Vinit,

   Could you provide more information on what you are trying
to do? In past discussion with designers, they seem to
separate the "optical" characteristics of the diode from the
"electrical" characteristics. For example, correct modeling of
the capacitance is critical because that effects the bandwidth
of the Trans-Impedance Amplifier. However,  the IC  designers
I have spoken with don't seem to care as much about
the "optical" characteristics of the photo-diode. Are you actually
trying to model the entire closed-loop system, for example, DVD
head positioningg, in order to model the loop dynamics?
Could you just use a table model to convert laser power
into current?

                                                    Best Regards,

                                                       Sheldon