Optical circuit switches are crucial components for reconfigurable optical networks, offering the ability to dynamically connect optical fibers and route high-bandwidth data streams. Google has used MEMS-based optical switches (OCSes) in its data centers for many years, citing benefits such as using 40% less power and reducing capex by 30%. [1] More recently, multiple other technologies are being considered as optical circuit switches, including robotic all-fiber systems. [2]  While the reliability of these switches is vital, the focus often falls on the mechanical aspects of the switching mechanisms themselves. Surprisingly, it's not the moving parts that typically cause problems, but rather the electronics – specifically high-voltage electronics used in MEMS systems. This post will delve into the reliability concerns of MEMS and robotic fiber optical circuit switches, highlighting the vulnerabilities beyond moving parts.

MEMS Optical Circuit Switches: The High-Voltage Factor

MEMS-based optical switches rely on electrostatically actuated micromirrors to redirect optical signals between fibers. This actuation necessitates the use of high-voltage electronics to generate the required electrostatic forces to move the micro-mirrors. While the mechanical components themselves are reliable, the high-voltage electronics required to actuate the MEMS devices are a different story. High-voltage electronics can be prone to failures, which can have significant consequences. A single faulty component can bring down an entire switch, creating a large “blast radius” impacting a large number of connections and causing widespread disruptions.

While the micromirrors themselves can be incredibly robust, the associated high-voltage drive circuitry presents several reliability challenges:

  • Component Failure: High-voltage capacitors, transistors, and other components in the drive electronics are susceptible to failure due to voltage stress, temperature variations, and manufacturing defects. A failure in even a single component can render a portion, or even the entire switch, inoperable.

  • Electrostatic Discharge (ESD) Sensitivity: High-voltage circuits are inherently more sensitive to ESD events, which can occur during manufacturing, installation, or maintenance. Undetected ESD damage can lead to latent failures that manifest later in the switch's operational life.

  • Dielectric Breakdown: The high voltages involved can stress the insulating materials within the electronic components and on the MEMS chip itself, potentially leading to dielectric breakdown and short circuits over time.

  • Control System Complexity: Managing and precisely controlling high voltages for a large array of MEMS actuators requires complex control electronics and software. Incorrect or insufficient power supply voltages can lead to erratic behavior or complete failure of the high voltage DAC component – creating a failure with the MEMS system.

It's important to note that while the moving parts in MEMS switches (the micromirrors) are generally designed for billions of cycles, the reliability of the entire system is heavily influenced by the longevity and stability of the supporting electronics.  It is important to remember that since the overall FIT (failures in time) rate is calculated as the sum of the individual FIT rate for the components, the overall FIT rate is determined by the lowest reliability component in the system, not the best.  

Robotic Fiber Optical Circuit Switches: Reliability Through Simplicity

Robotic fiber optical circuit switches, on the other hand, employ a robot to physically move and re-connect optical fibers. The Telescent system's patented algorithm enables reconfiguration of over 1,000 ports, and its density can be amplified with multi-fiber connectors like duplex or MPO-16, guaranteeing its position as the market's largest optical circuit switch.  While this approach involves macroscopic mechanical movement, its reliability concerns differ from those of MEMS.

A key advantage of the Telescent robotic system is the use of a latching mechanism. Once a connection is established, the fibers are magnetically locked place and power is no longer required to maintain the connection. This inherently provides a significant reliability benefit since it eliminates the concern of failure blast radius, where a single component failure can disrupt a large number of connections.

The "Failure Blast Radius" Advantage: Latching Robotic Systems

The latched nature of robotic fiber switches means that even if the control electronics or the robotic actuators were to fail, the existing optical connections would remain intact. This significantly limits the "failure blast radius." Live traffic flowing through the established paths would not be interrupted by a failure in the switch's electronics or mechanical drive system.

In contrast, as discussed earlier, a failure in the high-voltage electronics of a MEMS switch can directly lead to the loss of many optical connections, impacting all traffic routed through the affected part of the switch. This makes the potential impact of an electronic failure in a MEMS system much more severe.

Another Benefit with Latching - Field Repairable without Affecting Live Traffic

While some MEMS-based OCS systems have been designed for field repair, the system will still lose connectivity through a portion or all of the ports depending on the component being replaced. In contrast, since the robotic system offers a latched connection and does not require power to stay connected, this allows technicians to perform maintenance, diagnostics, or even replace any system component without interrupting the data flow. This ability to isolate failures and perform repairs without disrupting service is a key advantage of latching systems, eliminating the "failure blast radius" and enhancing the overall robustness of the network.

Conclusion

While the durability of moving parts is a valid consideration for optical circuit switches, the reliability of the supporting electronics, particularly the high-voltage systems in MEMS devices, should not be overlooked. The Telescent robotic fiber system with its latching design offers a significant advantage in this regard. The ability to maintain established connections even in the event of a system failure dramatically reduces the risk of service disruption and minimizes the "failure blast radius," making them a robust choice for critical optical networking infrastructure.

[1]   https://arxiv.org/pdf/2208.10041  Mission Apollo: Landing Optical Circuit Switching at Datacenter Scale

[2] Optical Circuit Switching for AI Scaling and Datacenter Automation - Cignal AI