Increasing Data Rates Drive a Need to Cool QSFPs

June 13, 2019

The majority of QSFP (quad small form-factor pluggable) transceivers have traditionally been used uncooled, as they were commonly used in datacenter applications with shorter reach runs where cooling wasn’t really necessary. But data rates are climbing, with 100G becoming more common, and 400G links are starting to be implemented inside the datacenter.

These data rate increases are happening within the same QSFP form factors, resulting in increasing heat densities which require thermoelectric cooling to protect laser performance. In order to have a negligible effect on package consumption and cost, this cooling needs to be done efficiently.

Why Thermoelectric Cooling?

Recently, the QSFP-DD (double density) form factor has been specified and released to support higher data rate requirements. Because they’re handling higher data rates within the same limited physical space, an increase in heat density is unavoidable. QSFP-DD brings an increase in generated heat by a factor of more than 2X as compared to a QSFP28 model.

This challenge is being exacerbated by two industry trends: higher ambient ranges (into I-temp) and co-located datacenter setups. More QSFP modules are now being required to perform in the higher I-temp range (-40°C to 85°C), as compared to the more temperate C-temp range. And to support the growth of hyperscale datacenter network designs, datacenters are trending toward co-located or regional setups, requiring longer reach runs than what was previously needed. These longer reach links often require coherent or DWDM optics to achieve performance requirements. All of that is leading to a need for thermoelectric cooling of the lasers inside QSFP transceivers.

However, designers need to consider that power limits are also going to be much higher in these form factors, because the electronics have a larger power draw, particularly in DD applications. This means that any TEC (thermoelectric cooler) that’s added to the package will just put more strain on the overall power budget, raising total package power consumption and, ultimately, cost. Photonic integration is also driving a trend towards more optical functions monolithically integrated into a single chip, so there is also a need to account for the combination of electronics and optics on the laser package.

Datacenters are cost-sensitive, so any cooling application will need to deliver performance without increasing cost much beyond that of a traditionally cheaper, uncooled laser package.

TEC Solutions for QSFPs

The right solution is a TEC that can handle higher heat densities and deliver peak performance without significantly impacting overall power consumption. Alternative approaches should also be considered to achieve cost-saving targets. Non-hermetic-rated TEC platforms can deliver performance on par with hermetic-rated TECs if the platform is redesigned to solve for the root cause of failure in highly-accelerated condensing environments.

ReefTEC™, Phononic’s non-hermetic TEC solution, re-engineers the TEC platform from the ground up to deliver highly-reliable cooling, without sacrificing performance or increasing package cost. Our engineers will consult with you to design a configuration that’s specific to your application. ReefTEC™ offers up to 30% lower power consumption and up to 60% better heat pumping density, and its compatibility with non-hermetic laser packaging makes it significantly more reliable in non-hermetic environments, where condensation is possible. Learn more about ReefTEC™ here.