DWDM Mux Demux Insertion Loss Testing

Updated on Feb 19, 2024 by

When adopting DWDM technology for easy capacity expansion on the existing network architecture, you may find the DWDM fiber link loss is much more complex than that of the regular fiber network. Considering that lower insertion loss means less investment in DWDM network deployment, this post will illustrate a simple method on how to test and calculate the insertion loss of DWDM Mux Demux and make an insertion loss value comparison for 40CH DWDM Mux Demux in the market, which will help you make informed decisions regarding the purchase and operation of DWDM Mux Demux.

Understand DWDM Mux Demux Insertion Loss

Insertion loss, usually measured by dB, is the total optical power loss caused by the insertion of optical components. As for DWDM Mux Demux, there are several types of port, such as channel port, line port, monitor port, 1310nm port and expansion port (if you want to konw more about them, please check: Ports on WDM Mux and Demux: What You Need to Know). No matter which type of port is connected to a DWDM network, insertion loss will occur immediately. Therefore, a high-quality DWDM multiplexer and demultiplexer should have a reasonable insertion loss value to ensure stable performance for a whole DWDM optical link. Using the 40CH DWDM Mux Demux as an example, the diagram below presents its port insertion loss details, including a 3.5dB typical IL line port, 3.5dB Typical IL channel ports for multiplexing different signals into one fiber, a 1.5dB IL 1310nm port for the existing legacy traffic, and a 26dB IL monitor port for easy troubleshooting without affecting traffic.

How to Test DWDM Mux Demux Insertion Loss

Since insertion loss has a profound influence on the whole DWDM optical networks, knowing how to test the insertion loss of multiplexer and demultiplexer is important. The following will use the 40CH DWDM Mux Demux as an example to illustrate detailed information, steps, and precautions for conducting insertion loss testing on DWDM MUX DEMUX.

DWDM Mux Demux Insertion Loss Test Equipment

In the testing, Cisco Catalyst 4948E switch and Cisco compatible DWDM SFP+ modules will be used as the light source to test the channel port insertion loss of a 40CH DWDM Mux Demux provided by FS.com. The DWDM Mux Demux has a typical insertion loss of 3.5 dB for each channel port. Insertion loss testing can be finished with an optical power meter if no professional equipment is available. Besides, there are some accessories required, including fiber patch cable, fiber optic adapter, fiber optic cleaner. The main equipment and tools prepared in DWDM mux and demux insertion loss testing are listed as following:

Testing Equipment & Tools Function
40CH DWDM Mux Demux Using its channel 25 port (3.5 dB typical IL) as the testing subject.
Cisco Catalyst 4948E Switch Working as the light source to be transmitted in the simple DWDM testing connection.
Cisco Compatible C25 DWDM SFP+
FOPM-201 Optical Power Meter Working as the main tool to test the insertion loss of the DWDM Mux channel port.
One-Push Fiber Optic Cleaner Removing dirt, dust, oil and grease quickly from optical interfaces.
LC-SC Simplex SMF Cable Eliminating the link interface restrictions and satisfying the testing fiber optic connection demands.
LC-LC Simplex SMF Cable
LC-LC Simplex SMF Adapter

DWDM Mux Demux Insertion Loss Test Procedures

Step 1. Clean All the Optical Interfaces

Before testing, we should resolve all stubborn stains on any optical interface which will be used in the following connections with the use of LC/SC one-push fiber optic cleaner, to ensure all the optical interfaces clean. So that, the accuracy of the testing result can be assured.

Step 2. Test the Optical Power of the Light Source

We should insert the 80km C25 DWDM SFP+ transceiver in the SFP+ port of Cisco Catalyst 4948E, and then connect the Tx port of the SFP+ transceiver with the SC optical power meter by using LC-SC/LC-LC single mode simplex fiber patch cables with LC-LC adapter. The whole fiber optic connection is shown in the following picture, which aims at testing the optical power of the light source from the Tx port of C25 DWDM SFP+ transceiver.

Once the fiber optic connection is finished, the optical signal passes LC-LC simplex SMF patch cable, LC-LC simplex SMF adapter and then LC-SC simplex SMF patch cable as shown in the above picture. As we press the λ button of the optical power meter to select the wavelength of 1550nm, we can get the optical power value (+1.08dBm) of the signal from the Tx port of the DWDM SFP+ transceiver, which is the output power of the transceiver (called Optical Power 1).

Step 3. Test the Optical Power of the Light Source with Mux Insertion Loss

We'll use the 40CH DWDM Mux Demux to replace the role of LC-LC single mode simplex fiber adapter used in the previous fiber link, which is a little more complex. Firstly, removing the fiber adapter and connecting the Tx port of the SFP+ transceiver to the Rx port of channel 25 port with the LC-LC single mode simplex fiber patch cable. Secondly, connecting the Tx port of DWDM Mux line port to the optical power meter with the LC-SC single mode simplex fiber patch cable. You can learn the second connection as below.

This time, we'll get the second power value (-2.12dBm) from the optical power meter, which is the final power value with the insertion loss of 40CH DWDM Mux Demux (called Optical Power 2). As the line port of the 40CH DWDM Mux Demux could be regarded as a fiber adapter, we can easily get the insertion loss of the DWDM Mux C25 Rx port:

Insertion Loss (CH25) = Optical Power 1 - Optical Power 2 = +1.08dBm - (-2.15dBm) = 3.23dB (REF value)

After testing the insertion loss of the C25 Rx port, we should confirm whether the Tx port of the C25 channel port also has the low insertion loss by connecting the Rx port of the DWDM Mux line port to the optical power meter and connecting the Tx port of the SFP+ transceiver to the Tx port of the channel 25 port. Then we can use the same formula to get the insertion loss value (3.38dB) of the C25 Tx port.

The testing insertion loss value might not be a very accurate value of the Mux channel port, but it is close to it. We can compare the two value results to FS.com 40CH DWDM Mux datasheet (Max 5.0dB IL, 3.5dB typical IL), and conclude that the channel port has passed the testing and 40CH DWDM Mux is a very low insertion loss equipment for deploying high-capacity and long-haul DWDM network.

DWDM Mux Demux Insertion Loss Test Considerations

In order to get the most accurate insertion loss value of the DWDM Mux channel, there is a simple to-do & not-to-do list required to follow before and during the testing:

  • Please keep all the fiber end faces, adapters and jumper cables clean which will be connected in the testing.

  • Please check the whole link to ensure that there is no loose connection, so as not to get an abnormal loss value.

  • Please ensure that there is no service transmitted in other channels, except the testing channel port. Thus the loss value result can be not affected.

  • Please note the DWDM transceiver wavelength should be consistent with the tested Mux channel port.

  • Do not connect the APC fiber patch cable to the 40CH DWDM Mux port which can cause excessive insertion loss, as the APC cable can not match with the UPC Mux channel port.

If you still get an abnormal loss value after checking the above list, you are suggested to directly contact the DWDM expert team of the Mux equipment supplier. It is convenient to provide a brief problem description and related test values, so that the expert team can analyze and resolve the problem as soon as possible.

DWDM Mux Demux Insertion Loss in the Market: Which One is Better

The higher the DWDM channel insertion loss is, the more operating cost needed as the optical amplifiers are required to deploy for keeping a balance signal power in the fiber link. After learning how great impact the insertion loss has on the whole fiber network links, we have researched many famous suppliers who provide a series of DWDM equipment. As a result, we conclude a graph showing the maximum insertion loss value of 40CH DWDM Mux from different vendors for reference.

In a DWDM network, the budget loss mainly comes from optical fiber path loss, DWDM OADM and Mux/Demux. If the loss of them is high, the network deployment cost will get higher certainly. In this graph, the vertical axis stands for the max insertion loss, and the horizontal axis shows several DWDM Mux suppliers like Cisco, Finisar, FS.com, Infinera, etc. From the comparison, we can see all the max insertion loss values of 40CH DWDM Mux are not very high. The max insertion loss of Infinera is 7dB, Cisco is 6dB and EDGE Optic is 5.9dB. Among these suppliers, 40CH DWDM Mux from FS.com or Finisar has the lowest max insertion loss—5dB. Besides, It is worth mentioning that the typical insertion loss of FS.com 40CH DWDM Mux is only 3.5dB, which would be the first choice for long-haul DWDM network deployment.


DWDM technology creates additional channels for more data transmission on the existing network architecture, which can not only expand network capacity, improve fiber utilization but also saving cost in high-capacity network design with the use of low insertion loss DWDM equipment. Besides the aforementioned 40CH DWDM Mux Demux, FS also offers other types of multiplexers characterized by low insertion loss, such as 8CH/16CH/96CH DWDM MUX and OADM modules to satisfy the high-capacity network needs, both of which can use the same or similar testing method to check the insertion loss as this post mentioned. If you are interested in these DWDM equipment but still have testing problems, visit our website or contact us for more detailed information.

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