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# Decoding CWDM and DWDM SFP+: A Comprehensive Buying Guide

Updated on May 4, 2023 by
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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

• Importance of Optical Power Budget (OPB)

The Optical Power Budget (OPB) indicates the available optical power for successful signal transmission. In long-distance transmissions, signals undergo attenuation, leading to signal weakening. Therefore, when selecting a 10G WDM module, it's crucial to ensure that the transceiver's optical power aligns with the specific transmission distance requirements.

• Optical Power Budget Calculation Formula

Question：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 if 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

Answer：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.

## Confirm 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

Dual fiber and single fiber WDM MUX/DEMUX are widely used in the market, offering different configurations for data transmission. For instance, the dual fiber type utilizes two separate fibers to independently handle data transmission, while the single fiber CWDM MUX/DEMUX uses a single-strand fiber for both sending and receiving data simultaneously. The following are the different applications of WDM SFP+Transceiver in two scenarios.

• SFP+ CWDM Modules are Used on Dual Fiber CWDM MUX/DEMUX

In a dual-fibre CWDM MUX/DEMUX, two separate optical fibres are used for transmitting and receiving data to ensure that the channels do not interfere with each other. In this configuration, it is only necessary to ensure that the wavelengths at both ends are the same in order to achieve normal communication, without having to worry about the possibility of different wavelengths at both ends.

As shown in the diagram, users can seamlessly integrate the configuration by relying on consistent wavelengths at both ends. This enables them to easily select CWDM SFP+ modules with the appropriate wavelengths, ensuring a smooth connection to the CWDM MUX/DEMUX. This flexibility allows users to tailor their network setup to specific bandwidth requirements and infrastructure considerations, eliminating concerns about complex wavelength matching issues.

• SFP+ CWDM Modules are Used on Single Fiber CWDM MUX/DEMUX

In a single-fibre CWDM MUX/DEMUX, a single fibre is used to send and receive data simultaneously. In order to avoid signal interference, it is often chosen to use optical modules of adjacent wavelengths. For example, if you use a 1470 wavelength module at Site A, Site B can use a 1490 wavelength module. This configuration ensures the wavelength difference between adjacent channels, thus minimising mutual interference between signals and maintaining communication stability.

Within the restricted reception range of optical modules at both ends, modules with adjacent wavelengths can establish normal connections. As shown in the figure below, take a pair of 4-channel single-fibre CWDM MUX/DEMUX as an example. The first CWDM MUX port at Site A uses 1470nm wavelength to transmit data, and needs to be connected to a 1470nm TX SFP+ CWDM module. The receiver should align its wavelength with that of the CWDM module to receive the corresponding optical signal, for instance, at 1490 nm. Ensuring the correct pairing of transmitter and receiver wavelengths is critical to ensure consistent signal transmission and reception.

Notice：

Building upon the aforementioned principles, SFP+ DWDM modules adhere to similar principles when coupled with DWDM MUX/DEMUX. Whether in a dual-fibre or single-fibre DWDM MUX/DEMUX configuration, the matching strategy remains consistent. For instance, in a single-fibre DWDM MUX/DEMUX setup, if the first port at Site A transmits data at 1550nm, a DWDM SFP+ module with a 1550nm TX should be selected for that specific connection. The receiver needs to match the wavelength of the DWDM module to receive the corresponding optical signal. There must be paired TX and RX wavelengths on the same port to ensure consistent data transmission.

## Guarantee Compatibility between Your Devices and New Modules

A myriad of network equipment brands, such as Cisco, Juniper, Arista, have emerged in the market. Ensuring new 10G WDM optical modules are compatible with devices from various brands is crucial. Note that original brand optical modules are often much pricier. Therefore, it's advisable to buy from reputable third-party suppliers. Third-party optical modules offer cost advantages and strengths, including flexible customization options and extensive compatibility, while maintaining excellent performance and quality. Opting for a highly reputable third-party supplier provides cost-effective, high-performance solutions, along with premium after-sales service and technical support.

## Consider Special Network Requirements

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. SFP+ tunable fiber transceivers are suitable solutions for users who need to tune the wavelength of the modules based on their actual demands.

## CWDM and DWDM SFP+ Transceivers: Q&A

Q: Is it Possible to Convert the Conventional Wavelength, like 850nm, into DWDM or CWDM Wavelength?

A: If you require the conversion of wavelengths into CWDM or DWDM wavelengths, you can utilize an Optical-Electrical-Optical (OEO) converter to achieve this. The OEO converter facilitates wavelength conversion through O-E-O transformation technology.

Q: How to Choose Between 100GHz and 50GHz in DWDM Channel Spacing?

A: When comparing 50GHz and 100GHz transceivers, the telecom industry commonly favors the 100GHz C-Band transceiver. With a channel spacing of 0.8nm around 1550nm, this configuration is widely adopted. Channels are designated by colors or wavelengths, and channels 17 to 61 are frequently employed.

Q: How to Select Suitable Fiber Cables for CWDM and DWDM SFP+ Transceivers?

A: The optical cable can be divided into two types: single-mode fiber optic cable and multimode fiber optic cable. The former is typically used for long-distance transmission, while the latter is suitable for short-distance transmission. To support CWDM and DWDM SFP+ transceiver links with distances of up to 80 kilometers, we opt for single-mode fiber optic cables with LC connectors.

## 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. Know more here: CWDM vs DWDM: What’s the Difference?

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