PsiQuantum’s optical switch puts the loss budget ahead of the port count

PsiQuantum is supplying selected prospective customers with samples of an 8 × 8 optical circuit switch that routes light without converting the traffic to electrical signals inside the switch. Its laboratory demonstration achieved typical insertion loss of 1.2 dB and reconfiguration below 3 ms.

The underlying silicon photonics platform was developed for quantum computing. This is its first publicly disclosed optical circuit switch for AI infrastructure, with commercial products still to follow. The demonstration has no moving parts and is described as strictly non-blocking, meaning an available input can connect to an available output without disturbing established connections.

Working within the optical budget

At 1.2 dB insertion loss, about 76% of the input optical power remains after the switch, calculated as 10 raised to the power of −1.2/10. Two such losses in series would leave about 58%, before fibre, connectors or other components are included. These are calculations from the reported typical value, not measurements of a deployed network.

Keeping more light in the path can allow a route to fit within the transmitter and receiver budget without changing the optical arrangement. That is a useful result even at this port count, although the budget has to accommodate the least favourable permitted path across the operating wavelengths and environmental conditions.

A typical loss figure does not show that spread between paths. PsiQuantum has not published the complete qualification dataset needed to establish it.

The company also reports 40 dB crosstalk and operation without amplification. These are results from its own laboratory.

Matching the circuit to the traffic

The reported reconfiguration time describes changing a connection. Data passing through an established path does not incur that setup time on every transfer, so the useful comparison depends on how long the path stays in use.

Repeated, substantial transfers between the same endpoints could let a controller keep a useful optical path in place. Short transfers between frequently changing endpoints are harder to accommodate because waiting for connections can consume the benefit gained in the optical hardware.

The traffic scheduler and the way optical paths coexist with the electrical network therefore matter as much as the switching element. Until those are evaluated together, the component results cannot establish how much accelerator utilisation or system energy consumption would change.

PsiQuantum also discusses a separate 64 × 64 barium-titanate switch used in its quantum systems. BTO is not required for this demonstration or its initial products. Larger commercial devices and their measured operating characteristics remain to be announced.

Sources

• PsiQuantum: 28 October optical circuit switch announcement
• PsiQuantum: optical circuit switching platform and demonstration specifications

Image: Fibre connections on a patch panel. Illustrative photograph, not PsiQuantum’s optical switch. Photo: Brett Sayles / Pexels. Image source. Licence.