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ECOC 2023 Innovation Trends: Transponders, Pluggables, Line Systems, and Fibers

headshot of Paul Momtahan

October 19, 2023
By Paul Momtahan
Director, Solutions Marketing

Bringing together over 1,400 attendees from 39 countries, the 2023 European Conference on Optical Communications (ECOC 2023) included an exhibition (October 2-4) where Infinera had a busy booth, as shown in Figure 1, and a technical conference (October 1-5). Both events were in Glasgow this year. Having spent most of my time in the technical conference, here are my key takeaways on the major innovation trends related to:

  • Transponder evolution
  • Coherent pluggables
  • Optical line systems and fibers

The Infinera Booth in The Exhibition Hall at ECOC 2023Figure 1: Infinera’s booth in the exhibition hall

Transponder Evolution

One important topic that came up in multiple sessions was transponder evolution. Subtopics included DSP evolution, novel modulators, and baud rates.

DSP Evolution

Infinera's Han Sun giving his DSP tutorial at ECOC 2023Figure 2: Infinera’s Han Sun giving his DSP tutorial

In terms of DSP evolution, Infinera played a key role, with Infinera’s Han Sun giving a DSP tutorial (“Subcarrier and Multi-rate DSP for High-capacity Single Wavelength Digital Coherent Transceivers”), as shown in Figure 2, while Infinera’s Domanic Lavery chaired “Signal Processing for Optical Communications Systems” and Infinera’s Bernhard Spinnler chaired “DSP Evolution for 2030 and Beyond.” Presentations also covered baud rates that might be possible with 2-nm CMOS and 1.5-nm CMOS and the possibility of offloading DSP functions into the photonic domain in order to reduce power consumption and latency. There were also multiple presentations on constellation shaping, including enhanced nonlinear performance and reduced power consumption for probabilistic constellation shaping (PCS) and potential uses for geometric shaping.

Novel Modulators

Novel modulators that leverage the Pockels effect with the potential for very high baud rates (i.e., 400+ Gbaud) were covered in multiple presentations. A key driver for these modulators is the limited bandwidth potential of silicon photonics modulators. These novel modulators included thin-film lithium niobate (TFLN), barium titanate (BTO), and plasmonic modulators that leverage very small dimensions to magnify the electro-optic effect, including silicon organic hybrids (SOH). While each of these has potential, they each face multiple challenges such as integration with silicon photonics, manufacturability, and a lack of intrinsic gain functions (laser, amplification), temperature stability (SOH), and high loss (plasmonics). On the other hand, indium phosphide also has a path to 400+ Gbaud, the ability to support highly integrated photonic integrated circuits (PICs) including laser and semiconductor optical amplifier (SOA) functions, and proven volume manufacturability. Indium phosphide was the material of choice for many of the new TROSAs targeting the 800ZR/ZR+ market announced at the show, as well as for Infinera’s previously announced ICTR140.

Baud Rates

So, what can we expect from baud rates in the future? The consensus from the session addressing this topic appeared to be that 400 Gbaud is very possible, up to 500 Gbaud might be possible, and higher than 500 Gbaud seems unlikely, with key high baud rate challenges related to the RF interconnects and DAC/ADC. However, several presenters questioned whether a multi-wavelength transponder approach might in fact make more sense when evolving beyond ~200-250 Gbaud. Furthermore, one proposed path for transponder evolution was a single multi-wave transponder that fills the entire C-band.

Coherent Pluggables

Coherent pluggables were another hot topic at ECOC in both the exhibition and the technical conference. Topics related to 800G pluggables included the interoperable PCS modes for 800 Gb/s and 600 Gb/s and the different options in terms of transmit power: class C (-13 dBm), class B (-7 dBm), and class A (-2 dBm). Inside the data center, improved IM-DD performance at 1.6T enabling 10 km reach appears to have diminished the opportunity for coherent until the 3.2T generation. One controversial topic was the longevity of coherent pluggables in routers (IPoDWDM), with several presentations seeing this as a passing phase while router ports and coherent ports align. With router card bandwidth increasing with a 40% CAGR while coherent pluggables increase bandwidth with a 20% CAGR, the suggestion was that this would no longer make sense in the future, especially if/when full-spectrum transponders emerge.

Point-to-multipoint coherent evolution was covered in a presentation from Infinera’s Stenio Ranzini that looked at the important application of PON overlay, which operates over a single fiber rather than a fiber pair. His paper/presentation explained how a dual laser approach in the transceiver (one for TX, one for RX) could double capacity relative to a single TX/RX laser approach, while solving the point-to-multipoint challenge of laser frequency control. Following the announcement of new members Altice, Edgecore Networks, and PICadvanced, the Open XR Optics Forum held a packed symposium in the exhibition hall with speakers from Verizon, TIM, LightRiver, BT, Telefonica, and Infinera.

Optical Line Systems and Fibers

As coherent optical engines take spectral efficiency closer and closer to the Shannon limit, the scope for increasing fiber capacity solely via optical engines becomes increasingly limited. And while advances in optical engine technology still have the potential to drive significant reductions in cost per bit, power consumption, and footprint, major capacity increases will have to come from other sources related to the optical line systems and new fiber types. A key approach to scaling capacity is space-division multiplexing (SDM), either by stacking parallel single-mode fibers or leveraging new multi-core fibers (MCF). While not announced at the show, Google’s planned deployment of MCF on a branch of their planned Taiwan-Philippines-U.S. submarine cable was mentioned as an important endorsement. Additional options for scaling capacity include increasing the spectrum of existing bands with Super C and Super L and lighting new bands, with the S-band (in addition to C+L-band) seen as the best candidate with commercial solutions three to five years away, though this will be driven by demand.

In addition to driving innovation in new fiber types (uncoupled MCF, coupled MCF, multi-mode fibers, hollow-core fibers), this also has the potential to drive significant change and innovation in optical line systems, especially as related to ROADMs and wavelength switching. One view was that this will drive the need for bigger ROADMs, with several presentations covering approaches to building bigger wavelength-selective switches and ROADMs, with up to 128 degrees. A contrasting view was that ROADMs had a limited future and would eventually be replaced by fiber switches and full-spectrum transponders, at least in core networks. Other discussed approaches included multi-layer optical switching: switching at the wavelength, band (S, C, L), and fiber levels. A core-selective switch (CSS) was proposed for switching between fiber cores at a node interconnecting MCFs. Probably the most “different” optical switching proposal was an AI robot that would manually switch fibers by disconnecting and connecting optical ports on a patch panel. Additional optical line system innovation focused on new amplifier technology, including wideband amplification for C+L-band or S+C+L-bands on a single device.

Summary

Infinera's Azmina Somani collecting the award for “Most Innovative Product - Chip-Scale Packaging/Optical Sub Assembly”Figure 3: Infinera’s Azmina Somani collecting the award for
“Most Innovative Product – Chip-Scale Packaging/Optical Sub Assembly”

Overall, it was a great event that also covered a wide range of additional interesting topics, including AI and machine learning, short-reach communications inside the data center, and optical network operations. An additional highlight for Infinera was winning the award for Most Innovative Product –Chip-Scale Packaging/Optical Sub Assembly for the ICTR64 TROSA, as shown in Figure 3.