Near-packaged optics (NPO)
Optical engines placed on the host board or a socketed substrate right beside the switch or accelerator package, rather than at the faceplate or inside the package. The intermediate step between pluggable modules and co-packaged optics, keeping the engines replaceable.
Datacenter optics can sit in three places relative to the chip whose data they carry. A pluggable module sits at the front panel, at the end of an electrical channel across the host board that is tens of centimeters long. Co-packaged optics put the optical engine on the same package substrate as the switch or accelerator die, millimeters from it. Near-packaged optics occupy the middle position: the optical engine is mounted next to the package, on the host board or on a separate substrate held in a socket, close enough that the electrical channel is short but not so close that the engine becomes part of the package.
The term is used loosely, and vendors apply it to arrangements that differ in detail, so the common thread is the pair of properties that motivate it rather than a single mechanical design. The shorter channel lets the host serdes drive the optics with less equalization than a faceplate link needs, which removes some or all of the retiming DSP and its power; in that respect NPO is to the board what LPO is to the module. And because the engine is socketed or otherwise demountable rather than soldered and underfilled beside the die, a failed engine can be replaced in the field without reworking the package, which is the serviceability that co-packaging gives up.
The trade against co-packaged optics is therefore power and density for serviceability and manufacturing risk. A co-packaged engine gets the shortest channel and the highest bandwidth density at the package edge, but its failure or its yield is the whole package's; an NPO engine pays for a longer channel and a connector in electrical loss, and gains a supply chain in which engines, switches, and boards are built, tested, and replaced separately. The lasers can live outside in both cases, in external laser sources fed by fiber, which removes the least reliable components from the hottest location either way.
Standards work has concentrated on the co-packaged end. The OIF's 3.2T co-packaged module implementation agreement (2023) defines a module and its electrical and optical interfaces for the co-packaged position; near-packaged designs reuse much of the same optical-engine technology on a socket instead of on the substrate. For the power figures and the serviceability argument across all four architectures, see Pluggable, LRO, LPO, CPO: where the DSP went and, for the laser side, co-packaged optics light sources.
References: OIF, 3.2T Co-Packaged Module Implementation Agreement, OIF-Co-Packaging-3.2T-Module-01.0 (2023).