求解 特征方程

global n1 n2 n3 r1 r2 lambda k V n1 = 1.4681; n2 = 1.4628; n3 = 1; R1 = 8.3E-6; R2 = 125E-6; r1 = R1/2; r2 = R2/2; lambda = (1548:0.01:1552)*1E-9; %%%%%%%%%%%%%%%%%%%%% ´¿¹èо for fused silica(SiO2) %n2 = sqrt(1+0.6961663*lambda.^2./(lambda.^2-0.0684043^2) ... % +0.4079426*lambda.^2./(lambda.^2-0.1162414^2) ... % +0.8974794*lambda.^2./(lambda.^2-9.896161^2)); %plot(lambda*1E3,n2) k = 2*pi./lambda; U_Trans = Feigin(n1,n2,n3,r1,r2,lambda); beta = sqrt(k.^2.*n1^2-U_Trans.^2/r1/r1); figure plot(lambda*1E9,beta) Lambda = 0.529e-6; delta = beta-pi/Lambda; L = [2 5 10 20].*1E-3; kappa = 5./L; s = zeros(length(L),length(lambda)); R = zeros(length(L),length(lambda)); for i = 1:length(L) s(i,:) = sqrt(kappa(i)^2-delta.^2); R(i,:) = 5*5*sinh(s(i,:).*L(i)).^2./(s(i,:).^2.*cosh(s(i,:).*L(i)).^2+delta.^2.*sinh(s(i,:).*L(i)).^2); end R = zeros(length(L),length(lambda)); for j = 1:length(L) R(j,:) = 5*5*sinh(s(j,:).*L(j)).^2./(s(j,:).^2.*cosh(s(j,:).*L(j)).^2+delta.^2.*sinh(s(j,:).*L(j)).^2); end figure for ii = 1:length(L) subplot(2,2,ii) plot(lambda*1E9,R(ii,:)/max(R(ii,:))) xlabel('²¨³¤/nm'); ylabel('·´ÉäÂÊ'); xlim([1548,1552]) legend('\kappaL=5')%%%%%%%%%%%%%%%%% end