Inertial sensor and inertial measurement unit

An inertial sensor 100 comprising one or more microresonators 102 with a corresponding optical resonance. The inertial sensor further comprises one or more electrodes for counteracting a deflection of a test mass 104 with an electrostatic force and one or more optical couplers 108 for coupling light into and out of a corresponding microresonator. The test mass may include one or more protrusions, each protrusion being located between two microresonators. The test mass may be larger than the microresonators. The inertial sensor further comprises one or more detectors 110 for detecting light received from the one or more microresonators by the one or more optical couplers. The test mass may have a thickness in the order of tens or hundreds of microns. The light transmitted into the optical couplers may be broadband or coherent single frequency light. The microresonators may be whispering gallery mode resonators. Also an inertial measurement unit comprising six inertial sensors as described.