#In order to force a constant effective index, set the group index and effective index to the same value
#In order to enter optical length simply set effective index/group index to '1'

#The center frequency for the waveguide propagation properties

f0 = 193.1e12;
ng = 8.05894;
neff = ng;
FSR = 120e9;
lambda = c / f0;

#Parameters to generate 
#Optical Half-Band Filters
#K. Jinguji and M. Oguma, "Optical Half-Band Filters"
#J. Lightwave Technol. 18, 252- (2000)

#The wavegude length
deltal = c / FSR  / ng;

#From table I (page 255)
#FIR chebyshev half-band filter
#circuit parameters (x*pi)

teta0 = 0.3498;
teta1 = 0.2448;
teta2 = 0.4186;
teta3 = 0.0797;
teta4 = 0.25;

#Phase shift multiplier

phi1 = 1.0;
phi2 = 0.0;
phi3 = 1.0;
phi4 = 0.0;

#The wavegude length

deltal1 = 2 * deltal;
deltal2 = 2 * deltal;
deltal3 = 2 * deltal;
deltal4 = deltal;

#constant phase shift
#shift = 2 * pi * f0 / c * deltal * ( neff - ng )
#estimate neff from phase shift multiplier
#effective index required to cause phin*pi phase shift:

neff1 = phi1 * c / 2.0 / f0 / deltal1 + ng;
neff2 = phi2 * c / 2.0 / f0 / deltal2 + ng;
neff3 = phi3 * c / 2.0 / f0 / deltal3 + ng;
neff4 = phi4 * c / 2.0 / f0 / deltal4 + ng;

#Coupling coefficients
r0 = sin( teta0 * pi ) ^ 2;
r1 = sin( teta1 * pi ) ^ 2;
r2 = sin( teta2 * pi ) ^ 2;
r3 = sin( teta3 * pi ) ^ 2;
r4 = sin( teta4 * pi ) ^ 2;

switchtodesign;

setnamed("WC1","coupling coefficient 1",r0);

setnamed("SW1","frequency",f0);
setnamed("SW1","length",deltal1);
setnamed("SW1","group index 1",ng);
setnamed("SW1","effective index 1",neff1);

setnamed("WC2","coupling coefficient 1",r1);

setnamed("SW2","frequency",f0);
setnamed("SW2","length",deltal2);
setnamed("SW2","group index 1",ng);
setnamed("SW2","effective index 1",neff2);

setnamed("WC3","coupling coefficient 1",r2);

setnamed("SW3","frequency",f0);
setnamed("SW3","length",deltal3);
setnamed("SW3","group index 1",ng);
setnamed("SW3","effective index 1",neff3);

setnamed("WC4","coupling coefficient 1",r3);

setnamed("SW4","frequency",f0);
setnamed("SW4","length",deltal4);
setnamed("SW4","group index 1",ng);
setnamed("SW4","effective index 1",neff4);

setnamed("WC5","coupling coefficient 1",r4);