April 30, 2014 at 9:45 am #11271Ahmad MustafaParticipant
I have a basic question on multimode fibers in OptiSystem. In the lab, I can connect a single mode laser with a multimode fiber and there I observe multimodes at the fiber output but in OptiSystem, I can not repeat the same as either the optical source has to be multimode if I want to use Measured-Index Multimode Fiber or Parabolic-Index Multimode Fiber blocks. If I use Linear Multimode Fiber block then I do not see any modes on the Spatial Visualizer. In this case, I can not use Spatial Optical Receiver or Spatial PIN Photodector because of absence of multimodes after the Linear Multimode Fiber block.
I have attached a simple .osd file to better understand my question.
Can anybody help me with the concept.
April 30, 2014 at 4:27 pm #11292Damian MarekParticipant
I’m posting a link to another topic where I explain the modeling of these components.
Basically, the Linear Multimode Fiber applies modal delays and modal dispersion to signals, but it does not affect the spatial profile. To get different mode excitations, you’ll need to use the Measured-Index Multimode Fiber or Parabolic-Index Multimode Fiber components.
April 30, 2014 at 5:25 pm #11294Tech SupportParticipant
Ahmad: Your assessment is correct. The Measured-Index Multimode Fiber and Parabolic-Index Multimode Fiber components are expecting multi-mode spatially defined signals. If you use the Multimode Generator with all the power allocated to the primary mode then you will obtain a single mode laser signal with extra information on the mode field type and size (complex field data in the x-y plane) – this resembles most closely your laser in the lab (since it has a field diameter). This information is used by the Measured-Index Multimode Fiber and Parabolic-Index Multimode Fibers for the overlap integrals (used in the mode solver). The accuracy is thus pretty good. For the Linear Multimode Fiber block there is no need for spatial complex field information as we do not call up a mode solver (only a transfer function is applied).
If you connect a Spatial Receiver or Spatial PIN to the output of the Measured Index or Parabolic Fiber then it will apply the spatial aperture against the modal field envelopes. The resulting truncated field data will then be applied as an attenuation to the time-domain waveform of the signal before being converted to an electrical signal. So the temporal effects associated with the signal (multimode dispersion) are held by the primary signal (I recommend that you try out the View Signal Visualizer – this will show you the baseline signal (complex signal as a function of time) and also the complex field data in the x-y plane for each calculated mode (this data sets are separate)).
May 6, 2014 at 11:35 am #11378Ahmad MustafaParticipant
Thanks Tech Support. I will work on your suggestions and will get back to you later.
May 5, 2016 at 10:23 am #38891umer ashraf waniParticipant
For coupling of light MFD Should be same
May 5, 2016 at 11:42 am #38892Rajguru M. MohanParticipant
Hi Ahmad Mustafa,
It is very practical and basic question asked.
Thanks to Damian Marek sir, and other members who explain the problem very briefly.+3
- You must be logged in to reply to this topic.