Redesigning the Network Core: The Rise of Optical Circuit Switching

At its core, optical circuit switching (OCS) is a technology that moves away from traditional electronic packet switching to create direct, reconfigurable optical circuits over a shared physical fiber infrastructure. This approach is driven by the exponential data demands of AI and hyperscale workloads, which are pushing electronic switching architectures to their limits. It offers a compelling solution to the power and latency limits of electronic switching, an architecture that is particularly compelling for the massive, east-west traffic patterns of large-scale AI training clusters, where establishing direct, persistent connections can dramatically improve performance.

This architectural shift, however, reframes the primary engineering challenge. The focus now moves from the switch itself to the performance and density of the underlying optical interconnects.

The core difference between traditional electronic packet switching (EPS) and OCS is how they establish a connection. This distinction directly impacts a network’s speed and power efficiency.

EPS relies on packet-based routing, operating much like a complex road network where each data packet is individually stopped and inspected. Every switch along the path must read the address information of each individual packet to make a routing decision, a step that consumes significant power and introduces latency. This process requires constant, power-intensive optical-to-electrical-to-optical (OEO) conversions at each switching stage to allow the electronic hardware to analyze the data. These operations, which include packet processing and buffering to manage congestion, add significant complexity to the network infrastructure.

OCS, in contrast, functions like a railroad switch for light. It establishes a dedicated, end-to-end physical light path for the duration of a connection, allowing data to flow unimpeded without any per-packet processing. By keeping data entirely in the optical domain, OCS eliminates the need for OEO conversions at every switch, resulting in a network that is faster, more power-efficient and more cost-effective over the long term. Because the switch is simply redirecting light, OCS is largely independent of data rates and formats, offering a more future-proof networking infrastructure that can span multiple technology generations.

Ultimately, the choice between EPS and OCS depends on the nature of the data traffic. EPS remains ideal for highly dynamic, unpredictable, many-to-many workloads, while OCS excels at handling the extensive, persistent few-to-few data flows characteristic of large-scale AI training and high-performance computing clusters.

The strongest evidence for the viability of optical circuit switching comes from Google's hyperscale data centers, where the technology has been deployed at a massive scale. Google's Mission Apollo initiative replaced traditional electronic switches with thousands of in-house OCS systems, which now form the core of its massive Jupiter network.

The Palomar System
The in-house systems, known as Palomar, use micro-electro-mechanical system (MEMS)-based mirrors to dynamically redirect beams of light. This technology creates direct, transparent optical paths between different parts of the network, allowing for a vast number of possible connection combinations in a compact and energy-efficient manner. To further increase bandwidth, the system also incorporates wavelength division multiplexing (WDM), which enables multiple data streams to be transmitted over a single optical fiber.

The Performance Results
The reported results of this deployment are significant. Google’s OCS-based network consumes 40% less power and experiences 50 times less downtime compared to its previous electronic switching solutions. This shift to a direct-connect topology has also simplified the network hierarchy, eliminating the need for an entire spine layer of switches.

The Physical Layer Takeaway
This real-world deployment, however, also sheds light on a critical physical challenge. Google's system has a worst-case insertion loss of 2 dB, a reminder that even in the most advanced optical networks, a small amount of signal power is lost at every connection point. This reality demands an exact and robust physical layer to maintain signal integrity at a massive scale. To compensate, the system must employ higher-power optical transceivers, reinforcing the need for a physical layer strategy that can manage both signal integrity and power delivery.

The shift to an all-optical core reframes the primary engineering challenge, moving the focus from the switching protocol to the two core physical problems of density and signal integrity. While the OCS architecture resolves the issues of electronic processing, it introduces a new class of hardware obstacles that must be overcome to make the system viable at a hyperscale level.

The Extreme Connector Density Challenge
An OCS is a massive cross connect where thousands of individual optical fibers must terminate in a highly constrained physical space, typically on the faceplate of the switch. This creates an extreme density challenge that pushes traditional connector designs to their breaking point. The arrangement requires connector solutions that can offer unprecedented fiber density in a minimal footprint without compromising the mechanical stability or the performance of the optical connections.

The Signal Power and Integrity Challenge
The insertion loss inherent in any optical connection, highlighted as a key challenge in the Google deployment, becomes a more significant problem in a large-scale OCS. Every connection point in the complex path contributes to a cumulative loss of signal power. This issue requires a physical layer solution with two critical components. First, it demands precise, low-loss connectors to minimize the loss at each point. Second, it calls for a robust strategy for delivering high optical power from the source to compensate for any signal degradation along the entire path. 

The performance of an optical circuit switching network is ultimately determined by the quality and innovation of its physical layer. Molex applies extensive engineering expertise across the entire interconnect path to address the core physical demands of an all-optical core, providing a portfolio of solutions that directly answers the challenges of density and signal integrity. 

To address the challenge of extreme connector density, MMC Cable Assemblies and Adapters use a very small form factor (VSFF) design. This allows them to deliver up to three times the fiber density of standard MPO/MTP solutions, a key requirement for making the physical construction of a large-scale, high-fiber-count OCS a practical reality.

To solve for signal power and integrity, the External Laser Source Interconnect System (ELSIS) supplies the high-power, serviceable and thermally managed light sources needed to overcome insertion loss. Furthermore, as the industry looks to the future, ELSIS provides the critical link for OCS to converge with co-packaged optics (CPO). This system-level expertise is essential for building and scaling the all-optical data center networks of the future.

Overcome the architectural challenges of hyperscale data centers. Explore Molex Hyperscale Data Center Connectivity Solutions.