Individual Signal Separation from Mixed Signal

Hi,

I have a signal 'I' which is consists of three signals. How can I separate those signals from the mixed signal 'I'. I did FFT but it did not give the satisfactory results. First three figures are the individual signal and fourth one is the mixed signal. How can I get the three individual from the mixed signals. Any help would be highly appreciated.

clc

clear all;

close all;

format long

m=1000;

I1=0.5;

I2=0.3;

I3=0.2;

L1=100*m;

L2=1000*m;

n1=1;

n2=1.444;

index=n1;

lam=m*(1.53:0.000001:1.565);

Q12=(4*pi*n1*L1)./lam;

Q23=(4*pi*n2*L2)./lam;

Q13=Q12+Q23;

figure(1)

I_first=I1+I2+2*sqrt(I1*I2).*cos(Q12);

subplot(4,1,1)

plot(lam,I_first)

I_second=I2+I3+2*sqrt(I2*I3).*cos(Q23);

subplot(4,1,2)

plot(lam,I_second)

I_third=I1+I3+2*sqrt(I1*I3).*cos(Q13);

subplot(4,1,3)

plot(lam,I_third)

I=I1+I2+I3+2*sqrt(I1*I2).*cos(Q12)+2*sqrt(I2*I3).*cos(Q23)+2*sqrt(I1*I3).*cos(Q13);

subplot(4,1,4)

plot(lam,I)