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Highlights from the 2021 Optical Fiber Communications Conference (OFC 2021)

by Dan Grossman | Jun 15, 2021

The Optical Fiber Communications Conference (OFC) is a singular annual event for the optical communications industry. It is both a trade show and a scientific/engineering conference. The sheer intellectual firepower on hand is both exhilarating and humbling. This year’s edition was virtual, because of the Pandemic. The format enhanced the conference aspects by making it possible to attend parallel sessions by recording but took away the show-and-tell elements from the trade show, as well as inhibited the face-to-face encounters that make both kinds of events so useful. A few announcements and themes were notable.   

Hollow Core Fiber (HCF) took a significant step from research to market. To oversimplify, unlike conventional fiber, light travels through free space in HCF rather than glass. This means much lower delay, since the speed of light through glass is roughly 2/3 that through a vacuum.  HCF also works in spectrum outside the conventional telecommunications bands, avoids certain non-linear impairments and handles very high-powered lasers. At OFC, a UK-based startup, Lumenisity and British Telecom that in a field trial, they were able to achieve error-free DWDM transmission with 38 channels of 400 Gbit/s through 10.25km of HCF. Separately, Lumenisity and Ciena announced a lab trial of 45 channels of 400 Gbps over 1,000km of HCF, using Ciena’s high-performance WaveLogic 5 coherent systems. These trials point to future deployment of HCF for hyper-latency sensitive uses like high-speed financial trading.

Passive Optical Networks research has begun in earnest toward 100 Gbps, in the wake of standardization of 50 Gbps PONs. As 50 GPON requires changes to transceiver architecture from the 10 Gbps PON standards, 100 GPON will require further changes, possibly moving from relatively simple intensity modulation/direct detection (IM-DD) to 4-level Pulse Amplitude Modulation (PAM4) or even coherent transmission. The key dilemma is the need to operate at such a high rate at an acceptable cost. Since commercial deployment of 50 GPON is expected to begin in 2025, and PON rates have been observed to proceed to the next higher step on a seven-year cadence, commercialization of 100 GPON is not expected until 2032. It will be deployed to enterprise customers, mid-haul and backhaul but not to consumers (see Strategy Analytics reports “Executive Summary: Is Fixed Broadband Traffic Growth Slowing Down?” and “‘Is the end in sight for Nielsen's Law? Despite dramatic increases during the pandemic, fixed broadband traffic growth may be slowing”.)

The Optical Internetworking Forum (OIF) announced completion of its 400ZR coherent optical interface implementation agreement in 2020.  At this year’s OFC, a number of vendors announced 400ZR and 400ZR+ modules in an array of pluggable form factors. 400ZR defines a 400 Gbps Ethernet transmission system with a reach up to 120 km. The 400ZR module simply plugs into a faceplate socket in a server, Ethernet switch or router. For the first time, it allows data center servers to connect directly to metro optical networks at speed, eliminating the need for intermediate transponders and thereby reducing cost, floorspace and power requirements for cloud service providers and other data center operators.

Corning introduced two new optical fibers in its SMF-28 product line. SMF-28 Contour fiber is the first to adhere to a new industry standard, ITU-T Recommendation G.657 A2, which specifies a tighter bend ratio than its predecessor, G.657 A1. What this means is that the fiber is more tolerant to poor installation techniques such as too-tight bends and pinching. It also allows for the higher stresses on individual fibers that plague very large fiber count cable. To top that off, it has lower optical loss than standard fiber and is available with a smaller diameter. The company also upgraded its ultra-low loss fiber to be bend tolerant to the G.657 A1 specifications. Improved bend tolerance in both fibers will reduce rework during installation and reduce risk of outages.

The trend toward Open and Disaggregated optical networks was highlighted at this year’s OFC. Operators have wanted for some time to break the tight integration between optical line systems –optical amplifiers, optical switches, Reconfigurable Add-Drop Multiplexors (ROADMS) and other active optical components --, transponders, and optical transport networks, as well as achieve multivendor interoperability. Presentations from the Facebook-sponsored Telecom Infrastructure Project (TIP) and Open Networking Foundation (ONF), as well as demos by Orange, Infinera/Microsoft and CESNET, demonstrated clear progress toward commercial deployment. This included  TIP’s open optical and packet/optical transponders, Phoenix and Cassini, open source network operating system,and open planning tools, OpenConfig, and Open Transport. One session highlighted network deployments, including both access and metro/inter-DC use cases.

Verizon and NEC Labs announced a field trial for a novel fiber sensing application. The fact that detectors can pick up vibrations in optical fiber has been applied for many years in applications like roadway monitoring. The field trial in Surf City, New Jersey (USA) uses this useful property to detect abnormal activity and assess, using AI techniques, excavation-related threats to Verizon’s cables. The advanced warning gives them time to find out whether the work was reported to DigSafe and to intervene, if necessary, before the cable is dug up. Since these “backhoe fades” are the most frequent cause of high-profile network outages, this has potential to vastly improve network reliability.

Infinera expanded its XR optics push to multi-vendor. XR is a multipoint coherent optical system that operates over a Passive Optical Network (PON), replacing standardized time-division multiplexed (TDM) systems like GPON and XGS-PON with a wavelength-and-frequency division multiplexing scheme. Multiples of 25 Gbps sub-carriers are assigned dynamically to each endpoint (i.e., ONT). The company positions XR as a solution for 5G fronthaul, which neither benefits from the statistical multiplexing of TDM PON, nor can tolerate its latency. At OFC, Infinera announced an OpenXR Forum, a multi-source agreement (MSA) to “advance development of XR optics-enabled products and services, accelerate adoption of coherent point-to-multipoint network architectures, and drive standardization of networking interfaces to ensure ease of multi-vendor interoperability and an open, multi-source solution ecosystem.” Interestingly, the founding members, in addition to Infinera, are Tier-1 service providers Verizon, British Telecom, Lumen (ex-CenturyLink), Liberty Global and Windstream. As of this writing, there are no other announced vendors or component suppliers. Regrettably, the virtual format this year precluded the side-conversations that would break through the hype and shed light on the true significance and openness of the XR Forum. Success will ultimately depend on whether the cost of coherent endpoint optical modules can become competitive with high-speed TDM and WDM PON solutions.

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