How OCS Optical Switches Are Revolutionizing Data Center Networks

Google has replaced traditional spine switches in its data‑center networks with OCS (Optical Circuit Switching) switches, which route light without any switching chips, achieving millisecond‑level switching, lower latency, and reduced power consumption.

Advantages of OCS Switches

OCS eliminates chip‑related speed limits, offering higher bandwidth and lower energy use, which is especially beneficial in large‑scale AI data‑center workloads where conventional spine switches face bandwidth bottlenecks.

1. 3D MEMS Optical Switch

A 3D MEMS switch consists of a fiber‑array unit (FAU), input and output MEMS mirror arrays, and associated drive and control electronics. Each mirror is a two‑axis reflective element; the N×N matrix routes light by tilting mirrors under electrical signals.

Typical drive methods include magnetic‑Lorentz, electrostatic comb‑drive, and thermoelectric actuation, each with trade‑offs in voltage, linearity, power, and speed. The mirrors are fabricated with semiconductor processes, and the optical path loss is minimized by precise alignment.

2. Digital Liquid Crystal (DLC) Optical Switch

DLC switches use the electro‑optic effect of liquid crystals combined with birefringent crystal wedges. An applied voltage rotates LC molecules, changing the phase delay and steering the beam. An N×N array of fiber collimators, polarization handling modules, and LC‑crystal wedge stacks enables arbitrary port‑to‑port routing.

The system can be scaled by stacking multiple LC‑crystal layers; for 256 ports, eight layers are required, theoretically supporting up to 512 ports.

3. Direct Light Beam Steering (DLBS) Optical Switch

DLBS places fiber collimators directly on piezoelectric ceramic actuators. By tilting the collimators, the input and output arrays are aligned, establishing a direct optical path without intermediate optics, which reduces insertion loss but requires larger actuator travel for high‑port counts.

4. Comparison of Optical Switch Technologies

The three technologies differ in switching speed, insertion loss, return loss, durability, and scalability. OCS switches generally provide millisecond‑level switching, low insertion loss, and chip‑free operation, making them protocol‑agnostic and suitable for high‑density data‑center environments.

In summary, OCS optical switches enable non‑blocking N×N port switching that is independent of wavelength, modulation format, or data rate, offering high scheduling efficiency and promising a future direction for data‑center network architecture.

Source: ODCC‑2024‑AI Network Optical Switch Technical Report (Communication Encyclopedia).