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.

2^nd Generation 3D Shaping Advances Coherent Performance
The CIM 8 is powered by Jannu, Acacia’s 8^th 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 2^nd Generation 3D Shaping) for Class 3 baud rate tunability.

The 5nm Jannu DSP ASIC in CIM 8 intelligently optimizes optical transmission using 2^nd 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 2^nd 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 2^nd 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

Achieving network optimization with 600G era coherent technology

The latest innovations in digital signal processing (DSP), optical, and mixed-signal component technologies have enabled the achievement of 600G-per-wavelength transmission speeds. High modulation orders (e.g., up to 64QAM) and high baud rates (e.g., up to ~70Gbaud) are now possible. In addition to this high speed achievement, these technologies also introduce advanced capabilities that allow the flexible fine-tuning of the optical transmission resulting in capacity optimization. Today’s coherent technology enables common optical hardware to achieve the high-performance finesse of a long-distance link, the sheer raw capacity for shorter DCI/edge links, and everything in between. This is the reason why some refer to 600G era coherent technology as multi-haul technology since the same set of hardware can address long-haul, metro, and DCI/edge networks.

Recently introduced, the Acacia AC1200 coherent module, powered by Acacia’s Pico DSP, a low-power solution based on 16 nm CMOS technology incorporates algorithms and processing power to address a wide range of applications. The AC1200 also includes a silicon photonics integrated circuit (PIC), and high-speed RF electronics to achieve 1.2Tbps capacity by using two wavelengths operating at 600Gbps each. The AC1200 is a leading product in the 600G era offering key capabilities that feature high-performance and high-flexibility, with the goal of enabling network operators to improve efficiency and maximize capacity utilization while reducing network costs.

Acacia recently published a white paper – Network Optimization in the 600G Era – that looks at long-haul, metro, and DCI/edge application and how the AC1200 provides benefits for each of these applications. Check it out to learn more.

For instance, 3D Shaping is a key feature in the recently introduced Pico-powered AC1200, a 1.2Tb coherent transceiver module which supports two wavelengths up to 600G each. There are three elements to 3D shaping, with each providing a real-world benefit. There’s shaping of probability, shaping of location, and shaping of spectral width.

Senior Manager of Technical Marketing, Eugene Park, breaks down the elements of 3D shaping and what it means to Acacia’s technology. Learn more in our video.

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.