Integrated photonic optical gyroscope based on ring waveguide with gain adjustment for improved performance

Abstract

An integrated photonic optical gyroscope made on a silicon nitride (SiN) waveguide platform includes a first straight waveguide to receive incident light and output emergent light to couple to a photodetector to provide an optical signal for rotational sensing. The gyroscope includes a first microresonator ring adjacent a first straight waveguide. Light is evanescently coupled from the first straight waveguide to the first microresonator ring and experiences propagation losses when circulating within the first microresonator ring as a guide beam. The guide beam is evanescently coupled from the first microresonator ring back to the first straight waveguide to provide an optical signal for rotational sensing after passing optical gain to the guide beam to counteract propagation loss. In a coupling ring configuration, a first microresonator ring acts as a loss ring, while optical gain is passed to a second microresonator ring that acts as a gain ring.

Description

[0001] This application is a divisional application of the invention patent application with application number 202080084699.8. Technical Field

[0002] The present disclosure relates to integrated photonics-based optical gyroscopes. Background Art

[0003] Gyroscopes (also referred to as "gyros") are devices that can sense angular velocity. Applications of gyroscopes include, but are not limited to, military, aircraft navigation, robotics, self-driving cars, virtual reality, augmented reality, gaming, etc. Gyroscopes can be mechanical or optical and can vary in accuracy, performance, cost, and size. Since optical gyroscopes do not have any moving parts, they have advantages over mechanical gyroscopes because they can withstand shock, vibration, and temperature changes better than mechanical gyroscopes with moving parts. The most common optical gyroscope is the fiber optical gyroscope (FOG), which works based on interferometry of optical phase shifts due to the Sagnac effect (a phenomenon caused by rotation encountered in interferometry). The construction of a FOG typically involves a coil including several turns of polarization-maintaining (PM) fiber. The laser is launched into both ends of the polarization-maintaining fiber coil so that the two beams propagate in opposite directions. If the fiber coil is moving, then the beams traveling in opposite directions experience different optical path lengths relative to each other. By setting up an interferometric measurement system, it is possible to measure the tiny path length difference, which is proportional to the loop area enclosed by the fiber coil turns and the angular velocity of the rotating fiber coil.

[0004] However, because the Sagnac effect is relatively weak, and to achieve high performance, FOGs are bulky, requiring hundreds to thousands of meters of fiber (in the form of a fiber coil with several turns). An alternative to FOGs is the resonant fiber optic gyroscope (RFOG), in which the resonant frequency shift caused by the rotation due to the Sagnac effect is more prominent than in FOGs. Therefore, the fiber length required in RFOGs is several orders of magnitude smaller than that of FOGs. Unlike the several turns of fiber coils in FOGs, a single fiber loop is used in RFOGs, in which light circulates. It should be noted that another resonant type gyroscope, called a ring laser gyro (RLG), is different from RFOGs and FOGs because RLGs do not have fibers, and the laser beam bounces in solid glass instead of in fibers.

[0005] Fiber-based gyroscopes can provide very high accuracy, but at the same time, they take up a larger area, are very expensive, and are difficult to assemble because the devices are built from discrete optical components that need to be precisely aligned. Often, this involves manual alignment, which is difficult to scale up for mass production.

[0006] The inventors propose to replace fibers with waveguide-based integrated photonic components for easy and low-cost integration on semiconductor platforms, which makes mass production of gyroscopes more promising. Summary of the invention

[0007] The following is a brief summary of the disclosure to provide a basic understanding of some aspects of the disclosure. This summary is not a comprehensive review of the disclosure. It is neither intended to identify the key or important elements of the disclosure, nor to describe any scope of a specific implementation of the disclosure or any scope of the claims. Its sole purpose is to present some concepts of the disclosure in a simplified form, as a preface to the more detailed description presented below.

[0008] An integrated photonic optical gyroscope made on a silicon nitride (SiN) waveguide platform includes a first straight waveguide for receiving incident light and outputting outgoing light to couple to a photodetector to provide an optical signal for rotation sensing. The gyroscope includes a first micro-resonator ring adjacent to the first straight waveguide. Light is evanescently coupled from the first straight waveguide to the first micro-resonator ring and experiences propagation loss while circulating within the first micro-resonator ring as a guided beam. The guided beam is evanescently coupled from the first micro-resonator ring back to the first straight waveguide to provide an optical signal for rotation sensing after transferring optical gain to the guided beam to offset the propagation loss.

[0009] In the coupled-ring configuration, the first microresonator ring acts as a loss ring, while the optical gain is transferred to the second microresonator ring, which acts as a gain ring.

[0010] In the coupled-ring configuration, the guided beam is evanescently coupled from the second microresonator ring back to the first microresonator ring and evanescently coupled from the first microresonator ring to the first straight waveguide to provide an optical signal for rotation sensing.

[0011] The first microresonator ring and the second microresonator ring can be made on the same physical layer or on different physical layers stacked vertically on top of each other. Light is evanescently coupled between the two physical layers separated vertically.

[0012] The gyroscope may have a second straight waveguide to receive incident pump light from one or more pump light sources, wherein the pump light provides optical gain to offset propagation losses. At least a portion of the second microresonator ring may be implanted with erbium dopants, which may be excited under pump light of a specific wavelength to provide optical gain. Pump light is coupled to the second microresonator ring from at least one side to excite the erbium dopants. Alternatively, pump light is coupled to the second microresonator ring from the top to excite the erbium dopants. The wavelength of the pump light may be 980 nm or 1440 nm-1480 nm, depending on the wavelength of the excitation of the erbium dopants. Pump light of a suitable wavelength may be coupled to the second microresonator ring to induce stimulated Raman scattering (SRS) and / or stimulated Brillouin scattering (SBS) to provide optical gain. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The present disclosure will be more fully understood through the detailed description given below and the accompanying drawings of various specific implementations of the present disclosure. Please note that the dimensions shown in the drawings are for schematic illustration only and are not drawn to scale.

[0014] Figure 1A A schematic top view of a waveguide-based resonant ring in an integrated photonic optical gyroscope sensor chip is shown.

[0015] Figure 1B Transmission electron micrograph of a silicon nitride waveguide used to construct a loss ring and a gain ring of a gyroscope according to the present disclosure. The gain ring may be doped with erbium or other optically enhanced gain materials therein.

[0016] Figure 2A A schematic top view of two waveguide-based resonant rings (one loss ring and one gain ring) coupled to each other in a coupled-ring integrated photonic optical gyroscope sensor chip according to an embodiment of the present disclosure is illustrated.

[0017] Figure 2B A schematic diagram of two waveguide-based resonant rings (one loss ring and one gain ring) coupled to each other in a coupled-ring integrated photonic optical gyroscope sensor chip according to another embodiment of the present disclosure is illustrated, wherein lasers having a signal wavelength and a pump wavelength are emitted from both ends of the sensor chip.

[0018] Figure 3 The concept centered on making an integrated photonic optical gyroscope based on a multilayer waveguide according to an embodiment of the present disclosure is illustrated, where the loss ring and the gain ring are in two different layers.

[0019] Figure 4Schematically illustrated is a top view of a pump laser integrated from the top to locally excite erbium dopants in a portion of a gain ring on the same layer as a loss ring according to an embodiment of the present disclosure.

[0020] Figure 5 Schematically illustrated Figure 4 Side view of the construction shown.

[0021] Figure 6 Schematically illustrates a side view of a pump laser integrated from the top to locally excite erbium dopants in a portion of a gain ring on a different layer than the loss ring according to an embodiment of the present disclosure.

[0022] Figure 7 The integration of a heater for varying the amount of evanescent coupling between a loss ring and a gain ring according to an embodiment of the present disclosure is schematically illustrated. DETAILED DESCRIPTION

[0023] Aspects of the present disclosure are directed to a compact ultra-low-loss silicon nitride waveguide-based angular rotation sensing chip that can be integrated with other system-level integrated photonic components for optical gyroscope applications.

[0024] Figure 1A 1 is a schematic top view of an embodiment 100, showing a waveguide-based sensing chip 110 having an input / output waveguide 115 and a waveguide-based resonant ring 130, which together replace the fiber coil of a FOG or the fiber loop of an RFOG. The combination of the input / output waveguide 115 and the waveguide-based resonant ring 130 is sometimes referred to as a micro-resonator due to its smaller size. An integrated photonic front-end chip (not shown) can be coupled with the waveguide-based sensing chip 110 to form an integrated photonic optical gyroscope module, which can be part of an inertial measurement unit (IMU) package. It should be noted that the IMU may have other components in addition to the optical gyroscope module, such as an accelerometer. Therefore, making the optical gyroscope module compact reduces the overall size, weight power and cost of the IMU. This weight reduction may be critical for certain applications, such as lightweight unmanned aerial vehicles. The IMU can be a much-needed technology component for use in conjunction with more mature autonomous vehicle sensing technologies such as LiDAR (Light Detection and Ranging), radar, and cameras that will be used in the next generation of autonomous vehicles (both land and air).

[0025] In a waveguide-based sensor chip 110 (sometimes also referred to as a "gyroscope chip"), the low-loss waveguide core may be made of silicon nitride (Si 3 N 4, referred to as SiN), and the waveguide coating can be made of fused silica or oxide. Figure 1B A longitudinal cross-sectional image of a waveguide chip obtained by a transmission electron microscope (TEM) is shown, which shows a silicon nitride core surrounded by oxide coatings from the top, bottom and both sides. This waveguide structure is also referred to as a SiN waveguide, and a chip containing a SiN waveguide is called a SiN waveguide chip. Note that the waveguide-based components on the front-end chip (which may have an on-chip light source, such as a laser, or may guide light coupled from an off-chip light source) may be based on Si or III-V compound semiconductors or a combination thereof, and may be mode selective, as described in previously filed co-owned provisional patent application 62 / 904,443, filed on September 23, 2019, and entitled “System Architecture for Silicon Photonics Optical Gyroscopes with Mode-Selective Waveguides,” which was converted into non-provisional application No. 16 / 659,424, filed on October 21, 2019, and entitled “System Architecture for Integrated Photonics Optical Gyroscopes,” both of which are incorporated herein by reference in their entirety.

[0026] Alternatively, the waveguide-based components of the front-end chip can also be made of SiN in a fully integrated implementation, as described in the previously filed co-owned provisional patent application No. 62 / 934,184 filed on November 12, 2019 and entitled “Multi-layer Silicon Nitride Waveguide Based Integrated Photonics Optical Gyroscopes.”

[0027] Re-reference Figure 1A , from a light source (such as a laser, not shown) with a signal wavelength λ sThe incident guided light 124 can be coupled to the input end 120 of the waveguide 115. A portion of the incident guided light 124 is evanescently coupled to the resonant ring 130 and circulates several times as the guided light 132 within the resonant ring 130 before being coupled back to the waveguide 115 and propagating toward the output end 122 of the waveguide 115. The emitted guided light 126 can be detected by a detector (e.g., a PID photodetector or an avalanche photodiode, not shown in the figure). The resonant ring 130 can have any geometric profile (e.g., circular, elliptical, racetrack shape, etc.). The exemplary embodiment shown in the figure shows a racetrack shape of the ring. Since in the racetrack shape, the spacing "w1" between the waveguide 115 and the resonant ring 130 can remain substantially constant for the coupling length T defined by the dashed rectangle 128, the evanescent resonant coupling can be optimized by appropriate design. It should be noted that the signal can be input from two directions, such as Figure 2B shown.

[0028] Figure 2A 200, two resonant waveguide rings (a loss ring 130a and a gain ring 130b) are coupled to each other in a coupled ring integrated photonic optical gyroscope sensor chip 210, rather than as shown in FIG. Figure 1A Only one waveguide ring is shown. Recently, it has been theoretically shown that when the loss ring and the gain ring operate under critical conditions (called the "exceptional point"), the Sagnac frequency shift of the coupled-ring integrated photonic optical gyroscope can reach 108 times that of its single-ring counterpart. Interested readers can refer to the academic journal article entitled "Loss-Gain Coupled Ring Resonator Gyroscope" written by Matthew J. Grant and Michael JFDigonnet and published in Proceedings of SPIE 10934, Optical, Opto-Atomic and Entanglement-Enhanced Precision Metrology (March 4, 2019). This article also shows simulation results, which demonstrate that the maximum rotational sensitivity of the coupled-ring gyroscope structure is not achieved at the exceptional point, but at the optimal value of the inter-ring coupling far away from the exceptional point. Therefore, controlling the loss and gain in the two waveguide rings is crucial to achieving optimal inter-ring coupling and then achieving the desired rotational sensitivity.

[0029] The inventors propose various embodiments of coupled ring gyroscopes based on loss rings and gain rings based on silicon nitride waveguides. Note that the loss rings 130a and 130b do not have to be the same size. Figure 41 and 12. An embodiment of the shapes of the different rings is shown. The shapes of the rings are designed to optimize the coupling between the two rings separated by a lateral distance "w2" in the dashed area 128b, as well as to optimize the coupling between the loss ring 130a and the waveguide 115 separated by a lateral distance "w1" in the dashed area 128a, and the coupling between the gain ring 130b and the waveguide 215 separated by a lateral distance "w3" in the dashed area 128c. The direction of the guided beam 132a in the loss ring 130a is opposite to the direction of the guided beam 132b in the gain ring 130b. In order to introduce optical gain into the guided beam 132b, a pump laser light 224 of a target wavelength can be launched into the input end 220 of the waveguide 215. The wavelength of the pump laser light 224 can be selected so that the wavelength of the amplified light coupled from the waveguide 215 to the gain ring 130b is equal to the signal wavelength λ of the laser emitted at the input end 120 of the waveguide 115. s . Signal wavelength λ s It can be 1550 nm or some other wavelength optimized by design for waveguide loss. The wavelength of the amplified light can be the Raman shifted or Brillouin shifted emission wavelength or its harmonics, depending on whether the pump laser is used to induce stimulated Raman scattering (SRS) or stimulated Brillouin scattering (SBS) as the gain mechanism. In certain embodiments of the erbium-doped gain ring 130b (similar to an erbium doped fiber amplifier (EDFA)), the pump laser wavelength does not need to match the signal wavelength λ s , but requires exciting the erbium dopant ions at, for example, -980 nm. (Note that the exact wavelength required to excite erbium depends on the type of erbium used.) Note that other typical wavelengths for pumping might be in the range of 1440 nm-1480 nm. This wavelength range might be more practical for pumping from the side (e.g. Figure 2A and Figure 2B as shown) rather than pumping from the top (as Figures 4 to 6 In another embodiment, the pump laser used to induce SRS or SBS and the 980 nm pump laser used to excite the erbium dopant ions can be used together to further enhance the signal and system performance. This concept is referred to below Figure 4 and Figure 5 Since the waveguide dimensions in the gain ring 130b may not be optimized to guide the 980 nm wavelength with low loss, in some embodiments, more than one pump laser may be coupled at the waveguide input end 220, i.e., one 980 nm pump laser and another one generating a wavelength equal to the signal wavelength λ sThe output end 222 of the waveguide 215 can be blocked, or the outgoing light 226 can be directed to a detector to measure how much optical power is coupled into the gain ring 130b.

[0030] Figure 2B Shown with Figure 2A Another similar embodiment, but in this embodiment, for the signal wavelength λ s and the pump wavelength λ p The laser light can be input from both sides of the chip 210. The wavelength is λ s The incident guided light can come from the same laser source or front-end chip, and the light is split into two beams (124 and 127) by a beam splitter. In addition, the incident guided light from the SBS or SRS having a wavelength λ optimized for SBS or SRS p The pump laser light can also be pumped from both sides of the ring as beams 224 and 227 to provide double gain in the system and ensure that both directions of the signal passing through the gain ring see the same amplification. Alternatively, beam 224 can have a wavelength that excites the erbium dopant ions (to be explained below) and beam 227 can have a wavelength suitable for causing SRS or SBS. Generally speaking, pumping from both sides of the ring (i.e., dual pumping) allows the laser signal to rotate through the ring in both directions, similar to a standard FOG (where light is emitted from two directions in a fiber coil). This is why a pump wavelength of 1440 nm-1480 nm is convenient to produce the desired results. The two circulating beams will then see the same temperature effects, the same path lengths, and other system differences. However, the resonance shift will be different depending on the direction the system is rotated. This can cancel out other effects and ensure that the signal being measured is from the Sagnac effect.

[0031] Please note that Figure 2A and Figure 2B The two rings (loss ring and gain ring) are shown fabricated on the same layer of the chip 210, and the evanescent coupling from ring to ring occurs laterally in the same transverse plane. However, in an alternative embodiment, when the loss ring and the gain ring are fabricated in two separate layers, the evanescent coupling from ring to ring may occur vertically in the longitudinal plane (e.g., Figure 6 ).

[0032] Figure 3An embodiment 300 is shown showing a first layer 310a having a loss ring 130a and a second layer 310b having a gain ring 130b. To illustrate that the two rings may be separated in the lateral direction (x-direction) by an amount "w2" (where "w2" may be zero), a projection of the loss ring 130a is shown on layer 310b as a dashed outline 330a. Evanescent vertical coupling of guided beams 132a and 132b occurs between the portion of the loss ring 130a within the dashed outline 328a on layer 310a and the portion of the gain ring 130b within the dashed outline 328b on layer 310b. Note that in some embodiments, the gain ring may be on the top layer and the loss ring on the bottom layer.

[0033] Figure 4 and Figure 5 An embodiment 400 is shown in which the waveguide core region of the gain ring 130b is implanted with erbium dopant ions, which can be excited by a suitable pump laser at a wavelength of 980 nm or 1440 nm. Specifically, Figure 4 A top view of a sensor chip 410 (similar to the sensor chip 210 in FIG. 2 ) is shown, and Figure 5 shows a chip 410 along Figure 4 A portion of the longitudinal section of the cutting line AA' is shown in FIG. Figure 4 2, but instead of using an additional waveguide 215 to emit pump laser light from the edge as in the case of the sensor chip 210, the pump laser 460 is coupled from the top of the sensor chip 410. The portion of the gain ring 130b directly below the pump laser 460 receives the laser light 524 ( Figure 4 Not shown, but in Figure 5 ), the laser light 524 excites erbium dopant ions 485 (stars represent excited erbium ions) around the SiN core 570 of the waveguide and amplifies the light beam 132b circulating in the gain ring 130b.

[0034] Figure 5 The depth of the implanted erbium dopant (largely confined within implant region 580, which is not a separate material layer, but represents the portion of the waveguide coating with erbium ions) is shown, which is determined by the depth at which the waveguide core 570 of the gain ring 132b resides from the top surface of the chip 410. A mirror 562 can be made on top of the pump laser 460 so that light 524 with a wavelength of 980nm is pumped into the chip 410 to excite the erbium dopant ions in the implant layer 580. Since most of the optical modes (shown by the dashed ellipse 565) are outside the SiN core 570, the excited erbium ions 585 within the spatially optical modes are able to optically amplify the guided beam 132b in the gain ring 130b.

[0035] In some embodiments, optical gain is introduced only in a portion of the gain ring 130b directly below the pump laser and away from the ring-to-ring coupling region 128b, such as Figure 4 In some other embodiments, the entire gain ring 130 b can be below the pump laser 460 .

[0036] In case of multi-layer configuration, the gain ring can be at the top and the loss ring can be at the bottom. Figure 6 In the illustrated embodiment 600, a longitudinal cross section of a sensor chip is shown, wherein a top layer 610b has a gain ring 130b (i.e., SiN waveguide cross sections 570a and 570b belong to the gain ring 130b), and a bottom layer 610a has a loss ring 130a (i.e., SiN waveguide cross sections 570c and 570d belong to the loss ring 130a). It should be noted that the waveguide cross sections 570b and 570c can be aligned relative to each other to obtain the best vertical coupling between the gain ring and the loss ring. For example, "w2" can be zero or even negative. The coupling efficiency also depends on the vertical spacing "h".

[0037] Figure 7 An embodiment 700 is shown in which a heater 780 is fabricated to cover the coupling region 128b on the top surface of the sensor chip 410 (a longitudinal cross section of which is shown in the figure). This particular embodiment shows a similar Figure 4 A single layer construction where the gain ring (waveguides 570a and 570b) and the loss ring (waveguides 570c and 570d) are all in the same layer. The gain ring can be pumped from the top or the side for optical amplification at the signal wavelength. By controlling the power of the heater 780, the amount of coupling between the gain ring and the loss ring can be controlled. In addition, the same concept of metal heaters can be deployed on other rings above regions W1 and W3 to adjust the amount of coupling in and out of the ring.

[0038] Note that although the pump laser is shown in the figures as being die attached or bonded on top of the layer with the gain ring, in some embodiments the pump laser can be formed or monolithically integrated into the rest of the sensing chip as a top third layer or edge coupled.

[0039] In the above description, implementations of the present disclosure have been described with reference to specific exemplary embodiments thereof. It will be apparent that various modifications may be made thereto without departing from the broader spirit and scope of implementations of the present disclosure as set forth in the claims below. Therefore, the present specification and drawings should be understood in an illustrative rather than a restrictive sense. Furthermore, directional terms, such as "top", "bottom", etc., do not limit the scope of the present disclosure to any fixed orientation, but rather encompass various permutations and combinations of orientations.

Claims

1. An integrated photonic optical gyroscope fabricated on a silicon nitride (SiN) waveguide platform, include: a first straight waveguide that receives incident light from one or more light sources and outputs outgoing light to be coupled to a photodetector to provide an optical signal for rotation sensing; a first microresonator ring adjacent to a portion of the first straight waveguide, wherein light is evanescently coupled from the portion of the first straight waveguide to the first microresonator ring, and the evanescently coupled light experiences propagation losses while circulating within the first microresonator ring as a guided beam, wherein after delivering optical gain to the guided beam to offset the propagation loss, the guided beam is evanescently coupled from the first microresonator ring back to the portion of the first straight waveguide to provide the optical signal for rotation sensing; a second microresonator ring adjacent to a portion of the first microresonator ring, wherein the guided beam is evanescently coupled from the portion of the first microresonator ring to a portion of the second microresonator ring, and the evanescently coupled guided beam experiences optical gain to offset propagation losses within the first microresonator ring and the second microresonator ring; and A pump chip is physically attached on top of the layer containing the second microresonator ring, wherein the pump chip provides a first pump light that delivers at least a portion of the optical gain to the guided beam. 2 . The integrated photonic optical gyroscope according to claim 1 , wherein the one or more light sources are located at one end of the first straight waveguide or at both ends of the first straight waveguide.

3. The integrated photonic optical gyroscope of claim 1 , wherein the guided beam is evanescently coupled from the second microresonator ring back to the first microresonator ring and from the first microresonator ring back to the portion of the first straight waveguide to provide the optical signal for rotation sensing.

4. The integrated photonic optical gyroscope according to claim 3, further comprising: include: A second straight waveguide receives a second pump light from one or more pump light sources, wherein a portion of the second straight waveguide is adjacent to the second microresonator ring, wherein the second pump light provides at least a portion of the optical gain to offset the propagation loss.

5. The integrated photonic optical gyroscope of claim 1, wherein the first micro-resonator ring and the second micro-resonator ring are of the same shape and size.

6. The integrated photonic optical gyroscope of claim 1, wherein the first microresonator ring has a shape, a size, or both that is different from the shape, the size, or both that of the second microresonator ring.

7. The integrated photonic optical gyroscope of claim 1 , wherein the first micro-resonator ring and the second micro-resonator ring are fabricated on two different physical layers stacked vertically on each other, and wherein light is evanescently coupled between the two different physical layers stacked vertically on each other.

8. The integrated photonic optical gyroscope of claim 7, wherein the first microresonator ring and the second microresonator ring are laterally offset relative to each other. 9 . The optical gyroscope according to claim 1 , wherein at least a portion of the second micro-resonator ring is implanted with erbium dopants, and the erbium dopants can be excited at a specific wavelength of the first pump light to provide the optical gain.

10. The optical gyroscope according to claim 9, wherein a second pump light is coupled to the second micro-resonator ring from a second straight waveguide, and the second pump light is emitted to the second straight waveguide from one end or from both ends.

11. The optical gyroscope of claim 9, wherein the pump chip is disposed on top of the portion of the second microresonator ring where the erbium dopant is implanted.

12. The optical gyroscope of claim 11, wherein a mirror is fabricated on top of the pump chip to enhance vertical injection of the first pump light toward the erbium dopant.

13. The optical gyroscope of claim 11, wherein the layer containing the second microresonator ring is a top vertical layer to which the pump chip is attached, and the first microresonator ring is contained in a bottom vertical layer below the top vertical layer.

14. The optical gyroscope of claim 13, wherein a heater is fabricated on top of the top vertical layer to adjust the amount of evanescent coupling between the second microresonator ring and the first microresonator ring.

15. The optical gyroscope of claim 1, wherein the first and second microresonator rings are fabricated on a common physical layer, and wherein a heater is fabricated on top of the common physical layer to adjust the amount of evanescent coupling between the second microresonator ring and the first microresonator ring.

16. The optical gyroscope of claim 1, wherein another pump light of a suitable wavelength is coupled to the second microresonator ring to induce stimulated Raman scattering (SRS) to provide the optical gain.

17. The optical gyroscope of claim 1, wherein another pump light of a suitable wavelength is coupled to the second microresonator ring to induce stimulated Brillouin scattering (SBS) to provide the optical gain.

18. The optical gyroscope of claim 1, wherein additional pump light is coupled to the second microresonator ring from at least one side.

19. The optical gyroscope according to claim 1, in, At least a portion of the first microresonator ring is implanted with erbium dopants, and the erbium dopants can be excited at a specific wavelength of the first pump light to provide at least a portion of the optical gain.

20. A coupled-ring integrated photonic optical gyroscope fabricated on a silicon nitride (SiN) waveguide platform, include: a first straight waveguide that receives incident light from one or more light sources and outputs outgoing light to be coupled to a photodetector to provide an optical signal for rotation sensing; a first microresonator ring adjacent a portion of the first straight waveguide, wherein light is evanescently coupled from the portion of the first straight waveguide to the first microresonator ring, and the evanescently coupled light experiences propagation losses while circulating within the first microresonator ring as a guided beam; a second microresonator ring adjacent to a portion of the first microresonator ring, wherein the guided beam is evanescently coupled from the portion of the first microresonator ring to a portion of the second microresonator ring, and the evanescently coupled light experiences optical gain to offset propagation losses within the first microresonator ring and the second microresonator ring; and A second straight waveguide, the second straight waveguide receiving the first pump light at a first end of the second straight waveguide and receiving the second pump light at a second end of the second straight waveguide, wherein a portion of the second straight waveguide is adjacent to the second microresonator ring, and wherein the first pump light and the second pump light provide the optical gain to offset the propagation loss.

21. The coupled-ring integrated photonic optical gyroscope of claim 20, wherein the guided beam is evanescently coupled from the second microresonator ring back to the first microresonator ring and evanescently coupled from the first microresonator ring to the portion of the first straight waveguide to provide the optical signal for rotation sensing.

22. The coupled-ring optical gyroscope of claim 21, wherein at least a portion of the second microresonator ring is implanted with dopants, and the dopants can be excited at a specific wavelength of the first pump light or the second pump light to provide at least a portion of the optical gain.

23. The coupled-ring optical gyroscope of claim 22, wherein a pump chip is physically attached on top of a layer containing the second microresonator ring to excite the dopants from the top to deliver at least a portion of the optical gain.

24. The coupled-ring optical gyroscope according to claim 22, wherein the dopant is an erbium dopant, and a wavelength of the first pump light or the second pump light depends on an excitation wavelength of the erbium dopant.

25. The coupled-ring integrated photonic optical gyroscope of claim 20, wherein the first microresonator ring and the second microresonator ring are fabricated on two different physical layers stacked vertically on each other, and wherein light is evanescently coupled between the two different physical layers stacked vertically on each other.

26. The coupled-ring optical gyroscope of claim 20, wherein one of the first pump light and the second pump light coupled to the second microresonator ring has a suitable wavelength to induce stimulated Raman scattering (SRS) to provide at least a portion of the optical gain.

27. The coupled-ring optical gyroscope of claim 20, wherein one of the first pump light and the second pump light coupled to the second microresonator ring has a suitable wavelength to induce stimulated Brillouin scattering (SBS) to provide at least a portion of the optical gain.

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