There is formula of Shennon wich describe relation between channel capacity and power of signal and noise in this channel. If we will use this formula for analyze some optical resonator (for example Fabri-Perrot) as telecommunication channel that we should use information about noises in it. If we imagine a simple Fabri-Perrot resonator then it will be two translucent mirrors. One mirror is input of system and another is output. This system is filter for light which pass across it. Where noise in here? What kind of noise i should analyze? The optical resonator is passiv system and i think only exist quantum noise in here.