Linear pluggable optics (LPO)
Pluggable transceivers that drop the internal DSP retimer and run the optical lanes as analog channels equalized by the host SerDes, cutting power and latency at the cost of link-budget margin and interoperability guarantees.
Linear pluggable optics are optical transceivers with no retiming DSP in the module: a linear driver runs the modulator or VCSEL directly, a linear transimpedance amplifier hands the received waveform straight back, and all equalization and clock recovery is done by the host ASIC's SerDes. The module becomes an analog channel between two host SerDes rather than a store-and-forward element.
The motivation is the power and latency budget of AI clusters. The DSP is the largest power consumer in a conventional module, and removing it cuts module power roughly in half, several watts per port at 800G, while removing the retiming latency. The cost is engineering margin: the end-to-end link must now close with the host's transmit equalization and receive DFE covering the optics, the host channel, and the fiber together, so LPO behavior depends on which switch and which module are paired. Interoperability is therefore the central open question, and half-retimed variants that keep a DSP in one direction exist as a hedge. Adoption began with 100G-per-lane systems inside single-operator AI fabrics, where one team controls both ends; whether fully linear links survive the move to 200G-per-lane 1.6T interfaces is the live debate in the standards and foundry ecosystem.
For test engineering the shift is substantial. A retimed module can be qualified alone against TDECQ-style eye metrics; a linear module cannot be separated cleanly from its host, so characterization moves to end-to-end bit-error-ratio walks, host-channel S-parameters, and linearity metrics for the analog chain, with the reference host specified alongside the result. The direction of travel pairs naturally with co-packaged optics, which removes the pluggable boundary altogether.
References: IEEE Electronics Packaging Society, Linear Pluggable Optics overview (2026); OIF CEI-112G and CEI-224G framework documents; IEEE 802.3dj drafts for 200G-per-lane signaling.