure optimal performance of cloud-based applications.

Like cable networks, enterprises will need to upgrade their existing 1G Ethernet private lines to 10G Ethernet to meet these requirements, consequently driving the demand for 100G coherent uplinks. Cable providers and operators will also seek to capitalize on their upgraded 10G PON networks by expanding the reach and capacity of their business services.

The business and enterprise services sector was an early adopter of 100G coherent uplinks, deploying “scaled-down” 400ZR transceivers in the QSFP-DD form factor when they were the available solution. However, since QSFP-DD slots also support QSFP28 form factors, the emergence of QSFP 100ZR solutions presents a more appealing upgrade for these enterprise applications, offering reduced cost and power consumption.

While QSFP28 solutions had struggled to gain widespread acceptance due to the requirement for new, low-power digital signal processors (DSPs), DSP developers and vendors are now actively involved in 100ZR development projects: Acacia, Coherent/ADVA, Marvell/InnoLight, and Marvell/OE Solutions. This is also why EFFECT Photonics has announced its plans to co-develop a 100G DSP with Credo Semiconductor that best fits 100ZR solutions in the QSFP28 form factor.

Table Comparison QSFP-DD and QSFP-28. — Figure 6: Comparison between QSFP-DD and QSFP-28 form factors for 100G applications.

Takeaways

In the coming years, deploying and applying 100G coherent uplinks will witness increasing prevalence across the network edge. Specific use cases in mobile access networks will require transitioning from existing 10G DWDM link aggregation to a single coherent 100G DWDM uplink.

Simultaneously, the migration of cable networks and business services from 1Gbps to 10Gbps customer links will be the primary driver for the demand for coherent 100G uplinks. For carriers providing converged cable/mobile access, these uplink upgrades will create opportunities to integrate additional business services and mobile traffic into their existing cable networks.

As the ecosystem for QSFP28 100ZR solutions expands, production will scale up, making these solutions more widely accessible and affordable. This, in turn, will unlock new use cases within access networks.

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Tags: 100G, 100G ZR, 100ZR, 10G, 10G PON, 5G, 5G deployment, aggregation, backhaul, bandwidth, business service, Business services, Cable access, cable networks, CCAP, Cloud connectivity, coherent, Coherent DWDM, Converged Cable Access Platforms (CCAPs), edge, Ethernet private lines, Fiber capacity, fronthaul, FTTH, IoT, Link aggregation, midhaul, mobile, mobile access network, mobile networks, Network providers, OLT, Optical line terminals (OLTs), PON, power, QSFP-DD, QSFP28, revenue, traffic, upgrade, uplink, Wide-area connectivity

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April 19, 2023

One Watt Matters

Data centers and 5G networks might be hot commodities, but the infrastructure that enables them…

Data centers and 5G networks might be hot commodities, but the infrastructure that enables them runs even hotter. Electronic equipment generates plenty of heat; the more heat energy an electronic device dissipates, the more money and energy must be spent to cool it down.

The Uptime Institute estimates that the average power usage effectiveness (PUE) ratio for data centers in 2022 is 1.55. This implies that for every 1 kWh used to power data center equipment, an extra 0.55 kWh—about 35% of total power consumption—is needed to power auxiliary equipment like lighting and, more importantly, cooling. While the advent of centralized hyperscale data centers will improve energy efficiency in the coming decade, that trend is offset by the construction of many smaller local data centers on the network edge to address the exponential growth of 5G services such as the Internet of Things (IoT).

These opposing trends are one of the reasons why the Uptime Institute has only observed a marginal improvement of 10% in the average data center PUE since 2014 (which was 1.7 back then). Such a slow improvement in average data center power efficiency cannot compensate for the fast growth of new edge data centers.

For all the bad reputation data centers receive for their energy consumption, though, wireless transmission generates even more heat than wired links. While 5G standards are more energy-efficient per bit than 4G, Huawei expects that the maximum power consumption of one of their 5G base stations will be 68% higher than their 4G stations. To make things worse, the use of higher frequency spectrum bands and new IoT use cases require the deployment of more base stations too.

Prof. Earl McCune from TU Delft estimates that nine out of ten watts of electrical power in 5G systems turn into heat. This Huawei study also predicts that the energy consumption of wireless access networks will increase even more quickly than data centers in the next ten years—more than quadrupling between 2020 and 2030.

Graph-estimated-electric-power — Figure 1 : Comparison of estimated ICT electric power consumption in 2020 and 2030, divided by different ICT sectors. Source: Anders Andrae (Huawei), 2020..

These power efficiency issues do not just affect the environment but also the bottom lines of communications companies. In such a scenario, saving even one watt of power per pluggable transceiver could quickly multiply and scale up into a massive improvement on the sustainability and profitability of telecom and datacom providers.

How One Watt of Savings Scales Up

Let’s discuss an example to show how a seemingly small improvement of one Watt in pluggable transceiver power consumption can quickly scale up into major energy savings.

A 2020 paper from Microsoft Research estimates that for a metropolitan region of 10 data centers with 16 fiber pairs each and 100-GHz DWDM per fiber, the regional interconnect network needs to host 12,800 transceivers. This number of transceivers could increase by a third in the coming years since the 400ZR transceiver ecosystem supports a denser 75 GHz DWDM grid, so this number of transceivers would increase to 17,000. Therefore, saving a watt of power in each transceiver would lead to a total of 17 kW in savings.

Figure-1watt-saving — Figure : Total power savings that can be obtained in a metro network of ten interconnected data centers if 400ZR transceivers save just one Watt of power each, as well as the equivalent carbon emissions. Carbon emissions were calculated with the Environmental Protection Agency (EPA) online calculator.

The power savings don’t end there, however. The transceiver is powered by the server, which is then powered by its power supply and, ultimately, the national electricity grid. On average, 2.5 Watts must be supplied from the national grid for every watt of power the transceiver uses. When applying that 2.5 factor, the 17 kW in savings we discussed earlier are, in reality, 42.5 kW. In a year of power consumption, this rate adds up to a total of 372 MWh in power consumption savings. According to the US Environmental Protection Agency (EPA), these amounts of power savings in a single metro data center network are equivalent to 264 metric tons of carbon dioxide emissions. These emissions are equivalent to consuming 610 barrels of oil and could power up to 33 American homes for a year.

Saving Power through Integration and Co-Design

Before 2020, Apple made its computer processors with discrete components. In other words, electronic components were manufactured on separate chips, and then these chips were assembled into a single package. However, the interconnections between the chips produced losses and incompatibilities that made their devices less energy efficient. After 2020, starting with Apple’s M1 processor, they fully integrate all components on a single chip, avoiding losses and incompatibilities. As shown in the table below, this electronic system-on-chip (SoC) consumes a third of the power compared to the processors with discrete components used in their previous generations of computers.

𝗠𝗮𝗰 𝗠𝗶𝗻𝗶 𝗠𝗼𝗱𝗲𝗹	𝗣𝗼𝘄𝗲𝗿 𝗖𝗼𝗻𝘀𝘂𝗺𝗽𝘁𝗶𝗼𝗻
𝗠𝗮𝗰 𝗠𝗶𝗻𝗶 𝗠𝗼𝗱𝗲𝗹	𝗜𝗱𝗹𝗲	𝗠𝗮𝘅
2023, M2	7	5
2020, M1	7	39
2018, Core i7	20	122
2014, Core i5	6	85
2010, Core 2 Duo	10	85
2006, Core Solo or Duo	23	110
2005, PowerPC G4	32	85
Table 1: Comparing the power consumption of a Mac Mini with an M1 and M2 SoC chips to previous generations of Mac Minis. [Source: Apple’s website]

The photonics industry would benefit from a similar goal: implementing a photonic system-on-chip. Integrating all the optical components (lasers, detectors, modulators, etc.) on a single chip can minimize the losses and make devices such as optical transceivers more efficient. This approach doesn’t just optimize the efficiency of the devices themselves but also of the resource-hungry chip manufacturing process. For example, a system-on-chip approach enables earlier optical testing on the semiconductor wafer and dies. By testing the dies and wafers directly before packaging, manufacturers need only discard the bad dies rather than the whole package, which saves valuable energy and materials. You can read our previous article on the subject to know more about the energy efficiency benefits of system-on-chip integration.

Another way of improving power consumption in photonic devices is co-designing their optical and electronic systems. A co-design approach helps identify in greater detail the trade-offs between various parameters in the optics and electronics, optimizing their fit with each other and ultimately improving the overall power efficiency of the device. In the case of coherent optical transceivers, an electronic digital signal processor specifically optimized to drive an indium-phosphide optical engine directly could lead to power savings.

When Sustainability is Profitable

System-on-chip (SoC) approaches might reduce not only the footprint and energy consumption of photonic devices but also their cost. The economics of scale principles that rule the electronic semiconductor industry can also reduce the cost of photonic systems-on-chip. After all, SoCs minimize the footprint of photonic devices, allowing photonics developers to fit more of them within a single wafer, which decreases the price of each photonic system. As the graphic below shows, the more chips and wafers are produced, the lower the cost per chip becomes.

Graph-cost-per-PIC — Figure 2: Modelling of photonic integrated chip (PIC) cost as a function of aggregate number of PICs produced per year. Exponential increases in production lead to an exponential decrease in cost. Source: Model and graph provided by Prof. Meint Smit, TU Eindhoven.

Integrating all optical components—including the laser—on a single chip shifts the complexity from the expensive assembly and packaging process to the more affordable and scalable semiconductor wafer process. For example, it’s much easier to combine optical components on a wafer at a high volume than to align components from different chips together in the assembly process. This shift to wafer processes also helps drive down the cost of the device.

Takeaways

With data and energy demands rising yearly, telecom and datacom providers are constantly finding ways to reduce their power and cost per transmitted bit. As we showed earlier in this article, even one watt of power saved in an optical transceiver can snowball into major savings that providers and the environment can profit from. These improvements in the power consumption of optical transceivers can be achieved by deepening the integration of optical components and co-designing them with electronics. Highly compact and integrated optical systems can also be manufactured at greater scale and efficiency, reducing their financial and environmental costs. These details help paint a bigger picture for providers: sustainability now goes hand-in-hand with profitability.

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Tags: 5G, data centers, EFFECT Photonics, efficiency, energy consumption, Photonics, Sustainability, Transceivers

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April 12, 2023

When will the Network Edge go Coherent?

Article first published 27 July 2022, updated 12 April 2023. Network carriers want to provide…

Article first published 27 July 2022, updated 12 April 2023.

Network carriers want to provide communications solutions in all areas: mobile access, cable networks, and fixed access to business customers. They want to provide this extra capacity and innovative and personalized connectivity and entertainment services to their customers.

Deploying only legacy direct detect technologies will not be enough to cover these growing bandwidth and service demands of mobile, cable, and business access networks with the required reach. In several cases, networks must deploy more 100G coherent dense wavelength division multiplexing (DWDM) technology to transmit more information over long distances. Several applications in the optical network edge could benefit from upgrading from 10G DWDM or 100G grey aggregation uplinks to 100G DWDM optics:

Mobile Mid-haul benefits from seamlessly upgrading existing uplinks from 10G to 100G DWDM.
Mobile Backhaul benefits from upgrading their links to 100G IPoDWDM.
Cable Access links could upgrade the uplinks of existing termination devices such as optical line terminals (OLTs) and Converged Cable Access Platforms (CCAPs) from 10G to 100G DWDM.
Business Services could scale enterprise bandwidth beyond single-channel 100G grey links.

However, network providers have often stuck to their 10G DWDM or 100G grey links because the existing 100G DWDM solutions could not check all the required boxes. “Scaled-down” coherent 400ZR solutions had the required reach and tunability but were too expensive and power-hungry for many access network applications. Besides, ports in small to medium IP routers used in most edge deployments often do not support the QSFP-DD form factor commonly used in 400ZR modules but the QSFP28 form factor.

Fortunately, the rise of 100ZR solutions in the QSFP28 form factor is changing the landscape for access networks. “The access market needs a simple, pluggable, low-cost upgrade to the 10G DWDM optics that it has been using for years. 100ZR is that upgrade,” said Scott Wilkinson, Lead Analyst for Optical Components at market research firm Cignal AI. “As access networks migrate from 1G solutions to 10G solutions, 100ZR will be a critical enabling technology.”

In this article, we will discuss how the recent advances in 100ZR solutions will enable the evolution of different segments of the network edge: mobile midhaul and backhaul, business services, and cable.

How Coherent 100G Can Move into Mobile X-haul

The upgrade from 4G to 5G has shifted the radio access network (RAN) from a two-level structure with backhaul and fronthaul in 4G to a three-level structure with back-, mid-, and fronthaul:

Fronthaul is the segment between the active antenna unit (AAU) and the distributed unit (DU)
Midhaul is the segment from DU to the centralized unit (CU)
Backhaul is the segment from CU to the core network.

Figure 1: Simplified diagram that shows and compares the building blocks of 4G (left) and 5G (right) access networks and the links between these blocks.

The initial rollout of 5G has already happened in most developed countries, with many operators upgrading their 1G SFPs transceiver to 10G SFP+ devices. Some of these 10G solutions had DWDM technology; many were single-channel grey transceivers. However, mobile networks must move to the next phase of 5G deployments, which requires installing and aggregating more and smaller base stations to exponentially increase the number of devices connected to the network.

These mature phases of 5G deployment will require operators to continue scaling fiber capacity cost-effectively with more widespread 10G DWDM SFP+ solutions and 25G SFP28 transceivers. These upgrades will put greater pressure on the aggregation segments of mobile backhaul and midhaul. These network segments commonly used link aggregation of multiple 10G DWDM links into a higher bandwidth group (such as 4x10G). However, this link aggregation requires splitting up larger traffic streams and can be complex to integrate across an access ring. A single 100G uplink would reduce the need for such link aggregation and simplify the network setup and operations. If you want to know more about the potential market and reach of this link aggregation upgrade, we recommend reading the recent Cignal AI report on 100ZR technologies.

Cable Migration to 10G PON Will Drive the Use of Coherent 100G Uplinks

According to Cignal AI’s 100ZR report, the biggest driver of 100ZR use will come from multiplexing fixed access network links upgrading from 1G to 10G. This trend will be reflected in cable networks’ long-awaited migration from Gigabit Passive Optical Networks (GPON) to 10G PON. This evolution is primarily guided by the new DOCSIS 4.0 standard, which promises 10Gbps download speeds for customers and will require several hardware upgrades in cable networks.

To multiplex these new larger 10Gbps customer links, cable providers and network operators need to upgrade their optical line terminals (OLTs) and Converged Cable Access Platforms (CCAPs) from 10G to 100G DWDM uplinks. Many of these new optical hubs will support up to 40 or 80 optical distribution networks (ODNs), too, so the previous approach of aggregating multiple 10G DWDM uplinks will not be enough to handle this increased capacity and higher number of channels.

Anticipating such needs, the non-profit R&D organization CableLabs has recently pushed to develop a 100G Coherent PON (C-PON) standard. Their proposal offers 100 Gbps per wavelength at a maximum reach of 80 km and up to a 1:512 split ratio. CableLabs anticipates C-PON and its 100G capabilities will play a significant role not just in cable optical network aggregation but in other use cases such as mobile x-haul, fiber-to-the-building (FTTB), long-reach rural scenarios, and distributed access networks.

Towards 100G Coherent and QSFP28 in Business Services

Almost every organization uses the cloud in some capacity, whether for development and test resources or software-as-a-service applications. While the cost and flexibility of the cloud are compelling, its use requires fast, high-bandwidth wide-area connectivity to make cloud-based applications work as they should.

Similarly to cable networks, these needs will require enterprises to upgrade their existing 1G Ethernet private lines to 10G Ethernet, which will also drive a greater need for 100G coherent uplinks. Cable providers and operators will also want to take advantage of their upgraded 10G PON networks and expand the reach and capacity of their business services.

The business and enterprise services sector was the earliest adopter of 100G coherent uplinks, deploying “scaled-down” 400ZR transceivers in the QSFP-DD form factor since they were the solution available at the time. However, these QSFP-DD slots also support QSFP28 form factors, so the rise of QSFP 100ZR solutions will provide these enterprise applications with a more attractive upgrade with lower cost and power consumption. These QSFP28 solutions had struggled to become more widespread before because they required the development of new, low-power digital signal processors (DSPs), but DSP developers and vendors are keenly jumping on board the 100ZR train and have announced their development projects: Acacia, Coherent/ADVA, Marvell/InnoLight, and Marvell/OE Solutions. This is also why EFFECT Photonics has announced its plans to co-develop a 100G DSP with Credo Semiconductor that best fits 100ZR solutions in the QSFP28 form factor.

Figure : Comparison between QSFP-DD and QSFP-28 form factors for 100G applications. — Figure 2 : Comparison between QSFP-DD and QSFP-28 form factors for 100G applications.

Takeaways

In the coming years, 100G coherent uplinks will become increasingly widespread in deployments and applications throughout the network edge. Some mobile access networks use cases must upgrade their existing 10G DWDM link aggregation into a single coherent 100G DWDM uplink. Meanwhile, cable networks and business services are upgrading their customer links from 1Gbps to 10Gbps, and this migration will be the major factor that will increase the demand for coherent 100G uplinks. For carriers who provide converged cable/mobile access, these upgrades to 100G uplinks will enable opportunities to overlay more business services and mobile traffic into their existing cable networks.

As the QSFP28 100ZR ecosystem expands, production will scale up, and these solutions will become more widespread and affordable, opening up even more use cases in access networks.

Tags: 5G, access, aggregation, backhaul, capacity, DWDM, fronthaul, Integrated Photonics, LightCounting, metro, midhaul, mobile, mobile access, network, optical networking, optical technology, photonic integrated chip, photonic integration, Photonics, PIC, PON, programmable photonic system-on-chip, solutions, technology

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March 29, 2023

What DSPs Does the Cloud Edge Need?

By storing and processing data closer to the end user and reducing latency, smaller data…

By storing and processing data closer to the end user and reducing latency, smaller data centers on the network edge significantly impact how networks are designed and implemented. These benefits are causing the global market for edge data centers to explode, with PWC predicting that it will nearly triple from $4 billion in 2017 to $13.5 billion in 2024. Various trends are driving the rise of the edge cloud: 5G networks and the Internet of Things (IoT), augmented and virtual reality applications, network function virtualization, and content delivery networks.

Several of these applications require lower latencies than before, and centralized cloud computing cannot deliver those data packets quickly enough. As shown in Table 1, a data center on a town or suburb aggregation point could halve the latency compared to a centralized hyperscale data center. Enterprises with their own data center on-premises can reduce latencies by 12 to 30 times compared to hyperscale data centers.

Type of Edge		Datacenter	Location	Number of DCs per 10M people	Average Latency	Size
On-premises edge		Enterprise site	Businesses	NA	2-5 ms	1 rack max
Network (Mobile)	Tower edge	Tower	Nationwide	3000	10 ms	2 racks max
	Outer edge	Aggregation points	Town	150	30 ms	2-6 racks
	Inner edge	Core	Major city	10	40 ms	10+ racks
Regional edge		Regional	Major city	100	50 ms	100+ racks
Not edge		Hyperscale	State/national	1	60+ ms	5000+ racks

Table 1: Types of edge data centers and their characteristics. Source: STL Partners

This situation leads to hyperscale data center providers cooperating with telecom operators to install their servers in the existing carrier infrastructure. For example, Amazon Web Services (AWS) is implementing edge technology in carrier networks and company premises (e.g., AWS Wavelength, AWS Outposts). Google and Microsoft have strategies and products that are very similar. In this context, edge computing poses a few problems for telecom providers. They must manage hundreds or thousands of new nodes that will be hard to control and maintain.

These conditions mean that optical transceivers for these networks, and thus their digital signal processors (DSPs), must have flexible and low power consumption and smart features that allow them to adapt to different network conditions.

Using Adaptable Power Settings

Reducing power consumption in the cloud edge is not just about reducing the maximum power consumption of transceivers. Transceivers and DSPs must also be smart and decide whether to operate on low- or high-power mode depending on the optical link budget and fiber length. For example, if the transceiver must operate at its maximum capacity, a programmable interface can be controlled remotely to set the amplifiers at maximum power. However, if the operator uses the transceiver for just half of the maximum capacity, the transceiver can operate with lower power on the amplifiers. The transceiver uses energy more efficiently and sustainably by adapting to these circumstances.

Fiber monitoring is also an essential variable in this equation. A smart DSP could change its modulation scheme or lower the power of its semiconductor optical amplifier (SOA) if telemetry data indicates a good quality fiber. Conversely, if the fiber quality is poor, the transceiver can transmit with a more limited modulation scheme or higher power to reduce bit errors. If the smart pluggable detects that the fiber length is relatively short, the laser transmitter power or the DSP power consumption could be scaled down to save energy.

The Importance of a Co-Design Philosophy for DSPs

Transceiver developers often source their DSP, laser, and optical engine from different suppliers, so all these chips are designed separately. This setup reduces the time to market and simplifies the research and design processes, but it comes with performance and power consumption trade-offs.

In such cases, the DSP is like a Swiss army knife: a jack of all trades designed for different kinds of PIC but a master of none. Given the ever-increasing demand for capacity and the need for sustainability both as financial and social responsibility, transceiver developers increasingly need a steak knife rather than a Swiss army knife.

As we explained in a previous article about fit-for-platform DSPs, a transceiver optical engine designed on the indium phosphide platform could be designed to run at a voltage compatible with the DSP’s signal output. This way, the optimized DSP could drive the PIC directly without needing a separate analog driver, doing away with a significant power conversion overhead compared to a silicon photonics setup, as shown in the figure below.

Figure 1: Comparison between the drive power and power consumption of three different PIC + DSP pairings: standard DSP with a silicon PIC, standard DSP with an InP PIC, and an optimized DSP with an InP.

Scaling the Edge Cloud with Automation

With the rise of edge data centers, telecom providers must manage hundreds or thousands of new nodes that will take much work to control and maintain. Furthermore, providers also need a flexible network with pay-as-you-go scalability that can handle future capacity needs. Automation is vital to achieving such flexibility and scalability.

Automation potential improves further by combining artificial intelligence with the software-defined networks (SDNs) framework that virtualizes and centralizes network functions. This creates an automated and centralized management layer that can allocate resources efficiently and dynamically. For example, the AI network controller can take telemetry data from the whole network to decide where to route traffic and adjust power levels, reducing power consumption.

Figure 2: Comparing a traditional network approach (left) with an SDN/NFC approach (right).

In this context, smart digital signal processors (DSPs) and transceivers can give the AI controller more degrees of freedom to optimize the network. They could provide more telemetry to the AI controller so that it makes better decisions. The AI management layer can then remotely control programmable interfaces in the transceiver and DSP so that the optical links can adjust the varying network conditions. If you want to know more about these topics, you can read last week’s article about transceivers in the age of AI.

Takeaways

Cloud-native applications require edge data centers that handle increased traffic and lower network latency. However, their implementation came with the challenges of more data center interconnects and a massive increase in nodes to manage. Scaling edge data center networks will require greater automation and more flexible power management, and smarter DSPs and transceivers will be vital to enable these goals.

Co-design approaches can optimize the interfacing of the DSP with the optical engine, making the transceiver more power efficient. Further power consumption gains can also be achieved with smarter DSPs and transceivers that provide telemetry data to centralized AI controllers. These smart network components can then adjust their power output based on the decisions and instructions of the AI controller.

Tags: 5G, AI, artificial intelligence, Augmented Reality, automation, cloud edge, Co-Design Philosophy, data centers, Delivery Networks, DSPs, Edge Cloud, Fiber Monitoring, Hyperscale Data Center, Internet of Things, IoT, latency, Network Function Virtualization, optical transceivers, power consumption, Software-Defined Networks, Telecom Operators, Virtual Reality

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