Hi Jojo Mathew,
as per you have mentioned about the three windows in optical domain, they are experimentally found out from the optical fiber characteristics, such as attenuation, dispersion. The optical fiber posses lowest dispersion (dispersion is pulse broadening due to multi-path propagation ) at the wavelength of 1310 nm often called as zero dispersion window. at wavelength of 1550 nm the optical fiber posses lowest attenuation (around 0.16 dB/km) known as zero loss windows (attenuation is degradation in signal power due to propagation).
So basically all the three windows are made depending on the fiber characteristics.
Regards,
Dhiman