An optical gyroscope integrated chip based on thin-film lithium niobate photonic integration platform

Abstract

The present invention discloses an optical gyroscope integrated chip based on a thin-film lithium niobate photonic integrated platform. The overall structure adopts a hybrid curved waveguide with multiple parts of continuously variable curvature, which reduces the insertion loss caused by the mode field mismatch between the straight waveguide and the curved waveguide at the junction, reduces the excitation of high-order modes, and helps to reduce the overall size of the chip. In addition, the curved waveguide increases the polarization extinction ratio of the chip and filters out quasi-TE 00 The present invention utilizes waveguide mode leakage to achieve single-mode, single-polarization operation of the lithium niobate waveguide. The single-TE mode lithium niobate waveguide on the entire chip, excluding the curved waveguide of the folded modulator and the coupler, forms a waveguide polarizer with a high polarization extinction ratio. This allows on-chip single-mode, single-polarization operation to be achieved without the need for an additional polarizer design, effectively reducing chip complexity, improving chip stability, and reducing chip size.

Description

Technical Field

[0001] The present invention relates to the field of inertial sensing technology, and in particular to an optical gyroscope integrated chip based on a thin-film lithium niobate photonic integrated platform. Background Art

[0002] A fiber optic gyroscope (FOG) is a high-performance inertial sensor based on the optical Sagnac interferometry effect. As an angular velocity sensor, it offers advantages such as high precision, high sensitivity, solid-state operation, and high reliability. Since the successful development of the first FOG in 1976 by Vali, Shorthill, and others at the University of Utah, over 40 years of development have made FOGs a mainstream solution for medium- and high-precision gyroscopes, with product accuracies ranging from 0.0005° / h to 10° / h. High-precision FOGs are primarily used in space technology, military applications, and scientific research, while low-cost medium- and low-precision FOGs are primarily used in civilian applications such as navigation and positioning, drone attitude control, and robotics.

[0003] A fiber optic gyroscope (FOG) consists of optical components such as a light source, a coupler, a phase folding modulator, a detector, a polarizer, and a fiber ring. In traditional FOG solutions, each core optical component is discrete. The cost of discrete optical components accounts for more than 70% of the total cost of the gyroscope, which makes it difficult to reduce system costs. On the other hand, FOGs based on discrete optical components are too large for small, high-performance applications such as drones, robots, cube satellites, self-driving cars, and underwater vehicles. Using discrete optical components to construct a Sagnac reciprocal interferometer requires additional optical interconnect technology, which can lead to parasitic interface reflections, increased insertion loss, and polarization misalignment, resulting in reduced system performance and reliability. In summary, the discrete core optical components make it difficult to improve the overall performance of the FOG in terms of size, weight, power consumption, and cost (SWaP-C), causing traditional FOGs to gradually lose their competitive advantage.

[0004] To address the aforementioned challenges faced by traditional fiber optic gyros (FOGs), the concept of integrated optical gyros (IOGs) emerged. Integrated FOGs (IOGs) employ integrated optical chips to partially or completely replace the multiple separate optical components found in traditional FOGs. In recent years, advancements in integrated photonics have led to breakthroughs in integrated optical chips for various functions, laying the foundation for the realization of integrated FOGs. IOOGs inherit the high precision of traditional optical gyros while offering advantages such as small size, low cost, and high reliability.

[0005] On the other hand, for interferometric closed-loop fiber gyroscopes, accurate phase modulation is a prerequisite for the chip to work well in high-precision inertial systems. Currently, bulk lithium niobate folded modulators have been widely used in fiber gyroscope systems due to their excellent electro-optical performance. However, commercial bulk lithium niobate folded modulators are based on lithium niobate waveguides formed by titanium diffusion or proton exchange. These waveguides typically have a low refractive index contrast of about 0.02 between the waveguide center and the cladding, which results in a large size of the optical mode. Weak light confinement requires that the metal electrodes be placed far away from the optical waveguide, thereby reducing the electro-optical modulation efficiency. Therefore, the size of the current bulk lithium niobate modulators is still large, even several centimeters long. Summary of the Invention

[0006] The present invention provides an optical gyroscope integrated chip based on a thin-film lithium niobate photonic integrated platform, thereby effectively improving stability, reliability and integration while also reducing and lowering costs.

[0007] The present invention provides an optical gyroscope integrated chip based on a thin-film lithium niobate photonic integrated platform, comprising: a first optical fiber-lithium niobate waveguide mode converter, a first optical coupler, a second optical coupler, a folding modulator, a second optical fiber-lithium niobate waveguide mode converter, a third optical fiber-lithium niobate waveguide mode converter, and a fourth optical fiber-lithium niobate waveguide mode converter; the first end of the first optical fiber-lithium niobate waveguide mode converter is used to connect to an external light source, and the second end of the first optical fiber-lithium niobate waveguide mode converter is connected to the first branch of the first optical coupler; the base waveguide of the first optical coupler is connected to the base waveguide of the second optical coupler via two 90° partially variable curvature hybrid curved waveguides; the first branch of the second optical coupler is connected to the first end of the second optical fiber-lithium niobate waveguide mode converter, and the second branch of the second optical coupler is connected to the third optical fiber. - is connected to the first end of a lithium niobate waveguide mode converter; the two arms of the folding modulator are two branches of the second optical coupler, and both arms of the folding modulator form a folded structure through two 180° partially variable curvature hybrid bend waveguides; the second end of the second optical fiber-lithium niobate waveguide mode converter is connected to one end of an external polarization-maintaining optical fiber ring; the second end of the third optical fiber-lithium niobate waveguide mode converter is connected to the other end of the polarization-maintaining optical fiber ring; the second branch of the first optical coupler is connected to the first end of the fourth optical fiber-lithium niobate waveguide mode converter, and the second end of the fourth optical fiber-lithium niobate waveguide mode converter is used to connect to an external photodetector; the single TE mode lithium niobate waveguide other than the hybrid bend waveguide of the folding modulator and the optical coupler forms a waveguide polarizer; the waveguide polarizer is composed of a shallowly etched and / or narrow-width lithium niobate waveguide.

[0008] Specifically, the waveguide polarizer consists of an air layer, a low-refractive index cover layer, a lithium niobate ridge waveguide, a SiO2 substrate layer and a Si substrate layer from top to bottom. The ridge waveguide is formed by etching away part of the lithium niobate layer outside the waveguide; the refractive index of the low-refractive index cover layer is 1-1.7.

[0009] Specifically, the width of the waveguide polarizer is less than 2.5 μm, the etching depth is less than 0.4 μm, and the operating wavelength range is 1210-1410 nm.

[0010] Specifically, the partially variable curvature hybrid curved waveguide is composed of a linear variable curvature arc waveguide and a constant curvature arc waveguide.

[0011] Specifically, the width of the 90° partially variable curvature hybrid curved waveguide is less than 2.5 μm, the angle of the linear variable curvature arc waveguide accounts for less than 95% of the total bending angle, and the minimum radius of the 90° partially variable curvature hybrid curved waveguide is greater than 80 μm.

[0012] Specifically, the width of the 180° partially variable curvature hybrid curved waveguide is less than 5 μm, the angle of the linear variable curvature arc waveguide accounts for less than 95% of the total bending angle, and the minimum radius of the 180° partially variable curvature hybrid curved waveguide is greater than 50 μm.

[0013] Specifically, the folding modulator is a lithium niobate electro-optical folding modulator, which uses an x-cut thin-film lithium niobate wafer, and the electrode structure of the folding modulator adopts a horizontal design, distributed on both sides and in the middle of the two branches of the second optical coupler, forming a push-pull structure.

[0014] Specifically, the first optical fiber-lithium niobate waveguide mode converter, the second optical fiber-lithium niobate waveguide mode converter, the third optical fiber-lithium niobate waveguide mode converter, and the fourth optical fiber-lithium niobate waveguide mode converter all adopt an inverted taper structure to achieve mode field matching between the lithium niobate waveguide at the end face and the polarization-maintaining optical fiber ring.

[0015] Specifically, the first optical coupler and the second optical coupler are Y-type couplers and / or 1×2 multimode interferometer couplers.

[0016] Specifically, the Y-type coupler includes: a base waveguide, a tapered region, a first branch and a second branch; the base waveguide leads to the first branch and the second branch through two ports respectively through the tapered region; the width of the tapered region widens according to a quadratic function; the gap between the first branch and the second branch gradually widens in the form of a rising cosine curve function.

[0017] One or more technical solutions provided in the present invention have at least the following technical effects or advantages:

[0018] 1. The overall structure adopts a hybrid curved waveguide with multiple parts of continuously variable curvature, which reduces the insertion loss caused by the mode field mismatch between the straight waveguide and the curved waveguide at the junction, reduces the excitation of high-order modes, and is conducive to reducing the overall size of the chip. The curved waveguide increases the polarization extinction ratio of the chip and filters out the quasi-TE 00 The present invention utilizes waveguide mode leakage to achieve single-mode and single-polarization operation of the lithium niobate waveguide. The single-TE mode lithium niobate waveguide on the entire chip, except for the curved waveguide and coupler of the folded modulator, forms a waveguide polarizer with a high polarization extinction ratio, thereby achieving on-chip single-mode and single-polarization operation without the need for additional polarizer design, effectively reducing the complexity of the chip, improving the stability of the chip, and reducing the volume. By integrating the core optical devices of the fiber optic gyroscope on the thin-film lithium niobate photonic platform through the present invention, the parasitic interface reflection, increased insertion loss and polarization misalignment problems caused by the additional optical interconnection required for discrete optical elements can be effectively overcome, further improving the reliability of the fiber optic gyroscope system, reducing the chip volume and reducing costs.

[0019] 2. The folded modulator uses a 180° hybrid curved waveguide, which increases the modulation length by folding. When the half-wave voltage is the same, that is, when the voltage-length product V π When L is the same, the driving voltage is reduced.

[0020] In summary, the present invention can effectively improve the stability, reliability and integration of the closed-loop fiber optic gyroscope while ensuring its accuracy, while reducing its size, power consumption and cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A schematic structural diagram of an optical gyroscope integrated chip based on a thin-film lithium niobate photonic integrated platform provided by an embodiment of the present invention;

[0022] Figure 2 A schematic cross-sectional view of a waveguide polarizer in an optical gyroscope integrated chip based on a thin-film lithium niobate photonic integrated platform provided by an embodiment of the present invention;

[0023] Figure 3 The waveguide polarizer of the embodiment of the present invention is based on the quasi-TM of the x-cut thin film lithium niobate wafer xz planar waveguide at a wavelength of 1310nm. 00 Leaky mode loss (dB / cm) and quasi-TE 10 How the existence of modes varies with waveguide width and etch depth;

[0024] Figure 4 The waveguide polarizer of the embodiment of the present invention is based on the quasi-TM of the x-cut thin film lithium niobate wafer xy plane waveguide at a wavelength of 1310nm. 00Leaky mode loss (dB / cm) and quasi-TE 10 How the existence of modes varies with waveguide width and etch depth;

[0025] Figure 5 The hybrid curved waveguide with a variable curvature at a 90° portion of the base waveguide connecting the first 3dB optical coupler 2 and the second 3dB optical coupler 3 in an embodiment of the present invention; (a) is a schematic top view of the hybrid curved waveguide; (b) shows how the curvature of the hybrid curved waveguide varies with waveguide path length;

[0026] Figure 6 A hybrid curved waveguide with a 180° partially variable curvature used in the folded modulator 4 in an embodiment of the present invention; (a) is a schematic top view of the hybrid curved waveguide; (b) shows how the curvature of the hybrid curved waveguide varies with the length of the waveguide path;

[0027] Figure 7 This is a schematic diagram of the cross-sectional structure of the folded modulator 4 in an embodiment of the present invention. The z-axis of the lithium niobate crystal is parallel to the waveguide plane, and the electrode structure adopts a horizontal design.

[0028] Figure 8 is the half-wave voltage-length product V of the folding modulator 4 in the embodiment of the present invention π The relationship between L and transmission loss as a function of metal spacing;

[0029] Figure 9 Schematic diagram of the structure of a Y-type coupler in an embodiment of the present invention;

[0030] Figure 10 Schematic diagram of the structure of a 1×2 multimode interferometer coupler in an embodiment of the present invention;

[0031] Figure 11 FIG. 4 is a schematic cross-sectional view of the stray light absorber 10 according to an embodiment of the present invention. DETAILED DESCRIPTION

[0032] The embodiment of the present invention provides an optical gyroscope integrated chip based on a thin-film lithium niobate photonic integrated platform, thereby effectively improving stability, reliability and integration while also reducing and lowering costs.

[0033] In order to better understand the above technical solution, the above technical solution will be described in detail below with reference to the accompanying drawings and specific implementation methods.

[0034] See also Figure 1The optical gyroscope integrated chip based on the thin-film lithium niobate photonic integrated platform provided in an embodiment of the present invention includes: a first optical fiber-lithium niobate waveguide mode converter 1, a first optical coupler 2, a second optical coupler 3, a folding modulator 4, a second optical fiber-lithium niobate waveguide mode converter 7, a third optical fiber-lithium niobate waveguide mode converter 8, and a fourth optical fiber-lithium niobate waveguide mode converter 9; the first end of the first optical fiber-lithium niobate waveguide mode converter 1 is used to be connected to an external light source via an optical fiber, and the external light source is coupled to the integrated chip along the direction of arrow 11. The second end of the first optical fiber-lithium niobate waveguide mode converter 1 is connected to the first branch of the first optical coupler 2; the base waveguide of the first optical coupler 2 is connected to the base waveguide of the second optical coupler 3 through two 90° partially variable curvature hybrid curved waveguides to avoid relative placement and realize filtering in the interference destructive mode; the first branch of the second optical coupler 3 is connected to the first end of the second optical fiber-lithium niobate waveguide mode converter 7, and the second branch of the second optical coupler 3 is connected to the first end of the third optical fiber-lithium niobate waveguide mode converter 8; the two arms 5 and 6 of the folding modulator 4 are two branches of the second optical coupler 3, and the two arms 5 and 6 of the folding modulator 4 are formed into a folded structure through two 180° partially variable curvature hybrid curved waveguides; the second end of the second optical fiber-lithium niobate waveguide mode converter 7 is connected to the outer polarization-maintaining fiber ring. One end is connected; the second end of the third optical fiber-lithium niobate waveguide mode converter 8 is connected to the other end of the polarization-maintaining fiber ring; the second branch of the first optical coupler 2 is connected to the first end of the fourth optical fiber-lithium niobate waveguide mode converter 9, and the second end of the fourth optical fiber-lithium niobate waveguide mode converter 9 is used to connect to an external photodetector. In the chip provided by the embodiment of the present invention, excluding the hybrid bending waveguide of the folded modulator 4 and the first and second optical couplers 2 and 3, the single TE mode lithium niobate waveguide forms a waveguide polarizer. This waveguide polarizer is composed of a shallowly etched, narrow width lithium niobate waveguide, and the rest of the chip is composed of this waveguide structure. The TM mode of this waveguide has high leakage loss. Waveguide mode leakage is used to achieve single-mode, single-polarization operation of the lithium niobate ridge waveguide, thereby achieving a high polarization extinction ratio, that is, it has a polarization function. Moreover, this waveguide polarizer does not occupy additional space and can polarize within the entire chip, effectively providing the polarization function. 11 is the direction of the external light source input, and 12 is the direction of the light output to the external detector.

[0035] like Figure 2 As shown, the waveguide polarizer in the embodiment of the present invention is composed of an air layer, a low-refractive index cover layer, a lithium niobate ridge waveguide, a SiO2 substrate layer and a Si substrate layer from top to bottom. The ridge waveguide is formed by etching away part of the lithium niobate layer outside the waveguide. The total thickness of the lithium niobate is 300nm, and the refractive index of the low-refractive index cover layer is 1-1.7.

[0036] Specifically, the width of the waveguide polarizer is less than 2.5 μm, the etching depth is less than 0.4 μm, and the operating wavelength range is 1210-1410 nm.

[0037] The folded modulator 4 in the embodiment of the present invention uses coplanar electrodes and utilizes the maximum electro-optic coefficient of the lithium niobate crystal to modulate the TE mode in the waveguide in the xz plane. Therefore, the single-mode single-polarization condition is a single TE mode. The single-mode single-polarization condition under different structural parameters is examined at an operating wavelength of 1310nm. The design goal of the embodiment of the present invention is to optimize the waveguide structure to have the largest possible quasi-TM mode. 00 Mode loss and TE polarization only has quasi-TE 00 Quasi-TM mode based on x-cut thin-film lithium niobate wafer xz planar waveguide at a wavelength of 1310nm 00 Leaky mode loss (dB / cm) and quasi-TE 10 The existence of the mode varies with the waveguide width and etching depth as shown in Figure 3 As shown. Figure 3 As shown in the results, the waveguide size in the embodiment of the present invention is selected as waveguide width 1μm and etching depth 0.06μm. 00 Mode transmission loss is about 332dB / cm, TE 10 The mode does not exist in the cutoff region, so there is only TE in the waveguide at this time. 00 It can transmit stably, and its calculated transmission loss is 2.6×10 -10 dB / cm, the waveguide is a single-mode single-polarization waveguide. Quasi-TM based on x-cut thin-film lithium niobate wafer xy plane waveguide at a wavelength of 1310nm 00 Leaky mode loss (dB / cm) and quasi-TE 10 The existence of the mode varies with the waveguide width and etching depth as shown in Figure 4 As shown. Figure 4 As shown in the results, the waveguide size in the embodiment of the present invention can be selected as a waveguide width of 1 μm and an etching depth of 0.06 μm. At this time, TM 00 The transmission loss of the mode due to lateral leakage is 125dB / cm, TE 10 The mode does not exist in the cutoff region, so there is only TE in the waveguide at this time. 00 It can transmit stably, and its calculated transmission loss is 3.2×10 -10 dB / cm, the waveguide is a single-mode single-polarization waveguide. The above two single-mode single-polarization waveguides constitute the waveguide polarizer in the embodiment of the present invention.

[0038] The structure of the partially variable curvature hybrid curved waveguide in an embodiment of the present invention is described in detail. The partially variable curvature hybrid curved waveguide is composed of a linear variable curvature arc waveguide and a constant curvature arc waveguide. The linear variable curvature arc waveguide reduces the insertion loss caused by the mode field mismatch between the straight waveguide and the curved waveguide at the junction, and reduces the excitation of high-order modes.

[0039] In this embodiment, the width of the 90° partially variable curvature hybrid waveguide is less than 2.5 μm, the angle of the linear variable curvature arc waveguide accounts for less than 95% of the total bending angle, and the minimum radius of the 90° partially variable curvature hybrid waveguide is greater than 80 μm. The width of the 180° partially variable curvature hybrid waveguide is less than 5 μm, the angle of the linear variable curvature arc waveguide accounts for less than 95% of the total bending angle, and the minimum radius of the 180° partially variable curvature hybrid waveguide is greater than 50 μm.

[0040] Specifically, Figure 5 (a) is a top view of a hybrid curved waveguide with a 90° partially variable curvature. The linear curvature of the curved waveguide accounts for 30% of the total bending angle. The starting and ending points of the curved waveguide are consistent with those of a constant curvature curved waveguide with a radius of 500 μm. The effective radius is 500 μm, and the minimum radius R min The value is 401.8μm. Figure 5 (b) shows the variation of the curvature of the hybrid curved waveguide with the length of the waveguide path. The curved waveguide is in the angle range of [0°, 13.5°], and the curvature linearly changes in the range of [0, 1 / R min ], in the angle range [13.5°, 76.5°], the curvature is 1 / R min , in the angle range of [76.5°, 90°], the curvature linearly changes in the range of [1 / R min , 0], maximum curvature 1 / R min 2488.8m -1 .

[0041] Four hybrid curved waveguides with 180° partially variable curvature are used inside the folded electro-optic device to achieve the folded placement of the modulation area. Figure 6 (a) is a top view of a hybrid curved waveguide with a partially variable curvature of 180°. The linear curvature of the hybrid curved waveguide accounts for 30% of the total bending angle. The starting and ending points of the hybrid curved waveguide are consistent with those of a constant curvature curved waveguide with a radius of 260 μm. The effective radius is 260 μm, and the minimum radius R min The value is 250.8μm. Figure 6 (b) shows the variation of the curvature of the hybrid curved waveguide with the length of the waveguide path. The curved waveguide is in the angle range of [0°, 27°], and the curvature linearly changes in the range of [0, 1 / R min], in the angle range [27°, 153°], the curvature is 1 / R min , in the angle range of [153°,180°], the curvature linear variation range is [1 / R min , 0], maximum curvature 1 / R min 3987.4m -1 The curvature of the linear transformation can reduce the mode field mismatch at the junction of the straight waveguide and the curved waveguide.

[0042] The structure of the folding modulator 4 is described in detail. It is a lithium niobate electro-optical folding modulator that utilizes the electro-optical properties of the lithium niobate material to achieve phase modulation, taking advantage of the maximum electro-optic coefficient of the lithium niobate crystal. An x-cut thin-film lithium niobate wafer is used, meaning the x-axis of the lithium niobate crystal is perpendicular to the plane of the thin-film lithium niobate. Waveguide cross-sections with different transmission directions in the yz plane of the thin-film lithium niobate correspond to different refractive index matrices. The total thickness of the lithium niobate film is 300 nm. The electrodes of the folding modulator 4 are horizontally designed, distributed on both sides and in the middle of the two branches of the second optical coupler, with the corresponding x-axis perpendicular to the chip plane. This forms a push-pull structure that exponentially reduces the driving voltage. The two arms 5 and 6 of the folding modulator 4 are set to a length difference of 900 μm based on the birefringence difference of the lithium niobate waveguide, thereby reducing the polarization error caused by polarization cross-coupling in the fiber optic gyroscope.

[0043] like Figure 7 As shown, the cross-sectional structure of the folded modulator 4 is, from left to right, metal electrode, waveguide, metal electrode, waveguide, and metal electrode. A 100nm-thick SiO2 layer separates the metal electrode and the lithium niobate (LiNbO3) slab to reduce metal absorption. The RF electric field distribution within the lithium niobate waveguide cross section is primarily horizontal, allowing the electrode spacing to be reduced to increase the RF electric field and waveguide quasi-TE. 00 The overlap factor between the optical mode fields is increased, thereby improving the modulation efficiency of the electro-optical folding modulator 4.

[0044] In order to improve the efficiency of electro-optical modulation and reduce the transmission loss of the waveguide mode, the embodiment of the present invention reasonably designs the electrode spacing. π The relationship between L and transmission loss as the metal spacing changes is as follows Figure 8 As shown. Figure 8 The results shown in FIG. 1 and FIG. 2 show that the embodiment of the present invention aims to reduce the loss to less than 0.1 dB / cm. In the embodiment of the present invention, the electrode spacing can be selected to be 7.5 μm. At this time, V π L is 2.57V.cm, and the waveguide transmission loss is 0.01dB / cm. The embodiment of the present invention avoids the quasi-TE in the lithium niobate waveguide by setting a reasonable electrode spacing. 00 The fundamental mode will be affected by the absorption of the metal electrode and add additional absorption loss.

[0045] The structure of the optical gyroscope integrated chip provided by an embodiment of the present invention is further described. The first fiber-lithium niobate waveguide mode converter 1, the second fiber-lithium niobate waveguide mode converter 7, the third fiber-lithium niobate waveguide mode converter 8, and the fourth fiber-lithium niobate waveguide mode converter 9 all employ an inverted taper structure to achieve mode field matching between the lithium niobate waveguide and the polarization-maintaining fiber ring at the end face. All fiber-lithium niobate waveguide mode converters are located on the same side of the chip, facilitating coupling with an external light source, detector, and fiber ring using a single fiber array (FA). The end face on this side is polished to reduce end face reflections.

[0046] The structures of the first optical coupler 2 and the second optical coupler 3 are described in detail. The first optical coupler 2 and the second optical coupler 3 are Y-type couplers and / or 1×2 multi-mode interferometer couplers.

[0047] In order to reduce the parasitic reflections generated by the device, such as Figure 9 As shown, the Y-coupler comprises a base waveguide 201, a tapered region 202, a first branch 205-1, and a second branch 205-2. The base waveguide 201 leads to the first branch 205-1 and the second branch 205-2 through two ports, respectively, via the tapered region 202. The width of the tapered region 202 varies from 1 μm to 3.5 μm according to a quadratic function. The gap between the first branch 205-1 and the second branch 205-2 gradually widens from 0.5 μm to 10 μm according to a raised cosine curve function. Furthermore, the gap between the two output ports 204-1 and 204-2 is increased to 0.5 μm. By widening the wider side 203 of the tapered region 202, the overlap integral of the modes on both sides is increased, ensuring high forward transmittance for the Y-coupler.

[0048] The structure of the 1×2 multimode interferometer in the embodiment of the present invention is as follows: Figure 10 As shown, partial etching is used to form channels 301 on both sides of the port, allowing light to leak into the plate, thereby reducing reflection. The edges of the entire plate region 302 are formed into a pointed cone structure, allowing light that leaks into the plate to escape through the pointed cone. In this embodiment, the width of the multimode region 303 is 10.2μm, and the length of the multimode region 303 is 93μm.

[0049] In order to absorb stray light, it also includes: a stray light absorber 10; the stray light absorber 10 is located on both sides of the first optical fiber-lithium niobate waveguide mode converter 1, the second optical fiber-lithium niobate waveguide mode converter 7, the third optical fiber-lithium niobate waveguide mode converter 8 and the fourth optical fiber-lithium niobate waveguide mode converter 9.

[0050] In this embodiment, the stray light absorber 10 is made of metal material. The cross-sectional view of the stray light absorber 10 is shown in FIG. Figure 11As shown in the figure, thin-film lithium niobate is etched onto the silicon dioxide substrate layer in areas on both sides of the four fiber-lithium niobate waveguide mode converters. Metal is then evaporated in these areas. When stray light from the lithium niobate waveguide slab is transmitted to the vicinity of the absorber, it is absorbed by the metal, achieving the desired absorption effect.

[0051] The lithium niobate waveguide in this embodiment of the present invention is a single-mode, single-polarization waveguide. After passing through the first 3dB optical coupler 2 and experiencing a 3dB loss, this mode of light enters the second 3dB optical coupler 3 and is split into two beams. These two beams undergo phase modulation in the two arms 5 and 6 of a folding modulator 4 before being coupled into the fiber ring via the second fiber-lithium niobate waveguide mode converter 7 and the third fiber-lithium niobate waveguide mode converter 8, respectively. After entering the fiber ring, the two beams propagate in opposite directions, clockwise and counterclockwise, respectively, before entering the other arm of the folding modulator 4. Due to the Sagnac effect of the fiber ring, when the fiber ring rotates in a plane, the two beams produce a phase difference related to the angular velocity of the rotation. Since the two beams are coherent, interference occurs when the two beams return to the second 3dB optical coupler 3 after passing through the folding modulator 4. This interference signal then returns to the first 3dB optical coupler 2 through another branch, enters the fourth fiber-lithium niobate waveguide mode converter 9, and is output along the direction of arrow 12 to the fiber array on the right side of the chip, where it is received by an external detector. When the angular velocity changes, the interference light intensity changes accordingly, and the angular velocity of the fiber ring rotation can be demodulated from this change. Since some light leaks into the waveguide slab layer during the fiber coupling, transmission, and beam combining processes, a stray light absorber 10 is provided in the lithium niobate slab layer near the first to fourth fiber-lithium niobate waveguide mode converters. By utilizing the metal's light absorption properties, this prevents stray light from freely propagating in the waveguide slab layer and entering the detector.

[0052] In summary, the embodiments of the present invention leverage the excellent electro-optical modulation properties of thin-film lithium niobate to simultaneously achieve full-chip polarization, low-loss optical transmission, beam splitting, and modulation. While maintaining the precision of the closed-loop fiber optic gyroscope, the embodiments of the present invention utilize a unique structural design to achieve a higher level of integration, lower drive voltage, and lower cost.

[0053] Any details not described in the embodiments of the present invention are well-known to those skilled in the art. Finally, it should be noted that the above embodiments are only intended to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present invention may be modified or replaced with equivalents without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or equivalents should be included in the scope of the claims of the present invention.

Claims

1. An optical gyroscope integrated chip based on a thin-film lithium niobate photonic integrated platform, characterized in that: include: a first optical fiber-lithium niobate waveguide mode converter, a first optical coupler, a second optical coupler, a folding modulator, a second optical fiber-lithium niobate waveguide mode converter, a third optical fiber-lithium niobate waveguide mode converter, and a fourth optical fiber-lithium niobate waveguide mode converter; The first end of the first optical fiber-lithium niobate waveguide mode converter is used to connect to an external light source, and the second end of the first optical fiber-lithium niobate waveguide mode converter is connected to the first branch of the first optical coupler; the base waveguide of the first optical coupler is connected to the base waveguide of the second optical coupler through two 90° partially variable curvature hybrid bending waveguides; the first branch of the second optical coupler is connected to the first end of the second optical fiber-lithium niobate waveguide mode converter, and the second branch of the second optical coupler is connected to the first end of the third optical fiber-lithium niobate waveguide mode converter; the two arms of the folding modulator are the two branches of the second optical coupler, and the two arms of the folding modulator both form a folded structure through two 180° partially variable curvature hybrid bending waveguides; the second optical fiber-lithium niobate waveguide The second end of the mode converter is connected to one end of an external polarization-maintaining fiber ring; the second end of the third optical fiber-lithium niobate waveguide mode converter is connected to the other end of the polarization-maintaining fiber ring; the second branch of the first optical coupler is connected to the first end of the fourth optical fiber-lithium niobate waveguide mode converter, and the second end of the fourth optical fiber-lithium niobate waveguide mode converter is used to connect to an external photodetector; the single TE mode lithium niobate waveguide other than the hybrid curved waveguide of the folding modulator and the optical coupler forms a waveguide polarizer; the waveguide polarizer is composed of a shallowly etched and / or narrow width lithium niobate waveguide; the partially variable curvature hybrid curved waveguide is composed of a linear variable curvature arc waveguide and a constant curvature arc waveguide; the partially variable curvature hybrid curved waveguide increases the polarization extinction ratio of the chip and filters out the quasi-TE 00 mode other than the waveguide mode.

2. The optical gyroscope integrated chip based on the thin film lithium niobate photonic integrated platform according to claim 1, characterized in that: The waveguide polarizer comprises, from top to bottom, an air layer, a low-refractive-index cover layer, a lithium niobate ridge waveguide, a SiO2 substrate layer, and a Si substrate layer. The ridge waveguide is formed by etching away part of the lithium niobate layer outside the waveguide. The refractive index of the low-refractive-index cover layer is 1-1.

7.

3. The optical gyroscope integrated chip based on the thin film lithium niobate photonic integrated platform according to claim 1 or 2, characterized in that: The waveguide polarizer has a width of less than 2.5 μm, an etching depth of less than 0.4 μm, and an operating wavelength range of 1210-1410 nm.

4. The optical gyroscope integrated chip based on thin-film lithium niobate photonic integrated platform according to claim 1, characterized in that: The width of the hybrid curved waveguide with a 90° partially variable curvature is less than 2.5 μm, the angle of the linear variable curvature arc waveguide accounts for less than 95% of the total bending angle, and the minimum radius of the hybrid curved waveguide with a 90° partially variable curvature is greater than 80 μm.

5. The optical gyroscope integrated chip based on thin film lithium niobate photonic integrated platform according to claim 1, characterized in that: The width of the 180° partially variable curvature hybrid curved waveguide is less than 5 μm, the angle of the linear variable curvature arc waveguide accounts for less than 95% of the total bending angle, and the minimum radius of the 180° partially variable curvature hybrid curved waveguide is greater than 50 μm.

6. The optical gyroscope integrated chip based on thin film lithium niobate photonic integrated platform according to claim 1, characterized in that: The folding modulator is a lithium niobate electro-optical folding modulator, which uses an x-cut thin-film lithium niobate wafer. The electrode structure of the folding modulator adopts a horizontal design and is distributed on both sides and in the middle of the two branches of the second optical coupler to form a push-pull structure.

7. The optical gyroscope integrated chip based on thin film lithium niobate photonic integrated platform according to claim 1, characterized in that: The first optical fiber-lithium niobate waveguide mode converter, the second optical fiber-lithium niobate waveguide mode converter, the third optical fiber-lithium niobate waveguide mode converter, and the fourth optical fiber-lithium niobate waveguide mode converter all adopt an inverted taper structure to achieve mode field matching between the lithium niobate waveguide and the polarization-maintaining optical fiber ring at the end face.

8. The optical gyroscope integrated chip based on thin film lithium niobate photonic integrated platform according to claim 1, characterized in that: The first optical coupler and the second optical coupler are Y-type couplers and / or 1×2 multimode interferometer couplers.

9. The optical gyroscope integrated chip based on thin film lithium niobate photonic integrated platform according to claim 8, characterized in that: The Y-type coupler includes: a base waveguide, a tapered region, a first branch, and a second branch; the base waveguide passes through the tapered region, and the first branch and the second branch are respectively led out from two ports; the width of the tapered region widens according to a quadratic function; and the gap between the first branch and the second branch gradually widens in the form of a rising cosine curve function.

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