On-chip non-reciprocity can be achieved by employing micron-sized optomechanical (OM) devices that are fabricated on-chip and which can be integrated with other optical elements. Non-linear coupling between light and a mechanical mode inside a resonator can provide a non-reciprocal response of the OM system, which can be induced and fully controlled by an external driving electromagnetic field. By choosing different resonator and/or waveguide configurations and by tuning different system parameters, the same OM coupling mechanism can be used to provide isolation (e.g., as an optical diode), non-reciprocal phase shifting, and/or routing applications. Even in the presence of a finite intrinsic mode coupling inside the resonator, non-reciprocal effects remain large for a sufficiently strong OM coupling. The disclosed systems, methods, and devices can be applied on a single photon level, which may find use for various non-reciprocal applications in the classical optical as well as the quantum regime.