LRO (linear receive optics)
A transceiver architecture that keeps a retiming DSP on the transmit path only and passes the received signal to the host linearly. The intermediate step between a fully retimed pluggable and fully linear LPO: roughly half the DSP power saving, with the interoperability risk concentrated where the host equalizer can manage it.
A conventional pluggable module retimes in both directions: its DSP recovers the clock, equalizes, and regenerates the signal on transmit and on receive, presenting clean interfaces to both the optics and the host. Linear pluggable optics removes that DSP entirely. LRO, linear receive optics (also called half-retimed), splits the difference by direction: the transmit path keeps a retimer, so the light launched into the fiber is fully conditioned, while the receive path is linear, handing the detected waveform to the host ASIC's own equalizer.
The asymmetry is deliberate and follows from where each function is hard to give up. On transmit, the module's DSP is what guarantees a conformant optical launch: a TDECQ-compliant eye is difficult to certify when the launched waveform depends on whichever host serdes happens to drive the module, which is the central interoperability problem of fully linear modules, acute at 100G per lane and worse at 200G. Retaining the transmit retimer means the module alone answers for its optical output, and any compliant host can receive it. On receive, modern switch serdes already contain long adaptive equalizers designed for lossy electrical channels; asking them to also absorb the optical channel's impairments is a smaller stretch, and the FEC that terminates in the host cleans up what remains.
The budget arithmetic is what motivates the whole ladder. The DSP is roughly half of a high-speed module's power; removing the receive half recovers on the order of half of that saving, placing LRO's per-module power between the full-DSP and LPO figures, with none of LPO's multi-vendor qualification burden on the transmit side. At the 1.6T generation, where full-DSP modules dissipate on the order of 20 W, vendors showed LRO variants at OFC 2025 as the pragmatic step while fully linear interop matures. The architecture comparison across all four steps, with the power figures in one place, is in Pluggable, LRO, LPO, CPO.
References: Juniper Networks, "Types of optics: LPO and LRO" (800G optics documentation); Eoptolink 1.6T LRO demonstrations, OFC 2025; the Datacenter Link Budget Explorer compares module architectures at fleet scale.