Re: [Meep-discuss] Doubt about concept of flux spectrum in MEEP
As far as I know, there remains the problem of the mode shape generally being different for different frequencies. In some specific cases, such as hollow metallic waveguide, the mode cross-section remains the same, so it is easy to excite/detect the first mode selectively at broad frequency range. Implementing this for e.g. optical fiber would require much more complicated spatio-temporal evolution of the port. However the difference between the mode shapes is smooth, so such a case could be composed by stacking about ten ports, each operating at different frequency range. F. 2014-04-15 2:08 GMT+02:00, Steven G. Johnson stevenj@gmail.com: A more general solution would be to use code similar to the eigenmode-source feature: call MPB to compute the modes for a given cross-section (and for each desired frequency), and use those to perform the relevant overlap integrals with the Fourier-transformed fields in the same cross-section. This is certainly do-able to implement (at least for dispersionless materials). On Apr 14, 2014, at 5:21 PM, Filip Dominec wrote: This is true - I mostly simulate the behaviour of an infinite periodic array of scatterers, so I am interested in perpendicular (or oblique) plane waves only. The simple flat recording plane can probably be generalized to all waveguides that can be approximated by LP modes. Other geometries perhaps need to introduce the concept of a port such as that is in CST Studio etc. 2014-04-14 22:57 GMT+02:00, Steven G. Johnson stevenj@gmail.com: Only if you are looking at planewaves or similar solutions where you know the forward/backward eigenmodes. ___ meep-discuss mailing list meep-discuss@ab-initio.mit.edu http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/meep-discuss ___ meep-discuss mailing list meep-discuss@ab-initio.mit.edu http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/meep-discuss
Re: [Meep-discuss] Doubt about concept of flux spectrum in MEEP
The frequency dependence isn't a major problem for computing output power in each mode, since generally you only need the power at a small number of frequencies (a few dozen to a few hundred), and Meep can compute the explicit Fourier transforms of the fields in the flux plane at these frequencies (the same as it does anyway when computing the flux spectrum). You could just call MPB for each one of these frequencies to compute the mode pattern separately, and then take the inner product of these modes with the fields. (Matters are more complicated for wave sources, since sources are not typically limited to a small number of frequency components. See also the discussion in our book chapter http://arxiv.org/abs/arXiv:1301.5366) On Apr 15, 2014, at 5:03 AM, Filip Dominec wrote: As far as I know, there remains the problem of the mode shape generally being different for different frequencies. In some specific cases, such as hollow metallic waveguide, the mode cross-section remains the same, so it is easy to excite/detect the first mode selectively at broad frequency range. Implementing this for e.g. optical fiber would require much more complicated spatio-temporal evolution of the port. However the difference between the mode shapes is smooth, so such a case could be composed by stacking about ten ports, each operating at different frequency range. F. 2014-04-15 2:08 GMT+02:00, Steven G. Johnson stevenj@gmail.com: A more general solution would be to use code similar to the eigenmode-source feature: call MPB to compute the modes for a given cross-section (and for each desired frequency), and use those to perform the relevant overlap integrals with the Fourier-transformed fields in the same cross-section. This is certainly do-able to implement (at least for dispersionless materials). ___ meep-discuss mailing list meep-discuss@ab-initio.mit.edu http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/meep-discuss
