# fix the mistake line 91 function

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abed on 3 Dec 2013
Commented: Image Analyst on 24 Aug 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;

Jos (10584) on 3 Dec 2013
You're more likely to receive an answer if you indicate what the mistake is. Note that we do not see any line numbers here ...
Please what is sym_ssf and where did you define it? I got an error in Matlab because of that.
Image Analyst on 24 Aug 2019
Did you see my solution below? It seems you overlooked it.

Image Analyst on 3 Dec 2013
You're calling sym_ssf() but the function is actually called symssf() with no underline.

abed on 3 Dec 2013
I did what you told me and still it didn't work they told me about that I should put semicolon inside the function I don't know why and the interval bracket has an error which I couldn't solve ??????
Image Analyst on 3 Dec 2013
See attached. It runs fine with no errors.
abed on 4 Dec 2013
thank you