NeoPhotonics : GaAs Drivers For SiPho Applications

By Nicolas Herriau on January 23, 2020 | Leave a Comment

The need for bandwidth in data centers is growing exponentially to meet the need of cloud computing, big data and AI representing a $214B market. Power consumption has become a big problem as data Centers will use up to 13% of the world's electricity by 2030, compared to 1% in 2010.

SiPho components (silicon photonics), which brings power savings and lowers the cost of optical transceiver modules because, can be made on a silicon wafer fab, bringing massive economies of scale. SiPho integrates lasers, modulators, and multiplexers on a single chip, thereby providing more bandwidth in smaller form factors.

Most of the need for optical modules in the data center is for intra-data center interconnections, meaning optical communication within the data center. At the core of the data center is a spine and leaf switched structure which requires a massive amount of transceiver modules.

Many hyper-scale data center operators have already upgraded to single mode fiber to handle the connection between the top of rack and the core of the data center. This is where upgrades are taking place, going to 100G or 400G PAM4.

Within SiPho, it would be easy to think the laser within the SiPho module is made of silicon, but it's not. The laser is still made of InP (Indium Phosphide). The modulator used to be an EML (Electro-absorption Modulator), but the trend is moving to 53Gb SiPho Mach/Zender modulator with DFB (distributed feedback) laser. This new solution saves a lot of power for one particular reason: the silicon modulator is not sensitive to temperature. In the old solution, the modulator was very sensitive to temperature and required TEC cooling, which uses a lot of power.

In order to make the solution work, the driving voltage of the modulator needs to be higher, and that is why we need GaAs (Gallium Arsenide) drivers, to get above 3 volts. Even though the driving voltage is higher, one the whole, the solution is much more energy-efficient than using TEC coolers.

The SiGe (Silicon Germanium) driver is interesting, but not supplying enough voltage. SiGe drivers are increasing voltage, and SiPho becoming more efficient, so perhaps in a year or two, SiGe could be a solution.