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Test Optical Splitters Loss With Optical Power Meter & Light Source

Posted on Oct 31, 2016
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Optical splitters are usually used in passive optical networks (PONs) to distribute fiber to individual homes or businesses. There is something different between testing an optical splitter and a patch cable although both of them use an optical power meter and light source to test. In this tutorial, we are going to introduce optical splitter loss testing with optical power meter and light source.

Brief Introduction to Optical Splitters

Optical splitters, including FBT (Fused Biconical Taper) couplers and PLC (Planar Lightwave Circuit) splitters, are common passive optical devices that split the fiber optic light into several parts by a certain ratio. For example, a splitter with a 1x2 certain ratio configuration means that it has one input and two outputs. Likewise, there are 1x4 splitter, 1x8 splitter, 1x16 splitter, 1x32 splitter, and so on. When the splitter has two inputs and four outputs, it is called a 2x4 splitter. Optical splitters play an important role in FTTH (Fiber to the Home) networks by allowing a single PON network interface to be shared among many customers. The following picture shows an optical splitter used in a PON system.

Loss Specifications of Optical Splitters

Insertion loss testing of the optical splitter is very important to ensure compliance to the optical parameters of the manufactured splitter in accordance with the GR-1209 CORE specification. Here is a table of typical losses for splitters. Signal loss within a system is expressed using the decibel (dB), which is a measure of signal power attenuation.

Splitter Ratio Ideal Loss / Port (dB) Excess Loss (dB, max) Typical Loss (dB)
1:2 3 1 4
1:4 6 1 7
1:8 9 2 11
1:16 12 3 15
1:32 15 4 19

Note:

1. Excess loss is the ratio of the optical power launched at the input port of the splitter to the total optical power measured from all output ports. It assures that the total output is never as high as the input.

2. Insertion loss is the ratio of the optical power launched at the given input port of the splitter to the optical power from any single output port. The insertion loss includes the splitting loss and excess loss.

How to Test Optical Splitter Loss With Optical Power Meter & Light Source?

Before discussing the details of splitter loss testing, here is a fact that we should know about it. The attenuation of signal through an optical splitter is symmetrical which means it is identical in both directions. Whether an optical splitter is combining signals in the upstream direction or dividing signals in the downstream direction, it still introduces the same attenuation to an optical input signal. Thus, the principle of optical splitter loss testing is to follow the same directions for a double-ended loss test.

Now, we test the simplest 1x2 optical splitter as the picture shown below. First, attach a launch reference cable to the optical light source of the proper wavelength (some splitters are wavelength dependent), and then calibrate the output of the launch reference cable with the optical power meter to set the 0dB reference. Attach the light source launch to the splitter and attach a receive launch reference cable to the output and the optical power meter, and then measure the loss.

Similarly, to test the loss to the second port—move the receive launch cable to the other port and read the loss from the meter. For the other direction from all the output ports, we should reverse the direction of the test.

For other 1xN optical splitters, e.g. 1x32 splitter, this test method can also be used. Just set the light source up on the input and use the power meter and reference cable to test each output port in turn. But for upstream, we have to move the light source 32 times and record the results on the meter.

So, how about the 2X2 splitter? In this case, a lot of data are involved sometimes but it needs to be tested. We would need to test from one input port to the two outputs, then from the other input port to each of the two outputs. In the same way, we can test other 2xN splitters.

Tips: What you are measuring is the loss of the splitter due to the split ratio, excess loss from the manufacturing process used to make the splitter, and the input and output connectors. So the loss you measure is the loss you can expect when you plug the splitter into a cable plant. Once installed, the splitter simply becomes one source of loss in the cable plant and is tested as part of that cable plant loss for insertion loss testing.

Conclusion

The optical splitter is a very important passive optical component used in PON architecture. Loss testing, as a necessary testing item of optical splitters, can be done by using an optical power meter and light source. This tutorial illustrated the details of using an optical power meter and light source to test optical splitter loss. Related products such as high-quality PLC splitters and testing tools such as optical power meters, light sources, and test cords are available in FS.