Inphi offers 100G PAM4 QSFP28 for 80-km data center interconnect

Working in collaboration with Microsoft, Inphi Corp. (NYSE: IPHI) has developed and released a reference design for a DWDM QSFP28 transceiver that uses PAM4 for 100-Gbps transmission. The "ColorZ" technology will serve data center interconnect requirements at reaches up to 80 km, say Inphi and Microsoft sources.

While we originally described the transceiver as a single-wavelength 100G device, subsequent investigation reveals that a pair of 50-Gbps wavelengths combine to create the 100-Gbps transmission. We regret the error (of course).

Inphi has been among the first to market with PAM4 silicon (see, most recently, "Inphi unveils second-generation PAM4 chipset for 50/100/400 Gigabit Ethernet"). According to Jeff Cox, senior director, network architecture at Microsoft, the software giant had determined that a direct detect approach would be ideal for data center interconnect within the 80-km envelope, but couldn't get a traditional module vendor to agree to tackle development of the necessary optical transceiver. Microsoft then turned to Inphi to see if the company would be willing to leverage its PAM4 silicon expertise to create such an optical transceiver.

While Inphi's announcement focuses on a reference design, company Radha Nagarajan CTO confirmed that Inphi will supply Microsoft with a module. A company that Nagarajan described as "a non-traditional supplier" will do the packaging. The design features silicon photonics based functional integration of modulators, photodetectors, and multi-channel multiplexers and demultiplexers, as well as optical power monitors and fiber coupling structures. The module also contains the Inphi-developed InphiNity Core DSP Engine, as well as a low-power PAM4 driver and amplifier. The design offers support of multiple programmable forward error correction (FEC) options with different levels of pre-FEC BER performance.

Cox says his company hopes to be able to plug the QSFP28 into its existing switches to enable direct optical connections across fiber-optic network connections. A demonstration at OFC 2016 in Anaheim this week shows ColorZ transceivers plugged into switches from Arista Networks and Cisco, with a passive muxing and amplifier unit from ADVA Optical Networking in between.

The module consumes 4.5 W, a Watt higher than the QSFP28 standard. However, Cox indicated he was unconcerned by this. He was also unconcerned about having a single supplier of the transceiver, expressing the hope that other module vendors would embrace the design.

Prototypes of the ColorZ transceiver are now in Microsoft's labs. Production volumes should begin to ramp in the second half of this year.

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