########################################################
# file: ring_group_delay_fdtd.lsf
#
# Description: Extract Hz from a time monitor
# 	to calcualte group delay caused by the ring	 
#
# Copyright 2013, Lumerical Solutions, Inc.
########################################################

#extract data from a time monitor
Hz = pinch(getdata("t_through","Hz"));
t = getdata("t_through","t");
plot(t*1e12,Hz, "t (ps)","H-Field");

#fourier transform and extract the phase
f = linspace(c/1600e-9,c/1500e-9,50000);
w = 2*pi*f;
Hw = czt(Hz,t,w)/sourcenorm(f);
phi = unwrap(angle(Hw));
plot(c/f*1e9,phi,"Wavelength(nm)","phase");

#differentiate phase w.r.t frequency
w2 = 0.5*(w(2:length(w))+w(1:length(w)-1));
l2 = c/(w2)*2*pi;
gd = phi(2:length(phi))-phi(1:length(phi)-1);
gd = gd / (w(2:length(w))-w(1:length(w)-1));
plot(l2*1e9,gd*1e12,"Wavelength (nm)","Group delay (ps)");