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| Full Name | Ahmad Mustafa |
| Organization | German Aerospace Center |
| Job Title | PhD Researcher |
| Country |
Forum Replies Created
here is the simulation file.
I have introduced the Spatial Connector block after Polarization Rotator having Rotation Angle= 90 deg. The Spatial Connector has 90 deg Y tilt (to polarize the signal in Y direction) and after the MUX, I can see the two signals on the OSA polarized in X and Y. After the Parabolic-Index MMF, the signal power is dropped down to zero although the length and attenuation values of the MMF is negligible.
If, however, I take out the Spatial Connector block then everything works fine.
I do not understand the role of Spatial Connector here as I would expect it to just rotate the polarization by 90 deg and it should not have effect on the signal power after the MMF.
Can you please elaborate if I am using this block correctly or if there is some other conceptual issue here?
Attached is my simulation file for your consideration.
Thanks!
Thanks all
Is there a file missing? Where is the input data to Subsystem_35 coming from?
Hi Rahul,
It would be interesting to know your detailed study. Could you share your report or simulation files if you like to.
Thanks!
Hi Damian,
Yes, I had written the same question to the OptiSystem team and got their reply. The good thing is this solution works to simulate step-index profile 🙂
I used MATLAB to generate the text file in the format I wanted 🙂
Thanks
Hi Damian,
These are great answers 🙂 They have helped alot. I have few more questions if you could help me understanding them:
1) How to know the fiber modes? I can select the number of fiber modes from the parameter LP(m,n) max but how to see the fundamental mode of the fiber itself? What I can see on the Spatial Visualizer is the result of mode mixing between the input modes and the fiber modes. Is there a way to see the fiber modes only?
2) As you say in the reply of point Nr. 3 that the spot size at the output is increased because of the larger spot size of the fundamental mode so how can I change the size of the fundamental mode of fiber? I do not see any parameter to do that. Does it depend on fiber core size?
3) you wrote in reply to the mode matching: “you could use a lens to focus the light into a smaller area or expand the beam into a larger area. OptiSystem has components to model this behavior”. Are you referring to Thin, Vortex lens and Spatial Aperture in OptiSystem?
Many thanks
Hi Damian,
What I observed is that the first mode is actually represented by Individual mode number=0 in Mode Selector Properties and not by 1. In your attached Mode_selecting.osd file, there are 12 modes generated (0-11) and not (1-12). So to select let us say, mode number 12, we have to set Individual mode number to 11 and not to 12 otherwise, I see an error if I connect Spatial Visualizers to the Mode Selectors and the final output after Power Combiner 4×1 is also different.
Please confirm if it is the right observation.
Cheers,
Ahmad
Also see this:
Hi Damian and Tech Support,
I worked on your suggestions and now have better understanding of how multimode components work in OptiSystem. I have come up with some more questions though. Attached is my .osd simulation file for understanding the questions better.
I have a single channel transceiver where the Spatial CW Laser centered at 193.1 THZ has only one mode as can be seen from the single Value of Power Ratio Array and Pol. X m,n index array to represent the single mode laser that I have in the lab. It can be seen on the Spatial Visualizer where I only see one mode. The length and Attenuation of Parabolic-Index Multimode Fiber are set to 0.4m and 0.61dB/km respectively according to my lab setup. The Min. Signal Power is set to -19dBm. Finally, the signal is received in the Spatial Optical Receiver and I get perfect Eye Diagram and 0 BER on the BER Analyzer. Following are my queries that I want to understand:
1) The spatial CW Laser generates only one mode but I see multiple modes on Spatial Visualizer after Parabolic-Index Multimode Fiber. Should I not see only the fundamental mode as the length of the multimode fiber and the attenuation value is really low to generate multiple modes in the fiber?
2) How can I measure the power of the individual mode after the MM fiber? I assume the power in the modes besides the fundamental mode is really less that they can be ignored in this case.
3) The spot size after MM fiber is bigger than the spot size right after Spatial CW laser. I believe it is because of Modal dispersion. Yes?
4) I have increased the Min. Signal Power to -19dBm from the default value which is -100dBm to reduce the number of modes and I can further reduce the number of modes by further increasing this min. signal power value but in my lab, I cannot simply do this because of the hardware limits. Can you make any suggestion how to reduce the number of unwanted modes coming out of the Parabolic-Index Multimode fiber because by increasing the power of the input laser and length of the MM fiber along with the higher attenuation value, the generation of higher number of modes and with that mode coupling effects would make the BER and Eye Diagram go bad as per my understanding.
Please let me know if anything is not clear regarding the questions I posed.
Many thanks
Attachments:
Thanks Tech Support. I will work on your suggestions and will get back to you later.
Thanks Damian. I will work on your suggestions and will get back to you later.
Hi Damien,
I can see the attachment now. Thanks
@ Asraful,
Do you mean a Wavelength Division Multiplexed FSO System or what Damien proposed as a solution?
@Damien,
I do not see any paper attached to your message. Could you please check it again?
Additionally, what is the difference between the OWC and FSO block? They both look the same having almost the same parameters.
Many Thanks. This is much quicker.