Comment on “Thermal phase noise in Fabry-Pérot resonators and fiber Bragg gratings”

Abstract

Skolianos et al. [Phys. Rev. A 89, 033818 (2014)] recently published a derivation of the thermal phase noise in a Fabry-P\'erot resonator. We point out that the thermally driven noise properties of an optical resonator can only be understood from the derivation of the signal-to-noise ratio and not from consideration of phase noise alone. The differences in expressions for the thermal phase noise given in the published literature (e.g., Ref. [5] of Skolianos et al. 2014) and those derived by Skolianos et al. [Phys. Rev. A 89, 033818 (2014)] arise only from differences in definition of optical phase and do not result in incorrect calculation of thermodynamically driven cavity length fluctuations.