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CLEANUP - changes to folder structure

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This commit is contained in:
Silas Oettinghaus
2026-03-25 10:57:48 +01:00
parent 0c5ad28f0a
commit 0ae846d3c3
351 changed files with 405 additions and 1294 deletions
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89
Theory/Optical/Dispersion/dispersion_10km.m Normal file
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%% ============================================================
% IM/DD Fading Notch – λ_null vs. Bandwidth (Fixed 10 km)
% ============================================================
clear; clc;
%% Fiber and dispersion parameters
lambda0 = 1310e-9; % Zero-dispersion wavelength [m]
S0 = 0.09; % Dispersion slope at ZDW [ps/(nm²·km)]
L = 10e3; % Fiber length [m]
c = physconst('lightspeed');
%% Frequency sweep (defines the desired first-fading notch)
f_targets = linspace(40e9, 150e9, 200); % [Hz]
f_GHz = f_targets / 1e9;
%% Compute wavelength λ_null for each target f_null
[lambda_vec, Dacc_vec] = lambda_for_first_null_full(f_targets, L, lambda0, S0);
lambda_nm = lambda_vec * 1e9; % Convert to nm
Dacc = Dacc_vec; % [ps/nm]
%% ------------------------------------------------------------
% Plot λ_null vs. f_null for 10 km fiber
% ------------------------------------------------------------
cols = cbrewer2('Paired',10);
figure('Color','w'); hold on;
hLine = plot(lambda_nm, f_GHz, ...
'LineWidth', 2, ...
'DisplayName', sprintf('L = %.1f km', L/1000), ...
'Color', cols(2,:));
xlabel('Wavelength λ [nm]');
ylabel('First fading notch f_{null} [GHz]');
title('IM/DD Fading Notch Position vs. Wavelength');
grid on; box on;
lim = (lambda0.*1e9) - [8, 40];
xlim([lim(2) lim(1)]);
yticks([56,75,90,112]);
%% ------------------------------------------------------------
% Custom DataTip Template
% ------------------------------------------------------------
% Add accumulated dispersion value to the DataTip
hLine.DataTipTemplate.DataTipRows(1).Label = 'λ [nm]';
hLine.DataTipTemplate.DataTipRows(2).Label = 'f_{null} [GHz]';
% Create a new row for Dacc
dRow = dataTipTextRow('D_{acc} [ps/nm]', Dacc);
hLine.DataTipTemplate.DataTipRows(end+1) = dRow;
%% ------------------------------------------------------------
% Helper function: lambda_for_first_null_full
% ------------------------------------------------------------
function [lambda_vec, Dacc_vec] = lambda_for_first_null_full(f_target, L, lambda0, S0)
c = physconst('lightspeed');
S0_si = S0 * 1e3; % ps/(nm²·km) -> s/(m³)
lambda_min = 1260e-9;
lambda_max = 1360e-9;
f_target = f_target(:);
N = numel(f_target);
lambda_vec = zeros(N,1);
Dacc_vec = zeros(N,1);
for k = 1:N
RHS = c * 0.5 / (f_target(k)^2 * L);
fun = @(lambda) -(S0_si/4).*(lambda - (lambda0^4)./(lambda.^3)).*lambda.^2 - RHS;
try
lambda_sol = fzero(fun, [lambda_min, lambda0 * 0.999]);
catch
lambda_sol = lambda_min;
end
lambda_sol = min(max(lambda_sol, lambda_min), lambda_max);
lambda_vec(k) = lambda_sol;
D_lambda = (S0_si/4) * (lambda_sol - (lambda0^4)/(lambda_sol^3)) / 1e-6; % ps/(nm·km)
Dacc_val = D_lambda * (L/1000); % ps/nm
Dacc_val = min(max(Dacc_val, -100), 100);
Dacc_vec(k) = Dacc_val;
end
end

77
Theory/Optical/Dispersion/dispersion_contour.m Normal file
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% Festen Betriebsparameter
lambda = 1290; % nm
L = 1; % km
mu_zwd = 1317; % nm
sigma_zwd = 2; % nm
mu_s0 = 0.0872; % ps / nm2 km
sigma_s0 = 0.0012; % ps / nm2 km
rho = -0.5; % Korrelation
% Gitter für lambda0 und S0
lambda0_vec = linspace(mu_zwd-10, mu_zwd+10, 100);
S0_vec = linspace(mu_s0-0.01, mu_s0+0.01, 100);
% Korrigierte meshgrid Reihenfolge
[S0, Lambda0] = meshgrid(S0_vec, lambda0_vec);
% Dispersion berechnen
D = (S0./4) .* ( lambda - (Lambda0.^4)./(lambda^3) ) * L;
%% 2D-Konturplot
figure('Color','w');
hold on
% --- 1. Hintergrund: Dispersions-Konturlinien (Gerundet für TikZ) ---
numLevels_D = 10;
% Erzeuge glatte, auf 1 Nachkommastelle gerundete Werte
levels_D = round(linspace(min(D(:)), max(D(:)), numLevels_D), 1);
levels_D = unique(levels_D); % Falls durch Rundung doppelte Werte entstehen
% Colormap in der Länge der verbliebenen Level erstellen
cmap_bg = cbrewer2('Blues', length(levels_D));
for i = 1:length(levels_D)
% WICHTIG: Das Level als [Wert, Wert] übergeben!
[C,h] = contour(S0, Lambda0, D, [levels_D(i), levels_D(i)], ...
'Color', cmap_bg(i,:),...
'LineWidth', 1.5, ...
'ShowText', 'on', ...
'LabelFormat', '%0.1f');
h.LabelColor = [0,0,0];
end
% --- NEU: Parameter für die Verteilungen ---
mu_zwd = 1317; % nm
sigma_zwd = 2; % nm
mu_s0 = 0.0872; % ps / nm2 km
sigma_s0 = 0.0012; % ps / nm2 km
rho = -0.5; % Korrelation
% --- 3. Randverteilungen (1D Gauss) an den Achsen ---
s0_vals = linspace(min(S0_vec), max(S0_vec), 500);
gauss_s0 = exp(-0.5*((s0_vals - mu_s0)/sigma_s0).^2);
scale_s0 = 4; % Skalierung für die Höhe in der Ansicht
plot(s0_vals, min(lambda0_vec) + gauss_s0 * scale_s0, 'k', 'LineWidth', 2);
zwd_vals = linspace(min(lambda0_vec), max(lambda0_vec), 500);
gauss_zwd = exp(-0.5*((zwd_vals - mu_zwd)/sigma_zwd).^2);
scale_zwd = 0.005; % Skalierung für die Auslenkung in der Ansicht
plot(min(S0_vec) + gauss_zwd * scale_zwd, zwd_vals, 'k', 'LineWidth', 2);
% Hilfslinien für die Mittelwerte
xline(mu_s0, '--k', 'Alpha', 0.4);
yline(mu_zwd, '--k', 'Alpha', 0.4);
% --- Achsenbeschriftung, Titel & Formatierung ---
xlabel('S0 ', 'FontSize', 12);
ylabel('ZDW [nm]', 'FontSize', 12);
% title(sprintf('Dispersion: %d km; %d nm', L, lambda), 'FontSize', 14);
axis([min(S0_vec) max(S0_vec) min(lambda0_vec) max(lambda0_vec)]);
grid on
hold off
%% Für den LaTeX Export
mat2tikz_improved("C:/Users/Silas/Documents/6971e0b65b380ca6d71c837f/02_IMDD_System/tikz/dispersion/dispersion_contour.tikz")

38
Theory/Optical/Dispersion/dispersion_first_notch_10km.m Normal file
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%% ------------------------------------------------------------
% Plot: Maximum usable IM/DD bandwidth vs wavelength
% ------------------------------------------------------------
% Fiber and dispersion parameters
lambda0 = 1310e-9; % [m]
S0 = 0.08; % [ps/(nm²·km)]
L = 10000; % [m]
c = physconst('lightspeed');
% Wavelength range around ZDW
lambda_vec = linspace(1250e-9, 1350e-9, 200); % [m]
% Compute D(lambda) using full model
lambda_nm = lambda_vec * 1e9;
lambda0_nm = lambda0 * 1e9;
D_lambda = (S0/4) .* (lambda_nm - (lambda0_nm.^4) ./ (lambda_nm.^3)); % [ps/(nm·km)]
% Convert D to [s/m²]
D_si = D_lambda * 1e-6;
% Compute first null frequency (f₀) for each wavelength
f_null = sqrt(c*(0.5) ./ (abs(D_si).*lambda_vec.^2*L)); % [Hz]
% Plot
figure('Color','w');
plot(lambda_vec*1e9, f_null/1e9, 'LineWidth', 1.6);
grid on; box on;
xlabel('Wavelength [nm]');
ylabel('First Fading Null Frequency [GHz]');
title(sprintf('IM/DD Bandwidth Limit vs. Wavelength (L = %.1f km)', L/1000));
% Highlight useful bandwidth thresholds
yline(25, '--', '25 GHz','Color',[0.4 0.4 0.4],'LabelHorizontalAlignment','left');
yline(50, '--', '50 GHz','Color',[0.2 0.6 0.2],'LabelHorizontalAlignment','left');
yline(100,'--', '100 GHz','Color',[0.6 0.2 0.2],'LabelHorizontalAlignment','left');
legend('First fading notch (f_{null})','Location','best');

165
Theory/Optical/Dispersion/dispersion_power_fading.m Normal file
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%% Chromatic Dispersion Power Fading Demonstration
% ------------------------------------------------------------
% This script computes and visualizes power fading after
% photodiode detection caused by chromatic dispersion in IM/DD links.
%
% It also determines the wavelength λ that produces the first
% fading null at a specified RF frequency f_target using the
% full physical dispersion model:
%
% D(λ) = (S0/4) * (λ - λ0^4 / λ^3)
%
% and compares the analytic null frequency with simulation.
% ------------------------------------------------------------
% clear; close all; clc;
%% Fiber and wavelength parameters
lambda0 = 1310e-9; % Zero-dispersion wavelength (ZDW) [m]
S0 = 0.08; % Dispersion slope at ZDW [ps/(nm^2·km)]
L = 10000; % Fiber length [m]
alpha_dB = 0; % Attenuation [dB/m] (ignored here)
%% Target null frequency
f_targets = linspace(55e9,58e9,10);
f_targets = 56e9;
% f_targets = 80e9;
% Compute wavelength that gives the first null at f_target
[lambda_vec, Dacc_vec] = lambda_for_first_null_full(f_targets, L, lambda0, S0);
% lambda_vec = 1293e-9;
fprintf('\n----------------------------------------------\n');
fprintf(' f_null [GHz] lambda [nm] Dacc [ps/nm]\n');
fprintf('----------------------------------------------\n');
fprintf('%10.1f %8.2f %+8.3f\n',[f_targets(:)/1e9, lambda_vec(:)*1e9, Dacc_vec(:)].');
fprintf('----------------------------------------------\n\n');
%% Frequency grid
f_simu = 500e9; % Simulation bandwidth [Hz]
N_freq = 500000;
faxis = linspace(-f_simu/2, f_simu/2, N_freq);
%% Derived fiber parameters
c = physconst('lightspeed');
S0_si = S0 * 1e3; % ps/(nm²·km) -> s/m³
% Convert wavelengths to nm for the D(lambda) model
lambda_nm = lambda_vec(end) * 1e9;
lambda0_nm = lambda0 * 1e9;
% Dispersion parameter [ps/(nm·km)]
D_lambda = (S0/4) * (lambda_nm - (lambda0_nm^4)/(lambda_nm^3));
% Convert to [s/m²]
D_si = D_lambda * 1e-6;
% β2 in [s²/m]
b2 = -D_si * lambda_vec(end)^2 / (2*pi*c);
%% IM/DD intensity response (simulation)
phi = 2*pi^2*b2*faxis.^2*L;
H_field_pos = exp(-1j*phi); % +f sideband
H_field_neg = exp(+1j*phi); % -f sideband
H_intensity = 0.5 * (H_field_pos + H_field_neg); % PD beating term
H_sim = abs(H_intensity);
%% Theoretical analytical IM/DD response
phi = 2*pi^2 * abs(b2) * faxis.^2 * L;
H_theoretical = abs(cos(phi));
%% Analytic first null (for verification)
f_null_analytic = sqrt(c*(0.5)/(abs(D_si)*lambda_vec(end)^2*L));
fprintf('Analytic first null from D,λ,L: %.2f GHz\n\n', f_null_analytic/1e9);
%% Plot
cols = linspecer(5);
figure('Color','w'); hold on; grid on; box on;
plot(faxis*1e-9, 10*log10(H_sim), 'DisplayName','$|H_{sim}|$ (IM/DD simulation)','Color',cols(1,:));
plot(faxis*1e-9, 10*log10(H_theoretical), 'DisplayName','|cos($\phi$)| (theory)','Color',cols(2,:),'LineStyle','--');
xline(f_targets(end)/1e9,'k:','LineWidth',1.2,'DisplayName','Target null (56 GHz)');
xline(f_null_analytic/1e9,'Color',[0.2 0.6 0.2],'LineStyle','-.','LineWidth',1.2,'DisplayName','Analytic null');
xlabel('Frequency [GHz]');
ylabel('Magnitude [dB]');
title(sprintf('Power Fading for %.2f nm, L = %.1f km',lambda_nm,L/1000));
legend('Location','best'); ylim([-30 0]);
%% Plot Bandwidth vs Lambda max
figure();
hold on;
plot(lambda_vec.*1e6,f_targets.*1e-9)
xlabel('wavelength');
ylabel('max. Bandwidth')
function [lambda_vec, Dacc_vec] = lambda_for_first_null_full(f_target, L, lambda0, S0)
% lambda_for_first_null_full (stable, single-branch + validity checks)
% --------------------------------------------------------------------
% Computes the wavelength(s) at which the first IM/DD fading null
% occurs at frequency/ies f_target using the full dispersion model:
%
% D(lambda) = (S0/4)*(lambda - lambda0^4 / lambda^3)
%
% Restricted to the NORMAL-dispersion branch (λ < λ0),
% and valid only in the O-band (1260–1360 nm).
%
% Inputs:
% f_target - scalar or vector of target null frequencies [Hz]
% L - fiber length [m]
% lambda0 - zero-dispersion wavelength (ZDW) [m]
% S0 - dispersion slope at ZDW [ps/(nm²·km)]
%
% Outputs:
% lambda_vec - wavelength(s) [m] where first null occurs (clamped to O-band)
% Dacc_vec - accumulated dispersion(s) [ps/nm] (NaN if out of valid range)
% --------------------------------------------------------------------
c = physconst('lightspeed');
S0_si = S0 * 1e3; % ps/(nm²·km) -> s/(m³)
% Define O-band boundaries (in meters)
lambda_min = 1255e-9;
lambda_max = 1361e-9;
% Force column vector
f_target = f_target(:);
N = numel(f_target);
lambda_vec = NaN(N,1);
Dacc_vec = NaN(N,1);
for k = 1:N
RHS = c * 0.5 / (f_target(k)^2 * L);
% Normal-dispersion branch (λ < λ0)
fun = @(lambda) -(S0_si/4).*(lambda - (lambda0^4)./(lambda.^3)).*lambda.^2 - RHS;
% Limit the search to [λ_min, λ0)
try
lambda_sol = fzero(fun, [lambda_min, lambda0 * 0.999]);
catch
% If the zero is not within bounds, skip this point
lambda_sol = NaN;
end
% Validate solution
if isnan(lambda_sol) || lambda_sol < lambda_min || lambda_sol > lambda_max
lambda_vec(k) = NaN;
Dacc_vec(k) = NaN;
continue
end
% Compute D(lambda) and accumulated dispersion
D_lambda = (S0_si/4) * (lambda_sol - (lambda0^4)/(lambda_sol^3)) / 1e-6; % ps/(nm·km)
Dacc_val = D_lambda * (L/1000); % ps/nm
% Sanity bound on dispersion (avoid unphysical > ±100 ps/nm)
if abs(Dacc_val) > 100
lambda_vec(k) = NaN;
Dacc_vec(k) = NaN;
else
lambda_vec(k) = lambda_sol;
Dacc_vec(k) = Dacc_val;
end
end
end

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Theory/Optical/Dispersion/dispersion_wavelength_notch.m Normal file
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%% Dependency f_null vs Delta_lambda
lambda0 = 1310e-9;
S0 = 0.09; % ps/(nm²·km)
L = 10e3; % m
c = physconst('lightspeed');
% Convert slope to SI
S0_si = S0 * 1e3; % s/m³
Delta_lambda = linspace(5e-9, 80e-9, 300); % [m] detuning
cols = [0.3467 0.5360 0.6907;...
0.9153 0.2816 0.2878;...
0.4416 0.7490 0.4322];
figure('Color','w');hold on
cnt = 1;
for L = [2,10,40]
f_null_10 = sqrt( c * 0.5 ./ (S0_si .* abs(Delta_lambda) .* lambda0.^2 .* L*1e3) );
plot(1310-Delta_lambda*1e9, f_null_10/1e9, 'LineWidth',2,'DisplayName',sprintf('%d km',L),'Color',cols(cnt,:));
cnt = cnt+1;
end
% yticks([56,75,90,112])
% tickse = 1310-[7.5, 12, 17, 31.5];
% xticks(flip(tickse));
xlabel('$\Delta \lambda$ from ZDW [nm]');
ylabel('$F_{null}$ [GHz]');
grid on; box on;
lim=1310-[5,60];
xlim([lim(2) lim(1)]);
ylim([10,130])
legend

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Theory/Optical/Dispersion/dispersion_wdm.m Normal file
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%% ============================================================
% IM/DD Fading Notch Design Map
% Shows λ_null vs. bandwidth (f_target) and fiber length (L)
% ============================================================
clear; close all; clc;
%% Parameters
lambda0 = 1310e-9; % Zero-dispersion wavelength [m]
S0 = 0.08; % Dispersion slope at ZDW [ps/(nm²·km)]
c = physconst('lightspeed');
% Frequency and length sweep
f_targets = linspace(20e9, 140e9, 80); % [Hz] → x-axis
L_values = linspace(0.5e3, 12e3, 80); % [m] → y-axis
% Preallocate result matrices
lambda_surface = zeros(numel(L_values), numel(f_targets));
Dacc_surface = zeros(numel(L_values), numel(f_targets));
%% Compute λ_null and Dacc for each (f_target, L)
for iL = 1:numel(L_values)
L = L_values(iL);
[lambda_vec, Dacc_vec] = lambda_for_first_null_full(f_targets, L, lambda0, S0);
lambda_surface(iL, :) = lambda_vec; % [m]
Dacc_surface(iL, :) = Dacc_vec; % [ps/nm]
end
%% Convert to display units
lambda_surface_nm = lambda_surface * 1e9; % [nm]
L_km = L_values / 1000; % [km]
f_GHz = f_targets / 1e9; % [GHz]
%% ------------------------------------------------------------
% Contour plot (λ_null as function of f_null and L)
% ------------------------------------------------------------
figure('Color','w');
% Define wavelength contour levels [nm]
lambda_levels = [1260:10:1290, 1290:5:1300, 1300:2:1310];
contourf(f_GHz, L_km, lambda_surface_nm, lambda_levels, ...
'LineWidth', 1.5, ...
'ShowText', 'on', ...
'LabelFormat', '%1.1d nm');
% Colormap and colorbar
colormap(flip(cbrewer2('RdYlGn',100)));
clim([1260 1310]);
% c = colorbar;
% ylabel(c, 'λ_{null} [nm]', 'Rotation', 90);
% Axis formatting
xlabel('Signal Bandwidth [GHz]');
ylabel('Fiber length L [km]');
% X-axis ticks (every 16 GHz starting at 56 GHz)
xticks(56:8:120);
xlim([56,120])
grid on; box on;
%% Optional overlay: accumulated dispersion contours
hold on;
[CS, h] = contour(f_GHz, L_km, Dacc_surface, 10, 'k--', 'LineWidth', 0.8);
clabel(CS, h, 'Color','k', 'FontSize',8);
legend('λ_{null} contours','|D_{acc}| [ps/nm]','Location','best');
%% ============================================================
% Helper function: lambda_for_first_null_full
% Stable, single-branch, clamped to O-band
% ============================================================
function [lambda_vec, Dacc_vec] = lambda_for_first_null_full(f_target, L, lambda0, S0)
c = physconst('lightspeed');
S0_si = S0 * 1e3; % ps/(nm²·km) -> s/(m³)
% Define O-band boundaries (in meters)
lambda_min = 1260e-9;
lambda_max = 1360e-9;
% Force column vector
f_target = f_target(:);
N = numel(f_target);
lambda_vec = zeros(N,1);
Dacc_vec = zeros(N,1);
for k = 1:N
RHS = c * 0.5 / (f_target(k)^2 * L);
% Normal-dispersion branch (λ < λ0)
fun = @(lambda) -(S0_si/4).*(lambda - (lambda0^4)./(lambda.^3)).*lambda.^2 - RHS;
% Solve within the normal-dispersion range
try
lambda_sol = fzero(fun, [lambda_min, lambda0 * 0.999]);
catch
lambda_sol = lambda_min;
end
% Clamp to O-band range
lambda_sol = min(max(lambda_sol, lambda_min), lambda_max);
lambda_vec(k) = lambda_sol;
% Compute D(lambda) and accumulated dispersion
D_lambda = (S0_si/4) * (lambda_sol - (lambda0^4)/(lambda_sol^3)) / 1e-6; % ps/(nm·km)
Dacc_val = D_lambda * (L/1000); % ps/nm
% Clamp to physical range
Dacc_val = min(max(Dacc_val, -100), 100);
Dacc_vec(k) = Dacc_val;
end
end

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Theory/Optical/Dispersion/power_fading_gif.m Normal file
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%% ============================================================
% IM/DD Power Fading Evolution GIF (1 km -> 20 km)
% Uses the provided GifWriter (serial mode)
% ============================================================
clear; close all; clc;
%% Fiber and system parameters
lambda0 = 1310e-9; % zero-dispersion wavelength [m]
lambda = 1275e-9; % operating wavelength [m]
S0 = 0.09; % dispersion slope [ps/(nm^2·km)]
c = physconst('lightspeed');
%% Derived quantities (length-independent)
D_lambda = (S0/4) * (lambda*1e9 - (lambda0*1e9)^4/(lambda*1e9)^3); % ps/(nm·km)
D_si = D_lambda * 1e-6; % s/m^2
b2 = -D_si * lambda^2 / (2*pi*c); % s^2/m
%% Frequency grid
f_max = 150e9;
f = linspace(0, f_max, 4000); % [Hz]
%% Figure setup (keep it stable for nicer GIFs)
fig = figure('Color','w');
ax = axes(fig); %#ok<LAXES>
hold(ax,'on'); grid(ax,'on'); box(ax,'on');
xlabel(ax,'Frequency [GHz]');
ylabel(ax,'Magnitude [dB]');
ylim(ax,[-30 0]);
xlim(ax,[0 f_max/1e9]);
%% GIF writer (serial mode; simplest)
g = GifWriter('Name','power_fading_evolution', 'DelayTime',0.12, 'Parallel',false);
%% Loop: 1 km to 20 km
L = [1:20,19:-1:1];
for L_km = L
L_meter = L_km * 1e3; % [m]
% IM/DD transfer function (power fading)
phi = 2*pi^2 * b2 * f.^2 * L_meter;
H = abs(cos(phi));
HdB = 10*log10(max(H, 1e-12)); % avoid -Inf for deep notches
% Clear and redraw (stable axes)
cla(ax);
plot(ax, f/1e9, HdB, 'LineWidth', 1.8, 'Color','black');
% Analytic first-null frequency marker
f_null = sqrt(c*(0.5)/(abs(D_si)*lambda^2*L_meter));
xline(ax, f_null/1e9, 'r--', 'LineWidth', 1.2, ...
'Label', sprintf('f_{null}=%.1f GHz', f_null/1e9), ...
'LabelOrientation','horizontal', ...
'LabelVerticalAlignment','bottom');
title(ax, sprintf('Power Fading for: %.0f km @ 1275 nm', L_km));
drawnow;
% Add frame to GIF
g.addFrame(fig);
end
%% Done
g.compile(fig.Number);
disp(fullfile(g.OutputDir, sprintf('%s_fig_%d.gif', g.Name, fig.Number)));

69
Theory/Optical/Dispersion/power_fading_gif_lambda_variation.m Normal file
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%% ============================================================
% IM/DD Power Fading Evolution vs Wavelength (L = 10 km)
% ============================================================
clear; close all; clc;
%% Fixed fiber parameters
lambda0 = 1310e-9; % zero-dispersion wavelength [m]
S0 = 0.09; % dispersion slope [ps/(nm^2·km)]
L = 10e3; % fiber length FIXED [m]
c = physconst('lightspeed');
%% Frequency grid
f_max = 150e9;
f = linspace(0, f_max, 4000); % [Hz]
%% Figure setup (stable axes for clean GIF)
fig = figure('Color','w');
ax = axes(fig);
hold(ax,'on'); grid(ax,'on'); box(ax,'on');
xlabel(ax,'Frequency [GHz]');
ylabel(ax,'Magnitude [dB]');
ylim(ax,[-30 0]);
xlim(ax,[0 f_max/1e9]);
%% GIF writer
g = GifWriter('Name','power_fading_vs_wavelength', ...
'DelayTime',0.12, ...
'Parallel',false);
%% Wavelength sweep (around ZDW)
lambda_vec = linspace(1260e-9, 1360e-9, 25); % 1260–1360 nm
for k = 1:length(lambda_vec)
lambda = lambda_vec(k);
%% Dispersion for current wavelength
D_lambda = (S0/4) * (lambda*1e9 - (lambda0*1e9)^4/(lambda*1e9)^3); % ps/(nm·km)
D_si = D_lambda * 1e-6; % s/m^2
b2 = -D_si * lambda^2 / (2*pi*c); % s^2/m
%% Power fading transfer function
phi = 2*pi^2 * b2 * f.^2 * L;
H = abs(cos(phi));
HdB = 10*log10(max(H, 1e-12));
cla(ax)
plot(ax, f/1e9, HdB, 'LineWidth',1.8,'Color','black');
%% First-null frequency
if abs(D_si) > 0
f_null = sqrt(c*(0.5)/(abs(D_si)*lambda^2*L));
xline(ax, f_null/1e9, 'r--', 'LineWidth',1.2, ...
'Label', sprintf('f_{null}=%.1f GHz', f_null/1e9), ...
'LabelOrientation','horizontal', ...
'LabelVerticalAlignment','bottom');
end
title(ax, sprintf('Power Fading for: 10 km @ %.0f nm', lambda*1e9));
drawnow;
g.addFrame(fig);
end
%% Compile GIF
g.compile(fig.Number);
disp(fullfile(g.OutputDir, sprintf('%s_fig_%d.gif', g.Name, fig.Number)));