Noise factor of Brillouin amplifiers*

Stimulated Brillouin scattering, a unique optical nonlinearity arising from photon-phonon interactions, has formed the basis for a large class of optical signal processing devices in fiber and on-chip systems, including Brillouin amplifiers. A limiting factor of these devices is the significant noise due to thermal-mechanical fluctuations that the phonons imprint on the optical signal. In this work, we fully characterize the Brillouin amplifier noise factor over an extended parameter space. Previous results have postulated a noise factor (F) depending only on the thermal occupation of the phonons (F≈n_th), based on an assumption of non-propagating phonons due to the large phonon decay rates of traditional Brillouin systems. However, our model shows this approximation breaks down in a host of emerging systems where phonon propagation drastically impacts the noise dynamics.