# fix the mistake line 91 function

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abed il 3 Dic 2013
Commentato: Image Analyst il 24 Ago 2019
% This program simulates a single-channel fiber transmission link
% using the symmetrized split-step Fourier algorithm.
%
% written by Jong-Hyung Lee
clear all
%=============================================
% Define Time Window and Frequency Window
%=============================================
taum = 2000;
dtau = 2*taum/2^11;
tunit= 1e-12; % make time unit in psec
tau = (-taum:dtau:(taum-dtau))*tunit;
fs = 1/(dtau*tunit);
tl = length(tau)/2;
w = 2*pi*fs*(-tl:(tl-1))/length(tau); % w=angular freq.
wst = w(2)-w(1);
%=============================================
% Define Physical Parameters
%=============================================
c = 3e5; %[km/sec] speed of light
ram0 = 1.55e-9; %[km] center wavelength
k0 = 2*pi/ram0;
n2 = 6e-13 ; %[1/mW]
gamm = k0*n2 ; %[1/(km*mW)]
alphaDB = 0.2 ; % [dB/km] Power Loss
alpha = alphaDB/(10*log10(exp(1))); %[1/km] Power Loss in linear scale
% Dispersion parameters (beta3 term ignored)
Dp = -2; % [ps/nm.km]
beta2 = -(ram0)^2*Dp/(2*pi*c); % [sec^2/km]
%=============================================
% Define Input Signal
%=============================================
% A single Gaussian pulse is assumed.
Po = 2; % [mW] initial peak power of signal source
C = 0; % Chirping Parameter
m = 1; % Super Gaussian parameter (m=1 ==> Gaussian)
t0 = 50e-12; %[sec] initial pulse width
at = sqrt(Po)*exp(-0.5*(1+1i*C)*(tau./t0).^(2*m)); % Input field in the
time domain
a0 = fft(at(1,:));
af = fftshift(a0); % Input field in the frequency domain
%=============================================
% Define Simulation Distance and Step Size
%=============================================
zfinal = 100; %[km] propagation distance
pha_max = 0.01; %[rad] maximum allowable phase shift due to the
nonlinear operator
% pha_max = h*gamma*Po (h = simulation step length)
h = fix(pha_max/(gamm*Po)); % [km] simulation step length
M = zfinal/h; % Partition Number
% Define Dispersion Exp. operator
% Dh = exp((h/2)*D^), D^=-(1/2)*i*sgnb2*P, P=>(-i*w)^2
Dh = exp((h/2)*(-alpha/2+(1i/2)*beta2*w.^2)); %
%================================================%
% Propagation Through Fiber %
%================================================%
% Call the subroutine, sym_ssf.m for the symmetrized split-step Fourier
method
[bt,bf] = sym_ssf(M,h,gamm,Dh,af);
% Optical amplifier is assumed ideal (flat frequency response and no noise)
GdB = 20; % [dB] optical amplifier power gain
gainA = sqrt(10^(GdB/10)); % field gain in linear scale
rt = gainA*bt;
% plot the received power signal
figure(1)
plot(tau,abs(rt).^2,'r')
function [to,fo] =symssf(M,h,gamma,Dh,uf0)
% Symmetrized Split-Step Fourier Algorithm
%
% ==Inputs==
% M = Simulation step number ( M*h = simulation distance )
% h = Simulation step
% gamma = Nonlinearity coefficient
% Dh = Dispersion operator in frequency domain
% uf0 = Input field in the frequency domain
%
% ==Outputs==
% to = Output field in the time domain
% fo = Output field in the frequency domain
%
% written by Jong-Hyung Lee
for k = 1:M
%=============================================================
% Propagation in the first half dispersion region, z to z+h/2
%=============================================================
Hf = Dh.*uf0;
%==========================================================
% Initial estimate of the nonlinear phase shift at z+(h/2)
%==========================================================
% Initial estimate value
ht = ifft(Hf); % time signal after h/2 dispersion region
pq = ht.*conj(ht); % intensity in time
u2e = ht.*exp(h*1i*gamma*pq); %Time signal
%=============================================================
% Propagation in the second Dispersion Region, z+(h/2) to z+h
%=============================================================
u2ef = fft(u2e);
u3ef = u2ef.*Dh;
u3e = ifft(u3ef);
u3ei = u3e.*conj(u3e);
%========================================================
% Iteration for the nonlinear phase shift(two iterations)
%========================================================
u2 = ht.*exp((h/2)*1i*gamma*(pq+u3ei));
u2f = fft(u2) ;
u3f = u2f.* Dh;
u4 = ifft(u3f);
u4i = u4.*conj(u4);
u5 = ht.*exp((h/2)*1i*gamma*(pq+u4i));
u5f = fft(u5);
uf0 = u5f.*Dh;
u6 = ifft(uf0); u6i = u6.*conj(u6);
%=============================================================
% Maximum allowable tolerance after the two iterations
etol = 1e-5;
if abs(max(abs(u6i))-max(abs(u4i)))/max(abs(u6i)) > etol
disp('Peak value is not converging! Reduce Step Size'), break
end
%=============================================================
end
to = u6; fo = uf0;
##### 3 CommentiMostra 1 commento meno recenteNascondi 1 commento meno recente
Modificato: Ghislaine Flore Kabadiang ngon il 23 Ago 2019
Please what is sym_ssf and where did you define it? I got an error in Matlab because of that.
Image Analyst il 24 Ago 2019
Did you see my solution below? It seems you overlooked it.

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### Risposta accettata

Image Analyst il 3 Dic 2013
You're calling sym_ssf() but the function is actually called symssf() with no underline.
##### 5 CommentiMostra 3 commenti meno recentiNascondi 3 commenti meno recenti
Image Analyst il 3 Dic 2013
See attached. It runs fine with no errors.
abed il 4 Dic 2013
thank you

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