Question

write a matlab code to simulate fiber optics communication system on matlab simulink

Answer 1

function output = ssprop_matlabfunction_modified(input)

nt = input(1);

u0 = input(2:nt+1);

dt = input(nt+2);

dz = input(nt+3);

nz = input(nt+4);

alpha_indB = input(nt+5);

betap = input(nt+6:nt+9);

gamma = input(nt+10);

P_non_thres = input(nt+11)

maxiter = input(nt+12);

tol = input(nt+13);

tic;

%tmp = cputime;

% This section solves the NLSE for pulse propagation in an optical fiber

using the SSF method

% The following effects are included: group velocity dispersion

% (GVD),higher order dispersion, loss, and self-phase modulation (gamma).

%

% USAGE

%

% u1 = ssprop(u0,dt,dz,nz,alpha,betap,gamma);

% u1 = ssprop(u0,dt,dz,nz,alpha,betap,gamma,maxiter);

% u1 = ssprop(u0,dt,dz,nz,alpha,betap,gamma,maxiter,tol);

%

% INPUT

%

% u0 - starting field amplitude (vector)

% dt - time step - [in ps]

% dz - propagation stepsize - [in km]

% nz - number of steps to take, ie, ztotal = dz*nz

% alpha - power loss coefficient [in dB/km], need to convert to linear to

% %have P=P0*exp(-alpha*z)

% betap - dispersion polynomial coefs, [beta_0 ... beta_m] [in ps^(m-1)/km]

% gamma - nonlinearity coefficient [in (km^-1.W^-1)]

% maxiter - max number of iterations (default = 4)

% tol - convergence tolerance (default = 1e-5)

%% OUTPUT

%% u1 - field at the output

%

% Convert alpha_indB to alpha in linear domain

%---------------

alpha = log(10)*alpha_indB/10; % alpha (1/km)

%---------------

ntt = length(u0);

w = 2*π*[(0:ntt/2-1),(-ntt/2:-1)]’/(dt*nt);

%w = 2*π*[(ntt/2:ntt-1),(1:ntt/2)]’/(dt*ntt);

clear halfstep

halfstep = -alpha/2;

for ii = 0:length(betap)-1;

halfstep = halfstep - j*betap(ii+1)*(w.^ii)/factorial(ii);

end

clear LinearOperator

% Linear Operator in Split Step method

LinearOperator = halfstep;

% pause

halfstep = exp(halfstep*dz/2);

u1 = u0;

ufft = fft(u0);

% Nonlinear operator will be added if the peak power is greater than the

% Nonlinear threshold

iz = 0;

while (iz < nz) & (max((abs(u1).^2 + abs(u0).^2)) > P_non_thres)

iz = iz+1;

uhalf = ifft(halfstep.*ufft);

for ii = 1:maxiter,

uv = uhalf .* exp(-j*gamma*(abs(u1).^2 + abs(u0).^2)*dz/2);

ufft = halfstep.*fft(uv);

uv = ifft(ufft);

%fprintf(‘You are using SSFM\n’);

if (max(uv-u1)/max(u1) < tol)

u1 = uv;

break;

else

u1 = uv;

end

end

if (ii == maxiter)

warning(sprintf(‘Failed to converge to %f in %d iterations’,...

tol,maxiter));

end

u0 = u1;

end

if (iz < nz) & (max((abs(u1).^2 + abs(u0).^2)) < P_non_thres)

% u1 = u1.*rectwin(ntt);

ufft == fft(u1);

ufft = ufft.*exp(LinearOperator*(nz-iz)*dz);

u1 = ifft(ufft);

%fprintf(‘Implementing Linear Transfer Function of the Fibre

Propagation’);

end

toc;

output = u1;

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