adding factor of 1 to coupling back into the same mode

src/new/coupling_coefficients/FT_Winkler_coupling.m

@@ -72,6 +72,12 @@ function [ann] = FT_Winkler_coupling(lambda,w,n,n_,tilt,h0,slambda,phi)
 %     % Final coupling coefficient
 %     ann = a0 * (A1+A2); 
 
+    % If coupling into the same mode
+    dnn = 0;
+    if n==n_
+        dnn = 1;
+    end
+
     p = min(n,n_);
     l = n-n_;
     
@@ -81,7 +87,7 @@ function [ann] = FT_Winkler_coupling(lambda,w,n,n_,tilt,h0,slambda,phi)
     
     gp = FT_init_gauss_param(lambda,1,'z',0,'w0',W);
     
-    ann = 2 * k * h0 * sqrt(pi/2) * W * abs(FT_LG_field(gp,p,l,r,0,[0,0,0])) * cos(phi + l*pi/2);
+    ann = dnn + 2 * k * h0 * sqrt(pi/2) * W * abs(FT_LG_field(gp,p,l,r,0,[0,0,0])) * cos(phi + l*pi/2);
     
 
 end