单模光纤与多模光纤的耦合

% 单模光纤与多模光纤的耦合

clear all

format long

a1 = 52.5e-6; % 多模光纤半径a

a0 = 4.1e-6; %单模光纤半径

wl = 1550e-9; %波长lambda

n01 = 1.4544; n02 = 1.45; %单模光纤折射率

n1 = 1.4574; n2 = 1.4420; %多模光纤折射率

V0 = 2*pi*a0/wl*sqrt(n01^2-n02^2); %单模归一化频率

w = a0/sqrt(log(2)*(0.65+1.619*V0^-1.5+2.879*V0^-6)); %高斯光束半高宽

v = 1:50; %纤芯模序数

V = 2*pi*a1/wl*sqrt(n1^2-n2^2); %多模归一化频率

uv = (2*v-1/2)*pi/2;

wv = sqrt(V^2-uv.^2);

up = 2*(w/a1)^2*exp(-0.5*w^2/a1*uv.^2);

down1 = besselj(0,uv).^2 + besselj(1,uv).^2;

down2 = besselk(1,wv).^2./besselk(0,wv).^2;

down3 = besselj(0,uv).^2;

down = down1+(down2-1).*down3;

eta = real(up./down);

%{

eta = 2*(w/a1)^2*exp(-0.5*w^2/a1*((2*v-1/2)*pi/2).^2)./ ...,

(besselj(0,((2*v-0.5)*pi/2)).^2 + besselj(1,((2*v-0.5)*pi/2)).^2+ ...,

(besselk(1,sqrt(V^2-((2*v-0.5)*pi/2).^2)).^2./besselk(0,sqrt(V^2-((2*v-0.5)*pi/2).^2)).^2 -1).* ...,

besselj(0,((2*v-0.5)*pi/2)).^2);

%}

plot(v,eta,'*','markersize',5)