Pump Coupler Co-propagating vs Power Combiner

[Parikhit Dutta]

Hello,

I am designing a Radio-over-Fiber (RoF) system using external modulation. My requirements are to separate the optical components (say f1, f2, f3 and f4) at the output of the the modulator and then recombining specific components (f1 with f4 and f2 with f3). In order to separate the components I am using FGBs centered at the frequency of interest. Using Optical Power Meters I noted the value of power at the output of the modulator and individual FBGs and found that the power value of the FBGs approximately add up to the value noted by a power meter at the modulator.

Now, when I combined the components f1 and f4 using a power combiner (loss set to 0 dB) I expected the powers to be added up but the power meter showed a different result. If I replace the power combiner with a pump coupler co-propagating, the power seems to adds up and is more than the input powers (with signal and pump attenuation both set to 0 dB). Also, if I use an x-coupler for a coupling coefficient of 0.5 the power levels at the two o/p arms approx. add up to the input power as displayed in the power meters.

My question is if the power combiner is equivalent to a single arm of the x-coupler? How different is a pump coupler from an x-coupler and power combiner?

Thank you.

[Damian Marek]

You can head into the Technical Background for the details but basically there is very little difference between the Pump Coupler and the power combiner. The difference being you can add loss to the different branches separately.

The X coupler is the most different as the complex fields are combined and not just the powers. Therefore, it is possible to get interference or accumulate phase shifts between the branches.

Regards

[Parikhit Dutta]

Thank you so much Damian. I have attached the project I am working on and I have used a Power Combiner as you suggested.

Project A used WDM Add and Drop Components while Project B is the same simulation using FBG and Power Combiner. The results are different in terms of power values. However, they both hint at the same result. In a practical scenario which one would be better?

I have another doubt on power penalty calculation. I have posted it as a new thread.

[Damian Marek]

The FBG layout is probably more accurate because it is modelling a grating with a non perfect reflectivity. Even though it is 0.999 the WDM Add/Drop is essentially modelling 1 because there is no loss.

[Parikhit Dutta]

Many thanks Damien. I’ll go ahead with the FBG layout itself.

[Parikhit Dutta]

Hello,

The attachment in the above post had an incorrect excel file. Attached is the rectified one.

Thanks.

Attachments:

1. POWER-PENALTY3.zip

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