A microchip optomechanical accelerometer

The monitoring of accelerations is essential for a variety of applications ranging from inertial navigation to consumer electronics [1]. The basic operation principle of an accelerometer is to measure the displacement of a flexibly mounted test mass; sensitive displacement measurement can be realized using capacitive [2, 3], piezo-electric [4], tunnel-current [5], or optical [6–9] methods. While optical readout provides superior displacement resolution and resilience to electromagnetic interference, current optical accelerometers either do not allow for chip-scale integration [6] or require bulky test masses [7, 8]. Here we demonstrate an optomechanical accelerometer that employs ultra-sensitive all-optical displacement read-out using a planar photonic crystal cavity [10] monolithically integrated with a nano-tethered test mass of high mechanical Q-factor [11]. This device architecture allows for full on-chip integration and achieves a broadband acceleration resolution of 10 μg/ √ Hz, a bandwidth greater than 20 kHz, and a dynamic range of 50 dB with sub-milliwatt optical power requirements. Moreover, the nano-gram test masses used here allow for optomechanical back-action [12] in the form of cooling [13] or the optical spring effect [14, 15], setting the stage for a new class of motional sensors.