Optomechanical reference accelerometer

Abstract

We present an optomechanical accelerometer with high dynamic range, high bandwidth and readout noise levels below 8 µg/ √ Hz . The straightforward assembly and low cost of our device make it a prime candidate for on-site reference calibrations and autonomous navigation. We present experimental data taken with a vacuum sealed, portable prototype and deduce the achieved bias stability and scale factor accuracy. Additionally, we present a comprehensive model of the device physics that we use to analyze the fundamental noise sources and accuracy limitations of such devices.

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

“…S IGNIFICANT progress in the field of optomechanics has stimulated a new generation of photonic motion detectors that surpass the sensitivity of current standards, with aims to approach fundamental limits set by quantum mechanics [1]. These systems rely on the coupling between mechanical motion and light, which is enhanced when using an optical resonator such as a Fabry-Perot cavity [2], spherical cavities that support whispering gallery modes (WGMs) [1], [3]- [10], and nanocavities in the form of photonic crystals [11], [12]. Through optimization of the optical field geometry and the mechanical test-mass, sensitivities on the order of 10 −18 m·Hz − 1 2 [1], [13], [14] can be reached, allowing laser cooling of macroscopic motion [1], [15], force sensing [8], and recently the discovery of gravitational waves [13].…”

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.…”

“…The excess noises shown in the measurements, with the acceleration PSD non‐flat at the low‐frequency region, are mainly from system noise such as the laser frequency noise, parasitic displacement noise, device thermal fluctuation, and thermal expansion noise among others. [ 33 ] We note that only the first 40 RF spectra (up to 154.8 mg) are used in the analysis to be well within the linear dynamic range (<0.05% standard deviation). We also measured other inertial sensor devices in our setup with similar geometries, including an inertial sensor mounted 180° opposite from Figure 3a (i.e., acceleration in the − y ‐axis direction); the mechanical resonance frequency shift is observed in opposite direction under the same acceleration ranges as detailed in Supporting Information III.B.…”

“…With the large mass oscillator and high driving powers, the thermal Brownian noise can be largely reduced [ 41,42 ] and then the measured frequency instability and acceleration sensitivity can be strongly improved, resulting in better resolution. The optical noise bound arising from quantum backaction noise a BA [ 33 ] is estimated to be ≈184 ng Hz −1/2 for our oscillator design and implementation parameters, and is detailed in Supporting Information VI.B. We note that, with this RF transduction readout approach instead of solely the optical intensity transmission readout, optical shot noise, and photodetector shot noise do not contribute significantly to the fundamental limit in our readout scheme, allowing our measured acceleration noise floor to be close to the thermal noise limit.…”

“…Such examples include nanobeam cavities at 10 µg Hz −1/2 (1 g = 9.81 m s −2 ) resolution (sensing bandwidth 5 to 25 kHz) with lock‐in detection, [ 30 ] cantilevered whispering gallery mode spherical silica cavities at 4.5 µg Hz −1/2 resolution (sensing bandwidth 10 to 100 Hz), [ 31 ] and bulk fiber‐optic cavities at 100 ng Hz −1/2 resolution (sensing bandwidth 1 to 10 kHz). [ 32,33 ] More details about the accelerometers performance comparisons are described in Supporting Information I. Optomechanical accelerometers with external piezoelectric stages and calibration have also been tested with outdoor operation. [ 34–37 ] Unlike these previously demonstrated optomechanical accelerometers, here we demonstrate a new transduction mechanism which is not based on the optical readout through measuring the shift or broadening of optical resonances via dispersive and dissipative optomechanical coupling.…”