How can I simulate Rayleigh backscatter in a single mode fibre?
In particle and surface scattering, there are several examples for simulating particle scattering. May you specify the properties (material, size, shape, location…) of the scatterer you would like to perform simulation with?
Thank you for your comment.
I am trying to model a Distributed Acoustic Sensor (DAS) , which is base on Raylegh backscatter.
The backscatter is not just from the small particles in this case, it comes from the variant in the material dendity in the fibre due to manufacturing.
Thank you for providing the information. From our initial understanding, this may possibly be modeled by s-parameter using our interconnect tool. However, we would like to learn more details in order to address your question properly. May you further provide the information listed below?
- What is the length of the fiber?
- Is the description of the scattering effect such as s-parameter available?
- What is the optical power level?
- Are there other non-linear effects needed to be taken into consideration as well?
- Is the scattering for omni or bi-directional propagation?
Here are the answers to your questions:
What is the length of the fiber?
A-Fibre length can be 1 to 40Km
Is the description of the scattering effect such as s-parameter available?
A-I don’t know.
What is the optical power level?
A- By considering non-linear effects the maximum power is 25dBm. More than this the system will suffer from non-linearity effects.
Are there other non-linear effects needed to be taken into consideration as well?
Is the scattering for omni or bi-directional propagation?
A- The scattering is for omni-direction.
Thanks again for the feedback.
For the fiber length of your interest, it may not be simulated with a component tool but may be simulated with interconnect. To perform the simulation with interconnect, the reflection and transmission for such scattering effect is needed so that the scatterer can be modeled as a separate element in addition to the fiber element. We have built-in models for certain types of nonlinear effects in fiber, may you also specify the type of non-linear effect you would like to include?
Thank you very much for your comments.
Could you please let me know how can I model the scatterer as a separate element in addition to the fibre element as I am kind of beginner in this software.
Regarding the non-linearity, self-phase modulation and modulation instability are the mains in our applications.
My colleague @ychen is away at the moment and we are picking up this conversation and follow up.
We are trying to work on a simple test case to show the idea and will update you once we are ready. Note that it is Easter Holiday right now and our replies will be slower than usual. Thanks for your patience.
Here is an example of using the s-parameter element as an external block to add-on to the fiber model and you can put your measurement/experimental data of the Rayleigh Backscattering into it: test_file.icp (182.3 KB).
As regard to the nonlinearities you mentioned, the Kerr effect (SPM) can be modelled in the Nonlinear Waveguide. This element need to be used in conjunction with the regular waveguide elements since it only defines the index perturbation instead of the whole index information. And the modulation instability can be to some extent modelled by the dispersion settings in the fiber or waveguide models.
Sorry for the late reply. I had a second look at this case and here are some further comments on it. For a short answer, the fiber model in INTERCONNECT does contain the regular higher order nonlinear effect and the Raman Scattering effect and Birefringence effect, but the Rayleigh back-scattering is not included in this model. It is very time consuming to simulate the back-scattering and it is actually easier to calculate it mathematically (for example solving the piece-wise equations in math tools like MatLab) than simulating it.
Then here comes the long answer if you really want to do it in INTERCONNECT. We can mimic the piece-wise calculation in INTERCONNET by breaking the fiber into short unit pieces, and for each piece, we can add a s-parameter unit to mimic the Rayleigh back-scattering effect. The signal will propagate bidirectionally with the s-parameter indicates the general light forward propagation transmission together with the reflection due to back-scattering. In order to mimic the Rayleigh back-scattering effect, the s-parameter files need to be generated based on simulations with randomized effective indices in FDTD or MODE. Here is an illustration of this setup: