clc;?clear?all;?close?all;?clf;
cputime=0;
tic;
ln=1;
i=sqrt（-1）;
Po=.00064;?%input?pwr?in?watts
alpha=0;?%?Fiber?loss?value?in?dB/km
alph=alpha/（4.343）;?%Ref?page#55?eqn?2.5.3?Fiber?optic?Comm?by?GP?Agrawal
gamma=0.003;?%fiber?non?linearity?in?/W/m
to=125e-12;?%initial?pulse?width?in?second
C=-2;?%Input?chirp?parameter?for?first?calculation
b2=-20e-27;?%2nd?order?disp.?（s2/m）
Ld=（to^2）/（abs（b2））;?%dispersion?length?in?meter
pi=3.1415926535;
Ao=sqrt（Po）;?%Amplitude
%----------------------------------------------------------
tau?=-?4096e-12:1e-12:?4095e-12;%??dt=t/to
?dt=1e-12;
?rel_error=1e-5;
?h=1000;%?step?size
for?ii=0.1:0.1:1.5?%the?various?fiber?lengths?can?be?varied?and?this?vector?can?be?changed
z=ii*Ld;
????u=Ao*exp（-（（1+i*（-C））/2）*（tau/to）.^2）;%page#47?G.P.AGrawal
????figure（1）
???plot（abs（u）‘r‘）;
???title（‘Input?Pulse‘）;?xlabel（‘Time‘）;?ylabel（‘Amplitude‘）;
grid?on;
hold?on;
l=max（size（u））;??
%%%%%%%%%%%%%%%%%%%%%%%
fwhm1=find（abs（u）>abs（max（u）/2））;
fwhm1=length（fwhm1）;
dw=1/l/dt*2*pi;
w=（-1*l/2:1:l/2-1）*dw;
u=fftshift（u）;
?w=fftshift（w）;
spectrum=fft（fftshift（u））;?%Pulse?spectrum
for?jj=h:h:z
spectrum=spectrum.*exp（-alph*（h/2）+i*b2/2*w.^2*（h/2））?;?
f=ifft（spectrum）;
f=f.*exp（i*gamma*（（abs（f））.^2）*（h））;
spectrum=fft（f）;
spectrum=spectrum.*exp（-alph*（h/2）+i*b2/2*w.^2*（h/2））?;?
end
f=ifft（spectrum）;
op_pulse（ln:）=abs（f）;%saving?output?pulse?at?all?intervals
fwhm=find（abs（f）>abs（max（f）/2））;
fwhm=length（fwhm）;
ratio=fwhm/fwhm1;?%PBR?at?every?value
pbratio（ln）=ratio;%saving?PBR?at?every?step?size
dd=atand（（abs（imag（f）））/（abs（real（f））））;
phadisp（ln）=dd;%saving?pulse?phase
ln=ln+1;
end
toc;
cputime=toc;
figure（2）;
mesh（op_pulse（1:1:ln-1:））;
title（‘Pulse?Evolution‘）;
xlabel（‘Time‘）;?ylabel（‘distance‘）;?zlabel（‘amplitude‘）;
figure（3）
plot（pbratio（1:1:ln-1）‘k‘）;
xlabel（‘Number?of?steps‘）;
ylabel（‘Pulse?broadening?ratio‘）;
grid?on;
hold?on;
figure（5）
plot（phadisp（1:1:ln-1）‘k‘）;
xlabel（‘distance?travelled‘）;
ylabel（‘phase?change‘）;
grid?on;
hold?on;
disp（‘CPU?time:‘）?disp（cputime）;

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