Modern Naval vessels utilize Inertial Navigation System (INS) as a navigation tool. Roll, pitch, and yaw data, commonly referred to as attitude data, require onboard gyroscopes and accelerometers. Many weapon systems such as the Navy’s Standard Missile (SM) family require inertial navigation data for operation. Current inertial navigation data for linear acceleration is provided by accelerometers, and rotational acceleration data by optical gyroscopes. However, there are inherent sensitivity limitations to these systems that are fundamentally related to the properties of measuring acceleration changes with a massless photon. If an INS system is being used as a primary method of navigation, it does not have the ability to be checked against another source to reset the drift. This happens when operating in a GPS-denied environment or other situations. Atom interferometry shows promise to provide both linear and rotational data simultaneously with an increase in sensitivity by orders of magnitude relative to current systems, all while being less affected by drift due to the intrinsic characteristics of the atoms which, by definition, do not change over time. Improving the attitude data that INS have access to will significantly enhance both the duration of time they are accurate, and the degree to which they maintain accuracy. This research will continue to investigate the physics of atom interferometry, and the application of this technology as an accelerometer and gyroscope.
Modern Naval vessels utilize Inertial Navigation System (INS) as a navigation tool. Roll, pitch, and yaw data, commonly referred to as attitude data, require onboard gyroscopes and accelerometers. Many weapon systems such as the Navy’s Standard Missile (SM) family require inertial navigation data for operation. Current inertial navigation data for linear acceleration is provided by accelerometers, and rotational acceleration data by optical gyroscopes. However, there are inherent sensitivity limitations to these systems that are fundamentally related to the properties of measuring acceleration changes with a massless photon. If an INS system is being used as a primary method of navigation, it does not have the ability to be checked against another source to reset the drift. This happens when operating in a GPS-denied environment or other situations. Atom interferometry shows promise to provide both linear and rotational data simultaneously with an increase in sensitivity by orders of magnitude relative to current systems, all while being less affected by drift due to the intrinsic characteristics of the atoms which, by definition, do not change over time. Improving the attitude data that INS have access to will significantly enhance both the duration of time they are accurate, and the degree to which they maintain accuracy. This research will continue to investigate the physics of atom interferometry, and the application of this technology as an accelerometer and gyroscope.
Inertial navigation systems (INSs) are a redundant form of navigation for modern naval platforms and a primary form in Global Positioning System (GPS) denied environments. Current technologies like ring laser gyroscopes (RLG) are used by INSs to measure rotation and acceleration. These measurements are then used to determine position via dead reckoning. There are, however, limitations to the accuracy and stability of this technology. The fundamental sensitivity of an RLG is determined by the effective mass of the photon, which is very small. RLGs are also prone to measurement drift, leading to errors that compound over time. Atomic interferometers show increases in both accuracy and stability over time. Atomic interferometer measurements are fundamentally tied to the mass of an atom, which is ten orders of magnitude larger than the photon’s effective mass. These systems have significantly reduced measurement drift because atomic parameters, which can be tied to gyroscope parameters like scale factors, do not change over time. We discuss the complications of using atomic interferometers as gyroscopes. Two area-reversed interferometers are needed for an atomic gyroscope to distinguish between rotation and acceleration. We explore the addition of a second atomic beam to form a second interferometer in the NPS apparatus. Both atomic beams are characterized separately to verify optimal apparatus settings before a laser is used to simultaneously detect counter-propagating beams.
Current sensors used for inertial navigation are based on technology with inherent sensitivity limitations. Atom interferometry is a very promising replacement, which could yield many orders of magnitude of improvement in sensitivity, leading to more accurate navigation over longer periods of time relative to current technology. This research investigates the physics of atom interferometry through the construction and characterization of an atomic accelerometer/gyroscope combination. In contrast to current state-of-the-art atomic sensors, which use pulsed cold atom sources and pulsed laser beams, the apparatus investigated relies purely on continuous atomic and laser beams. These differences would result in a sensor that lends itself more readily to smaller sizing, lower power consumption, and reduced complexity. This change in approach to atomic interferometry also introduces challenges resulting from laser and atomic beam divergences and the velocity averaging due to both longitudinal and transverse temperature, which this dissertation shows how to overcome. The work contained herein explores many stages of construction of an atomic gyro including the demonstration and characterization of two-dimensional laser cooling of atoms, stimulated Raman transitions, and Ramsey and spin echo interference. The implications for future research are also outlined and discussed.
Inertial sensors based on cold atom interferometry exhibit many interesting features for applications related to inertial navigation, particularly in terms of sensitivity and long-term stability. However, at present the typical atom interferometer is still very much an experiment—consisting of a bulky, static apparatus with a limited dynamic range and high sensitivity to environmental effects. To be compliant with mobile applications further development is needed. In this work, we present a compact and mobile experiment, which we recently used to achieve the first inertial measurements with an atomic accelerometer onboard an aircraft. By integrating classical inertial sensors into our apparatus, we are able to operate the atomic sensor well beyond its standard operating range, corresponding to half of an interference fringe. We report atom-based acceleration measurements along both the horizontal and vertical axes of the aircraft with one-shot sensitivities of 2.3 × 10−4 g over a range of ∼ 0.1 g. The same technology can be used to develop cold-atom gyroscopes, which could surpass the best optical gyroscopes in terms of long-term sensitivity. Our apparatus was also designed to study multi-axis atom interferometry with the goal of realizing a full inertial measurement unit comprised of the three axes of acceleration and rotation. Finally, we present a compact and tunable laser system, which constitutes an essential part of any cold-atom-based sensor. The architecture of the laser is based on phase modulating a single fiber-optic laser diode, and can be tuned over a range of 1 GHz in less than 200 μs.
Classical inertial navigation systems integrate inertial measurements from triads of accelerometers and gyroscopes to determine their position, but the computed trajectory is typically limited by the intrinsic time-varying bias of these inertial sensors. In addition, the exploitation of quantum physics led to the development of matter-wave interferometers, sensitive to inertial effects due to the mass of the atoms. While they are free-falling, these atoms constitute a perfect inertial frame of reference and allow for an absolute measurement with outstanding accuracy and stability. Substantial technical developments have allowed bringing quantum gravimeters to the market, enabling static, long-term measurements. Nevertheless, the use of cold-atom sensors for navigation and positioning still requires addressing many scientific and technological challenges to be compatible with onboard applications such as compactness, measurement continuity and operation in the presence of strong vibrations and rotations.The Joint Laboratory iXAtom brings together the expertise of the Laboratoire de Photonique, Numérique et Nanosciences (LP2N) in matter-wave interferometry and the French technology company Exail, specialized in high-performance inertial navigation systems and industrial quantum sensors, with the aim of building a new generation of high-end inertial sensors through the hybridization of classical accelerometers and gyroscopes with quantum sensors based on matter-wave interferometry.After successfully building a multi-axis cold-atom interferometer measuring the three components of the acceleration vector with a static apparatus, this quantum inertial sensor has been fully hybridized with a triad of classical accelerometers, increasing the bandwidth and dynamic range without the usual limitation due to the bias drift of the mechanical accelerometers. Moreover, this hybridization technique features a real-time correction of the laser phase which allows retrieving the acceleration information out of atomic fringes scrambled by parasitic vibrations. As regards the rotations of the instrument throughout an interferometer, their compensation remains the next major issue to tackle for strapdown applications as they induce a drastic reduction of the atomic fringes’ visibility coupled to a scrambling of the interferometric phase shift.This thesis work focuses on the mitigation of the rotation-induced performance deterioration of the hybrid accelerometer. Through a theoretical investigation, a model for both the angular velocity-dependent decay of the fringes contrast and the systematic phase shift arising from the complex trajectory of the atomic cloud in the rotating frame of the interrogation laser is established. A real-time rotation compensation system, employing the measurement of the rotation rate with high-end fiber-optic gyroscopes to drive a piezo-actuated tip-tilt platform, has been implemented to stabilize the orientation of the interrogation laser in the external frame in order to preserve the contrast of the atomic interference pattern and extend the measurement range of the rotating atom interferometer. A rectification of the theoretical model accounting for the rotation of the laser as well as the hybridization with the classical accelerometers enables reconstructing the atomic fringes and retrieving the inertial measurement, paving the way for strapdown onboard hybrid accelerometry.
Positioning currently relies heavily on Global Navigation Satellite Systems (GNSS). Combined with classical accelerometers and gyroscopes, precise determination of orientation and position at any given time become available. However, but the availability of GNSS (e.g. GPS) is limited and not guaranteed at all times.In this paper we present an alternative based on atom interferometry using cold atom ensembles. An inertial sensor based on cold atoms allows, in theory, for nearly drift-free measurements of inertial forces with accuracies unreached by classical sensors, but the technology is still locked away in large physics laboratories [1].This paper introduces a compact device called SECAMP, which is capable of cooling atoms down to μ-Kelvin. SECAMP has the potential to measure inertial acceleration in three degrees of freedom. In the following, we present the current experimental setup of the apparatus and outline the next steps for the inertial sensor.
This report assesses the potential of gyroscopes and accelerometers based on cold atom interferometry (CAI) for space and defence applications, by analysing their strengths and weaknesses in comparison with devices based on other working principles. Indeed, it is widely recognized that quantum sensors based on atomic interferometry provide absolute measurements with the potential for high sensitivity and long-term stability. This last property is particularly valuable for accelerometers and gyroscopes to be used for inertial navigation, since it guarantees precise positioning without the need for frequent recalibrations, a shortcoming which affects several devices presently in use. \nHigh-performance inertial sensors play an important role both in space applications, where gyroscopes are widely used e.g. to orientate a satellite and its on-board communications and sensing equipment, and in defence, where gyroscopes and accelerometers constitute the core of the inertial measurement units to be used for autonomous navigation, e.g. in GNSS-denied conditions. The EU has a well-established role in space with the Copernicus and Galileo programmes, and a fledging but increasing involvement in the defence industry. An independent assessment of a quantum technology such as cold atom interferometry which may in time acquire a significant role in these fields is a precondition to advance well-grounded suggestions for EU policy initiatives.