Figure 1: Schematic diagram of a double-cavity photonic molecule optomechanical system coupled to a waveguide.
From: Tunable high-order sideband spectra generation using a photonic molecule optomechanical system
Sin (Sout) represents the input (output) field propagating in the waveguide. 
denotes the bosonic annihilation operator of the first (second) cavity field. The first cavity supports a mechanical mode with angular frequency Ωm. J is the cavity-cavity coupling rate, which can be efficiently adjusted by the distance between the cavities. κe denotes the coupling rate between the first cavity and the waveguide. κi1 and κi2 are the intrinsic cavity decay rates.
