长周期光纤光栅.m

数值计算长周期光纤光栅

clear 
format long 
n=1024;m=4;
neff=1.45;
bolong=1e-9*linspace(1540,1560,n);
bolongb=1550e-9;dn=2e-3;v=1;



dbeta=2*neff*pi*(1./bolong-1./bolongb);
k=pi*dn/bolongb;
L=4/k/m;
q=sqrt(k.^2-dbeta.^2);


for j=1:n 
%  Fai(j)=0;
%  S11(j,1)=(cosh(q(j)*L)-i*dbeta(j)/q(j)*sinh(q(j)*L))*exp(-i*Fai(j)/2);
%  S12(j,1)=-(i*k/q(j)*sinh(q(j)*L))*exp(i*Fai(j)/2);
%  S21(j,1)=(i*k/q(j)*sinh(q(j)*L))*exp(-i*Fai(j)/2);
%  S22(j,1)=(cosh(q(j)*L)+i*dbeta(j)/q(j)*sinh(q(j)*L))*exp(i*Fai(j)/2);
%  
% jj=1; 

 Fai(1)=0;L(1)=220e-6;
 S11(j,1)=(cosh(q(j)*L(1))-i*dbeta(j)/q(j)*sinh(q(j)*L(1)))*exp(-i*Fai(1)/2);
 S12(j,1)=-(i*k/q(j)*sinh(q(j)*L(1)))*exp(i*Fai(1)/2);
 S21(j,1)=(i*k/q(j)*sinh(q(j)*L(1)))*exp(-i*Fai(1)/2);
 S22(j,1)=(cosh(q(j)*L(1))+i*dbeta(j)/q(j)*sinh(q(j)*L(1)))*exp(i*Fai(1)/2);

 SS11(j,1)=S11(j,1);
 SS12(j,1)=S12(j,1);
 SS21(j,1)=S21(j,1);
 SS22(j,1)=S22(j,1);
 
 
for jj=2:m
    if jj==2|jj==3
       Fai(jj)=pi;L(jj)=502e-6;
%     elseif 
%         Fai(jj)=pi;
%     elseif jj==7
%         Fai(jj)=pi;
    else
        Fai(jj)=pi;L(jj)=220e-6;
    end
    S11(j,jj)=(cosh(q(j)*L(jj))-i*dbeta(j)/q(j)*sinh(q(j)*L(jj)))*exp(-i*Fai(jj)/2);
    S12(j,jj)=-(i*k/q(j)*sinh(q(j)*L(jj)))*exp(i*Fai(jj)/2);
    S21(j,jj)=(i*k/q(j)*sinh(q(j)*L(jj)))*exp(-i*Fai(jj)/2);
    S22(j,jj)=(cosh(q(j)*L(jj))+i*dbeta(j)/q(j)*sinh(q(j)*L(jj)))*exp(i*Fai(jj)/2);
    
    SS11(j,jj)=S11(j,jj)*SS11(j,jj-1)+S12(j,jj)*SS21(j,jj-1);
    SS12(j,jj)=S11(j,jj)*SS12(j,jj-1)+S12(j,jj)*SS22(j,jj-1);
    SS21(j,jj)=S21(j,jj)*SS11(j,jj-1)+S22(j,jj)*SS21(j,jj-1);
    SS22(j,jj)=S21(j,jj)*SS12(j,jj-1)+S22(j,jj)*SS22(j,jj-1);
    
    
   
    
end
R(j)=(abs(SS21(j,1)/SS22(j,1))).^2;

%R(j)=(abs(-SS21(j,jj)/SS22(j,jj))).^2;
end
% figure(1)
% plot(dbeta,R,'r')
figure(2)
plot(bolong*1e9,1-R,'b')