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    • 专利摘要:
    The invention relates to a hybrid inertial measurement system comprising a cold-atom interferometric inertial sensor (50) comprising a laser source (20) generating a sequence of laser pulses (21, 22, 23, 29) in the direction of a burst of cold atoms (10) and a conventional inertial sensor (4, 100) fixed to the inertial reference frame of the interferometric inertial sensor. According to the invention, the hybrid system comprises a signal processing system (40, 41, 42) adapted to receive an inertial measurement signal (14, 141, 148) of the conventional inertial sensor (4, 100) and to generate in real-time non-linear frequency modulation signal (140, 420), the feedback loop electronic system being configured to modulate in real time the central optical frequency of the laser (20) according to the modulation signal (140). , 420), so that the interferometric cold atom interferometric sensor (50) generates a first hybrid inertial measurement signal (151) by atomic interferometry corrected for the relative movements of the inertial reference frame.
    公开号:FR3063141A1
    申请号:FR1751457
    申请日:2017-02-23
    公开日:2018-08-24
    发明作者:Brynle BARRETT；Baptiste Battelier；Philippe Bouyer；Fabien Napolitano
    申请人:Centre National de la Recherche Scientifique CNRS；Universite de Bordeaux；Institut dOptique Graduate School；iXBlue SAS；
    IPC主号:
    专利说明:

    Holder (s): IXBLUE Simplified joint-stock company, GRADUATE SCHOOL INSTITUTE OF OPTICS, NATIONAL CENTER FOR SCIENTIFIC RESEARCH Public establishment, UNIVERSITE DE BORDEAUX Public establishment.
    Extension request (s)
    Agent (s): JACOBACCI CORALIS HARLE Simplified joint-stock company.
    HYBRID INERTIAL MEASUREMENT SYSTEM AND METHOD BASED ON A COLD ATOMISED AND LIGHT PULSE INTERFEROMETER.
    FR 3 063 141 - A1 (5 /) The invention relates to a hybrid inertial measurement system comprising an interferometric cold atom inertial sensor (50) comprising a laser source (20) generating a sequence of laser pulses (21,22, 23, 29) in the direction of a burst of cold atoms (10) and a conventional inertial sensor (4, 100) fixed to the inertial reference frame of the interferometric inertial sensor.
    According to the invention, the hybrid system comprises a signal processing system (40, 41,42) adapted to receive an inertial measurement signal (14, 141, 148) from the conventional inertial sensor (4,100) and to generate in real time a non-linear frequency modulation signal (140, 420), the electronic feedback loop system being configured to modulate in real time the central optical frequency of the laser (20) according to the modulation signal (140, 420 ), so that the cold atom interferometric inertial sensor (50) generates a first hybrid signal (151) for inertial measurement by atomic interferometry corrected for the relative movements of the inertial reference frame.
    149 i

    Technical field to which the invention relates
    The present invention relates generally to the field of inertial measuring instruments for measuring a rotational speed or a local acceleration due for example to gravity.
    It relates more particularly to an inertial measurement instrument and method based on the use of a cold atom interferometer for very high precision measurements.
    It relates more particularly to an inertial acceleration, gravity and / or rotation sensor based in particular on an atomic interferometer.
    Technological background
    Inertial sensors based on atomic interferometry offer great sensitivity and find applications in inertial navigation, seismology or geophysics to measure gravity locally.
    For the past twenty years, atomic interferometry techniques have made it possible to develop new measuring instruments, for example gravimeters, gradiometers, accelerometers, gyroscopes, atomic clocks and electromagnetic field sensors.
    An atomic interferometer combines optical and atomic technologies. A cold atom interferometer is a device in which waves of matter propagate along spatially separated paths which delimit a closed surface. An atomic interferometer is sensitive to inertial effects such as accelerations and rotations.
    On the one hand, an atomic interferometer comprises a source of atoms and a cold atom trap configured to generate a puff of atoms initially propagating in a determined direction. On the other hand, the atomic interferometer includes a laser source emitting a sequence of light interrogation pulses intended to interact with the fine structure of atoms by photon transfer. Finally, the atomic interferometer includes a device for measuring the state of the atom.
    Atomic interferometry systems have advanced considerably since the development of atomic cooling techniques in the 1980s and 1990s. Atomic interferometry systems have a sensitivity several times greater than that of conventional mechanical sensors. However, these atomic interferometry systems face limits in terms of robustness to inclinations and vibrations. On the other hand, atomic interferometry systems today have a reduced sensitivity range compared to conventional sensors.
    Depending on the orientation of the atom source and the atomic interferometer, it is thus possible to measure an acceleration and / or a rotation in a determined direction. Atomic interferometers allow extremely precise measurements. Atomic interferometers find applications in inertial sensors of the gravimeter, gradiometer, accelerometer and gyrometer type with cold atoms.
    A particularly important application of atomic interferometry relates to cold atom accelerometers (CAA). Most cold atom accelerometers (CAA) are built in a gravimeter configuration, the purpose of which is to measure the gravitational acceleration as precisely as possible. The measurement axis of a gravimeter is defined by the normal to the surface of a retro-reflecting mirror arranged so as to reflect the interrogation field towards the cloud of cold atoms. This normal is generally aligned on the vertical direction. The retro-reflecting mirror thus determines a reference frame of the inertial cold atom sensor. These cold atom accelerometers are critically based on this standard.
    Most cold atom accelerometers are bulky and heavy systems designed to operate in a controlled laboratory environment and within a limited acceleration range.
    In mobile applications, for example inertial navigation, various factors mainly limit the operation and performance of cold atom accelerometers. First, the interferometer no longer works when its orientation varies randomly or when its movements are random. In fact, the movements of the inertial system affect the stability of the reflecting surface. On the other hand, a misalignment between the normal to the mirror and the local vertical axis introduces a systematic measurement error. These questions are of a technical nature and result from the use of inertial cold atom sensors outside their nominal operating zone.
    The publication J. Le Gouët et al. "Limits of the sensitivity of a low noise compact atomic gravimeter", Appl. Phys. B 92, 133-144 (2008) describes a cold atom gravimeter and a vibration compensation technique. According to this publication, a seismometer attached to the retro-reflecting mirror acquires measurements of external vibrations and a pre-compensation loop makes it possible to correct, according to the previous interferometric measurements, the phase shift between two laser sources of the Raman pulse generation system. to counterbalance the interferometric phase shift induced by these vibrations. However, the effectiveness of vibration rejection remains limited in practice. In addition, the seismometer operating as a high-pass filter, low frequency vibrations persist on gravity measurements.
    The publication S. Merlet et al. "Operating an atom interferometer beyond its linear range", Metrologia 46, 87-94 (2009) describes a cold atom gravimeter and compares a post-process correction technique by fringe fitting with a technique for correcting vibrations between two interferometric measurements. According to this publication, the post-process fringe adjustment technique gives better results than vibration correction, which however has better temporal resolution.
    The publication R. Geiger et al. ("Detecting inertial effects with airborne matter-wave interferometry", Nature Comm., 2: 474, DOI: 10.1038 / ncomms1479, 2011) describes a method of hybridization of acceleration measurements from mechanical accelerometers with measurements from d 'an atomic interferometer. A mechanical accelerometer makes it possible to estimate the inertial phase shift in order to deduce therefrom a number of half-fringes, so as to center the phase shift of the atomic interferometer on a central fringe. Then, the phase shift measurement by the atomic interferometer is reversed in this half-fringe to obtain a more precise value of the phase shift. We then calculate the sum of the rough phase shift measurement obtained by the mechanical accelerometer and the fine phase shift measurement obtained by the atomic interferometer. This hybrid method and device enables continuous measurements and the measurement range to be extended using the conventional sensor, while benefiting from the very high accuracy and long-term stability of the inertial cold atom sensor.
    The document J. Lautier et al. "Hybridizing matter-wave and classical accelerometers" describes a system and method for hybridizing acceleration measurements from a conventional mechanical accelerometer with measurements from an interferometric cold atom accelerometer. The system also includes a real-time pre-compensation loop by adjusting the laser phase to limit the influence of vibrations on interferometric measurements. This device and this hybridization method make it possible to obtain very high precision over a large measurement dynamic with long-term stability. However, the operating range of a cold atom interferometric accelerometer remains limited in dynamics and in direction of acceleration.
    The main problem encountered during the operation of an inertial sensor based on an atomic interferometer is that because of its high sensitivity, vibrations even of low amplitude and low frequency, can exceed the phase shift measurements. Since the atomic interferometer has a non-linear periodic response, which limits its dynamics, the interference fringes can be blurred by random accelerations caused by vibrations. To overcome this difficulty, it is necessary to extend the sensitivity range of an inertial cold atom sensor, to extract the measurements on a large number of fringes or to dynamically slave the central fringe with respect to a signal d strongly varying acceleration.
    In a cold atom gravimeter, subjected to the force of gravity, it is known to apply a linear modulation to the laser frequency of the Raman beams to compensate for an offset induced by Doppler effect between counter-propagating beams propagating in the vertical direction. The coefficient of the frequency ramp is fixed and pre-determined. This compensation makes it possible to compensate for a constant acceleration in a predetermined direction, in particular due to the Doppler effect between the counter-propagating Raman beams along the vertical axis.
    However, this compensation does not generally correct all parasitic vibrations or accelerations, in any direction.
    Object of the invention
    In order to overcome the aforementioned drawback of the state of the art, the present invention provides a hybrid inertial measurement system comprising an interferometric cold atom inertial sensor comprising a laser source adapted to generate a sequence of laser pulses in the direction d '' a puff of cold atoms and a system for detecting an inertial measurement signal by atomic interferometry relating to an inertial reference frame, and a conventional inertial sensor fixed to the inertial reference frame of the interferometric cold atom inertial sensor, the conventional inertial sensor being adapted to provide a conventional inertial measurement signal of the inertial reference frame.
    More particularly, a hybrid system is proposed according to the invention comprising an electronic system with a feedback loop comprising a signal processing system adapted to receive an inertial measurement signal from the conventional inertial sensor, the signal processing system being adapted to generate a non-linear frequency modulation signal in real time as a function of the inertial measurement signal, each laser pulse of the laser pulse sequence having a predetermined optical frequency detuning with respect to a central optical frequency of the laser source , the electronic feedback loop system being configured to modulate in real time the central optical frequency of the laser as a function of the modulation signal, so as to modulate said laser pulse sequence in real time and so that the inertial sensor atom atom interferometry generates a first hybrid inertial measurement signal by atomic interferometry c mapped relative movements of the inertial reference frame with respect to the puff of cold atoms during a measurement cycle.
    This system allows to correct the frequency of the laser and not only its phase. In addition, the correction is carried out in real time during the measurement of the cold atom interferometric sensor and not between two interferometric measurements.
    This system also makes it possible to compensate in real time for the continuous and / or frequency modulated accelerations of the reference frame with respect to the cold atoms, due for example to the movement of the vehicle on which the inertial system is on board. Thus, this system makes it possible to avoid a drop in sensitivity of the measurement due to the movements of the sensor.
    This system makes it possible to compensate for parasitic phase shifts on the interference fringes, due to the mechanical vibrations of the reference frame. In fact, the vibrations of the frame linked to the reflecting retro mirror 3063141 are directly measured to control the optical frequency of the laser in real time.
    In addition, this system enables the interferogram to be refocused on a central fringe, where the absolute acceleration can be measured along the sensitive axis of the inertial system. This advantageously makes it possible to measure slow drifts of the orientation of the measurement axis of the inertial system.
    Other non-limiting and advantageous characteristics of the hybrid inertial measurement system according to the invention, taken individually or in any technically possible combination, are the following:
    the inertial reference frame comprises a reflective optical component arranged so as to retro-reflect the sequence of laser pulses and to generate a sequence of counter-propagating laser pulses in the direction of the puff of cold atoms, the conventional inertial sensor being attached to the reflecting optical component of the cold atom interferometric inertial sensor;
    - The signal processing system is adapted to further generate a phase shift correction signal from the laser source;
    - the system further comprises a phase jump generator configured to generate a sampling suitable for extracting an interference fringe phase measurement;
    - The signal processing system is adapted to generate frequency modulation signal comprising a linear modulation component and a non-linear modulation component as a function of time.
    According to a particular and advantageous embodiment, the conventional inertial sensor comprises a seismometer, an accelerometer based on MEMS, a gyrometer based on MEMS, a laser gyrometer or a fiber optic gyrometer.
    Advantageously, the system comprises a computer adapted to receive a portion of the first hybrid signal, the computer being adapted to generate a second hybrid inertial measurement signal as a function of the conventional inertial measurement signal and of the portion of the first hybrid signal from the cold atom interferometric inertial sensor.
    According to a particular embodiment, the cold atom interferometric inertial sensor is adapted to generate an error signal by difference between the inertial measurement signal by atomic interferometry corrected to a recurrence N of the measurement cycle and the inertial measurement signal by atomic interferometry at an N-1 recurrence, where N is a natural integer greater than or equal to two, and in which the computer is adapted to receive the error signal and a first part of the inertial measurement signal from the conventional inertial sensor, the computer being adapted to deduce therefrom the second hybrid inertial measurement signal.
    Advantageously, the signal processing system is adapted to receive the second hybrid inertial measurement signal and in which the signal processing system is adapted to take part of the second hybrid inertial measurement signal to replace the inertial measurement signal of the sensor. conventional inertial and for generating in real time a non-linear frequency modulation signal as a function of said part of the second hybrid inertial measurement signal.
    In a particular embodiment, further comprising a coupler configured to take another part of the inertial measurement signal from the conventional inertial sensor in real time, a low-pass filter adapted to filter a direct component of said other part of the signal inertial measurement, a comparator adapted to compare a continuous component of said other part of the conventional inertial measurement signal with the inertial measurement signal by atomic interferometry to deduce therefrom a bias error signal from the conventional inertial sensor, and the computer being adapted to receive the bias error signal and the first part of the inertial measurement signal signal from the conventional inertial sensor, the computer being adapted to calculate in real time the second hybrid inertial measurement signal by difference between the first part of the signal inertial measurement of the conventional inertial sensor and the bia error signal is.
    Advantageously, further comprising a coupler configured to take in real time another part of the inertial measurement signal from the conventional inertial sensor, a low-pass filter adapted to filter a continuous component of said other part of the inertial measurement signal, a comparator adapted to compare a DC component of said other part of the conventional inertial measurement signal with the inertial measurement signal by atomic interferometry to deduce therefrom a bias error signal from the conventional inertial sensor, and the computer being adapted to receive the signal d bias error and the first part of the signal of the inertial measurement signal of the conventional inertial sensor, the computer being adapted to calculate in real time the second hybrid inertial measurement signal by difference between the first part of the inertial measurement signal of the inertial sensor conventional and the bias error signal.
    Advantageously, the computer is adapted to transmit another part of the second hybrid inertial measurement signal to an output of the hybrid inertial measurement system.
    In a particular and advantageous embodiment, the conventional inertial sensor and the computer are part of an inertial navigation unit comprising three accelerometers, three gyrometers and a computer adapted to generate an inertial navigation signal based on the measurements of the three accelerometers and of the three gyros, the inertial navigation unit being adapted to receive said part of the first hybrid signal, the inertial navigation unit being adapted to generate a hybrid inertial navigation signal as a function of the inertial navigation signal and of the part of the first hybrid signal from the interferometric cold atom inertial sensor.
    Advantageously, the inertial navigation unit is adapted to receive part of the first hybrid inertial measurement signal and / or of the second hybrid inertial measurement signal and to generate a hybrid inertial navigation signal.
    According to a particular aspect, the inertial interferometric cold atom sensor is configured to measure an acceleration signal by atomic interferometry, the feedback loop comprises a microprocessor adapted to integrate the acceleration signal as a function of time to deduce therefrom measurement of instantaneous speed relative to the inertial reference frame with respect to the puff of atoms, and the modulation signal of the center frequency of the laser comprises a ramp proportional to the measurement of instantaneous speed.
    The invention also provides a hybrid inertial measurement method comprising the following steps:
    at. Generation of a sequence of laser pulses in the direction of a burst of cold atoms, each laser pulse of the sequence of laser pulses having a predetermined optical frequency detuning with respect to a central optical frequency of the laser source, and detection of an inertial measurement signal by atomic interferometry relating to an inertial reference frame;
    b. Detection of a conventional inertial measurement signal from the inertial reference frame;
    vs. Processing of the conventional inertial measurement signal to generate a non-linear frequency modulation signal in real time as a function of the inertial measurement signal,
    d. Real time modulation of the central optical frequency of the laser as a function of the modulation signal, so as to modulate said laser pulse sequence in real time and generate a first hybrid inertial measurement signal by atomic interferometry corrected for the relative movements of the frame. inertial reference to the puff of cold atoms during a measurement cycle.
    Detailed description of an exemplary embodiment The following description with reference to the accompanying drawings, given by way of non-limiting examples, will make it clear what the invention consists of and how it can be carried out.
    In the accompanying drawings:
    - Figure 1 schematically shows the principle of a cold atom interferometer;
    - Figure 2 shows schematically a cold atom interferometer in Mach-Zehnder configuration;
    - Figure 3 shows an example of a cold atom accelerometer;
    - Figure 4 illustrates acceleration measurements in a cold atom interferometer with pre-compensation for a constant acceleration between the frame reference frame and the cold atoms and real-time phase compensation;
    - Figure 5 schematically shows a hybrid measurement system with double feedback loop to correct in real time the measurements of a conventional inertial sensor by means of the signal from an inertial cold atom sensor;
    - Figure 6 schematically shows a variant of a feedback loop measurement system for correcting in real time the measurements of an inertial cold atom sensor by means of the signal from a conventional inertial sensor;
    - Figure 7 schematically shows another variant of a feedback loop measurement system for correcting in real time the measurements of an inertial cold atom sensor using signals from a conventional sensor;
    FIG. 8 schematically represents another example of a hybrid measurement system with feedback loop for correcting in real time an error of bias in a conventional accelerometer by means of measurements from an inertial cold atom interferometer and the compensation of the random Doppler effect to maintain the contrast of the interferometer;
    - Figure 9 illustrates acceleration measurements in a cold atom interferometer with real-time correction of bias errors in a conventional accelerometer using measurements from an inertial cold atom interferometer and compensation for the Doppler effect random to maintain the contrast of the interferometer.
    In this document, real-time correction means a correction made during an interferometric measurement and not between two interferometric measurements.
    Device
    In Figure 1, there is shown schematically the principle of an atomic interferometer. Consider a cloud of atoms or a puff of cold atoms 10. Generally, the puff of cold atoms 10 is initially immobilized in an atom trap, formed for example by three pairs of counter-propagating laser beams arranged along three axes orthogonal. The laser beams are possibly combined with a magnetic field to form a magneto-optical trap (MOT for magneto-optical trap). At an instant t = 0, we open the atom trap to launch or drop by gravity the puff of atoms in a predetermined direction.
    A laser source emits an interrogation field made up of a sequence of light pulses, so as to interact with the fine structure of atoms by transfer of photons between the interrogation field and the cold atoms. The laser pulse sequence produces a coherent separation of the atomic puff, at least one redirection and then a coherent recombination of the atomic beams.
    The light pulses of a sequence are generally spaced in time by a duration T. We generally use a sequence of three light pulses called sequence "π / 2- π - π / 2". The "π / 2" pulses allow the waves of matter associated with atoms to be separated or recombined. The "π" pulses deflect the matter waves. Other sequences of more than three pulses are also used, notably a sequence of four light pulses, "π / 2- π - π - π / 2 >>. In all cases, a first light pulse 21 interacts with the puff of atoms 10 coming from the source of atoms so as to spatially separate the wave associated with each atom into a first wave of atoms 11 moving along a first path and, respectively, a second wave of atoms 12 moving along a second path. At least one second light pulse 22 interacts with the two separate atom waves 11,12 to redirect them. Finally, a last light pulse 29 spatially recombines the two atom waves 11, 12. The area defined by the paths of the two atom waves 11, 12 between separation and recombination defines an atomic interferometry area. The sensitivity of the atomic interferometer is generally proportional to the area delimited by the two paths.
    A detection system makes it possible to measure the atomic phase shift accumulated between the two waves of atoms 11, 12 on their respective paths between their separation and their recombination. The atomic interferometer produces amplitudes of probabilities of the number of atoms on two output channels 51,52. We denote by Ni the population or the number of atoms in a first state, and, respectively, N 2 the population or the number of atoms in a second state. The number of atoms N 1; respectively N 2 , on each output channel 51, respectively 52, oscillates sinusoidally as a function of the total phase shift ΑΦ. In general, complementary signals are detected on the two output channels 51 and 52, as illustrated in FIG. 1.
    Atomic interferometers based on the light-matter interaction are based on the principle that, when an atom absorbs or emits a photon, it receives a momentum hk. A resonant light wave is used to excite an atom by moment transfer. The most frequent light pulse atomic interferometers are based on transitions with two photons selective in speed, or, in other words in optical frequency difference, the optical frequency f and the speed v being linked by Doppler effect according to the formula: f = kv A common example of this type of two-photon transition corresponds to a Raman transition, where two laser beams of optical frequencies ωΐ and ω2 are adjusted in the vicinity of an optical transition in the atom considered, all being sufficiently detuned so that the level of excited population is sparsely populated. The frequency mismatch (ωΐ - ω2) is chosen to be resonant with a radio-frequency transition between two fundamental hyperfine levels of the atom considered. A Bragg multiphoton or Bloch oscillation transition can also be used to construct an atomic interferometer. In the last mentioned cases, instead of producing transitions between two hyperfine fundamental levels, the atoms remain in the same fundamental state and only their momentum changes.
    In the following description, we take as an example the case of Raman transitions for rubidium 87 ( 87 Rb) atoms. However, the principle also applies to other multi-photon transitions, for example Bragg or Bloch. The same principle also applies to other atoms, for example lithium, sodium, potassium or cesium.
    FIG. 2 shows a schematic example of an atomic interferometer based on a sequence of photon transfers by Raman interaction with two photons. Two counter-propagating laser beams detuned in frequency with respect to the center frequency f c of the laser source are used here to generate each interaction between the interrogation field and the cold atoms. More precisely, two-photon transitions are made between a ground state | 1, p0> and an excited state | 2, pO + hkeff> where k e ff = ki + k 2 s 2ki. The speed of the atoms induces a quadratic shift of the energy of the states, which are separated in frequency from the sum of the hyperfine separation, denoted cohf, between these two atomic states, of the Doppler shift, denoted ω 0 , induced by the relative velocity atoms, and the frequency of recoil, noted ro re c, induced by the absorption with two photons.
    A puff of atoms 10 is initially in the atomic state | 1, p0>. A laser source device generates a first pair of counterpropagating pulses defined by a wave vector ki and respectively -k 2 . More precisely, two co-propagating pulses of wave vectors ki and respectively k 2 are generated. A mirror 8 is arranged so as to reflect the two co-propagating pulses and form two other co-propagating pulses of wave vectors -ki and respectively -k 2 The optical frequencies of the laser pulses are selected according to the atomic levels of the puff of atoms so as to interact via a nonresonant two-photon interaction. A first pair of counter-propagating pulses is used here consisting of a wave vector pulse ki and respectively a wave vector pulse -k 2 . This first pair of pulses makes it possible to separate the puff of atoms 10 into a first wave of atoms 11 and a second wave of atoms 12. During this interaction, the atom diffuses a photon from each beam for a transfer of moment equal to h (Æ r / f2) · The detuning δ between the two photons which determines the resonance condition for the Raman transition is given by:
    δ = (Q e ff - (COhf + CÛd + CQ re c) where “Vf = king - ω 2 is the difference in optical frequency between the two laser beams, cûhf is the separation between the two hyperfine levels of the ground state (gühf ~ 2πχ 6.8 GHz for the atom 87 Rb), cq d represents the Doppler shift due to the speed of the atoms (ω 0 ~ 2πχ 100 kHz) and ro rec is the recoil frequency (or the Doppler shift due to the recoil of a photon by an atom of mass M, türec ~ 2πχ 15 kHz). The force of the Raman transition is greater when the central optical frequency (denoted f c ) of the laser is adjusted so that δ = 0. Under these conditions, the population of atoms oscillates between two internal states as a function of the interaction time with the lasers, so that the Raman pulses can be adjusted to coherently separate or reflect the waves of atoms. contra-propagative (k 2 ~ -k 1 ), this transition is accompanied by an exchange of moment approximately equal to double of a transition to a photon: h (k 2 -k 1 ) ~ 2hk 1 . This produces a strong sensitivity to the Doppler effect associated with the relative movement of the atom.
    There are different types of atom interferometers: for example the Mach-Zehnder type atomic interferometer with 3 light pulses, the Ramsey Bordé atomic interferometer with 4 light pulses, or the Talbot Lau / contrast / Kapitza Dirac interferometers at N pulses where N is an integer greater than 4.
    The most commonly used atomic interferometer geometry is based on a pulse sequence "π / 2 - π - π / 2". This gives a Mach-Zehnder atomic interferometer as illustrated in FIG. 2. Here, the first pair of counter-propagating pulses 21, denoted "π / 2", excites an atom in an initial state to generate a first wave of atoms 11 and a second wave of atoms 12. During a period T, the two waves of atoms propagate separately. A second pair of pulses 22, denoted “π”, redirects the first wave of atoms 11 and the second wave of atoms 12. After another time interval T, a last pair of counter-propagating pulses 29, denoted “π / 2”, recombines the first wave of atoms 11 and the second wave of atoms 12 to make them interfere.
    Interference is measured by detecting on one of the two output ports 51, respectively 52, the relative population N 1; respectively N 2 , associated with one of the two states, ie corresponding to one of the waves of atoms 11, respectively 12. These populations N-ι, respectively N 2 , are generally measured by resonant fluorescence , several photons can be scattered by a single atom.
    The three-pulse Raman interferometer excites only two paths. The interferogram follows a sinusoidal function:
    p ± 2 = = 1 (i + c cosJ <2> tot )
    Nt + Nz 2 v C0CJ where C represents the contrast of the interference fringes and ΔΦ ιυι the total accumulated interferometric phase shift.
    Depending on the orientation of the atom source and the atomic interferometer, the interferometric phase shift is sensitive to acceleration and / or rotation in a determined direction. Atomic interferometers find applications in inertial sensors of the gravimeter, gradiometer, accelerometer and gyrometer type with cold atoms. A particularly important application of atomic interferometry relates to cold atoms accelerometer (CAA).
    Figure 3 shows an example of an accelerometer based on a cold atom interferometer (CAA). A cloud of cold atoms 10 is formed in a vacuum enclosure 1. A laser beam 20 is incident on the cloud of atoms 10 through a transparent window 6. The laser beam 20 is oriented in a direction defined by a vector k. A mirror 8 is arranged so as to retro-reflect the laser beam 20. In other words, the normal 18 on the surface of the mirror 8 is aligned in the direction of the vector k. Thus, the cold atom accelerometer performs a measurement along the laser beam, parallel to the vector k. A conventional inertial sensor 4, for example based on MEMS, is fixed to the rear face of the mirror 8. The conventional sensor is arranged so as to be sensitive along the measurement axis k of the interferometric sensor. Preferably, the measurement of the conventional sensor is carried out along the same axis k. Alternatively, it is sufficient to know the angle between the axis of the conventional measurement and the axis of the measurement by atomic interferometry. The conventional sensor and the interferometric sensor can be sensitive to different quantities. For example, the conventional sensor measures a rotation around the axis of vector k and the interferometric sensor measures an acceleration along the axis of vector k.
    We denote Z the vertical direction and X a horizontal direction of an orthonormal coordinate system (X, Y, Z). In general, we consider a rotation of the orientation of the cold atom accelerometer with respect to the vertical axis Z and an acceleration vector a, which is generally off-axis with respect to the vector k. Such a rotation and such an acceleration constitute non-negligible sources of errors for the cold atom accelerometer and / or for the conventional sensor, which generally does not have a measurement of the rotation and the acceleration according to the three directions of the orthonormal coordinate system (X, Y, Z). The purpose of this disclosure is to correct these errors.
    The total phase shift of the cold atom accelerometer is expressed as follows:
    ΔΦίοί = k ef f. aT 2 - Φ ο where Φο is a constant and a represents the relative acceleration of the atoms with respect to the reference mirror. The amount Φο can be related to the phase of the laser for example. The quantity Φ ο is generally used as a control parameter to sweep the interference fringes, which makes it possible to measure the phase shift due to acceleration a. The above equation shows the high sensitivity of atomic interferometers to inertial effects, such as gravity. As this phase shift is proportional to T 2 , with an interrogation time of T ~ 10 ms and k eff of the order of 1.6 × 10 7 rad / m at a wavelength of 780 nm, the acceleration due to the gravity induces a phase shift of 1.6x10 4 rad. Assuming an uncertainty of phase shift of the order of 1 mrad per stroke, the sensitivity of the accelerometer to gravity is approximately 6 × 10 -8 g.
    It is known in a cold atom gravimeter to linearly modulate the frequency difference between the interferometric beams at a rate a suitable for canceling the frequency offset induced by the Doppler effect. Thus, the atoms remain in resonance with the transition to two photons when they fall by gravity. In this case, the frequency difference is written ω β // (ί) = δ 0 + a (t)
    The total phase shift is reduced to:
    ΔΦίοί = (k eff .ga) T 2 (9)
    This relationship makes it possible to measure the gravity g according to the following method. We are looking for the value of a = k eff .g for which the total phase shift of the interferometer is canceled:
    ΔΦ ίοί = 0 Then we deduce g = a / k eff
    It is assumed here that the angle between the incident laser beam and the reflected laser beam is zero. As the output signal is sinusoidal, a minimum (or respectively a maximum) is obtained on the fringes at each phase shift of 2π. Consequently, the determination of the linear coefficient a of frequency modulation which cancels gravity for a certain duration of interrogation T is ambiguous modulo 2π.
    However, equation (9) is independent of the interrogation time T if and only if g = a / k ef f. It is possible to determine the central fringe by comparing two interferograms obtained for two distinct interrogation time values T. The central fringe indeed has an absolute reference phase equal to a = k eff .g unchanged regardless of the value of T. Once the central fringe is identified, new gravity measurements can be obtained quickly, once per cycle of CAA, for example every 0.2 to 1s. This is obtained by inverting the probability Pi, 2 in the domain of reciprocity of the cosine function to obtain the total phase shift:
    ΔΦ ίοί = cos- 1 ^^ - 1) / C)
    We deduce g = - + ^^ ~ a k eff k eff T2
    The first term of this equation corresponds to the position of the central fringe (i.e. the linear frequency modulation which cancels the Doppler effect induced by gravity on the atoms) and the second term corresponds to a small correction d acceleration which takes into account uncontrolled phase shifts (for example vibrations of the mirror 8 defining a reference frame) of at most n / k eff T 2 . For example, if T = 10ms and k eff = 1.6x10 7 rad / s the maximum acceleration correction is 200 pg. This also implies that the value of a is determined with a relative precision better than 10 ' 4 For example, for rubidium atoms 87, δα “2π.2.5 kHz / s for α ~ 2πχ25 MHz / s is required to cancel the gravity g with T = 10 ms.
    FIG. 4 illustrates an example of acceleration measurement according to the prior art. FIG. 4A shows a signal a (t) recorded as a function of time by means of a conventional accelerometer 4 fixed to the retro-reflecting mirror 8 during a sequence of pulses 21, 22, 23 or in an equivalent manner π / 2-π-π / 2. In FIGS. 4A and 4B, a constant acceleration ao is applied applying to cold atoms. In FIG. 4B, a linear modulation of frequency f (t) is also shown applied to the frequency difference between incident laser beams for the interaction with two photons, this linear modulation of frequency f (t) being adjusted to cancel l Doppler effect induced by the constant acceleration ao on cold atoms. In FIGS. 4A and 4B, the curve 14 retraces the vibration measurements on the mirror 8 obtained by means of the conventional accelerometer 4. The curve 15 represents a control phase applied to generate a phase jump just before a sequence of pulses, so that the interferometer operates in the vicinity of the half-fringe, in the signal linearity range.
    In FIG. 4C, two measurements 53, 54 of the signal from the atomic interferometer are observed in the vicinity of the total phase shift of ± π / 2. These measurements 53, 54 allow an evaluation of ao.
    However, there is a loss of contrast C. This loss of contrast leads to a loss of sensitivity of the atomic interferometer. If the contrast C falls below a contrast threshold, the interferometer no longer works.
    It follows from the present disclosure that this loss of contrast is due to the Doppler shift induced by the vibrations which are not compensated for during each laser pulse.
    A first solution consists in isolating the frame supporting the mirror from vibrations. However, this solution does not apply in inertial navigation applications, where vibrations are part of the movement of the vehicle.
    In the context of this disclosure, another solution is based on a real-time measurement of the vibrations in the same direction as the CAA by means of a conventional sensor 4 of accelerometer or seismometer type and on an evaluation of the phase shift associated with these vibrations. using the sensitivity of the atomic interferometer to the movement of the reference frame. For example, a conventional accelerometer measures acceleration in real time. In another example, a seismometer measures speed. The frame of reference is defined by an orthonormal reference linked to the atomic interferometer. For example, the orthonormal reference frame of the reference frame comprises the normal 18 on the surface of the mirror and two axes transverse to this normal 18.
    The conventional sensor is oriented so as to be sensitive along the axis of measurement of the CAA. It is assumed that the angle between the measurement axis of the conventional sensor and the measurement area of the CAA is known. Preferably, these two axes are combined.
    We define the sensitivity of an atomic interferometer geometry to the physical effects inducing a phase shift by a sensitivity function w (t). This sensitivity can be defined in terms of speed w v (t) or acceleration w a (t) for vibrations of the reference frame. The associated phase shift can be calculated by integration as a function of time:
    z-2T
    Φ (ί) = I w v z-2T (t) v vib (t) dt = I w a (t) a vib (t) dt
    Where r vifc (t) = fa vib (t) 'dt' is a speed induced by vibration of the reference frame at time t. It is assumed here that a vi b does not include the constant acceleration a 0 due for example to a gravity component.
    According to a particular embodiment, the signals from the conventional inertial sensor 4 are integrated in real time in order to deduce therefrom at each instant t a measurement of the speed induced by the vibrations of the reference frame.
    FIG. 5 schematically represents a hybrid inertial navigation system based on a conventional inertial sensor 4 and a cold atom inertial sensor 50. A laser source 20 generates an interrogation field of the cold atom inertial sensor 50. The interrogation field includes a sequence of laser pulses. The inertial navigation system also comprises a real-time feedback loop comprising a signal processing system 40 which applies a modulation signal to the laser source 20. Finally, the inertial navigation system comprises a second feedback loop reaction in real time comprising a device 30 for correcting the signal from the conventional inertial sensor 4.
    The cold atom inertial sensor 50 can be any type of atomic interferometer. The inertial cold atom sensor 50 is for example an accelerometer, a gravimeter, a gyroscope, a gradiometer, a magnetometer, using one or more sources of atoms (such as rubidium, potassium, etc.). The cold atom inertial sensor 50 is here assumed to be more precise than the conventional inertial sensor 4.
    During a first recurrence, part 132 of the raw signal 14 from the conventional inertial sensor 4 is transmitted to the signal processing system 40. The signal processing system 40 generates a modulation signal 140 which integrates the elements necessary to compensate for the effects of low frequency rotation, acceleration or vibration of the reference frame used by the cold atom inertial sensor 50.
    This modulation signal 140 is transmitted to the laser source 20 which generates the interrogation field of the cold atom inertial sensor 50. The modulation signal 140 generates in real time a modulation 120 of the central frequency of the laser source. The interrogation field is thus modulated in real time according to the measurements of the conventional inertial sensor 4.
    In a particular and advantageous embodiment, the cold atom inertial sensor 50 produces an error signal 150 which is used to correct the bias drift of the conventional inertial sensor 4 in the second feedback loop.
    At the following recurrence, a computer 30 corrects a new measurement 14 coming from the conventional inertial sensor 4 as a function of the error signal 150. The computer 30 therefore provides a corrected signal 130 which constitutes a second hybrid inertial measurement signal. A portion 131 of the corrected signal 130 is transmitted for use to an inertial navigation unit 100. The inertial navigation unit 100 generally comprises three gyroscopes, three accelerometers and a computer. This corrected signal 130 is much more precise than the raw signal 14 coming from the conventional inertial sensor 4. Another part 132 of the corrected signal 130 is transmitted to the signal processing system 40 to ensure the updating of the feedback loop. in real time at the next recurrence.
    In this way, the raw signal 14 from the conventional inertial sensor 4 is corrected periodically using the output signal from the cold atom inertial sensor 50. This gives a corrected signal 130 from the conventional inertial sensor 4.
    FIG. 6 illustrates a variant comprising an inertial navigation center 100, an inertial cold atom sensor 50 and a conventional inertial sensor 4 fixed to the reference frame of the inertial cold atom sensor 50. The same reference signs designate the same elements as on the FIG. 5. In this embodiment, the conventional inertial sensor 4 generates a raw signal 14. Part of the raw signal 14 is transmitted to the inertial navigation unit 100 and another part of the raw signal 14 is transmitted to the processing system of the signal 40 which generates a modulation signal 140. The modulation signal 140 is applied to the laser source 20 to modulate the center frequency of the laser source. Thus, a frequency difference of the laser source 20 is monitored in real time. In this way, the cold atom inertial sensor 50 generates a first hybrid signal 151 of inertial measurement by atomic interferometry which is corrected in real time for the movements measured by the conventional inertial sensor 4. This correction makes it possible to ensure the operation of the cold atom inertial sensor 50 despite random movements of the reference frame.
    Optionally illustrated in dotted lines in FIG. 6, the cold atom inertial sensor 50 produces an error signal 150 which is used to apply feedback directly to the inertial navigation system 100, without correction of the conventional inertial sensor 4. The error signal 150 consists of part of the first hybrid signal 151. In this way, the cold atom inertial sensor 50 and conventional inertial sensor 4 are mutually corrective.
    FIG. 7 illustrates another variant comprising a conventional inertial sensor 4, a computer 30 and an inertial sensor with cold atoms 50. In this variant, the conventional inertial sensor 4 is fixed to the reference frame of the inertial sensor with cold atoms 50. The inertial sensor conventional 4 can be similar to that described in connection with the embodiments illustrated in FIGS. 5 and 6.
    In an exemplary embodiment, the conventional inertial sensor 4 is part of an inertial navigation unit providing conventional inertial measurements in the reference frame of the inertial cold atom sensor 50. For example, the inertial navigation unit provides acceleration measurements and rotation in 3 dimensions.
    In the embodiment of FIG. 7, the conventional inertial sensor 4 and the computer 30 generate an inertial measurement signal 148, for example of measurement of rotation and / or acceleration along one or more determined axes. As indicated above, the inertial measurement signal 148 comes for example from conventional sensors of an inertial navigation unit, for example based on MEMS components. This inertial measurement signal 148 is transmitted to the signal processing system 40 which generates a modulation signal 140. The modulation signal 140 is applied to the laser source 20 to modulate the center frequency of the laser source. Thus, a frequency difference of the laser source 20 is monitored in real time. In this way, the cold atom inertial sensor 50 generates a first hybrid signal 151 of inertial measurement by atomic interferometry which is corrected in real time for the movements measured by the conventional inertial sensor 4 and the computer 30. This correction makes it possible to ensure the operation of the inertial sensor with cold atoms 50 whatever the random variations of orientation and / or position of the reference frame.
    Optionally illustrated in dotted lines in FIG. 7, the cold atom inertial sensor 50 produces an error signal 150. The error signal 150 consists of part of the first hybrid signal 151. The error signal 150 is used to apply feedback directly to the computer 30 to finely correct the measurements of the conventional inertial sensor 4, and possibly of the inertial navigation system 100 incorporating this sensor 4, as a function of the measurement of the cold atom inertial sensor 50. Thus, the cold atom inertial sensor 50 and the conventional inertial sensor 4 correct each other.
    FIG. 8 represents an exemplary implementation according to another embodiment. In this example, the conventional inertial sensor 4 is an accelerometer, for example based on MEMS. The cold atom inertial sensor is a cold atom accelerometer which measures the movements of the reference frame.
    The conventional accelerometer 4 continuously produces an acceleration measurement 14, denoted a c i (t). This acceleration measurement 14 includes an acceleration component a 0 which corresponds to the acceleration of the system that one wishes to measure, another acceleration component, denoted by V ib (t), which is associated with the vibrations of the device and a parasitic component of bias b (t), which varies slowly with time. Hence the equation:
    a cl (t) = a 0 + a vib (t) + b (t)
    The inertial navigation unit includes a computer 90. The device further includes a clock 80, a microprocessor 41, a converter 42 and an optical frequency modulator 43.
    A part 142 of the raw measurement 14 from the conventional accelerometer 4 is transmitted to a low frequency filter 9. The low frequency filter 9 extracts a measurement 19 from the continuous acceleration component aoc. A computer 70 subtracts this continuous acceleration component aoc from the acceleration measurement 155 produced by the cold atom accelerometer 50. The computer 70 thus produces a error signal 170. Another computer 30 calculates the sum of the other part 141 of the raw measurement 14 and of the error signal 170. The computer 30 thus produces an acceleration signal 130 which is corrected for the bias drift of the conventional accelerometer 4. It is noted that the error signal 170 is updated at each measurement cycle of the cold atom accelerometer 50.
    The acceleration signal 130 corrected for the bias drift is transmitted to the computer 90. The computer 90 corrects the acceleration measurement of the effects induced by movements, for example of rotation and generates an acceleration measurement ai (t ), also noted 190. A part 191 of the acceleration measurement a, (t) can be transmitted to an inertial navigation system 100 for example.
    Advantageously, the computer of the inertial navigation unit 100 can transmit a data stream 193 to the computer 90. This data stream 193 comprises, for example, rotation measurements carried out by the gyrometer (s) of the inertial navigation unit 100.
    Another part 192 of the acceleration measurement a, (t) is transmitted to the microprocessor 41. The microprocessor 41 performs two functions. On the one hand, the microprocessor 41 integrates the acceleration measurement a, (t) as a function of time to deduce therefrom a relative speed measurement 411 between the reference frame and the atoms, which are for example in free fall. Clock 80 triggers a signal 180 at the start of a measurement and integration cycle. On the other hand, the microprocessor 41 calculates a control phase 412 which ensures that the interferometer always works in the vicinity of a half-fringe, where the sensitivity is maximum. The relative speed measurement 411 is transmitted to a microprocessor 42 comprising for example a combination of digital-analog converter ADC and / or DDS. The microprocessor 42 converts the relative speed measurement 411 into a radio frequency signal 420 which corresponds to the Doppler frequency fodu frame of reference via the relation: fo (t) = keff v, (t) / 2π
    An operator 43 calculates the sum of the radio frequency signal 420 Doppler and the central frequency 2 of the laser source 20. For example, we choose f c ~ 6.8 GHz for the Raman transition of the rubidium atom 87. We thus obtain another radio frequency signal 430 which is transmitted to the laser source 20 so as to adjust the central frequency of this laser source 20.
    The control phase 412 is also transmitted to the laser source 20 so as to trigger a phase jump just before the last pulse at 2T.
    The laser source 20 generates a pulse sequence 120, for example π / 2- π- π / 2, in the direction of the cold atom accelerometer 50. Thus, during each pulse, the frequency difference between the laser beams contra -propagants varies in real time according to the continuous component of acceleration of atoms induced by gravity and according to the frequency modulated accelerations due to vibrations and movements of the device. This real-time feedback loop ensures that the total phase shift induced by the accelerations remains near zero and that the contrast of the fringes is not reduced by Doppler shift of the frequency f c of the laser source. During the last pair of π / 2 pulses, a controlled phase jump of ± π / 2 is applied to control the position of the central fringe, and ensure the sensitivity of the acceleration measurement.
    During the same measurement cycle, the comparator 70 compares the acceleration measurement 155 from the cold atom accelerometer 50 and the measurement 19 of the continuous acceleration component aoc from the conventional accelerometer 4. The comparator 70 in deduces an error signal 170 for the next measurement cycle. Thus, the servo process based on a feedback loop is completed.
    During a cycle [0; 2T], we acquire a measurement of a continuous component component of the acceleration measurement 14. We calculate the average of the acceleration measurement 14 over the time interval [0; 2Tj. The output of the cold atom accelerometer 50 provides an accurate measurement of ao in each cycle.
    In FIG. 9 illustrates an example of acceleration measurement according to an exemplary embodiment based on a system as described in connection with FIG. 5 or FIG. 8.
    FIG. 9A shows a signal a (t) recorded as a function of time by means of a conventional accelerometer 4 fixed on the retro-reflecting mirror 8 during a sequence of pulses 21, 22, 23 or in an equivalent manner π / 2-π-π / 2. The raw signal shown in Figure 9A is analogous to the signal in Figure 4A. In FIGS. 9A, 9B and 9C, there is shown a constant acceleration at 0 applying to cold atoms. The signal a (t) records the vibrations of the reference mirror 8 continuously and in real time during the laser pulses of the Roma interface being at cold atoms.
    In FIG. 9B, an integral of the acceleration signal supplied by the conventional accelerometer has also been represented as a function of time. The signal of FIG. 9B corresponds to the relative speed v c i (t) between the atoms and the reference mirror 8. The signal of Figure 9B includes the relative movements of the reference frame induced by vibrations.
    In FIG. 9C, the signal 411 of the relative speed v c i (t) is converted into a non-linear frequency ramp 420. The non-linear frequency ramp 420 is added to the frequency f c to form a frequency signal 430 modulated in real time. The non-linear frequency ramp makes it possible to automatically cancel the phase shifts induced by accelerations or vibrations of the reference frame, in other words of the mirror 8, and compensates for the Doppler effect.
    A phase jump is applied just before the last pulse 23 of a sequence of pulses, so that the interferometer operates in the vicinity of the half-fringe, in the signal linearity range.
    In FIG. 9D, two measurements 55, 56 of the signal coming from the atomic interferometer are observed in the vicinity of the total phase shift of ± π / 2. These measurements 55, 56 allow a precise evaluation of the acceleration at 0 .
    Indeed, no loss of contrast is observed due to the suppression in real time of the effect of the vibrations.
    We have described an embodiment based on the hybridization of a conventional acceleration sensor and an accelerometer based on a cold atom interferometer (CAA).
    However, the principle of a hybrid feedback loop system also applies to other types of inertial sensors.
    In another example, the conventional inertial sensor is used, a gyrometer adapted to measure a rotation of the system around an axis of rotation and variations in rotation. In this case, the cold atom interferometer is advantageously configured to measure a rotation, preferably around the same axis of rotation.
    In a particularly advantageous manner, the conventional inertial sensor is a sensor adapted to measure the accelerations and rotations according to 6 degrees of freedom and, in a similar way, the interferometric system with cold atoms is configured to measure the accelerations and rotations according to 6 degrees of freedom. We thus have a complete inertial system, corrected for each of the 6 degrees of freedom.
    Such a hybrid system provides position and orientation measurements over a very wide range of measurements, these measurements being corrected for movements of the inertial system reference frame.
    权利要求:
    Claims (15)
    [1" id="c-fr-0001]
    1. Hybrid inertial measurement system comprising:
    a cold atom interferometric inertial sensor (50) comprising a laser source (20) adapted to generate a sequence of laser pulses (21, 22, 23, 29) in the direction of a puff of cold atoms (10) and a system for detecting an inertial measurement signal by atomic interferometry relating to an inertial reference frame, and
    - a conventional inertial sensor (4, 100) fixed to the inertial reference frame of the cold atom interferometric inertial sensor (50), the conventional inertial sensor (4, 100) being adapted to supply a conventional inertial measurement signal (14, 148 ) of the inertial reference frame, characterized in that the hybrid system comprises an electronic feedback loop system comprising:
    - a signal processing system (40, 41,42) adapted to receive an inertial measurement signal (14, 141, 148) from the conventional inertial sensor (4, 100), the signal processing system (40, 41, 42) being adapted to generate in real time a non-linear frequency modulation signal (140, 420) as a function of the inertial measurement signal (14, 141, 148),
    - each laser pulse of the laser pulse sequence (21,22, 23, 29) having a predetermined optical frequency detuning with respect to a central optical frequency (2) of the laser source (20), the electronic loop system of feedback being configured to modulate in real time the central optical frequency of the laser (20) as a function of the modulation signal (140, 420), so as to modulate in real time said sequence of laser pulses (21,22, 23, 29) and that the interferometric cold atom inertial sensor (50) generates a first hybrid signal (151) of inertial measurement by atomic interferometry corrected for relative movements of the inertial reference frame with respect to the puff of cold atoms (10) during a measurement cycle.
    [2" id="c-fr-0002]
    2. Hybrid system according to claim 1 in which the inertial reference frame comprises a reflecting optical component (8) arranged so as to retro-reflect the sequence of laser pulses (21, 22, 23, 29) and to generate a sequence of counterpropagating laser pulses towards the puff of cold atoms (10), the conventional inertial sensor (4, 100) being fixed to the reflecting optical component (8) of the interferometric cold atom inertial sensor (50).
    [3" id="c-fr-0003]
    3. Hybrid system according to one of claims 1 to 2 wherein the signal processing system (40, 41,42) is adapted to further generate a phase shift correction signal (412) of the laser source (20) .
    [4" id="c-fr-0004]
    4. Hybrid system according to one of claims 1 to 3 further comprising a phase jump generator configured to generate a sampling suitable for extracting an interference fringe phase measurement.
    [5" id="c-fr-0005]
    5. Hybrid system according to one of claims 1 to 4 in which the signal processing system (40, 41, 42) is adapted to generate frequency modulation signal comprising a linear modulation component and a non-linear component of modulation as a function of time.
    [6" id="c-fr-0006]
    6. Hybrid system according to one of claims 1 to 5 wherein the conventional inertial sensor (4) comprises a seismometer, a MEMS-based accelerometer, a MEMS-based gyrometer, a laser gyrometer or a fiber optic gyrometer.
    [7" id="c-fr-0007]
    7. Hybrid system according to one of claims 1 to 6 comprising a computer (30) adapted to receive a part (150) of the first hybrid signal (151), the computer (30) being adapted to generate a second inertial measurement signal hybrid (130, 132, 148, 149) as a function of the conventional inertial measurement signal (14) and of the part (150) of the first hybrid signal coming from the cold atom interferometric inertial sensor (50).
    [8" id="c-fr-0008]
    8. Hybrid system according to claim 7 in which the cold atom interferometric inertial sensor (50) is adapted to generate an error signal (150, 170) by difference between the inertial measurement signal (150, 155) by atomic interferometry corrected to a recurrence N of the measurement cycle and the inertial measurement signal (150, 155) by atomic interferometry to a recurrence N-1, where N is a natural integer greater than or equal to two, and in which the computer (30 ) is adapted to receive the error signal (150, 170) and a first part of the inertial measurement signal (14, 141) from the conventional inertial sensor (4), the computer (30) being adapted to deduce the second signal therefrom hybrid inertial measurement (130, 132, 148, 149).
    [9" id="c-fr-0009]
    9. Hybrid inertial measurement system according to claim 8, in which the signal processing system (40, 41, 42) is adapted to receive the second hybrid inertial measurement signal and in which the signal processing system (40, 41 , 42) is adapted to take part of the second hybrid inertial measurement signal (130, 132, 148, 192) in replacement of the inertial measurement signal (14, 141, 148) of the conventional inertial sensor (4, 100) and for generating in real time a non-linear frequency modulation signal (140, 420) as a function of said part of the second hybrid inertial measurement signal (130, 132, 148, 192).
    [10" id="c-fr-0010]
    10. Hybrid system according to one of claims 8 to 9 further comprising a coupler configured to take in real time another part of the inertial measurement signal (142) from the conventional inertial sensor (4), a filter (9) passes -based adapted to filter a DC component of said other part of the inertial measurement signal (142), a comparator (70) adapted to compare a DC component (19) of said other part of the conventional inertial measurement signal with the measurement signal inertial (155) by atomic interferometry to deduce a bias error signal (170) from the conventional inertial sensor, and the computer (30) being adapted to receive the bias error signal (170) and the first part of the signal of the inertial measurement signal (14, 141) of the conventional inertial sensor, the computer (30) being adapted to calculate in real time the second hybrid inertial measurement signal (130) by difference between the first part of the inertial measurement signal (14,
    141) of the conventional inertial sensor (4) and the bias error signal (170).
    [11" id="c-fr-0011]
    11. Hybrid inertial measurement system according to one of claims 8 to 10 wherein the computer (30) is adapted to transmit another part of the second hybrid inertial measurement signal (131, 191) to an output of the hybrid measurement system inertial.
    [12" id="c-fr-0012]
    12. Hybrid inertial measurement system according to claim 7 alone or in combination with one of claims 8 to 11 in which the conventional inertial sensor (4, 100) and the computer (30) are part of an inertial navigation unit (100) comprising three accelerometers, three gyrometers and a computer adapted to generate an inertial navigation signal based on the measurements of the three accelerometers and three gyrometers, the inertial navigation center being adapted to receive said part (150) of the first hybrid signal (151), the inertial navigation unit (100) being adapted to generate a hybrid inertial navigation signal (152) as a function of the inertial navigation signal and of the part (150) of the first hybrid signal coming from the atomic interferometric inertial sensor cold (50).
    [13" id="c-fr-0013]
    13. Hybrid inertial measurement system according to claim 12, in which the inertial navigation unit is adapted to receive a part (150) of the first hybrid inertial measurement signal (151) and / or of the second hybrid inertial measurement signal (131, 191) and to generate a hybrid inertial navigation signal.
    [14" id="c-fr-0014]
    14. Hybrid system according to one of claims 7 to 13 in which the cold atom interferometric inertial sensor (50) is configured to measure an acceleration signal by atomic interferometry, the feedback loop comprising a microprocessor (41) adapted to integrate the acceleration signal as a function of time in order to deduce therefrom a measurement of relative instantaneous speed of the inertial reference frame with respect to the puff of atoms (10), and in that the modulation signal (420) of the center frequency of the laser has a ramp proportional to the instantaneous speed measurement.
    [15" id="c-fr-0015]
    15. Hybrid inertial measurement method comprising the following steps:
    at. Generation of a laser pulse sequence (21,22, 23, 29) in the direction of a puff of cold atoms (10), each laser pulse in the laser pulse sequence (21,22, 23, 29 ) having a predetermined optical frequency detuning with respect to a central optical frequency (2) of the laser source (20), and detection of an inertial measurement signal by atomic interferometry relating to an inertial reference frame;
    b. Detection of a conventional inertial measurement signal (14, 148) of the inertial reference frame;
    vs. Processing of the conventional inertial measurement signal (14, 148) to generate in real time a non-linear frequency modulation signal (140, 420) as a function of the inertial measurement signal (14, 141, 148),
    d. Real-time modulation of the central optical frequency of the laser (20) as a function of the modulation signal (140, 420), so as to real-time modulate said sequence of laser pulses (21,22, 23, 29) and generate a first hybrid signal (151) for inertial measurement by atomic interferometry corrected for relative movements of the inertial reference frame with respect to the puff of cold atoms (10) during a measurement cycle.
    1/5 γ ο
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    同族专利:
    公开号 | 公开日
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    US11175139B2|2021-11-16|
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    FR1751457A|FR3063141B1|2017-02-23|2017-02-23|HYBRID SYSTEM AND METHOD OF INERTIAL MEASUREMENT BASED ON A COLD ATOM AND LUMINOUS PULSES INTERFEROMETER|
    FR1751457|2017-02-23|FR1751457A| FR3063141B1|2017-02-23|2017-02-23|HYBRID SYSTEM AND METHOD OF INERTIAL MEASUREMENT BASED ON A COLD ATOM AND LUMINOUS PULSES INTERFEROMETER|
    US16/488,398| US11175139B2|2017-02-23|2018-02-23|Hybrid inertial measurement system and method using a light pulse cold atom interferometer|
    PCT/FR2018/050440| WO2018154254A1|2017-02-23|2018-02-23|Hybrid inertial measurement system and method using a light pulse cold atom interferometer|
    EP18709698.7A| EP3586084A1|2017-02-23|2018-02-23|Hybrid inertial measurement system and method using a light pulse cold atom interferometer|
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