100G DWDM QSFP28 80km and 120km modules application guide

We offer both of 100G DWDM QSFP28 80km and 120km modules, the DWDM-100G-Q28-120 and the DWDM2-100G-Q28-80, and we also frequently get a lot of questions regarding these modules, their differences and their specifications. So we decided to compare both of these modules. In this article you will find all of the right answers to your questions.

You’re here to find out which of 100G DWDM QSFP28 80km and 120km modules fit best for your exact needs. We can help you with that, the key differences in the modules them selves are distance, and hardware. Both of the modules are PAM4 which is an evolution from the two state (NRZ) modulation. The DWDM2-100G-Q28-80 has a dual CS connector, where as the DWDM-100G-Q28-120 module has a double LC connector, and is a Single Lambda module.

DWDM2-100G-Q28-80

  • An unamplified module can typically reach upwards of 40km the exact range 40-80km, solely based fiber loss and dispersion.
  • Just like with the DWDM 100G PAM4 Double LC transceiver model with an EDFA and dispersion compensation in theory it could be possible to exceed 80km, but it depends on the network conditions.
  • Not having dispersion compensation can degrade performance if you’re going beyond the 80km mark, requiring for you to do additional network optimization.

DWDM-100G-Q28-120

  • With an unamplified module you can reach up to 80km without any external amplifiers.
  • With an amplified module it is possible to push the modules up to 120km (With EDFA).
  • With dispersion compensation and additional amplification it is possible to exceed 120km but performance will get impacted depending on the network design and the fiber conditions.

Are DCM’s necessary ?

Before we go deeper it is vital for us to know what is a DCM ? DCM stands short for dispersion compensation module, it’s a passive dispersion management element that can be inserted into an optical fiber network to control the overall chromatic dispersion. A DCM can be used to compensate dispersion across the entire C-band.

It depends on the fiber length and integrity requirements, if the modules or for that matter any modules use coherent modulation with built in DSP’s, it’s not generally necessary considering that the built in DSP’s can compensate for the dispersion making an external DCM unnecessary.

In case you don’t have coherent technology a DCM may be required beyond the 40-80km range, because signals like DWDM experience chromatic dispersion, and non-coherent rely on the DCM for signal correction at longer distances

But, in case you’re using modules that don’t have coherent technology and you’re not sure if the distance wont degrade the signal due to chromatic dispersion, I would suggest for you to get a DCM, for better optimization and insurance that your network will bet at the up most quality.

So, If your modules has built in DSP (common for the modern 100g DWDM QSFP28 coherent optics) a external DCM device would not be needed.

In the off-chance your module doesn’t have coherent technology using a DCM would be necessary for distances that exceed 40km to maintain the signal integrity.

Platform support

Well since the modules are QSFP28 that pretty much means that they are compatible with networking equipment that has QSFP28 ports and does support DWDM optical networking. These modules can be used in switches, routers and transport equipment from the major vendors, provided they do support 100G DWDM QSFP28 optics.

Compatible Switches & Routers include:

  • Cisco
  • Juniper
  • Arista
  • Huawei
  • Nokia
  • Ciena

A must for compatibility – Switch or router must have QSFP28 slots, some platforms may require FEC or tunable DWDM configurations and lastly if the modules are being used in the longer distance links ~80-120km, EDFA could be a necessity.

Coding

First we have to understand what is this so called hybrid solution : Customized (hybrid) coding refers to the situations when vendors originally did not have specific optical transceiver hardware type in supported transceiver list. For the full article click here.

So, since it is a special product we would use a 100GBASE-ER4 code, which is a hybrid solution. But mostly the coding solely depends on what system you are using for your modules, referencing a different article written by us:

“We recently had successful 100G-QSFP28-80 (ZR4) tests in Nokia routers (7210 SAS-Sx, 7750 SR1 and 7250 IXR). Originally these Nokia routers not support 100G ZR4 module, but we made a hybrid solution, where hardware remains 100G-QSFP28-80 (ZR4) and code is 100GBASE-ER4 (40km), with such hybrid solution we can have ZR4 80km link performance, but optical transceiver is recognized as ER4 40km and is accepted by the networking gear.”

So overall, it depends in what systems the modules are being used in, by testing and configuring hybrid coding it can help utilize modules in un-supported systems.

EDFA

What even is an EDFA ? well EDFA is now most commonly used to compensate the loss of an optical fiber in long-distance optical communication. It’s an optical amplifier used in the C-band and L-band, where loss of telecom optical fibers becomes lowest in the entire optical communication bands. Another important characteristic is that EDFA can amplify multiple optical signals simultaneously, and thus can be easily combined with WDM technology.

An EDFA can amplify multiple channels, up to 96 wavelengths in the c-band in fact. But you have to ensure enough output power, noise control and gain flattering for the most optimal performance, but of course there are limits.

All good things must come to an end, which is why EDFA’s have a maximum output power, typically between +20 to +25. If you have more 100G channels it means that you get less power per channel, which in return means that you may get a reduced signal quality and also overloading the EDFA can leaf to nonlinear effects. You also have to take into consideration distance and dispersion, a single EDFA usually might be enough for a distance of 80-120km, going over 120km is where you may require multiple EDFA’s.

Parallel Lambdas

Also at Edgeoptic, we have a DDMD-40 module that allows us to transmit 40 parallel wavelengths (lambdas) over a single fiber pair, one for TX, one for RX. However, there are factors that you need to consider when deploying 40 channels simultaneously.

For one, your DWDM MUX is designed for 40 specific IUT-T grid wavelengths in the C-band (1525-1565nm) meaning each 100G DWDM transceiver must be tuned to one of these wavelengths, also take into consideration your module and make sure that it does support tunable optics.

If you need or want to 40 channels think about the power that it will consume, having 40 channels = High aggregate power, which in return means that you might have to deploy an EDFA for long distances. The MUX/DEMUX introduces insertion loss which is around (4-6db per unit), this ensures that power levels stay balanced.

Also, running 40 active channels increases optical noise and it is possible that a FEC may be required. If used in longer distances OSNR degradation can limit the reach if not properly managed.

Over longer haul links that exceed the distance of 100km chromatic dispersion can cause signal distortion, and may require DCMs, but if you’re using transceivers that have coherent technology, then the built in dispersion compensation will be sufficient enough and an external DCM wont be required.

DWDM MUX/DEMUX filters should have high isolation (~30 dB) to prevent channel interference, but older or lower quality MUX filters can cause cross talk between adjacent channels.

So which is better ?

There is no clear winner, each has it’s perks and drawbacks. But if you had to choose, it would come down to what is it that you need for your systems and architecture.

The key differences are that clearly, the 120km module has a longer max reach, Optical budget for the 120km module is ~28-30dB, where as the 80km module has a budget of ~22-24dB. For the 80km module an SD-FEC is required only for longer reach, but for the 120km module an SD-FEC is required. Same goes with Amplification, for the 80km module it is optional if not using max reach, but for the 120km module it is required if you’re using the full reach so the EDFA can compensate for signal loss over long fiber spans. Taking into consideration the DCM and dispersion compensation, the 80km module may work without it, but at 120km, chromatic dispersion becomes ever so increasingly more noticeable. If supported you could also use coherent optics.

And the thing we are all thinking about is that the 120km are of course more expensive and consume more power, roughly ~4-5W higher, than the 80km modules. So to put it bluntly choose the 80km module for metro networks with low optical loss, and the 120km modules for long-haul networks, ensuring that EDFA’s and DCM’s are in place.

Alternative Solutions for 100G long distance WDM connections

Alternative and in some cases cost-effective solutions to 100G DWDM2 80 and 100G DWDM 120km modules are:

Product name Product description
DDMD-40 40 Channels Double Fiber Passive 100 GHz DWDM Mux/Demux
DWDM2-100G-Q28-80 MSA Compatible 100G QSFP28 DWDM Transceiver: DWDM2-100G-Q28-80
DWDM-100G-Q28-120 MSA Compatible 100G QSFP28 DWDM Transceiver: DWDM-100G-Q28-120

FAQ

Do I need a DCM (Dispersion Compensation Module) for my 100G DWDM QSFP28 setup?

The necessity of a DCM primarily depends on your module technology and distance requirements. For modern modules equipped with coherent technology and built-in DSPs, you typically won’t need a DCM since the built-in DSPs can handle dispersion compensation internally. However, if you’re using non-coherent modules and operating beyond the 40-80km range, installing a DCM is recommended to maintain signal quality and integrity. For shorter distances under 40km, you can generally operate without a DCM regardless of which module type you’re using.

What are the key differences between the 80km and 120km DWDM QSFP28 modules?

The primary distinctions between these modules lie in their technical capabilities and operational requirements. The 120km module features a higher optical budget of 28-30dB compared to the 80km module’s 22-24dB, but this comes with increased power consumption of approximately 4-5W more. The 120km version requires SD-FEC for all operations, while the 80km module only needs it for longer distances. Additionally, EDFA amplification is mandatory for the 120km module when using its full reach, whereas it’s optional for the 80km version. From a practical standpoint, the 80km module is more cost-effective and better suited for metro networks with low optical loss, while the 120km module, though more expensive, is optimized for long-haul networks.