OTDR- backscattered light not detected by apd

[Zofia WalczewskaParticipant]

Hello everybody. I have problem with simulating OTDR in optisystem. I am very new at this and have been trying for a while to achieve any results, but it seems to still not be working correctly. The APD photodetector doesn’t detect the backscattered light from the fiber, as I am performing the simulations I can see that Optical Spectrum Analyzer does see some backscattered light, but the optical time domain visualizer doesn’t give any results. I am really confused and don’t know what is wrong with my project, please help me. Thank you in advance.

[Ahmad AtiehParticipant]

Hello Zofia,
You may try the new release OptiSystem 16.0, you can measure Rayleigh backscattered signal in the time domain. You could try it to build your OTDR.
Regards,
Ahmad

[Zofia WalczewskaParticipant]

Hello Ahmad,

Thank you very much for your response. I will try that.

Best regards,
Zofia.

[Zofia WalczewskaParticipant]

Dear Ahmad,

I simulated my otdr project in new optisystem, but unfortunately it is still not working as I cannot see the backscatered signal in the output of the circulator where the apd detector is. On the other hand I can see the backscattered signal on the optical time domain visualizer. Do you have any ideas what might cause that?

Best regards,
Zofia Walczewska

Attachments:

1. 

   2019-03-12-23.png
   

[Steve DodsParticipant]

Zofia, This part of the Optiwave website is Forums > FIBER. That means it is about OptiFiber. On the other hand, it appears your question is about OptiSystem. I recommend you post your question under Forums > SYSTEM. There it is more likely to be seen by someone who knows the answer to your question.

Regards, Steve

[Ahmad AtiehParticipant]

Dear Zofia,
the design you have has no spatial information on the fiber. The Rayleigh backscattered signal is represented as a parametric signal which is an average power signal on a single frequency or as a time signal. You need to create a means to analyze this reflected noise signal.
Currently, we are looking into a possible solution for OTDR design in OptiSystem.
Regards,
Ahmad

[Zofia WalczewskaParticipant]

Thank you everyone for replying. I will post my questions about it in SYSTEM, I didn’t know it works like that.
Dear Ahmad, that explains a lot of my doubts considering the interpretation of the response. When I do not use the circulator the signal looks like it was reflexed from the fiber, not distracted along its length. The intensity of the reflexed impulse changes with its length, but it still looks like one point reflex.
Do you happen to have any idea how to interpret and analyze this signal?
Furthermore, when I add the circulator th backsacttered signal completely dissapear, I am really confused why it happens.

Thank you very much.

[Ahmad AtiehParticipant]

Dear Zofia,
Yes you are correct. It is a one point reflex.
We need to enter spatial effect for the reflected signal as one option, or creating different model of the fiber.
Did you check the signal at the input and output of the fiber? You may need to check the index of the visualizers once you place a delay element, the index has to increase from 0 to 1.
Regards,
Ahmad