Data center operators tasked with building AI clusters are increasingly facing the demand for higher bandwidth without the ability to expand their power and spatial resources. A solution that is gaining traction is the advanced management of light for data transmission.
Wavelength-division multiplexing (WDM) technology enhances fiber capacity by allowing multiple light wavelengths to be transmitted through a single fiber strand. However, for this method to be economically viable and operationally efficient, data center operators require numerous stable wavelengths that are cost-effective and reliable.
Traditionally, achieving this has meant using separate lasers for each wavelength, which has become unsustainable as channel configurations grow. With each added wavelength comes another laser, driver, and control mechanism, thereby escalating power consumption, costs, and potential points of failure. Here, optical frequency comb generators present an innovative alternative by generating many evenly spaced wavelengths from a single laser source instead of utilizing multiple individual lasers.
While comb-based light sources are not a novel concept—having been the subject of telecommunication research for some time—the vision for their widespread integration alongside co-packaged optics is still in early developmental stages, as many designs remain beyond the pilot production phase.
Experts like Frank Smyth from Pilot Photonics highlight that these comb lasers enable the utilization of more wavelengths packed closely together without interference concerns. On a spectrum analyzer, the output from a comb source appears as evenly spaced lines, resembling the teeth of a comb. Unlike conventional laser arrays, which require an increase in hardware with each additional wavelength, comb technology allows a single pump laser combined with silicon nitride to produce all wavelengths simultaneously on a predetermined grid.
However, the scaling of traditional laser arrays becomes problematic as the number of channels increases. As Marcello Girardi, CEO of Solinide, points out, arrays perform adequately for a few channels, but face hurdles when complexity rises past eight wavelengths, as component count and complexity skyrocket.
Comb lasers benefit from fixed spacing created through lithography, meaning adjustments in output can be made without changing the number of lasers needed for a preset number of channels. Quintessent’s Steven Estrella explains that this reduces the number of lasers needed, translating to fewer failure points and heightened reliability—a critical advantage amidst a current shortage of indium phosphide lasers.
As the demands for dense wavelength division multiplexing (DWDM) increase, moving from 4 to 32 channels, challenges arise such as wavelength drift and manufacturing yield. This is where the comb technology can shine, providing an effective solution for these limitations.
Estrella notes that Quintessent’s comb lasers are particularly suited for shorter link distances within racks between 30 to 100 meters, where bandwidth and power challenges are most pronounced. According to Vivek Raghunathan from Xscape Photonics, these lasers will be effective for interconnections among GPUs and switches, which is crucial for developing standardized designs.
Yet the technology is not without its challenges. Despite initial setbacks in adoption due to concerns over reliability and stability, companies like Solinide have ventured into production. Ultimately, the success of comb lasers hinges on the establishment of a standardized external laser source module and collaborative efforts to avoid vendor lock-in through standards like ELSFP and OCI MSA.
As wavelength demands climb higher, transitioning to comb technologies could mean moving from an array of options to a dominant architecture, addressing the limitations of current systems and setting the stage for future advancements in data center networking.
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