Eye diagram

[Rohan katti]

I am working in all optical digital encoders. At the output bits i have got the eye diagram and the BER patterns which i have attached here.
1) What inference can i draw from the BER pattern which i have obtained?
2) How can i calculate the extinction ratio from the eye diagram plot ?

[Damian Marek]

Rohan,

1) The BER pattern is a simple tool that gives a spatial visualization of the BER as a function of decision instant and threshold. The decision instant is the x axis generally a fraction of the bit period and the threshold is the y axis. You will also notice on the sidebar of the window that it gives a BER for the 5 different BER patterns. Basically it tells you for a given decision instant and threshold value that lie within the pattern, then you are more or less guaranteed the corresponding BER.

2) From wikipedia, http://en.wikipedia.org/wiki/Extinction_ratio you can use the highest and lowest part of the eye diagram to calculate the extinction ratio.

Let me know if this helps!

[Rohan katti]

Thank You very much for the reply.
Regarding the BER pattern , is the shape any matter of concern because in an encoder design for every output bit i get BER as zero but the shape differs.
Also you have mentioned about threshold. so can i know for which parameter is that threshold for?

[Damian Marek]

To answer your first question I would have to look at your project. If your BER is 0, I don’t think the BER pattern will tell you much. IS the BER 0 for all the patterns?

The threshold is the value that the BER Analyzer will use decide whether a detected signal is a binary 1 or 0. You can manually change it by right clicking the component and go to Component Properties and changing it.

Regards

[Rohan katti]

Very Sorry for the delay. I am designing all optical Gray code to binary code conversion using Mach- Zehndr Interferometer. By adjusting the delay between the arms of the MZI i am getting the BER as zero for all bits. For one of the bit i dint get it as zero but was reaching to zero very very small value so i added an EDFA before combining the outputs of the MZI and i got the BER as zero for that bit also.

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