Adtran breaks the 1W barrier with 800G linear pluggable optics

Adtran has announced an 800-gigabit linear pluggable optics (LPO) transceiver designed for short-reach data centre links.

The LiteWave800 is an OSFP 800G-DR8 module with a reach of 500 metres that consumes less than 1 watt of power, enabled by the use of 100-gigabit single-mode VCSEL lasers.

“We have partners that we have been working with on single-mode VCSELs, and the devices are going to be part of our LPO platform that we’re announcing at [the upcoming] OFC [show],” says Saeid Aramideh, Vice President of Business Development, Optical Engines business unit at Adtran.

AI workloads and the push for LPO

“AI workloads are driving everything, and these require much higher interconnect bandwidth than what we are typically used to seeing,” says Aramideh.

Not only are AI clusters driving the need for higher interconnect speeds, but the designs are also raising issues of link reliability, latency, system cost, and energy efficiency.

“Power consumption has become the most critical limiting factor in large-scale data centres, and is directly impacting rack density: how many pluggables you can put in there, cooling requirements and so on,” says Aramideh. “Ultimately, the issue of power is going to impact the economic viability of the infrastructure.”

The attraction of LPO is that it uses an optimised electrical-optical interface with the host IC driving the optical link. The approach eliminates the need for the pluggable module to have its own digital signal processor (DSP), a key contributer to the overall power consumption.

First-generation LPO modules consume between 5–8W, compared with well over 10W for conventional DSP-based 800-gigabit pluggables, says Aramideh.

Adtran set itself an energy consumption target of 1pJ/b for its LiteWave800 design. At 800 gigabits-per-second (Gbps), an energy efficiency of 1pJ/b corresponds to roughly 0.8W total module power, significantly lower than conventional DSP-based modules.

Design approach

To achieve the ambitious power target, Adtran used its in-house electronics IC design team, along with using single-mode VCSEL technology operating in the 1310nm band for the optics.

“The choice of single-mode VCSELs in the module is the most essential defining factor when it comes to reducing the power,” says Aramideh. Using EML lasers or a silicon photonics modulator approach yields much higher energy numbers, ranging from 5-15pJ/b.

Multi-mode VCSELs are an established industry technology. Developing single-mode VCSELs is challenging, as is creating a supply of such devices. But the laser device has advantages such as its low drive voltage and good linear performance.

Adtran has also been using single-mode VCSELs for its 10×10 gigabit MicroMux pluggable product and says it has two supply partners for its VCSELs.

Adtran also decided to make its own electronics as typical driver and trans-impedance amplifiers in the pluggable consume up to 3pJ/b.

“But low power is essentially meaningless if you cannot have good signal integrity,” says Aramideh. Given that signal integrity is the biggest challenge with an LPO design, Adtran’s focus was on how to close the loop between the optics and the host driver IC.

Making use of the OIF’s Common Management Interface Specification, or CMIS, Adtran created a set of controls known as the Versatile Control Set (VCS).

“VCS lets you manage certain attributes on the host DSP, and these attributes set the operating margin and tune parameters to coordinate the signal integrity between the module and the host, and control them dynamically,” says Aramideh.

LiteWave800 architecture

The 800-gigabit module has eight 100-gigabit channels, each operating at a 53-gigabaud symbol rate and the PAM4 modulation format.

The drivers interface to the VCSELs which also use a thermal-electric cooler. However, based on testing results, such coolers may be optional depending on the pluggables’ environmental conditions. On the receive side of the pluggable, there are photodiodes and two quad trans-impedance amplifiers (TIA).

The expertise Adtran brings is in controlling the single-mode VCSEL, interfacing the drivers and the VCSELs, and the overall link control.

Roadmap beyond 100 gigabit-per-lane

One question facing the industry is whether LPO architectures can scale to 200 gigabits-per-lane, where tighter electrical margins may require alternative approaches. Is Adtran’s LiteWave design thus a one-generation product?

“There is a roadmap, but it may not necessarily be LPO,” says Aramideh. He cites the use of near-packaged optics for next-generation AI clusters, where the optics are brought closer to the host IC.

Using near-packaged optics based on single-mode VCSELs and linear electronics and addressing the challenges of serviceability and thermal coupling might prove a better approach, argues Aramideh.

“Can we get to 200 gigabit per lane? The answer is absolutely, and we must. This is what industry is asking for,” says Aramideh. “Would the answer be an LPO? At this point, that is a question mark and maybe near packaged optics would prove a better solution.”

Market implications

Aramideh hopes there will be an uptake of single-mode VCSELs, leading to wider adoption of the technology in the data centre.

He also believes that the LiteWave800 design benefits pluggables overall by offering an attractive alternative to the low-power argument used by co-packaged optics proponents. Such designs typically consumes 5pJ/b.

“Having a product at 800 gigabit that hits one picojoules per bit, that sets the industry standard,” says Aramideh.

The product will be available as samples in the third quarter of this year and will be in production early 2027.