Link equation used to calculate received power

[Marvi grover]

Hello everyone !!

received power calculated using the equation given in FSO component’s ‘help’ does not match with received power results given by optical power meter. i calculated the received power manually using the given equation and the same parameters as used for simulation, but the results do not match with power given by optical power meter. Can somebody help me with this
what is the formula used to calculate received power in optisystem FSO system. the system used is shown in the attachement with the parameters used . can anybody tell me the received power of this link??
i shall be really thankful to you

Regards
Marvi

[Marvi grover]

the system used is attached here

[Aabid Baba]

Hello Marvi,
I am attaching a link of one paper where received power analysis is done. This may help your cause. I would suggest you to go through this paper.
http://research.ijcaonline.org/iceice/number3/iceice020.pdf

I hope this will help you.
Regards

[Aabid Baba]

You may also look through this
http://digitalcommons.mtu.edu/cgi/viewcontent.cgi?article=1060&context=etds

[Marvi grover]

Thank you so much sir. I will look into these papers and revert back.

Regards
Marvi

[Marvi grover]

Sir

In the optisystem ‘help’ of ‘FSO component’ , a link equation is given to calculate the recieved power.When i am calculating the received power manually using this equation, the result does not match with that given by the optical power meter in optisystem. please tell me why is this happening. i am attaching the snippets of optisystem and parameters used and also the matlab code used to calculate the power manually.
please help me with this. i shall be really grateful to you.

Regards
Marvi

[Aabid Baba]

Hello Marvi,
I completely got your problem. As far as the link equation is concerned can you tell what is the unit your are calculating the received power in? I mean is it dB or dBm or mW ?
as far as i understand the power calculated should be same for the both procedures.
Regards

[Hamza Ali Abbas Khan]

Hello.

I think you should connect power meter after the combiner. See if there is some change in measurement.
Thanks
Regards

[Marvi grover]

Thankyou so much for having a look.
i tried to connect the power meter after the ‘select’ component in my system, but the power still doesnt match with calculated one.

[Hamza Ali Abbas Khan]

Hi
As i can already see that your problem has been solved. It could have been only the manual calculation as presumed. Anyway good work.Keep it up.
Thanks
Regards

[Marvi grover]

Aabid bashir Baba and Sidra Khan

i am using the unit mentioned in the ‘help’ for the link equation i.e. meters for the transmitter and receiver aperture,
kilometers for the ‘range’, dB/km for the attenuation and milliradian for the beam divergence, transmitted power in dBm.
i think received power should be in ‘dBm’.
following parameters are used in the optisystem design.

transmitter aperture:0.05 meter
receiver aperture : 0.2 meter
transmitted power : 10 dBm
range : 1 kilometer
attenuation: 25 dB/km
beam divergence: 2 mrad

you can use these parameters and check the results manually. please let me know your result. i might be doing some mistake. i am also attaching the .osd file for the results given by optical power meter.

[Aabid Baba]

Hello Marvi,
I was of the opinion that you may have taken different units while calculating power. The power meter shows you are taking the power reading in dBm and according to you , you are calculating manually in dBm too. So I think it may have something to do with calculation. I don’t think the calculated power should vary a lot. What is the exact variation around ?
Regards

[Marvi grover]

i am getting it as -35.2144 dbm and optical power meter gives it to be -38.421

[Aabid Baba]

Hello Marvi,
Well it is almost 3dBm difference between the two values. I would suggest you to go through the manual calculation once again and see if you have taken all the parameters correctly. Your estimation is pretty close. Check if the values of some constants you have taken is correct. If the difference between two values narrows down to 1 dBm then it is very much fine.
Best Wishes (y)
Regards

[Marvi grover]

Hello Aabid!!

i got to know my mistake. i was using the transmitted power as it is in the manual calculation.
but my system had a MUX and modulator attached after the laser source which led to some power loss. so the actual power launched in th channel was less than 10dBm and this power was to be used in the calculation.
i hope i am able to make my point.

Regards
Marvi

[Aabid Baba]

Hello Marvi,
I could see from the snapshot you had shared that it is transmitted power mentioned in the equation. I think you got to use the transmitted power. I am not sure that the launch power is equal to the power you measure at the start of the channel. I presume that launch power is actually the transmitted power from the source and the losses are already taken for standard calculation. You will have to look into that i suppose.
Anyway for this case what is the difference between the power you calculated and one shown by the power meter?

Regards

[Marvi grover]

in this case the power calculated manually is same as that given by optical power meter.

[Aabid Baba]

okay I see. Probably you are doing right but here I want to mention that you are doing calculations discarding any transmission losses which do exist in practical scenario and any mathematical model may or may not include these losses.
It was a good discussion.All the best.
Regards

[Marvi grover]

Thank you so much 🙂

[Aabid Baba]

you are welcome 🙂

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