41 lines
1.4 KiB
Matlab
41 lines
1.4 KiB
Matlab
%% ============================================================
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% Minimal IM/DD Power Fading Plot
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% ============================================================
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%% Fiber and system parameters
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lambda0 = 1310e-9; % zero-dispersion wavelength [m]
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lambda = 1275e-9; % operating wavelength [m]
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S0 = 0.09; % dispersion slope [ps/(nm²·km)]
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L = 10e3; % fiber length [m]
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c = physconst('lightspeed');
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%% Derived quantities
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S0_si = S0 * 1e3; % → s/m³
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D_lambda = (S0/4) * (lambda*1e9 - (lambda0*1e9)^4/(lambda*1e9)^3); % ps/(nm·km)
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D_si = D_lambda * 1e-6; % → s/m²
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b2 = -D_si * lambda^2 / (2*pi*c); % s²/m
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%% Frequency grid
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f_max = 150e9;
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f = linspace(0, f_max, 4000); % [Hz]
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%% IM/DD transfer function (power fading)
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phi = 2*pi^2 * b2 * f.^2 * L;
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H = abs(cos(phi));
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%% Plot
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figure('Color','w');
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plot(f/1e9, 10*log10(H), 'LineWidth', 1.8,'Color','black');
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grid on; box on;
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xlabel('Frequency [GHz]');
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ylabel('Magnitude [dB]');
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title(sprintf('IM/DD Power Fading: 10 km; 1275nm', lambda*1e9, L/1000),"Interpreter","latex");
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ylim([-30 0]);
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%% Mark analytic first-null frequency
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f_null = sqrt(c*(0.5)/(abs(D_si)*lambda^2*L));
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xline(f_null/1e9, 'r--', 'LineWidth', 1.2, ...
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'Label', sprintf('f_{null}=%.1f GHz', f_null/1e9), ...
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'LabelOrientation', 'horizontal', 'LabelVerticalAlignment', 'bottom');
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