MultiPhy unveils 100G single-wavelength PAM-4 chip

A chip to enable 100-gigabit single-wavelength client-side optical modules has been unveiled by MultiPhy. The 100-gigabit 4-level pulse amplitude modulation (PAM-4) circuit will also be a key building block for 400 Gigabit Ethernet interfaces that use four wavelengths.

Source: MultiPhy

Dubbed the MPF3101, the 100-gigabit physical layer (PHY) chip is aimed at such applications as connecting switches within data centres and for 5G cloud radio access network (CRAN).

“The chip has already been sent out to customers and we are heading towards market introductions,” says Avi Shabtai, CEO of MultiPhy.

The MPF3101 will support 100-gigabit over 500m, 2km and 10km.

The IEEE has developed the 100-gigabit 100GBASE-DR standard for 500m while the newly formed 100G Lambda MSA (multi-source agreement) is developing specifications for the 2km 100-gigabit single-channel 100G-FR and the 10km 100G-LR. 

MultiPhy says the QSFP28 will be the first pluggable module to implement a 100-gigabit single-wavelength design using its chip. The SFP-DD MSA, currently under development, will be another pluggable form factor for the single-wavelength 100-gigabit designs. 

The chip has already been sent out to customers and we are heading towards market introductions

400 Gigabit

The 100-gigabit IP will also be a key building block for a second MultiPhy chip for 400-gigabit optical modules needed for next-generation data centre switches that have 6.4 and 12.8 terabits of capacity. “This is the core engine for all these markets,” says Shabtai. 

Companies have differing views as to how best to address the 400-gigabit interconnect market. There is a choice of form factors such as the OSFP, QSFP-DD and embedded optics based on the COBO specification, as well as emerging standards and MSAs.

The dilemma facing companies is what approach will deliver 400-gigabit modules to coincide with the emergence of next-generation data centre switches.

One consideration is the technical risk associated with implementing a particular design. Another is cost, with the assumption that 4-wavelength 400-gigabit designs will be cheaper than 8x50-gigabit based modules but that they may take longer to come to market.

For 400 gigabits, the IEEE 803.3bs 400 Gigabit Ethernet Task Force has specified the 400GBASE-DR4, a 500m-reach four-wavelength specification that uses four parallel single-mode fibres. The 100G Lambda MSA is also working on a 400-gigabit 2km specification based on coarse wavelength-division multiplexing (CWDM), known as 400G-FR4, with work on a 10km reach specification to start in 2018. 

We are hearing a lot in the industry about 50-gigabit-per-lambda. For us, this is old news; we are moving to 100-gigabit-per-lambda and we believe the industry will align with us.

And at ECOC 2017 show, held last week in Gothenburg, another initiative - the CWDM8 MSA - was announced. The CWDM8 is an alternative design to the IEEE specifications that sends eight 50-gigabit non-return-to-zero signals rather that PAM-4 over a fibre. 

“We are hearing a lot in the industry about 50-gigabit-per-lambda,” says Shabtai. “For us, this is old news; we are moving to 100-gigabit-per-lambda and we believe the industry will align with us.”

Chip architecture

The MPF3101, implemented using a 16nm CMOS process, supports PAM-4 at symbol rates up to 58 gigabaud.

The chip’s electrical input is four 25-gigabit lanes that are multiplexed and encoded into a 50-plus gigabaud PAM-4 signal that is fed to a modulator driver, part of a 100-gigabit single-channel transmitter optical sub-assembly (TOSA). A 100-gigabit receiver optical sub-assembly (ROSA) feeds the received PAM-4 encoded signal to the chip’s DSP before converting the 100-gigabit signal to 4x25 gigabit electrical signals (see diagram).

“If you need now only one laser and one optical path [for 100 gigabits] instead of four [25 gigabits optical paths], that creates a significant cost reduction,” says Shabtai.

The advent of a single-wavelength 100-gigabit module promises several advantages to the industry. One is lower cost. Estimates that MultiPhy is hearing is that a single-wavelength 100-gigabit module will be half the cost of existing 4x25-gigabit optical modules. Such modules will also enable higher-capacity switches as well as 100-gigabit breakout channels when connected to a 400-gigabit four-wavelength module. Lastly, MultiPhy expects the overall power consumption to be less.   

Availability

MultiPhy says first 100-gigabit single-wavelength QSFP28s will appear sometime in 2018.

The company is being coy as to when it will have a 400-gigabit PAM-4 chip but it points out that by having working MPF3101 silicon, it is now an integration issue to deliver a 4-channel 400-gigabit design.

As for the overall market, new high-capacity switches using 400-gigabit modules will start to appear next year. The sooner four-channel 400-gigabit PAM-4 silicon and optical modules appear, the less opportunity there will be for eight-wavelength 400-gigabit designs to gain a market foothold.

“That is the race we are in,” says Shabtai.