Bandwidth of WDM Demux

[Aadil Raza]

Dear All,

As we know the default 3-dB bandwidth of WDM Demux is 10 Ghz. can we have this bandwidth less than 10 Ghz ( 5 0r 7 Ghz etc) practically. if yes the upto which extent we can have this bandwidth?

[alistu]

Hi Aadilqau,

The bandwidth can be reduced further using filters, but then the system performance may degrade from a point on. Therefore, there is a trade-off between the bandwidth used for the channel and the system performance in terms of the error. So you’d better decrease it to the point where you think the BER is still acceptable.

Regards

[Ranjeet Kumar]

Hi alistu sir,

I am agree with your points. when we decrease the bandwidth of wdm mux below certain limits the system performance degraded to some greater extent if further decreament in bandwidth. I am attaching osd file DWDM system for this.

[Aadil Raza]

Ok thanks for reply. I wanna ask does such demux component practically exsist having bandwidth of each channel= 5Ghz or near about. If yes can you share me its data sheet.

[alistu]

You’re welcome. Unfortunately, I don’t know of such commercially available MUX components with the bandwidth of 5GHz and I believe commercially available components correspond to the prevailing standards and vise versa. However, the reduction in bandwidth can be made for theoretical analysis.

Regards

[Aabid Baba]

Hello Alistu,
I want to ask you what is the theoretical aspect of WDM MUX and the bandwidth leaving apart the simulation scene in optisystem? Please can you explain it or share some paper which explains about the WDM Mux and the bandwidth thing. I am very much confused about this realization between WDM MUx and bandwidth.

Best Regards

[alistu]

Hi Aabid,

When the bandwidth is reduced, many signals with higher frequencies get distorted as they fall out of the pass band of the filter. This means they cannot be correctly detected at the receiver. This is the basic and complete theoretical explanation of why the bandwidth reduction causes system degradation.

Regards

[Aabid Baba]

Hello Alistu,
Okay i got it mate. It is a very very important point you are making here regarding this bandwidth thing . I had never given a thought to it. It means for a system to work properly you must set bandwidth of every component such that the bandwidth of transmitted signals lies in the range of used components. I must look into my design again and set the Bandwidth thing right if there is some correction required.

Thank you so much Alistu for sharing such valuable and important points.
Regards

[alistu]

You’re welcome Aabid. It is actually a very important point in the system implementation. However, good news is most of the the OptiSystem filters calculate bandwidth with regard to the bit rate or the symbol rate in script mode by default. This helps users get proper results in many cases even if they have forgotten to set the bandwidths.

Regards

[Aadil Raza]

Thanks Alitsu

[alistu]

You’re welcome Aadilqau.

Regards

[Aabid Baba]

Hi Alistu,
To be quite honest I had never ever checked for the bandwidth criteria of any component like WDM Mux or Demux because i thought other parameters like power, system bit rate , symbol rate blah blah are most important parameters to better the performance of the system and because my results were improving just because of changing such parameters i never thought of bandwidth thing. Anyways i am so grateful for sharing such valuable points.
regards

[alistu]

You’re welcome.

Regards

[Aabid Baba]

Hi alistu,
i would like to take this opportunity to ask you that if i consider fiber bragg grating or Mux for simplicity sake, what is the optimum value of Bandwidth i must take. As you know we usually work on third optical window and the wavelength requirement is nearly about 1550nm (193 Thz)
, what bandwidth should i take. By default it is set around 10 Ghz and for fiber bragg grating if i remember it is around 120 Ghz ( i am not sure though).. Any suggestions ??

[Naazira Badar]

Hi all..
I have a query about the bandwidth of WDM MUX as well. The default value is 10 Ghz. Does it mean it provides one channel this much bandwidth to get transmitted?

[Aabid Baba]

Hello naazira,
A very good question indeed. I would also like to know about it. Because if we consider a 4 input WDM MUX , incase it is 10 GHz for each channel then i would be using 40 GHz for my system which is very huge bandwidth.
From the discussion i had with Alistu , i guess this Bandwidth would be to accommodate every channel although i am not sure.

Regards

[Naazira Badar]

Hi Aabid. Actually what I’m saying is that..A WDM MUX combines signals and transmits simultaneously. And there’s a relation between the bit rate and the bandwidth of the system. But no matter how much we set the bit rate at the source, how come the bandwidth of the WDM MUX still remain same?
Alistu has mentioned that Optisystem calculates the BW as per bit and symbol rate, but I think had it been so, after the simulation run was over, the bandwidth value of the WDM MUX must also have been auto changed.

Another point remains that how come no matter what the value of N in N X 1 MUX, the MUX bandwidth remains same? If there are more no. of inputs channels, the MUX bandwidth should also vary.

[alistu]

Hi Naazira,

I believe you could have easily seen that the script mode has not been used in case of WDM MUX and DEMUX . I mentioned in my above comment MOST of the OptiSystem filters are set that way. So as you know, MUX is not a filter component, although it has filters in it and besides, MOST does not mean ALL.

Regards

[Aabid Baba]

Hello naazira,
If you read through my question in the post #30597, i was asking about the same thing. That is what my question was but i could not put it in a better way. I had also asked Alistu what bandwidth should be optimum to accommodate every channel where i meant if we increase transmitter frequency , should the bandwidth remain same or should we change it manually because Mux by default sets bandwidth i guess 10GHz .
Please Alistu can you explain a bit further on that?

regards

[alistu]

Hi Aabid,

Sure. If the transmitter frequencies are changed (for example laser frequencies in a WDM system), then the MUX frequencies must change, and not the bandwidth. But if the bit rate of the system changes, you are probably going to have to change the bandwidth of the filters.

Regards

[Aabid Baba]

Hi Alistu,
you are not getting me. I have started a bew topic where i have explained what is confusing me. i would post the link of that post. Please go through that. May be you would get what exactly i am trying to say.

Bandwidth parameter for each component

Regards

[alistu]

I read your post and provided an answe. I believe the explanations you have provided in here and in the other topic you have started differ somewhat. However, you can see my answer there and we can continue the discussion there if you agree.

Regards

[Aabid Baba]

Sure! Thank you anyways.

[Naazira Badar]

Yes Aabid, I went through your query on a similar post.

Tell me if we have two signals with 193.1 Thz and 193.2 THz frequency respectively, what is the bandwidth requirement for their transmission?

Regards.

[alistu]

Hi Naazira,

The bandwidth requirements for their transmission does not change. The bandwidth is theoretically constant. What needs to be changed in this case in the center frequency of the laser, due to the change in the carrier frequency of the laser. So you can use the same bandwidth for both of the two signals.

Regards

[Aabid Baba]

Hi naazira,
Please Follow the link below
https://optiwave.com/forums/topic/bandwidth-parameter-for-each-component/.
we have further discussed it there only. I have also attached screenshot of results in case we increase bandwidth of MUX. Please refer to the link. You can understand it there.

Thanks and Regards

[Author]

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