Portable optical gyroscope and compass unit

Abstract

The present disclosure relates to integrating an integrated photon-based optical gyroscope and an optical fiber-based optical gyroscope into a portable device that may include a compass feature. The novel small-occupied-space modularized fully-integrated photon optical gyroscope is used for a non-key axis. However, for at least one key axis, a fiber optic gyroscope may be used to provide a bias stability of less than 0.1 DEG / hour that is directly related to positioning accuracy over a predicted centimeter range. The positioning accuracy comes from the compass positioning capability of a gyroscope (called a gyro compass) for calculating the course by utilizing the rotation of the earth.

Description

Technical Field

[0001] The present disclosure relates to integrating an integrated-photonics-based optical gyroscope and a fiber-optic-based optical gyroscope into a portable device that may include compass features. Background Art

[0002] A gyroscope (sometimes also referred to as a "gyro") is a sensor capable of measuring angular velocity. Gyroscopes can be mechanical or optical and can vary in terms of accuracy, performance cost, and size. Mechanically based gyroscopes that rely on the Coriolis effect are generally less costly but cannot achieve very high performance and are susceptible to measurement errors caused by temperature, vibration, and electromagnetic interference (EMI). Optical gyroscopes generally have the highest performance and rely on interferometry based on the Sagnac effect (a rotation-induced phenomenon encountered in interferometry). Since optical gyroscopes do not have any moving parts, they have an advantage over mechanical gyroscopes in that they can better withstand the effects of shock, vibration, and temperature variations than mechanical gyroscopes with moving parts.

[0003] Multiple gyroscopes and other sensors such as accelerometers and, in some cases, magnetometers can be packaged together as an inertial measurement unit (IMU) in a moving object to sense various motion parameters along the X, Y, and Z axes. For example, a 6-axis IMU can package a 3-axis accelerometer and a 3-axis gyroscope together to measure the absolute spatial displacement of a moving object. Applications of IMUs include, but are not limited to, military maneuvers (e.g., fighter jets, submarines, drones), commercial aircraft / drone navigation, robotics, autonomous vehicle navigation, virtual reality, augmented reality, gaming, etc.

[0004] For navigation applications, an IMU can be part of an inertial navigation system (INS) that can be assisted by navigation data provided by a global navigation satellite system (GNSS) such as the Global Positioning System (GPS), GLONASS, Galileo, Beidou, etc. A GNSS-assisted INS receiver uses sophisticated fusion algorithms to provide precise position, velocity, and orientation for a moving object by combining data from various local physical sensors and data obtained from the GNSS. (Note that in the following specification, GNSS is also generally described as "GPS" even though GPS is just one type of GNSS). However, when GNSS signals are absent or degraded, data from local physical sensors becomes the sole source for making precise position predictions using alternative algorithms. For example, in an automobile, when the vehicle does not have a GNSS signal, such as in a tunnel or an urban canyon, a dead reckoning (DR) algorithm is used. A receiver with DR capabilities uses data from gyroscopes, accelerometers, odometers, wheel speed sensors, etc. to predict the upcoming position and direction of movement (heading) of a moving object based on the last known position.

[0005] For certain scenarios, rugged portable (e.g., hand-held) positioning devices with high-performance precision gyroscopes can be mission-critical. In many such scenarios, global positioning signals may be unavailable or deliberately disabled to avoid detection. Examples of such scenarios can include, but are not limited to, defense operations, rescue operations in remote or natural disaster-affected areas, and underground operations such as excavation, tunneling, mining, drilling, etc. For hand-held devices, the small footprint of the gyroscope is useful because of the limited space in hand-held devices.

[0006] Mechanical gyroscopes (such as MEMS-based gyroscopes) are useful for small form factors, but they are typically prone to measurement errors and thus result in lower performance. For example, MEMS-based gyroscopes may have high bias instability (e.g., a stable value of 3.5° / hour or higher). High bias estimation errors in gyroscope measurements can render the data meaningless, especially when the sensor also experiences thermal variations. For example, MEMS gyroscopes may have a bias estimation error in the range of 100° / hour or even higher at high temperatures. Large thermal errors make bias estimation based on mechanical gyroscopes impractical. In addition, these gyroscopes do not work well under vibration conditions.

[0007] Optical gyroscopes offer better performance due to their low bias instability and are largely unaffected by thermal or vibration errors. The most common optical gyroscope is the fiber optic gyroscope (FOG). The construction of a FOG typically involves a long loop of polarization-maintaining (PM) fiber (the loop can form a coil including multiple turns). Laser light (or light from a superluminescent light-emitting diode (SLED)) is launched into both ends of the PM fiber and propagates in different directions. If the fiber loop / coil moves, the light beams will experience different optical path lengths from each other. By establishing an interferometric measurement system, one can measure the small path length difference proportional to the area of the closed loop and the angular velocity of the rotating coil.

[0008] However, since high-performance FOGs often have relatively large form factors, it is unlikely that FOGs can be used for any of these applications, especially for all three axes, in a portable (e.g., handheld) device. The present inventors have realized a solution: using a high-performance FOG for one critical axis in a portable device and using an integrated-photonics-based optical gyroscope for the other axes. Some embodiments may also use an integrated-photonics-based optical gyroscope for all three axes. An integrated-photonics-based optical gyroscope has been described in a previously filed patent application Ser. No. 17 / 071,697, entitled "Integrated Photonics Optical Gyroscopes Optimized for Autonomous Terrestrial and Aerial Vehicles," filed Oct. 15, 2020, which application is incorporated herein by reference in its entirety. This application was published as US2021 / 0116246 on Apr. 22, 2021.

[0009] Furthermore, there is currently no small-form-factor battery-powered portable gyroscope with compass features. The present inventors have realized a north-seeking gyroscope (referred to as a gyrocompass) that does not rely on magnetic fields and uses the Earth's rotation rate to calculate the navigation direction. SUMMARY OF THE INVENTION

[0010] The present disclosure describes an optical gyroscope device that houses both an optical fiber coil and an integrated-photonics-based waveguide coil / microresonator loop as sensing elements for different axes of motion. The novel small-footprint modular fully integrated-photonics optical gyroscopes (i.e., having waveguide-based sensing elements) disclosed herein can provide a bias stability of less than 0.5° / hour (which can be reduced by an order of magnitude with improved design), making them comparable in performance to fiber optic gyroscopes but much less costly. However, for at least one axis, a fiber optic gyroscope can be used to provide a stability of less than 0.1° / hour, which is directly related to the positioning accuracy within the predicted centimeter range. The positioning accuracy stems from the compass positioning (compassing) ability of the gyroscope (referred to as a gyrocompass) to calculate the heading using the Earth's rotation.

[0011] The user (also referred to as the operator) can orient the portable device along various axes to align the ultra-high-precision fiber optic gyroscope along the most critical axis, while the less critical axes of the positioning measurement can be aligned with the modular integrated photonic optical gyroscope. For example, if the portable gyroscope device has a size suitable for being held in the hand, the user can continuously change the orientation by moving their hand. The device can also be mounted on wearable or portable items such as helmets, belts, headbands, armbands, backpacks, shoulder straps, leg straps, face masks, body armor, or on a vehicle with a changeable mounting orientation. Alternatively, the user can walk in a specific pattern or in circles to initially calibrate the device.

[0012] When the critical axis (also referred to as the special sensor axis or the preferred sensor axis) with the fiber optic gyroscope is manually pointed by the user in any horizontal direction approximately horizontal (i.e., approximately parallel to the ground), the accelerometer in the IMU can account for any horizontal errors and offsets of this special sensor axis, thereby creating a perfectly horizontal virtual sensor. The low noise and drift of this preferred sensor (i.e., the fiber optic gyroscope) enable the Earth's rotation on the horizontal plane to be easily observed. The horizontal component of the Earth's rotation rate is 15° / hour at the equator and varies in degrees with the sine of the latitude angle.

[0013] Based on the observed amount of the Earth's rotation and the approximate latitude where the operator is located, the Earth rotation signal is converted into a rough heading. For example, if the reading is the maximum positive Earth rate at a given latitude, the instrument is pointed north. Due to the low noise of the fiber optic gyroscope, this basic rough determination can be obtained within a few seconds after rotating the instrument.

[0014] Based on the initial heading estimate, the operator can further improve the measurement accuracy by pointing the preferred sensor axis in the east direction and waiting for an additional time. The operator can use the previously obtained rough heading to guide this action. Pointing the device east or west provides the maximum measurement sensitivity. When perfectly aligned with the east or west, the horizontally aligned gyroscope signal should be zero. The deviation from zero represents the angular difference from the east-west line. The accuracy of this value after a period of time (e.g., 1 - 2 minutes) will be better than 0.1 degree of true heading or even higher. True heading is an important parameter for navigation. The gyrocompass described here provides a reliable true heading measurement that is ten to a hundred times more accurate than a typical magnetic compass.

[0015] Since the gyrocompass disclosed herein does not rely on the Earth's magnetic field to calculate direction, it is not affected by magnetic interference caused by common magnetic materials (such as iron and steel) in the environment and the magnetic fields generated by electric currents.

[0016] As described above, for at least one axis of the handheld device, ultra-high precision is required for accurate position calculation, and for this axis, a modular fully integrated photonic optical gyroscope may not be sufficient. For this axis, an optical fiber spool is used as the sensing element, and for the other two axes, a modular fully integrated photonic optical gyroscope is used. The optical fiber spool is structurally supported by a rigid frame such that the entire assembly is as robust as the modular fully integrated photonic optical gyroscope. This rigid frame can be embedded using the periphery of the handheld device and / or using the inner shell of the handheld device. Structural hardening is crucial for use as a handheld device in harsh scenarios such as battlefields, rescue operations, military training, or extreme adventures.

[0017] It is noted that the term "integrated photonic optical gyroscope" encompasses a wide variety of gyroscope configurations. For example, a modular "integrated" photonic optical gyroscope may have a front-end chip that has a number of waveguide-based optical elements (such as couplers / splitters, mode selection filters, etc.) and waveguide-based sensing elements. However, discrete optical elements, such as electro-optic or piezoelectric phase shifters, may be fiber-coupled to the waveguide-based optical elements or sensing elements. Alternatively, the front-end chip may be a "fully integrated" photonic chip made of silicon photonics, silicon nitride, III-V materials, or other platforms. The phase shifter may also be hybrid integrated with the waveguide-based optical elements by depositing, growing, or bonding a thin film material of metal or other materials with electro-optic / piezoelectric properties. The same front-end chip may also be coupled to an optical fiber loop serving as a sensing coil. Alternatively, the optical fiber loop may be coupled to discrete optical elements, such as a piezoelectric disk or a lithium niobate phase modulator. It should be noted that these examples are illustrative and non-limiting.

[0018] Another aspect of the handheld device is the simplicity of its power supply. If a power outlet is available, the illustrated embodiments herein may have a built-in power socket for charging the optical gyroscope and other components of the handheld device. However, the handheld device can also operate using simple and easily replaceable standard batteries (such as AA or AAA batteries that the user can stock on their own) without relying on the availability of a power outlet.

[0019] A handheld device with an optical gyroscope can be an "add-on" component that can be mechanically locked onto a handheld GPS receiver that a user can carry around. The add-on component is similar to an external battery pack but has gyroscope and compass features. When the GPS signal is disrupted or deliberately turned off to avoid detection, the handheld optical gyroscope and compass become the primary position detection mechanism relying on local inertial sensors. When GPS is used safely, the optical gyroscope can be turned off to save power or turned on to supplement GPS-based navigation. In some embodiments, the fiber optic gyroscope is always on, and GPS-based navigation is turned off or on. There is usually an algorithm to determine whether to primarily rely on the fiber optic gyroscope, GPS, or both. However, the user can also make this determination.

[0020] A modular fully integrated photonic optical gyroscope for non-critical axes can be based on silicon photonics, although integrated optical gyroscopes based on compound semiconductors (III-V semiconductors) or other novel materials (such as electro-optic or piezoelectric materials) are also within the scope of this disclosure. Additionally, as described below, the integrated optical gyroscope can have a front-end chip made of integrated photonics that can emit light into the rotation sensing element and receive light returning from the rotation sensing element. The rotation sensing element of the integrated photonic optical gyroscope can include another integrated photonics waveguide chip (such as a coil or microresonator ring based on silicon nitride waveguides) or an optical fiber.

[0021] The integrated photonic optical gyroscope has two main components. The first component is an integrated photonics chip that is designed with a higher-level system architecture and key performance parameters in mind, including but not limited to laser (or SLED) performance, tuning parameters, detector parameters, and packaging considerations. This chip houses a laser (or SLED), phase shifters, detectors, optical splitters, etc. The second component can be an optical fiber coil. Alternatively, the second component can be a waveguide-based optical gyroscope chip ("OG chip" or "gyro chip" or "sensing chip") that has a waveguide coil (or helix) or a ring resonator (also called a microresonator). The waveguide can be made of silicon nitride (SiN). Thus, in these embodiments, the SiN waveguide-based OG chip can also be referred to as the "SiN waveguide chip" or simply the "SiN chip". In one embodiment, the OG chip is hybrid integrated with the integrated photonics chip. In some advanced embodiments, the integrated photonics chip and the OG chip can be monolithically fabricated on the same chip or stacked through wafer bonding. Low waveguide loss in the gyro chip is key to the desired gyroscope sensitivity value associated with lower bias estimation error.

[0022] An integrated photonic optical gyroscope can be modularized on a printed circuit board (PCB) using standard pick-and-place techniques (e.g., an integrated photonic chip and a sensing chip can be encapsulated together). The PCB can also have control electronics for the integrated photonic chip and can be integrated with a motherboard that supports the main architecture of the IMU. The modular design allows the same optical gyroscope product to be introduced into different IMU PCBs customized for different markets because the form factor specifications of the optical gyroscope module remain unchanged. One such market is the advanced driver assistance system (ADAS) for autonomous vehicles, but those skilled in the art should understand that the scope of the present disclosure is not limited to ADAS only because the same module can also be installed inside a handheld device. Wafer-level processing and standard IC packaging and assembly techniques enable the mass production of integrated-photonic-based optical gyroscope modules for various system architectures for various markets, including both commercial and military applications.

[0023] Specifically, the present disclosure claims a device in a portable form factor that serves as an optical gyrocompass, the device including: a rigid frame that forms part of the housing of the device; and an optical fiber gyroscope having an optical fiber coil wound around the rigid frame, wherein the optical fiber coil serves as a rotation sensing element of the optical fiber gyroscope that provides high-precision inertial navigation data along a key axis, and wherein the optical fiber gyroscope further includes an integrated photonic front-end chip coupled to the optical fiber coil. For other non-critical axes, a modular integrated photonic optical gyroscope can be used, which can be attached to the rigid frame or an extension of the rigid frame inside the housing of the gyrocompass device. A local or additional attachment-type power supply provides power to operate the optical fiber gyroscope and other components inside the housing. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present disclosure will be more fully understood from the following detailed description and the accompanying drawings of various embodiments of the present disclosure. It should be noted that the dimensions shown in the figures are for illustrative purposes only and are not drawn to scale.

[0025] Figure 1 Illustrates the main components of a single-axis integrated photonic optical gyroscope module according to an embodiment of the present disclosure.

[0026] Figure 2 Illustrates Figure 1 a perspective schematic view of the single-axis integrated photonic optical gyroscope shown in

[0027] Figure 3 Illustrates a schematic diagram of a printed circuit board (PCB) of an IMU having a single-axis integrated photonic optical gyroscope module according to an embodiment of the present disclosure.

[0028] Figure 4Illustrated is a schematic diagram of three single-axis integrated photonics optical gyroscope modules packaged together according to an embodiment of the present disclosure to implement a three-axis gyroscope.

[0029] Figure 5 Illustrated is a schematic diagram of an embodiment of a 3-axis optical gyroscope according to an embodiment of the present disclosure, the 3-axis optical gyroscope including two additional single-axis integrated photonics optical gyroscope modules for two additional axes, packaged together on a PCB to which an existing single-axis integrated photonics optical gyroscope module is attached.

[0030] Figure 6 Illustrated are various components of a three-axis optical gyroscope assembled together according to an embodiment of the present disclosure, wherein at least one axis has a fiber-based sensing coil.

[0031] Figure 7 Illustrated is another configuration according to an embodiment of the present disclosure, wherein a printed circuit board is mounted on top within a frame.

[0032] Figure 8 Illustrated is a conventionally used handheld GPS receiver unit.

[0033] Figure 9 Illustrated is an additional optical gyroscope unit having the same footprint attached to a handheld receiver unit according to an embodiment of the present disclosure.

[0034] Figure 10 Illustrated is an additional optical gyroscope unit before being attached to a GPS receiver unit according to an embodiment of the present disclosure.

[0035] Figure 11 Illustrated is a longitudinal cross-section of an additional optical gyroscope unit having an integrated photonics optical gyroscope module inserted therein according to an embodiment of the present disclosure.

[0036] Figure 12 Illustrated is a perspective view of an additional optical gyroscope unit having two integrated photonics optical gyroscope modules inserted therein according to an embodiment of the present disclosure, and the upper surface is removed to show the PCB.

[0037] Figure 13 Illustrated is a perspective view of an additional optical gyroscope unit having two integrated photonics optical gyroscope modules inserted therein according to an embodiment of the present disclosure, and the PCB is removed to show the fiber optic coil around the frame inserted into the housing.

[0038] Figure 14 Illustrated is a perspective view of an additional optical gyroscope unit having two integrated photonics optical gyroscope modules inserted therein according to an embodiment of the present disclosure, and the PCB and the frame with the fiber optic coil are removed to show the lower surface of the housing that houses the battery.

[0039] Figure 15 A perspective view of a frame with an optical fiber coil in a housing with access to an additional optical gyroscope unit is shown, in accordance with an embodiment of the present disclosure. Detailed Description

[0040] Aspects of the present disclosure relate to integrating a compact, ultra-low loss waveguide-based optical gyroscope module and an optical fiber coil with other system-level electronic components to produce a high-performance inertial measurement unit (IMU).

[0041] Some sensing applications may only require a single axis of ultra-high precision optical gyroscope to supplement (or replace) relatively low precision measurements via a fully integrated photonics-based optical gyroscope module. Note that "relatively low precision" is entirely a comparison of the precision of the fully integrated photonics optical gyroscope performance with that of a fiber-based optical gyroscope performance. However, even the "relatively low precision" of a fully integrated photonics-based optical gyroscope is far higher than that of a mechanical (e.g., MEMS-based) low-cost, low-precision gyroscope. Consider a scenario where high-precision angle measurements may only be required for the Z-axis for determining heading, as the user holding the gyroscope moves on the X-Y plane of a rigid surface. In this scenario, angle measurements for the X and Y axes may not be safety-critical. The present inventors recognize that reducing the cost of ultra-high precision fiber optic gyroscopes for at least two axes will translate to a reduction in the total cost of the IMU, thus facilitating larger scale production.

[0042] Sensor fusion algorithms are used for the IMU, using data from gyroscopes, accelerometers, and magnetometers, as well as alternative sensing technologies such as light detection and ranging (LIDAR) and camera-based systems to predict position. Local gyroscopes in a handheld unit also provide redundancy, as the IMU can rely on algorithm-based position determination for a longer period when alternative sensing technologies fail or are deliberately turned off. This redundancy can be invaluable for safety-critical applications, such as when satellite signals for navigation are lost ("GPS denied environment").

[0043] Figure 1Illustrated are the main components of a single-axis fully integrated photonic optical gyroscope module 100 according to embodiments of the present disclosure. Module 100 includes an integrated photonic chip 120 and a waveguide chip 110. The waveguide chip 110 may have SiN waveguides and is thus referred to as the SiN chip. The waveguide chip 110 has a waveguide gyro coil 115 (helical) that receives an optical signal from a laser (or SLED), which may be located on the integrated photonic chip 120 or elsewhere on the package substrate 105. The integrated photonic chip 120 and the waveguide chip 110 may be assembled together on the package substrate 105, which may be a printed circuit board (PCB). There may also be other control electronics in the form of one or more separate ICs 122 (e.g., 122a-c).

[0044] An optical signal from the integrated photonic chip 120 may be coupled to the waveguide chip 110, and after passing through the waveguide coil 115, the optical signal is ultimately coupled back to the integrated photonic chip 120 for detection by a photodetector that measures the optical phase change due to the Sagnac effect. This detector is sometimes referred to as the Sagnac detector. The system-level integration of the integrated photonic chip and the waveguide chip has been covered in the provisional application 62 / 872,640 (entitled "System Architecture for Silicon Photonics Optical Gyroscopes") filed on July 10, 2019, and the provisional application 62 / 904,443 (entitled "System Architecture for Silicon Photonics Optical Gyroscopes with Mode-Selective Waveguides") filed on September 23, 2019. These provisional applications have been converted to non-provisional application number 16 / 659,424, which has been granted as U.S. Patent No. 10,731,988. The applications are incorporated herein by reference. Note that in addition to what is described in those applications, for built-in redundancy, two independent waveguide chips may be coupled to a single integrated photonic chip having two sets of integrated photonic components. Alternatively, a second layer in the waveguide chip may be used for built-in redundancy, i.e., two complete waveguide coils may be used to couple to the integrated photonic chip. These redundancy concepts are described in patent application number 17 / 071,697 (entitled "Integrated Photonics Optical Gyroscopes Optimized for Autonomous Terrestrial and Aerial Vehicles", filed on October 15, 2020), which is incorporated herein by reference in its entirety. This application has been published as US2021 / 0116246.

[0045] Figure 2 FIG. shows a perspective schematic view of the single - axis integrated photonic optical gyroscope module 100. Note that although not drawn to scale, the waveguide chip 110 can be significantly larger than the integrated photonic chip 120 and can determine the overall form factor of the module 100. Note that the back surface of the package substrate 105 can have additional circuitry and can have designated bonding pads for attachment to another package substrate of a larger module (such as an IMU).

[0046] Figure 3 FIG. shows a schematic view of a printed circuit board (PCB) 305 with a single - axis integrated photonic optical gyroscope module 100 according to an embodiment 300 of the present disclosure. The PCB 305 can have a processor 330 to process data from the module 100 and other signals / data received by the IMU (e.g., accelerometer data, GNSS data, magnetometer data). The processor 330 can have a central processing unit (CPU), which can be combined with a digital signal processor (DSP) or an analog locking circuit to control the gyro. In addition, other ICs 332 can also be on the same PCB. The single - axis integrated photonic optical gyroscope module 100 can be assembled on the PCB 305 by flip - chip bonding or other standard packaging techniques.

[0047] Figure 4 FIG. shows a schematic view of three single - axis integrated photonic optical gyroscope modules packaged together according to an embodiment 400 of the present disclosure. These single - axis integrated photonic optical gyroscope modules are interchangeable and orthogonal to each other. Embodiment 400 can have a three - dimensional housing 450 to attach three SiPhOG modules 100a, 100b, and 100c for the Z, X, and Y axes, respectively. As illustrated in the later figures, the housing 450 can be part of the housing of a handheld device. In addition, depending on the configuration of the handheld device, two modules 100a and 100b can be used, where the module 100c is changed by removing the waveguide coil 110 and attaching an integrated photonic chip 120 with an optical fiber coil to make an ultra - high - precision fiber - based optical gyroscope.

[0048] Generally speaking, fiber - based gyroscopes provide higher sensitivity to diagonal motion compared to integrated - photonic waveguide coils. The gyroscope sensitivity varies according to the physical dimensions related to the gyroscope. The phase signal of an optical gyroscope is proportional to the Sagnac effect multiplied by the angular rotation speed, as shown in the following formula (Formula 1):

[0049] Δφ=(8πNA / λc)Ω

[0050] where N = the number of turns of the gyroscope,

[0051] A = the enclosed area,

[0052] Ω = angular rotation rate,

[0053] Δφ = optical phase difference signal,

[0054] λ = wavelength of light,

[0055] c = speed of light.

[0056] Since the fiber optic coil is not limited by integrated photonics manufacturing parameters (such as mask size, exposure field, etc.), longer fibers can be used to increase the sensitivity for at least one key axis.

[0057] Figure 5 A schematic diagram showing two single-axis integrated photonics optical gyroscope modules 100c and 100b packaged together according to an embodiment 500 of the present disclosure is illustrated. Optionally, a third single-axis integrated photonics optical gyroscope module 100a can be installed on the PCB 305 to provide redundancy for the fiber optic sensing coil for the Z-axis, as Figure 6 shown. The mechanical structure 550 can be part of the housing of a handheld device.

[0058] Figure 6 A diagram illustrates how the single-axis integrated photonics optical gyroscope modules 100c and 100b (and possibly also 100a) are inserted into the frame 600. The frame 600 can be a metal frame or made of other structurally rigid materials to provide rigid support for the fiber optic coil 650 wound around it. The height "h" of the frame should be sufficient to mount the single-axis integrated photonics optical gyroscope module 100 along its inner wall, with the PCB 305 at the bottom. Alternatively, as Figure 7 shown, the PCB 305 can be located at the top of the frame 600 and support the front-end chip ( Figure 7 not shown in the figure) that emits light into the fiber optic coil 650.

[0059] Figure 8Shows a conventional handheld GPS receiver device 800, which has a position calculation processor inside that can receive GPS signals and provide navigation data on screen 850. The device may have local sensors, such as a low-precision mechanical accelerometer and gyroscope, to supplement GPS data for position prediction. The position calculation processor can execute a sensor fusion algorithm. In cases where GPS data is unavailable, the sensor fusion algorithm predicts the position and trajectory of a moving object by combining data from all available physical sensors. However, the effectiveness of the sensor fusion algorithm depends on the measurement accuracy of the physical sensors. There are several buttons on the handheld GPS receiver, and one button (such as 855) can be assigned to turn on or off GPS operation according to use case scenarios. For example, since the GPS receiver sends and receives signals from satellites, those signals can be intercepted to detect the position of the GPS receiver user (such as a soldier on the battlefield). When the user wants to avoid being detected, or when the user enters an environment where GPS signals are interfered with, the user needs to rely on local sensors for position calculation and navigation.

[0060] The present inventors propose attaching an additional gyroscope unit 900 to the conventional handheld GPS receiver 800 to make it more accurate and multi-purpose for possible "GPS denied" environments (such as battlefields, rescue operations, tunnels, caves, etc.), as Figure 9 shown. The additional unit 900 can be attached to the handheld GPS receiver 800 using a standard latch / slot or other attachment mechanisms provided on the rear surface of the GPS receiver 800. The additional gyroscope unit 900 has a processor (such as processor 330 on PCB 305) that can run a sensor fusion algorithm which calculates position using only local sensors, but is capable of using data received from the GPS receiver 800 to verify the position if using GPS signals is safe.

[0061] In a GPS denied environment, the sensor fusion algorithm receives as input data from a Z-axis fiber optic gyroscope and integrated photonics optical gyroscopes on other axes, as well as from an on-board accelerometer. Additional sensor data (such as magnetometers, cameras, radars, pedometers, etc.) can also be used in the sensor fusion algorithm.

[0062] Figure 10 Shows the relative external dimensions of the housing of the additional gyroscope unit 900. The height "H" on one side of the housing should be sufficient to accommodate a fully integrated photonics optical gyroscope module (such as module 100) mounted on the inner wall (see Figure 12 and 13 ). The length L1 and width W can be substantially the same as the length of the GPS receiver 800 to which the additional unit 900 is attached, but longer or shorter dimensions can also be used. The length L2 should be such that it can accommodate the frame 1127 (seeFigure 11 , 13 and 15), the frame 1127 provides a rigid structural support around which the fiber optic coil 1125 is wound. The fiber optic coil 1125 is a sensing element for a fiber optic-based ultra-high precision optical gyroscope for one axis (the most critical axis).

[0063] Figure 11 A longitudinal cross-section of the additional optical gyroscope unit 900 is illustrated, which shows the integrated photonics optical gyroscope module 1113 mounted on one of the side walls visible in the longitudinal view. The module 1113 is similar to Figure 2 the module 100 shown and can be used in various devices after being packaged and encapsulated and connected. The module 1113 can have an integrated photonics optical gyroscope and a low-precision mechanical gyroscope (such as a MEMS-based gyroscope). In one example, the module 1113 can be installed in an advanced driver assistance system (ADAS) in an autonomous vehicle or in a drone or a submarine or an augmented reality headset or in a robotic device. In the case of a handheld device (like Figure 9 shown), the additional gyroscope unit 900 has a housing 1105, the rigid inner wall of which is suitable for mounting a module like 1113. The upper surface of the housing 1105 has a latch 1107 (or other fastening mechanism) for attachment to the handheld GPS receiver 800. The frame 1127 around which the fiber optic coil 1125 is wound is inserted into the housing 1105. Figure 11 A longitudinal cross-sectional view of the frame 1127 and the fiber optic coil 115 is visible. The printed circuit board (PCB) 1109 can interface with the fiber optic coil 1125. The PCB 1109 can have a front-end chip like 120 to emit light into the fiber optic coil 1125. Another PCB 1111 can be equivalent to the PCB 305 and interface with the integrated photonics optical gyroscope modules 1113 and 1115 (as Figure 13 shown). Note that the front-end chip 120 for the fiber optic coil can have integrated photonics waveguides or discrete optical components, such as lithium niobate phase modulators, hybrid integrated photodetectors, coupling lenses, isolators, etc., all of which can be mounted on the PCB.

[0064] Figure 12 A perspective view of the additional optical gyroscope unit 900 is illustrated, in which two integrated photonics optical gyroscope modules 1113 and 1115 are inserted and the upper surface of the housing 1105 is removed to show the PCB 1109. Note that the two integrated photonics optical gyroscope modules 1113 and 1115 are identical interchangeable modules mounted along two different axes (usually relatively non-critical axes), while the fiber optic coil 1125 serves as the sensing element for the most critical axis. Another module like 1113 or 1115 ( Figure 12(not explicitly shown in the figure) can be mounted on the PCB 1111 to provide redundancy along the critical axis, such as Figure 4 , 5 and as shown in 6.

[0065] Figure 13 The perspective view of the additional optical gyroscope unit 900 is shown, where the PCB 1109 is removed to show the fiber optic coil 1125 around the frame 1127 inserted into the housing 1105. The enclosed area 1131 is large enough to ensure that the fiber optic gyroscope provides ultra-high rotational measurement accuracy because hundreds or thousands of feet of sensing fiber 1125 can be wound around the frame 1127. In addition to the length of the fiber, since the perimeter of the frame 1127 is substantially larger than that of a fully integrated photonic optical gyroscope (and thus the enclosed area 1131 is substantially large), according to Equation 1, the length of the fiber does not need to be too long because the optical phase shift is proportional to the product of the fiber length (i.e., a high number of turns N) and the enclosed area “A”. In other words, when the enclosed area “A” is large, for the same phase shift, the number of turns “N” can be small. In one example, if the enclosed area is 10 square inches, the length of the fiber spool can be in the range of 1500 feet. The smaller the enclosed area, the longer the fiber length. The combination of the fiber length and the enclosed area should be such that an angle random walk (ARW) drift consistent with an acceptable bias stability value (e.g., less than 0.1° / hour) for a high-performance gyroscope is achieved. ARW is a noise parameter that describes the average deviation or error that occurs when integrating the gyroscope signal over a finite time to calculate the angular movement of a moving object. This error is a key component of the position prediction algorithm. Generally, a low bias stability value corresponds to a low ARW and a low bias estimation error, which means more accurate position prediction. The turn-on drift of a high-performance fiber optic gyroscope should be substantially less than 0.1° / hour.

[0066] Figure 14A perspective view of an additional optical gyroscope unit 900 is shown, with the PCB 1109 and the frame 1127 with the fiber optic coil 1125 removed to show the lower surface of the exposed housing 1105. Area 1131 is large enough to accommodate a battery that serves as a power source for a handheld device. Since it may not be easy to charge a handheld device in a harsh environment (such as a battlefield or a disaster area), it is very important for the entire handheld device (including the gyroscope unit 900) to have the ability to be powered by standard batteries 1133 (such as AA and AAA, or even rechargeable batteries) that are easy to store and insert into the device. An additional battery can be inserted on top of the PCB 1111, especially when the third redundant module (such as 1113) is not used to supplement the fiber optic sensing coil 1125. The number of batteries should be such that it can support operation for as many hours as possible without recharging. To save power, the single-axis rotation measurement mode can be switched to instead of measuring the angular rotation of all three axes. Additionally, to save power, the low-precision and low-power mechanical gyroscopes included in modules 1113 and 1115 can be used for non-critical axes until precise position tracking becomes critical, at which point the optical gyroscope is powered on. Alternatively, one can rotate three different optical gyroscopes according to the orientation of the handheld device to improve battery life and operation.

[0067] Note that the battery can be enclosed within the housing of the device or attached to the housing as an external additional battery pack. The housing of the device has a mating socket to receive the external battery pack such that electrical connection can be made to the fiber optic gyroscope and other electronic circuits enclosed within the housing.

[0068] Figure 15 A perspective view of the frame 1127 with the fiber optic coil 1125 entering the housing of the additional optical gyroscope unit 900 is shown.

[0069] In one embodiment, all available optical gyroscopes along the three axes do not have to be used simultaneously all the time, especially when power saving is an important factor. Since the device has a 3-axis accelerometer (e.g., a MEMS accelerometer), when the user is walking, running, or in a vehicle moving on the ground, the algorithm can analyze the accelerometer data to determine which axis is pointing downwards due to gravity. The user's body position may also change, such as when the user is a soldier crawling in a trench or a rescue worker crawling in a tunnel, where the gyroscope is mounted on his helmet or in his backpack. The user's body position may also change during gyroscope calibration. Selectively choosing gyroscopes along the dynamically changing axis of interest enhances the battery life of the portable device because the gyroscopes for the other two axes can be temporarily powered off and powered on when needed.

[0070] In the foregoing specification, embodiments of the present disclosure have been described with reference to specific exemplary embodiments of the present disclosure. However, it will be apparent that various modifications can be made thereto without departing from the broader spirit and scope of the present disclosure as set forth in the claims. Accordingly, the specification and drawings are to be interpreted in an illustrative rather than a restrictive sense. In addition, directional terms, such as "top", "bottom", etc., do not limit the scope of the present disclosure to any fixed orientation, but rather encompass various arrangements and combinations of orientations.

Claims

1. An apparatus in a portable form factor that serves as an optical gyrocompass, the apparatus comprising: A rigid frame that forms part of the housing of the apparatus; And An optical fiber gyroscope having an optical fiber coil wound around the rigid frame, wherein the optical fiber coil serves as a rotation sensing element of the optical fiber gyroscope that provides high-precision inertial navigation data along a key axis, and wherein the optical fiber gyroscope further includes an integrated photonics front-end chip coupled to the optical fiber coil.

2. The apparatus of claim 1, wherein the optical fiber gyroscope includes a semiconductor-based light source integrated on or coupled to the integrated photonics front-end chip, the semiconductor-based light source emitting light to and receiving light from the optical fiber coil.

3. The apparatus of claim 2, wherein the semiconductor-based light source is a semiconductor laser or a superluminescent light-emitting diode (SLED).

4. The apparatus of claim 1, the apparatus further comprising: One or more integrated photonics optical gyroscope modules attached to the rigid frame or an extension of the rigid frame within the housing of the apparatus, each integrated photonics optical gyroscope module providing additional inertial navigation data along a respective axis perpendicular to the key axis.

5. The apparatus of claim 4, wherein each integrated photonics optical gyroscope module is self-contained to include a respective semiconductor-based light source, a respective front-end chip, and a respective integrated-photonics-based rotation sensing element encapsulated within the module.

6. The apparatus of claim 4, wherein a local power source provides power to operate the one or more integrated photonics optical gyroscope modules.

7. The apparatus of claim 1, wherein the apparatus is held in a user's hand such that the user can move their hand to orient the optical fiber coil along the key axis.

8. The apparatus of claim 1, wherein the apparatus is mounted on a wearable item of a user's body such that the user can move their body to orient the optical fiber coil along the key axis.

9. The apparatus of claim 8, wherein the wearable item is one of: a helmet, a belt, a headband, an armband, a backpack, a shoulder strap, a leg strap, a face mask, body armor.

10. The apparatus of claim 1, wherein the apparatus is mounted on a rotatable base of a moving vehicle, the rotatable base being capable of orienting the optical fiber coil along the key axis.

11. The apparatus of claim 1, wherein the apparatus is configured to be attached as an add-on unit to a handheld navigation device.

12. The apparatus of claim 11, wherein the handheld navigation device includes a receiver for global navigation satellite system (GNSS) signals.

13. The apparatus of claim 12, wherein the user can optionally turn off the GNSS signals to and from the receiver to avoid detection of the user's presence.

14. The device according to claim 11, wherein the gyroscope function can be turned on or off to extend the life of the local power supply.

15. The device according to claim 14, wherein when a GNSS signal is detected as absent or impaired, the gyroscope function relies primarily on manual selection or by an automatic algorithm.

16. The device according to claim 1, wherein the fiber optic gyroscope is used as a north-seeking compass independent of the magnetic field.

17. The device according to claim 16, wherein the north-seeking compass utilizes the Earth's rotation rate to calculate the navigation direction.

18. The device according to claim 1, the device further comprising a power supply that provides power to operate the fiber optic gyroscope.

19. The device according to claim 1, wherein the power supply includes one or more replaceable batteries.

20. The device according to claim 19, wherein the one or more replaceable batteries include standard AAA or AA batteries.

21. The device according to claim 19, wherein the one or more replaceable batteries include rechargeable batteries.

22. The device according to claim 19, the device further comprising a built-in power socket for powering the fiber optic gyroscope and other components when a power outlet is available, thereby extending the life of the one or more replaceable batteries.

23. The device according to claim 19, wherein the power supply is local and enclosed within the housing of the device.

24. The device according to claim 19, wherein the power supply is an external accessory physically attached to the housing of the device and electrically connected to the fiber optic gyroscope and other components within the housing through a mating connector.

25. The device according to claim 5, wherein the integrated photonics-based rotation sensing element includes a waveguide coil or a microresonator ring.

26. The device according to claim 25, wherein the waveguide coil or the microresonator ring includes a low-loss silicon nitride waveguide.

27. The device according to claim 26, wherein the low-loss silicon nitride waveguide is stacked in two or more vertically layers that are evanescently coupled to each other.

28. The device according to claim 1, the device further comprising a main board within the housing, wherein the main board contains electronic circuitry to operate the fiber optic gyroscope.

29. The device according to claim 28, wherein the accelerometer is mounted on the main board.

30. The device according to claim 28, wherein the power supply is electrically connected to the main board to provide power to the electronic circuitry.

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