Example3.m

P = BPMmatlab.model;

% This example starts in the same way as example 1. To demonstrate that in
% media with uniform refractive index n_background, either the FFTBPM or FDBPM
% solver can be used for propagation. The output of example 1 is propagated
% 2e-4 m through a medium of uniform refractive index 1.45 with both
% solvers. You can see that the results are identical by comparing figures
% 2 and 3.

% The example also demonstrates the use of non-standard color maps for the
% plots.

%% Part 1 run with FDBPM
%% General and solver-related settings
P.name = mfilename;
P.useAllCPUs = true; % If false, BPM-Matlab will leave one processor unused. Useful for doing other work on the PC while simulations are running.
P.useGPU = false; % (Default: false) Use CUDA acceleration for NVIDIA GPUs

%% Visualization parameters
P.figNum = 1;
P.updates = 30;            % Number of times to update plot. Must be at least 1, showing the final state.
P.plotZoom = 1;  % Zooms in on figures. Set to 1 for no zooming.  

% The colormap options for the different subplots are 
% GPBGYR, HSV, parula, gray, cividis
P.intensityColormap = 'cividis';
P.phaseColormap = 'hsv';
P.nColormap = 'gray';

%% Resolution-related parameters (check for convergence)
P.Lx_main = 20e-6;        % [m] x side length of main area
P.Ly_main = 20e-6;        % [m] y side length of main area
P.Nx_main = 200;          % x resolution of main area
P.Ny_main = 200;          % y resolution of main area
P.padfactor = 1.5;  % How much absorbing padding to add on the sides of the main area (1 means no padding, 2 means the absorbing padding on both sides is of thickness Lx_main/2)
P.dz_target = 1e-6; % [m] z step size to aim for
P.alpha = 3e14;             % [1/m^3] "Absorption coefficient" per squared unit length distance out from edge of main area

%% Problem definition
P.lambda = 1000e-9; % [m] Wavelength
P.n_background = 1.45; % [] (may be complex) Background refractive index, (in this case, the cladding)
P.n_0 = 1.46; % [] reference refractive index
P.Lz = 2e-3; % [m] z propagation distances for this segment

P = initializeRIfromFunction(P,@calcRI);
P = initializeEfromFunction(P,@calcInitialE);

% Run solver
P = FD_BPM(P);

%% Part 2 run with FDBPM
P.figNum = 101;
P.figTitle = 'FD BPM';

P.n_0 = 1.45;
P = initializeRIfromFunction(P,@calcRIuniform);

P.Lx_main = 100e-6;        % [m] x side length of main area
P.Ly_main = 100e-6;        % [m] y side length of main area
P.Nx_main = 500;          % x resolution of main area
P.Ny_main = 500;          % y resolution of main area
P.alpha = 8e13;             % [1/m^3] "Absorption coefficient" per squared unit length distance out from edge of main area

P.Lz = 2e-4; % [m] z propagation distances for this segment

% Run solver but do not pass the results back into P, just discard them
FD_BPM(P);

%% Part 2 run with FFTBPM for comparison
P.figNum = 201;
P.figTitle = 'FFT BPM';

% Run solver. Here P has the same simulation parameters provided as input
% to the FD_BPM propagator, so we can compare the results
FFT_BPM(P);

%% USER DEFINED E-FIELD INITIALIZATION FUNCTION
function E = calcInitialE(X,Y,Eparameters) % Function to determine the initial E field. Eparameters is a cell array of additional parameters such as beam size
w_0 = 2.5e-6;
offset = 2.5e-6;
amplitude = exp(-((X-offset).^2+Y.^2)/w_0^2);
phase = zeros(size(X));
E = amplitude.*exp(1i*phase); % Electric field
end

%% USER DEFINED RI FUNCTIONS
function n = calcRI(X,Y,n_background,nParameters)
% n may be complex
n = n_background*ones(size(X)); % Start by setting all pixels to n_background
n(X.^2 + Y.^2 < 5e-6^2) = 1.46;
end

function n = calcRIuniform(X,Y,n_background,nParameters)
% n may be complex
n = n_background*ones(size(X));
end