FADY MASOUD 800G COHERENT PLUGGABLES
OF 800G COHERENT PLUGGABLES THINK THIN: UNLOCKING THE POWER
MARKET DRIVERS Major improvements in increasing fiber capacity have come from the evolution of optical engines – from direct-detect to coherent – and from increased wavelength bit rate enabled by the higher order modulations schemes. However, optical engines are approaching the Shannon limit. As a result, fiber capacity has begun to flatten as spectral efficiency is becoming constrained. This has triggered service providers and network operators to begin looking at new strategies for increasing the capacity of their networks including the use of multi-fiber strategies to connect locations. As network operators shift to these multi-fiber strategies it can cause a significant shift in their priorities when selecting network solutions. When networks are designed using a single fiber pair between location, capacity per fiber is typically the most important factor in selecting an optical engine. However, when multi-fiber strategies are used, capacity per fiber becomes significantly less important enabling network operators to focus on other factors – such as power and space efficiency. This shift in priorities is aligning perfectly with the evolution of coherent pluggables. Advances in DSP and CMOS technology – from 28nm to 7nm to 3nm – have led to significant enhancements in optical performance, increasing capacity-reach in compact form factors such as QSFP-DD and OSFP. And while these coherent pluggable optical engines provide less fiber capacity compared to their embedded optical engine counterparts, they provide a significant reduction in power consumption and footprint per bit. While every application will have its own set of drivers, with embedded engines continuing to be the technology
The second model is the deployment of coherent pluggables directly into routers , commonly referred to as IP over DWDM (IPoDWDM). This model has the advantages of low CAPEX, low power consumption, and reduced footprint by eliminating the need for an optical transport platform. Moreover, coherent pluggables benefit from a complete eco- system of Multi-source Agreements (MSA) and interoperability forums for a seamless line interworking and service provisioning. However, IPoDWDM presents operational challenges related to management and compatibility across different host devices and operating systems. Furthermore, this model does not come at par with fully-fledged transponder-based platforms due to the lack of complete traffic aggregation capabilities and operational functionality. Additionally, the IPoDWDM model has a direct one-to-one mapping between the router port speed and the pluggable speed – for example, where 400G pluggables are deployed in 400G router ports and 800G pluggables in 800G router ports. Nonetheless, sometimes the coherent pluggables must be dialed down to operate at a lower bit rate, such as 600 Gb/s or 400 Gb/s to close a specific link which results in a wasted router port capacity. Moreover, pluggables cannot fully replicate the optical functionality of embedded transponders.
of choice when fibers are scarce and adding incremental fibers is high, the compelling economics of coherent pluggables coupled with the shift in priorities away from maximizing fiber capacity and toward cost, space, and power efficiency is significantly expanding the applications scope. CURRENT DEPLOYMENT MODELS There have historically been two main deployment models of coherent optical engines: 1. High-performance optical engines embedded in a transponder card in an optical transport platform 2. Coherent pluggables hosted in IP/ Ethernet platforms such switches and routers. Embedded optical engine based transponders are designed and built from the ground-up to maximize fiber capacity with best-in-class optical performance (capacity-reach). They aggregate traffic from various types of client interfaces onto one or two high bit-rate wavelengths such as 1.2 Tb/s. Designed for deployment in fully-fledged optical transport platforms, they typically support multiple client ports for aggregation in addition to a full suite of integrated optical functions designed for traffic grooming, aggregation, hairpinning, protection, alarm correlation, and so on. In addition to the performance and host of traffic management features, another advantage of embedded transponders is the operational domain separation , acting as a demarcation point between the IP and the optical domain. This is useful in lawful interceptions or enforcing SLAs through setting clear boundaries and business demarcation. However, transponders come with trade-offs such as high power consumption and large footprint.
EXPANDING DEPLOYMENT MODULES WITH THIN TRANSPONDERS
Thin Transponders introduce a third deployment model , that combines some of the strengths from the other two models without their associated disadvantages. Thin transponders are a set of small modules or “sleds” that are optimized for coherent pluggables and
Figure 1: Expanding deployment models with Thin Transponders
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| ISSUE 42 | Q3 2025
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