How to Deploy a Coherent QSFP-DD Module in an Existing DWDM Network?
Start with the Fibre, Not the Module
The biggest mistake in projects like this is ordering modules before anyone looks at the fibre they are meant to run over. QSFP-DD coherent modules, including the GBC Photonics 400G OpenZR+, have specific requirements for the optical path. The signal must reach the receiver with adequate power and quality. If the route on which you plan to run the modules has multiple ROADMs, dispersion compensators, or a very long distance, those requirements may not be met.
That is why, before ordering anything, you measure the distance and the current OSNR values. Check whether your link’s parameters will allow you to run a transmission at the throughput you require.
Check Your Existing DWDM System
The second step, often skipped, is the compatibility of your current optical line system with the module you want to deploy. There are three questions you must ask the vendor of your OLS (Open Line System) or DWDM system.
01
Does the system support flex-grid?
400G OpenZR+ modules operate at 60 Gbaud and require a channel at least 75 GHz wide. If your DWDM has a fixed 50 GHz grid, the maximum throughput is 200G instead of 400G.
Fixed 50 GHz grid limits to 200G02
What signal power is required at the multiplexer input?
Most DWDM systems are calibrated for a signal between minus 3 and 0 dBm. Most OpenZR+ modules transmit at minus 10 dBm, so an EDFA amplifier must be added. That means extra cost, higher power draw, and worse OSNR.
The most common project blocker03
The GBC Photonics solution: native 0 dBm
GBC Photonics 400G OpenZR+ modules transmit a signal natively at 0 dBm. They plug directly into the multiplexer without modifying the system, and the power can be tuned precisely within a 10 dB range to match the specific path.
No EDFA amplifier, no reworkThe first question concerns flex-grid. 400G OpenZR+ modules operate at 60 Gbaud and require a channel at least 75 GHz wide. If your DWDM has a fixed 50 GHz grid, the maximum throughput you will achieve is 200G instead of 400G.
The second question concerns the signal power at the multiplexer input — and this is exactly where projects most often get blocked. Most DWDM systems are calibrated for a signal power between minus 3 and 0 dBm at the multiplexer input. Meanwhile, most OpenZR+ modules on the market transmit a signal at minus 10 dBm. The effect is that you cannot plug the module in directly — you have to add an EDFA amplifier between the module and the multiplexer. That means extra cost, extra power draw, and worse OSNR for the whole system.
GBC Photonics 400G OpenZR+ modules solve this problem differently, because they transmit a signal natively at 0 dBm. They plug directly into the multiplexer without any modifications to the existing system, and the power can be tuned precisely within a 10 dB range to match the specific path.
Check the Router or Switch You Are Plugging the Module Into
This is where projects most often stall, already after the hardware has been delivered. Not every device with a QSFP-DD port supports coherent modules. The port fits physically, but the device’s software and firmware must be able to talk to such a module. The CMIS (Common Management Interface Specification) standard defines how the host communicates with the module, but not all devices have up-to-date firmware with full CMIS support for coherent modules.
Check the compatibility list for your router or switch before ordering. If your device is not on it, call the manufacturer and ask about their roadmap for CMIS and QSFP-DD coherent module support. Sometimes a firmware update is enough, and sometimes it is a more serious matter. GBC Photonics modules work in routers and switches from all leading network hardware vendors compliant with the OpenZR+ standard, and compatibility is confirmed in real-world deployments, not just in the laboratory.
Channel Configuration — Faster Than You Think
Once you are confident that the fibre, the DWDM system, and the router are ready, configuring the module turns out to be surprisingly simple. GBC Photonics modules are fully tunable across the C-band, and setting the required transmission channel takes about 10 seconds. The channel grid is also adjustable, so the module can operate in Flex-Grid systems with maximally efficient use of the available spectrum.
Compatibility with a specific active-equipment vendor is configured through the SRD (Smart Recode Device) environment. You can do this from a computer or — which matters for field deployments — from a smartphone via the SRD Go app. An engineer at a node in a remote location does not have to wait for someone from the office, but programs the module on the spot in a few minutes.
Three Things Engineers Regret After the Fact
01
An unverified route
The project assumed certain parameters, but the actual route had an OSNR level far worse than the documentation showed. The system ran unstably. They had to give up throughput or buy additional ZR++ modules.
Measure OSNR and distance before you order anything.
The most common mistake
02
Firmware not updated
The coherent module was not visible in the management system. The router appeared to work, but telemetry was empty. Updating router firmware in an operator network requires thorough testing and is not a quick task.
Check CMIS support and plan the update in advance.
A costly mistake
03
No measurement documentation after deployment
Six months later the operator wanted to add another channel on the same path, but nobody knew what the actual parameters were at commissioning. The measurements had to be repeated from scratch.
Record the path parameters at commissioning — you will save work later.
A documentation mistake
The first is an unverified route. The project assumed certain parameters, but the actual route had an OSNR level far worse than the documentation showed. The system ran unstably and they had to either give up throughput or buy additional ZR++ modules.
The second is firmware that was not updated. The coherent module was not visible in the management system. The router appeared to work, but telemetry was empty. Updating router firmware in an operator network is not a task you do quickly, because it requires thorough testing to ensure network stability.
The third is the lack of measurement documentation after deployment. Six months later the operator wanted to add another channel on the same path, but nobody knew what the actual path parameters were at commissioning. The measurements had to be repeated from scratch.
Step 1
Measure the fibre
Measure the distance and current OSNR values on the route. Check whether the link parameters will allow you to run a transmission at the required throughput. This is the foundation of the entire project.
Step 2
Verify the DWDM system
Ask your OLS vendor about flex-grid support and the required signal power at the multiplexer input. GBC Photonics modules with native 0 dBm plug in directly, without an EDFA amplifier.
Step 3
Check the router or switch
Verify the compatibility list and CMIS support for coherent modules. The QSFP-DD port fits physically, but the firmware must be able to talk to the module.
Step 4
Configure the channel
Setting the channel in the C-band takes about 10 seconds. Compatibility with a specific vendor is configured through SRD, from a computer or a smartphone in the SRD Go app.
Result
Transponder eliminated from the architecture
The module communicates directly with the optical system. No more separate transponders, their power, cooling, and management. Remember to record the path parameters at commissioning.
FAQ
FAQ — Deploying a QSFP-DD Module in a DWDM Network
With the fibre, not the module. The biggest mistake in projects like this is ordering modules before anyone looks at the optical path they are meant to run over. Measure the distance and the current OSNR values on the route, then check whether the link parameters will allow you to run a transmission at the throughput you require. If the route has multiple ROADMs, dispersion compensators, or a very long distance, the path requirements may not be met. This is the foundation of the entire project and the point from which everything begins.
It depends on the throughput you want to achieve. 400G OpenZR+ modules operate at 60 Gbaud and require a channel at least 75 GHz wide. If your DWDM has a fixed 50 GHz grid, the maximum throughput you will get is 200G instead of 400G. Ask your optical line system vendor directly whether it supports flex-grid. If you need the full 400G on a single channel, that question must be asked before ordering the modules, not after delivery.
This is the issue that most often blocks projects in practice. Most DWDM systems are calibrated for a signal power between minus 3 and 0 dBm at the multiplexer input. Meanwhile, most OpenZR+ modules on the market transmit a signal at minus 10 dBm. The result is that you cannot plug the module in directly — you have to add an EDFA amplifier between the module and the multiplexer. That means extra cost, higher power draw, and worse OSNR for the whole system. GBC Photonics 400G OpenZR+ modules transmit a signal natively at 0 dBm, so they plug directly into the multiplexer without modifying the system, and you tune the power within a 10 dB range to match the specific path.
No, and this is where projects most often stall, already after the hardware has been delivered. The port fits physically, but the device’s software and firmware must be able to talk to a coherent module. The CMIS standard defines how the host communicates with the module, but not all devices have up-to-date firmware with full CMIS support for coherent modules. Check the compatibility list for your router or switch before ordering. If your device is not on it, ask the manufacturer about their support roadmap. Sometimes a firmware update is enough, and sometimes it is a more serious matter.
Surprisingly short, once the fibre, DWDM system, and router are ready. GBC Photonics modules are fully tunable across the C-band, and setting the required transmission channel takes about 10 seconds. The channel grid is also adjustable, so the module operates in Flex-Grid systems with maximally efficient use of the spectrum. Compatibility with a specific active-equipment vendor is configured through the SRD environment, from a computer or a smartphone via the SRD Go app. An engineer at a node in a remote location does not have to wait for someone from the office, but programs the module themselves, on the spot, in a few minutes.
Three. The first is an unverified route. The project assumed certain parameters, but the actual OSNR was far worse than the documentation showed. The system ran unstably and they had to give up throughput or buy additional ZR++ modules. The second is firmware that was not updated. The module was not visible in the management system, the router appeared to work but telemetry was empty, and updating firmware in an operator network requires thorough testing and is not a quick task. The third is the lack of measurement documentation after deployment. Six months later someone wanted to add another channel on the same path, but nobody knew the actual parameters at commissioning and the measurements had to be repeated from scratch.
You eliminate the transponder from the architecture. In the traditional setup the router connects to a transponder that converts the signal to a DWDM wavelength, with another transponder waiting at the far end. A coherent module communicates directly with the optical system, so the separate transponder disappears along with its power, cooling, and management. That means less hardware in the rack, fewer points of failure, and lower maintenance costs. Provided, however, that you first go through the route measurement, DWDM system verification, and router check — because it is precisely these three steps that decide the success of the entire deployment.
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