  # Quality factor analysis

Hi, Where I have to put the Q analysis in ring resonator… Now I placing in Center of the ring resonator.
Kindly let me with thanks

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Hi Nanda,

First I would mention that you can calculate the Q factor of a specific channel in your ring resonator by taking the peak wavelength of given resonance and dividing it by the related full width half maximum(FWHM) as it is shown in this example.

If you want to use the Q analysis, consider that the tool is using point monitors to record E-fields in time domain in order calculate the Q factor. Generally, this means that the point monitors must be placed in a cavity where you expect the resonant, slow decaying fields. In case of a ring resonator, this would be the circular waveguide. Given the ring shape, it is easiest to use one, two or four time monitors as it is shown in the following screenshot: You could also place the time monitors into the optical waveguide of your interest(drop or through) as it is shown here: Note that it is better to use more time monitors to decrease the chance that you place the monitor into a mode node. Also, do not forget to align the analysis group in z direction to make sure that the monitors are inside of the waveguide.

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I am not getting the point what is the use of time monitors? I am using the low and high Q analysis monitors from object library, and I measured the Q factor the procedure is correct?
kindly let me.

The high and low Q analysis is an analysis group that is using monitors to obtain data from the simulation in order to complete the calculation of Q factor. When you expand the analysis group, you can see the time monitors: The number of time monitors used and their position is then defined in the Qanalysis properties: A post was split to a new topic: Ring resonator and TM mode propagation

Dear @mbenes, I used your method and find the Q-value using Q analysis group.I used all the time monitors in the center of the circular wave guide of ring resonator (also center in z dimension) .I used the source with wavelength from 1.5 um to 1.6 um. But I got the Q-value for the wavelength start at 1.7 to 1.74 um.Why the Q-value did not come for the wavelength which we applied (1.5 to 1.6 um).

Hi,
Such result is theoretically possible even if your simulation is set correctly. The reason is that even if you specify certain wavelength range in the source properties, the injected spectrum will be broader as shown on the following screenshot:

Additionally, the q analysis script is looking for n strongest resonant peaks in the spectrum. By default n=2, but it can be changed in the analysis group properties. Hence, if the spectrum shows the highest resonances outside of your source min/max wavelength settings, it will calculate the Q factor for them even if it is outside of the specified band.

Example plots from the Q analysis group to show the overall spectrum and the two selected resonances for Q factor calculation:

Therefore, the first step would be to check if the spectrum looks correct for your simulated structure and that the resonant peaks are at the expected frequencies. If yes, you could try to inject narrower spectrum. For example, by unchecking the “optimize for short pulse” option in the source settings.