Why did Microsoft just buy a fiber optic cable company? • The Register

Dec 26, 2023

Major cloud providers and hyperscalers go to considerable lengths to secure technical advantages over their rivals, and Microsoft last week made just such a move by acquiring fiber optic cable maker Lumenisity.

Acquiring a cable-maker is less obviously advantageous than AWS creating its own Arm CPUs or Google's tensor processing unit.

Buying Lumenisity is all about reducing latency, an issue the acquired company addresses with hollow-core fiber (HCF) optic cables that can curb the time needed to move data between cloud datacenters.

Spun off from the University of Southampton's Optoelectronics Research Center in 2017, Lumenisity's HCF cables are designed to carry laser light using air rather than the silica glass used in something like Cornings SMF-28.

While we think of the speed of light as fixed, it can vary depending on the medium through which it travels. For reference light travels through glass fiber at roughly 200 million meters per second compared to 300 million meters per second through air. According to Lumenisity, this means light travels about 47 percent faster through HCF than silica glass fiber.

Dell'Oro analyst Jimmy Yu told The Register matters because it helps to improve network performance. "I can extend my reach for the same amount of latency, or I can reduce the time altogether," he said.

To this end, Lumenisity says its cables can maintain the same latency at 90 kilometers as a glass fiber at 60km.

And while modern fiber optic cables are incredibly precise, irregularities in the glass and cable sheathing can result in losses that require expensive and latency-inducing amplifiers or repeaters to correct. If Lumenisity tech helps Microsoft to achieve ultra-low-loss HCF over long distances as the software giant hopes, Yu believes the savings associated with eliminating or using fewer repeaters would be significant.

While fiber optics are used for everything from connecting individual servers to switches, zones to zones, and regions to regions, latency incurred by optical cables only tends to make a meaningful difference over longer geographic distances.

As such, Microsoft's interest in HCF cables likely centers around datacenter interconnect (DCI).

The fact that Lumenisity's HCF single-mode cables are designed with wave-division multiplexing (WDM) in mind, a technology predominantly used in telco line systems and DCI, would seem to back this up. While your typical pluggable optic might transmit a single signal, WDM-capable optics allow for substantially higher aggregate bandwidths by muxing multiple signals onto the fiber.

Compared to glass fiber, Lumenisity claims its HCF cables can carry more WDM channels and thereby achieve higher capacity per strand. However, this greater capacity appears to come at the cost of reach. The company quotes attenuation rate — signal loss — of 2.5dB per kilometer for 1310nm wavelengths. By comparison Corning's SMF-28, which is commonly used in long-haul networks, manages 0.32dB/km.

Lumenisity's fiber don't require specialized equipment to terminate, and work with many of the optics used in telecom networks today, including those from Ciena and Infinera.

While Microsoft didn't disclose the terms of the deal, the acquisition comes just over a week after Lumenisity completed construction of a 40,000 square-foot HCF manufacturing facility in Romsey, UK.

Microsoft declined to comment on the acquisition, other than with a blog post . ®

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