Portable Optical Gyroscope and Compass Unit

Abstract

This disclosure relates to the integration of integrated photonics-based optical gyroscopes and fiber-based optical gyroscopes into a portable device that may include compass features. A novel, small-footprint, modular, fully integrated photonics optical gyroscope is used for non-critical axes. However, for at least one critical axis, a fiber optic gyroscope can be used to provide bias stability of less than 0.1° / Hr, which directly correlates to predicting position accuracy in the centimeter range. Position accuracy comes from the compass capabilities of the gyroscope (called a gyrocompass) to calculate orientation using the Earth's rotation.

Description

[Technical Field]

[0001] The present disclosure relates to the integration of integrated photonics-based optical gyroscopes and fiber-based optical gyroscopes into portable devices that may include compass features. [Background technology]

[0002] A gyroscope (sometimes called a "gyro") is a sensor capable of measuring angular velocity. Gyroscopes can be mechanical or optical and vary in accuracy, performance, cost, and size. Mechanical gyroscopes based on the Coriolis effect are typically cheaper but cannot provide very high performance and are susceptible to measurement errors caused by temperature, vibration, and electromagnetic interference (EMI). Optical gyroscopes typically have the highest performance and rely on interferometry based on the Sagnac effect (a phenomenon encountered in rotation-induced interferometry). Optical gyroscopes have an advantage over mechanical gyroscopes because they have no moving parts and can withstand the effects of shock, vibration, and temperature changes much better 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) on a moving body to sense various motion parameters along the X, Y, and Z axes. For example, a 6-axis IMU may have 3-axis accelerometers and 3-axis gyroscopes packaged together to measure the absolute spatial displacement of the moving body. Applications of IMUs include, but are not limited to, military operations (e.g., by 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 aided by navigation data provided by a global navigation satellite system (GNSS), such as the Global Positioning System (GPS), GLONASS, Galileo, or BeiDou. GNSS-aided INS receivers use sophisticated fusion algorithms to combine data from various local physical sensors with data derived from GNSS to provide accurate position, velocity, and orientation for a mobile vehicle. (Note that while GNSS is generally referred to as "GPS" in the following description, GPS is only one type of GNSS.) However, when GNSS signals are absent or degraded, data from local physical sensors becomes the only source of accurate position predictions using alternative algorithms. For example, in automobiles, dead reckoning (DR) algorithms are used when the vehicle cannot obtain GNSS signals, such as in tunnels or urban canyons. A receiver with DR capabilities uses data from gyroscopes, accelerometers, odometers, wheel speed sensors, etc. to predict the approaching position and direction of movement (heading) of a moving object based on its last known position.

[0005] For certain situations, a robust portable (e.g., handheld) positioning device with a high-performance, high-precision gyroscope can be mission-critical. In many of these situations, global positioning signals may not be available or are intentionally disabled to avoid detection. Examples of such situations include, but are not limited to, defense operations, rescue operations in remote areas or areas affected by natural disasters, and underground operations such as excavation, tunneling, mining, and drilling. Because handheld devices occupy limited space, a gyroscope with a small footprint is useful for handheld devices.

[0006] Mechanical gyroscopes (such as microelectromechanical systems (MEMS)-based gyroscopes) are useful for small form factors but are typically prone to measurement errors and are assumed to have lower performance. For example, MEMS-based gyroscopes can have high bias instability (e.g., stability values ​​of 3.5° / Hr or greater). High bias estimation errors in gyroscope measurements can render the data meaningless, especially when the sensor also undergoes thermal changes. For example, MEMS gyroscopes can have bias estimation errors in the range of 100° / Hr, or even larger bias estimation errors at higher temperatures. Large thermal errors make mechanical gyroscope-based bias estimation impractical. These gyroscopes also perform poorly under vibration conditions.

[0007] Optical gyroscopes offer much better performance with smaller bias instabilities and are less susceptible to thermal or vibration errors. The most common optical gyroscope is the fiber optic gyroscope (FOG). FOG construction typically involves a long loop of polarization-maintaining (PM) fiber (the loop can constitute a coil with several turns). Laser light (or light from a superluminescent diode (SLED)) is launched into opposite ends of the PM fiber traveling in different directions. When the fiber loop / coil is moving, the light beams have different optical path lengths relative to each other. By setting up an interferometry system, it is possible to measure the small optical path length difference, which is proportional to the area of ​​the enclosed loop and the angular velocity of the rotating coil.

[0008] However, because high-performance FOGs tend to have larger form factors, using a FOG for any of the aforementioned applications, especially for all three axes, may be impossible in portable (e.g., handheld) devices. The inventors have developed a solution in which a high-performance FOG is used in a portable device for one critical axis, along with an integrated photonics-based optical gyroscope for the other axis. In some embodiments, an integrated photonics-based optical gyroscope may be used for all three axes. One type of integrated photonics-based optical gyroscope is described in U.S. Patent Application No. 17 / 071,697, filed October 15, 2020, and entitled "Integrated Photonics Optical Gyroscopes Optimized for Autonomous Terrestrial and Aerial Vehicles," the contents of which are incorporated herein by reference. This application was published on April 22, 2021, as U.S. Patent Application Publication No. 2021 / 0116246. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] US Patent Application Publication No. 2021 / 0116246 [Patent Document 2] U.S. Patent No. 1,073,1988 Summary of the Invention [Problem to be solved by the invention]

[0010] Currently, there are no small form factor, battery powered, portable gyroscopes with compass features. The inventors have implemented a north-pointing gyroscope, called a gyrocompass, that does not rely on magnetic fields and uses the Earth's rotation rate to calculate direction for navigation.

[0011] This disclosure describes an optical gyroscope device that incorporates both a fiber coil and an integrated photonics-based waveguide coil / microresonator ring as sensing elements for different axes of motion. The novel, small-footprint, modular, fully integrated photonics optical gyroscope (i.e., with a waveguide-based sensing element) disclosed herein can provide bias stability of less than 0.5° / Hr (orders of magnitude lower with improved designs). While the fully integrated photonics optical gyroscope is comparable in performance to a fiber optic gyroscope, its cost is significantly lower than that of a fiber optic gyroscope. However, for at least one axis, the fiber optic gyroscope can be used to provide stability of less than 0.1° / Hr, which directly correlates to predicted position accuracy in the centimeter range. The position accuracy comes from the gyroscope's compass capability (referred to as a gyrocompass) to calculate orientation using the Earth's rotation.

[0012] A user (also called an operator) can orient the portable device along various axes to align the ultra-high precision fiber optic gyroscope along the most critical axis, while aligning less critical axes of position measurement with the modularized integrated photonics optical gyroscope. For example, if the portable gyroscope device has dimensions suitable for being held in the hand, the user can continuously change the orientation by moving their hand. The device may be mounted on a wearable or portable item such as a helmet, belt, headband, armband, backpack, shoulder strap, leg band, face shield, bulletproof vest, or on a vehicle whose mounting orientation can be changed. Alternatively, the user can walk around in a specific pattern or in a circle to initially calibrate the device.

[0013] When the critical axis (also called the special sensor axis or preferred sensor axis) associated with the fiber optic gyroscope is roughly horizontal (i.e., roughly parallel to the ground) and manually oriented by the user in any horizontal direction, the accelerometer in the IMU can account for horizontal errors and deviations of this special sensor axis to create a virtual sensor that is perfectly horizontal. The low noise and drift of this preferred sensor (i.e., the fiber optic gyroscope) makes it easy to observe the Earth's rotation in the horizontal plane. The horizontal component of the Earth's rotation rate is 15° / Hr at the equator and varies with angle as the sine of the latitude angle.

[0014] Based on the amount of Earth rotation observed and knowledge of the approximate latitude at which the operator is located, the Earth rotation signal is converted to a coarse heading. For example, if the reading is the maximum positive Earth velocity for a given latitude, the device is pointed north. This basic coarse determination is available within a few seconds of reorienting the device due to the low noise of fiber optic gyroscopes.

[0015] Based on the initial heading estimate, the operator can further improve the accuracy of the measurement by pointing the preferred sensor axis eastward and waiting an additional time period. The operator can use the previously obtained heading to guide this task. Orienting the device east or west provides the greatest sensitivity of the measurement. When perfectly aligned east or west, the signal of a horizontally aligned gyroscope should be zero. Deviation from zero represents the angular difference from the east-west line. After a certain time period (e.g., 1-2 minutes), this deviation will have an accuracy of better than 0.1 degrees relative to the true heading, or better. True heading is an important parameter for navigation. The gyrocompass described herein provides reliable true heading measurements that are tens to hundreds of times more accurate than typical magnetic compasses.

[0016] Because the gyrocompass disclosed herein does not rely on the Earth's magnetic field to calculate direction, it is immune to magnetic disturbances arising from common magnetic materials in the environment, such as iron and steel, as well as magnetic fields created by electric currents.

[0017] As mentioned above, for at least one axis of the handheld device, extremely high accuracy is required to accurately calculate position, and for that axis, a modular, fully integrated photonics optical gyroscope may not be sufficient. For that axis, a fiber spool is used as the sensing element, while for the other two axes, a modular, fully integrated photonics optical gyroscope is used. The fiber spool is structurally supported by a rigid frame to make the entire assembly as robust as the modular, fully integrated photonics optical gyroscope. This rigid frame may be embedded within the periphery of the handheld device and / or within the inner case of the handheld device. Structural robustness is essential for use as a handheld device in harsh conditions such as on the battlefield, rescue operations, military training, or dangerous adventures.

[0018] It is noted that the term "integrated photonics optical gyroscope" encompasses a wide variety of gyroscope configurations. For example, a modularized "integrated" photonics optical gyroscope can have a front-end chip that includes many waveguide-based optical elements (couplers / splitters, mode-selective filters, etc.) as well as a waveguide-based sensing element. However, separate optical elements, such as electro-optic or piezoelectric phase shifters, can be fiber-coupled to the waveguide-based optical or sensing elements. Alternatively, the front-end chip can be a "fully integrated" photonic chip made with silicon photonics, silicon nitride, III-V materials, or other platforms. Phase shifters can be hybrid-integrated with waveguide-based optical elements by depositing, growing, or bonding metallic or other thin-film materials with electro-optic / piezoelectric properties to the waveguide-based optical elements. The same front-end chip can be coupled to a fiber loop as a sensing coil. Alternatively, the fiber loop can be coupled to a separate optical element, such as a piezoelectric disk or lithium niobate phase modulator. It should be noted that these examples are illustrative and non-limiting.

[0019] Another aspect of the handheld device is its simplicity of power supply. The embodiments shown herein can have a built-in power socket for charging the optical gyroscope and other components of the handheld device when a power outlet is available. However, the handheld device can also operate on simple, easily replaceable standard batteries, such as AA or AAA batteries, that can be stockpiled by the user, without having to rely on the availability of an electrical outlet.

[0020] A handheld device with an optical gyroscope can be an "add-on" component that can be mechanically hooked onto a handheld GPS receiver that a user can carry anywhere. The add-on component can be similar to an external battery pack, but with gyroscope and compass features. When GPS signals are jammed or intentionally turned off to avoid detection, the handheld optical gyroscope and compass become the primary local inertial sensor-based location mechanism relied upon. When it is safe to use GPS, the optical gyroscope can be turned off to conserve 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. Typically, there is an algorithm that determines whether to primarily rely on the fiber optic gyroscope, GPS, or both. However, the user can also make that decision.

[0021] A modular, fully integrated photonics optical gyroscope for use on a non-critical axis may be based on silicon photonics, but 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. Furthermore, as described below, the integrated optical gyroscope can have a front-end chip made of integrated photonics that can emit light to and receive light from the rotation sensing element. The rotation sensing element of an integrated photonics optical gyroscope can comprise another integrated photonics waveguide chip (e.g., a silicon nitride waveguide-based coil or microresonator ring) or fiber.

[0022] An integrated photonics optical gyroscope has two main components. The first component is an integrated photonics chip, which is designed with 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 the laser (or SLED), phase shifter, detector, optical splitter, etc. The second component can be a fiber coil. Alternatively, the second component can be a waveguide-based optical gyroscope chip ("OG chip," "gyro chip," or "sensing chip") with a waveguide coil (or helix) or ring resonator (also called a microresonator). The waveguides can be made from silicon nitride (SiN). Therefore, a SiN waveguide-based OG chip may be referred to as a "SiN waveguide chip" or simply a "SiN chip" in these embodiments. In one embodiment, the OG chip is hybrid-integrated with the integrated photonics chip. In some preferred embodiments, the integrated photonics chip and the OG chip may be fabricated together on the same chip or may be stacked via wafer bonding. Low waveguide loss in the gyro chip is key to desired gyroscope sensitivity values ​​associated with smaller bias estimation errors.

[0023] The integrated photonics optical gyroscope can be modularized (e.g., the integrated photonics chip and the sensing chip can be packaged together) on a printed circuit board (PCB) using standard pick-and-place techniques. The PCB may contain control electronics for the integrated photonics 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 deployed on different IMU PCBs tailored for different markets, since the form factor of the optical gyroscope module remains the same. One such market is automated driver assistance systems (ADAS) for autonomous vehicles, although those skilled in the art will understand that the scope of this disclosure is not limited to ADAS alone, as the same module can also fit inside handheld devices. Wafer-level processing and standard IC packaging and assembly techniques enable large-scale mass production of integrated photonics-based optical gyroscope modules for a variety of system architectures for a variety of markets, including both commercial and military applications. [Means for solving the problem]

[0024] Specifically, the present disclosure claims a device that acts as an optical gyrocompass with a portable form factor, comprising: a rigid frame forming a portion of the device's housing; and a fiber optic gyroscope having a fiber coil wound around the rigid frame. The fiber coil is used as the rotation-sensing element of the fiber optic gyroscope to provide high-precision inertial navigation data along a critical axis. The fiber optic gyroscope further comprises an integrated photonics front-end chip coupled to the fiber coil. For other non-critical axes, a modular integrated photonics optical gyroscope can be used that can be mounted to the rigid frame or to an extension of the rigid frame within the gyrocompass device's housing. A local or additional accessory power source provides power to operate the fiber optic gyroscope and other components within the housing. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 2 is a diagram of the main components of a single-axis integrated photonics optical gyroscope module, according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a schematic perspective view of the single-axis integrated photonics optical gyroscope module shown in FIG. 1. [Figure 3] FIG. 1 is a schematic diagram of a circuit board (PCB) of an IMU with a single-axis integrated photonics optical gyroscope module, according to an embodiment of the present disclosure. [Figure 4] FIG. 1 is a schematic diagram of three single-axis integrated photonics optical gyroscope modules packaged together to implement a three-axis gyroscope, according to an embodiment of the present disclosure. [Figure 5] FIG. 1C is a schematic diagram of an embodiment of a three-axis optical gyroscope with two additional single-axis integrated photonics optical gyroscope modules for two additional axes packaged together on a PCB to which a single-axis integrated photonics optical gyroscope module is already attached, in accordance with an embodiment of the present disclosure. [Figure 6]FIG. 1 is a diagram of various components of a three-axis optical gyroscope assembled together, with at least one of the axes having a fiber-based sensing coil, according to an embodiment of the present disclosure. [Figure 7] FIG. 10 illustrates another configuration in which a printed circuit board is mounted inside and on a frame, according to an embodiment of the present disclosure. [Figure 8] 1 is a diagram of a conventionally used handheld GPS receiver. [Figure 9] FIG. 10 is a diagram of an additional optical gyroscope unit with the same footprint attached to a handheld receiver unit according to an embodiment of the present disclosure. [Figure 10] FIG. 10 is a diagram of an additional optical gyroscope unit before being attached to a GPS receiver unit, according to an embodiment of the present disclosure. [Figure 11] FIG. 10 is a longitudinal cross-sectional view of an additional optical gyroscope unit into which an integrated photonics optical gyroscope module is inserted, according to an embodiment of the present disclosure. [Figure 12] FIG. 10 is a perspective view of an additional optical gyroscope unit with two integrated photonics optical gyroscope modules inserted, with the top surface removed to show the PCB, according to an embodiment of the present disclosure. [Figure 13] FIG. 10 is a perspective view of an additional optical gyroscope unit with the PCB removed to show the fiber coil around the frame being inserted into the container and two integrated photonics optical gyroscope modules inserted, according to an embodiment of the present disclosure. [Figure 14] FIG. 10 is a perspective view of an additional optical gyroscope unit with the PCB and frame with fiber coil removed to show the bottom of the container that holds the batteries, and with two integrated photonics optical gyroscope modules inserted, according to an embodiment of the present disclosure. [Figure 15] FIG. 10 is a perspective view of a frame with a fiber coil entering into a housing of an additional optical gyroscope unit according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0026] The present disclosure will become more fully understood from the detailed description provided below and from the accompanying drawings of various implementations of the present disclosure, and it should be noted that the dimensions shown in the figures are for illustrative purposes only and are not drawn to scale.

[0027] Aspects of the present disclosure are directed to the integration of a compact, ultra-low-loss waveguide-based optical gyroscope module and fiber coils with other system-level electronic components to create a high-performance inertial measurement unit (IMU).

[0028] Some sensing applications may require an ultra-high-precision optical gyroscope for only one axis to compensate for (or replace) the relatively lower-precision measurements provided by a fully integrated photonics-based optical gyroscope module. Note that the “relatively lower precision” refers to the overall comparison of the performance of a fully integrated photonics-based optical gyroscope with that of a fiber-based optical gyroscope. However, the “relatively lower precision” of a fully integrated photonics-based optical gyroscope is much higher than that of a low-cost, low-precision mechanical (e.g., MEMS-based) gyroscope. Consider a situation in which a user holding the gyroscope is moving in the XY plane of a rigid surface, so high-precision angle measurement may be desired only for the Z axis to determine orientation. Angle measurements for the X and Y axes may not be critical to safety in this situation. The inventors have recognized that reducing the cost of ultra-high-precision fiber optic gyroscopes for at least two axes will lead to a reduction in the overall cost of the IMU, facilitating higher-volume production.

[0029] Sensor fusion algorithms are used in IMUs to predict position using data from gyroscopes, accelerometers, and magnetometers, as well as alternative sensing technologies such as light detection and ranging (LIDAR) and camera-based systems. The local gyroscope in the handheld unit also provides redundancy, as the IMU can rely on purely algorithm-based position determination for longer periods of time when the alternative sensing technologies fail or are intentionally turned off. This redundancy can be extremely beneficial in safety-critical applications, for example, when satellite signals for navigation are lost ("GPS-denied environments").

[0030] FIG. 1 illustrates the main components of a single-axis fully integrated photonics optical gyroscope module 100 according to an embodiment of the present disclosure. The module 100 includes an integrated photonics chip 120 and a waveguide chip 110. The waveguide chip 110 may have a SiN waveguide and is referred to herein as a SiN chip. The waveguide chip 110 has a waveguide gyro coil 115 (spiral) that receives an optical signal from a laser (or SLED), which may be in the integrated photonics chip 120 or elsewhere in a packaging substrate 105. The integrated photonics chip 120 and the waveguide chip 110 may be assembled together on the packaging substrate 105, which may be a printed circuit board (PCB). There may be other control electronics in the form of one or more individual ICs 122, e.g., 122a-122c.

[0031] The optical signal from the integrated photonics chip 120 can be coupled to the waveguide chip 110, and after passing through the waveguide coil 115, the optical signal finally couples back to the integrated photonics chip 120 to be detected by a photodetector that measures the optical phase change due to the Sagnac effect. This detector is sometimes referred to as a Sagnac detector. System-level integration of an integrated photonics chip and a waveguide chip is addressed in U.S. Provisional Patent Application No. 62 / 872,640, filed July 10, 2019, and entitled "System Architecture for Silicon Photonics Optical Gyroscopes," and U.S. Provisional Patent Application No. 62 / 904,443, filed September 23, 2019, and entitled "System Architecture for Silicon Photonics Optical Gyroscopes with Mode-Selective Waveguides." These provisional patent applications were converted into U.S. Nonprovisional Patent Application No. 16 / 659,424, which published as U.S. Pat. No. 10,731,988. These patent applications are incorporated by reference herein. In addition to what is described in those patent applications, two separate waveguide chips may be coupled to a single integrated photonics chip having two sets of integrated photonics components for built-in redundancy. Alternatively, a second layer in the waveguide chip may be used for built-in redundancy, meaning two complete waveguide coils are available for coupling to the integrated photonics chip. These redundancy concepts are shown in U.S. Patent Application No. 17 / 071,697, entitled "Integrated Photonics Optical Gyroscopes Optimized for Autonomous Terrestrial and Aerial Vehicles," filed October 15, 2020, which is incorporated by reference in its entirety. This application has been published as U.S. Patent Application Publication No. 2021 / 0116246.

[0032] 2 shows a schematic perspective view of single-axis integrated photonics optical gyroscope module 100. While not drawn to scale, it should be noted that waveguide chip 110 may be substantially larger than integrated photonics chip 120 and may determine the overall form factor of module 100. Packaging substrate 105 may have additional circuitry on its backside and may have designated bond pads for attachment to another packaging substrate of a larger module (such as an IMU).

[0033] FIG. 3 shows a schematic diagram of a circuit board (PCB) 305 with a single-axis integrated photonics optical gyroscope module 100 according to an embodiment of the present disclosure. The PCB 305 may have a processing unit 330 to process data from the module 100 as well as other signals / data received by the IMU (e.g., accelerometer data, GNSS data, magnetometer data). The processing unit 330 may have a central processing unit (CPU) that may be combined with a digital signal processor (DSP) or analog lock-in circuit to control the gyro. Other ICs 332 may also be on the same PCB. The integrated photonics optical gyroscope module 100 may be assembled on the PCB 305 by flip-chip bonding or other standard packaging techniques.

[0034] FIG. 4 shows a schematic diagram of three co-packaged single-axis integrated photonics optical gyroscope modules according to an embodiment of the present disclosure, an apparatus 400. These single-axis integrated photonics optical gyroscope modules are interchangeable and orthogonal to one another. The embodiment of the apparatus 400 may have a three-dimensional housing 450 for mounting three SiPhOG modules 100a, 100b, and 100c, one for each of the Z-axis, X-axis, and Y-axis. As shown with respect to later figures, the housing 450 may be part of the container of a handheld device. Depending on the configuration of the handheld device, two modules 100a and 100b may be used, and module 100c may be modified by removing the waveguide coil 110 and attaching the integrated photonics chip 120 to an optical fiber coil to create an ultra-high-precision fiber-based optical gyroscope.

[0035] Generally, fiber-based gyroscopes offer better sensitivity to angular motion than integrated photonics-based waveguide coils. The sensitivity of a gyroscope varies depending on the physical dimensions associated with the gyroscope. The phase signal of an optical gyro is proportional to the angular rotation rate as a multiple of the Sagnac effect, as shown in Equation (1) below:

[0036] Δφ=(δπNA / λc)Ω (1)

[0037] In formula (1), N = number of turns of the gyro A = enclosed area Ω=angular rotation speed Δφ=optical phase difference signal λ = wavelength of light c = speed of light is.

[0038] The fiber optic coil is not limited by the fabrication parameters of integrated photonics (reticle dimensions, area of ​​exposure, etc.), and longer lengths of fiber can be used to increase sensitivity about at least one critical axis.

[0039] 5 shows a schematic diagram of two single-axis integrated photonics optical gyroscope modules 100c, 100b packaged together according to an apparatus 500 of an embodiment of the present disclosure. Optionally, a third single-axis integrated photonics optical gyroscope module 100a may be mounted on the PCB 305 to provide redundancy for the optical fiber sensing coil for the Z axis, as shown in FIG. 6. The mechanical structure 550 may be part of the housing of the handheld device.

[0040] FIG. 6 shows how the single-axis integrated photonics optical gyroscope modules 100c and 100b (and possibly 100a) can be inserted inside a frame 600. The frame 600 can be a metal frame or made from other structurally strong materials to provide rigid support for the fiber coil 650 wrapped around it. The frame's height "h" should be high enough to mount the single-axis integrated photonics optical gyroscope module 100 along the frame's inner wall, with the PCB 305 located at the bottom. Alternatively, as shown in FIG. 7, the PCB 305 can be on top of the frame 600 and support a front-end chip (not shown in FIG. 7) that emits light into the fiber coil 650.

[0041] FIG. 8 shows a conventional handheld GPS receiver device 800 that includes a position calculation processor that receives GPS signals and can provide navigation data on a screen 850. The device may include local sensors, such as low-precision mechanical accelerometers and gyroscopes, to supplement GPS data for position prediction. The position calculation processor can execute a sensor fusion algorithm that combines data from all available physical sensors to predict the position and trajectory of a moving object when GPS data is unavailable. However, the effectiveness of the sensor fusion algorithm depends on the measurement accuracy of the physical sensors. The handheld GPS receiver device has several buttons, and one button 855, for example, can be assigned to turn GPS operation on or off depending on the situation. For example, because the GPS receiver device transmits and receives signals from satellites, these signals can be intercepted to detect the location of the GPS receiver device user (e.g., a soldier on the battlefield). When a user wishes to avoid detection or enters an environment where GPS signals are obstructed, the user must rely on local sensors for position calculation and navigation.

[0042] The inventors propose attaching an additional gyroscope unit 900 to a conventional handheld GPS receiver device 800 to make it more accurate and versatile for possible "GPS-denied" environments (e.g., battlefields, rescue operations, tunnels, caves, etc.), as shown in FIG. 9 . The additional gyroscope unit 900 can be attached to the handheld GPS receiver device 800 using a standard latch / slot or other attachment mechanism on the back of the GPS receiver device 800. The additional gyroscope unit 900 has a processing unit (such as the processing unit 330 in the PCB 305) capable of running a sensor fusion algorithm that can calculate position using only local sensors, but can authenticate position using data received from the GPS receiver device 800 when it is safe to use GPS signals.

[0043] In a GPS-denied environment, the sensor fusion algorithm receives input data from the fiber optic gyroscope on the Z axis and the integrated photonics optical gyroscopes on the other axes, as well as from the on-board accelerometer. Additional sensor data (e.g., from magnetometers, cameras, radar, pedometers, etc.) may also be used in the sensor fusion algorithm.

[0044] FIG. 10 shows the relative external dimensions of the housing for the additional gyroscope unit 900. The height "H" of one side of the housing should be sufficient to accommodate a fully integrated photonics optical gyroscope module (such as module 100) mounted on the interior wall (see FIGS. 12 and 13). The length L1 and width W can be substantially the same as the length and width of the GPS receiver device 800 to which the additional gyroscope unit 900 is attached, although longer or shorter dimensions can also be used. The length L2 should be able to accommodate the frame 1127 (see FIGS. 11, 13, and 15). The frame 1127 provides rigid structural support for winding the fiber coil 1125 around it. The fiber coil 1125 is the sensing element for the fiber-based ultra-high precision optical gyroscope along one axis (the most critical axis).

[0045] FIG. 11 shows a longitudinal cross section of the additional gyroscope unit 900, showing an integrated photonics optical gyroscope module 1113 mounted on one of the side walls visible in the longitudinal view. The module 1113 is similar to the module 100 shown in FIG. 2 after being encapsulated, packaged, and connected for use in various devices. The module 1113 can include not only an integrated photonics optical gyroscope but also a low-precision mechanical gyroscope (e.g., a MEMS-based gyroscope). In examples, the module 1113 may be mounted in an advanced driver assistance system (ADAS) in an autonomous vehicle, a drone, a submarine, an augmented reality headset, or a robotic device. In the case of a handheld device (similar to that shown in FIG. 9), the additional gyroscope unit 900 includes a container 1105 whose rigid inner wall is suitable for mounting a module such as 1113. The top of the container 1105 has a latch 1107 (or other fastening mechanism) that attaches to the handheld GPS receiver device 800. A frame 1127, around which the fiber coil 1125 is wrapped, is inserted into the container 1105. A longitudinal cross-section of the frame 1127 and the fiber coil 1125 can be seen in FIG. 11 . A printed circuit board (PCB) 1109 can interface with the fiber coil 1125. The PCB 1109 can have a front-end chip, such as 120, to direct light into the fiber coil 1125. Another PCB 1111, which can be equivalent to PCB 305, can interface with the integrated photonics optical gyroscope modules 1113, 1115 (shown in FIG. 13 ). It should be noted that the front-end chip 120 for the fiber coil may have an integrated photonics waveguide, which may all be mounted on a PCB, or may have separate optical components, such as lithium niobate phase modulators, hybrid integrated photodetectors, coupling lenses, isolators, etc.

[0046] FIG. 12 shows a perspective view of the additional optical gyroscope unit 900 with two integrated photonics optical gyroscope modules 1113 and 1115 inserted, with the top of the container 1105 removed to reveal the PCB 1109. Note that the two integrated photonics optical gyroscope modules 1113 and 1115 are identical, interchangeable modules mounted along two different axes, typically relatively non-critical axes, but that a fiber coil 1125 is used as the sensing element for the most critical axis. Another module, such as 1113 or 1115, not explicitly shown in FIG. 12, may be mounted on the PCB 1111 to provide redundancy along the critical axis (as shown in FIGS. 4, 5, and 6).

[0047] FIG. 13 shows a perspective view of the additional optical gyroscope unit 900 with the PCB 1109 removed to show the fiber coil 1125 around the frame 1127 being inserted into the container 1105. Because the frame 1127 may have hundreds or thousands of feet of sensing fiber 1125 wound around it, the enclosure area 1131 is large enough to ensure that the fiber optic gyroscope provides ultra-high precision rotation measurements. In addition to the fiber length, because the perimeter of the frame 1127 is substantially larger than that of a fully integrated photonics optical gyroscope (and, by extension, the enclosure area 1131 is substantially larger), the fiber length does not need to be as long, according to equation (1), because the optical phase shift is proportional to the product of the fiber length (i.e., the number of turns N is large) and the enclosure area "A." In other words, when the enclosure area "A" is larger, the number of turns "N" can be smaller for the same phase shift. In one example, the length of the fiber spool can be in the range of 1500 feet if the enclosure area is 10 square inches. The fiber length is longer when the enclosure area is smaller. The combination of fiber length and enclosure area should achieve an angle random walk (ARW) drift consistent with an acceptable bias stability value (e.g., less than 0.1° / Hr) for a high-performance gyroscope. ARW is a noise parameter that represents the average deviation or error that occurs when the gyroscope signal is integrated over a finite length of time to calculate the angular movement of a mobile 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 leads to more accurate position prediction. A high-performance fiber optic gyroscope should have an on-time drift substantially less than 0.1° / Hr.

[0048] FIG. 14 shows a perspective view of the additional optical gyroscope unit 900 with the PCB 1109 and frame 1127 with the fiber coil 1125 removed to reveal the exposed bottom of the enclosure 1105. Area 1131 is large enough to accommodate a battery as a power source for the handheld device. Because it may not be easy to charge the handheld device in harsh conditions (such as a battlefield or disaster area), it is important that the entire handheld device, including the optical gyroscope unit 900, be powered by standard batteries 1133 (such as AAA or AA batteries, or even rechargeable batteries) that are easy to stockpile and insert into the device. Additional batteries can be inserted at the top of the PCB 1111, especially if a 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 the longest possible time of operation can be supported without the need for recharging. To save power, it is possible to switch to measuring a single axis of rotation rather than measuring all three axes for angular rotation. Also, to save power, the lower precision and lower power mechanical gyroscopes included in modules 1113, 1115 may be used for non-critical axes until accurate position tracking becomes important and the optical gyroscopes are powered on. Alternatively, to improve battery life and operation, rotation may be through three different optical gyros depending on the orientation of the handheld device.

[0049] It should be noted that the battery may either be enclosed within the device housing or may be attached to the housing as an external add-on battery pack, with the device housing having a mating receptacle for receiving an external battery pack so that electrical connections can be made to the fiber optic gyroscope and other electronic circuitry enclosed within the housing.

[0050] FIG. 15 shows a perspective view of a frame 1127 with a fiber coil 1125 that extends into the housing of an additional optical gyroscope unit 900 .

[0051] In one embodiment, the optical gyroscopes available along three axes do not need to be used simultaneously all the time, especially when conserving power is an important factor. Because the device has a three-axis accelerometer (e.g., a MEMS accelerometer), when the user is walking or running, or in a vehicle moving on the ground, an algorithm can analyze the accelerometer data to determine which axis is pointing down due to gravity. The user's body position may also change, for example, when the user is a soldier crawling in a trench or a rescue worker crawling in a tunnel and the gyroscope is mounted on their helmet or in their backpack. The user's body position may also change while calibrating the gyroscope. Dynamically selecting selective gyroscopes along changing axes of interest improves battery life in portable devices because the gyroscopes for the other two axes can be temporarily powered off and powered on when needed.

[0052] In the foregoing description, implementations of the present disclosure have been described with reference to specific implementation examples. It will be apparent that various modifications can be made without departing from the broader spirit and scope of implementations of the present disclosure as set forth in the following claims. Accordingly, the specification and drawings are to be interpreted in an illustrative, rather than a restrictive, sense. Furthermore, directional terms such as "top" and "bottom" do not limit the scope of the present disclosure to any fixed orientation, but rather encompass various permutations and combinations of orientations. [Explanation of symbols]

[0053] 100, 100a, 100b, 100c Single-axis fully integrated photonics optical gyroscope module, SiPhOG module 105 Packaging Substrate 110 Waveguide chip, waveguide coil 115 Waveguide gyro coil, fiber coil 120 Integrated photonics chips, front-end chips 122, 122a, 122b, 122c IC 305 Printed Circuit Board (PCB) 330 Processing equipment 332 IC 400 Embodiments 450 cabinet 500 Embodiments 550 Mechanical structure 600 frames 650 Fiber Coil 800 Handheld GPS Receiver 850 screen 855 Button 900 additional gyroscope units 1105 Container 1107 Hook stopper 1109 Printed Circuit Board (PCB) 1111 Another PCB 1113, 1115 Integrated photonics optical gyroscope module 1125 Fiber coil, optical fiber sensing coil 1127 frames 1131 Encircled Area 1133 battery h Frame height L1, L2 length W width

Claims

1. 1. A device that acts as an optical gyrocompass with a portable form factor, comprising: a rigid frame forming part of the housing of the device; a fiber optic gyroscope having a fiber coil wound around the rigid frame, the fiber coil being used as a rotation-sensing element of the fiber optic gyroscope to provide high-precision inertial navigation data along a critical axis, the fiber optic gyroscope further comprising an integrated photonics front-end chip coupled to the fiber coil; An apparatus comprising:

2. 10. The apparatus of claim 1, wherein the fiber optic gyroscope comprises a semiconductor-based light source integrated into or coupled to the integrated photonics front-end chip that emits light into and receives light from the fiber coil.

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

4. 10. The device of claim 1, further comprising one or more integrated photonics optical gyroscope modules mounted within the housing of the device to the rigid frame or to an extension of the rigid frame, each integrated photonics optical gyroscope module providing additional inertial navigation data along a respective axis perpendicular to the critical axis.

5. 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 packaged within the integrated photonics optical gyroscope module.

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

7. 10. The device of claim 1, wherein the device is held in a user's hand, allowing the user to move their hand to orient the fiber coil along the critical axis.

8. 10. The device of claim 1, wherein the device is mounted to a wearable article on a user's body, allowing the user to move their body to orient the fiber coil along the critical axis.

9. 9. The device 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 band, a face shield, and a bulletproof vest.

10. 10. The apparatus of claim 1, wherein the apparatus is mounted on a mobile vehicle on a rotatable base capable of orienting the fiber coil along the critical axis.

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

12. 12. The apparatus of claim 11, wherein the handheld navigation device comprises a receiver for Global Navigation Satellite System (GNSS) signals.

13. 13. The device of claim 12, wherein a user can optionally turn off the Global Navigation Satellite System (GNSS) signals to and from the receiving device to avoid detection of the user's presence.

14. 12. The device of claim 11, wherein the gyroscope function can be switched on or off to extend the life of the local power source.

15. a receiving device for Global Navigation Satellite System (GNSS) signals; 15. The device of claim 14, wherein when the Global Navigation Satellite System (GNSS) signals are detected as being absent or tampered with, the gyroscope function relies primarily on either manual selection or an automatic algorithm.

16. 10. The apparatus of claim 1, wherein the fiber optic gyroscope acts as a compass that points north independent of magnetic fields.

17. 17. The device of claim 16, wherein the north-pointing compass utilizes the rotation rate of the Earth to calculate navigation directions.

18. 10. The apparatus of claim 1, further comprising a power supply for providing power to operate the fiber optic gyroscope.

19. 20. The device of claim 18, wherein the power source comprises one or more replaceable batteries.

20. 20. The device of claim 19, wherein the one or more replaceable batteries comprise AAA or AA batteries.

21. 20. The device of claim 19, wherein the one or more replaceable batteries comprise a rechargeable battery.

22. 20. The device of claim 19, further comprising an internal power socket for powering the fiber optic gyroscope and other components when power output is available, thereby extending the life of the one or more replaceable batteries.

23. 20. The device of claim 19, wherein the power source is local and contained within the housing.

24. 20. The apparatus of claim 19, wherein the power source is an additional accessory physically attached external to the housing and electrically connected to the fiber optic gyroscope and other components within the housing through mating connectors.

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

26. 26. The apparatus of claim 25, wherein the waveguide coil or the microresonator ring comprises a low-loss silicon nitride waveguide.

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

28. Further comprising a motherboard in the housing; 10. The apparatus of claim 1, wherein the motherboard includes electronic circuitry for operating the fiber optic gyroscope.

29. 30. The device of claim 28, wherein an accelerometer is mounted on the motherboard.

30. 30. The apparatus of claim 28, wherein a power supply is electrically connected to the motherboard for providing power to the electronic circuitry.

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