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Refactoring/ Organization

Theory/Optical/Dispersion/dispersion_power_fading.m

@@ -17,7 +17,7 @@
 %% 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]
+L        = 8000;      % Fiber length [m]
 alpha_dB = 0;         % Attenuation [dB/m] (ignored here)
 
 %% Target null frequency

Theory/Optical/Dispersion/power_fading.m

@@ -0,0 +1,50 @@
+%% ============================================================
+%  Minimal IM/DD Power Fading Plot
+% ============================================================
+
+
+%% Fiber and system parameters
+lambda0 = 1309e-9;       % zero-dispersion wavelength [m]
+lambda  = 1370e-9;       % operating wavelength [m]
+S0      = 0.092;          % dispersion slope [ps/(nm²·km)]
+L       = 30e3;          % fiber length [m]
+c       = physconst('lightspeed');
+
+%% Derived quantities
+S0_si = S0 * 1e3;                                    % → s/m³
+D_lambda = (S0/4) * (lambda*1e9 - (lambda0*1e9)^4/(lambda*1e9)^3); % ps/(nm·km)
+D_si = D_lambda * 1e-6;                              % → s/m²
+b2   = -D_si * lambda^2 / (2*pi*c);                  % s²/m
+
+Dacc = D_lambda * L;
+fprintf('Accumulated Dispersion: %.2f ps/nm \n', Dacc / 1e3);
+
+%% Frequency grid
+f_max = 200e9;
+f = linspace(0, f_max, 5000);                        % [Hz]
+
+%% IM/DD transfer function (power fading)
+phi = 2*pi^2 * b2 * f.^2 * L;
+H = abs(cos(phi));
+
+%% Plot
+figure('Color','w');
+plot(f/1e9, 10*log10(H), 'LineWidth', 1,'Color','black');
+grid on; box on;
+xlabel('Frequency [GHz]');
+ylabel('Magnitude [dB]');
+% title(sprintf('IM/DD Power Fading: 10 km; 1275nm', lambda*1e9, L/1000),"Interpreter","latex");
+ylim([-20 0]);
+
+%% Mark analytic null frequencies up to order 5
+max_order = 3;
+for n = 0:max_order
+    f_null_n = sqrt( c*(2*n + 1)/(2*abs(D_si)*lambda^2*L) );
+    xline(f_null_n/1e9, '--', 'LineWidth', 1.2, ...
+        'Color', [0.1216, 0.4706, 0.7059]);
+    text(f_null_n/1e9, -15, sprintf('$f_{\\mathrm{null}, %d}=%.1f$ GHz', n, f_null_n/1e9), ...
+        'BackgroundColor', 'w', 'EdgeColor', 'k', 'Interpreter', 'latex', ...
+        'HorizontalAlignment', 'center', 'VerticalAlignment', 'middle');
+end
+
+% mat2tikz_improved('C:\Users\Silas\Documents\6971e0b65b380ca6d71c837f\02_IMDD_System\tikz\dispersion\power_fading.tikz')