rcwa - Script command

Calculates the reflection and transmission of a plane wave through a layered periodic media using the RCWA solver. This function returns various results, including the fraction of transmitted and reflected power for both S and P polarizations as well as the electric and magnetic field values at specified locations. All results are returned in a single dataset as a function of frequency and incidence angle. Optionally, the results can be returned as a function of grating order as well.

In order to use the rcwa command, a 3D FDTD solver object must be included in the simulation to define a mesh grid. The span of the FDTD object should match the span of the RCWA solver, but otherwise the FDTD object properties do not affect the RCWA simulation.

For more information on the RCWA solver, see RCWA Solver Introduction.

Note: As of release 2023 R2, the rcwa command have been deprecated. We recommend using the RCWA solver object to run RCWA simulations instead. This object can be used to set up and run RCWA simulations in scripts with the addrcwa, set, and run commands.

Device Geometry

The device geometry used in the RCWA simulation is created using geometry objects, similar to the FDTD solver. The geometry struct used as an argument to the rcwa command determines the:

• Injection axis of the plane wave source
• Span of the multilayer structure along the injection axis
• Span of the unit cell in the transverse directions
• Positions of the interfaces between the layers

The geometry struct has the following fields:

A layer for the cladding/substrate on either side of the stack should be included to account for reflections from the interfaces between the cladding/substrate and the first/last layers of the stack.

Plane Wave Source Properties

The properties of the plane wave used as a source in the RCWA simulation are set using the excitation argument of the rcwa command.

The excitation argument is a struct defining the incident plane wave with the following fields:

The frequency points and incident angles of the source can be set as single values or matrices containing a range of values. The RCWA solver results will be calculated at each combination of these frequency and angle values.

The polarization of the source can be set with the s_pol and p_pol fields. If both s_pol and p_pol are set to zero, results for both the S and P polarized source plane waves will be calculated. If one is set to 1 and the other is set to 0, only the results for the polarization set to 1 will be calculated.

Other Options

The maximum number of k-vectors, whether to report results in terms of the grating orders, and the locations where the electric and magnetic field values are to be returned can be set with the options argument of the rcwa command. The options argument is a struct with the following fields:

All of the fields are optional. Increasing the maximum number of k-vectors will increase the accuracy of the simulation, but the simulation time required will be increased as well.

If report_grating_orders is false, only the total reflected/transmitted power will be returned. If it is set to true, the transmission into each of the grating orders will be calculated as well.

Results

The results of the RCWA solver simulation are returned by the rcwa command as a struct with the following fields:

Example

The following script can be run on an empty FDTD simulation file to run the RCWA solver for a simple photonic crystal structure. The total power reflected and transmitted with a plane wave source at normal incidence is calculated with the RCWA solver and plotted. The calculated E and H fields along the z-axis will also be plotted.

a = 1e-6;

# set RCWA solver properties
geometry = struct;
geometry.injection_axis = "z-axis";
geometry.x_min = -a/2;
geometry.x_max = a/2;
geometry.y_min = -a/2;
geometry.y_max = a/2;
geometry.z_min = -a/2;
geometry.z_max = a/2;
geometry.layer_positions = [-a/4,a/4];

excitation = struct;
excitation.f =0.5*c/a;
excitation.phi = 0;
excitation.theta = 15;

discretization = linspace(-a/2,a/2,51); # z locations where fields will be calculated

options={"max_N":10,
"fields_monitor_z":discretization,
"fields_monitor_x":[0],
"fields_monitor_y":[0]};

# create geometry
addrect;
set("x min",geometry.x_min);
set("x max",geometry.x_max );
set("y min",geometry.y_min);
set("y max",geometry.y_max);
set("z min",geometry.layer_positions(1));
set("z max",geometry.layer_positions(2));
set("index",sqrt(12));

addcircle;
set("z min",geometry.layer_positions(1));
set("z max",geometry.layer_positions(2));
set("radius",0.2*a);
set("index",1);

# add FDTD solver region
addfdtd;
set("x min",geometry.x_min);
set("x max",geometry.x_max);
set("y min",geometry.y_min);
set("y max",geometry.y_max);
set("z min",geometry.z_min);
set("z max",geometry.z_max);

# run RCWA solver and plot results
result = rcwa(geometry, excitation, options);

fields = result.Fields; 
Es = pinch(fields.Es); 
Hs = pinch(fields.Hs); 
Ep = pinch(fields.Ep); 
Hp = pinch(fields.Hp); 
plot(options.fields_monitor_z,sqrt(sum(abs(Es)^2,2)),"z (m)","|Es|","","linewidth=2");
legend("");

TE = result.TotalEnergy;
plot(excitation.f,TE.Rs,TE.Ts,TE.Rp,TE.Tp,"frequency (Hz)","Power");
legend("Rs","Ts","Rp","Tp");

See Also

• Lumerical scripting language - Alphabetical list
• RCWA Solver Introduction
• Photonic Crystal Slab (RCWA)
• Metalens - Zemax Interoperability
• rcwasweeppropagation - Script Command