Photonics

Photonics

CW normalization and source amplitude

    • Kyle
      Ansys Employee
      Note: This post was copied over from the Lumerical Knowledge ExchangenIn order to interpret the results from power monitors correctly it is important to understand (1) the normalization used and (2) the effect of the source amplitude.nThere are two normalization states: “CW normalization” and “No normalization”. You can select this in the “Setting” menu as shown below:nnWhen CW normalization is chosen, the results for the fields in the power monitors are normalized by the Fourier transform of the source signal s(t), this returns the impulse response:nnThe source signal is shown in the “Frequency/Wavelength” tab of the source settings:nnBy default, the CW normalization is used. CW normalization is explained in more detail on this page: nTo disable CW normalization you have to select “No normalization” in the “Normalization state”.nThe second issue, is the effect of changing the source amplitude. This can be done in the “General” tab of the Edit source window. The source signal s(omega) does not depend on the source amplitude, but the fields in the simulation do depend on it. Therefore, if the source amplitude is 100 times larger the E field shown by the monitor will be 100 times larger. This scaling happens for both “CW normalization” and “No normalization”nWe can look at a simple example of a plane wave propagating in free space to understand the points above:nn In the simulation a plane wave is propagating in free space. The figure below shows the calculated electric field (real part) for different settings recorded by the monitor (yellow line in the screenshot).nnNote that when CW normalization is used the electric field curve is flat, even though the source signal is not; this is expected because the source signal is used for the normalization. The small deviations from the flat behavior are the result of numerical grid dispersion. The value of the field (1 or 100 in the example) depends on the source amplitude. On the other hand, if “no normalization” is used then the E field curve follows the shape of the source signal, as expected.n
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