Mode Converter

[Abdallah Ismail]

Dear All;
I’m working on Mode Division multiplexing system.I used Multimode fiber to generate LP modes to use them as carriers,then i used mode selectors after power splitters to get different modes.
But the system is not working well.
1)Does MZM work with different LP modes?
2)Do anyone help me with matlab code to convert modes?
3)Does mode Combiner convert any mode to fundamental mode? or what is its main function?

Best Regards,
Abdallah

[Damian Marek]

Hi Abdallah,

1) The MZM should be working with the spatial modes. Can you send your project file so that I can take a look?

2) What kind of conversion do you want to do? You want to change the spatial profile from one mode to another?

3) The mode combiner combines multiple modes into a single mode time domain signal.

Thanks

[Abdallah Ismail]

Thanks Damian,
The project is attached.
I need to convert any LP mode to the fundamental mode and The reverse.
Do you mean that the mode combiner take different mode have the same information and converting it to single mode.

I attached two files,One for the project where I’m trying to carry two QPSK systems over two modes and demultiplexing it.
But i noted that the QPSK system is not working well,Because it give me only two cases BER=0 or BER is very large or equal to 1.
So i tried to build QPSK system which attached and the same problem is exist.Also the same problem with the file that i downloaded from Optiwave downloads “NRZ-QPSK” when i add optical fiber instead of back to back.
The eye diagram is not normal,I think that the eye diagram should appear like women hair.
Wait your response .
Best regards,
Abdallah

Attachments:

1. MDM_Test-8-6-2013.osd
2. QPSK.osd

[Damian Marek]

Hi Abdallah,

The mode combiner basically strips away the spatial information of a signal and leaves you with a time domain signal. You could then run the signal through a Multimode Generator to attach the spatial information you want (Convert the modes).

The problem you are facing with the eye diagram visualizer is that there are m-ary threshold detectors in these project files, which depending on your defined threshold will assign a m-ary value to each bit. Using this sequence to drive a NRZ Generator results in a “perfect” signal with no noise or variation, this is what accounts for the eye diagram appearing as a single line instead of many. This is also the reason why the BER and Q factor are giving you unrealistic results.

Hope this helps!

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