Hi everyone!
Today I will continue to write about reflectance testing. In this article, I will write about measuring reflectance. In the previous article, I explained problems and solutions, now, I will show you instruments and methods for testing. Let’s get started.
There are two ways to measure reflection. The first method is to use an OCWR or optical power meter, test source and referent cable, and the second is to use an OTDR instrument. No method is accurate enough, the error is about +/- 1 or 2 dB. When testing reflection, it is very important to minimize the reflections of those parts that are not tested. This is achieved in several ways. In addition, the reflection is sensitive to the effects of polarization, and this is difficult to control in all conditions.
It is mandatory to clean the optical connectors before all measurements. I write about it all the time. There are various optical microscopes and cleaning tools. In this case, the reflection is very sensitive to dirty connectors. Therefore, clean connectors must be provided. For more about it, you can read my articles at the following link: Troubleshooting process for dirty optical connectors.
OCWR is an abbreviation from Optical Continuous Wave Reflectometer. This is the main optical method for reflectance testing. We use this method for testing optical connectors on patchcords or short optical cables. The industrial standard is TIA FOTP-107 or IEC 61300-3-6. In the next figure, we can see the method for measuring reflectance or return loss.
Figure 1. Measuring reflectance or return loss
In this way, the test source sends an optical signal through the coupler to test the connection - the connector connection between the test source reference cable and the coupler connector. After the signal is reflected, it returns to the source, but a portion of that signal is measured using an optical power meter. As I said, we need to minimize all other reflections. There are two ways to do this, and these are optical termination at the end of the optical connector and using a very tight mandrel wrap. This method is used only for singlemode fibers.
I will continue to write about this theme in the next link >> Reflectance testing (3): OTDR method for measuring reflectance.
Thank you!
