FTTH using OCDMA

[Liju Mohan]

Hi. I have been trying to create a 15 user sac-ocdma system using Modified Quadratic Congruence coding.

I followed the example given for 7 users from the optiwave site. However, i am facing some issues. The users seem to work reliably well when ON individually, but when multiple users are ON simultaneously, i get no output whatsoever, even with just 3 users. Would anyone be able to provide any solution for this issue? I did make changes to the FBGs in accordance with the codes used.

I have used MQC codes with prime number 3 (should be sufficient for 3 to 15 users).

[Liju Mohan]

Any help would be appreciated..

[Damian Marek]

Hi Liju,

I’m away from the office right now but if you attach your project I could take a look at it. From your description though it might be a filtering issue. If more than one user is on then they are interfering with each other. Try to make sure the filters are set at the right frequency and bandwidth.

Regards

[Liju Mohan]

Hi Damian,

Thank you for responding to my issue. I believe the issue begins at the power combining stage before the transmission via the optical fiber. Or it could be an issue faced because of the code. I generated the code manually using Matlab, and have based the encoding and decoding sections based on this code. The codes are mentioned on the respective encoders. I hope the issue is a rather simple one i seem to be overlooking. I have attached the initial osd project.

Regards

[Damian Marek]

I just tried it out and all of the users work individually, but the when turning on the third user they all interfere. I would think that the coding or gratings are wrong with the third user.

[Liju Mohan]

I had that doubt myself, so i changed the codes for the 2nd user and the 3rd user (just to be sure) and tried again. The result was the same. When they are ON together, it simply doesnt produce the required output.

[Damian Marek]

Ok yes then something is happening. I’ll see what I can find out. I’ll be back in the office Monday next week, so you can expect a response then!

Thanks for your patience!

[Liju Mohan]

Thank you for taking the time to respond to my problem. I shall look forward to hearing from you on Monday.

[Liju Mohan]

Hi Damian,

I have just tried the SAC OCDMA structure using another set of codes, more specifically using Multi-Diagonal codes for 3 Users. Here again i seem to be facing a similar issue, only this time it doesnt work with even 2 users simultaneously ON. Perhaps it is an issue with my set up?

[Damian Marek]

Yes, I was looking at your project yesterday, but I did not find anything new. However, there was one issue perhaps. The White Light source bandwidth depends on the sample rate (Nyquist theorem) and I found that in your original project some of the gratings were out of the bandwidth of the white light (essentially ineffective). Fixing the problem did not help with the MQC code in your original file, but perhaps that is the issue in your new multi diagonal code project.

Do you by chance have a link to a reference paper that you are basing your MQC project on?

Regards

[Liju Mohan]

Thank you for taking the time to look into it. Would you perhaps still happen to have the file where in you have fixed the bandwidth issue? I will check out the project with the MD codes as you have suggested. As for the reference paper on MQC, i have the main paper i have referred, to learn the construction of the code. The link for the paper is http://115.248.50.245:7777/jlf/search/generalredirect?rurl=http://ieeexplore.ieee.org/xpl/articleDetails.jsp?tp=&arnumber=948274&queryText%3Dmodified+quadratic+congruence

[Damian Marek]

There was one grating that was out of the range. 1553.5 nm

[Damian Marek]

I cannot open that link. Can you just give the reference or citation of the paper? Title, authors and paper

[Liju Mohan]

It is not a very recent paper, but it is the most descriptive paper i have read on MQC codes. The other main reference i use is a book “Optical CDMA Networks Principles, Analysis and Applications by Hooshang and Massoud.

[Damian Marek]

Hi Liju,

I had to delete that post because we cannot support attaching the actual article in PDF form, because it does not belong to us. I was only hoping for the reference.

[Liju Mohan]

I am truly sorry, I did know that. I’ll make sure i do not do that again. IF you haven’t yet, this is the paper “Modified Quadratic Congruence Codes for Fiber Bragg-Grating-Based Spectral-Amplitude-Coding Optical CDMA Systems” – Zou Wei and H. Ghafouri-Shiraz. It is an IEEE journal paper.

[Damian Marek]

Thanks!

[Damian Marek]

Looking at the paper I do see some differences. For example to encode the data you use the transmitted signal through each FBG while in the paper the use the reflected power from an array of FBG’s.

[Liju Mohan]

Hi,

I did attempt that method at first, but i did not manage to get an acceptable output for it and hence moved on to try using the technique employed for the sample. Would you perhaps be able to make a sample using just one user based on that?

[Liju Mohan]

Hi, I managed to clear out the issues with the MD codes project. I used a different encoder and decoder scheme. Would you have any references on FBG arrays in optisystem? OH, and Happy Easter!

[Damian Marek]

Great to hear! I was pretty sure the actual project file was working fine. We do not have any default components that act as FBG arrays, besides say the Periodic optical filter and WDM Demux components. Is there something in particular you want to know?

Thanks!

[Liju Mohan]

Thank you Damian. I did have to try an alternate setup for it since there are no components that acts as FBG arrays.

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