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Varying the order of diffraction in Plasmonic Wire Grating

Posted 11 avr. 2013, 15:56 UTC−4 Version 4.2 2 Replies

Snehanshu MAiti
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Hi,
I am simulating in Comsol 4.2.I started simulating the PLASMONIC WIRE GRATING given in the model library.the simulation there is done by varying the angle of incidence.(in the parametric sweep angle of incidence is varied).

I want to modify this a little bit.So instead of angle of incidence i want to vary m(the diffraction order)

i have made the necessary changes .

In global variables i have taken the transmission angle beta_m=asin((m*lam0)/(d*nb)) which comes from m*lam0=d(nb*sin(beta_m)-na*sin(alpha)) here alpha=0 for normal incidence
na=R.I of air(upper domain of simulation)
nb=R.I of glass(lower domain of simulation)

The propagation vectors which i have defined are :

ka=emw.k0
kb=nb*emw.k0
kbmx=kb*sin(beta_m)
kbmy=kb*cos(beta_m)

The geometries and material properties have been defined as usual

In port1 i have taken the upper boundary ,wave excitation on and Eo=exp(-i*ka*x) and beta=abs(ka)

In port2 i have taken the lower boundary ,the Eo=-cos(beta_m)*exp(-i*kbmx*x)
and Eo= sin(beta_m)*exp(-i*kbmx*x) and beta=abs(kbmy)

Then i have added the periodic boundary condition as Floquet condition

In the parametric sweep i have varied m(-2,0.1,2)

But this gives me erroneous results!!
probably i am unable to vary /parametric sweep m.

Kindly help I want to find the transmiision for various m
2 Replies Last Post 14 avr. 2013, 01:40 UTC−4
Alexander Kuznetsov
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Posted: 1 decade ago 12 avr. 2013, 12:43 UTC−4
"Varying the order of diffraction" is meaningless in terms of FEM. You launch a wave on a grating, and whatever orders exist, they we be modeled. In the near-field, you can't separate diffraction orders. Moreover, non-propogating (evanescent) modes will also contribute to the field patterns.
"Varying the order of diffraction" is meaningless in terms of FEM. You launch a wave on a grating, and whatever orders exist, they we be modeled. In the near-field, you can't separate diffraction orders. Moreover, non-propogating (evanescent) modes will also contribute to the field patterns.
Snehanshu MAiti
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Posted: 1 decade ago 14 avr. 2013, 01:40 UTC−4
In the model library where they have simulated the Plasmonic wire grating they are showing the 1D plot.(Transmission vs angle of incidence for varying orders).In definition of variables they have calculated the propagation vectors for different orders if u see the details of the model.So they get a 1D plot for transmittivity for different orders .But in subwavelenth grating the diffracted light might always not be confined in the integral orders.They may be present in the non integral orders also if u carefully analyse the grating eqn.So i tried to vary different orders.

If this makes sense can the modes be separated in the far field.I guess the 1D plot in the model have been done for far field

Ultimately i want to plot the transmittivity at the far field in polar coordinates.(i mean the transmitted light as a func of angular variation of the space coordinates at far field)for the normal angle of incidence.What exactly needs to be done.Kindly tell the details

Thanking you

Snehanshu
In the model library where they have simulated the Plasmonic wire grating they are showing the 1D plot.(Transmission vs angle of incidence for varying orders).In definition of variables they have calculated the propagation vectors for different orders if u see the details of the model.So they get a 1D plot for transmittivity for different orders .But in subwavelenth grating the diffracted light might always not be confined in the integral orders.They may be present in the non integral orders also if u carefully analyse the grating eqn.So i tried to vary different orders. If this makes sense can the modes be separated in the far field.I guess the 1D plot in the model have been done for far field Ultimately i want to plot the transmittivity at the far field in polar coordinates.(i mean the transmitted light as a func of angular variation of the space coordinates at far field)for the normal angle of incidence.What exactly needs to be done.Kindly tell the details Thanking you Snehanshu

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