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How To Make a Photonic Integrated Circuit

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November 9, 2022

Leveraging the Power of External Foundries in Photonics

Working with a world-class high-volume foundry makes scaling up from low to high volume as…

Working with a world-class high-volume foundry makes scaling up from low to high volume as easy as putting a purchase order in place. Instead of having to buy equipment, develop processes, and train operators over many years, a fabless photonics developer can leverage foundries who already have these capabilities and knowledge.

Thanks to wafer scale technology, electronics has successfully driven down cost per transistor for many decades. This allowed the world to enjoy chips that every generation became smaller and provided exponentially more computing power for the same amount of money. This scale-up process is how everyone now has a computer processor in their pocket that is millions of times more powerful than the most advanced computers of the 1960s that landed men on the moon.

This progress in electronics integration is a key factor that brought down the size and cost of coherent transceivers, packing more bits than ever into smaller areas. However, photonics has struggled to keep up with electronics, and now the optics dominate the optical transceiver’s cost. If the transceiver cost curve does not continue to decrease, it will be difficult to achieve the goal of making coherent technology more accessible across the entire optical network. This will make it more difficult to provide the services needed by cloud providers and the growing 5G access networks.

As we mentioned in our previous article, photonics manufacturing must move into wafer-scale territory to provide faster, more affordable, and sustainable coherent transmission.

However, most photonic chip developers don’t have human and financial resources to own and operate their own wafer-scale photonic foundries. Fortunately, electronic chip developers have shown a more viable and cost-effective alternative: the fabless model.

A Lower Upfront Investment

Increasing the volume of photonics manufacturing is a big challenge. Some photonic chip developers choose to manufacture their chips in-house within their own fabrication facilities. This approach has some strong advantages, as it gives component manufacturers full control over their production process. By vertically integrating the whole chip design, manufacturing, and testing process within the same company, it’s often easier to try out new changes and innovations to the product.

Figure 1: Simplified value chain diagram of a vertically-integrated optical transceiver developer. The developer handles the PIC design, manufacturing, and packaging

However, this approach has its trade-offs. If a vertically-integrated chip developer wants to scale up in volume, they must make a hefty investment in more equipment and personnel to do so. They must develop new fabrication process which not only need money, but also time to develop and train personnel. Especially in the case of an optical transceiver market that is not as big as that of consumer electronics, it’s hard not to wonder whether that initial investment is cost-effective.

Electronics manufacturing had a similar problem during their 1970s boom, with smaller chip start-ups facing almost insurmountable barriers to enter the market because of the massive capital expenditure (CapEx) required. Electronics solved this problem by moving into what we call a fabless model, with companies designing and selling the chips but outsourcing the manufacturing.

For example, transceiver DSP chip developers design the chip, but then outsource the actual fabrication to a large-volume manufacturing plant (usually called a foundry). This business model works by leveraging the design, research, development, and distribution networks of the fabless company, and the specialized manufacturing skill of the chip foundry.

Figure 2: Simplified value chain diagram of a vertically-integrated optical transceiver developer. The developer handles the PIC design, manufacturing, and packaging.

This model reduces the capital expenditure burden on the DSP developers, because instead of spending all the time and energy in scaling up their own facilities, they can work with a foundry that already did that investment and has the required manufacturing volume. In other words, instead going through a more costly, time-consuming process, the troubles of scaling up are outsourced and (from the perspective of the fabless company) become as simple as putting a purchase order in place. Furthermore, the fabless model also allows companies to concentrate their R&D resources on the end market. If photonics is to move into million-scale volumes, this is likely the way forward.

Economies of Scale and Operating Expenses

Even if an optical transceiver developer could move forward with the CapEx required for its own large-scale fab and a vertically-integrated model, market demand and operational expenses become the next pain point. Transceivers are a B2B market, and their demand is significantly smaller than of B2C consumer electronics. For example, LightCounting estimates that 55 million optical transceivers will be sold in 2021, while the International Data Corporation estimates that 1.4 billion smartphones will be sold in 2021. The latter figure is 25 times larger than that of the transceiver market.

The smaller demand of transceivers means that even if a vertically-integrated transceiver developer upgrades to a larger-scale manufacturing facility, it will likely have more manufacturing capacity than what their customers need. In such a situation, the facility could run at a reduced capacity. However, fabs are not only expensive to build, but also to operate. Unless they can be kept at nearly full utilization, operating expenses (OpEx) will become a drain on the finances of the facility owners.

This issue was something the electronics industry faced in the past, during the 1980s. Integrated electronics manufacturers had excess production capacity, and this situation paved the way for the fabless model too. The large-scale manufacturers ended up selling that excess capacity to smaller, fabless chip developers. Ultimately, the entire electronics industry relied increasingly on the fabless model, to the point where pure play foundries like the Taiwan Semiconductor Manufacturing Corporation (TSMC) appeared and focused entirely on manufacturing for other fabless companies.

In this scenario, everyone ended up winning. The foundries serviced multiple companies and could run their facilities at full capacity, while the fabless companies could outsource manufacturing and reduce their expenditures.

Working with the Best in the Business

The other advantage of pure play foundries is that they not only have state-of-the art equipment but also the best personnel and technical expertise. Even if a vertically-integrated developer transceiver can make the required CapEx to scale up their facilities, developing processes and training people inevitably takes years, delaying the return on investment even further.

By working with an established and experienced foundry, fabless companies take advantage of the highly trained and experience personnel of these facilities. These operators, technicians, and engineers have worked day in, day out with their equipment for years and already developed processes that are finely tuned to their equipment. Thanks to their work, fabless transceiver developers do not have to reinvent the wheel and come up with their own processes, saving valuable time and many, many headaches.

Takeaways

To make transceivers more accessible to world and connect more people together, transceiver developers need to reach production scales in the millions. At EFFECT Photonics, we believe that the way to achieve this goal is by having photonics follow the blueprint laid out by the electronics industry. Using a fabless model, we can reduce the capital expenditure and scale up more quickly and with fewer risks.

Tags: coherent, coherent optics, external foundries, foundries, Integrated Photonics, LightCounting, optical transceivers, photonic integration, Photonics, photonicwafer, pluggables, Transceivers, wafer

The Light Path to a Coherent Cloud Edge Banner

Insights

November 8, 2022

Improving Edge Computing with Coherent Optical Systems on Chip

Smaller data centers placed locally have the potential to minimize latency, overcome inconsistent connections, and…

Smaller data centers placed locally have the potential to minimize latency, overcome inconsistent connections, and store and compute data closer to the end-user. 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. 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.

This situation leads to hyperscalers 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 too. They must manage hundreds or thousands of new nodes that will be hard to control and maintain.

At EFFECT Photonics, we believe that coherent pluggables with an optical System-on-Chip (SoC) can become vital in addressing these datacom and telecom sector needs and enabling a new generation of distributed data center architectures. Combining the optical SoCs with reconfigurable DSPs and modern network orchestration and automation software will be a key to deploying edge data centers.

Edge data centers are a performance and sustainability imperative

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 the streaming latency and improve the performance of AR/VR applications.

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		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 rack max
	Outer edge	Aggrega- tion points	Town	150	30 ms	2-6 rack max
	Inner edge	Core	Major city	10	40 ms	10+ rack max
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

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.

Figure 1 Global data center traffic vs. useable data created per year. Graphic sourced from Cisco Global Cloud Index.

Edge data centers therefore allow more sensor data to be aggregated and processed to make systems worldwide smarter and more efficient. The ultimate goal is to create entire “smart cities” that use this sensor data to benefit their inhabitants, businesses, and the environment. Everything from transport networks to water supply and lightning could be improved if we have more sensor data available in the cloud to optimize these processes. Distributing data centers is also vital for future data center architectures. While centralizing processing in hyper-scale data centers made them more energy-efficient, the power grid often limits the potential location of new hyperscale data centers. Thus, the industry may have to take a few steps back and decentralize data processing capacity to cope with the strain of data center clusters on power grids. For example, data centers can be relocated to areas where spare power capacity is available, preferably from nearby renewable energy sources. EFFECT Photonics envisions a system of datacentres with branches in different geographical areas, where data storage and processing are assigned based on local and temporal availability of renewable (wind-, solar-) energy and total energy demand in the area.

Figure 2: High-speed fiber-optic connections allow data processing and storage to move to locations where excess (green) energy is available. If power is needed for other purposes, such as charging electric vehicles, data can be moved elsewhere

Coherent technology simplifies the scaling of edge data center interconnects

As edge data center interconnects became more common, the issue of how to interconnect them became more prominent. Direct detect technology had been the standard in the short-reach data center interconnects. However, reaching the 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 small enough modules 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. If needed, extended reach 400ZR+ pluggables can cover several hundreds of kilometers. Cignal AI forecasts that 400ZR shipments will dominate in the edge applications, as shown in Figure 3.

Figure 3: Forecast of 100G port equivalents shipped for edge applications. These shipments are overwhelmingly 400ZR standard technology. Source: Cignal AI Transport Applications Report Q42021.

Further improvements in integration can further boost the reach and efficiency of coherent transceivers. For example, by integrating all photonic functions on a single chip, including lasers and optical amplifiers, EFFECT Photonics’ optical System-On-Chip (SoC) technology can achieve higher transmit power levels and longer distances while keeping the smaller QSFP-DD form factor, power consumption, and cost.

Maximizing Edge Computing with Automation

With the rise of edge data centers, telecom providers must manage hundreds or thousands of new nodes that will be hard to control and maintain. Furthermore, providers also need a flexible network with pay-as-you-go scalability that can handle future capacity needs. Fortunately, several new technologies are enabling this scalable and automated network management.

First of all, the rise of self-tuning algorithms has made the installation of new pluggables easier than ever. They eliminate additional installation tasks such as manual tuning and record verification. They are host-agnostic, can plug into any third-party host equipment, and scale as you grow. Standardization also allows modules from different vendors to communicate with each other, avoiding compatibility issues and simplifying upgrade choices. The communication channels used for self-tuning algorithms can also be used for remote diagnostics and management, such as the case of EFFECT Photonics NarroWave technology.

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, AI in network management will become a significant factor in reducing the energy consumption of future telecom networks.

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

Future smart transceivers with reconfigurable digital signal processors (DSPs) can give the AI-controlled management layer even more degrees of freedom to optimize the network. These smart transceivers will relay more device information for diagnosis, and depending on the management layer instructions, they can change their coding schemes to adapt to different network requirements

Takeaways

Cloud-native applications require edge data centers with lower latency, and that better fit the existing power grid. However, their implementation came with the challenges of more data center interconnects and a massive increase in nodes to manage. Fortunately, coherent pluggables with self-tuning can play a vital role in addressing these datacom and telecom sector challenges and enabling a new generation of distributed data center architectures. Combining these pluggables with modern network orchestration and automation software will boost the deployment of edge data centers. EFFECT Photonics believes that with these automation technologies (self-tuning, SDNs, AI), we can reach the goal of a self-managed, zero-touch automated network that can handle the massive scale-up required for 5G networks and edge computing.

Tags: 400ZR, artificial intelligence, cloud, coherent, computing, data centers, DSP, edge, edge data centers, infrastructure, latency, network, network edge, operators, optical system-on-chip, pluggables, self-tuning, services

Insights

November 4, 2022

What’s Inside a Coherent DSP?

Coherent transmission has become a fundamental component of optical networks to address situations where direct…

Coherent transmission has become a fundamental component of optical networks to address situations where direct detect technology cannot provide the required capacity and reach.

While direct detect transmission only uses the amplitude of the light signal, coherent optical transmission manipulates three different light properties: amplitude, phase, and polarization. These additional degrees of modulation allow for faster optical signals without compromising the transmission distance. Furthermore, coherent technology enables capacity upgrades without replacing the expensive physical fiber infrastructure on the ground.

The digital signal processor (DSP) is the electronic heart of coherent transmission systems. The fundamental function of the DSP is encoding the electronic digital data into the amplitude, phase, and polarization of the light signal and decoding said data when the signal is received. The DSP does much more than that, though: it compensates for impairments in the fiber, performs analog-to-digital conversions (and vice versa), corrects errors, encrypts data, and monitors performance. And recently, DSPs are taking on more advanced functions such as probabilistic constellation shaping or dynamic bandwidth allocation, which enable improved reach and performance.

Given its vital role in coherent optical transmission, we at EFFECT Photonics want to provide an explainer of what goes on inside the DSP chip of our optical transceivers.

There’s More to a DSP Than You Think…

Even though we colloquially call the chip a “DSP”, it is an electronic engine that performs much more than just signal processing. Some of the different functions of this electronic engine (diagram below) are:

*Figure 1: Layout of the electronic engine used in a coherent optical transceiver, including the sequence the signal follows when processed by the engine.*

Analog Processing: This engine segment focuses on converting signals between analog and digital formats. Digital data is composed of discrete values like 0s and 1s, but transmitting it through a coherent optical system requires converting it into an analog signal with continuous values. Meanwhile, a light signal received on the opposite end requires conversion from analog into digital format.
Digital Signal Processing: This is the actual digital processing. As explained previously, this block encodes the digital data into the different properties of a light signal. It also decodes this data when the light signal is received.
Forward Error Correction (FEC): FEC makes the coherent link much more tolerant to noise than a direct detect system and enables much longer reach and higher capacity. Thanks to FEC, coherent links can handle bit error rates that are literally a million times higher than a typical direct detect link. FEC algorithms allow the electronic engine to enhance the link performance without changing the hardware. This enhancement is analogous to imaging cameras: image processing algorithms allow the lenses inside your phone camera to produce a higher-quality image.

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.

Framer: While a typical electric signal sent through a network uses the Ethernet frame format, the optical signal uses the Optical Transport Network (OTN) format. The framer block performs this conversion. We should note that an increasingly popular solution in communication systems is to send Ethernet frames directly over the optical signal (a solution called optical Ethernet). However, many legacy optical communication systems still use the OTN format, so electronic engines should always have the option to convert between OTN and Ethernet frames.
Glue Logic: This block consists of the electronic circuitry needed to interface all the different blocks of the electronic engine. This includes the microprocessor that drives the electronic engine and the serializer-deserializer (SERDES) circuit. Since coherent systems only have four channels, the SERDES circuit converts parallel data streams into a single serial stream that can be transmitted over one of these channels. The opposite conversion (serial-to-parallel) occurs when the signal is received.

We must highlight that each of these blocks has its own specialized circuitry and algorithms, so each is a separate piece of intellectual property. Therefore, developing the entire electronic engine requires ownership or access to each of these intellectual properties.

So What’s Inside the Actual DSP Block?

Having clarified first all the different parts of a transceiver’s electronic engine, we can now talk more specifically about the actual DSP block that encodes/decodes the data and compensates for distortions and impairments in the optical fiber. We will describe some of the critical functions of the DSP in the order in which they happen during signal transmission. Receiving the signal would require these functions to occur in the opposite order, as shown in the diagram below.

*Figure 3. Layout of the digital signal processing blocks and the sequence followed by the signal when transmitted and received.*

Signal Mapping: This is where the encoding/decoding magic happens. The DSP maps the data signal into the different phases of the light signal—the in-phase components and the quadrature components—and the two different polarizations (x- and y- polarizations). When receiving the signal, the DSP will perform the inverse process, taking the information from the phase and polarization and mapping it into a stream of bits. The whole process of encoding and decoding data into different phases of light is known as quadrature modulation. Explaining quadrature modulation in detail goes beyond the scope of this article, so if you want to know more about it, please read the following article.
Pilot Signal Insertion: The pilot signal is transmitted over the communication systems to estimate the status of the transmission path. It makes it easier (and thus more energy-efficient) for the receiver end to decode data from the phase and polarization of the light signal.
Adaptive Equalization: This function happens when receiving the signal. The fiber channel adds several distortions to the light signal (more on that later) that change the signal’s frequency spectrum from what was initially intended. Just as with an audio equalizer, the purpose of this equalizer is to change specific frequencies of the signal to compensate for the distortions and bring the signal spectrum back to what was initially intended.

*Figure 4: How the equalizer in a communication systems work. The example in this figure is an equalizer for RF coaxial transmission (not optical), but the principle is the same. Source:* *Broadband Library*

Dispersion and Nonlinear Compensation: This function happens when receiving the signal. 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 that try to offset these dispersion and nonlinear distortions.
Spectrum Shaping: Communication systems must be efficient in all senses, so they must transmit as much signal as possible within a limited number of frequencies. Spectrum shaping is a process that uses a digital filter to narrow down the signal to the smallest possible frequency bandwidth and achieve this efficiency.

When transmitting, the signal goes through the digital-to-analog conversion after this whole DSP sequence. When receiving the signal, it goes through the inverse analog-to-digital conversation and then through the DSP sequence.

Recent Advances and Challenges in DSPs

This is an oversimplification, but we can broadly classify the two critical areas of improvement for DSPs into two categories.

Transmission Reach and Efficiency

The entire field of communication technology can arguably be summarized with a single question: how can we transmit more information into a single frequency-limited signal over the longest possible distance?

DSP developers have many tools in their kit to answer this question. For example, they can transmit more data using more states in their quadrature-amplitude modulation process. The simplest kind of QAM (4-QAM) uses four different states (usually called constellation points), combining two different intensity levels and two different phases of light.

By using more intensity levels and phases, more bits can be transmitted in one go. State-of-the-art commercially available 400ZR transceivers typically use 16-QAM, with sixteen different constellation points that arise from combining four different intensity levels and four phases. However, this increased transmission capacity comes at a price: a signal with more modulation orders is more susceptible to noise and distortions. That’s why these transceivers can transmit 400Gbps over 100km but not over 1000km.

One of the most remarkable recent advances in DSPs to increase the reach of light signals is probabilistic constellation shaping (PCS). In the typical 16-QAM modulation used in coherent transceivers, each constellation point has the same probability of being used. This is inefficient since the outer constellation points that require more power have the same probability as the inner constellation points that require lower power.

*Figure 5: Comparison of conventional 16-QAM and a 16-QAM that uses probabilistic constellation shaping (PCS). Original diagram source:* *Infinera*.

PCS uses the low-power inner constellation points more frequently, and the outer constellation points less frequently, as shown in Figure 5. This feature provides many benefits, including improved tolerance to distortions and easier system optimization to specific bit transmission requirements. If you want to know more about it, please read the explainers here and here.

Energy Efficiency

Increases in transmission reach and efficiency must be balanced with power consumption and thermal management. Energy efficiency is the biggest obstacle in the roadmap to scale high-speed coherent transceivers into Terabit speeds.

Over the last two decades, power ratings for pluggable modules have increased as we moved from direct detection to more power-hungry coherent transmission: from 2W for SFP modules to 3.5 W for QSFP modules and now to 14W for QSSFP-DD and 21.1W for OSFP form factors. Rockley Photonics researchers estimate that a future electronic switch filled with 800G modules would draw around 1 kW of power just for the optical modules.

Figure 6: Normalized power breakdown of the internal blocks of a 400ZR pluggable module. Although this breakdown may vary a bit among different vendors, the authors find it to be generally valid for various DSP-based modules, both IM-DD and coherent. Source: *R. Nagarajan et al., IEEE JLT (2021)*

Around 50% of a coherent transceiver’s power consumption goes into the DSP chip. Scaling to higher bandwidths leads to even more losses and energy consumption from the DSP chip, and its radiofrequency (RF) interconnects with the optical engine. DSP chips must therefore be adaptable and smart, using the least amount of energy to encode/decode information. You can learn more about this subject in one of our previous articles. The interconnects with the optical engine are another area that can see further optimization, and we discuss these improvements in our article about optoelectronic co-design.

Takeaways

In summary, DSPs are the heart of coherent communication systems. They not only encode/decode data into the three properties of a light signal (amplitude, phase, polarization) but also handle error correction, analog-digital conversation, Ethernet framing, and compensation of dispersion and nonlinear distortion. And with every passing generation, they are assigned more advanced functions such as probabilistic constellation shaping.

There are still many challenges ahead to improve DSPs and make them transmit even more bits in more energy-efficient ways. Now that EFFECT Photonics has incorporated talent and intellectual property from Viasat’s Coherent DSP team, we hope to contribute to this ongoing research and development and make transceivers faster and more sustainable than ever.

Tags: 100G, 5G, 6G, access, access networks, aggregation, backhaul, capacity, coherent, DWDM, fronthaul, Integrated Photonics, live events, metro, midhaul, mobile, mobile access, mobile networks, network, optical networking, optical technology, photonic integrated chip, photonic integration, Photonics, PIC, PON, programmable photonic system-on-chip, solutions, technology, VR, WDM

Insights

November 3, 2022

How to Increase Bandwidth Density in Photonics

In the past, optical transceivers were too bulky, too expensive, and not efficient enough, so…

In the past, optical transceivers were too bulky, too expensive, and not efficient enough, so they could only be used for long-haul telecom networks or data centers with massive bandwidth requirements. Electronic and photonic integration broke this paradigm, miniaturizing optical transceivers to the size of a large USB stick and reducing their cost. Through these advances, optical component manufacturers could pack exponentially more bandwidth into a smaller transceiver area within the last decade. Thanks to this exponential progress, component manufacturers managed to keep up with the exponentially-growing worldwide demand for data.

*Figure 1: Exponential growth of bandwidth density over time through the evolution of types of transceiver module standards.*

However, the next wave of innovative network services—autonomous vehicles, the Internet of Things, Industry 4.0—demands even more bandwidth and other requirements. Optical links that connect 5G controller units to the rest of the network must upscale from 10G to 100G. The links from metro networks to datacenters must upscale from 100G to 400G or 800G, and the links within datacenters must operate at Terabit speeds. These services require not only more bandwidth but also lower latencies and more reliability. Further electronic integration cannot keep up by itself; photonic integration must also continue pushing the envelope on bandwidth density.

In our previous articles and videos, we have already discussed one way to increase the bandwidth density through coherent transmission. Coherent technology can pack more bits into a laser signal because it encodes data in the laser light’s amplitude, phase, and polarization. The use of digital signal processing in these devices improves the reach and bandwidth of the signal even further. Coherent transmission allows network operators to reach higher bandwidths without upgrading their existing optical fiber infrastructure. Conserving and reusing existing fiber infrastructure is also a sustainability measure because it avoids spending additional energy and resources on manufacturing more fiber and laying it down on the roads.

However, another way to improve the bandwidth density is by moving to full photonic integration. Let’s use an analogy from electronics to explain what this means.

*Figure 2: Example of integrating a laser to other photonic components through different integration approaches.*

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 different chips produced losses and incompatibilities that made the device less efficient. After 2020, starting with Apple’s M1 processor, they now fully integrate all components on a single chip, making the device more energy efficient and reducing its footprint.

Full photonic integration achieves something similar to Apple’s approach, but with optical components instead of electronic components. By integrating all optical elements required for optical transmission (lasers, detectors, modulators, etc.) into a single System-on-Chip (SoC), we can minimize the losses and reduce the chip’s footprint, transmitting more bits over the same chip area. Furthermore, as we discussed in a previous article, a fully integrated system-on-chip reduces materials wastage while at the same time ensuring increased energy efficiency of the manufacturing, packaging, and testing process.

Coherent transmission and full photonic integration approaches must synergize to achieve the highest possible bandwidth density. For example, EFFECT Photonics taped out a fully-integrated coherent optical System-on-Chip (SoC) last year. This device can push hundreds of Gigabits per second within a chip that fits inside your fingertip, and we want to turn this breakthrough into a world-class coherent product. We believe it is the next step in packing exponentially more data into optical chips, allowing the world to keep up with the exponential increase in data for years to come.

In the coming weeks, we will discuss more photonic integration and how to implement it in larger volumes to make coherent transmission more widespread around the world.

Tags: bandwidth, coherent, coherent optics, Density, fiber networks, increase bandwidth density, Integrated Photonics, LightCounting, network operators, optical transceivers, photonic integration, Photonics, pluggables, Transceivers

Press Releases

September 28, 2022

Meet the team behind the EFFECT Photonics & Aston University partnership to bring greater bandwidth to a greener future

The optical transceiver market is expected to double in size by 2025, and coherent optical…

The optical transceiver market is expected to double in size by 2025, and coherent optical technology has come a long way over the past decade to become more accessible and thus have a greater impact on this market. When Nortel (later Ciena) introduced the first commercial coherent transponder in 2008, the device was a bulky, expensive line card with discrete components distributed on multiple circuit boards.

Recently, EFFECT Photonics and Aston University announced that they would collaborate as part of the newly formed Royal Academy of Engineering Research Chair in Highly Integrated Coherent Optical Fibre Communications.

To learn more about this industry/academic partnership, we interviewed the three lead researchers in this project: Prof. Wladek Forysiak, Dr. Ian Phillips, and Dr. Stylianos Sygletos.

Tell us a little more about yourself and the team

Wladek: My background goes back almost to the start of the Aston Institute of Photonics Technology (AIPT). AIPT was formed by a couple of guys who came out of British Telecom and what was then part of the GEC Telecom Company. The institute has deep industrial roots, and hence the people who work at AIPT often like to participate in projects close to the industry with relatively short timescales. I joined the institute as a post-doc and then subsequently became an academic staff member.

Around 2000, I left alongside five others for a “virtual startup” with the Marconi company, and we formed an entity called Marconi Solstis. At that time, we developed a record-breaking terrestrial ultra long haul system, and we installed our first system in Australia, linking the cities of Perth and Adelaide. Marconi then morphed into Ericsson, and I stayed there for another six to seven years.

In 2010, I moved to Oclaro (now Lumentum), which does somewhat similar technology to what’s being developed by EFFECT Photonics on their integrated indium phosphide platform. I spent three or four years there before returning to academic life at Aston. As for the team, we have funding for three full-time Ph.D. students we’re currently working to recruit. They will be the cement, the foundation of our project.

Ian: I’m of a similar background to Wladek. My expertise is in transceivers, especially characterization and design. I completed my Ph.D. at Aston in 1997 in optical signal processing. British Telecom (BT) sponsored the project, and I worked there for a year after my Ph.D. Corning subsequently purchased the BT Photonics Lab in 2000, and I stayed there for another year. Afterward, I moved to Marconi Solstis with Wladek and stayed there until 2010, when Ericsson closed the site. I then worked in Italy for two years, transferring some system knowledge to the Ericsson research group there, and finally, I joined Aston in 2012.

Stylianos: I completed my Ph.D. at the National Technical University of Athens in 2006, focusing on the physical layer modeling of optical communication systems. I worked for a year at Athens Information Technology (i.e., a research center of Intracom, the largest telecom system provider in Greece). Between 2007 and 2009, I moved for a post-doc position in the Karlsruhe Institute of Technology, working with Juerg Leuthold to model quantum-dot semiconductor optical amplifiers.

I then moved to the Tyndall National Institute in Ireland in 2009 to join the group of Andrew Ellis. I focused on the design and experimental implementation of phase-sensitive amplifiers and optical phase-locking solutions for these amplifiers.

After 2012, I joined AIPT as a research fellow, where my research interests eventually changed to digital signal processing and machine learning. I want to apply machine learning to the physical layer of optical communication systems. I’m now the director of two Master’s programs at Aston: the Smart Telecom and Sensing Networks (SMARTNET) and the Erasmus Mundus Photonic Integration and Networks (PIXNET), in collaboration with different universities in Europe and Japan.

What attracted you to collaborate with EFFECT Photonics?

Wladek: This project came about through a conversation between James (EFFECT Photonics’ CEO) and myself where he said, “Well, I’m interested in growing research activities to enhance our systems capability, and I have confidence in the experience of you and the Aston team”. So I said to him that one way to build a long-term relationship between a company and a university is through Ph.D. studentships.

AIPT is very much about doing applied research, and James was very much about the value of user-directed research that is close to the market and based on real-world situations. So he and I shared that vision around the partnership.

Another reason was, of course, that EFFECT Photonics has technology complementary to ours. EFFECT can be a source of advanced technology for us to build the best experiments that compete with the best in the world. Our competition is in the advanced labs of Japan, the US, and other areas in Europe, and having access to great components is key to matching their capabilities.

We also found attractive the ambition and drive of a startup company and its ability to make quick decisions. When I reached out to James with ideas, I could get an immediate yes or no answer, often on the call, for authorization.

Ian: James explained to us really well what EFFECT Photonics was doing, its ambitions, and how it aligned with our work. When we visited the facility in Brixham and were shown around the labs, it was all indicative of a company that wanted to get things done quickly, and hopefully, we can help them in that process.

Stylianos: On top of what Wladek already mentioned, it’s great to work with a startup that is more open to testing new technologies. I’m passionate about machine learning, and the prospect of applying machine learning algorithms to EFFECT Photonics’ novel technology platform is very exciting. I feel like there is an opportunity to make a big impact.

In what ways do the facilities of Aston University complement what EFFECT Photonics has?

Wladek: EFFECT Photonics develops advanced components that interest people like us working on optical communication systems and networks. We’re used to thinking about integrating these advanced components into our systems and getting the maximum capacity from point A to B.

We have a history of 30 years with optical fiber transmission, so we have all the necessary facilities for system modeling and testing. Stelios also brings to the party his expertise in DSP software, which is also critical to what EFFECT Photonics may do in the future.

Ian: We also see our job as training the Ph.D. students to pass on our knowledge of system design and how that reflects in EFFECT Photonics’ transceiver design. We want to train the students and get them to creatively and effectively use the components.

Stylianos: It depends on how the project goes, but we can even develop device models of EFFECT Photonics units and identify the device parameters that can meet network and system-level targets. We can even combine it with machine learning for extra optimization of those parameters.

What are some of the main challenges you hope to address?

Wladek: Looking for a greener future is a big challenge in optical comms. We’ve all witnessed it in the last couple of years with the pandemic. We need greater network capacity but also cheaper and greener. We cannot let that demand for capacity just be the same old technology since power consumption would go up and up and up.

The challenges are similar to what they’ve always been, in a way, but even more acute. And we need to do it all without really spending more money. Nobody wants to pay more for their comms at the end of the day.

We should also go in other directions to increase the capacity. For example, EFFECT Photonics’ current components are made for the optical C-band, but people in long-haul and other areas are looking at creating multiband components that can also operate in the L-band. We’ve also got projects currently looking at the S-band and shorter wavelengths. Researchers are also looking at different fibre structures to carry more and more signals.

At the same time, there’s an industry drive never to pay for more. Ultimately, that mindset has driven even more technical innovation. Capacity has gone up, but the price has gone down. It’s a relentless game, and everyone keeps saying there’s going to be a point at which we don’t need any more capacity, but if it’s there, we always find ways of using it.

Ian: One key challenge many companies are working on is increasing the baud rate, which is quite a technical problem. If you increase the baud rate, you increase the channel capacity too. It was stuck at around 28 GBaud for a long time, and now it’s going up 64 and even 100 GBaud.

Stylianos: I want to mention how important is network optimization to improve performance and reduce power consumption, which would lead to greener networks.

Network operators need to maintain large performance margins to secure a robust operation in different network conditions. In practice, however, these margins mean more power consumption. Ideally, you would like to reduce those margins by a more efficient design of your system and performance that can adapt to the different conditions. We can achieve these goals through machine learning.

This requires solutions for multi-objective optimization. For example, we are not just interested in designing the transmitter subsystem, but we want to see how transmitter performance is connected to network-level performance, as measured by throughput and power consumption. This is a complex problem that involves different layers of the system.

Takeaways

Moving towards a higher-capacity and greener future requires strong collaboration between academic and industrial partners with shared goals. EFFECT Photonics and Aston University share a vision around this greener future and the value of applied research.

This joint project will unite EFFECT Photonics’ component development expertise with Aston’s expertise in optical fiber transmission modeling, testing, and network optimization through machine learning. This union can enable faster, more affordable, and sustainable coherent products that give greater bandwidth to a greener future.

As Wladek mentioned in the interview, this joint project is looking for three PhD students to drive it forward, with the positions available to start in March, July, or October 2022. If you are interested in applying or know someone who might be interested, please visit the following link: https://jobs.aston.ac.uk/Vacancy.aspx?ref=R210549 .

Tags: Aston University, bandwidth, coherent, coherent optics, CoherentPIC, digital signal processing, DWDM, Green Energy, optical network, photonic integration, Photonics, programmable optical system-on-chip, Royal Academy of Engineers, sustainability telecommunication energy efficency, Sustainable

Press Releases

September 19, 2022

EFFECT Photonics partners with Aston University to bring greater bandwidth to a greener future

EFFECT Photonics would like to congratulate Professor Wladek Forysiak from Aston University on his recently…

EFFECT Photonics would like to congratulate Professor Wladek Forysiak from Aston University on his recently announced appointment as the Royal Academy of Engineering Research Chair in Highly Integrated Coherent optical fibre Communications.

In this joint industry/academia research partnership, the HICC project will leverage the System-on-Chip technology and expertise in high density photonic integration and manufacturing from EFFECT Photonics. The Wavelength Division Multiplexing (WDM) system design, performance testing and digital signal processing capabilities from Aston University will help further push the boundaries to broker a new era of short-distance optical networking based on “digital coherent” techniques. The aim is to identify and enable new network applications that will take coherent optics into new spaces. By further reducing the cost and power requirements of these components, sub-systems, and systems, this project will contribute to a more sustainable and greener future by providing greater bandwidth to everyone.

“EFFECT Photonics has the unique technology to build a fully integrated coherent optical system on a chip, with world leading energy efficiency that enables high performance in a small module. Prof. Forysiak embodies a distinctive combination of cutting-edge optical systems academic research with extensive industrial sector experience at Marconi, Ericsson and Oclaro, and is embedded within Aston University, one of Europe’s leading universities for optical transmission research. The Royal Academy of Engineering funding and expertise brings these elements together. With this partnership we can build a powerhouse that will push the envelope of very high bandwidth internet close to the user for the benefit of all society. I am very excited about this collaboration!” – James Regan, CEO.

“I am delighted to be supported by The Royal Academy of Engineering, EFFECT Photonics, and Aston University to work on the HICC project, together with my close colleagues, Dr Ian Phillips and Dr Stelios Sygletos. The complimentary expertise of EFFECT Photonics in highly integrated System-on-Chip photonics technology and Aston’s long experience in WDM systems R&D provides an ideal platform for this industry/academia research partnership. Together, we have a compelling vision, and I am particularly delighted by the prospect of collaborating with the innovators at EFFECT Photonics, and experiencing the energy, drive and ambition of its start-up working culture.” – Prof. Wladek Forysiak.

EFFECT Photonics’ programmable System-on-Chip technology lies at the heart of its developments in coherent optics. The aim is to provide products that offer line card performance and functions in a pluggable form factor with a very high energy efficiency. This means that performance that has historically been big and expensive, will be pushed to the edges of the network including the encryption and data security you would normally expect to find in a line card. In addition, by lowering the cost and energy consumption per bit, the next generation EFFECT Photonics solutions will enable a more sustainable and greener optical network.

About EFFECT Photonics

EFFECT Photonics delivers highly integrated optical communications products based on its Dense Wavelength Division Multiplexing (DWDM) optical System-on-Chip technology. The key enabling technology for DWDM systems is full monolithic integration of all photonic components within a single chip and being able to produce these in volume with high yield at low cost. With this capability, EFFECT Photonics is addressing the need for low cost DWDM solutions driven by the soaring demand for high bandwidth connections between datacentres and back from mobile cell towers. Headquartered in Eindhoven, The Netherlands, with additional R&D, manufacturing in South West UK and a facility opening soon in the US, with sales partners worldwide.

http://www.effectphotonics.com
Press contact: press@effectphotonics.com

Insights

September 19, 2022

Introducing our new Coherent Product Line Manager – Vladi Veljanovski

Last year, EFFECT Photonics taped out the world’s first fully integrated coherent optical transceiver chip.…

Last year, EFFECT Photonics taped out the world’s first fully integrated coherent optical transceiver chip. We are now ready to turn this engineering breakthrough into a product. To lead this process, EFFECT Photonics has hired Vladimir Veljanovski as our first Coherent Product Line Manager. To give you more insight into our new colleague and what drives him, we asked him a few questions.

Tell us a little more about yourself and your background

I was born in Macedonia and moved to Germany for my university studies, graduating in 2006 with an Engineering degree in Communication and Information Technology from the Technical University in Munich. I did my master thesis with the R&D department of Siemens Fixed Networks (later Coriant) and started working there after graduation. I started my job by simulating optical transmission systems and extracting system design rules. Soon after, I moved to the lab, which definitely attracted me more as it was closer to reality and work done on the field.

Around that time, we started testing our first 40G coherent product in the lab. Coherent was a major technology change, and customers were struggling to believe and buy into it. Hence, R&D needed to go to the customers and demonstrate the new technology. That’s when I discovered my preference for working closer to the customers. I remained in this customer-facing role until 2014, doing lots of introductory work for coherent technology in terrestrial and submarine networks. In 2014, I moved to Switzerland to work for Huawei in a technical sales role as the Sales Project Manager responsible for the Swisscom transport network. In four exciting years there, we renewed the network by introducing 200G and 400G coherent products into the network backbone and 100G coherent into the metro network.

After the Huawei experience, I wanted more of a network-level overview, which was hard to get when working with the network of a telecom carrier. Thus, I spent the next two years working in the enterprise environment. The company was smaller and more easily manageable. There I could see the whole network as an entity, not just the optics but also the switching, the firewalls, the network management, etc. And in June 2021, I joined EFFECT Photonics. I am thrilled with this transition, even though we have a lot of work to bring the product out as soon as possible.

What do you find exciting about coherent technology?

Coherent technology is not new. It has been around for a while. However, it is incredible that now those complicated benchtop systems I built in the lab back in 2009, with all the discrete components that were cumbersome to connect, can now fit into something the size of a sugar cube thanks to photonic integration. And these systems even have better performance than back then. You see that progress and think, “man, that’s awesome!”.

Coherent technology was reserved for premium long-distance links where performance is everything. Metro and access networks could not use this higher-performance technology since on the one hand, it was too bulky and expensive, and on the other, the bandwidth demand was yet to grow.

Photonic integration technology like EFFECT’ Photonics’ helped bring these big, proprietary, and expensive systems into a router pluggable form factor. This tech has squeezed more performance into a smaller area and at lower power consumption, making the device more cost-effective. Photonic integration will be a disruptive technology that will simplify network design and operation and reduce the capital and operating expenses of network operators.

What do you find exciting about working at EFFECT Photonics?

I love working with smart people with a good team spirit. I get to study and learn new things, and I continue to grow and challenge myself, which makes all the work even more fun.

I figured out that by working at EFFECT Photonics, I would be surrounded by great professionals who have worked on photonic integration for ten years or more and know and identify with this technology very well. It’s a fascinating and challenging environment for me to be in.

On that note, photonic integration technology was a big reason why I chose to work at EFFECT Photonics. I was amazed to see how a company of this size, with relatively few people, can work on such a potentially disruptive technology. I get to work on new and exciting technology, and at the same time, I can get to know almost everyone in the company. I clearly feel the “scale-up winds” blowing in my daily work.

Having worked in both R&D and sales of coherent products with network carriers and enterprise providers, Vladi possesses deep insight into coherent technology itself and how to sell it to customers. At EFFECT Photonics, we are excited to work with him, and we look forward to what he can do to turn our technology into a fantastic coherent product.

Tags: coherent, Integrated Photonics, photonic integration

Insights

September 19, 2022

How Many DWDM Channels Do You Really Need?

Optical fiber and dense wavelength division multiplex (DWDM) technology are moving towards the edges of…

Optical fiber and dense wavelength division multiplex (DWDM) technology are moving towards the edges of networks. In the case of new 5G networks, operators will need more fiber capacity to interconnect the increased density of cell sites, often requiring replacing legacy time-division multiplexing transmission with higher-capacity DWDM links. In the case of cable and other fixed access networks, new distributed access architectures like Remote PHY free up ports in cable operator headends to serve more bandwidth to more customers.

A report by Deloitte summarizes the reasons to expand the reach and capacity of optical access networks: “Extending fiber deeper into communities is a critical economic driver, promoting competition, increasing connectivity for the rural and underserved, and supporting densification for wireless.”

*Figure 1: Comparison between legacy and future deep fiber deployments in access networks. Yellow lines represent copper links, blue represents coaxial, and the green represents optical fiber.*

To achieve such a deep fiber deployment, operators look to DWDM solutions to expand their fiber capacity without the expensive laying of new fiber. DWDM technology has become more affordable than ever due to the availability of low-cost filters and SFP transceiver modules with greater photonic integration and manufacturing volumes. Furthermore, self-tuning technology has made the installation and maintenance of transceivers easier and more affordable.

Despite the advantages of DWDM solutions, their price still causes operators to second-guess whether the upgrade is worth it. For example, mobile fronthaul applications don’t require all 40, 80, or 100 channels of many existing tunable modules. Fortunately, operators can now choose between narrow- or full-band tunable solutions that offer a greater variety of wavelength channels to fit different budgets and network requirements.

Example: Fullband Tunables in Cable Networks

Let’s look at what happens when a fixed access network needs to migrate to a distributed access architecture like Remote PHY.

A provider has a legacy access network with eight optical nodes, and each node services 500 customers. To give higher bandwidth capacity to these 500 customers, the provider wants to split each node into ten new nodes for fifty customers. Thus, the provider goes from having eight to eighty nodes. Each node requires the provider to assign a new DWDM channel, occupying more and more of the optical C-band. This network upgrade is an example that requires a fullband tunable module with coverage across the entire C-band to provide many DWDM channels with narrow (50 GHz) grid spacing.

Furthermore, using a fullband tunable module means that a single part number can handle all the necessary wavelengths for the network. In the past, network operators used fixed wavelength DWDM modules that must go into specific ports. For example, an SFP+ module with a C16 wavelength could only work with the C16 wavelength port of a DWDM multiplexer. However, tunable SFP+ modules can connect to any port of a DWDM multiplexer. This advantage means technicians no longer have to navigate a confusing sea of fixed modules with specific wavelengths; a single tunable module and part number will do the job.

Figure 2: Example of a point-to (multi-)point system with fullband tunable modules. Each of the 10G SFP+ modules is a full C-band tunable covering ITU channels 14 to 61. This link uses the different wavelengths for up-and downstream transmission, allowing for a full-duplex transmission across a single fiber and multiplexer.

Overall, fullband tunable modules will fit applications that need a large number of wavelength channels to maximize the capacity of fiber infrastructure. Metro transport or data center interconnects (DCIs) are good examples of applications with such requirements.

Example: Narrowband Tunables in Mobile Fronthaul

The transition to 5G and beyond will require a significant restructuring of mobile network architecture. 5G networks will use higher frequency bands, which require more cell sites and antennas to cover the same geographical areas as 4G. Existing antennas must upgrade to denser antenna arrays. These requirements will put more pressure on the existing fiber infrastructure, and mobile network operators are expected to deliver their 5G promises with relatively little expansion in their fiber infrastructure.

*Figure 3: Simplified diagram that shows and compares the building blocks of 4G (left) and 5G (right) access networks and the links between these blocks.*

DWDM solutions will be vital for mobile network operators to scale capacity without laying new fiber. However, operators often regard traditional fullband tunable modules as expensive for this application. Mobile fronthaul links don’t need anything close to the 40 or 80 DWDM channels of a fullband transceiver. It’s like having a cable subscription where you only watch 10 out of the 80 TV channels.

This issue led EFFECT Photonics to develop narrowband tunable modules with just nine channels. They offer a more affordable and moderate capacity expansion that better fits the needs of mobile fronthaul networks. These networks often feature nodes that aggregate two or three different cell sites, each with three antenna arrays (each antenna provides 120° coverage at the tower) with their unique wavelength channel. Therefore, these aggregation points often need six or nine different wavelength channels, but not the entire 80-100 channels of a typical fullband module.

With the narrowband tunable option, operators can reduce their part number inventory compared to grey transceivers while avoiding the cost of a fullband transceiver.

Synergizing with Self-Tuning Algorithms

The number of channels in a tunable module (up to 100 in the case of EFFECT Photonics fullband modules) can quickly become overwhelming for technicians in the field. There will be more records to examine, more programming for tuning equipment, more trucks to load with tuning equipment, and more verifications to do in the field. These tasks can take a couple of hours just for a single node. If there are hundreds of nodes to install or repair, the required hours of labor will quickly rack up into the thousands and the associated costs into hundreds of thousands.

*Figure 4: Short description and comparison of different approaches to DWDM tunable modules.*

Self-tuning allows technicians to treat DWDM tunable modules the same way they treat grey transceivers. There is no need for additional training for technicians to install the tunable module. There is no need to program tuning equipment or obsessively check the wavelength records and tables to avoid deployment errors on the field. Technicians only need to follow the typical cleaning and handling procedures, plug the transceiver, and the device will automatically scan and find the correct wavelength once plugged. This feature can save providers thousands of person-hours in their network installation and maintenance and reduce the probability of human errors, effectively reducing capital and operational expenditures.

Self-tuning algorithms make installing and maintaining narrowband and fullband tunable modules more straightforward and affordable for network deployment.

Takeaways

Fullband self-tuning modules will allow providers to deploy extensive fiber capacity upgrades more quickly than ever. However, in use cases such as mobile access networks where operators don’t need a wide array of DWDM channels, they can opt for narrowband solutions that are more affordable than their fullband alternatives. By combining fullband and narrowband solutions with self-tuning algorithms, operators can expand their networks in the most affordable and accessible ways for their budget and network requirements.

Tags: 100G, 5G, 6G, access, access networks, aggregation, backhaul, capacity, coherent, DWDM, fronthaul, Integrated Photonics, LightCounting, live events, metro, midhaul, mobile, mobile access, mobile networks, network, optical networking, optical technology, photonic integrated chip, photonic integration, Photonics, PIC, PON, programmable photonic system-on-chip, solutions, technology, VR, WDM

Insights

September 19, 2022

The Future of Passive Optical Networks

Like every other telecom network, cable networks had to change to meet the growing demand…

Like every other telecom network, cable networks had to change to meet the growing demand for data. These demands led to the development of hybrid fiber-coaxial (HFC) networks in the 1990s and 2000s. In these networks, optical fibers travel from the cable company hub and terminate in optical nodes, while coaxial cable connects the last few hundred meters from the optical node to nearby houses. Most of these connections were asymmetrical, giving customers more capacity to download data than upload.

That being said, the way we use the Internet has evolved over the last ten years. Users now require more upstream bandwidth thanks to the growth of social media, online gaming, video calls, and independent content creation such as video blogging. The DOCSIS standards that govern data transmission over coaxial cables have advanced quickly because of these additional needs. For instance, full-duplex transmission with symmetrical upstream and downstream channels is permitted under the most current DOCSIS 4.0 specifications.

Fiber-to-the-home (FTTH) systems, which bring fiber right to the customer’s door, are also proliferating and enabling Gigabit connections quicker than HFC networks. Overall, extending optical fiber deeper into communities (see Figure 1 for a graphic example) is a critical economic driver, increasing connectivity for the rural and underserved. These investments also lead to more robust competition among cable companies and a denser, higher-performance wireless network.

*Figure 1. Comparison between legacy fiber deployments in access networks vs. future deep fiber deployments.*

Passive optical networks (PONs) are a vital technology to cost-effectively expand the use of optical fiber within access networks and make FTTH systems more viable. By creating networks using passive optical splitters, PONs avoid the power consumption and cost of active components in optical networks such as electronics and amplifiers. PONs can be deployed in mobile fronthaul and mid-haul for macro sites, metro networks, and enterprise scenarios.

Despite some success from PONs, the cost of laying more fiber and the optical modems for the end users continue to deter carriers from using FTTH more broadly across their networks. This cost problem will only grow as the industry moves into higher bandwidths, such as 50G and 100G, requiring coherent technology in the modems.

Therefore, new technology and manufacturing methods are required to make PON technology more affordable and accessible. For example, wavelength division multiplexing (WDM)-PON allows providers to make the most of their existing fiber infrastructure. Meanwhile, simplified designs for coherent digital signal processors (DSPs) manufactured at large volumes can help lower the cost of coherent PON technology for access networks.

The Advantages of WDM PONs

Previous PON solutions, such as Gigabit PON (GPON) and Ethernet PON (EPON), used time-division multiplexing (TDM) solutions. In these cases, the fiber was shared sequentially by multiple channels. These technologies were initially meant for the residential services market, but they scale poorly for the higher capacity of business or carrier services. PON standardization for 25G and 50G capacities is ready but sharing a limited bitrate among multiple users with TDM technology is an insufficient approach for future-proof access networks.

This WDM-PON uses WDM multiplexing/demultiplexing technology to ensure that data signals can be divided into individual outgoing signals connected to buildings or homes. This hardware-based traffic separation gives customers the benefits of a secure and scalable point-to-point wavelength link. Since many wavelength channels are inside a single fiber, the carrier can retain very low fiber counts, yielding lower operating costs.

Figure 2: Example of a simplified WDM-PON architecture with 64 different wavelengths. It includes multiplexers (MUX) and demultiplexers (DEMUX) as well as a splitter device based on arrayed waveguide gratings (AWGs). This splitter is found between the optical line terminal (OLT) at the company headend and the optical network unit (ONU) at the customer’s end. Figure sourced from *this paper* *from Sharma et al.*

WDM-PON has the potential to become the unified access and backhaul technology of the future, carrying data from residential, business, and carrier wholesale services on a single platform. We discussed this converged access solution in one of our previous articles. Its long-reach capability and bandwidth scalability enable carriers to serve more customers from fewer active sites without compromising security and availability.

Migration to the WDM-PON access network does require a carrier to reassess how it views its network topology. It is not only a move away from operating parallel purpose-built platforms for different user groups to one converged access and backhaul infrastructure. It is also a change from today’s power-hungry and labor-intensive switch and router systems to a simplified, energy-efficient, and transport-centric environment with more passive optical components.

The Possibility of Coherent Access

As data demands continue to grow, direct detect optical technology used in prior PON standards will not be enough. The roadmap for this update remains a bit blurry, with different carriers taking different paths. For example, future expansions might require using 25G or 50G transceivers in the cable network, but the required number of channels in the fiber might not be enough for the conventional optical band (the C-band). Such a capacity expansion would therefore require using other bands (such as the O-band), which comes with additional challenges. An expansion to other optical bands would require changes in other optical networking equipment, such as multiplexers and filters, which increases the cost of the upgrade.

An alternative solution could be upgrading instead to coherent 100G technology. An upgrade to 100G could provide the necessary capacity in cable networks while remaining in the C-band and avoiding using other optical bands. This path has also been facilitated by the decreasing costs of coherent transceivers, which are becoming more integrated, sustainable, and affordable. You can read more about this subject in one of our previous articles.

For example, the renowned non-profit R&D center CableLabs announced a project to develop a symmetric 100G Coherent PON (C-PON). According to CableLabs, the scenarios for a C-PON are many: aggregation of 10G PON and DOCSIS 4.0 links, transport for macro-cell sites in some 5G network configurations, fiber-to-the-building (FTTB), long-reach rural scenarios, and high-density urban networks.

CableLabs anticipates C-PON and its 100G capabilities to play a significant role in the future of access networks, starting with data aggregation on networks that implement a distributed access architecture (DAA) like Remote PH. You can learn more about these networks here.

Combining Affordable Designs with Affordable Manufacturing

The main challenge of C-PON is the higher cost of coherent modulation and detection. Coherent technology requires more complex and expensive optics and digital signal processors (DSPs). Plenty of research is happening on simplifying these coherent designs for access networks. However, a first step towards making these optics more accessible is the 100ZR standard.

100ZR is currently a term for a short-reach (~80 km) coherent 100Gbps transceiver in a QSFP pluggable size. Targeted at the metro edge and enterprise applications that do not require 400ZR solutions, 100ZR provides a lower-cost, lower-power pluggable that also benefits from compatibility with the large installed base of 50 GHz and legacy 100 GHz multiplexer systems.

Another way to reduce the cost of PON technology is through the economics of scale, manufacturing pluggable transceiver devices at a high volume to drive down the cost per device. And with greater photonic integration, even more, devices can be produced on a single wafer. This economy-of-scale principle is the same behind electronics manufacturing, which must be applied to photonics.

Researchers at the Technical University of Eindhoven and the JePPIX consortium have modeled how this economy of scale principle would apply to photonics. If production volumes can increase from a few thousand chips per year to a few million, the price per optical chip can decrease from thousands of Euros to tens of Euros. This must be the goal of the optical transceiver industry.

Figure 3: Modelling of photonic integrated chip (PIC) cost as a function of the aggregate number of PICs produced per year. Exponential increases in production lead to an exponential decrease in cost. Model and graph provided by Prof. Meint Smit, TU Eindhoven.

Takeaways

Integrated photonics and volume manufacturing will be vital for developing future passive optical networks. PONs will use more WDM-PON solutions for increased capacity, secure channels, and easier management through self-tuning algorithms.

Meanwhile, PONs are also moving into incorporating coherent technology. These coherent transceivers have been traditionally too expensive for end-user modems. Fortunately, more affordable coherent transceiver designs and standards manufactured at larger volumes can change this situation and decrease the cost per device.

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