Combining two Optical signals to be fed into a single fiber

[Shahbaz Qureshi]

Hi, I was trying to combine the two signals from two OLTs (WDM PON & GPON) of different wavelengths and then separate them at ONU. What component shall I use? A Mux or power combiner?

[alistu]

Hi Shahbaz,

Since the system is using the WDM access scheme, I assume the two signal you are talking about have different frequencies (or wavelengths). So you can simply use a multiplexer. However, you can use power combiner either. In this case, at the receiving side, you need to use a power splitter and then for every user, you have to use an optical filter that only passes the wavelength corresponding to the user. You can take a look at a recent discussion about this issue here:

optiwave.com/forums/topic/twdm-pon-2/

Also, you can upload your osd file if you needed more specific help.

Regards

[Shahbaz Qureshi]

I have already used WDM Mux in one OLT, now I want combine the signal coming from GPON OLT with the other one. I am attaching a simulation file plz take a look. I am unable to combine the two to be fed into a single fiber.

[alistu]

Hi Shahbaz, I would appreciate it if you please attach the paper whose system you are trying to simulate. Or perhaps introduce some papers that would give a background about what you are trying to do. Thank you.

[Shahbaz Qureshi]

I was referring to the diagram attached. Here you can see optical signals from two OLTs are combined and then separately detected at ONUs. What co existence element shall I use? Because there would be signals coming in upstream and aswell as downstream. I was confused between using power splitter, circulator. I have already used Mux in one of the OLTs.

Attachments:

1. 

   images-1.jpg
   

[alistu]

In the image you have attached there is one OLU, which has a signal going (downstream) and coming (upstream). In your design there is already a signal going out of your OLU and no signal entering it (which should be the upstream signal). Do you want to use another signal going out of it?

[Shahbaz Qureshi]

Yes Alistu, I want to combine the two downstream signal into one. As you can see, there is one CO, having wavelengths of GPON and TWDM PON generated from 2 OLTs inside the central office. 4 wavelengths of TWDM PON are combined using WDM MUX into one signal. Now i want to merge this signal with GPOn’s signal of 1490 nm.

I am not considering the upstream signal at the moment.

[alistu]

So this is not the same as what is shown in the image you have attached. Do you know any papers on this matter to intoduce? In the meanwhile, I believe if the wavelengths of OLU1 downstream and OLU2 downstream are not the same, then you can simply use the MUX to combine. You can also go with the power combiner, too. Then, at the receiver you must use power splitter and then filters at each user the way I depicted before. It is as if you are using one OLU.

[Shahbaz Qureshi]

Thanks Alistu, I’ll do that. But using a MUX after WDM would be appropriate? it will occur loss.

[alistu]

Now that you have used two separate WDM MUX for the two OLTs, you can use a power combiner to combine the two signals from these two multiplexers. And on the receiver side, you can use a power splitter, followed by two WDM demultiplexers. You could have used just one MUX and one DEMUX at each side, but since the OLUs are not probably in the same place, I think you should do as suggested.

Regards

[Author]

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