Chip scale atomic gyroscope

The present invention generally relates to the field of atomic-based sensing devices. More specifically, the present invention relates to chip-scale atomic gyroscopes and methods for detecting orientation and rate.

Government Assistance: The invention was made with the assistance of the United States Government under DARPA Agreement No. N66001-02-C-8019. The US Government may have certain rights to the invention.

Gyroscopes are used in a variety of applications to detect the orientation (direction) and inertial motion of an object. For example, in the design of navigation and communication systems, such devices are useful for detecting small fluctuations in the linear and rotational motion of an object traveling in space. For example, navigation-grade gyroscopes allow highly accurate follow-up of desired flight paths, especially in environments where GPS guidance is not available.

The field of gyroscope design covers a wide range of technologies, including mechanical, fiber optic, and ring laser based designs. More recent trends have emphasized ultra-compact, high-performance architectures such as microelectromechanical systems (MEMS) -based devices, and semiconductor manufacturing techniques for forming miniaturized components on the surface of wafers. Is used. For example, in one such design, often referred to as a MEMS vibration rate gyroscope, a resonant structure such as a proof mass is suspended by flexures fixed to a substrate such as a silicon or glass wafer. Suspension structures commonly practiced may include interdigitalized comb-shaped members, cantilever beams, discs, and / or ring structures. To detect displacement or acceleration in response to device motion about the rate axis, the proof mass is typically driven into a high Q resonant state using several drive electrodes. Under angular rotation, the Coriolis force resulting from the device's motion with respect to the rate axis induces motion in the direction of the sensing axis perpendicular to the proof mass motion, which is then capacitively detected. It can be output as a rate signal.

Since mechanical gyroscopes such as MEMS vibration rate gyroscopes often operate in high Q impact environments, such devices tend to drift over time due to aging, material degradation, and stress, and gyroscopes. It results in the instability of the scale factor (scale factor) in. In some cases, the stiffness and damping of the cross-coupling between the drive and detection directions can affect the performance of the gyroscope, leading to bias drift problems. In addition, the suspension structure is susceptible to shock and vibration, which can affect the ability of the device to accurately detect subtle changes in directional and / or angular rotation. Due to the relatively small output and measured capacitance detection signals, MEMS vibration rate gyroscopes often require high stability and accuracy detection electronics, which consumes a lot of power and is complicated to manufacture. become.

To overcome many of the shortcomings associated with mechanical gyroscopes, atomic-based gyroscopes have been proposed that rely on the precession rate of alkali metal atoms to detect angular rotation. And measure. One exemplary design, often referred to as the Larmor precession gyroscope, uses a vapor cavity filled with alkali metal and two rare gas isotopes to detect rotation. In a non-rotating frame, a static magnetic field is applied and the isotopes are spin aligned using optical pumping. Two vertical vibrating magnetic fields are then applied at frequencies close to the Larmor precession frequency for each isotope, thereby inducing precession for the static magnetic field, which uses magneto-optical techniques. Can be measured. As the system rotates, the angular velocity changes the precession frequency, which can then be extracted numerically to determine the rotation rate of the gyroscope.

One major problem with the Larmor precession gyroscope is the need to use two separate isotopes with similar relaxation time constants in order to accurately extract the rotation rate. For example, in some designs, two different nuclei, each with a different gyromagnetic ratio, may be configured to precess at different rates in the applied magnetic field. The mechanical rotation rate of the gyroscope is then derived by simultaneously tracking the precession rate of each nucleus and then subtracting the contribution of the magnetic field from the measured precession rate. However, such proposed designs are difficult to implement in practice because small magnetic field gradients can cause atoms to precess at different rates, resulting in output fluctuations. In addition, due to differences in relaxation rates, isotopes lose spin coherence at different rates, leaving the system in a complex and uncharted state. Since such a gyroscope required synchronous precession information from both isotopes, it is difficult to obtain high signal fidelity with such a design. High cross-axis sensitivity of the device Such aspects, which are associated with sensitivity and extreme sensitivity to magnetic gradients and transients, result in complex systems that are under normal field triaxial rotational motion. It is difficult to extract the angular rotation of.

<p> Therefore, there is a need for improved atomic sensors used to sense direction and / or rate.</p>

<p> The present invention relates to chip-scale atomic gyroscopes and methods for direction and rate detection. An exemplary chip-scale atomic gyroscope was adapted to include alkali metal atoms, rare gas atoms, and vaporized sources of one or more buffer gases. It can include a vapor cell having a vapor cavity. The vapor cell can be included within the packaging structure of the gyroscope by including one or more individual enclosed cavities. In other embodiments, the vapor cell may be defined by a multi-wafer stack. Several storage chambers are defined to store the supply of alkali metal and rare gas atoms. In some embodiments, several nested shields may be provided for packaging structures for magnetic and heat shielding. In addition, the packaging structure may also include one or more other elements such as magnetic field sources and heating sources.</p><p> A pump laser source adapted to generate a pump laser beam along the optical pumping axis of the gyroscope can be used to photopump the alkali metal atoms in the steam cavity into an excited state. For example, in some embodiments, the laser beam output by the pump laser source is maintained at a wavelength that corresponds to the carrying wavelength of the alkali metal atoms, producing angular momentum at the alkali metal atoms, which is the rare gas atom. Induces polarization of nuclear spins in. Fixing the pump laser source to the carrier wavelength of the alkali metal atom is, for example, a servo mechanism adapted to receive a feedback signal from a photodetector that is in optical contact with the pump laser beam and steam cavity. Can be achieved through.</p><p> In addition, the detection laser source may be configured to generate a second laser beam along the probe axis across the optical pumping axis to determine the angle of polarization of the rare gas atom in the vapor cavity. Detection of the polarization angle of rare gas atoms can be achieved by ellipsometry techniques that use a detection laser beam and at least two vertical polarizing filters that optically communicate with a second photodetector. The detection laser source can be fixed to the detuned wavelength of the alkali metal atom via a second servo mechanism adapted to receive a feedback signal from the second photodetector.</p><p> An exemplary method of detecting and measuring the mechanical rotation of a moving object using an atomic gyroscope is to photopump the alkali metal atoms in the steam cavity to an excited state and rare gas atoms through ultrafine spin exchange. In the steam cavity, the step of inducing the nuclear spin polarization in, and the step of directing the detection laser beam across the pump laser beam to determine the angle of polarization of the rare gas atom in the steam cavity. It can include a step of measuring the rotation angle of the rare gas atom and then a step of outputting the measurement result of the mechanical rotation of the gyroscope.</p>

<figref num="1">FIG. 1 is a schematic top view of a chip-scale atomic gyroscope according to an exemplary embodiment of the present invention.</figref><figref num="2">FIG. 2 is a schematic side view of the example chip-scale atomic gyroscope of FIG.</figref><figref num="3A">Figures 3A to 3C show⁸⁷Rb alkali metal atom and¹²⁹It is a schematic diagram which shows the operation of the exemplary atomic gyroscope of FIGS. 1 and 2 using the source of Xe rare gas atom.</figref><figref num="3B">Figures 3A to 3C show⁸⁷Rb alkali metal atom and¹²⁹It is a schematic diagram which shows the operation of the exemplary atomic gyroscope of FIGS. 1 and 2 using the source of Xe rare gas atom.</figref><figref num="3C">Figures 3A to 3C show⁸⁷Rb alkali metal atom and¹²⁹It is a schematic diagram which shows the operation of the exemplary atomic gyroscope of FIGS. 1 and 2 using the source of Xe rare gas atom.</figref>

The following description should be read with reference to the drawings, in which similar elements in different drawings are similarly numbered. These drawings are not necessarily scaled and show selected embodiments and are not intended to limit the scope of the invention. Examples of configurations, dimensions, and materials for various elements will be shown, but it will be appreciated by those skilled in the art that many of the examples provided have suitable alternatives that can be used.

1 and 2 are schematic views of the upper surface and the side surface showing the chip-scale atomic gyroscope 10 according to the exemplary embodiment of the present invention, respectively. As shown in FIGS. 1-2, the atomic gyroscope 10 can be manufactured from a 3-wafer stack that includes a lower wafer substrate 12, a central wafer substrate 14, and an upper wafer substrate 16. Together form a packaging structure 18, which is for use in detecting directional and / or angular rotation by monitoring the effects of external rotation on alkali metal atoms and rare gases. , Constructed to support some optical and electrical components. For example, as also discussed in more detail below, the atomic gyroscope 10 can include a vapor cell 20 having a vapor cavity 22 containing an alkali metal, a rare gas isotope, and a suitable buffer gas. The atomic population can be optical pumped into an excited state using a pump laser source 24, which allows the alkali metal atoms in the steam cavity 22 to gain angular momentum, which in turn is a rare gas isotope. It is transmitted to the nucleus of the body. The detection laser source 26 can be used to determine the relative change in the angle of polarization of the isotope, thereby allowing the mechanical rotation of the atomic gyroscope 10 to be measured.

The underside wafer substrate 12 of the packaging structure 18 can be formed from glass material and provides the structural basis for the various optical and electrical components of the atomic gyroscope 10. The central wafer substrate 14 can be formed from silicon and has various side walls 28, 30 of the vapor cavity 22 and several vacuum filled chambers 32, 34 for the storage of alkali metal atoms and rare gas isotopes, respectively. It is configured to support and. As an alternative, in another embodiment, the central wafer substrate 14 of the packaging structure 18 can be configured to support the vapor cavity 22 in situ and insert it into the wafer stack. In addition, the central wafer substrate 14 may include several mirror surfaces 36, 38 for directing the laser beam emitted from the pump laser source 24 into the vapor cavity 22 and then towards the photodetector 40. it can. The upper wafer substrate 16 can be formed from glass and provides a heat insulating vacuum enclosure 42 for the vapor cell 20, which the atomic gyroscope 10 has at relatively low power levels, and about -55 °. Allow operation in an environment with a temperature range between C and about + 85 ° C. Manufacture of various wafer substrates 12, 14, 16 can be achieved using semiconductor manufacturing techniques commonly used in MEMS manufacturing such as lithography and surface microfabrication.

The lower wafer substrate 12 can be connected to the central wafer substrate 14 by some brazing and / or adhesive bonds 44, 46 located at or near each end 48, 50 of the atomic gyroscope 10. The upper wafer substrate 16 is connected to the central wafer substrate 14 by some second wax and / or adhesive bonds 52, 54 similarly located at or near each end 48, 50 of the atomic gyroscope 10. be able to. Further, if desired, other connecting means are provided to optically and electrically connect the various components of the atomic gyroscope 10 to other external devices. For example, in some embodiments, optical and / or electrical feedthrough is provided at the periphery of the packaging structure 18 to allow the atomic gyroscope 10 to be connected to an inertial measurement unit (IMU). ..

The atomic gyroscope 10 is relatively insensitive to fast transients and gradients, but the presence of an external DC and / or low frequency magnetic field causes the servo-controlled field canceling mechanism (servo) used by the gyroscope 10. controlled field cancellation It biases the mechanism) and induces nuclear magnetic resonance (NMR). To dampen magnetic field interference, the packaging structure 18 can be formed or housed inside several nested shields, which nest the various components of the atomic gyroscope 10. It is configured to shield both magnetically and thermally. For example, in the exemplary embodiments of FIGS. 1-2, two such shields 56, 58 are schematically shown to contain the components of the atomic gyroscope 10. However, depending on the operating environment of the atomic gyroscope 10, more or fewer shields may be provided. The composition of the shields 56, 58 typically depends on the characteristics of the magnetic field. For example, a uniaxial field coil can be used to achieve total magnetic field cancellation so that the primary effect due to arbitrary magnetic field interference is zero. A nested 3-axis 3-coil configuration can also be used to eliminate the secondary effects that cause magnetic field interference. In some embodiments, the laser source (24, 26) is located outside the shields 56, 58, in which case the optical signal is supplied through the shields 56, 58.

Shields 56, 58 are made of suitable materials that are opaque to DC and low frequency magnetic fields. For example, in some embodiments, the shields 56, 58, respectively, may include a Supermalloy or Permalloy® material having a nickel-iron composition, which material is Insensitive to magnetic field gradients and transients, which are common in many gyroscope applications. However, it should be understood that other materials may be used to form the shields 56, 58 if desired. To further assist the occlusion, optical and electrical feedthroughs can be made to pass through the occlusions 56, 58 in a zigzag configuration, further preventing the entry of magnetic fields into the packaging structure 18.

The atomic gyroscope 10 can further include a getter material 60, such as titanium, for capturing any residual oxidized liquid and / or gas contained within the packaging structure 18. The getter material 60 can be formed, for example, in the upper vacuum chamber 42 of the atomic gyroscope 10 and can communicate with the vapor cell 20 via a small opening or tunnel 62. The getter material 60 can be formed by depositing encapsulated getter dots on the inner surface 64 of the upper wafer substrate 16 and then fresh when the wafer substrates 12, 14, 16 are hermetically sealed. Melt or heat the encapsulated getter material 60 to release a good getter. In use, the getter material 60 can be used to chemically absorb any contaminants within the packaging structure 18, which are outgassing of common atmospheric gases and packing material vapors during processing. And can be caused by the diffusion or microleakage of such materials into the packaging structure 18 over time.

The vapor cell 20 can be formed at least partially on the lower wafer substrate 12 using a suitable process such as etching. For example, in some techniques, silicon dioxide (SiO)₂) Etc. can be grown or deposited on the lower wafer substrate 12 to form a portion of the vapor cell 20. The steam cell 20 can generally be divided into one or more storage chambers 32, 34 and a steam cavity 22. Storage chambers 32, 34 can be configured to act as holding chambers for alkali metal and rare gas atoms, respectively, which are placed in storage chambers 32, 34 and are non-existent, such as aluminum layers. It can be covered with an activating layer. As an alternative, storage chambers 32, 34 may be formed outside the wafer stack using appropriate geometry and materials and then inserted into the stack during wafer stack processing. The steam cavity 22 communicates with the laser beam 66 from the pump laser source 24 and the photodetector 40, and provides a source of alkali metal atoms deposited in the retention storage chamber 32 and a small opening or tunnel 68. Can be connected via. The alkali metal atoms in the storage chamber 32 can be configured to vaporize and fill the vapor cavity 22 when heated. Typically, the vapor pressure of the alkali metal is sufficient for the vaporized alkali metal to fill the vapor cavity 22 to a saturated vapor pressure at the desired operating temperature, for example 200 ° C. .. However, the exact temperature at which saturated vapor pressure is achieved typically depends on the composition of the atomic population, the size of the vapor cavity 22, and other factors.

The vapor cell 20 is surrounded by or contained within one or more walls or layers 70 made of a highly thermally conductive material, the walls or layers having an insulating gap to keep the temperature in the vapor cavity 22 stable. Form a thermal enclosure that acts as. A thermal bridge 72 can also be provided adjacent to the steam cell 20 to help maintain a stable temperature within the steam cavity 22. In some embodiments, some active heating elements (not shown) are used to heat the steam cell 20 to maintain the operating temperature in the steam cavity 22 at a constant temperature (eg + 200 ° C). ) Can be used. The heating element can include, for example, wire windings, power transistors in heat dissipation mode, or other suitable means for providing heat to the steam cell 20. A temperature sensor can be used to provide feedback to the temperature controller, which controls the current through the wire windings to keep the alkali metal atoms at the desired temperature.

To assist in insulating from the environment, a heat insulating structure as described in US Patent Application No. 11/276538, which is co-pending with this application, named "Passive Analog Thermal Isolation Structure". , Can be formed or coupled to one of the wafer substrates 12, 14, 16. The adiabatic structure allows tight control of the temperature inside the steam cavity 22 and uses lower levels of heating power to reduce the total power consumption required to operate the atomic gyroscope 10. To do.

Several window apertures 74, 76 located on each side of the steam cell 20 are such that the laser beam 66 from the pump laser source 24 is directed along the direction of the optical pumping shaft 78. It can be configured to be sent to the photodetector 40 through the wall 70 of the. The second few window apertures 80, 82 located at the top and bottom of the steam cell 20 have the laser beam 84 from the detection laser source 26 in the direction of the detection axis 88 perpendicular to the optical pumping axis 78. Along, it can be configured to be sent upwards through the steam cell 20 to the second photodetector 86. Window apertures 74, 76, 80, 82 can be formed from optically transparent materials such as glass, fused quartz, crystal, and / or sapphire, thereby resulting in ultrafine frequencies of alkali metal atoms. Allows the laser beam to pass through apertures 74, 76, 80, 82 without shift. Window apertures 74, 76, 80, 82 are, for example, deep reactive ion. It can be manufactured using etching techniques such as etching) (DRIE) and can be airtightly sealed using Pb-Sn reflow brazing. In some embodiments, window apertures 74, 76, 80, 82 are referred to in US Patent Application No. 11/1644445, which is co-pending with this application, entitled "Miniature Optically Transparent Window." It can be manufactured using the etching techniques described and the entire patent application is incorporated herein by reference. However, it should be understood that other manufacturing techniques may be utilized if desired.

The steam cavity 22⁸⁵Rb and⁸⁷Rb and¹³³Alkali metal atoms such as Cs and¹²⁹Xe and¹³¹Xe and³Rare gas isotopes such as He and N to reduce out-of-phase collisions in the vapor cavity 22₂Includes sources with suitable buffer gases such as, Ar, Kr, and / or Ne. However, the choice of alkali metal, rare gas, and / or buffer gas may vary depending on the particular application. For example, a combination of alkali metal atoms and rare gas atoms may be used to provide a wide range of spin-exchange coupling constants, which is desired for the atomic gyroscope 10. It can be implemented to provide properties. Such combinations may also be chosen to alter the relaxation time constant used by the atomic gyroscope 10, which affects the pressure in the vapor cavity 22.

The scale factor of the atomic gyroscope 10 can be changed by adjusting the wavelength of the detection laser beam 84 and / or the vapor pressure of the alkali metal atoms in the vapor cavity 22. For example, in some embodiments, the change in vapor pressure can be achieved by adjusting the temperature of the cells in the vapor cavity 22. It is also possible to control the density of alkali metal atoms, rare gas atoms, and / or buffer gas atoms to regulate the vapor pressure in the vapor cavity 22, thereby controlling the scale factor. For example, in some embodiments, the density of rare gas atoms in the vapor cavity 22 may be stoichiometrically controlled to balance the polarization transmission and signal levels of the atomic gyroscope 10. ..

Similarly, the pressure of the buffer gas must be adjusted to minimize the effect of the vapor cavity walls 28, 30 on the rotating atoms. In some embodiments, mineral oil or other suitable material can be used to coat the inner wall of the vapor cavity 22, which causes spin fracture of alkali metal atoms due to factors such as gas density and thermal velocity. Used to control the rate. Other system characteristics, such as pump time and signal level, also depend, at least in part, on the relative pressure of the buffer gas in the steam cavity 22.

The pump laser source 24 can be placed adjacent to the packaging structure 18 and in the steam cavity 22 to generate angular momentum at the alkali metal atom that induces nuclear spin polarization at the rare gas atom. It can be configured to light pump an atomic population. For example, in some embodiments, the pump laser source 24 can include a vertical cavity surface emitting laser (VCSEL), which consumes a relatively small amount of power and is an alkali metal atom. Can operate at the carrier wavelength of. However, other suitable laser sources may be used to light pump the vapor cavity 22. An example of an alternative laser source is a distributed Bragg that uses a gallium arsenide (GaAs) semiconductor laser diode to generate the laser emission. Can include reflector) (DBR). In order to enable optical pumping in the vapor cavity 22, the pump laser source 24 is configured to continuously output polarized light close to the carrier wavelength of the alkali metal atom. For example, as a source of alkali metal atoms⁸⁷Rb or⁸⁵In embodiments where Rb is used, the pump laser source 24 is typically maintained at a wavelength of about 795 nm, which corresponds to the D1 absorption line for the rubidium atom.

In the exemplary embodiments of FIGS. 1-2, the laser beam 66 emitted from the pump laser source 24 is directed through an electrochromic or passive neutral density filter (ND filter) 90, which filter. Can be used to reduce the laser beam intensity. The quarter wave plate 92 can be configured to convert the linearly polarized light emitted from the pump laser source 24 into circularly polarized light. Other light modulation elements may be used to alter the properties of the laser beam as desired. Examples of such elements may include, but are not limited to, beam magnifiers, collimators, attenuators, focusing lenses, and the like.

The circular polarization output from the quarter wave plate 92 can be sent through an optical fiber or waveguide 94, which allows the optical fiber or waveguide 94 to direct the laser beam into the lower wafer substrate 12. Turn. After passing through the lower wafer substrate 12, the laser beam 66 then hits the first mirror surface 36 of the central wafer substrate 14 and is redirected to pass through the vapor cavity 22. The laser beam 66 through the vapor cavity 22 is then redirected to hit a second mirror surface 38 of the central wafer substrate 14, which directs the laser beam 66 toward the photodetector 40.

During operation, the laser beam 66 from the pump laser source 24 is used to light pump the alkali metal atoms in the steam cavity 22 to illuminate both the alkali metal atoms and the rare gas, as further discussed below. It can be spin-aligned along the direction of the pumping axis 78. Optical pumping of alkali metal atoms in the steam cavity 22 is achieved by fixing the wavelength of the laser beam emitted by the pump laser source 24 to the exact transport wavelength of the alkali metal atoms in the steam cavity 22. be able to. For example, as a source of alkali metal atoms⁸⁷In embodiments where Rb is used, the pump laser source 24 can be fixed at a carrier frequency of about 794.97 nm, which corresponds to the ultrafine frequency of the rubidium atom. However,¹³³Cs,²³Na,³⁹For other types of alkali metal atoms such as K, the carrier wavelengths are typically different. Fixing the pump laser source 24 to the carrier wavelength uses, for example, a servo mechanism 96 configured to adjust the current supplied to the pump laser source 24 based on the feedback signal from the photodetector 40. And can be achieved. However, other means for fixing the pump laser source 24 to the carrier wavelength may be used, depending on the application.

As further seen in FIGS. 1-2, the detection laser source 26 can be placed adjacent to the packaging structure 18 and configured to generate a laser beam 84, which laser beam 84 It can be used to detect the rotation of rare gas atoms due to optical pumping of alkali metal atoms by the pump laser source 24. As generally indicated by arrow 88, the laser beam 84 emitted from the detection laser source 26 can be directed across the laser beam 66 used for optical pumping into the vapor cavity 22. In some embodiments, the wavelength of the laser beam emitted from the detection laser source 26 is alkaline using a servo mechanism 122 configured to receive a feedback signal from the second photodetector 86. It can be detuned with respect to the carrier wavelength and the fixed wavelength of the metal atom.

During operation, the rotation of rare gas atoms can be measured using ellipsometry techniques, which employ a set of vertical polarizing filters 124, 126 to eliminate the detection beam emission. For example, in the exemplary embodiments of FIGS. 1-2, a horizontal polarizing filter 124 and a vertical polarizing filter 126 can be used to zero the detection laser beam 84. If desired, other optical modulation elements such as optical fibers and waveguides 127 may be further provided to optically communicate with the laser beam 84 emitted from the detection laser source 26. it can. As the detection beam 84 passes upward through the steam cavity 22, its polarization is rotated by an amount that depends on the projected magnetic field strength of the detection radiation along the detection axis 88, which is the mechanical of the atomic gyroscope 10. It is a function of the angle of rotation. Thus, the polarization rotation of the detection beam radiation provides a signal proportional to the net mechanical rotation angle of the atomic gyroscope 10.

Figures 3A to 3C show⁸⁷Rb alkali metal atom and¹²⁹It is a schematic diagram which shows the operation of the exemplary atomic gyroscope 10 of FIGS. 1 and 2 using a source of Xe rare gas atoms. As shown at the initial start position at time t = 0 in FIG. 3A, the laser beam emitted from the pump laser source 24 is directed through the filter 90 to the quarter wave plate 92 and is quadrant. One wave plate 92 converts a linearly polarized laser beam into circularly polarized laser radiation. The wavelength of the laser beam output by the pump laser source 24 is⁸⁷Of Rb atom²S_1/2Their lowest from the ground state²P_1/2It can be adjusted to accommodate transients to the excited state, which corresponds to a wavelength λ of approximately 794.97 nm. To D1 absorption line⁸⁷Due to such excitation of the Rb atom⁸⁷Rb atoms absorb photons in the vapor cavity 22 to gain angular momentum. This angular momentum is then transferred to the nucleus of the rare gas atom, causing the rare gas atom to spin up. The time required to spin up the atomic gyroscope 10 typically includes the temperature within the vapor cavity 22, the size of the vapor cavity 22, the density of alkali metal and rare gas atoms, and other factors. Depends on several factors.

Wavelength λ of pump / laser source 24⁸⁷The wavelength of the laser beam 66 emitted from the pump laser source 24 is detected by the photodetector 40 in order to fix it to the D1 absorption line of Rb. In some embodiments, the pump laser source 24 emits a laser beam 66 from the pump laser source 24.⁸⁷It is connected to the first servo mechanism 96 to fix it to the exact wavelength for excitation of the Rb atom to the excited state. In embodiments where another alkali metal source is used as the source for pumping atoms, the wavelength of the pump laser source 24 is such that the alkali metal atoms are optical pumped into their excited state, if necessary. Can be changed. When a significant portion of the rare gas nucleus is spin-aligned along the optical pumping axis "z", the collective nuclear magnetic moment of the rare gas is a net magnetic field (-λM) up to a few milligauss in the steam cell 20._z) Is generated.

The pump and the detection laser sources 24 and 26 are configured to operate orthogonally to each other, that is, the laser beam emitted from the pump laser source 24 becomes the pumping / polarization axis "z" from the detection laser source 26. The emitted laser beam can be configured to be the detection axis "x" of the atomic gyroscope 10. In preparation for initial use, the atomic gyroscope 10 can be placed in a non-rotating reference frame, which calibrates the orientation of the atomic gyroscope 10, as further understood in connection with FIG. 3A. Can be used later to. In the steam cavity 22⁸⁷When Rb atoms are continuously pumped into their excited states, the nuclear spins of the rare gas atoms contained within the steam cavity 22 are quasi-stable vandels formed from the complex of alkali metal and rare gas atoms. Ultrafine spin exchange in the Whirls molecule causes polarization along the z-axis. Such exchange between atoms induces nuclear spin polarization in rare gas atoms, which provides the desired criteria for atomic gyroscope 10.

Optical pumping axis z using several magnetic elements 128, 130 arranged in the packaging structure to cancel the effect of the net magnetic field-λMz generated from the nuclear spin polarization of the rare gas atom. Static magnetic field B along_zCan be applied. For example, static magnetic field B_zCan be generated using several Helmholtz coils disposed on either side of the vapor cavity 22 as shown.

The decomposed σ + and σ- parts of the linearly polarized radiation beam are⁸⁷It receives different photoresonance frequencies when pumping the [m = + 1/2] and [m = -1 / 2] states of the Rb atom. Using ellipsometry techniques, the σ + and σ- components of the detection beam 84 receive different indices n + and n-. This effect results in different phase rates for the σ + and σ- components of the beam, resulting in a net rotation of the forward scattered beam. As a result, the linearly polarized light of the detection beam 84 is rotated by an angle φ, which is calculated by the following equation. (1) φ = (n)₊-n_-) (1 / λ) Can be generally understood from.

When the magnetic field-λMz is zeroed, then in FIG. 3B, as further shown for time t&gt; 0, the atomic gyroscope 10 detects rotation about the detection axis "y" of the atomic gyroscope 10. Can be configured. If there is a rotation about the y-axis, the nuclear spins of the rare gas do not occur immediately and are delayed by a period of time with respect to the mechanical rotation. During this delay period, a net magnetic field Bx is present in the atomic gyroscope 10 and induces a polarization rotation of the measurement signal that is directly proportional to the mechanical rotation of the gyroscope 10. The scale factor of the atomic gyroscope 10 can then be used to determine the relationship between the rotation of the polarization in the measurement signal and the mechanical rotation of the atomic gyroscope 10. Typically, only the projection of the residual magnetic field Bx can induce a change in the polarization of the detection beam 84. During operation, this phenomenon helps the atomic gyroscope 10 operate with low cross-axis sensitivity.

As the atomic gyroscope 10 continues to rotate, the angle between the applied magnetic field Bz and the nuclear spin direction of the rare gas is along the current direction, as further shown in FIG. 3c for later time. It can increase or decrease depending on the relative rate of mechanical rotation of the atomic gyroscope 10 to the rate of pumping that rearranges the rare gas isotopes. In such a configuration, the direction of the rare gas continuously follows the rotation of the system, inducing a non-equilibrium state, thereby allowing the mechanical rotation of the atomic gyroscope 10 to be measured.

Optical pumping from the pump laser source 24 can be configured to continuously rearrange the rare gas isotopes along the new "z" axis within a relatively short response time, thereby detecting. Allows the laser beam to detect subtle changes in the mechanical rotation of the atomic gyroscope 10 about the y-axis. For example, in some embodiments, the response time of the system can be set so that the atomic gyroscope 10 can achieve a relatively high bandwidth (eg 300 Hz).

The bandwidth and sensitivity of the atomic gyroscope 10 can be adjusted over several orders of magnitude by adjusting various parameters such as vapor pressure and / or cell temperature in the vapor cavity 22. To increase the bandwidth to allow rotation detection at relatively high rotation rates, the nuclear spins of the rare gas isotopes must be periodically rearranged, otherwise atomic magnetization. The direction may not be able to accurately track the rotation angle indicated by the detection beam axis "y". Rare gas atom (eg¹²⁹Xe) nuclear spin polarization was optical pumped⁸⁷It can be realized by a spin exchange collision with Rb vapor, which can be determined by the following equation.

(2) P_Xe(t) = &lt;P_Rb&gt; (1-exp (-γ)_set)

(3) γse = n_Rb[σ_seν + (K_xe/ n_Xe)]

With the above formula P_RbIs⁸⁷It is the polarization of Rb, n_xIs the density, σ_seIs the rate averaged binary spin exchange cross-sectional area, K_xeIs due to spin exchange in the van der Waals complex Is.

¹²⁹The time required to achieve the optimum polarization of the Xe atom is⁸⁷With Rb density¹²⁹Affected by both the density of Xe. A relatively small polarization time can be achieved by maintaining a relatively high temperature within the vapor cavity 22. The time integral of the read signal is the mechanical rotation Ω of the atomic gyroscope 10 about the y-axis._yMechanical rotation Ω in proportion to the total angle of_yIt is independent of the time dependence of. Moreover, the net angle of rotation generated by any magnetic field transient is equal to zero as long as the spin polarization is rotated by a small angle during the transition. Therefore, such features ensure high dynamic range and bias stability, as well as high bandwidth.

The atomic gyroscope 10 can be used in several applications where reliability, size, power consumption, vibration resistance, and / or cost are important design considerations. For example, in some applications, the atomic gyroscope 10 can be used in organic air vehicle (OAV) control and other navigation systems that require high reliability and low power consumption. .. Other applications such as autonomous ground vehicle navigation, ground vehicle navigation, robotics, underground equipment navigation, and / or light aircraft control and navigation are also envisioned. For example, in some cases, the atomic gyroscope 10 can be used in personal navigation systems in places where GPS is not available, such as inside caves or large buildings.

The atomic gyroscope 10 uses the magnetic and optical properties of spin-polarized steam gas, so that in a nuclear magnetic resonance (NMR) gyroscope that measures Larmor precession, the B and light fields are non-uniform. Relatively less susceptible to gender and fluctuations. Moreover, atomic gyroscopes have very low cross-axis sensitivity, which contributes to the complexity of many conventional atomic gyroscope designs. Moreover, the atomic gyroscope 10 is relatively insensitive to frequency shift and bias drift, which are common in atomic gyroscopes that pump and detect along one axis. In contrast to the MEMS vibration gyroscope, which uses mechanical excitation and detection, which is more susceptible to vibration, aging, and material degradation, the atomic gyroscope 10 has no moving or vibrating parts and is therefore subject to error. Hard to receive. Also, unlike some ring laser gyroscope designs, the atomic gyroscope 10 does not accept immobilization (lock-in) at low rotation rates.

Although some embodiments of the present invention have been described above, those skilled in the art can easily understand that other embodiments within the scope of the claims attached to the present specification can be prepared and used. Let's do it. Some of the advantages of the invention covered by this document have been described above. It should be understood that this disclosure is merely exemplary in many respects. Modifications can be made with respect to the various elements described herein without going beyond the scope of the present invention.