Characterization and Testing of a Micro-g Whispering Gallery Mode Optomechanical Accelerometer

Abstract

Navigation, bio-tracking devices and gravity gradiometry are amongst the diverse range of applications requiring ultrasensitive measurements of acceleration. We describe an accelerometer that exploits the dispersive and dissipative coupling of the motion of an optical whispering gallery mode (WGM) resonator to a waveguide. A silica microsphere-cantilever is used as both the optical cavity and inertial test-mass. Deflections of the cantilever in response to acceleration alter the evanescent coupling between the microsphere and the waveguide, in turn causing a measurable frequency shift and broadening of the WGM resonance. The theory of this optomechanical response is outlined. By extracting the dispersive and dissipative optomechanical rates from data we find good agreement between our model and sensor response. A noise density of 4.5 µg·Hz − 1 2 with a bias instability of 31.8 µg (g = 9.81 m·s −2 ) is measured, limited by classical noise larger than the test-mass thermal motion. Closedloop feedback is demonstrated to reduce the bias instability and long term drift. Currently this sensor outperforms both commercial accelerometers used for navigation and those in ballistocardiology for monitoring blood flowing into the heart. Further optimization would enable short-range gravitational force detection with operation beyond the lab for terrestrial or space gradiometry.

Strain-controlled power devices as inspired by human reflex

“…One of the critical parts of the field of AI is to realize the accelerate-feedback-control. Emerging AI applications, such as autopilot or robot walking, require effectively control output power according to the changes of environment, e.g., acceleration [31][32][33][34][35] . In a self-driving car, the output power of engine needs to be realized at the self-adjusted and unsupervised conditions in rapid response to emergency braking or other accidents, as schematically shown in Fig.…”

A Chip‐Scale Oscillation‐Mode Optomechanical Inertial Sensor Near the Thermodynamical Limits

“…Figure 3e illustrates the measured bias instability and VRW noise of ≈5.23 mg and 1.8 mg Hz −1/2 , respectively, which are the two very important parameters indicating the minimum achievable low‐frequency acceleration reading limited by flicker noise and the total noise density. [ 31,33 ] Figure 3f shows the converted acceleration power spectrum density (PSD) which indicates the non‐flat noise density in the low frequency range from 0.001 to 20 Hz. Theoretically, in pre‐oscillation mode, the thermal noise frequency fluctuation is given by: [ 41,42 ] δ Ω th = [( k B T / E C ) × (Ω m Δ f / Q m )] 1/2 , from the measured power spectra density and with Δ f the acquisition rate corresponding to the integration time, and E C = m x Ω m 2 〈 x c 2 〉 the energy in the carrier in the oscillator and 〈 x c 〉 the constant mean square amplitude.…”

Field Evaluation of a Portable Whispering Gallery Mode Accelerometer

“…Unprecedented levels of displacement sensitivity down to 10−18 m Hz−1/2 have been reached using cavity optomechanics [4,5], driven by techniques originating from experiments at gravitational wave observatories. Bench-top systems comprising of Fabry–Perot cavities, spherical micro-cavities that support whispering gallery mode (WGM) resonances, and chip-scale photonic crystals exploit these principles [4,5,6], and many show great promise as optical accelerometers, reaching sensitivities of ≤micro-g Hz−1/2 (g = 9.81 ms−2) [6,7,8], sufficient for detecting, for example, the acceleration of blood through the heart [9]. Subtle technical differences limit the sensitivity, known as the spectral noise density, between optomechanical and capacitive accelerometers but, in general, capacitive sensors require larger test-mass deflections and heavier proof masses to obtain a micro-g resolution, which in turn reduces the sensing bandwidth [10].…”