A high-resolution microchip optomechanical accelerometer

The monitoring of acceleration is essential for a variety of applications ranging from inertial navigation to consumer electronics(1,2). Typical accelerometer operation involves the sensitive displacement measurement of a flexibly mounted test mass, which can be realized using capacitive(3,4), piezoelectric(5), tunnel-current(6,7) or optical(8-11) methods. Although optical detection provides superior displacement resolution(8), resilience to electromagnetic interference and long-range readout(7), current optical accelerometers either do not allow for chip-scale integration or utilize relatively bulky test mass sensors of low bandwidth(8-10). Here, we demonstrate an optomechanical accelerometer that makes use of ultrasensitive displacement readout using a photonic-crystal nanocavity(12) monolithically integrated with a nanotethered test mass of high mechanical Q-factor(13). This device achieves an acceleration resolution of 10 mu g Hz(-1/2) with submilliwatt optical power, bandwidth greater than 20 kHz and a dynamic range of greater than 40 dB. Moreover, the nanogram test masses used here allow for strong optomechanical backaction(14-17), setting the stage for a new class of motional sensors.