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Everything You Need to Know Before Buying CWDM and DWDM SFP+ Transceivers

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John

Posted on January 15, 2015
December 2, 2020
1825

WDM (Wavelength-division Multiplexing) transceiver modules include CWDM and DWDM modules. They can use CWDM or DWDM wavelengths to multiplex several optical signals onto a single fiber, which will increase network bandwidth and serve as a cost-effective solution in long-haul applications like MANs, LANs, campus networks, etc. Then, what should be considered when choosing CWDM and DWDM SFP+ transceivers for your WDM networks? Here focus on 10G SFP+ CWDM and SFP+ DWDM modules to offer you a buying guide.

Pay Attention to Optical Power Budget of 10G WDM Transceiver

Optical power budget (OPB) defines the amount of optical power available for successful signal transmitting. But the signals will be weakened in a long-distance transmission because of attenuation. So when choosing a 10G WDM module, users should confirm whether the transceiver's optical power could meet the actual transmitting distance demand. For example, one needs to deploy a CWDM link that covers 2 connectors (0.6d loss for each) and 4 fusion splicing points (0.1 dB loss for each), the total link length is about 35km. How to check the OPB of selected SFP+ CWDM transceiver meets the demand? Here takes the Cisco CWDM-SFP10G-1550 compatible CWDM SFP+ transceiver as an example.

The standard OPB = TX power - RX power = (-1dBm) - (-16dBm) = 15dB

The total power loss = 2×0.6dB – 0.1×4dB = 1.6dB

The worst OPB = the standard OPB - total optical power loss = 15dB - 1.6dB – 3dB(safety factor at 1550nm)= 10.4 dB

Transmission distance in worst case = (worst case OPB) / (cable loss at 1550nm) =10.4dB/0.25dB/km = 41.6km

Counted all the possible power loss, the Cisco CWDM-SFP10G-1550 compatible SFP+ CWDM module can support 41.6km transmission length. Therefore, this 10G CWDM module can be used for the exampled 35km link. But note that, the optical power budget is based on a theoretical calculation, and is just for reference. Attenuators also should be considered on actual demands.

Confirming the Wavelength of 10G CWDM and DWDM Modules

CWDM modules and DWDM modules work on different wavelengths. CWDM fiber transceivers support wavelength ranging from 1270nm to 1610nm, and DWDM optics run on 50GHz (0.4nm spacing) and 100GHz (0.8nm spacing) C band wavelength. Usually, 1470nm and 1550nm are the most widely used wavelengths in WDM networks. Users can buy the corresponding optical modules based on actual demand. Note that, a CWDM 10G SFP+ transceiver can not directly connect with a DWDM SFP+ module, but users can use an OEO converter to transfer CWDM wavelength to DWDM wavelength.

Select WDM SFP+ Transceiver Based on WDM MUX/DEMUX

Single fiber and dual fiber WDM MUX/DEMUX are the two common types on the market. Usually, single fiber CWDM MUX/DEMUXes use one-strand fiber to send and receive data, and they are used in pairs since TX and RX wavelength of the same port are different. This means the transceiver module should use the corresponding TX to connect the CWDM MUX/DEMUX. Here uses a pair of 4 channels single fiber CWDM MUX/DEMUX as an example (as figure 1 shows). On site A, the first port on CWDM MUX uses 1470nm wavelength to send data, so an SFP+ CWDM module with 1470nm TX should be used. On site B, the CWDM MUX uses 1490nm to send data, then the 10G CWDM transceiver with 1490nm TX should be deployed.

Figure 1: SFP+ CWDM modules are used on single fiber CWDM MUX/DEMUX

As figure 2 shows, dual fiber CWDM MUX/DEMUX uses two separate fibers to process data, noninterference. Thus, users just choose CWDM SFP+ modules that have matched wavelengths to connect the CWDM MUX/DEMUX.

Figure 2: SFP+ CWDM modules are used on dual fiber CWDM MUX/DEMUX

Guaranteeing the Compatibility between Your Devices and New Modules

There are many brands of network equipment on the market, such as Cisco, Juniper, Arista, etc. It’s important to make sure the interoperability and compatibility of the new 10G WDM optical modules and the devices. Besides, It’s known that the 10G SFP price of the original brand transceiver is several times higher than the third-party transceiver (know more about third-party vs original brand transceivers). So, it’s advised to buy modules from a reputable third-party supplier which will provide good after-sale services and technical support.

Don’t Forget Special Network Demands

10G BiDi and tunable modules are special types of 10G CWDM and DWDM optical transceivers. If users need to increase their network capacity and require an easier cabling system, BiDi SFP+ fiber transceivers will suit their demands since the modules send and receive data over one-strand fiber (learn more about BiDi optical modules). SFP+ tunable fiber transceivers are suitable solutions for users who need to tune the wavelength of the modules based on their actual demands (see more about tunable modules).

Conclusion

Choosing suitable 10G SFP+ CWDM and DWDM transceivers will help users build a stable and reliable network. It’s wise for users to consider aspects like WDM transceivers' optical power budget, wavelength, the connected WDM MUX, form factors and so on before buying WDM modules.