Integrated photonic gyroscope and chip for an integrated photonic gyroscope

Abstract

An integrated photonic gyroscope silicon chip, a gyroscope, and a method of fabrication thereof. The chip includes a silicon chip substrate; at least one waveguide formed on the substrate, the at least one waveguide being configured to optically connect with a laser source, the at least one waveguide being configured to optically connect with a pair of photodetectors; at least one phase modulator formed on the substrate, the at least one phase modulator being arranged and configured to modulate light propagating through the at least one waveguide; and a resonator ring formed on the silicon chip substrate, the resonator ring being in optical communication with the at least one waveguide, the at least one waveguide and the at least one phase modulator being disposed within a circumference of the resonator ring.

Description

INTEGRATED PHOTONIC GYROSCOPE ANDCHIP FORAN INTEGRATED PHOTONIC GYROSCOPECROSS-REFERENCE

[0001] The present application claims priority to U.S. Provisional Patent Application No.63 / 747,191, entitled “Integrated Photonic Gyroscope and Chip for an Integrated Photonic Gyroscope”, filed January 20, 2025, the entirety of which is incorporated by reference herein.TECHNICAL FIELD

[0002] The present technology generally relates to photonic integrated chip gyroscopes and chips for same.BACKGROUND

[0003] In recent years, the need for inertial sensing has grown in applications such as autonomous vehicles, unmanned aerial systems, industrial robotics, and space exploration. Gyroscopes based on optical principles, such as fiber optic gyroscopes (FOGs) and ring laser gyroscopes (RLGs), have been widely used in these areas due to their ability to provide rotation sensing without moving mechanical parts.

[0004] A typical FOG consists of a long optical fiber coil, which can be as long as 5 km, to measure rotational phase shifts using the Sagnac effect. RLGs, in contrast, utilize a closed-loop laser cavity in which counter-propagating laser beams experience a frequency shift proportional to the rotation rate. While these gyroscopes have demonstrated high accuracy and stability, they often require precise optical alignment, large-scale fabrication, and complex stabilization mechanisms, limiting their scalability and cost-effectiveness.

[0005] There thus remains a desire for improvements in this area.304941099.4 40745 / 61SUMMARY

[0006] At least some techniques have been developed to use gyroscopes based on photonic integrated circuits (PICs) as a potential alternative to conventional FOGs and RLGs. In these integrated designs, optical components such as waveguides, resonators, and phase modulators are fabricated on a silicon-based microchip instead of using discrete optical fibers or laser cavities. Typical integrated photonic gyroscopes are implemented using either an interferometric design or a resonant design.

[0007] Interferometric photonic gyroscopes operate similarly to FOGs by splitting a beam into two counter-propagating waves and measuring the phase shift due to rotation. Resonant photonic gyroscopes, on the other hand, utilize a ring resonator structure where the frequency shift of circulating optical waves is used to determine angular velocity.

[0008] However, one challenge associated with integrated photonic gyroscopes is optical losses in waveguides, which can affect sensitivity and long-term stability. Unlike fiber optic gyroscopes, which use long, low-loss optical fiber, integrated photonic gyroscopes rely on miniaturized waveguides that may introduce scattering and absorption losses, particularly at waveguide sidewalls and interfaces. These losses can reduce the quality factor (Q) of resonators, impacting signal-to-noise ratio and detection sensitivity.

[0009] Additionally, backscattering effects and fabrication-induced phase noise can introduce errors, making it difficult to achieve consistent performance. Some implementations of integrated photonic gyroscopes also require active stabilization mechanisms, increasing power consumption and system complexity. Furthermore, temperature fluctuations and process variations can affect the refractive index of waveguides, leading to wavelength shifts that influence gyroscope accuracy. Bias drift can further limit stability of the gyroscope, particularly in applications requiring precise navigation.

[0010] The present technology provides an integrated photonic gyroscope silicon chip for constructing a photonic gyroscope and an integrated photonic gyroscope. Using optical components formed from silicon nitride and disposed in silicon dioxide, the gyroscope components are formed directly on a silicon substrate chip. Recesses are formed therein to receive a laser gain304941099.4 40745 / 61medium and two photodetectors. In the present implementation, the resonant ring of the gyroscope extends around the other components, reducing the overall footprint of the device.

[0011] It is contemplated that embodiments of the present technology may have a variety of advantages. Some embodiments of the present technology may enable high-precision inertial sensing with a compact form factor by integrating photonic components onto a single silicon chip. Additionally, some embodiments of the present technology may achieve performance comparable to fiber optic gyroscopes (FOGs) while offering a smaller footprint and lower power consumption. Furthermore, some embodiments may offer improved resistance to mechanical shock, vibration, and electromagnetic interference (EMI) by utilizing a fully photonic design with no moving parts. Compared to Micro Electro-Mechanical-Systems (MEMS) gyroscopes, which remain fundamentally mechanical and are susceptible to environmental vibrations, some embodiments of the present technology may provide more robust operation in dynamic conditions. Some embodiments may also minimize optical losses by employing optimized silicon nitride waveguides with low propagation loss, enhancing signal -to-noise ratio and measurement accuracy. Additionally, some embodiments may allow for wafer-level fabrication and heterogeneous integration, which may reduce system complexity, manufacturing costs, and assembly requirements compared to discrete microchip approaches.

[0012] Some embodiments of the present technology can be used in autonomous navigation systems, including self-driving vehicles, drones, and robotic platforms, where precise inertial sensing is required for reliable operation in Global Navigation Satellite System (GNSS)-denied environments. Additionally, some embodiments can be used in aerospace and defense applications, such as spacecraft attitude control, missile guidance, and submarine navigation, where compact, low-power, and high-stability gyroscopes are beneficial. Some embodiments may also be applicable in industrial automation, including robotic arms, precision manufacturing, and motion tracking systems, where high-resolution orientation sensing is needed. Furthermore, some embodiments may be utilized by technology developers working on next-generation navigation and positioning systems for sensor fusion, augmented inertial navigation, and experimental applications in quantum sensing and artificial intelligence (Al)-driven robotics.304941099.4 40745 / 61

[0013] In at least one aspect of the present technology, there is provided an integrated photonic gyroscope silicon chip, comprising: a silicon chip substrate; at least one waveguide formed on the silicon chip substrate, the at least one waveguide being configured to optically connect with a laser source, the at least one waveguide being configured to optically connect with a pair of photodetectors; at least one phase modulator formed on the silicon chip substrate, the at least one phase modulator being arranged and configured to modulate light propagating through the at least one waveguide; and a resonator ring formed on the silicon chip substrate, the resonator ring being in optical communication with the at least one waveguide, the at least one waveguide and the at least one phase modulator being disposed within a circumference of the resonator ring.

[0014] In some embodiments of the integrated photonic gyroscope silicon chip, the chip further comprises a first silicon dioxide layer and a second silicon dioxide layer formed on the silicon chip substrate; and wherein the at least one waveguide and the resonator ring are formed at least partially between the first and second silicon dioxide layers.

[0015] In some embodiments of the integrated photonic gyroscope silicon chip, the at least one waveguide and the resonator ring are formed from silicon nitride.

[0016] In some embodiments of the integrated photonic gyroscope silicon chip, the chip further comprises a laser filter formed on the silicon chip substrate, the laser filter being configured to filter light from the laser source.

[0017] In some embodiments of the integrated photonic gyroscope silicon chip, the laser filter is formed from silicon nitride.

[0018] In some embodiments of the integrated photonic gyroscope silicon chip, the at least one phase modulator includes at least one stress optic phase modulator connected to the substrate, the at least one waveguide being disposed between the silicon chip substrate and the at least one stress optic phase modulator.

[0019] In some embodiments of the integrated photonic gyroscope silicon chip, the at least one stress optic phase modulator is formed from at least one lead zirconium titanate (PZT) electrode.304941099.4 40745 / 61

[0020] In some embodiments of the integrated photonic gyroscope silicon chip, the at least one PZT electrode includes a pair of PZT electrodes.

[0021] In some embodiments of the integrated photonic gyroscope silicon chip, the resonator ring is spaced from the at least one waveguide.

[0022] In some embodiments of the integrated photonic gyroscope silicon chip, the chip further comprises a pair of circulators formed on the silicon chip substrate, each one of the pair of circulators being configured to optically connect the at least one waveguide to a corresponding one of the pair of photodetectors.

[0023] In some embodiments of the integrated photonic gyroscope silicon chip, each one of the pair of circulators is formed from silicon nitride.

[0024] Another aspect the present technology provides a silicon chip integrated photonic gyroscope, comprising: a silicon substrate; a first silicon dioxide layer and a second silicon dioxide layer formed on the silicon substrate; a laser gain medium connected to the substrate, the laser gain medium being disposed in a laser recess formed in at least the silicon substrate, the laser gain medium forming at least part of a laser source; a waveguide loop connected to the substrate, the waveguide loop being disposed between the first and second silicon dioxide layers, the waveguide loop being in optical communication with the laser source via the laser gain medium; at least one phase modulator formed on the second silicon dioxide layer, the at least one phase modulator being arranged and configured to modulate light propagating through the waveguide loop; a resonator ring formed on the silicon chip substrate, the resonator ring being in optical communication with the waveguide loop; and a pair of photodetectors connected to the substrate, each photodetector of the pair of photodetectors being disposed in one of a pair of photodetector recesses formed in at least the silicon substrate, the pair of photodetectors being in optical communication with the waveguide loop, the waveguide loop, the at least one phase modulator, the pair of photodetectors, and the laser gain medium being disposed within a circumference of the resonator ring.

[0025] In some embodiments of the gyroscope, the waveguide loop and the resonator ring are formed from silicon nitride.304941099.4 40745 / 61

[0026] In some embodiments of the gyroscope, the gyroscope further comprises a laser filter disposed between the first and second silicon dioxide layers, the laser filter being formed from silicon nitride, the laser filter being arranged to filter light from the laser source and optically communicate filtered light to the waveguide loop.

[0027] In some embodiments of the gyroscope, the at least one phase modulator is formed at least in part from lead zirconium titanate (PZT) disposed on the second silicon dioxide layer.

[0028] Another aspect the present technology provides a method for fabricating an integrated photonic gyroscope silicon chip, the method comprising: forming a first silicon oxide layer on a silicon wafer substrate; forming at least a waveguide loop and a resonator ring of silicon nitride on the first silicon oxide layer; forming a second silicon oxide layer over the waveguide loop and the resonator ring; forming a laser recess and a pair of photodetector recesses in at least the second silicon oxide layer; and forming at least one phase modulator on the second silicon oxide layer.

[0029] In some embodiments of the method, the method further comprises: forming a laser filter from silicon nitride; and forming a pair of circulators from silicon nitride.

[0030] In some embodiments of the method, the first and second silicon oxide layers and components of silicon nitride are fabricated in a lead-free facility; and the at least one phase modulator is fabricated in a second facility, the second facility having lead-compatible fabrication capabilities.

[0031] Another aspect the present technology provides a method for fabricating a silicon chip integrated photonic gyroscope, the method comprising: fabricating the integrated photonic gyroscope silicon chip; connecting a laser gain medium to the chip, the laser gain medium being inserted into the laser recess; and connecting a pair of photodetectors to the chip, each one of the pair of photodetectors being inserted into a corresponding one of the pair of photodetector recesses.

[0032] In the context of the present technology, “integrated photonic gyroscope” refers to a rotation-sensing device fabricated on a photonic chip, where optical components such as waveguides, resonator rings, phase modulators, and photodetectors are integrated onto a common304941099.4 40745 / 61substrate. The gyroscope operates based on the Sagnac effect, wherein a phase shift between counter-propagating optical signals is used to determine angular velocity.

[0033] In the context of the present technology, “heterogeneous integration” refers to the process of combining photonic and electronic components from different material platforms onto a single microchip. This allows for improved optical coupling, reduced footprint, and enhanced system performance by integrating various functional elements directly onto a common substrate.

[0034] In the context of the present technology, “waveguide” refers to an optical transmission structure that confines and directs light within a photonic chip. The waveguide may be fabricated from materials such as silicon nitride and is configured to guide optical signals between components such as the laser gain medium, resonator ring, and photodetectors.

[0035] In the context of the present technology, “resonator ring” refers to a closed-loop optical path that enables light to circulate multiple times, facilitating phase accumulation for rotation sensing. The resonator ring interacts with the waveguide through evanescent coupling, allowing counter-propagating optical signals to experience a phase shift proportional to angular velocity.

[0036] In the context of the present technology, “phase modulator” refers to a component that introduces controlled phase shifts in the propagating optical signal to enhance gyroscope performance. The phase modulator may use electro-optic, stress-optic, or carrier-injection mechanisms to modify the optical phase dynamically.

[0037] In the context of the present technology, “photodetector” refers to a device configured to receive optical signals and convert them into electrical signals for further processing. The photodetector may be implemented using silicon or germanium-based semiconductor materials and is used to measure phase differences between optical signals in the gyroscope.

[0038] In the context of the present technology, “Sagnac effect” refers to the physical phenomenon where counter-propagating light waves in a rotating reference frame experience a phase shift proportional to the angular velocity. This effect is utilized in the photonic gyroscope to measure rotation by detecting phase differences in the circulating optical signals.304941099.4 40745 / 61

[0039] In the context of the present technology, “laser gain medium” refers to an optical amplification component that provides coherent light for the gyroscope. The gain medium may be based on III-V semiconductor materials such as indium phosphide or gallium arsenide and may be heterogeneously integrated onto the photonic chip.

[0040] In the context of the present technology, “tunable laser filter” refers to an optical filtering component that selectively transmits specific wavelengths while suppressing unwanted spectral components. The filter may be implemented using ring resonators, Fabry -Perot resonators, or Mach-Zehnder interferometers.

[0041] In the context of the present technology, “circulator” refers to an optical component configured to control the directional flow of light within the photonic gyroscope. The circulator directs optical signals between the waveguide and photodetectors while minimizing unwanted back reflections.

[0042] In the context of the present technology, “control unit” refers to an electronic processing system that receives gyroscope data and integrates it with other sensor inputs for navigation or motion control. The control unit may include processors, field-programmable gate arrays (FPGAs), and digital signal processing (DSP) units for real-time computation.

[0043] In the context of the present technology, “inertial measurement unit (IMU)” refers to a sensor system that measures angular velocity and linear acceleration to track motion and orientation. The IMU may include the photonic gyroscope along with accelerometers and additional sensors for enhanced navigation capabilities.

[0044] In the context of the present technology, "die-to-wafer bonding" refers to a heterogeneous integration technique where individual photonic or electronic dies are transferred and bonded onto a larger wafer. This method enables alignment and integration of components such as III-V semiconductor lasers, photodetectors, and phase modulators onto a silicon photonic platform.

[0045] In the context of the present technology, "butt coupling" refers to an optical interconnect technique where the facets of two optical components, such as waveguides or fiber ends, are placed in direct physical contact to enable light transmission.304941099.4 40745 / 61

[0046] In the context of the present technology, "evanescent coupling" refers to an optical transfer mechanism where light energy is exchanged between two closely spaced waveguides or optical structures via their evanescent fields. This coupling technique is used to transfer optical signals between the waveguide and the resonator ring in the integrated photonic gyroscope.

[0047] In the context of the present technology, "micro-transfer printing" refers to a fabrication technique where small photonic or electronic components are selectively picked up from a donor substrate and precisely placed onto a target wafer. This technique allows heterogeneous integration of different material platforms without requiring full-wafer bonding.

[0048] In the context of the present technology, "lock-in detection" refers to a signal processing technique used to extract weak signals buried in noise by using a reference modulation frequency. In the photonic gyroscope, lock-in detection is employed to enhance the accuracy of phase measurements by isolating the phase shift induced by the Sagnac effect.

[0049] In the context of the present technology, "transimpedance amplifier (TIA)" refers to an electronic circuit that converts an input current signal into a voltage signal, typically used in photodetector signal conditioning. The TIA in the gyroscope system amplifies the weak photocurrent from the photodetectors before further processing.

[0050] In the context of the present technology, "lead zirconium titanate (PZT)" refers to a piezoelectric material used in stress-optic phase modulators. PZT-based modulators introduce a phase shift in the propagating optical signal by inducing mechanical stress on the waveguide through an applied voltage.

[0051] In the context of the present technology, "Mach-Zehnder interferometer (MZI)" refers to an optical device that splits and recombines light to produce interference effects, enabling phase modulation and filtering.

[0052] In the context of the present technology, "Fabry -Perot resonator" refers to an optical resonator consisting of two parallel reflective surfaces that create interference-based wavelength selection.304941099.4 40745 / 61

[0053] In the context of the present technology, "thin-film lithium niobate (TFLN)" refers to a material used for high-speed electro-optic modulation due to its strong nonlinear optical properties. TFLN-based phase modulators may be integrated into the gyroscope to enable precise phase control of optical signals.

[0054] In the context of the present technology, "chemical-mechanical planarization (CMP)" refers to a semiconductor fabrication process used to smooth and planarize wafer surfaces. In the photonic gyroscope, CMP may be employed to achieve uniform deposition of dielectric layers such as silicon dioxide.

[0055] In the context of the present specification, the words “first”, “second”, “third”, etc. have been used as adjectives only for the purpose of allowing for distinction between the nouns that they modify from one another, and not for the purpose of describing any particular relationship between those nouns. Thus, for example, it should be understood that, the use of the terms “first server” and “third server” is not intended to imply any particular order, type, chronology, hierarchy or ranking (for example) of / between the server, nor is their use (by itself) intended imply that any “second server” must necessarily exist in any given situation. Further, as is discussed herein in other contexts, reference to a “first” element and a “second” element does not preclude the two elements from being the same actual real-world element. Thus, for example, in some instances, a “first” server and a “second” server may be the same software and / or hardware, in other cases they may be different software and / or hardware.

[0056] Implementations of the present technology each have at least one of the above-mentioned object and / or aspects, but do not necessarily have all of them. It should be understood that some aspects of the present technology that have resulted from attempting to attain the above-mentioned object may not satisfy this object and / or may satisfy other objects not specifically recited herein.

[0057] The examples and conditional language recited herein are principally intended to aid the reader in understanding the principles of the present technology and not to limit its scope to such specifically recited examples and conditions. It will be appreciated that those skilled in the art may devise various arrangements which, although not explicitly described or shown herein,304941099.4 40745 / 61nonetheless embody the principles of the present technology and are included within its spirit and scope.

[0058] Furthermore, as an aid to understanding, the following description may describe relatively simplified implementations of the present technology. As persons skilled in the art would understand, various implementations of the present technology may be of a greater complexity.

[0059] In some cases, what are believed to be helpful examples of modifications to the present technology may also be set forth. This is done merely as an aid to understanding, and, again, not to define the scope or set forth the bounds of the present technology. These modifications are not an exhaustive list, and a person skilled in the art may make other modifications while nonetheless remaining within the scope of the present technology. Further, where no examples of modifications have been set forth, it should not be interpreted that no modifications are possible and / or that what is described is the sole manner of implementing that element of the present technology.

[0060] Moreover, all statements herein reciting principles, aspects, and implementations of the present technology, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof, whether they are currently known or developed in the future.

[0061] It should be understood that chemical deposition, as described herein, of various layers on the substrate and other layers provides immovable attachment of the layers to the substrate and the other layers, respectively.

[0062] Additional and / or alternative features, aspects and advantages of implementations of the present disclosure will become apparent from the following description, the accompanying drawings and the appended claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Further features and advantages of the present disclosure will become apparent from the following detailed description, taken in combination with the appended drawings, in which:304941099.4 40745 / 61

[0064] Figure 1 is a top plan, schematic view of an integrated photonic gyroscope on a silicon chip in accordance with at least some non-limiting embodiments of the present technology;

[0065] Figure 2 is a perspective view of the integrated gyroscope of Figure 1 ;

[0066] Figure 3 is the perspective view of Figure 2, with internal components illustrated in broken lines;

[0067] Figure 4 is a cross-sectional view of the integrated gyroscope of Figure 1, taken along line A- A of Figure 1;

[0068] Figure 5 is a block diagram of a signal processing pipeline for processing data generated by the integrated photonic gyroscope of Figure 1, in accordance with at least some non-limiting embodiments of the present technology; and

[0069] Figure 6 is a schematic representation of an autonomous vehicle integrating the photonic gyroscope of Figure 1, in accordance with at least some non-limiting embodiments of the present technology.

[0070] It is noted that the Figures may not be drawn to scale. It is to be understood that throughout the appended drawings and corresponding descriptions, like features are identified by like reference characters. Furthermore, it is also to be understood that the drawings and ensuing descriptions are intended for illustrative purposes only and that such disclosures do not provide a limitation on the scope of the claims.DETAILED DESCRIPTION

[0071] The instant disclosure is directed to systems and methods to address the deficiencies of the current state of the art. To this end, the instant disclosure describes an integrated photonic gyroscope, formed on a silicon chip substrate.

[0072] Objects of the current technology include creating a cost effective, compact, and low loss photonic gyroscope chip with a fully integrated silicon nitrate (SiN) optical which can be fabricated on a silicon chip.304941099.4 40745 / 61

[0073] With reference to Figures 1 and 2, a silicon chip-based integrated photonic gyroscope 100 according to a non-limiting embodiment of the present technology. The gyroscope 100 includes a waveguide 101, a resonator ring 102, a laser gain medium 103, photodetectors 104 and 105, phase modulators 106 and 107, a tunable laser filter 108, and circulators 180 and 185, all of which are integrated onto a common substrate 110. The waveguide 101 optically connects the laser gain medium 103 to the resonator ring 102, with the signal ultimately received by the photodetectors 104 and 105. The gyroscope structure is encapsulated within two silicon dioxide layers 120, which provide structural stability and optical confinement.

[0074] By the present technology, the resonator ring 102 surrounds remaining components of the gyroscope arrangement. By forming a compact light path and a large resonating area, an overall reduced footprint of the device 100 can be formed.

[0075] Figure 3 depicts internal components in broken lines, revealing the heterogenous integration of the components within two silicon dioxide layers 120.

[0076] In the context of the present technology, heterogeneous integration refers to the process of integrating multiple photonic and electronic components from different material platforms, for example, silicon (Si), silicon nitride (SislSk), indium phosphide (InP), gallium arsenide (GaAs), lithium niobate (LiNbCh), and germanium (Ge) etc., onto a single microchip. Unlike traditional discrete microchip assembly methods that rely on chip-to-chip interconnects using optical fiber arrays or butt coupling, heterogeneous integration eliminates excess optical coupling losses and reduces power consumption.

[0077] For the integrated photonic gyroscope 100, heterogeneous integration enables the direct bonding of active and passive photonic components onto a single Si3N4-based Sagnac rotation sensor microchip. For example, the resonator ring 102 and waveguide 101 may be fabricated directly on a silicon substrate 110, while additional functional elements such as thin-film lithium niobate (TFLN)-based phase modulators 106 and 107, III-V semiconductor-based laser gain medium 103, and photodetectors 104 and 105 may be integrated using die-to-wafer bonding or micro-transfer printing. It is contemplated that in some embodiments, this wafer-level integration approach may allow for compact device footprints and improved optical alignment,304941099.4 40745 / 61which is further demonstrated in Figures 3 and 4 through the embedded structure of the components of the gyroscope 100.

[0078] The laser gain medium 103 is an active optical component responsible for generating and amplifying the coherent light used in the gyroscope. It can be implemented using a III-V semiconductor material, such as indium phosphide (InP) or gallium arsenide (GaAs). The gain medium 103 is housed within a laser recess 113 (as depicted in Figure 4) in the silicon substrate 110. Depending on the specific embodiment, the gain medium 103 may function as a semiconductor optical amplifier (SO A), where it amplifies externally injected light, or as an integrated laser source that generates light internally. In some embodiments, the gain medium may be configured as a distributed feedback (DFB) laser or a Fabry-Perot laser.

[0079] In operation, the laser gain medium 103 is optically or electrically pumped to produce stimulated emission, generating a coherent optical signal that propagates into the tunable laser filter 108. The emitted light undergoes spectral shaping through the tunable laser filter 108, ensuring that only the desired wavelength range is transmitted.

[0080] The tunable laser filter 108, fabricated from silicon nitride 190, selectively transmits specific wavelengths of the optical signal while suppressing unwanted spectral components. The specific wavelengths allowed by the filter 108 depend on specific embodiments. For example, for an embodiment designed for navigation-grade gyroscopes, wavelengths 1550 nm or 1310 nm may be allowed, whereas for an embodiment designed for defense and aerospace applications, wavelengths 1064 nm or 1550 nm may be allowed. In other embodiments, for quantum sensing or precision metrology applications, the filter 108 may be designed to allow 780 nm or 850 nm wavelengths.

[0081] Different configurations of the tunable laser filter 108 include thermally tunable ring filters, MEMS-based Fabry -Perot etalons, or Mach-Zehnder interferometric filters, optimizing spectral filtering accuracy and stability.

[0082] The optical signal filtered by the tunable laser filter 108 propagates through the waveguide 101. The waveguide 101 is a low-loss optical transmission structure fabricated from silicon nitride 190. It provides the primary optical path for guiding light between different304941099.4 40745 / 61components, including the laser gain medium 103, resonator ring 102, and photodetectors 104 and 105. The waveguide 101 is embedded within silicon dioxide layers 120. In different embodiments, the waveguide 101 may include rib, ridge, or strip geometries, with variations influencing light confinement, propagation losses, and mode dispersion.

[0083] The optical signal propagating through the waveguide 101 is partially coupled into the resonator ring 102 via evanescent coupling. Before entering the resonator ring 102, the optical signal is split into two counter-propagating optical signals. This splitting typically occurs at a directional coupler (not depicted) or Y-junction (not depicted) in the waveguide 101, where a portion of the light is coupled into the ring in one direction, while another portion is coupled into the ring in the opposite direction.

[0084] The splitting occurs due to the bidirectional nature of evanescent coupling, which allows light to enter the ring resonator in both directions. As a result, two counter-propagating optical signals are established within the resonator ring 102, traveling along the closed-loop path in opposite directions. These signals then experience different effective path lengths in the presence of rotation, leading to the Sagnac-induced phase shift used for gyroscopic sensing.

[0085] The phase-shifted optical signal is subsequently coupled back into the waveguide 101 via evanescent coupling or a directional coupler. The waveguide then routes the optical signal through circulators 180 and 185 fabricated from silicon nitride 190.

[0086] The circulators 180 and 185 guide the phase-modulated optical signal to the photodetectors 104 and 105, and prevent unwanted back-reflections that could degrade measurement accuracy. Depending on the embodiment, the couplers 180, 185 may be implemented using Y-junction splitters, tapered waveguide transitions, or Mach-Zehnder interferometric structures.

[0087] The photodetectors 104 and 105 are placed in dedicated photodetector recesses 123 (depicted in Figure 4) within the silicon substrate 110, as shown in Figure 4. Once the phase-modulated light signal reaches the photodetectors 104 and 105, the signals undergo balanced detection, where the intensity variations due to phase modulation are extracted. The detected signals may be further processed using lock-in detection techniques to extract small phase304941099.4 40745 / 61variations. The processed signals provide angular velocity measurements, which can be integrated over time to determine orientation.

[0088] The resonator ring 102 is a closed-loop optical path fabricated from silicon nitride 190, enabling high-precision rotational sensing based on the Sagnac effect. It is optically coupled to the waveguide 101, forming a closed feedback loop where light undergoes multiple circulations.

[0089] Different embodiments of the resonator ring may include single-layer rings, vertically coupled dual-ring structures, or photonic crystal-based ring resonators, with variations affecting resonance quality factor (Q-factor), sensitivity, and noise performance.

[0090] The phase modulators 106 and 107 introduce controlled phase shifts in the propagating optical signal to enhance gyroscope sensitivity. These modulators alter the phase of the optical signal before it couples with the resonator ring 102, allowing precise control over light interference and resonance conditions. The modulation process is used to encode rotation-induced phase shifts, enabling high-accuracy signal extraction.

[0091] Different embodiments may include thin-film lithium niobate (TFLN) electro-optic phase modulators, lead zirconium titanate (PZT)-based stress-optic phase modulators, and carrier-injection-based silicon phase modulators, with variations influencing modulation speed, power efficiency, and noise performance.

[0092] To illustrate the operation of the integrated photonic gyroscope in a real -world setting, an example scenario can be considered where the gyroscope is embedded in an inertial measurement unit (IMU) of an autonomous vehicle 6000, as shown in Figure 6. The gyroscope is used to detect rotational motion and assist in navigation by providing real-time angular velocity data. The vehicle is equipped with multiple sensing elements, including a camera 610, a GNSS (Global Navigation Satellite System) receiver 620, and a control unit 630, which processes data from these sensors. The integrated photonic gyroscope 650 is placed within the vehicle's IMU and functions as a component for determining precise orientation and motion.

[0093] The Sagnac effect enables the integrated photonic gyroscope to measure rotational motion. When a coherent light beam is split into two counter-propagating waves within the resonator ring 102, the phase difference between these waves is affected by the angular velocity304941099.4 40745 / 61of the gyroscope. This phase shift arises because the effective optical path length for each beam changes due to rotation. If the gyroscope is rotating with an angular velocity Q, the counterpropagating waves accumulate a relative phase shift Acp, which is given by the equation:where R is the radius of the resonator ring, X is the wavelength of the light, and c is the speed of light in vacuum.

[0094] In the context of an autonomous vehicle 600 (schematically illustrated in Figure 6), as the vehicle turns, the gyroscope 650 experiences rotation, introducing a phase shift Acp between the counter-propagating waves in the resonator 102. The phase-modulated optical signal thus generated exits the resonator 102 and is directed toward the photodetectors 104 and 105 through circulators 180 and 185. The photodetectors 104 and 105 convert the received optical signals into electrical signals.

[0095] As illustrated in the signal processing pipeline 500 (Figure 5), the electrical signal from the photodetectors 104 and 105 signal is fed to a transimpedance amplifier (TIA), which boost the signal strength. Following amplification, the signal is digitized using an analog-to-digital converter (ADC) 530. The digitized signal is then sent to a field-programmable gate array (FPGA) 540, which performs further processing. The FPGA 540 serves multiple roles, including: generating the sinusoidal frequencies that drive the phase modulators (PMs), filtering unwanted noise using internal band-pass filters (BPFs), applying lock-in amplification (LIA) to extract the phase shift information, providing the final digital output of the gyroscope’s measured angular velocity Q.

[0096] The data from the FPGA 540, including the angular velocity Q is transmitted as an analog and digital output module 540, which is integrated into the vehicle’s control unit 630. The control unit fuses the gyroscope data with inputs from other sensors, such as the GNSS 620 and camera 610, to provide real-time position and orientation data for autonomous navigation.304941099.4 40745 / 61

[0097] The control unit 630 can be implemented using a combination of embedded processors, digital signal processing (DSP) units, and field-programmable gate arrays (FPGAs) to process real-time sensor data.

[0098] The subsequent description of the fabrication process is provided as an example of how the integrated photonic gyroscope can be practically implemented. It is understood that various modifications, adaptations, and alternative fabrication techniques may be employed without departing from the scope of the present technology. The specific methods, materials, and process parameters described herein are not intended to be limiting, but rather illustrative of one possible approach. Other fabrication techniques, such as different deposition methods, alternative material choices, or variations in integration strategies, may be used depending on manufacturing constraints, performance requirements, and application-specific considerations.

[0099] The fabrication of the integrated photonic gyroscope can be carried out using different approaches depending on process constraints, available materials, and performance requirements. One approach involves a wafer-scale processing method, incorporating thin-film deposition, photolithography, etching, and heterogeneous integration techniques. Another approach may rely on sequential die-to-wafer bonding for assembling individual photonic components. In some cases, a combination of these techniques may be used to optimize optical coupling, minimize fabrication defects, and improve overall yield.[000100] One example of a fabrication approach involves forming the waveguide 101 and resonator ring 102 on a silicon substrate 110, which is coated with a silicon dioxide layer 120. A layer of silicon nitride 190 can be deposited using plasma-enhanced chemical vapor deposition (PECVD), followed by photolithography and reactive ion etching (RIE) to define the waveguide and resonator structures. In some embodiments, an alternative deposition method, such as low-pressure chemical vapor deposition (LPCVD), may be used instead of PECVD to achieve more uniform film thickness. Some implementations may also include thermal annealing or hydrogen passivation to reduce optical losses at the waveguide sidewalls.[000101] Another approach may involve the integration of the phase modulators 106 and 107, which can be fabricated using different techniques depending on the modulation mechanism. In some embodiments, thin-film lithium niobate (TFLN) phase modulators may be transferred onto304941099.4 40745 / 61the silicon dioxide layer 120 using micro-transfer printing, allowing precise placement. In other embodiments, lead zirconium titanate (PZT) stress-optic phase modulators may be deposited and patterned using sol -gel or sputtering techniques, enabling stress-induced phase modulation. A third approach may involve carrier-injection-based silicon phase modulators, where doped regions are formed in the silicon substrate to modulate the refractive index through electrical injection. Each of these techniques may be selected based on trade-offs between power consumption, speed, and fabrication complexity.[000102] The laser gain medium 103 may also be integrated using different approaches. One approach involves die-to-wafer bonding of a III-V semiconductor laser, such as indium phosphide (InP) or gallium arsenide (GaAs), onto the silicon substrate 110. In another approach, a hybrid silicon laser may be formed by edge-coupling an InP gain section to a silicon waveguide. In some cases, direct epitaxial growth of III-V material on silicon may be used to form the laser gain medium, though this method may introduce additional material strain that requires further processing adjustments.[000103] The photodetectors 104 and 105 can be implemented using different materials and integration techniques. One approach involves germanium-on-silicon photodiodes, which may be integrated using epitaxial growth or wafer bonding. Another approach involves heterogeneous integration of III-V semiconductor photodetectors, which may offer higher responsivity at specific wavelengths. The photodetectors are typically positioned within dedicated recesses in the silicon substrate 110, ensuring alignment with the waveguide 101 for efficient optical signal collection.[000104] The tunable laser filter 108, which may be formed from silicon nitride 190, can be fabricated using different approaches depending on the desired filtering mechanism. One implementation involves thermally tunable ring resonators, where local heating elements enable wavelength selection through thermo-optic tuning. Another approach may use a MEMS-based Fabry-Perot filter, where mechanical actuation is used to control the spectral transmission characteristics. A third alternative involves a Mach-Zehnder interferometer filter, which uses interference effects to achieve tunable spectral filtering.[000105] The circulators 180 and 185, which may be fabricated from silicon nitride 190, can also be implemented using different methods. One approach involves a non-reciprocal magneto-304941099.4 40745 / 61optic circulator, where an external magnetic field induces directional optical propagation. Another approach may involve a passive interferometric waveguide circulator, where phase shifts in the optical paths control the signal routing. In some embodiments, a microresonator-based optical isolator may be used to achieve similar functionality without requiring an external magnetic field.[000106] Once the photonic components are integrated, encapsulation and electrical interfacing may be carried out. In one approach, a second silicon dioxide layer 120 is deposited over the photonic components, embedding them within a protective dielectric structure. Electrical contacts for the phase modulators and photodetectors may then be patterned using metal deposition and lift-off techniques. In another approach, chemical-mechanical planarization (CMP) may be performed to smooth the surface and improve layer uniformity before metal deposition. The completed photonic gyroscope chip may then undergo annealing and surface passivation to stabilize the material properties and minimize optical scattering losses.304941099.4 40745 / 61

Claims

Claims:

1. An integrated photonic gyroscope silicon chip, comprising:a silicon chip substrate;at least one waveguide formed on the silicon chip substrate, the at least one waveguide being configured to optically connect with a laser source, the at least one waveguide being configured to optically connect with a pair of photodetectors;at least one phase modulator formed on the silicon chip substrate, the at least one phase modulator being arranged and configured to modulate light propagating through the at least one waveguide; anda resonator ring formed on the silicon chip substrate, the resonator ring being in optical communication with the at least one waveguide,the at least one waveguide and the at least one phase modulator being disposed within a circumference of the resonator ring.

2. The chip of claim 1, further comprising a first silicon dioxide layer and a second silicon dioxide layer formed on the silicon chip substrate; andwherein the at least one waveguide and the resonator ring are formed at least partially between the first and second silicon dioxide layers.

3. The chip of claim 2, wherein the at least one waveguide and the resonator ring are formed from silicon nitride.

4. The chip of any one of claims 1 to 3, further comprising a laser filter formed on the silicon chip substrate, the laser filter being configured to filter light from the laser source.

5. The chip of claim 4, wherein the laser filter is formed from silicon nitride.

6. The chip of any one of claims 1 to 5, wherein the at least one phase modulator includes at least one stress optic phase modulator connected to the substrate, the at least one waveguide being disposed between the silicon chip substrate and the at least one stress optic phase modulator.304941099.4 40745 / 617. The chip of claim 6, wherein the at least one stress optic phase modulator is formed from at least one lead zirconium titanate (PZT) electrode.

8. The chip of claim 7, wherein the at least one PZT electrode includes a pair of PZT electrodes.

9. The chip of any one of claims 1 to 8, wherein the resonator ring is spaced from the at least one waveguide.

10. The chip of any one of claims 1 to 9, further comprising a pair of circulators formed on the silicon chip substrate, each one of the pair of circulators being configured to optically connect the at least one waveguide to a corresponding one of the pair of photodetectors.

11. The chip of claim 10, wherein each one of the pair of circulators is formed from silicon nitride.

12. A silicon chip integrated photonic gyroscope, comprising:a silicon substrate;a first silicon dioxide layer and a second silicon dioxide layer formed on the silicon substrate; a laser gain medium connected to the substrate, the laser gain medium being disposed in a laser recess formed in at least the silicon substrate, the laser gain medium forming at least part of a laser source;a waveguide loop connected to the substrate, the waveguide loop being disposed between the first and second silicon dioxide layers, the waveguide loop being in optical communication with the laser source via the laser gain medium;at least one phase modulator formed on the second silicon dioxide layer, the at least one phase modulator being arranged and configured to modulate light propagating through the waveguide loop;a resonator ring formed on the silicon chip substrate, the resonator ring being in optical communication with the waveguide loop; anda pair of photodetectors connected to the substrate, each photodetector of the pair of photodetectors being disposed in one of a pair of photodetector recesses formed in at least the304941099.4 40745 / 61silicon substrate, the pair of photodetectors being in optical communication with the waveguide loop,the waveguide loop, the at least one phase modulator, the pair of photodetectors, and the laser gain medium being disposed within a circumference of the resonator ring.

13. The gyroscope of claim 12, wherein the waveguide loop and the resonator ring are formed from silicon nitride.

14. The gyroscope of claim 12 or 13, further comprising a laser filter disposed between the first and second silicon dioxide layers, the laser filter being formed from silicon nitride, the laser filter being arranged to filter light from the laser source and optically communicate filtered light to the waveguide loop.

15. The gyroscope of any one of claims 12 to 14, wherein the at least one phase modulator is formed at least in part from lead zirconium titanate (PZT) disposed on the second silicon dioxide layer.

16. A method for fabricating an integrated photonic gyroscope silicon chip, the method comprising:forming a first silicon oxide layer on a silicon wafer substrate;forming at least a waveguide loop and a resonator ring of silicon nitride on the first silicon oxide layer;forming a second silicon oxide layer over the waveguide loop and the resonator ring; forming a laser recess and a pair of photodetector recesses in at least the second silicon oxide layer; andforming at least one phase modulator on the second silicon oxide layer.

17. The method of claim 16, further comprising:forming a laser filter from silicon nitride; andforming a pair of circulators from silicon nitride.304941099.4 40745 / 6118. The method of claim 16, wherein:the first and second silicon oxide layers and components of silicon nitride are fabricated in a lead-free facility; andthe at least one phase modulator is fabricated in a second facility, the second facility having lead-compatible fabrication capabilities.

19. A method for fabricating a silicon chip integrated photonic gyroscope, the method comprising:fabricating the integrated photonic gyroscope silicon chip of claim 16;connecting a laser gain medium to the chip, the laser gain medium being inserted into the laser recess; andconnecting a pair of photodetectors to the chip, each one of the pair of photodetectors being inserted into a corresponding one of the pair of photodetector recesses.304941099.4 40745 / 61

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