I sat down with Argemiro Sousa, Chief Operations Officer for Equipment at Padtec, who shed some light on the development of this new product line and the company’s plans for the future. As Argemiro pointed out “The LightPad Max platform not only demonstrates our commitment to offer state-of-the-art innovative products, but it also furthers Padtec’s goal to extend our leadership in the Brazilian market while expanding our presence in the international market.” This includes a focus on Latin America, the United States, Europe, and Africa.
Development Goals: Performance, Time-to-Market, Form Factor and Robustness
As Argemiro explained, developing a new transponder is a long-cycle project and the transmission module is a key component for its success. Each year, coherent technology is improving its power consumption, advanced DSP algorithms and maximum GBaud rate. As the industry approaches the Shannon limit in fiber optics, these improvements are what make it possible to continue lowering the cost per bit in Padtec’s customers’ networks. Padtec chose Acacia’s CIM 8 because it enabled them to meet the following key requirements:
- Performance: Enabling channels with up to 140 GBaud is essential to continue reducing the cost per bit in DWDM networks. The minimum received OSNR required by the CIM 8 enabling rates of 400G and above, making these high rates feasible in ultra-long-haul and long-haul networks.
- Time to market: As an equipment manufacturer, Padtec starts developing its products before the optical modules are commercially available. “From previous experiences, we see Acacia as an aggressive player in getting to the market first and delivering cutting edge technology,” added Argemiro.
- Form factor: The CIM 8 is a module focused on performance and yet is pluggable. Since its transponder design considers two modules, Padtec can offer a pay-as-you-grow model to its customers.
- Robustness: Padtec needed a module that was highly reliable and had low rates of defect and they knew from experience that this was an Acacia strength.
Disaggregated Design Drives Cost Effectiveness in New LightPad Max Platform
Padtec’s goal with the LightPad Max was to repeat the success of its TM800G in Latin America by entering the Terabit era with a very competitive product that lowers total cost of ownership. Designed to optimize density and legacy compatibility, each line interface has 6 associated client interfaces capable of working both with 400GbE based on QSFP-DD and 100GbE QSFP-28 legacy interfaces, which are still prevalent in Padtec’s customers’ routers and switches.
One Product Family Spanning Multiple Markets
Targeting medium, long and ultra-long distances, the LightPad Max platform not only delivers scalability and cost effectiveness, but its disaggregated design also reduces space on customers’ infrastructure. And as a bonus, the standalone form factor makes the product more attractive to Alien Wavelength scenarios and the architecture is aligned to SDN technological trends.
Since the LightPad Max is a programmable transponder, operators can configure it with different rates and operational modes according to its needs. “This feature has great potential for the product to adapt to several network characteristics,” claimed Argemiro. “For instance, LightPad Max will make it possible to reach long haul and ultra long haul distances with 400G line rate, as well as higher rates of 1T or above in short distances such as data center interconnect scenarios.”
Padtec and Acacia’s Long-Standing Partnership
With the successful launch of the first LightPad Max family members, Padtec also plans to release future versions with advanced functionalities to be delivered by firmware updates throughout 2024 and 2025. The company already has agreements with some of its main customers to deploy in their networks.
At Acacia, we could not be more thrilled to see Padtec succeed on a global scale. We are also extremely proud of our long-term partnership, which dates back to 2016 when Padtec launched its 200G line cards based on Acacia’s CFP2-DCO. Recently, these same line cards were adapted and qualified to use Acacia’s new generation 400G CPF2-DCO, based on the Greylock DSP.
Padtec was an early adopter of Acacia’s AC1200 module with its TM800G and TM1200G products, which Padtec has sold thousands of units of since 2020. And we can’t forget our 400G pluggable family – the fastest growing coherent ramp-up of all time. Padtec launched a disaggregated TMD400G standalone offering using Acacia’s 400G QSFP-DD OpenZR+ in 2023.
Lighting up the Future with Padtec Innovation and Customer Loyalty
Padtec ended 2023 with net revenue of R$ 368 million (US $70 million) which represented record gross profit and distribution of dividends. It was also the year the company saw a significant increase in its customer loyalty index, measured by survey based on the Net Promoter Score (NPS) methodology. Padtec achieved a NPS index of +77, a result that places it in the “Excellence zone.” This was a significant jump compared to 2022, when the company’s NPS was +55, and the highest historical level since the survey began in 2017.
As Argemiro explained, “The NPS survey showed that we are on the right path, by reinforcing our position of commitment to the success of our customers and investing increasingly in the technological evolution of our solutions and in expanding our service portfolio. The flexibility to meet customer needs, both from a commercial point of view and in the offering of products and services, is an important differentiator for Padtec that was recognized in this research. We are constantly seeking ways to expand and enhance our services, and as a result, we aim to serve our customers better with each passing day.”
Customer loyalty and technological innovation are clearly what drives Padtec day in and day out. On behalf of the entire Acacia team, we look forward to seeing what the company achieves in the future and are excited to continue our trusted partnership to help them grow and succeed.
]]>To date, multiple system vendors have converged around Class 3-based solutions (Figure 1), recently announcing their next generation offerings. This industry convergence creates the benefit of economies of scale and broad industry investments into the technology used in this baud rate class, the same class being used for 800G MSA pluggable solutions.
Figure 1. Acacia and other coherent vendors have announced Class 3 Terabit Era solutions.
Advancements Resulting in 65% Power-per-Bit Savings Over Current Competing Solutions
Doubling the baud rate from Class 2 to Class 3 in silicon was a significant engineering achievement, combining design advancements in high-speed Radio Frequency (RF) and Analog to Digital Converter (ADC) and Digital to Analog Converter (DAC) components plus well-designed co-packaging integration of silicon and silicon photonic (SiPh) components. These achievements led to Acacia’s successful 140Gbaud in-house capability that is being leveraged in the commercially available CIM 8 solution.
With high-volume shipments of multiple coherent Class 2 module products utilizing Acacia’s 3D Siliconization, this proven co-packaging integration solution provided the foundation for extending this capability to Class 3 140Gbaud implementation utilized in the CIM 8 (Figure 2). 3D Siliconization maximizes signal integrity by co-packaging all high-speed components including the coherent Digital Signal Processor (DSP) application-specific integrated circuit (ASIC), transmitter and receiver silicon photonics, and 3D stacked RF components into a single device that is manufactured in a standard electronics packaging house. Silicon technology has demonstrated cost and power advantages over alternative technologies, making it the material system of choice for these higher baud rates. These advancements enabling a doubling of the baud rate have led to a 65% power-per-bit savings of CIM 8 over current competing solutions that utilize alternative optical material systems. In addition, the size and power savings of this latest generation enabled the ability to house this 1.2T 140Gbaud solution in a pluggable form-factor.
Figure 2. An example of 3D Siliconization used in the CIM 8 module, resulting in a volume electronics manufacturable high-speed single device larger than a quarter.
2nd Generation 3D Shaping Advances Coherent Performance
The CIM 8 is powered by Jannu, Acacia’s 8th generation coherent DSP ASIC. The design greatly expands on the success of the Pico DSP ASIC predecessor used in the widely deployed performance-optimized Class 2 AC1200 module (Figure 1). The AC1200 was the first module to introduce 3D Shaping, which provided finely tunable Adaptive Baud Rate up to 70Gbaud as well as finely tunable modulation up to 6 bits/symbol. The AC1200 had achieved record breaking spectral efficiency at the time of its introduction, as evidenced by a subsea trial over the MAREA submarine cable connecting Virginia Beach, Virginia to the city of Bilbao in Spain. Finely tunable baud rate helps maximize spectral efficiency in any given passband channel, converting excess margin into additional capacity/reach, and avoids wasted bandwidth due to network fragmentation.
Figure 3. A popular feature is the fine-tunability of baud rate introduced by Acacia with the Class 2 AC1200; CIM 8 incorporates the same Adaptive Baud feature (as part of 2nd Generation 3D Shaping) for Class 3 baud rate tunability.
The 5nm Jannu DSP ASIC in CIM 8 intelligently optimizes optical transmission using 2nd Generation 3D Shaping with an increased Adaptive Baud Rate tunable range up to 140Gbaud, as well as finely tunable modulation up to 6 bits/symbol using enhanced Probabilistic Constellation Shaping (PCS). With 2nd Generation 3D Shaping, the CIM 8 module can achieve a 20% improvement in spectral efficiency.
Terabit Era Solutions Provide Full Network Coverage
Class 3 technology not only ushers in the terabit era, but also enables full multi-haul network coverage as the high baud rate capabilities transport nx400GbE client traffic across a service provider’s entire network. Full network coverage is not only enabled by adjustment of the modulation, but also implies the capability to optimize for various network conditions which include overcoming transmission impairments.
Figure 4. CIM 8 1.2T, 1T, 800G, and 400G transmission constellations operating at Class 3 baud rates providing wide network coverage addressing multiple applications.
CIM 8 offers significant power-per-bit reductions as well as cost efficiencies for various optical network transport applications.
DCI/Metro Reaches
For transporting 3x400GbE or 12x100GbE client traffic with metro reaches in a single carrier, the CIM 8 is tuned to ~6 bits/symbol (equivalent to 64QAM, example constellation on left). Data center interconnect (DCI) applications would take advantage of this high-capacity 1.2T transport capability to tie data center locations together. This amounts to 38.4T per C-band fiber capacity.
Long-Haul Reaches
For transporting 2x400GbE with long-haul reaches, the CIM 8 is tuned to ~4 bits/symbol (equivalent to 16QAM, example constellation on the right). Wide 800G network coverage is achieved with the Class 3 140Gbaud capabilities enabling service providers to provide end-to-end 2x400GbE, 8x100GbE, or native 800GbE transport across their networks, covering essentially all terrestrial applications.
Ultra-Long-Haul/Subsea Reaches
And for ultra-long-haul/subsea reaches, the CIM 8 is tuned to ~2 bits/symbol (equivalent to QPSK, example constellation on the left). As with the previous scenarios, spectral efficiency with a wavelength channel is optimized by fine-tuning of the baud rate. These high spectrally efficient modes can carry mixed 100GbE and 400GbE traffic over the longest subsea routes in the world with lowest cost per bit. It’s worth noting that almost a decade ago, Acacia demonstrated SiPh capabilities for subsea coherent deployments. CIM 8 incorporates second generation non-linear equalization (NLEQ) capabilities to mitigate the non-linear effects of optical transmission especially for these ultra-long-haul/subsea links providing additional OSNR.
In all the above scenarios, the CIM 8 utilizes advanced power-efficient algorithms to compensate for chromatic and polarization dependent dispersion. In addition, the module accounts for coverage of aerial fiber network segments that require fast state-of-polarization (SOP) tracking and recovery due to lightning strikes. The SOP tracking speed of CIM 8 is double the speed of its predecessor. This fast SOP tracking feature can also be utilized for sensing applications.
Network Operators Achieve Record Breaking Field Trials with CIM 8
CIM 8 capabilities have already been put to the test as illustrated by multiple record breaking field trials across a wide range of applications. These include >5600km 400G transmission over a mobile carrier’s backbone network, 2200km 800G transmission over a research and education network, and >540km 1T transmission over a wholesale carrier’s network.
Acacia continues to demonstrate its technology leadership by leveraging mature knowledge in proven silicon-based coherent technology, producing the first shipping coherent solution to lead the industry into the Terabit Era with the 1.2T pluggable CIM 8 module. With the breakthrough capability of 140Gbaud transmission along with the advanced Jannu DSP ASIC using 2nd Gen 3D Shaping and leveraging 3D Siliconization, network operators can support full network coverage for multi-haul applications, especially to support growing demands for nx400GbE and upcoming 800GbE traffic.
References:
Blog: Terabit Today: Maximize Network Coverage
Blog: How Industry Trends are Driving Coherent Technology Classifications
Blog Series: The Road Ahead for Next-Generation Multi-Haul Designs Part 1, Part 2, Part 3
Acacia is excited to share the results of three breakthrough live network trials showing Ultra Long Haul, Long Haul and Regional distances recently completed by Adtran with NYSERNet, China Mobile with ZTE, and Windstream Wholesale, all leveraging Acacia’s Coherent Interconnect Module 8 (CIM 8). As these trials demonstrate, the CIM 8 enables network operators to achieve the highest capacity and reach today while maximizing transmission data rate across a wide range of multi-haul network applications including DCI, metro, long haul, and subsea.
Adtran Breaks Industry Record for Single-Carrier 800G Long-Haul Transport
Adtran announced that it successfully completed a field trial of 800G single-carrier transport, achieving error-free transmission over a record distance of 2,220km in NYSERNet’s production network. The test route passed through 14 route-and-select flexgrid ROADMs comprising a total of 28 wavelength-selective switches. Leveraging Acacia’s 140GBd DSP technology, this result was made possible by Adtran’s use of continuous symbol rate tuning and probabilistic constellation shaping offered by the CIM 8 module. The trial showcases an opportunity for network operators to increase capacity and efficiency while minimizing complexity and cost.
A post-deadline paper accepted by OFC, using the NYSERNet production network, describes the 800G trial over a distance of 2,220km, an error-free 1T single-carrier real-time transmission over 869km, and an error-free transmission of single-carrier 138 Gbaud 800G over 1,422km with filtering from 24 wavelength selective switches (WSS) from in-line reconfigurable optical add drop multiplexers (ROADMs) configured to 150-GHz slot width.
According to Sorin Tibuleac, director of system architecture at Optical Networks at Adtran, “We’ve taken single-carrier 800Gbit/s data transmission further than ever before. And we’ve achieved it not in a lab but in a real-world network also carrying live traffic. What’s more, we succeeded without any optimization to the line system, maintaining the same amplifier settings used before the field trial. We’ve demonstrated that the highest capacity and reach can now be accomplished even over deployed fiber comprising a mix of standard G.652 and G.655 and including multiple network nodes and flexgrid ROADMs. Building on the success of our TeraFlexTM CoreChannelTM technology, these results represent the next milestone in the development of high-speed optical networks. The potential to enhance throughput while minimizing opex and operational complexity is immense.”
China Mobile’s 400G All-Optical Network Sets Record for Ultra Long Distance Transmission
China Mobile announced the world’s longest distance 400G optical transmission with help from ZTE. Using 400G QPSK non-electric relay network transmission the distance set a record. The network spans Zhejiang, Jiangxi, Hunan, and Guizhou provinces, involving 45 optical discharge segments, achieving 5,616 kilometers of ultra-long-distance real-time network transmission.
The trial was completed to accelerate the development of 400G high-speed optical transmission in the industry. China Mobile believes the construction of a 400G all-optical network will provide strong support for faster transmission, greater capacity, and lower latency of computing network services.
Windstream Wholesale Sets Live Network Record with 1T Wave over 540km
Windstream Wholesale announced the completion of a live network trial that successfully deployed a 1T wave over 541 kilometers across Windstream’s Intelligent Converged Optical Network (ICON) network between Dallas and Tulsa. The trial employed Acacia’s CIM 8, which is powered by the Jannu DSP and is the industry’s first pluggable module in the “High-Performance” category that represents the next evolution in driving high-capacity optical connections to expand the network. The team also looped the circuit to establish an 800G link over a live network measuring 1,082 kilometers.
The 1T trial marked the first use of pluggable modules in the High-Performance category. Acacia’s modules reduce power consumption by more than 65% while being more than 70% smaller than traditional network gear. In addition, the performance gains allow for a significant jump in route coverage of high line rates such as 800G and above.
According to Art Nichols, Chief Technology Officer for Windstream, “With this trial, Windstream Wholesale and Acacia have broken through the Terabit limit, once again demonstrating the power and benefit of an open, disaggregated network. Our success here further validates Windstream Wholesale’s early adoption of the latest evolution advancements of coherent pluggables, and our strong partnership with Acacia enables us to understand and meet the rapidly evolving bandwidth needs of our customers.”
“As Windstream Wholesale is demonstrating, our CIM 8 module is breaking the Terabit threshold with deployable performance on a real network,” said Benny Mikkelsen, Chief Technology Officer at Acacia. “By leveraging silicon photonics, we’ve been able to achieve the power consumption needed to bring the CIM 8 into a pluggable form factor and that is going to help Windstream cost-effectively meet their customers’ growing bandwidth demands.”
Join the Terabit Era
If you’re ready to join the Terabit Era with CIM 8, contact us to schedule a field trial.
]]>As an example, Acacia’s high-performance Pico DSP-based 1.2 Terabit solution is currently deployed in well over one hundred networks around the globe and has been adopted by three of the four largest hyperscalers. In 2020 alone, Acacia shipped more than 30,000 Pico-based ports as customers increasingly recognized the competitive benefits that high-performance, flexible coherent transmission solutions can provide.
Network Transmission Flexibility Benefits
Multi-haul coherent solutions like the Pico DSP-based 1.2 Terabit solution are software configurable transponder modules that provide various transmission capacities and reaches. By varying the modulation order and baud rate settings, it can provide flexible options for service providers.
A multi-haul coherent solution addresses a range of network applications.
Balancing Modulation Order and Baud Rate
A common method of increasing throughput of a coherent channel is to increase the modulation order. However, this may result in a reduction in reach due to reduced optical signal to noise ratio (OSNR) tolerance for the higher modulation orders. Alternatively, the baud rate could be increased while maintaining a lower modulation order which provides additional capacity per channel with minimal sacrifice to reach.
Maximizing the channel capacity using continuously tunable baud rate can convert unused spectrum into usable capacity, with the goal to fill up the available channel bandwidth. However, as discussed in this whitepaper, increasing baud rate provides minimal improvements in fiber capacity once the transmission is well-matched to the channel.
Increasing transmission baud rate proportionally increases the transmission spectrum and can be used to convert unused spectrum into useable extra capacity.
With transmission flexibility, service providers can configure their client traffic with the following flexible options:
- 12×100 GbE or 3×400 GbE with 64 QAM modulation for DCI edge applications
- 8×100 GbE or 2×400 GbE with 16 QAM modulation for metro/regional and long haul
- 4×100 GbE or 1×400 GbE QPSK for the most challenging terrestrial and submarine networks
To ensure a smooth migration from 100GbE to 400GbE, it’s important to have a solution that can efficiently transport either type of traffic, or a combination of both, without restrictions on performance and functionality.
Increase Performance and Reach with 400GbE Long Haul
With 400GbE becoming the “common currency” for high-capacity Ethernet transmission, it’s important to have a solution that can support this traffic over long distances. For service providers supporting 400GbE traffic they can use Acacia’s Pico DSP-based solution and choose from various configurations, as previously mentioned, including the option to combine two 400GbE client signals into an 800G 150 GHz channel for transmission over their metro and long-haul networks.
Leveraging Acacia’s Pico DSP-based solution service providers can combine two 400GbE client signals into an 800G 150GHz channel for long haul transmission.
Migrating from 100G to Higher Speeds Just Got Easier
Multi-haul coherent solutions enable network operators to easily migrate from 100G traffic toward 400G and higher speeds to deploy new and exciting applications and services. Networks utilizing flexible coherent transmission can provide support for growing client traffic across the entire network—from DCI edge, metro, long-haul, and all the way to submarine. Learn more in this video.
Acacia is gearing up for a great show at ECOC 2019 – and Dublin is a great place to host Europe’s largest optical communications event. We look forward to having another opportunity to discuss the latest trends and innovations with our customers and partners including multi-haul applications, 400GbE, 400ZR and open optical standards.
Network operators are looking to support today’s 100GbE clients, as well as emerging 400GbE clients, across key network segments such as DCI edge, metro, long-haul and submarine in an efficient, scalable, and cost-effective manner. Multi-haul coherent solutions, software configurable transponders that provide various transmission capacities and reaches by varying the modulation order and baud rate settings, can provide flexible options for network operators.
Introducing the AC1200-SC2 Coherent 1.2T Single-Chip, Single-Channel Module
One such solution is the AC1200-SC2 (‘SC squared’). Powered by Acacia’s 1.2T Pico DSP chip, the AC1200-SC2 coherent 1.2T single-chip, single-channel module was designed to enable network operators to support today’s 100GbE clients, as well as emerging 400GbE clients.
Figure 1: Acacia’s AC1200-SC2 Coherent 1.2T Single-Chip, Single-Channel Module
We are excited to demonstrate our newest AC1200 family member just announced last week. The AC1200-SC2’s high-performance and flexibility make it ideally suited for multi-haul applications ranging from high-capacity 1.2T DCI edge to the most challenging terrestrial and submarine networks that require 400G transport over QPSK modulation. The module also features Acacia’s 3D shaping technology designed to optimize fiber capacity and reach by filling gaps in margin and spectrum. Check out this video to learn how 3D shaping allows for the fine-tune adjustment of the modulation order and baud rate to provide network operators with the ability to adapt the transmission characteristics to meet the requirements of both greenfield and brownfield deployments.
Standardized Coherent Interconnects
Standardization activities have defined a variety of interoperability modes supporting operation ranging from 100G to 400G. Recently there have been many opinions on the idea of ZR+. What if a mode was created to combine the benefits of elements from 400ZR and OpenROADM, two existing standards, to define and deliver an interoperable ZR+ mode called OpenZR+?
The result is an open, flexible and interoperable coherent solution in a small form factor pluggable module. By simply defining a data path that includes the appropriate functionality, an interoperable OpenZR+ mode can be established. These enhanced modes will allow an OpenZR+ module in a QSFP-DD or OSFP form factor to support reaches well beyond 400ZR. The OpenZR+ modes are supported by merchant DSP vendors who have exchanged test vectors to ensure the interoperability of these OpenZR+ implementations. The availability of merchant DSP solutions supporting OpenZR+ will further expand the ecosystem of module vendors supporting OpenZR+. We’re sure to hear more about OpenZR+ at ECOC. For a more detailed explanation of OpenZR+ and its growing momentum please refer to the Optical Connections Magazine contributed article titled “OpenZR+ Offers Performance and Interoperability.”
Acacia Thought Leaders Speaking at ECOC
We are proud to have our Acacia experts sharing their views about some of the topics mentioned above.
- Tom Williams, Acacia’s Vice President of Marketing, is speaking on a Market Focus Panel titled “Next Generation Coherent – Beyond Transport Networks.” Tom’s panel is scheduled for Tuesday, September 24th at 13:15.
- Hongbin Zhang, Acacia’s Principal DSP Designer, is speaking on a panel titled “Real-Time Transmission of Single-Carrier 400 Gb/S And 600 Gb/S 64QAM Over 200km-Span Link, scheduled for Tuesday, September 24th at 14:45.
If We are “Lucky,” We’ll See you there!
If you are attending ECOC 2019, we’d love to see you. To set up a meeting at the show, contact us.
]]>Coherent transmission w/ varying baud rates and modulation modes applicable to multiple types of networks has been referred to as multi-haul, as described in the OFC 2018 Show Report. A ROADM-rich network design is typically attributed to traditional metro networks. However, with the rise of multi-haul capable coherent technology, the lines between what is considered metro and long haul are sometimes blurred. A previous blog post provided a brief tutorial of coherent optical communications and how it is applied to long-haul, DCI, and metro networks. I encourage you to read that post as it provides a good background for this blog post.
A benefit of coherent optical transmission is that the bandwidth capacity of a link can be increased by moving to a higher modulation order (e.g, from 2-bits/symbol QPSK to 4-bits/symbol 16QAM), as long as there is sufficient optical signal-to-noise ratio (OSNR) margin to overcome the resulting penalty. Acacia’s patented Fractional QAM (F-QAM) provides a higher level of granularity compared to traditional quantized integer-bits/symbol modulation orders, by enabling non-integer bits-per-symbol (e.g, 3.3 bits/symbol) modulation, to better optimize link capacity. Another adjustable “knob” to increase capacity is the transmission baud rate, which directly varies the spectral width of the signal. Similar to traditional quantized modulation orders, coherent technology has previously implemented quantized baud rates. However, these quantized baud rates may result in sub-optimal use of the available channel bandwidth—that is, the spectral width of the transmission does not fill up the channel’s available passband. Adaptive Baud Rate provides the granularity to enable increased optimization of the available passband. F-QAM and Adaptive Baud Rate are elements of the Acacia AC1200 coherent transponder module’s 3D shaping capability.
In a multi-haul network where optical transmission between end points may encounter numerous cascaded optical filters, one challenge is to spectrally optimize the optical transmission to fit within the aggregate passband of these filters from either fixed or reconfigurable add/drops of the network’s line system, as shown in Figure 1.
Figure 1. Spectrally quantized transmission may leave spectral gaps in aggregate passband.
As previously mentioned, quantized baud rates may not allow enough flexibility and granularity to fill up the passband. However, by using Adaptive Baud Rate, the capacity can be increased to more closely match the available spectrum within the aggregate passband of the cascaded filters with fine granularity, as shown in Figure 2.
Figure 2. Acacia’s Adaptive Baud Rate can optimize the spectral transmission to more closely match the available aggregate passband spectrum.
The aggregate passband of the cascaded filters contributes to the upper bound limit of capacity increase one can achieve in a multi-haul network optical link. In this case, I am not referring to the theoretical Shannon Limit. Rather, I am referring to the practical passband constraints that come from the implementation in a network of cascaded imperfect optical filter passbands due to variations of the filter conditions. Variations may become more prevalent if the optical transmission passes through a multi-vendor line system environment, a potential situation in a disaggregated network architecture. Having the ability to vary modulation and baud rate allows for maximal flexibility in optimizing the transmission to more closely match the line system’s available passband, as opposed to matching the line system to the terminal equipment’s optical characteristics.
As previously mentioned, Acacia’s 3D Shaping capability, as illustrated in Figure 3, enables the “dialing-in” of both modulation mode and baud rate.
Figure 3. Acacia’s 3D shaping capability enables optimization of link capacity and reach; shaping of spectral width is achieved using Adaptive Baud Rate.
This capability equates to the ability of the optical transmission spectrally “molding itself” to the line system’s passband on a link-by-link basis. By using 3D Shaping, to a certain extent the coherent DWDM source can be decoupled from the line system since the optical transmission is optimized regardless of the pass band characteristics of the line system. This capability lends itself nicely to the disaggregation of terminal equipment and line systems.
Whether multi-haul networks use flexible ROADM architectures with flexible passbands or architectures with fixed grid spacing (50GHz, 75GHz, 100GHz), the AC1200 with 3D Shaping can be used to optimize capacity with any of these type of line systems.
]]>A Brief History
Coherent optical technology was first introduced in long haul applications to overcome fiber impairments that required complex compensation techniques when using direct detection receivers. Leveraging advanced CMOS processing nodes and reduction in design complexity, coherent solutions have moved from long haul to metro and even shorter reach optical interfaces.
With the introduction of Acacia’s CFP-DCO module in 2014, coherent became an even more compelling solution for metro and data center interconnect (DCI) applications due to its pluggable pay-as-you-grow benefits, and integrated DSP design. Today, coherent is moving from metro core to access aggregation networks (Figure 1). Looking forward, the industry is working to standardize coherent solutions for even shorter reach interfaces.
Figure 1. Coherent solutions transitioning to shorter reaches.
This model of new technology adoption in long haul interfaces, followed by a migration to shorter reach applications, has been demonstrated in the industry before: the copper-to-fiber optics transition followed a very similar path starting in the 1980’s. Technologies, such as dense wavelength division multiplexing (DWDM) and forward error correction (FEC), also followed this same pattern. It is anticipated that this trend of shorter reach applications benefiting from initial long-haul technology investment as it applies to coherent will be no different.
Industry organizations such as the Optical Internetworking Forum (OIF), IEEE, and Cable Labs have initiated coherent standardization activities, recognizing the trend towards using coherent for shorter distances. The OIF is defining a coherent standard for DWDM interfaces in DCI applications with reaches up to 120km; CableLabs is defining coherent standards for cable access networks; and IEEE is considering coherent for unamplified applications beyond 10km. All of this standardization activity reinforces the view of coherent moving to shorter reach, high volume applications. As the applications move from 100G to 400G and beyond, it is likely that coherent will be used in even shorter reach interfaces.
Demand for Bandwidth is Driving New Coherent Markets
Today, coherent technology is already being deployed into markets with a wide array of applications ranging from 10’s of kilometers to 1000’s of kilometers. While network operators in each of these markets need to manage network expansion at the lowest cost, differences in network architectures and demands drive a unique set of priorities for each. Some of these key market applications we’ll explore in this blog include: Long Haul, Metro, DCI, Remote PHY Cable Access, 5G, and applications with unamplified interfaces. We’ll discuss these applications and the factors that drive solutions for their optical interconnecting requirements.
100G Long Haul: Many Fiber Spans with Optical Amplifiers
The long haul market, where coherent was first widely adopted, is still a large segment of the coherent ports shipped each year.
Figure 2. Typical Long Haul network.
This market is highly sensitive to performance because longer reach interfaces eliminate the need for additional costly regeneration. A key optical interconnection performance parameter for coherent DWDM long haul networks is optical signal-to-noise ratio (OSNR).
OSNR & Optical Amplifier Refresher
OSNR describes the relative energy of the signal carrying the information to the energy of the noise from other sources. Optical receivers are specified based on their ability to detect the desired signal in the presence of noise.
So, why is OSNR so critical to long haul DWDM networks? Optical signals are amplified as they are transmitted across the network. At each amplifier, the signal is degraded slightly–the level of the noise is amplified relative to the signal. When the signal level is so close to the noise that it is nearly un-detectable, it needs to be regenerated—the optical signal is converted to the electrical domain where the data can be accurately decoded. The same data is then recoded, retimed, and converted back to the optical domain with a high signal to noise ratio capable of passing through additional amplifiers.
Higher performance coherent optical interfaces allow longer reaches without needing regeneration, which ultimately lowers the cost of deploying and managing these networks.
Currently, 100G QPSK modulation is still widely used in long haul networks because it offers exceptional performance due to achievable OSNR margins and maturity of technology based on 25G electronics. Fiber capacity can be further enhanced by reducing channel spacing from 50GHz to 37.5GHz. Alternatively, capacity can also be increased over the channel by increasing the baud rate. For example, doubling to 200G capacity can be achieved by maintaining QPSK modulation while doubling the baud rate. However, this would require an increase to the channel spacing. To ensure the required channel spacing remains unaltered (e.g., 50GHz), the modulation order also needs to be increased (e.g., from QPSK to 8QAM) as the baud rate is increased.
Simply put, there is an interdependency among baud rate, modulation order, required OSNR, and channel spacing. Transmission capacity can be increased by: (1) increasing the baud rate without changing modulation order, requiring wider channel spacing; (2) holding baud rate constant while moving to a higher modulation order, resulting in narrower channel spacing at the cost of OSNR margin—higher modulation order requires higher OSNR margin; or (3) increasing baud rate and moving to a higher modulation order, requiring no changes to channel spacing but assumes there is sufficient OSNR margin when moving to the higher modulation order. Thus to upgrade to higher capacity with minimal changes to the line system optics, (3) is an attractive option assuming there is sufficient OSNR margin.
Metro: High Density Solutions for ROADM Networks
Coherent interconnections have also been widely adopted in metro core networks (Figure 3). The dynamics in these networks are somewhat different from long haul. Metro core networks usually consist of many reconfigurable optical add-drop multiplexer (ROADM) nodes where wavelengths are dropped, added, or routed to other destinations. This is done using wavelength selective switches (WSSs)–each WSS is effectively an optical filter that can narrow the total bandwidth of the channel. Passing through multiple ROADM nodes can result in significant narrowing of the available spectrum of the complete optical path. These WSSs can introduce additional impairments, such as polarization dependent loss. Though the reaches in these applications are less than long haul, they still require a high level of performance due to the many link impairments.
Metro networks are not entirely about optical performance, though. Central offices can often be crowded and power limited. High density solutions that are power efficient can be particularly valuable in these applications.
Figure 3. Typical Metro network.
In addition, metro networks handle a wide range of traffic. These networks quickly become complex to manage, with different equipment required depending on the requirements. Common solutions that can be leveraged across multiple platforms, supporting a wide variety of traffic types, and scale capacity in a cost effective manner allow network operators to manage their operational costs more effectively.
Data Center Interconnect: Cost and Power Optimized Coherent
In the last 10 years, the optical networking industry has been transformed by the requirements of large cloud network operators. High capacity interconnections are necessary between these hyperscale data centers to enable cloud functionality (Figure 4).
Figure 4. Typical DCI/Cloud network.
These DCI connections differ from traditional carrier networks in that they are usually point-to-point with no ROADMs in between, and can be within the same city or across oceans. Cost and power are generally the most critical parameters for these applications. Some use cases can be fiber constrained, making spectral efficiency a higher priority. Customers in these markets tend to be early adopters of new technology and have short product life cycles.
Large cloud network operators, along with some of the more traditional carriers, are driving changes in how network functions are partitioned between vendors, allowing them greater freedom to transition between vendors and product generations with minimal changes in the software used to control the network.
Remote PHY/Fiber Deeper: Coherent Technology for Cable Access
Access networks are an emerging opportunity for coherent interconnections. The cable industry is taking the lead in this segment by driving standardization of coherent for access aggregation.
Figure 5. Remote PHY network.
As the hybrid fiber-coax (HFC) networks evolve toward remote PHY architectures, fiber is being deployed deeper in the network (Figure 5), resulting in increased available bandwidth to residential end-user customers, while eliminating bottlenecks in the HFC network. 10G optical interfaces are pushed closer to the end users resulting in aggregation points in the network where 10-20 remote PHY devices come together.
Coherent can be an effective way to transport these aggregated signals back to the hub. In some cases, it may only be necessary to transport a single coherent wavelength back to the hub, but since coherent is inherently a DWDM technology, this approach provides the capability to expand capacity by up to two orders of magnitude in the future.
CableLabs is the standards organization of the cable industry and has recognized the need for this solution in the market. In 2017, they kicked off a project to define coherent standards for cable access aggregation applications. Acacia is participating in this project, along with many other leading optical networking vendors, as well as several large MSOs.
5G Drives Backhaul Growth
Another emerging access application is 5G backhaul (Figure 6). It is clear that backhaul demands in wireless networks are going to need to increase significantly. As more capacity is delivered to end users, the connections back to the core network must scale, as well.
Coherent offers several benefits in these access aggregation applications compared to traditional direct detect solutions. At higher data rates, it becomes very challenging to deploy direct detect solutions over 10’s of km’s without using dispersion compensation. Alternatively, solutions may consider many parallel optical interfaces, but that drives up the cost of the solution.
Figure 6. 5G Backhaul network.
Today’s coherent implementations are generally based on tunable laser technology. While fixed laser implementations are a consideration in these applications, tunable solutions can offer operational benefits by significantly reducing the number of spares that need to be stocked. Tunable solutions also tend to support shorter lead times, accelerating the ability to turn up new services. Lastly, coherent solutions are future proof with the ability to scale capacity by increasing data rate or adding additional wavelengths.
Adoption of coherent technology in access networks could offer an additional benefit that may not be obvious at first. Since the same solutions can address a wide range of network interfaces (e.g., access aggregation, metro, and regional), it may be possible to collapse the supply chain for multiple applications into a single solution. This could offer significant operational efficiencies for network operators.
Unamplified Point-to-Point Interfaces
Unamplified point-to-point interfaces are essentially client optical interfaces for connections between buildings (Figure 7). As data rates have increased, it has been more and more challenging for direct detect solutions to address these kinds of applications. At 100G and 200G, proprietary coherent solutions are already used for links in the 40-80km range.
Figure 7. Point-to-point.
Looking forward to 400G, this application is within the scope of the OIF 400ZR project. In addition, the IEEE study group that is considering solutions beyond 10km for data rates of 50G, 100G, 200G, and 400G is evaluating coherent alternatives for these applications.
Since these interconnections are not amplified, they are not characterized by their tolerance to low OSNR. In these applications, transmitter power and receiver sensitivity are the key parameters that define the usable link budget.
Coherent detection offers the same increase in performance for power limited sensitivity as it does for noise limited applications. Volumes for these applications can be larger than transport applications and coherent implementations will need to be cost effective and extremely power efficient.
Coherent is moving to shorter reach as data rates increase
As we’ve outlined in this blog, there are a number of applications for which coherent is well suited. DCI, metro, and long haul are existing markets that have benefited from coherent for several years now. Emerging applications such as Remote PHY for cable access, 5G backhaul, and unamplified “ZR” interfaces are evolving as standards efforts and deployment strategies are still in the early stages. What is clear is that operators struggling to meet the growing demands of bandwidth are motivated to optimize their optical networks for capacity and reach in order to minimize cost. And space and power restrictions continue to be a challenge as additional hardware is deployed in constrained environments. Standardization will help advance the coherent evolution underway.
Stay tuned for upcoming blog posts in which we will focus on how advanced 3D shaping of coherent modulation can optimize various types of coherent networks.
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