- This topic has 13 replies, 2 voices, and was last updated 9 years ago by
Damian Marek.
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November 24, 2015 at 6:24 am #28039
Jaivaun White
ParticipantGood day all,
I am using the OptiFDTD package, to simulate a waveguide structure. Been looking at the Maths behind it all,Maxwell Equations, however not sure as to why TE or TM mode I run the solver in gives me different Poynting vector intensities. I mean I use a vertical source and launch my Gaussian wave. However, when the Poynting vector comes out, I seem like inital intensity of one mode 183 and other mode 0.0112 for the TE and TM modes when run the simulation. What may be causing these differences in Poynting vectors magnitudes, if structure is same for TE and TM modes when running simulation. Thank You.
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November 25, 2015 at 1:44 pm #28086
Damian Marek
ParticipantHard to say without your project file what exactly is going on, can you please attach it?
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November 25, 2015 at 2:51 pm #28090Participant
These are the files playing with to try understand why TE and TM give different Poynting vectors of order 10^5
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November 26, 2015 at 8:49 am #28114Participant
Not sure I understand what you are looking at because there are no detector objects. What data are you investigating?
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November 26, 2015 at 10:45 am #28117Participant
I am investigating the Total energy from start to end. And how energy vary depending on mode the light is launched in. In the analyzer file, I look at the poynting vector. Is it that am to use a detector to measure the poynting vector,instead of the method am using now?
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November 26, 2015 at 1:20 pm #28121Participant
I would suggest adding some observation points and/or observation lines as well as an XZ observation area. You must be using the 32 bit version of OptiFDTD then right?
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November 26, 2015 at 1:38 pm #28122Participant
Yes correct,that is the version of the software I am using. The 32 bit, I been trying to acquire the 64 bit,but not with much luck. I was told I would be contacted back, however no correspondence since.
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November 30, 2015 at 5:06 pm #28231Participant
I tried what you suggested, however I am concerned as to why the Poynting vectors for both TE and TM are so different, when the excitation comes from the same direction; as in for both TE and TM modes of study the excitation is done in the vertical plane.
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December 1, 2015 at 9:27 am #28266Participant
Ok the issue here is that for TE and TM input fields the fields are scaled the same but the power is not! For example, in TE the Ey field is scaled to 1 V/m and in the case of TM the Hy field is scaled to 1 A/m. This results in wildly different Poynting vector values, since the TM case will have MUCH larger electric field components. I would place a detection line at the input to the waveguide as well as one at the output. Then you can match the input power for the TE and TM case by using the reference line as a gauge. In the point source, try an amplitude of about 1000 times less for the TM case.
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December 1, 2015 at 2:19 pm #28276Participant
Okay seem to be getting values close but not exact, for both modes when used the W/m instead the A/m setting for input wave. And When used the 1.0 A/m setting for impulse and the 346 W/m for TE mode got similar magnitudes. Thanks again, can hardly believe overlooked that fact,about the differences in the A/m vs the W/m, as neglected to pay attention to the units, oversight on my part. I used this site “http://www.computational-photonics.eu/oms.html to check the modes and it gave me the exact same figures and number of modes. This seemed to clear up a lot for me now, regarding the difference in the magnitude of Poynting vectors. Attached are the files used.
PS the 1000 W/m for the TE mode gave me a factor of 10 difference in the Poynting vector, so I began using trial and error to find the number which would give me almost equal to 1 A/m and so came up with the 346 W/m. Thanks again for your help.-
December 1, 2015 at 4:24 pm #28277Participant
You are welcome! Just want to confirm that the units of electic field are given in V/m not “W/m”. THe magnetic field is given in A/m.
Makes sense since the impedance of free space is about 377 Ohm = E/H, but since there are some other materials here it is probably a bit smaller.
Regards
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December 1, 2015 at 4:32 pm #28278Participant
Yes it is smaller,however figures are off by some decimals, as seen in the files uploaded and yes thanks for the correction with the units.
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December 2, 2015 at 8:41 pm #28331Participant
I getting a good feel of the program, however am wondering if the negative power in the observation window is an issue of direction. As I am using the observation line, to give me the power at that surface. Please see the attached copy of file working on. I just noticed that the power was negative, and as such, wondering if is an issue of direction. Thank You.
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December 3, 2015 at 9:21 am #28374Participant
A negative power does indeed mean the direction of power flow is in the opposite direction.
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