Ask an Engineer: Modeling Fiber Coupling

  • 2 February 2022
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Join us for our monthly “Ask an Engineer” event! On February 17th at 8am PST, Hui Chen will be answering your questions about modeling fiber coupling in OpticStudio. This event will be hosted on this thread in text form with a focus on the spotlighted topic…

 

Topic: Modeling Fiber Coupling in OpticStudio

Dates: February 3rd - February 17th

Live Discussion Time: 8am - 9am PST, February 17th

Engineer: @Hui Chen  - Senior Application Engineer at Ansys

Submit your questions for Hui as a reply to this thread between now and the end of the event. Questions added to the discussion will be answered starting at 8am Pacific on February 17th. Once the event is concluded, the thread will be closed.

If your question pertains to a particular file, the question may be moved to a private support case. In that situation, your license support status will be considered. 

 

Do you have a topic you want to see during these events? Let us know here: Ask an Engineer proposed topics.


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If you are interested in this topic, take a look at our Lasers & Fibers course in OpticsAcademy - taught by @Hui Chen!

Find it here: Laser & Fiber Learning Plan – Zemax 

Hi,

How to get Multimode Fiber coupling efficiency for different Tolerance? Instead of using merit function for tolerancing, How to directly get the multimode fiber coupling efficiency in the tolerance summary?

Hi,

I have performed some tests to check the coupling efficiency in a system using ball lenses. For this I have used FICL and POPD, looking for the optimal position of the fibers in a symmetric system with a fixed distance between lenses. To check the changes introduced in the system due to an axial displacement of the first fiber, I used Universal Plot 1D. The results obtained are somewhat different. 
Also in the definition of the system I have used two different criteria: in the first one we defined an intermediate surface as aperture and in the second one we defined as STOP the second surface of the first lens (With this the simulations with FICL are worse, but in POPD there is no change). 
I would like to know which would be in this case the best definition of the system and also why the results of both Merit functions are so different.
I send you the files of the FICL and POPD simulations: the file with the name “Axial_Linsenabstand_8mm_POP_VP” corresponds to the system without intermediate aperture.

thanks in advance

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Hi everyone! I'm online for the next hour answering your questions on modeling fiber coupling using OpticStudio. In you have any questions related to this topic, send them as a reply to this thread.

Thank you Mathu and Marcos for posting your questions. I’ll address them in the order the questions were posted. I’ll also post some FAQs about the tools.

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Hi @Mathu ,

Thank you for sharing your question here!

In general, it’s recommended to use the Geometric Image Analysis (GIA) to model multimode fiber coupling efficiency. You can find a KBA describing this process at “How to model multi-mode fiber coupling”. The operand that reports the % efficiency from the GIA analysis is IMAE.

If you want to perform tolerancing using this % efficiency as the Tolerancing Criterion, you’ll have to choose Merit function from the Criterion list and in the Merit function you’ll need to enter the IMAE operand.

If you do not use a Compensator, meaning no optimization process is involved in the Tolerancing, then you can enter a single IMAE operand in the MFE and leave its Target to 0, and Weight to 1. This way the MFE value will simply be the coupling efficiency reported by the IMAE operand. The Criterion value you see in the Tolerance Summary will just be the MFE value which is the coupling efficiency in this case.

However, if you plan to use Compensator, meaning there will be optimization happening during tolerancing, then the above approach won’t work. In that case in the MFE you’ll have to set the Target for the IMAE operand to 1. This means now the MFE value, or the Criterion value you see in the Tolerance Summary will no longer be coupling efficiency, but rather it’s 1-Coupling efficiency.  

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Hi @Marcos González 

Thank you for sharing your question here! We are trying to keep the discussion topic general to a broader audience for this event and questions directly related to a specific lens design might be better handled by the technical support team, mainly due to the limited time of this Ask An Engineer event. This is also to protect users because this discussion here is open so any information or lens files you shared here can be viewed by the general public.

That said, the question you raised is in fact a discussion topic very often seen in our support inbox. OpticStudio provides two tools to model single mode fiber coupling efficiency. One is the Single Mode Fiber coupling analysis with operand FICL, and the other is Physical Optics Propagation (POP) with operand FICP or POPD data 0.

The main difference between the two tools is that POP models coherent beam propagation right from the beginning starting at the beam launch, very often at the object plane; while Single Mode Fiber coupling propagate the beam as geometric ray bundle starting on the Object plane all the way to the exit pupil, and there the overlap integral between the incoming ray-modeled wavefront and the receiving fiber mode is computed as the receiver efficiency. In other words, when using POP to model fiber coupling efficiency, it will include all diffraction effects, for example diffraction due to an aperture clipping beam, or beam size changing due to diffraction propagation, all these effects will be included in POP analysis, but will not be taken into account in the Single Mode Fiber coupling tool.

As for your question on why when you change the aperture definition and move Stop surface location in the two designs you see big impact in the Single Mode Fiber Coupling analysis but little change in the POP analysis, I think this is as expected. As I mentioned early, Single Mode Fiber coupling tool uses geometric ray bundle to model the beam propagation so any changes made to the System Aperture definition, like Aperture size or Stop location will have a direct impact on the size of the ray bundle launched; whereas POP analysis is its own independent unit with the starting beam size and location defined inside POP so will likely not be affected by the System aperture definition.  

I’m afraid I won’t have enough time during this event to investigate your design file. If none of the above pointers help you understand the discrepancy between FICL and POPD, would it be possible for you to send this inquiry to support@zemax.com ? In this case, our support engineer can investigate the issue further and address it fully to your satisfaction. Let me know if that works for you. 

Hi @Marcos González 

Thank you for sharing your question here! We are trying to keep the discussion topic general to a broader audience for this event and questions directly related to a specific lens design might be better handled by the technical support team, mainly due to the limited time of this Ask An Engineer event. This is also to protect users because this discussion here is open so any information or lens files you shared here can be viewed by the general public.

That said, the question you raised is in fact a discussion topic very often seen in our support inbox. OpticStudio provides two tools to model single mode fiber coupling efficiency. One is the Single Mode Fiber coupling analysis with operand FICL, and the other is Physical Optics Propagation (POP) with operand FICP or POPD data 0.

The main difference between the two tools is that POP models coherent beam propagation right from the beginning starting at the beam launch, very often at the object plane; while Single Mode Fiber coupling propagate the beam as geometric ray bundle starting on the Object plane all the way to the exit pupil, and there the overlap integral between the incoming ray-modeled wavefront and the receiving fiber mode is computed as the receiver efficiency. In other words, when using POP to model fiber coupling efficiency, it will include all diffraction effects, for example diffraction due to an aperture clipping beam, or beam size changing due to diffraction propagation, all these effects will be included in POP analysis, but will not be taken into account in the Single Mode Fiber coupling tool.

As for your question on why when you change the aperture definition and move Stop surface location in the two designs you see big impact in the Single Mode Fiber Coupling analysis but little change in the POP analysis, I think this is as expected. As I mentioned early, Single Mode Fiber coupling tool uses geometric ray bundle to model the beam propagation so any changes made to the System Aperture definition, like Aperture size or Stop location will have a direct impact on the size of the ray bundle launched; whereas POP analysis is its own independent unit with the starting beam size and location defined inside POP so will likely not be affected by the System aperture definition.  

I’m afraid I won’t have enough time during this event to investigate your design file. If none of the above pointers help you understand the discrepancy between FICL and POPD, would it be possible for you to send this inquiry to support@zemax.com ? In this case, our support engineer can investigate the issue further and address it fully to your satisfaction. Let me know if that works for you. 

Hi Hui, 

thank you very much for your answer. I figured the timing would be a little tight. I will contact your support service. 

Greetings. Marcos

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Some general FAQs:

Depending on whether you want to model single mode fiber coupling efficiency, or multi-mode fiber coupling efficiency, OpticStudio provides different tools for your application.

For Multi-mode fiber coupling, the recommended tool is Geometric Image Analysis (GIA). This is to model the coupling efficiency using geometric ray bundle. This method is only valid for multi-mode fiber that supports a large number of modes. This is because due to the very many transverse modes supported the degree of coherence is insignificant. So essentially you can treat this fiber as a light pipe and rays are a good approximation. There is an NA setting in the GIA analysis that allows you to simulate the numeric aperture of the receiving fiber. You can think of this as the acceptance angle of the receiving fiber and any rays outside of this NA will be ignored.

For Single-Mode fiber coupling, there are two tools one can use, the Single Mode Fiber coupling analysis and the Physical Optics Propagation analysis. They use different methods to model beam propagation and fiber coupling. I have listed some differences in the post above, but mainly is that POP does coherent wavefront propagation right from the beam launch while Single Mode Fiber coupling analysis models beam propagation using ray bundle from the object plane to the exit pupil and the diffraction effect is only considered from the exit pupil to the image surface. Therefore, you may not see the same coupling efficiency reported between the two tools. As a designer you need to understand the difference between these tools and choose the one that best fits your design needs.

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To share a few good resources on how to model fiber coupling efficiency in OpticStudio:

  1. KBA, How to model multi-mode fiber coupling
  2. KBA, Single-mode fiber coupling in OpticStudio
  3. Help documentation on when to use POP to model beam propagation, The Analyze Tab (sequential ui mode) > Laser and Fibers Group > About Physical Optics Propagation
  4. Help documentation explaining System Efficiency, Receiver Efficiency and Coupling Efficiency computation in Single Mode Fiber coupling analysis, The Analyze Tab (sequential ui mode) > Laser and Fibers Group > Fiber Coupling > Single Mode Coupling

  5. Help documentation on how POP computes coupling efficiency, The Analyze Tab (sequential ui mode) > Laser and Fibers Group > About Physical Optics Propagation > Computing Fiber Coupling

  6.  

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Hi All, 

Thanks for participating in this Ask An Engineer event! Also special thanks to @Mathu @Marcos González  for submitting your questions on this thread! I’ll be signing off soon but you can continue to post on this thread if you have any questions or would like to know more about fiber coupling tools in OpticStudio. 

We will make this Ask An Engineer a monthly event. If you have any topics that you are interested in learning, please share your thoughts with us under the Ask An Engineer announcement post. 

Have a wonderful day and see you all next time!

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