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50G PON Advances Toward Commercialization

by Dan Grossman | 3月 16, 2022

It’s not too soon to update my recent report,  Technology Roadmap for Passive Optical Networks: The Next Step is 50G PON.  A lot has happened since it was published, including the Optical Fiber Communications Conference (OFC), which is the industry’s most important occasion for vendor announcements, operator guidance -- and analyst discussions.  

We continue to project 50G PON field trials and product announcements in late 2023, with volume production starting in 2024. While Chinese operators and vendors are particularly active in driving 50G-PON, component and system vendors see interest in all regions. I think that China will be 2-3 years ahead of the rest of the world in commercializing and deploying 50G PON.

50G-PON supporting component technology is maturing

Component vendors tell me that they are being pressured by their equipment vendor customers to bring in their schedules.

On the opto-electronic side, Sumitomo is sampling lasers and Avalanche Photodiodes (APD) to meet the 50G-PON standard, ITU-T Recommendation G.9804.3.  A 25G APD, combined with a Digital Signal Processor (DSP) and the G.9804.2 forward error correction (FEC) to counter signal distortion and dispersion, provide the necessary sensitivity. A transmit-only subassembly (TOSA) combines an electro-absorption modulated laser (EML) with a semiconductor optical amplifier (SOA) to provide sufficient optical power. Similarly, NTT Electronics has announced an SOA+EML device with a launch power of +9 dBm, and a 25 Gbps APD.

In a recent paper, Huawei demonstrated a monolithically integrated EML+SOA with +13 dBm output power, which meets the optical specifications of G.9804.3.  With DSP equalization, it can achieve a link budget of 35.8 dB in a 20 km link and can even work with 40 km of fiber.

Semtech produces analog and mixed-signal electronics for the PON Physical Media Dependent (PMD) layer: laser drivers, transimpedance amplifiers (TIAs), limit amplifiers (LAs). The company tells me that they have accelerated development of its 50G downstream and 25G upstream parts. The current schedules are consistent with our projections of field trials in late 2023.

At OFC, MA/COM demonstrated its recently announced 25 Gbps upstream components, including burst-mode laser driver, TIA, Limiting Amplifier and Clock/Data Recovery (CDR). The company partnered with module vendor AOI for a prototype SFP+. The demonstration showed error-free back-to-back operation of two ONUs, without forward error correction (FEC). The TIA also meets the stringent burst mode settling time specification in G.9804.3 (this spec determines the efficiency of upstream operation). All of those parts are currently sampling.

The one component that might be lagging a bit commercially is the DSP. I spoke with one vendor that has one in development but is not yet ready to discuss its progress. They point out that while the DSP chip is relatively straightforward, the algorithms will require fine-tuning to provably operate over a variety of marginal upstream channels. Fortunately, leading vendors have a path forward on the DSP by using FPGAs or ASICs.

HiSense has a 50G-PON OLT transceiver module and an ONU transceiver, both in a QSFP-112 package. These are prototypes and provided to vendors for demonstration purposes only. The ONU only has enough optical power to support a 5 km reach and a 16:1 split ratio, but that is fine for demo purposes.

Vendor Prototypes Advance

Huawei unveiled the 4th generation of its 50G-PON prototype. It is based on the company’s SmartMax 5800 OLT chassis. The 50G Line Card has two ports. Notably, the transceivers are in a pluggable (SFP+) form factor, as opposed to an external breadboard. Its outward appearance is similar to currently shipping OLT line cards. The ONUs are enclosed in generic metal enclosures. Huawei fabricated enough of these prototypes not only for their lab testing, but also for some early customer lab trials. Since the prototype was built with commercially available components, including a DSP implementation in an FPGA (rather than an application-specific standard part (ASSP) or ASIC), it had some limitations that will be eliminated when the 50G PON opto-electronic ecosystem is commercialized. Nonetheless, the prototype demonstrates 39.948 Gbps downstream service throughput and a 15.986 Gbps upstream service throughput, with forwarding delays in the DS direction between 79.755 and 80.753μs

FiberHome has a 50G PON prototype. The company developed a 50G-PON line card for its AN6000 OLT platform. The prototype achieves service rates of 40.3 Gbps downstream, 12.3G upstream.

ZTE recently announced it 50G-PON prototype. It claims to be the first to fully implement the ITU-T G.9804-series Recommendations. It also claims breakthroughs in ultra-high-speed TIAs and DSP algorithms[. The prototype is built on ZTE’s ZXA 600 platform. It will be available shortly for lab demonstrations, with trials to start toward the end of 2022.

Three other major vendors I have spoken with are working on their own prototypes but are not ready to comment publicly. My sense is that they might be waiting for the component ecosystem to mature to the point that all the necessary parts – including the DSP -- are at least sampling. They also are not feeling a sense of urgency from their customers in Europe and the Americas.

Operators Announce First Lab Trials

At the prestigious European Conference on Optical Communication (ECOC) in November, 2021 China Telecom and Huawei presented a detailed report on lab trials of Huawei’s 4th generation 50G PON prototype. The Optical Distribution Network (ODN) was limited to 10 km with a 1:32 split, consistent with China Telecom’s GE-PON deployments but less than the maximum reach permitted by ITU-T PONs. The prototype demonstrated that with the help of the DSP, 25 Gbps-class opto-electronic components can offer satisfactory performance at 50 Gbps.

On 11-Oct-2021, the Lianyungang (Jiangsu Province, China) branch of China Mobile announced that it had completed a test of a 50G PON system on a live network. The test demonstrated that the 50G PON has a capacity of 41 Gbps downstream, 16 Gbps upstream, with 80 μs of upstream latency.  It also demonstrated operation on existing ODN infrastructure and co-existence with 10G PON.

On 8-Oct-2020, Swisscom announced that it had demonstrated 50G PON in their lab. The demo used an earlier generation of the Huawei prototypes. This was the first public demonstration by an operator.

On 15-Dec-2021, Fiberhome announced a “technology pilot project” with an unnamed operator in Baoding, (Hebei Province, China).  The demonstration also included backhauling a 5G small cell.

I expect that other operator lab trials are either underway or planned, but not yet announced.

Leading Operators Support 50G PON Momentum

Public support from global Tier-1 operators gives momentum to 50G-PON development:

  • China Mobile
  • China Telecom
  • China Unicom
  • Orange
  • Swisscom
  • Telefonica
  • TurkCell

The common themes I hear from these operators are that they are preoccupied with their 10G-PON deployments, that 50 Gbps is the right speed for the next step, that they have no business case for proceeding with an interim solution (such as a 25 Gbps downstream), and that the timing for 50-GPON roll-out is consistent with their needs.

Other operators, such as AT&T and Openreach, are adopting a wait-and-see approach toward the next generation, waiting for their business cases to mature and for more clarity from vendors as to availability and pricing. Some of these are doing lab trials with the alternative technologies as vendor prototypes become available and have announced lab trials of 25GS-PON but no commitment beyond that.

Analyst Commentary

50 GPON is on track for field trials and commercial launch in late 2023, to be followed by ramp-up in 2024-25. The component ecosystem is advancing consistent with this timing. Chinese vendors and operators will be first, followed in a few years by vendors and operators elsewhere. In my view, this timing is in line with the needs of the market.

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