Towards Navigation-Grade and Deployable Optomechanical Accelerometry

Abstract: We design and experimentally demonstrate an architecture for achieving navigation-grade, fiber-packaged optomechanical accelerometers that can operate with a large dynamic range, over a wide temperature range, and without sophisticated laser sources. Our accelerometer architecture is based on a novel set of design principles that take advantage of the strengths of optomechanical accelerometry while eliminating many of its historical weaknesses. Displacement readout is provided by an integrated, differential strain-sensing Mach-Zehnder interferometer (DSMZI) attached to an ultra-rigid, bulk-micromachined proof mass having a 93.4 kHz fundamental resonance frequency (22.5 pm/g displacement). Despite the extreme rigidity, the high displacement sensitivity provides an insertion loss limited 4.2 $\mu g/\sqrt{\mathrm{Hz}}$ acceleration resolution, with a straight-forward path to achieving 330 $n g/\sqrt{\mathrm{Hz}}$ by improving the fiber-to-chip coupling. Further, we show that the combination of high rigidity and intrinsic differential optical readout makes the device insensitive to the common causes of bias instability, and we measure a bias instability of 6.3 $\mu g$ at 243 seconds. The DSMZI provides a 17 nm optical bandwidth and a temperature operating range of greater than 20 $^\circ\mathrm{C}$, both orders of magnitude larger than previous demonstrations of optomechanical accelerometers. The high rigidity and large optical bandwidth yield an expected dynamic range of 165.4 dB. The combination of high acceleration resolution, high dynamic range, low bias instability, and intrinsic insensitivity to wavelength, temperature, and package stresses makes our device well suited for deployment in realistic environments demanded by real-world applications and demonstrates a path for optomechanical accelerometers to ultimately exceed the performance of all other chip-based accelerometers.