CLEANUP - changes to folder structure

Theory/Optical/Dispersion/dispersion_10km.m

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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