Miniature Interferometric Integrated Photonic Gyroscope

Abstract

A small interferometric integrated photonic gyroscope structure having upper silicon oxide, intermediate silicon oxide, and bottom silicon oxide deposited on a silicon substrate includes a broadband light source or a semiconductor optical amplifier with a silicon nitride ring resonator wavelength filter, which is connected to a thin film lithium niobate or piezoelectrically actuated silicon nitride phase modulator vertically coupled to a silicon nitride waveguide spiral loop. The silicon nitride waveguide spiral loop is patterned on a thin bottom oxide layer having an air trench thereunder and is connected via photonic wire bonding to a germanium detector or is vertically integrated via a reflective mirror embedded in a silicon wafer. Describe various bonding methods of alternative materials and the possibility of connecting multiple spiral waveguides for sensitivity improvement in gyroscope applications.

Description

Technical Field

[0001] Cross - reference to Related Applications This application claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 351,894, filed on June 14, 2022, the entire disclosure of which is incorporated herein by reference.

[0002] This technology generally relates to a miniaturized interferometric integrated photonic gyroscope.

Background Art

[0003] As remotely - controlled and autonomous vehicles (such as drones) become more common, interest in gyroscopes as sensors for measuring angular velocity is increasing. One type of gyroscope in the field of measuring angular velocity is an integrated photonic gyroscope, in which the effect of rotation on an optical signal is monitored to detect the rotation speed of the device. In such a device, the optical phase shift due to the Sagnac effect is used for measuring angular velocity. Since there are no moving parts, such devices have an inherent advantage of reliability compared to competing technologies.

[0004] Optical gyroscopes, such as optical (fiber - optic) gyroscopes based on optical ring resonators, use optical elements such as lasers, beam splitters, polarizers, phase modulators, circulators, resonators, and photodetectors. In order to achieve accurate measurements, it is necessary to align various optical elements accurately and stably. In some cases, bulky mechanical supports may be required to accurately and reliably align different optical elements.

[0005] Optical gyroscopes also require electrical or electronic components such as wave generators, lock-in amplifiers, FPGAs, computer-implemented devices, etc. These components can be bulky, and the miniaturization of the gyroscope is limited by the sizes of different optical and electrical components. However, in many applications such as drones, smaller gyroscopes would be desirable (or necessary). All components, both optical and electrical / electronic, further require electrical connections between the components.

[0006] Further progress in inertial measurement systems is desired.

Summary of the Invention

Problems to be Solved by the Invention

[0007] The object of the present technology is to improve at least some of the disadvantages existing in the prior art or to provide a method for improving device performance.

[0008] It should be understood that at least some of the elements described herein can be fabricated by deposition. Chemical vapor deposition techniques or physical deposition techniques, as well as other deposition techniques such as layer bonding of various layers onto substrates and other layers as described herein, each provide immovable attachment of the layers to the substrates and other layers.

[0009] As used herein, the term "deposition" with respect to fabrication methods broadly refers to methods and processes for mechanically and / or chemically applying materials to one or more desired locations or as layers on a surface, as well as methods and processes for patterning or removing selected areas of the deposited film. Methods and processes included in the term "deposition" herein include, but are not limited to, spin coating, photoresist development and etching, photolithography, electron beam lithography, thermal oxidation, plasma etching, wet etching, electron beam deposition, low-pressure chemical vapor deposition, plasma-enhanced chemical vapor deposition, and physical vapor deposition.

[0010] The amounts or values described in this specification are meant to refer to actual given values. The term "about" is used herein to refer to an approximation of such a given value that would be reasonably inferred based on ordinary skill in the art, and includes equivalents and approximations resulting from experimental and / or measurement conditions related to such a given value.

Means for Solving the Problem

[0011] According to a non-limiting embodiment of the present technology, there is provided an integrated photonic gyroscope including a light source, a wavelength filter optically connected to the light source, at least one interferometric spiral loop optically connected to the wavelength filter and formed of silicon nitride, and a detector optically connected to the interferometric spiral loop for receiving light therefrom.

[0012] In some embodiments, the wavelength filter includes at least one ring resonator filter formed of silicon nitride.

[0013] In some embodiments, the integrated photonic gyroscope further includes a phase modulator optically connected between at least one interferometric spiral loop and the detector.

[0014] In some embodiments, the integrated photonic gyroscope further includes a phase modulator optically connected between the wavelength filter and at least one interferometric spiral loop.

[0015] In some embodiments, the integrated photonic gyroscope further includes a substrate, at least one wavelength filter is formed in a first material layer disposed on the substrate, and the phase modulator is formed in a second material layer disposed parallel to the first layer.

[0016] In some embodiments, the integrated photonic gyroscope further includes a substrate, and at least one wavelength filter and phase modulator are formed in a material layer connected to the substrate.

[0017] In some embodiments, the phase modulator is at least one thin-film lithium niobate waveguide (TFLN) phase modulator, and at least one TFLN phase modulator includes at least one lithium niobate waveguide and a plurality of metal electrodes disposed adjacent to the at least one lithium niobate waveguide.

[0018] In some embodiments, the phase modulator is at least one SiN / PZT phase modulator, and at least one SiN / PZT phase modulator includes a silicon nitride waveguide and an electrode including lead zirconate titanate (PZT), and the electrode is displaced horizontally from the waveguide.

[0019] In some embodiments, the integrated photonic gyroscope further includes at least one photonic wire bond that connects the waveguide to the detector.

[0020] In some embodiments, the integrated photonic gyroscope further includes a waveguide formed from thin-film lithium niobate (TFLN) and a germanium detector formed on a silicon substrate.

[0021] In some embodiments, the integrated photonic gyroscope further includes a plurality of horizontally linear and tapered evanescent field vertical couplers, and the evanescent coupling occurs between vertically disposed dissimilar silicon nitride waveguides and silicon waveguides.

[0022] In some embodiments, the integrated photonic gyroscope further includes a tapered silicon nitride straight waveguide having a width of about 0.5 μm and a thickness of about 100 nm, a silicon waveguide having a width of about 500 nm and a thickness of about 220 nm, and a vertical separation between the silicon nitride straight waveguide and the silicon waveguide, the vertical separation including a vertical separation of about 1.95 μm for 10% coupling, 0.88 μm for 50% coupling, and 0.18 μm for 97% coupling.

[0023] In some embodiments, the integrated photonic gyroscope further includes a plurality of horizontally linear and tapered evanescent field vertical couplers, and the evanescent coupling occurs between vertically disposed dissimilar silicon nitride waveguides and lithium niobate waveguides.

[0024] In some embodiments, the integrated photonic gyroscope further includes a silicon nitride straight waveguide having a width of about 2.8 μm and a thickness of about 100 nm, a lithium niobate waveguide having a width of about 1.5 μm and a thickness of about 100 nm, and a vertical separation between the silicon nitride straight waveguide and the lithium niobate waveguide, the vertical separation including a vertical separation of about 0.825 μm for 99.97% coupling.

[0025] In some embodiments, the integrated photonic gyroscope further includes a reflective mirror formed from silicon, and the reflective mirror provides optical coupling between at least one interferometric spiral loop and at least one detector.

[0026] In some embodiments, the integrated photonic gyroscope further includes at least one vertical coupler and a plurality of etched cavities defined within a material below at least one interferometric spiral loop, and none of the plurality of etched cavities is defined in a region immediately below a coupling region defined around the at least one vertical coupler.

[0027] In some embodiments, the light source includes at least one of a distributed feedback (DFB) laser, a superluminescent diode (SLD) light source, and an amplified spontaneous emission (ASE) light source.

[0028] In some embodiments, the light source includes a semiconductor optical amplifier (SOA).

[0029] According to some non-limiting examples of the present technology, an integrated photonic gyroscope is provided that includes a semiconductor optical amplifier (SOA), at least one interferometric spiral loop formed from silicon nitride optically connected to a wavelength filter, and a detector optically connected to the interferometric spiral loop to receive light therefrom.

[0030] Each of the embodiments of the present disclosure has at least one of the above-described objects and / or aspects, but does not necessarily have all of them. It should be understood that some aspects of the present disclosure resulting from attempting to achieve the above object may not satisfy this object and / or may satisfy other objects not specifically recited herein.

[0031] Additional and / or alternative features, aspects, and advantages of the embodiments of the present disclosure will become apparent from the following description, the accompanying drawings, and the appended claims.

[0032] To better understand the present technology and other aspects and further features, reference is made to the following description used in conjunction with the accompanying drawings.

Brief Description of the Drawings

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DETAILED DESCRIPTION OF THE INVENTION

[0034] It should be understood that throughout the accompanying drawings and the corresponding description, similar features are identified by similar reference numerals. Further, it should be understood that the drawings and the following description are for illustrative purposes only and such disclosure is not intended to limit the scope of the claims. Note that the figures may not be drawn to scale unless otherwise specified.

[0035] The present disclosure is directed to systems, methods, and apparatuses for addressing deficiencies in the current state of the art.

[0036] In a gyroscope of the type described herein, the phase difference is determined using the Sagnac effect. To obtain high responsiveness in a compact device, the phase difference between two counter-propagating waves is accumulated in a long optical waveguide coil (also called a loop). For an ideal integrated optical waveguide and components, the output optical generation current I can be described by the following equation: I1 = I 01 (l - cos φs), Equation (1) I2 = I02 (l + cosφs), and Equation (2) I0 = σP / 2, Equation (3) where φs is the so-called Sagnac phase shift, σ is the responsivity of the photodetector, and P is the power coupled to the input integrated optical waveguide.

[0037] The Sagnac phase shift (φs) is the phase shift difference between two counter-propagating waves along the same optical path and is described by the following expression: φs = Ω×(2πNLD / λc), Equation (4) where Ω is the angular velocity, λ is the vacuum wavelength, N is the number of loops of the integrated optical waveguide coil, D is the diameter of the integrated optical waveguide coil, and L is the length of the integrated optical waveguide coil.

[0038] Figure 1 is a perspective schematic view of an interferometric integrated photonic gyroscope 101. The gyroscope 101 includes an interferometric sensing element or spiral, a phase modulator, a photodiode, a light source or laser diode, and an insulating support element such as a silicon oxide layer, all on a support wafer or substrate. The phase modulator includes an actuator electrode for electrically adjusting the phase and can be made of lithium niobate with a metal electrode or silicon nitride with a piezoelectric electrode. The spiral is composed of a silicon nitride optical waveguide that serves to confine the optical mode propagating in the waveguide when surrounded by silicon oxide.

[0039] In this embodiment, the phase modulator 190 is disposed between the spiral loop 110 and the detector 315. The phase modulator 190 can be a lithium niobate thin film (TFLN) phase modulator as shown in FIG. 5, or a lead zirconate titanate (PZT) phase modulator as shown in FIGS. 17 and 18. Also, for example, see "Ultra-low power stress-based phase actuation in TriPleX photonic circuits", Everhardt et al., Proc. SPIE 12004, Integrated Optics: Devices, Materials, and Technologies XXVI, 1200405 (March 5, 2022). This is referred to herein as "Everhardt" and is hereby incorporated by reference in its entirety.

[0040] Light from the broadband laser or semiconductor optical amplifier (SOA) 150 is emitted into the input waveguide 130 of the spiral loop 110. When the light source 150 is an SOA, it is externally coupled to the wavelength filter 140. In the case of a broadband laser, the wavelength filter 140 is not necessary. The wavelength filter 140 is made of a silicon nitride ring resonator with the Vernier effect and is placed after the SOA 150 to further narrow the linewidth of the SOA 150. The light passes through the silicon nitride spiral loop input waveguide 130 and reaches the spiral loop 110 that forms the sensing element of the gyro for measuring the Sagnac effect. In the coupling region 160, the output light from the center 120 of the spiral loop is perpendicularly coupled to the input straight waveguide 170 or input tapered waveguide 171 of the lithium niobate thin film waveguide 180 arranged between the two metal electrodes 191 and 192 that constitute the thin film lithium niobate (TFLN) phase modulator 190. Similarly, an SiN phase modulator can also be used and is actuated by a horizontally coupled PZT. In the coupling region 160, the coupling waveguide can be a straight waveguide 170 or a straight waveguide 151 or a tapered waveguide 171 or a tapered waveguide 152, as shown in FIG. 1 and more specifically as shown in FIG. 5. The silicon / germanium detector 315 is attached to the silicon substrate 335. The output light from the phase modulator is coupled to the silicon / germanium detector 315 via the photonic wire bonding 114 fabricated using two-photon polymerization-based direct laser 3D lithography. First, the detector 315 is fixed on the silicon substrate 335, and then the interconnecting region between the lithium niobate waveguide 180 and the detector 315 is embedded in a photosensitive polymer. Then, the shape of the photonic wire bond waveguide is designed using two-photon lithography. Layers 111, 112, 113 form the upper layer, buffer layer, and bottom layer of the waveguide 101 formed on the silicon substrate 335. The silicon nitride ring 110 is patterned on the oxide bottom layer 113.

[0041] In some embodiments, the light source 150 can be replaced with an SLD or an ASE broadband light source to minimize the backscattering noise of the spiral loop 110. The SLD or ASE broadband light source can have an operating wavelength of about 1310 nm or 1550 nm.

[0042] In another embodiment, the positions of the laser and the SOA can be interchanged with the position of the detector together with a wavelength filter.

[0043] FIG. 2 is a cross-sectional view of the miniaturized interferometric integrated photonic gyroscope of FIG. 1, additionally showing that the phase modulator 190 is disposed between the spiral loop 110 and the detector 315.

[0044] FIG. 3 is a perspective schematic view 301 of a miniaturized interferometric integrated photonic gyroscope in which the phase modulator 390 is disposed between the light source (laser or SOA) 350 and the spiral loop 310. The phase modulator 390 can be a thin film lithium niobate (TFLN) phase modulator as shown in FIG. 5, or a SiN / PZT phase modulator as also shown in FIGS. 17 and 18 and Everhardt.

[0045] The light from the light source 350 is emitted to the center 320 of the spiral loop 310 formed by a silicon nitride waveguide. When the light source 350 is an SOA, it is externally coupled to the wavelength filter 340. In the case of a broadband laser, the wavelength filter 340 is not necessary. The wavelength filter 340 is formed by a silicon nitride ring resonator that utilizes the Vernier effect and is arranged after the SOA 350 to further narrow the linewidth of the SOA 350. The output of the waveguide filter 340 made of silicon nitride is coupled to a lithium niobate waveguide 380 via a spot converter (not shown) and is arranged between two metal electrodes 391 and 392 that constitute a thin-film lithium niobate (TFLN) phase modulator 390. In the coupling region 360, the coupling waveguide can be a straight waveguide 370, a straight waveguide 351, a tapered waveguide 371, or a tapered waveguide 352 as shown in FIG. 1 or, more specifically, as shown in FIG. 5. The modulated light is coupled to the center 320 of the spiral loop 310 that forms the sensing element of the gyro for measuring the Sagnac effect via the coupling region 360 through the straight waveguide 370 or through the vertically tapered coupler 371 that is tapered in the horizontal direction. The light from the output waveguide 330 of the spiral loop 310 is coupled to a silicon / germanium detector 315 in the coupling region 355. In the coupling region 355, the silicon nitride waveguide is tapered down to a straight waveguide with a width of 1.5 μm so that the effective index matches the effective index of the silicon waveguide 365. The silicon / germanium detector 315 is fabricated on or attached to the silicon 325. In the illustrated embodiment, the silicon layer 325 supports the spiral loop 310 and the output 330 of the spiral loop and has a plurality of air trenches 375 formed therein (also referred to as an etched cavity). Note that the air gap 375 as shown in the figure is merely representative of the region 375 where many air trenches are formed. For additional information regarding the formation and effect of the air cavity, see also U.S. Patent Application No. 18 / 110,989, filed on February 17, 2023, which is hereby incorporated by reference in its entirety. There is a thin oxide layer 313 between the silicon nitride spiral loop 310 and the air cavity 375.

[0046] FIG. 4 is a cross-sectional view 401 of the small interferometric integrated photonic gyroscope of FIG. 3, in which a phase modulator 390 is disposed between a wavelength filter 340 and a spiral loop 310. In this FIG. 4, the labeling of components and layers remains the same as in FIG. 3.

[0047] FIG. 4(a) is a perspective schematic view 401a of the small interferometric integrated photonic gyroscope in which beams propagate in the clockwise and counterclockwise directions. In this figure, a laser, a 3-port coupler that also functions as a circulator, and a spiral loop are disposed in a first material layer, and a two-phase modulator, each of whose two consists of thin-film lithium niobate and two metal electrodes, is disposed in a second material layer parallel to the first material layer. The arrows in the figure indicate the direction of vertical coupling from silicon nitride to thin-film lithium niobate, and vice versa. The clockwise beam and the counterclockwise beam are combined, and the 3-port coupler forms an interference beam. When there is no rotation, no Sagnac phase shift occurs, but when there is rotation, a Sagnac phase shift occurs.

[0048] FIG. 5 is a perspective schematic view of an evanescent field vertical coupler 501 in which evanescent coupling occurs between two vertically disposed silicon nitride waveguides and a lithium niobate waveguide in coupling regions 570 or 580. Coupling region 570 can have a coupled silicon nitride straight waveguide 5211 and a lithium niobate straight waveguide 5221, or a tapered silicon nitride straight waveguide 521 and a tapered lithium niobate waveguide 522. Similarly, coupling region 580 can have a coupled silicon nitride straight waveguide 5231 and a lithium niobate straight waveguide 5241, or a tapered lithium niobate straight waveguide 523 and a tapered silicon nitride waveguide 524. Light from the lower silicon nitride waveguide 521 or 5211 is vertically coupled to the upper lithium niobate waveguide 522 or 5221 in the vertical coupling region 570 by vertical evanescent coupling. The power coupled to waveguide 530 can be varied by changing the vertical gap between waveguides 510 and 530 and by changing the length of the overlap region between waveguides 5211 and 5221 or 521 and 522. Similarly, light can be recoupled from the upper lithium niobate waveguide 530 to the lower silicon nitride waveguide 520 in the vertical coupling region 580 by vertical evanescent coupling. The advantage of the tapered waveguides of silicon nitride and lithium niobate in coupling regions 570 and 580 is to provide efficient vertical coupling with a much smaller coupling length. The input waveguide 510 and the output waveguide 520 are patterned on the silicon oxide layer 513, and the lithium niobate waveguide 530 is patterned on the silicon oxide layer 512. The surface-to-surface gap between the upper lithium niobate waveguide 530 and the lower silicon nitride input waveguide 510 and the lower silicon nitride output waveguide 520 can be varied to adjust the maximum vertical coupling efficiency. The light beam propagating within the thin film lithium niobate waveguide (TFLN) 530 is phase modulated via two electrodes 541 and 542 disposed adjacent to the TFLN waveguide 530, and this phase-modulated light beam is emitted through the output waveguide 520. Layers 511, 512, and 513 form the upper layer, buffer layer, and bottom layer of the waveguide 105 formed on the silicon substrate 535.

[0049] Figure 6 shows the simulation result 601 regarding the vertical power coupled from the input lower silicon nitride straight waveguide 510 to the output upper lithium niobate straight waveguide 530 in the coupling region 570 of Figure 5. As can be seen from this figure, when the width of the silicon nitride waveguide is 2.8 μm, the thickness is 100 nm, the width of the lithium niobate waveguide is 1.5 μm, and the thickness is 100 nm, when the surface gap between the two vertical waveguides is 0.825 μm and the coupling length is 9.6 μm, the output power remaining in the input silicon nitride waveguide 510 is 0.00035, or the power coupled to the output vertical lithium niobate waveguide 530 is 0.9997, that is, 99.97%. Similarly, in the coupling region 580 of Figure 5, the vertical power coupled from the upper lithium niobate waveguide 530 to the lower silicon nitride waveguide 520 is 99.97%. In this simulation, the refractive index of silicon nitride was set to 2.08 and the refractive index of lithium niobate was set to 2.2.

[0050] Figure 7 shows the simulation result 701 of the vertical power coupled from the silicon nitride waveguide 345 to the silicon waveguide 365 attached to the detector 315 as shown in Figure 3. The vertical coupling occurs in the coupling region 355 as shown in Figure 3. Referring to Figure 7, when the vertical gap between the upper surface of the silicon waveguide 365 in Figure 3 and the lower surface of the silicon nitride waveguide 345 is 0.18 μm, approximately 97% of the light is coupled to the silicon waveguide 365 in Figure 3. On the other hand, when the vertical gap between the upper surface of the silicon waveguide 365 and the lower surface of the silicon nitride waveguide 345 increases to 2.38 μm, the coupled light decreases to 7.7%. However, at a typical vertical gap of 1.95 μm, approximately 9.3% of the light is coupled from the silicon nitride waveguide 345 to the waveguide 365. The simulation was performed for a tapered single-mode silicon nitride waveguide 345 with a width of 0.5 μm and a thickness of 100 nm and a fab-recommended standard single-mode silicon waveguide 365 with a width of 0.5 μm and a thickness of 0.22 μm.

[0051] FIG. 8 is a perspective schematic view 801 of four spiral loops on separate dies connected via two silicon nitride waveguide evanescent field vertical couplers, shown by dashed lines 815 and 816 and also schematically shown in FIG. 9. In some embodiments, instead of the single spiral loop shown in FIGS. 1 and 3, these four spiral loops can be implemented. By increasing the length of the loop beyond what can be achieved on a single die, the sensitivity can be improved. Referring to FIG. 8, the four spiral loops are formed from the single spiral loop of FIGS. 1 and 3, but represent a way of connecting four adjacent dies to increase the loop area and improve the sensitivity. FIG. 12 shows that there is no advantage in increasing the length of the silicon nitride waveguide in the case of a high-loss waveguide with a loss of 3 dB per meter, but there is some advantage in the case of the low-loss silicon nitride waveguide of FIG. 11.

[0052] Referring to FIG. 8, a method of increasing the gyroscope sensitivity to increase the maximum spiral length achievable with the area of a single die by bridging multiple dies when the loss of the waveguide is low enough is shown. To enhance the Sagnac effect, all the spirals must be wound in the same direction. The input silicon nitride waveguide 810, the output silicon nitride waveguide 820, loop 1 (821), loop 2 (822), loop 3 (823), and loop 4 (824) are of a first level of silicon nitride as shown by the continuous lines and are patterned on silicon oxide 830, while the vertical couplers 815 and 816 are of a second level of silicon nitride as shown by the dashed lines and are patterned on a 1.95 μm thick intermediate silicon oxide layer. The bridging nitride layer can be formed in one step by a lithography process across the dicing line, or can be formed by stitching or offset lithography as needed.

[0053] Referring to FIG. 8, the light from the laser 810 is emitted into loop 1 (821), vertically upward coupled to the silicon nitride vertical coupler 815 via the coupling region 841, and vertically downward coupled to loop 2 (822) via the coupling region 842. The light from loop 2 (822) propagates to loop 3 (823) via the connection waveguide (817). From loop 3 (823), the light is vertically coupled to loop 4 (824) via the coupling region 843 leading to the vertical coupler 816, vertically coupled to loop 4 (824) via the coupling region 844, and emitted through the output waveguide 820. The amount of light coupled in the coupling regions 841, 842, 843 and 844 is shown in FIG. 10 and described in para 46.

[0054] FIG. 9 is a perspective schematic view of an evanescent field vertical coupler 901 in which evanescent coupling occurs between two vertically arranged silicon nitride waveguides in a coupling region 970 or 980. The coupling region 970 can have coupled silicon nitride straight waveguides 9211 and 9221, or tapered silicon nitride straight waveguides 921 and 922. Similarly, the coupling region 980 can have coupled silicon nitride straight waveguides 9231 and 9241, or tapered silicon nitride straight waveguides 923 and 924. Light from the lower input silicon nitride waveguide 921 or 9211 is vertically coupled to the upper silicon nitride waveguide 922 or 9221 in the vertical coupling region 970 by vertical evanescent coupling. The power coupled to the waveguide 930 can be varied by changing the vertical gap between the waveguides 910 and 930, and also by changing the length of the overlap region between the waveguides 9211 and 9221 or 921 and 922. In a similar manner, light can be recoupled from the upper silicon nitride waveguide 930 to the lower silicon nitride waveguide 920 in the vertical coupling region 980 by vertical evanescent coupling. The advantage of the silicon nitride tapered waveguides in the coupling regions 970 and 980 is that they provide efficient vertical coupling with a much smaller coupling length. The input waveguide 910 and the output waveguide 920 are patterned on the silicon oxide layer 913, and the silicon nitride waveguide 930 is patterned on the silicon oxide 912. The surface-to-surface gap between the upper silicon nitride waveguide 930 and the lower silicon nitride input waveguide 910 and the lower silicon nitride output waveguide 920 can be varied to adjust the maximum vertical coupling efficiency. Layers 911, 912, and 913 form the upper layer, buffer layer, and bottom layer of the waveguide 901 formed on the silicon substrate 935.

[0055] FIG. 10 shows the simulation result 1011 of the vertical power coupled from the lower silicon nitride straight waveguide 910 to the upper silicon nitride straight waveguide 930 in the coupling regions 970 and 980 of FIG. 9. As can be seen from this figure, when the width of the silicon nitride waveguide is 2.8 μm and the thickness is 100 nm, when the surface gap between the two vertical waveguides is 1.95 μm and the coupling length is 150 μm, the power remaining in the input silicon nitride waveguide 910 is 0.0064, or the power coupled to the output vertical waveguide 930 is 0.9944, that is, 99.34%. Similarly, in the coupling region 980 of the same FIG. 5, the vertical power coupled from the upper silicon nitride waveguide 930 to the lower silicon nitride waveguide 920 is 99.34%. In this simulation, the refractive index of silicon nitride was set to 2.08.

[0056] FIG. 11 shows the plot 1111 of the minimum rotation (deg / h / sqrt(Hz)) versus the spiral length (meter) for two types of noise, namely shot noise and thermal noise, when the propagation loss of the spiral loop is 0.5 dB / km at a wavelength of 1550 nm. Both types of noise have an optimal value when plotted as the spiral length. For a source input power of 100 mW and a spiral loop length of 22.2721 meters, the number of loops required to fit into a 2 cm × 2 cm reticle with the same silicon nitride waveguide having a width of 28 μm, a thickness of 100 nm, and a surface-to-surface spiral waveguide spacing of 10 μm is approximately 526. The corresponding minimum rotations for shot noise and thermal noise are 0.28 (deg / h / sqrt(Hz)) and 0.5 (deg / h / sqrt(Hz)), respectively, and the total noise (the sum of shot noise and thermal noise) is 0.78 (deg / h / sqrt(Hz)).

[0057] However, as shown through plot 1211 in FIG. 12, when the propagation loss of the spiral loop increases to 3 dB / km at a wavelength of 1550 nm, with the surface-to-surface spiral waveguide spacing of silicon nitride remaining at 10 μm, for the same source input power of 100 mW, the spiral loop length decreases to 5.38875 meters, corresponding to a smaller number of loops, 90. In this case, the corresponding minimum rotations of shot noise and thermal noise increase to 1.57 (deg / h / sqrt(Hz)) and 1.59 (deg / h / sqrt(Hz)), respectively, and the total noise (the sum of shot noise and thermal noise) increases to 3.16 (deg / h / sqrt(Hz)).

[0058] For the case of a low-loss silicon nitride waveguide where the propagation loss is on the order of 0.5 dB / meter at a wavelength of 1550 nm, the simulation showed that a spiral length of approximately 22 m that fits within a 2 cm × 2 cm reticle is required with a silicon nitride waveguide having a width of 2.8 μm, a thickness of 100 nm, and a surface-to-surface waveguide spacing of 10 μm to obtain a total detector noise (sum of shot noise and thermal noise) rotation rate of 0.78 (deg / h / sqrt(Hz)). However, for a propagation loss of 0.1 dB / meter at a wavelength of 1550 nm, the spiral loop length becomes much larger than 22.2721 m and does not fit within one reticle, thus requiring multiple reticles. The shape shown in FIG. 8 is a way to achieve a longer spiral when guaranteed by a low-loss waveguide.

[0059] FIG. 13 is a perspective schematic view 1311 of a spiral loop having a waveguide intersection. The spiral loop 1350 having a waveguide intersection can be replaced with the single spiral loop of FIGS. 1 and 3. The spiral loop 1350 of FIG. 13 does not require vertical coupling from the second layer of silicon nitride waveguides as shown in FIGS. 1, 3, and 5, thereby simplifying manufacturing. However, the spiral loop 1350 increases the loss for each intersection, which is twice, once when the input beam propagates from A to B and once again when the output beam propagates from B to C. Referring to the same FIG. 13, light from the laser light source is incident on the silicon nitride loop 1350 through the silicon nitride input waveguide 1310 and exits through the silicon nitride output waveguide 1320. While propagating from A to B, the input beam propagates through the intersections 1347, 1346, 1345, 1344, 1343, 1342, 1341, and while propagating from B to C, the output beam propagates through the intersections 1341, 1342, 1343, 1344, 1345, 1346, 1347. The input waveguide 1310, the output waveguide 1320, and the loop 1350 are patterned on the thermally grown silicon oxide 1330 on the silicon wafer 1360. The phase modulators of FIGS. 5, 17, and 18 can be placed immediately after the input waveguide 1310 or immediately before the output waveguide 1320.

[0060] Figure 14 shows the simulated loss 1411 of the output optical beam during propagation from B to C. In this case, the optical beam propagates through seven waveguide intersections labeled 1341, 1342, 1343, 1344, 1345, 1346, 1347, similar to the waveguide intersection in Fig. 13. Referring to Figs. 13 and 14, the power remaining in the output waveguide 1320 is approximately 0.87, i.e., 87%, which means that about 13% of the power is lost while propagating through the seven intersections, i.e., 1.85% (0.06 dB) of the power is lost while propagating through each intersection. In the simulation, the thickness of the silicon nitride waveguide is considered to be 100 nm, while the width remains 2.8 μm, supporting only the fundamental TE mode and no higher-order TE modes. The waveguide intersection loss of 90 loops during propagation from A to B and then from B to C in Fig. 13 was estimated to be 10.8 dB (0.06 dB × 2 × 90). In all cases, the intersections must be perpendicular to the spiral loop because any deviation therefrom can result in additional coupling between the intersecting waveguides.

[0061] Figure 15 is a perspective schematic view 1511 of the spiral loop 1550, and the silicon under the region (area) enclosed between the dashed lines 1560 is selectively etched away. This spiral loop can be replaced with a single spiral loop such as those in Fig. 1 or 3. Referring to Fig. 15, light is incident on the silicon nitride spiral loop 1550 through the silicon nitride input waveguide 1510 and exits from the silicon nitride output waveguide 1520. The spiral loop 1550 can be replaced with the spiral loop 1350 in Fig. 13 or Figs. 1 and 3. The phase modulators in Figs. 5, 17, and 18 can be placed immediately after the input waveguide 1510 or immediately before the output waveguide 1520. As shown in Fig. 15, the silicon under the region (area) enclosed by the dashed lines 1560 is etched with XeF2 (xenon difluoride), and a plurality of cavities are formed therein. For reference, please refer again to U.S. Patent Application No. 18 / 110,989.

[0062] FIG. 16 is a perspective schematic view 1611 of the spiral loop 1650. At the center of the spiral loop 1620, a reflection mirror 1690 is constructed that reflects a beam in the vertical direction 1640 to the detector 1680. The spiral loop 1650 can be replaced with the single spiral loop of FIG. 1. Referring to FIG. 16, light is incident on the silicon nitride spiral loop 1650 through the silicon nitride input waveguide 1610, then exits from the silicon nitride output waveguide 1620 and is reflected vertically by the mirror 1690, and is detected by the germanium detector 1680 having a boundary on the upper silicon oxide 1670. The input waveguide 1610, the output waveguide 1620, and the loop 1650 are patterned on the thermally grown silicon oxide 1630 on the silicon wafer 1660. The mirror 1690 can be formed by crystallographic etching of silicon or can be added to a trench etched in silicon dioxide so that the reflection angle for the input beam and the output beam is between 45 degrees and 54.7 degrees. The phase modulator of FIG. 5 can be arranged immediately after the input waveguide 1610.

[0063] FIG. 17 is a perspective cross-sectional view 1711 of a SiN / PZT phase modulator having a PZT material 1720. The PZT material 1720 is vertically sandwiched between two metal electrodes 1710 and 1711 for electrical operation. The single stripe silicon nitride waveguide 1730 is patterned on the thermally grown bottom silicon oxide 1732 formed on the silicon substrate 1735. The layer 1731 is an upper oxide layer that separates the silicon nitride waveguide 1730 from the bottom electrode 1711 so that the evanescent field in the fundamental TE mode is not attenuated by the bottom metal electrode 1711. This SiN / PZT phase modulator 1711 can be replaced with the lithium niobate phase modulator of FIG. 5.

[0064] FIG. 18 is a perspective cross-sectional view 1811 of a PZT phase modulator having a U-shaped PZT material 1820, also shown by a top view 1890. The U-shaped PZT material 1820 is vertically sandwiched between two metal electrodes 1810 and 1811. A single stripe silicon nitride waveguide 1830 is patterned on a thermally grown bottom silicon oxide 1832 formed on a silicon substrate 1835. Layer 1831 is an upper oxide layer that separates the silicon nitride waveguide 1830 from the bottom electrode 1811 so that the evanescent field of the fundamental TE mode is not attenuated by the bottom metal electrode 1811. This PZT phase modulator can be replaced with the lithium niobate phase modulator of FIG. 5 or the PZT modulator shown in FIG. 17.

[0065] Changes and improvements to the above-described embodiments of the present technology will be apparent to those skilled in the art. The foregoing description is intended to be illustrative rather than limiting.

Claims

1. An integrated photonic gyroscope, Light source and A wavelength filter optically connected to the light source, An interferometric spiral loop optically connected to a wavelength filter, wherein the at least one interferometric spiral loop is formed from silicon nitride, and A detector optically connected to the interferometric spiral loop to receive light from the interferometric spiral loop, An integrated photonic gyroscope equipped with [the necessary components].

2. The integrated photonic gyroscope according to claim 1, wherein the wavelength filter comprises at least one ring resonator filter formed from silicon nitride.

3. A phase modulator optically connected between the at least one interferometric spiral loop and the detector. The integrated photonic gyroscope according to claim 1, further comprising:

4. A phase modulator optically connected between the wavelength filter and the at least one interferometric spiral loop. The integrated photonic gyroscope according to claim 1, further comprising:

5. The integrated photonic gyroscope further comprises a substrate, The at least one wavelength filter is formed in a first material layer disposed on the substrate, The phase modulator is formed in a second material layer arranged parallel to the first layer. The integrated photonic gyroscope according to claim 1.

6. The integrated photonic gyroscope further comprises a substrate, The at least one wavelength filter and the phase modulator are formed in a material layer connected to the substrate. The integrated photonic gyroscope according to claim 1.

7. The phase modulator is at least one thin-film lithium niobate waveguide (TFLN) phase modulator, The at least one TFLN phase modulator is At least one lithium niobate waveguide, A plurality of metal electrodes arranged adjacent to at least one lithium niobate waveguide, The integrated photonic gyroscope according to claim 3, including the above.

8. The phase modulator is at least one SiN / PZT phase modulator, The at least one SiN / PZT phase modulator is silicon nitride waveguides and An electrode containing lead zirconate titanate (PZT), wherein the electrode is displaced horizontally from the waveguide, The integrated photonic gyroscope according to claim 3, including the above.

9. The integrated photonic gyroscope according to claim 1, further comprising at least one photonic wire bond connecting a waveguide to the detector.

10. Waveguides formed from thin-film lithium niobate (TFLN), A germanium or silicon detector added to a silicon substrate, The integrated photonic gyroscope according to claim 1, further comprising:

11. The integrated photonic gyroscope further comprises a plurality of horizontally linear and tapered evanescent field vertical couplers, Evanescent coupling occurs between vertically positioned silicon nitride waveguides of different types and silicon waveguides. The integrated photonic gyroscope according to claim 1.

12. A vertical coupling region, A tapered silicon nitride straight waveguide having a width of approximately 0.5 μm and a thickness of approximately 100 nm, A silicon waveguide having a width of approximately 500 nm and a thickness of approximately 220 nm, Vertical isolation between a silicon nitride linear waveguide and a silicon waveguide, Approximately 1.95 μm for 10% binding, 0.88 μm for 50% binding, and 0.18 μm for 97% binding Vertical separation and A vertical coupling region comprising The integrated photonic gyroscope according to claim 11, further comprising:

13. The integrated photonic gyroscope further comprises a plurality of horizontally linear and tapered evanescent field vertical couplers, Evanescent coupling occurs between vertically positioned silicon nitride waveguides and lithium niobate waveguides of different types. The integrated photonic gyroscope according to claim 1.

14. A vertical coupling region, A silicon nitride straight waveguide having a width of approximately 2.8 μm and a thickness of approximately 100 nm, A lithium niobate waveguide having a width of approximately 1.5 μm and a thickness of approximately 100 nm, Vertical separation between the silicon nitride linear waveguide and the lithium niobate waveguide, with a thickness of only about 0.825 μm for 99.97% bonding, A vertical coupling region comprising The integrated photonic gyroscope according to claim 13, further comprising:

15. A reflective mirror formed from silicon, wherein the reflective mirror provides optical coupling between the at least one interferometric spiral loop and the at least one detector. The integrated photonic gyroscope according to claim 1, further comprising:

16. The integrated photonic gyroscope is At least one vertical coupler, A plurality of etched cavities defined within the material below the at least one interference spiral loop, Furthermore, The integrated photonic gyroscope according to claim 1, wherein none of the plurality of etched cavities are defined in the region immediately below the coupling region defined around the at least one vertical coupler.

17. The aforementioned light source is Superluminescent diode (SLD) light source, and Amplified Spontaneous Emission (ASE) Light Source An integrated photonic gyroscope according to claim 1, comprising at least one of the following.

18. The integrated photonic gyroscope according to claim 1, wherein the light source comprises a semiconductor optical amplifier (SOA).

19. An integrated photonic gyroscope, Semiconductor optical amplifier (SOA), An interferometric spiral loop optically connected to a wavelength filter, wherein the at least one interferometric spiral loop is formed from silicon nitride, and A detector optically connected to the interferometric spiral loop to receive light from the interferometric spiral loop, An integrated photonic gyroscope equipped with [the necessary components].

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