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ECOC Theroy stuff

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Silas Oettinghaus
2025-09-26 14:25:52 +02:00
parent 2c0e7a81aa
commit 9d63457030
9 changed files with 397 additions and 175 deletions
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19
projects/ECOC_2025/theory/analytic_mpi_evaluation.m
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@@ -1,13 +1,13 @@
% This script is used to evaluate Fig. 1b) in the paper "Adaptive Removal of Multipath Interference in Short Reach 112 GBd PAM-4 IM/DD Systems"
%% Parameters
df = 1e6;%150e3; % Laser linewidth [Hz]
df = 1e6; % Laser linewidth [Hz]
SIR_dB = 20; % Interference attenuation [dB]
alpha = 10^(-SIR_dB/20); % Interference attenuation [linear]
n_fiber = 1.467; % Refractive index
c = physconst('lightspeed'); % [m/s]
L = linspace(0,400,40); % Interference delay [m]
L = linspace(0,250,50); % Interference delay [m]
tau = n_fiber./c.*L; % Interference time (= tau) [s]
tau_c = 1/(pi*df); % laser coherence time [s]
@@ -22,7 +22,7 @@ N = round(Tsim*fs); % number of samples for each realization
max_delay_samples = round(max(tau)*fs); % largest delay that is evaluated (based on max. Interference delay)
phase_noise_std = sqrt(2*pi*df/fs); % standard dev. phase noise
num_realizations = 10; % number of parallel runs
num_realizations = 50; % number of parallel runs
monte_carlo_variance = zeros(num_realizations, length(L));
parfor r = 1:num_realizations
@@ -48,7 +48,9 @@ avg_of_mc_variances = mean(monte_carlo_variance, 1);
std_of_mc_variances = std(monte_carlo_variance, 0, 1);
%% Analytic variance
analytic_variance = 2*alpha^2 * (1 - exp(-2*pi*df.*tau)).^2;
L_ = linspace(0,250,500); % Interference delay [m]
tau_ = n_fiber./c.*L_;
analytic_variance = 2*alpha^2 * (1 - exp(-2*pi*df.*tau_)).^2;
%% Plot
cols = [0.3467 0.5360 0.6907
@@ -62,20 +64,21 @@ hold on;
plot(L, avg_of_mc_variances, 'LineWidth',2, 'DisplayName','Simulation','Color',cols(1,:),'LineStyle','-');
errorbar(L, avg_of_mc_variances,std_of_mc_variances, 'LineWidth',0.7,'LineStyle','none', 'DisplayName','Simulation','Color',cols(1,:),'HandleVisibility','off');
plot(L, analytic_variance, 'LineWidth',2, 'DisplayName','Analytic','Color',cols(2,:),'LineStyle','-');
plot(L_, analytic_variance, 'LineWidth',2, 'DisplayName','Analytic','Color',cols(2,:),'LineStyle','-');
xticks(coherence_length_multiples.*L_c);
xticklabels(round(coherence_length_multiples.*L_c));
xticklabels(round(coherence_length_multiples.*L_c,1));
norm_to_coherence_len = 1;
if norm_to_coherence_len
xticklabels(coherence_length_multiples);
xlabel('$\tau_c$', 'FontSize',12);
xlabel('$n \cdot L_c$', 'FontSize',12);
else
xlabel('Interference Delay [m]', 'FontSize',12);
end
xline(L_c.*coherence_length_multiples, 'LineWidth',1.5, 'DisplayName','Coh. Length','HandleVisibility','off','Color',[0.7,0.7,0.7],'LineStyle','-');
xlim([0,L(end)]);
yline(var_sat, '-.k','LineWidth',1.5, 'DisplayName','Saturation: 2$\alpha ^2$');
xlabel('Interference Delay [m]', 'FontSize',12);
grid on;
ylabel('Intensity Variance', 'FontSize',12);
title(sprintf('MPI Variance; %d MHz; SIR: %d dB',df.*1e-6,SIR_dB), 'FontSize',14);

38
projects/ECOC_2025/theory/coherence_length_plot.m
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@@ -1,32 +1,32 @@
%% Parameters
df = linspace(100e3,50e6,10000); % Laser FWHM linewidth [Hz]
df = linspace(1,50e6,10000); % Laser FWHM linewidth [Hz]
n_fiber = 1.467; % Fiber group index
c = 3e8; % Speed of light [m/s]
% Compute coherence length (1/e of mean-fringe decay)
tau_c = 1./(pi*df);
L_c = (c/n_fiber) .* tau_c; % Coherence length [m]
L_c = (c.* tau_c/n_fiber) ; % Coherence length [m]
%% Plot
figure('Color','w');
loglog(df/1e6, L_c, 'LineWidth',2,'LineStyle','-'); % linewidth in MHz
xticks([0.1, 1, 10, 50]);
yticks([1, 10, 100, 1000]);
yticklabels({'1','10','100','1000'})
% xticks([0.1, 1, 10, 50]);
% yticks([1, 10, 100, 1000]);
% yticklabels({'1','10','100','1000'})
grid on; box on;
xlabel('Laser linewidth [MHz]','FontSize',12,'Interpreter','none');
ylabel('Coherence length [m]','FontSize',12,'Interpreter','none');
title('Coherence Length vs. Laser Linewidth','FontSize',14,'Interpreter','none');
xlabel('Laser linewidth [MHz]','FontSize',12,'Interpreter','latex');
ylabel('Coherence length [m]','FontSize',12,'Interpreter','latex');
title('Coherence Length vs. Laser Linewidth','FontSize',14,'Interpreter','latex');
%% Annotate some key points
hold on;
freqs = [150e3, 1e6, 10e6, 50e6]; % [Hz]
for f = freqs
x = f/1e6;
y = (c/n_fiber) * (1/(pi*f));
scatter(x,y,'Marker','x','LineWidth',1,'MarkerEdgeColor','black');
text(x*1.1,y, sprintf('%.2f MHz', f/1e6), ...
'FontSize',10,'HorizontalAlignment','left');
end
% hold on;
% freqs = [150e3, 1e6, 10e6, 50e6]; % [Hz]
% for f = freqs
% x = f/1e6;
% y = (c/n_fiber) * (1/(pi*f));
% scatter(x,y,'Marker','x','LineWidth',1,'MarkerEdgeColor','black');
%
% text(x*1.1,y, sprintf('%.2f MHz', f/1e6), ...
% 'FontSize',10,'HorizontalAlignment','left');
%
% end