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BCJR implementation

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WDM code added (Pol Cont., Opt MUX/DEMUX, Opt Atten, DP_Fiber) -> the codebase is not optimized to always work with dp signals!
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Silas Oettinghaus
2025-09-17 13:58:58 +02:00
parent f4a22d23a2
commit 4099f6820f
37 changed files with 3643 additions and 593 deletions
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122
Classes/02_optical/Optical_Demultiplex.m Normal file
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classdef Optical_Demultiplex < handle
% Dual-Polarization optical demultiplexer
% - Input: total-field signal
% - Output: single-channel dual-pol signal objects in cell array
%
% Notes:
% Opt_sig_wdm_demux = Optical_Demultiplex("attenuation",0,"B",200e9,"filtype",1,"fs_out",Opt_sig_wdm_rx.fs/4,"fs_in",Opt_sig_wdm_rx.fs,"lambda_center",1310).process(Opt_sig_wdm_rx);
% Opt_sig_wdm_demux{1}.spectrum("fignum",1100,"displayname",'bla','normalizeTo0dB',0,'max_num_lines',4);
% Opt_sig_wdm_demux{2}.spectrum("fignum",1100,"displayname",'bla','normalizeTo0dB',0,'max_num_lines',4);
properties (Access=public)
fs_in % [Hz] (optional; inferred from data_in.fs if omitted)
fs_out % [Hz]
lambda_center % [nm] center wavelength of the WDM grid
wavelengthplan % [nm]
attenuation = 0 % [dB] insertion loss
filtype = 1 % 1=Gaussian, 2=Rectangle, 3=No filter
B = 200e9 % [Hz] 3 dB bandwidth (Gaussian) or width (Rect)
mgauss = 3 % Gaussian order (multiple of 1/2)
% Derived/utility
c = physconst('lightspeed') % [m/s]
end
methods (Access=public)
function obj = Optical_Demultiplex(options)
arguments
options.fs_in = []
options.fs_out
options.lambda_center
options.wavelengthplan
options.attenuation = 0
options.filtype = 1
options.B = 2.5e10
options.mgauss = 3
end
fn = fieldnames(options);
for n = 1:numel(fn)
try obj.(fn{n}) = options.(fn{n}); end
end
end
function signalclasses_out = process(obj, signalclass_in)
% ---- Infer wavelength: either given or from input total signal
if isempty(obj.wavelengthplan)
obj.wavelengthplan = signalclass_in.lambda; %meter
else
if all(500e-9 < obj.wavelengthplan) && all(obj.wavelengthplan < 1500e-9) %check if given in nm
obj.wavelengthplan = obj.wavelengthplan.*1e-9;
end
end
% ---- Infer input sampling rates
if isempty(obj.fs_in)
assert(isprop(signalclass_in,'fs') && ~isempty(signalclass_in.fs), ...
'Dual_Pol_Demultiplexer: data_in.fs missing and options.fs_in not provided.');
obj.fs_in = signalclass_in.fs;
end
% Runs demultiplexing in one go and appends a logbook entry.
[x_envelopes,y_envelopes] = obj.process_(signalclass_in.signal);
for n = 1:min(size(x_envelopes))
signalclasses_out{n} = signalclass_in;
signalclasses_out{n}.signal = [x_envelopes(:,n), y_envelopes(:,n)];
signalclasses_out{n} = signalclasses_out{n}.resample("fs_in",obj.fs_in,"fs_out",obj.fs_out);
signalclasses_out{n}.lambda = obj.wavelengthplan(n);
lbdesc = ['Opt. Demux ', num2str( obj.wavelengthplan(n)),' nm'];
signalclasses_out{n} = signalclasses_out{n}.logbookentry(lbdesc);
end
end
function [x_envelopes,y_envelopes] = process_(obj, signal_in)
% Core demux:
% - frequency translate target channel to baseband
% - apply optical filter H
% - resample to fs_out
arguments (Input)
obj
signal_in
end
w = obj.fs_out ./ obj.fs_in ;
blocklen_in = length(signal_in);
blocklen_out = w*blocklen_in;
att = 1/10^(obj.attenuation/10);
faxis=linspace( -obj.fs_in/2 , obj.fs_in/2 , blocklen_in+1 );
faxis=ifftshift(faxis(1:end-1));
switch obj.filtype
case 1
H=exp(-(faxis/obj.B).^(2*obj.mgauss)*log(2)*2^(2*obj.mgauss-1)).';
case 2
%all zero filter
H=zeros(1,length(faxis)).';
%set filter = 1 inside bandwidth -B/2 <-> B/2
H(abs(faxis)<=obj.B/2)=1;
case 3
H = 1;
end
f_mid = obj.c/(obj.lambda_center*1e-9); % center frequency of WDM grid [Hz]
f_channels = obj.c./(obj.wavelengthplan) ;
N = numel(f_channels);
df_T = f_mid - f_channels;
pha = mod(-2*pi*(0:blocklen_in-1).'.*df_T/obj.fs_in, 2*pi);
lo = cos(pha)+1i*sin(pha);
x_envelopes = ifft(fft(att.*signal_in(:,1).*lo).*H);
y_envelopes = ifft(fft(att.*signal_in(:,2).*lo).*H);
end
end
end