OBJECTIVE: Develop a chip-integrated optomechanical micro-electromechanical systems (MEMS) accelerometer with 100 ng/Hz^1/2 sensitivity and 10 kHz bandwidth using high finesse optics to readout and dynamically tune sensor parameters. DESCRIPTION: Inertial navigation systems (INS) are a critical asset to the DoD in environments where GPS is either denied or unavailable. At the heart of these systems are precision acceleration and rotation sensors. Recently, MEMS-based accelerometers have found widespread use in INS owing to their small size and ease of fabrication. However they still lack the sensitivity and bandwidth required for accurate long-distance navigation. Typically, MEMS accelerometers use capacitive measurement; their sensitivities are limited by thermal-electronic noise in the readout circuitry . Optical interferometric methods eliminate electronic noise and can approach the thermal-mechanical limit , . This thermal-mechanical noise imposes a fundamental trade-off between the sensitivity (ath) and bandwidth (BW) of the accelerometer: ath proportional to (BW/mQ)^1/2, where m is the mechanical resonator mass and Q is its quality factor. Therefore, to achieve a high sensitivity for a given bandwidth, the product mQ needs to be maximized. Furthermore, for high bandwidth devices, a high resolution displacement (x) measurement is required (x proportional to BW^-2), thus imposing requirements on the finesse (F) and input power (P) of the optical readout cavity (x proportional to (F^-1P^-1/2)), which is ultimately limited by laser shot noise. For example, to achieve a sensitivity of a few ng/Hz^1/2 at a bandwidth of 10 kHz, one would require mQ>1 kg and F>1000. Such a sensitivity and bandwidth combination has not been achieved in a commercial device and would reduce the INS error, allowing longer-duration navigation in the absence of GPS. Recently, accelerometers based on optomechanical devices have been developed, which exhibit a sensitivity of a few ng/Hz^1/2 with a bandwidth greater than 10kHz, in a compact form-factor , . Optomechanical devices are strongly coupled optical and mechanical systems, in which a high finesse optical cavity is used to both measure and manipulate high-quality MEMs. Such devices have enabled optical radiation-pressure cooling of MEMs to their quantum ground state , eliminating thermal noise and enhancing the achievable bandwidth by broadening the mechanical resonance without loss of sensitivity. Furthermore, the cavity-enhanced optical field enables displacement measurement at the standard quantum limit , an important fundamental limit for acceleration sensing. Finally, utilizing the high circulating power achievable in a high finesse cavity, one can dynamically control the bandwidth of the MEMS accelerometer via the optical spring effect , thus enabling unprecedented in-situ control of accelerometer performance. While optomechanical devices have demonstrated exciting results in the laboratory, significant development is necessary to construct a robust packaged device that incorporates the laser, the optomechanical device, and optical readout circuitry. PHASE I: Design a robust, packaged MEMS accelerometer with highsensitivity optical readout approaching the standard quantum limit for displacement measurement. Such a system should exhibit high opticalmechanical coupling such that a pump laser can manipulate MEMS parameters such as resonance frequency and damping rate. The chosen work should be compatible with an accelerometer with less than100 ng/Hz^1/2 sensitivity and greater than a 10 kHz bandwidth. Exhibit the feasibility of the approach through a laboratory demonstration. Phase I deliverables will include a design review including expected device performance and a report presenting the plans for Phase II. Experimental data demonstrating feasibility of the proposed device is favorable. PHASE II: Fabricate and test a prototype device demonstrating the device performance outlined in Phase I. The Transition Readiness Level to be reached is 5: Component and/or bread-board validation in relevant environment. PHASE III: Once developed, compact, integrated optomechanical accelerometers with high-sensitivity and high-bandwidth would greatly improve military inertial navigation systems, requiring less frequent error correction and updates from GPS. Innovations in Phases I and II will enable such devices to transition out of the laboratory and into fieldable devices. 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