two.m

calculating fiber eigen modes

%两层模型的色散方程的图解法
function y=two(wl,l,neff)

r1=4e-6;
nc=1.458;
n=1.45;


k=2.*pi./wl;
beta=k.*neff;
u=r1.*sqrt(k.^2.*nc.^2-beta.^2);
w=r1.*sqrt(beta.^2-k.^2.*n.^2);

left=u.*besselj(l-1,u)./besselj(l,u);
right=-w.*besselk(l-1,w)./besselk(l,w);

y=left-right;