Part 2: 400-gigabit coherent pluggables
NeoPhotonics has unveiled its first two 400-gigabit coherent pluggable modules that support the OIF’s 400ZR coherent standard and extended ZR+ modes.
Ferris LipscombThe company has delivered samples of its ClearLight CFP2-DCO module for trials. The CFP2-DCO supports 400ZR, metro, and long-haul optional transmissions.
NeoPhotonics has also delivered to a hyperscaler the first samples of a 400-gigabit OSFP pluggable that supports 400ZR and 400ZR+.
Both modules use Inphi’s latest Canopus 7nm CMOS coherent digital signal processor (DSP) chip.
Module types
The OIF has developed the 400ZR standard to enable 400-gigabit signals to be sent between switches or routers in data centres up to 120km apart.
The main three pluggable modules earmarked for 400ZR are the QSFP-DD, OSFP and CFP2-DCO.
These modules differ in size and power envelope, ranging from the QSFP-DD, which is the most compact and has the smallest power envelope, to the CFP2-DCO module which supports the highest power and size.
It is the two client-side module form factors - the QSFP-DD and the OSFP - that will be mainly used for 400ZR.
“The CFP2 has more of a power envelope available so it tends to be used for longer reach applications,” says Ferris Lipscomb, vice president of marketing at NeoPhotonics.
These applications include specialist data-centre-interconnect applications and the metro and long-haul needs of the telecom operators.
400G CFP2-DCO
NeoPhotonics’ ClearLight CFP2-DCO uses an extension of a fibre’s C-band spectrum, what Huawei calls the Super C-band while NeoPhotonics refers to its implementation as C++.
The Super C-band covers 6THz of the spectrum compared to the standard C-band’s 4THz. The extended band can fit 120, 50GHz-wide channels or 80, 75GHz-wide channels.
NeoPhotonics can send 64-gigabaud (GBd), 400-gigabit signals over a 75GHz channel such that using ClearLight CFP2-DCO modules, 32 terabits can be sent overall.
The CFP2-DCO module uses NeoPhotonics’s ultra narrow-band line-width tunable laser that has had its tuning range extended to span the Super C-band. NeoPhotonics also uses its 64GBd intradyne coherent receiver (ICR) and coherent driver modulator.
The ClearLight CFP2-DCO can also send 400-gigabit signals over distances greater than 400ZR’s 120km. In addition, the module supports 200-gigabit transmissions over greater distances.
Sending a 200-gigabit at 64GBd using a 75GHz channel and quadrature phase-shift keying (QPSK) modulation, an optical signal-to-noise ratio (OSNR) of under 14dB is needed. Alternatively, using a 50GHz channel at 32GBd and 16-ary quadrature amplitude modulation (16-QAM), the OSNR is 16dB.
“With these [decibel] numbers, lower is better,” says Lipscomb. “You can go further with 64 gigabaud and QPSK; it’s 2dB better.”
Lipscomb says one use case for the 400-gigabit CFP2-DCO promises significant volumes: “The Super C-band has been used for deployments particularly by the Chinese carriers where they want to get more channels down a fibre.”
OSFP
NeoPhotonics has also unveiled its ClearLight OSFP module that enables the 400ZR standard and 400-gigabit transmissions for metro.
The module incorporates NeoPhotonics’s nano integrated tunable laser assembly (Nano-ITLA) and its silicon photonics-based coherent optical sub-assembly (COSA) that integrates the coherent receiver and modulator driver functions.
The OSFP tunes over 75GHz- or 100GHz-spaced channels, enabling 85 and 64 channels, respectively, as specified by the OIF. The OSFP also supports longer metro reaches at 400 gigabits.
NeoPhotonics also makes arrayed waveguide gratings (AWG) suited for 64GBd and 75GHz channel spacings that both modules support. “You need broader passbands and different channel spacings for 64 gigabaud,” says Lipscomb.
ZR+ interop?
Lipscomb is not a proponent of enforcing standardisation for the ZR+ extended modes, as has been done with 400ZR, despite the resulting lack of interoperability between optical modules from different vendors.
“There will always be the temptation in cases where you need it, to give up interoperability for increased [optical] performance,” he says.