High harmonic optomechanical oscillations in the lithium niobate photonic crystal nanocavity

We explore the optomechanical coupling in an on-chip lithium niobate (LN) photonic crystal nanocavity. A mechanical frequency shift and nonlinear mechanical oscillations are observed with the intracavity power increasing. A 14th harmonic oscillation is generated at the intracavity power of 430 μW in the LN photonic crystal, which potentially can function as a mechanical frequency comb. The photonic crystal structure also shows the positive temperature coefficient of frequency, while the LN crystal has a negative intrinsic temperature coefficient. These characters of optomechanics in LN may play important roles in photon-phonon coupling or detector systems such as sensitive displacement and the mass and force detection.