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A Guide to Selecting Optical Transceivers for DWDM Multiplexer and Demultiplexer

Updated on Jun 1, 2022 by
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DWDM technology is an ideal solution for long-distance data transmission. It enables optical fiber networks to transmit signals of multiple wavelengths simultaneously, extending the bandwidth of optical communication networks to achieve high-speed, greater-channel capacity network transmission. DWDM multiplexer and demultiplexer and optical transceivers are vital components in such DWDM transmission. How to choose appropriate optical transceivers for DWDM Mux Demux is important for high-quality DWDM transmission. This article gives the answer.

Optical Transceivers for DWDM Multiplexer and Demultiplexer Common Ports

The common ports necessary for DWDM Multiplexer and Demultiplexer are used to connect external optical fibers with the line ports of the Mux Demux and the channel ports used for multiplexing and demultiplexing different wavelengths. The selection of optical modules corresponding to these two ports can be considered from two aspects: wavelength and transmission distance.

Choose Optical Transceivers Based on DWDM Wavelength

Generally speaking, the commonly used frequency bands of 100Ghz DWDM are C21~C60 (some will choose C20~C59). Take FS 40CH DWDM Mux Demux as an example, its wavelength range is C21-C60. The wavelength band of the optical modules can be matched with it. If there is no need to use all the 40 channels of the fiber Mux Demux, it's better to choose optical modules from low band, that is C21, C22, C23...

DWDM

The common frequency bands of FS 16CH DWDM Mux Demux and 8CH DWDM Mux Demux are C21~C36 and C53~C60. Their transceiver selection is the same as the 40CH DWDM Mux Demux, just sort from the low band to high. It is worth noting that C53~C60 can be connected with the 1530nm channel port in the CWDM system to realize the upgrade of DWDM services on the CWDM system.

Choose Optical Transceivers Based on Transmission Distance

It's known that optical loss caused by the equipment and optical cables exists in all the transmission processes. Therefore, the actual transmission of DWDM transceivers is shorter than the nominal transmission distance of the module, especially in aged optical fiber transmission systems. If necessary, EDFA and DCM devices can be added to extend the transmission distance in the DWDM network.

Faced with the different transmission distances, it is necessary to make a power budget plan in advance for the use of multiplexer and demultiplexer. Taking 10G network as an example, the maximum insertion loss of one FS 40CH DWDM Mux Demux is 5dB. A complete point-to-point transmission link requires two DWDM fiber Mux Demux, so the total insertion loss is 10dB. The FS 10G 80km DWDM optical module has a power budget of 23dB. In addition, the system needs to prepare an extra margin of 3dB in order to cope with the additional loss caused by the subsequent link aging and loosening joints.

Power budget reference formula:

Module budget - Fiber Mmux Demux insertion loss * 2 - system margin = power budget available for link transmission. (23-5-5-3=10dB)

DWDM transmission distance is calculated with reference to the loss coefficient of 0.25dB/km. The theoretical transmission distance is power budget available for link transmission/fiber loss coefficient = transmission distance. (10/0.25=40km)

To be note that this, calculation takes the maximum loss of DWDM multiplexer and demultiplexer. In fact, the typical FS 40CH DWDM Mux Demux loss is 3.5dB, so the actual transmission distance will be longer than the theoretical distance.

10G 80km DWDM transceiver module with 40CH Mux Demux, the transmission theoretical distance is about 40km if the system is the most stable. Hence, when you choose an optical transceiver in a DWDM network, you need to match the appropriate optical transceiver according to the transmission distance, and also consider the loss value of the link at the wavelength of 1550nm and the equipment loss of Mux Demux. Only when the optical transceiver cannot meet the transmission requirements, additional equipment such as EDFA and DCM need to be added.

Optical Transceivers for DWDM Multiplexer and Demultiplexer Function Ports

In addition to the necessary channel ports and line ports, DWDM Mux Demux also adds other special ports: 1310nm and 1550nm ports, monitoring ports, and expansion ports.

1310nm Ports

The 1310nm port supports traffic transmission at any rate. Therefore, when choosing a optical transceiver module for the 1310nm port, there are two major considerations: the wavelength of the optical module must be 1310nm, and the transmission distance that the optical module supports. FS LR4/ER4/ER8 optical modules are suitable for 1310nm ports and support 40G, 100G service transmission. You can choose a suitable optical transceiver for your DWDM Mux Demux according to the business transmission needs.

Products SFP-10GLR-31 QSFP-40G-ER4 QSFP-100G-ER4L-S BiDi SFP-10G-BX BiDi SFP-10G-BX40U BiDi SFP-10G-BX80
Max Data Rate 10.3125Gbps 44.6Gbps (4×11.2Gbps) 103.125Gbps (4x 25.78Gbps) 11.3168Gbps 10.3125Gbps 10.3125Gbps
Wavelength 1310nm 1310nm 1310nm 1330nm-TX/1270nm-RX 1330nm-TX/1270nm-RX 1330nm-TX/1270nm-RX
Distance 10km 40km 25km-40km 10km 40km 80km

Monitor and Expansion Ports

The monitor and expansion ports are not connected to the optical transceivers, but to the corresponding device.

The monitor port is mainly used for network monitoring and management. It can divide the combined power of all signals on the backbone link by 1%. The Monitor port provides flexible monitoring methods, with different monitoring devices, such as optical power meters, spectrometers, and OPMs, to test the power, wavelength, and optical signal-to-noise ratio (OSNR) of optical signals without interrupting services.

The EXP port is used to upgrade other bands than the current channel. For example, the current band of 16CH Mux Demux with EXP port is C21~C36. When upgrading the service, you can connect a Mux Demux with any number of channels on EXP port without C21~C36, such as 8CH Mux Demux of C53~C60.

DWDM

Conclusion

In summary, choosing suitable transceivers is vital for quality transmission for DWDM multiplexer and demultiplexer. It is necessary to considers wavelength, distance, and power budget to manage optical loss. Special ports, like 1310nm for versatile traffic and monitor/expansion ports, aid network management and upgrades. Choosing optical transceivers according to these factors ensures optimal DWDM network performance.

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