Learning Forum

[ceshi xiazai]

Dear all,

I set a dipole source inside a paramid microcavity to see the resonance mode with a center wavelength of 840nm and the span is 60nm.

(which is supposed to be 420nm because I wanna investigate the SHG signal inside the cavity. I set it mistakenly to 840nm)

Then I set a point DFT monitor to get the spectrum inside the cavity to see the peaks.

Accidently, I got the exact result that I wanted. I did not set a chi2 or chi3, just taking the material as a sampled 3D material.Why did I get a enhanced peak at around 420nm?I am very very very confused about all of this stuff.

Thank you!

[Guilin Sun]

This is mainly due to the source pulse: even though you set a single wavelength source, since the injection is a pulse, and its spectrum is a Gaussian shape with extremly broadband. Thus you can find reult at 420nm. Please check.

[ceshi xiazai]

Then why cannot I  get any peaks from a spectrum monitor with around 840nm when the wavelength of the dipole source is 840nm

[Guilin Sun]

let me first summarize your question:

you mistakenly used 840nm source and the correct one should be 420nm; you found there was a peak at 420nm without nonlinear material.  Then you expect to find a peak at 840nm.  right?

Whether the wavelength has the peak or not depends on the device interaction with light: when it satifies the resonance condition it will have a peak. FOr exmaple around 420nm the phase difference is to constructive (eg phase difference is pi) so it has a peak. However 840nm may not becuase its optical path difference is less than pi, probably just around half pi.

Please review intererence of two light beams.