Optical circuit switching (OCS)
Switching whole light paths with movable mirrors or equivalent optics instead of routing packets, giving a bit-rate-transparent, near-zero-power fabric that reconfigures in milliseconds.
An optical circuit switch connects input fibers to output fibers as whole light paths, most commonly with two arrays of MEMS mirrors that steer any port to any port. Nothing is converted to electronics inside: no optical-electrical-optical hop, no buffering, no awareness of bit rate, modulation format, or wavelength grid. The switch is a reconfigurable patch panel with millisecond actuation, insertion loss of a couple of decibels, and essentially zero per-bit power.
The consequence is architectural. A packet switch must be replaced every generation to track lane rates; an OCS is transparent to them, so the same fabric that carried 100G circuits carries 800G and 1.6T unchanged. Google ran this argument at scale with its Apollo deployment, replacing the spine layer of its datacenter networks and reconfiguring topology to match traffic, including the block topologies used for large training runs. The approach has since moved from proprietary to communal: the Open Compute Project stood up an OCS standardization effort with a first white paper in April 2026, and multiple vendors now ship MEMS, piezo, and liquid-crystal based switches. The practical limits are equally concrete: milliseconds is fast for topology management and slow for per-flow switching, and every pass through the switch spends optical budget.
Characterization is bread-and-butter optics rather than networking: per-connection insertion loss and return loss matrices across the port count, repeatability of loss after reconfiguration, switching time, polarization-dependent loss, and crosstalk to unselected ports. Those numbers, multiplied by the number of OCS hops a path may take, set how much margin the transceivers on either end must carry, which is one reason OCS and low-margin linear pluggable optics have to be engineered as a pair rather than adopted independently.
References: Open Compute Project, Optical Circuit Switching for AI white paper (April 2026); Poutievski et al., Jupiter evolving, and the Mission Apollo deployment reports, ACM SIGCOMM (2022).