Transmission spectrum for optical waveguide

Topics: 4.2a, RF Module

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Frédéric Peyskens

Frédéric Peyskens

August 8, 2012 1:17pm UTC

Transmission spectrum for optical waveguide

Hello,

I am currently trying to extract a transmission spectrum from a Si waveguide on top of SiO2 substrate. There are some gold particles on top of the Si (this configuration is taken from an article in which they simulate it with FDTD). I tried several things to extract the transmission spectrum:

1) S21 parameter in dB
2) ratio of the Poynting flux at the input and output (tried both with fields Ex,Ey,Ez, emw.Hx, emw.Hy and emw.Hz and with fields from the Boundary mode electric/magnetic field)

I am however not able to get the right profile (for some wavelenghts I even get quit high gains which is unphysical).

It seems that also reflections are taken into account, but in an experiment you will only take the ratio of the actual input power (which is forward propagating) and the forward propagating output power.

Does anybody know how to extract a sensible transmission spectrum (which you would obtain in experiments).

Thanks in advance.

F. Peyskens

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Alexander Kuznetsov

Alexander Kuznetsov

August 9, 2012 6:53pm UTC in response to Frédéric Peyskens

Re: Transmission spectrum for optical waveguide

plasmonic wire grating example is a good start. In general, the approach shown there gives the right reflection/transmission.

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Frédéric Peyskens

Frédéric Peyskens

August 10, 2012 8:44am UTC in response to Alexander Kuznetsov

Re: Transmission spectrum for optical waveguide

Thank you for the answer. I tried however a similar reasoning with the waveguide: input of the waveguide is port 1 and output is port 2. Then I extract the S21, but this gives me not the right transmission spectrum. I tried it through the z-component of the Poynting vector (as the waveguide propagates waves in the + z-direction), but this also does not give me the right results. In case of this 2-port system I would expect that the transmission is defined as

(Power propagating in the + z-direction at the output port)/(Power calculated in the Boundary Mode Analysis at the input port)

Or am I seeing this wrong? At least, this is what you would measure experimentally.

Kind regards,
F. Peyskens

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Alexander Kuznetsov

Alexander Kuznetsov

August 10, 2012 5:14pm UTC in response to Frédéric Peyskens

Re: Transmission spectrum for optical waveguide


input of the waveguide is port 1 and output is port 2.

port 1 is input as well as output for the reflected wave.
abs(S11)^2 would be reflectivity coefficient, and abs(S21)^2 - transmission.
To validate your model you can use it to calculate reflectivity (or transmission) of SiO2 film and compare to theoretical value.

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Frédéric Peyskens

Frédéric Peyskens

August 12, 2012 10:17am UTC in response to Alexander Kuznetsov

Re: Transmission spectrum for optical waveguide

Hello,

Thank you for your fast response. I have tried what you suggested, but the problem with the S-parameters is that in transmission it gives me large gains for some wavelengths, which is unphysical. I would try to extract transmission through the Poynting vector, but I only want the forward propagating power at the output (and not the reflected power going back to the input as you mention) and I guess part of the reflected power is taken into account too. Is there a way to extract:
1) the excitation power at the input (and not taking the reflective power into account)
2) the forward propagating output power

Thanks in advance.

Kind regards,
F. Peyskens

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Brian West

Brian West

August 29, 2012 6:45pm UTC in response to Frédéric Peyskens

Re: Transmission spectrum for optical waveguide

COMSOL's sign convention for the imaginary part of dielectric constants is opposite to that of most other photonic modeling software. Your non-physical gain might be caused by this.

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Frédéric Peyskens

Frédéric Peyskens

September 12, 2012 8:29am UTC in response to Brian West

Re: Transmission spectrum for optical waveguide

Thank you for this response. We got the same answer from the comsol helpdesk and they now found indeed a loss instead of a gain.

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Richie Guo

Richie Guo

January 5, 2013 4:18am UTC in response to Frédéric Peyskens

Re: Transmission spectrum for optical waveguide


Thank you for this response. We got the same answer from the comsol helpdesk and they now found indeed a loss instead of a gain.


Hi, I have meet similar problem with you. Can you share your mph file? thank you.

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Richie Guo

Richie Guo

January 11, 2013 3:21am UTC in response to Richie Guo

Re: Transmission spectrum for optical waveguide

Hi, thank you very much for your fast response.

How do you calculate the transmission spectrum, use S21 or output power/input power?

I attached my ring resonator and need to simulate the transmission spectrum, I try but always fail, would you please help me?

Attachments:   Ring.mph  

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Sruthi R

Sruthi R

March 20, 2013 12:17pm UTC in response to Frédéric Peyskens

Re: Transmission spectrum for optical waveguide

hi,
im also experiencing a similar problem like yours. can u pls share ur mph file so that i will come to know how u have taken the transmission spectrum.

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