Ciena's multi-format 400G coherent QSFP-DD pluggable

Ciena showcased a working 400-gigabit Universal coherent pluggable module at the ECOC 2022 conference and exhibition in Basel, Switzerland.

Ciena is using its WaveLogic 5 Nano coherent digital signal processor (DSP) for the Universal QSFP-DD coherent pluggable module.

"We call it universal because it supports many transmission modes - interoperable and high performance; the most in the industry," says Helen Xenos, senior director of portfolio marketing at Ciena. 

A look inside Ciena's 400-gigabit Universal coherent pluggable module. TOF is the tunable optical filter. Source: Ciena

The pluggable has custom extended-performance modes and supports three industry formats: the 400ZR interoperable standard, the 400ZR+ multi-source agreement (MSA), and the OpenROADM MSA. (See tables below).

IP over DWDM

Communications service providers (CSPs) want to add pluggable coherent modules to their IP routers, removing the need for a separate transponder card or box linking the router to the optical line system.

The advent of coherent QSFP-DD pluggables has meant the same form factor can be used for client-side and line-side optics, ensuring efficient use of the router ports.

The CSPs want the coherent QSFP-DD module to have sufficient optical performance to meet their demanding networking requirements. For example, the module's output signal can pass through the filtering stages of reconfigurable optical add-drop multiplexers (ROADMs) along the optical link.

Optical amplification and filtering

Ciena's coherent QSFP-DD adds a fibre-based optical amplifier and a tunable optical filter to the coherent photonics and electronic ICs.

The optical amplification enables the high-performance mode and the launching of a 4dBm output signal. In contrast, 400ZR and 400ZR+ have a launch power of -10dBm.

"This is the industry's highest [QSDP-DD] transmit power," says Xenos.

The tunable optical filter improves the optical performance of the coherent receiver.

In an optical line system with colourless ROADMs, the Erbium-doped fibre amplifiers (EDFAs) generate out-of-band transmission noise - amplified spontaneous emission (ASE). The noise sources superimpose and become significant, impairing wavelength and system performance dramatically.

The tunable optical filter eliminates this effect and simplifies deployment over any photonics line system. In addition, Ciena says the pluggables can now work alongside high-baud rate transponders in existing ROADM applications.

The QSFP-DD's tunable optical filter means its optical performance closely matches that of the CFP2-DCO, aiding the two classes of pluggables working together.

Source: Ciena and Gazettabyte

Modes of operation

400ZR defines the module's baseline coherent performance. The OIF developed the 400ZR standard so hyperscalers can link their equipment in two separate data centres up to 120km apart.

The 400ZR specification delivers just enough optical performance to meet the optical link budget. The OIF produced a low-cost, interoperable, pluggable coherent specification.

400ZR supports a single baud rate - 60 gigabaud (GBd), and modulation scheme - dual-polarisation 16-QAM, and carries Ethernet frames.

Google, Meta, Microsoft and Alibaba were all involved in the OIF development, with the 400ZR Implementation Agreement published in early 2020.

400ZR supports two-channel widths: 75GHz and 100GHz, while the forward error correction scheme used is CFEC.

The 400ZR+ MSA enhances the performance by supporting other data rates - 100, 200 and 300 gigabits-per-second (Gbps) - as well as 400Gbps. In addition, it uses several modulation schemes and the enhanced O-FEC error correction scheme that extends reach.

Ciena's module also meets the OpenROADM MSA, supporting Ethernet and OTN and an enhanced reach at 400Gbps.

Source: Ciena and Gazettabyte

Ciena's Universal module's extended performance modes up the symbol rate to 65 and 70 gigabaud (GBd) and uses probabilistic constellation shaping (PCS).

PCS maps the bitstream onto the constellation to maximise the data recovery at the coherent receiver, thereby improving overall optical performance. The scheme also allows the fine-tuning of the data rate sent.

At ECOC, Ciena showed the module implementing the high-performance mode at 70GBd and PCS.

ECOC innovation award

The ECOC Exhibition Market Focus Advisory Committee awarded the most innovative product award to Ciena's WaveLogic 5 Nano 400G Universal QSFP-DD.