A half-way house between DSP modules and LPO: the DSP stays on the transmit side, the receive path goes linear.
What Is Linear Receive Optics?
LRO removes the DSP from one direction only. The transmit path keeps its digital signal processing, so the light launched into the fibre is still a clean, retimed waveform. The receive path is linear: the photodiode output is amplified and passed straight to the host SerDes without digital regeneration.
It is a deliberate compromise, and a well-chosen one. Most of the interoperability difficulty with fully linear optics lives on the transmit side, because that is where a distorted host output turns directly into a distorted optical signal that somebody else's receiver has to cope with.
Why the Asymmetry Helps
Keep the transmit DSP and an LRO module launches a signal any compliant receiver can handle — including a conventional DSP module at the far end, from a different vendor, in a fabric nobody jointly qualified. That single property makes LRO deployable in mixed estates where full LPO is not.
The cost is that the saving is smaller: roughly 20 to 30 per cent of module power against LPO's 30 to 50. You are removing one of two DSP functions, so you recover something less than half the benefit — the receive-side DSP is generally the smaller of the two.
What the Host Has to Do
On receive, the host SerDes now sees a signal that has crossed the fibre, been converted by a photodiode and amplified, with nothing having cleaned it up. Its equalisation has to be good enough to recover that unaided.
Modern switch SerDes generally are, at short reach. What to check is whether the specific platform's receive equalisation has been characterised for linear operation — some vendors publish this, some do not, and ‘our SerDes are excellent’ is not the same as a measurement.
Where You Meet It
The same short-reach data-centre roles as LPO: in-rack and in-row at 400G and 800G. Vendors also use it as a stepping stone — ship LRO now, move to full LPO once host capability and interoperability testing catch up.
If you are weighing the two, the deciding question is usually not technical but organisational: can you guarantee that both ends of every link come from a qualified pairing? If yes, LPO saves more. If no, LRO is the version that survives contact with procurement.
LRO versus the alternatives
| Transmit path | conventional DSP — retimed, regenerated |
|---|---|
| Receive path | linear TIA straight to the host SerDes |
| Power saving | roughly 20–30% of module power |
| Interoperability | easier than LPO — the far end sees a clean signal |
| Host requirement | SerDes must equalise the received signal unaided |
| Also called | half-retimed optics |
Related Terms
LPO, the module DSP, CPO, and the four-way comparison.