How to compare RF-LO dBc/Hz values with my optical LO

i have a RF-LO specification
-50dBc/Hz @ 1KHz
-70dBc/Hz @ 10KHz
-90dBc/Hz @ 100KHz
-110dBc/Hz @1MHz

now i like to compare this with an optically generated LO whose PSD is

S(f)=(2*A/pi)*(w/(4*(f-f0)^2+w^2))
where, A=is the amplitude;
f0=carrier frequency;
w=LO linewidth;
i have calculated the LO power (carrier) and plot this PSD of the phase noise S(f) as dBc/Hz.
Then varies the w to know on which linewidth (FWHM) of the beat signal it fits to the RF-LO and it comes as 30Hz. This means the laser linewidth (FWHM) is 15 Hz.

what i am doing wrong? can anyone plz help?

thanks a lot
Reza