Super-long waveguide ring structure on three-dimensional integrated chip and preparation process

Abstract

The invention belongs to the technical field of integrated optics and optical sensing, and particularly relates to a super-long waveguide ring structure on a three-dimensional integrated chip and a preparation process. The ultra-long waveguide ring structure is integrated on a single silicon-based chip and comprises a top waveguide layer 1, a plurality of middle waveguide layers 2, a bottom waveguide layer 3 and a substrate layer 4, the top waveguide layer 1, the plurality of middle waveguide layers 2, the bottom waveguide layer 3 and the substrate layer 4 are parallel to one another, and the top waveguide layer 1, the plurality of middle waveguide layers 2, the bottom waveguide layer 3 and the substrate layer 4 are sequentially stacked in the vertical direction and are symmetrical about the mid-vertical plane of the ultra-long waveguide ring structure; light is interconnected between adjacent waveguide layers in a vertical coupling mode to form an optical loop.

Description

Technical Field

[0001] The present invention belongs to the field of integrated optics and optical sensing technology, and specifically relates to an ultra-long waveguide ring structure on a three-dimensional integrated chip and a preparation process thereof. Background Art

[0002] Fiber optic gyroscopes based on the Sagnac effect are widely used as angular rate sensors for inertial navigation systems in military fields such as aviation, navigation, and land navigation systems. The discrete packaged devices of traditional fiber optic gyroscopes are fused to form an optical path, and the size and cost advantages are not obvious. It is gradually difficult to meet the requirements of future weapon systems for lightweight, low cost, and high reliability. The use of photonic integrated chips to replace traditional discrete devices to achieve monolithic integrated optical gyroscopes is an inevitable trend of development. For interferometric fiber optic gyroscopes, the theoretical accuracy of the gyroscope is positively correlated with the length of the sensitive fiber optic ring. The fiber optic rings of hundreds of meters or even thousands of meters have complex symmetrical winding processes, large volumes, and large full-temperature creep, which are the core factors that ultimately affect the size, cost, and performance of the gyroscope. However, the current single-layer sensitive ring based on planar optical waveguides cannot achieve ultra-long waveguide rings at a smaller chip size, which has become the biggest problem in achieving high-precision monolithic integrated gyroscopes. Summary of the invention

[0003] The technical problem solved by the present invention is that the current single-layer sensitive ring based on planar optical waveguide cannot realize an ultra-long waveguide ring under a smaller chip size. The present invention provides an ultra-long waveguide ring structure and a preparation process on a three-dimensional integrated chip.

[0004] The technical solution of the present invention:

[0005] In a first aspect, the present invention provides a three-dimensional integrated on-chip ultra-long waveguide ring structure, wherein the ultra-long waveguide ring structure is integrated on a monolithic silicon-based chip, and the structure comprises:

[0006] A top waveguide layer 1, a plurality of intermediate waveguide layers 2, a bottom waveguide layer 3, and a substrate layer 4; the top waveguide layer 1, the plurality of intermediate waveguide layers 2, the bottom waveguide layer 3, and the substrate layer 4 are parallel to each other, and the top waveguide layer 1, the plurality of intermediate waveguide layers 2, the bottom waveguide layer 3, and the substrate layer 4 are stacked in sequence in a vertical direction and are symmetrical about the mid-vertical plane of the ultra-long waveguide ring structure;

[0007] Light is interconnected between adjacent waveguide layers through vertical coupling to form an optical circuit.

[0008] Furthermore,

[0009] The top waveguide layer 1 includes: an input straight waveguide 1-1, a first S-bend waveguide 1-2, a first loop waveguide 1-3, a first coupling structure 1-4, a second coupling structure 1-5, a second loop waveguide 1-6, a second S-bend waveguide 1-7, and an output straight waveguide 1-8;

[0010] One end of the input straight waveguide 1-1 is flush with the end face of the silicon-based chip, and the other end is connected to one end of the first loop waveguide 1-3 through the first S-bend waveguide 1-2, and the other end of the first loop waveguide 1-3 is connected to the first coupling structure 1-4; the second coupling structure 1-5 is connected to one end of the second loop waveguide 1-6, and the other end of the second loop waveguide 1-6 is connected to the output straight waveguide 1-8 through the second S-bend waveguide 1-7.

[0011] Furthermore,

[0012] An intermediate waveguide layer 2 includes: a third coupling structure 2-1, a third loop waveguide 2-2, a fourth coupling structure 2-3, a fifth coupling structure 2-4, a fourth loop waveguide 2-5, a sixth coupling structure 2-6, a seventh coupling structure 2-7, a fifth loop waveguide 2-8, an eighth coupling structure 2-9, a ninth coupling structure 2-10, a sixth loop waveguide 2-11, and a tenth coupling structure 2-12;

[0013] The third coupling structure 2-1 is connected to the fourth coupling structure 2-3 through the third loop waveguide 2-2; the fifth coupling structure 2-4 is connected to the sixth coupling structure 2-6 through the fourth loop waveguide 2-5; the seventh coupling structure 2-7 is connected to the eighth coupling structure 2-9 through the fifth loop waveguide 2-8; the ninth coupling structure 2-10 is connected to the tenth coupling structure 2-12 through the sixth loop waveguide 2-11.

[0014] Furthermore,

[0015] The bottom waveguide layer 3 includes: an eleventh coupling structure 3-1, a seventh ring waveguide 3-2, a connecting straight waveguide 3-3, an eighth ring waveguide 3-4, and a twelfth coupling structure 3-5;

[0016] The eleventh coupling structure 3-1 is connected to one end of the connecting straight waveguide 3-3 through the seventh loop waveguide 3-2, and the other end of the connecting straight waveguide 3-3 is connected to the twelfth coupling structure 3-5 through the eighth loop waveguide 3-4.

[0017] Furthermore,

[0018] The incident light enters the first ring waveguide 1-3 through the input straight waveguide 1-1 and the first S-bend waveguide 1-2, is transmitted from the top waveguide layer to the middle waveguide layer through the vertical coupling effect of the first coupling structure 1-4 and the third coupling structure 2-1, enters the third ring waveguide 2-2, enters the fourth ring waveguide 2-5 through the vertical coupling effect of the fourth coupling structure 2-3 and the fifth coupling structure 2-4, and further enters the seventh ring waveguide 3-2 of the bottom waveguide layer through the vertical coupling effect of the sixth coupling structure 2-6 and the eleventh coupling structure 3-1;

[0019] The light continues to be transmitted along the connecting straight waveguide 3-3 and the eighth ring waveguide 3-4, and is transmitted from the bottom waveguide layer to the fifth ring waveguide 2-8 of the middle waveguide layer through the vertical coupling effect of the twelfth coupling structure 3-5 and the seventh coupling structure 2-7, and is further transmitted to the sixth ring waveguide 2-11 through the vertical coupling effect of the eighth coupling structure 2-9 and the ninth coupling structure 2-10, and further enters the second ring waveguide 1-6 of the top waveguide layer through the vertical coupling effect of the tenth coupling structure 2-12 and the second coupling structure 1-5, and is finally output through the second S-bend waveguide 1-7 and the output straight waveguide 1-8.

[0020] Furthermore,

[0021] The intermediate waveguide layer 2 can be repeatedly added, and the number of the intermediate waveguide layer 2 is N (N=0, 1, 2...), then under the same silicon-based chip area, the length of the waveguide ring on the vertical integration chip can be increased by 2N times.

[0022] Furthermore,

[0023] The input straight waveguide 1-1 and the output straight waveguide 1-8 are both arranged on the top waveguide layer 1 and are parallel to each other;

[0024] The waveguide structures of each layer in the ultra-long waveguide ring structure do not cross each other;

[0025] The spiral directions of the ring waveguides in adjacent waveguide layers are opposite, ensuring that when light is transmitted in the ultra-long waveguide ring, it is always transmitted in the same direction relative to the axial direction of the ring waveguide; the axial direction of the ring waveguide is a direction perpendicular to the plane of the waveguide layer, and the same direction is a clockwise direction or a counterclockwise direction.

[0026] Furthermore,

[0027] The input straight waveguide 1-1, the output straight waveguide 1-8, the first S-bend waveguide 1-2, the second S-bend waveguide 1-7, the connecting straight waveguide 3-3 and the ring waveguide have the same size and structure, and adopt a flat silicon nitride or silicon oxynitride waveguide structure with a cross-sectional aspect ratio>10.

[0028] Furthermore,

[0029] All coupling structures adopt the same inverted cone structure that gradually narrows linearly from wide;

[0030] The two coupling structures that produce vertical coupling should be placed in opposite directions according to the narrowing direction of the inverted cone, and the two coupling structures should be aligned in a direction perpendicular to the plane of the waveguide layer.

[0031] In a second aspect, the present invention further provides a process for preparing an ultra-long waveguide ring structure on a three-dimensional integrated chip, wherein the process is used to prepare an ultra-long waveguide ring structure as described in any one of claims 1 to 9;

[0032] The top waveguide layer 1 further includes: a first waveguide cladding 1-9, each intermediate waveguide layer 2 further includes: a second waveguide cladding 2-13, a third waveguide cladding 2-14, and the bottom waveguide layer 3 further includes: a fourth waveguide cladding 3-6, and the first waveguide cladding 1-9, the second waveguide cladding 2-13, the third waveguide cladding 2-14, and the fourth waveguide cladding 3-6 are all made of silicon dioxide material;

[0033] The preparation process is as follows:

[0034] (1) First, a silicon dioxide cladding layer is grown on the substrate layer 4 by using a plasma enhanced chemical vapor deposition (PECVD) or a low pressure chemical vapor deposition (LPCVD) process, and then the silicon dioxide cladding layer is flattened and uniformly processed by using a metal chemical polishing process (CMP);

[0035] (2) growing a silicon nitride or silicon oxynitride core layer by an LPCVD process and annealing it, and planarizing the core layer by a CMP process;

[0036] (3) Using photolithography and etching processes to complete the waveguide core structure processing;

[0037] (4) Based on step 3, a silicon dioxide cladding layer is grown by plasma enhanced chemical vapor deposition (PECVD) or low pressure chemical vapor deposition (LPCVD) process, and then the silicon dioxide cladding layer is flattened and uniformly processed by metal chemical polishing process (CMP) to obtain a bottom waveguide layer 3;

[0038] (5) Repeat the above process on the bottom waveguide layer 3 to obtain the intermediate waveguide layer 2;

[0039] (6) Repeat the above process on the middle waveguide layer 2 to obtain the top waveguide layer 1.

[0040] The three-dimensional integrated chip ultra-long waveguide ring structure proposed in the present invention adopts a vertically integrated multi-layer waveguide ring, which can double the length of the waveguide ring under the same chip size; the spatial coupling structure is used to achieve efficient coupling of adjacent layers, and the waveguide ring loss is greatly reduced in combination with the low-loss optical waveguide structure design. At the same time, the vertically integrated waveguide ring is prepared with the help of mature CMOS technology and can be mass-produced at low cost. Using the vertically integrated waveguide ring to replace the traditional optical fiber ring can greatly improve the full-temperature performance of the gyroscope, and can eliminate the optical fiber interconnection of the optical path device. The complexity of the gyroscope assembly process is significantly reduced, and the consistency and long-term reliability of the gyroscope performance are effectively improved, which provides a feasible solution for realizing a small-volume, high-precision monolithic integrated optical gyroscope, and meets the low-cost and miniaturization requirements of future weapon systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1A schematic diagram of a three-dimensional integrated on-chip ultra-long waveguide ring structure provided by an embodiment of the present invention;

[0042] Figure 2 A schematic diagram of the top waveguide layer structure provided by an embodiment of the present invention;

[0043] Figure 3 A schematic diagram of a vertical coupling structure provided by an embodiment of the present invention;

[0044] Figure 4 A simulation diagram of a vertically coupled structured light field provided by an embodiment of the present invention;

[0045] Figure 5 A schematic diagram of the cross-sectional structure of a waveguide ring provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0046] In view of the shortcomings of the fiber optic gyroscope, such as the large volume of the fiber optic ring, the complex symmetrical winding process, the high cost, and the poor full-temperature characteristics, and the current single-layer planar waveguide ring length and size cannot support the high-precision monolithic gyroscope, the present invention provides a vertically integrated on-chip ultra-long waveguide ring structure solution and preparation process.

[0047] The present invention is further described in detail with reference to the accompanying drawings.

[0048] See also Figure 1 The vertically integrated on-chip ultra-long waveguide ring of the present invention is mainly composed of a top waveguide layer 1, an intermediate waveguide layer 2, a bottom waveguide layer 3, a substrate layer 4, etc. The top waveguide layer 1, the intermediate waveguide layer 2, the bottom waveguide layer 3, and the substrate layer 4 are parallel to each other and stacked in the vertical direction. Light is interconnected between adjacent waveguide layers by vertical coupling to form a loop.

[0049] like Figure 1 and Figure 2 As shown, the top waveguide layer includes: an input straight waveguide 1-1, a first S-bend waveguide 1-2, a first loop waveguide 1-3, a first coupling structure 1-4, a second coupling structure 1-5, a second loop waveguide 1-6, a second S-bend waveguide 1-7, and an output straight waveguide 1-8; one end of the input straight waveguide 1-1 is flush with the chip end face, and the other end is connected to one end of the first loop waveguide 1-3 through the first S-bend waveguide 1-2, and the other end of the first loop waveguide 1-3 is connected to the first coupling structure 1-4; the second coupling structure 1-5 is connected to one end of the second loop waveguide 1-6, and the other end of the second loop waveguide 1-6 is connected to the output straight waveguide 1-8 through the second S-bend waveguide 1-7.

[0050] The intermediate waveguide layer includes: a third coupling structure 2-1, a third loop waveguide 2-2, a fourth coupling structure 2-3, a fifth coupling structure 2-4, a fourth loop waveguide 2-5, a sixth coupling structure 2-6, a seventh coupling structure 2-7, a fifth loop waveguide 2-8, an eighth coupling structure 2-9, a ninth coupling structure 2-10, a sixth loop waveguide 2-11, and a tenth coupling structure 2-12; the third coupling structure 2-1 is connected to the fourth coupling structure 2-3 through the third loop waveguide 2-2; the fifth coupling structure 2-4 is connected to the sixth coupling structure 2-6 through the fourth loop waveguide 2-5; the seventh coupling structure 2-7 is connected to the eighth coupling structure 2-9 through the fifth loop waveguide 2-8; the ninth coupling structure 2-10 is connected to the tenth coupling structure 2-12 through the sixth loop waveguide 2-11.

[0051] The bottom waveguide layer includes: an eleventh coupling structure 3-1, a seventh loop waveguide 3-2, a connecting straight waveguide 3-3, an eighth loop waveguide 3-4, and a twelfth coupling structure 3-5; the eleventh coupling structure 3-1 is connected to one end of the connecting straight waveguide 3-3 through the seventh loop waveguide 3-2, and the other end of the connecting straight waveguide 3-3 is connected to the twelfth coupling structure 3-5 through the eighth loop waveguide 3-4.

[0052] The substrate layer 4 is a wafer substrate made of single crystal silicon material.

[0053] The incident light enters the first ring waveguide 1-3 through the input straight waveguide 1-1 and the first S-bend waveguide 1-2, and is transmitted from the top waveguide layer to the middle waveguide layer through the vertical coupling effect of the first coupling structure 1-4 and the third coupling structure 2-1, and enters the third ring waveguide 2-2, and enters the fourth ring waveguide 2-5 through the vertical coupling effect of the fourth coupling structure 2-3 and the fifth coupling structure 2-4, and further enters the seventh ring waveguide 3-2 of the bottom waveguide layer through the vertical coupling effect of the sixth coupling structure 2-6 and the eleventh coupling structure 3-1; the light continues to connect the straight waveguides 3-3, the eighth ring waveguide 3-4 is transmitted, and through the vertical coupling effect of the twelfth coupling structure 3-5 and the seventh coupling structure 2-7, it is transmitted from the bottom waveguide layer to the fifth ring waveguide 2-8 of the middle waveguide layer, and further through the vertical coupling effect of the eighth coupling structure 2-9 and the ninth coupling structure 2-10, it is transmitted to the sixth ring waveguide 2-11, and further through the vertical coupling effect of the tenth coupling structure 2-12 and the second coupling structure 1-5, it enters the second ring waveguide 1-6 of the top waveguide layer, and is finally output through the second S-bend waveguide 1-7 and the output straight waveguide 1-8.

[0054] The vertically integrated on-chip ultra-long waveguide ring has no crossover in each layer of the waveguide structure, thus avoiding crosstalk between waveguides.

[0055] The intermediate waveguide layer 2 can be repeatedly increased periodically. The number of layers of the intermediate waveguide layer 2 is taken as N (N=0, 1, 2...). Then, under the same chip area, the length of the waveguide ring on the vertical integrated chip is increased by about 2N+1 times compared with the length of the single-layer optical waveguide ring.

[0056] The spiral directions of the waveguides in adjacent layers are opposite, ensuring that when light is transmitted in the ultra-long waveguide ring on the vertical integrated chip, it is always transmitted in the same direction clockwise or counterclockwise relative to the axial direction of the waveguide ring, which is perpendicular to the waveguide layer plane.

[0057] The ring waveguide may take a circular or rectangular structure;

[0058] The input straight waveguide 1-1, the output straight waveguide 1-8, the first S-bend waveguide 1-2, the second S-bend waveguide 1-7, the connecting straight waveguide 3-3 and the ring waveguide have the same size structure, and adopt a flat waveguide structure with a cross-sectional aspect ratio>10, which effectively reduces the waveguide transmission loss caused by rough etching. In a specific embodiment of the present invention,

[0059] like Figure 3 As shown, the first coupling structure, the second coupling structure ... the twelfth coupling structure adopt the same inverted cone structure that gradually narrows linearly from wide to narrow;

[0060] The coupling structure that produces vertical coupling should be placed in the opposite direction of the inverted cone narrowing direction, and the coupling structure should be precisely aligned in the vertical direction, such as Figure 4 As shown, by designing the facing inverted cone structure, the interlayer vertical coupling efficiency of >98% can be achieved;

[0061] like Figure 5 As shown, the core layer of the waveguide ring structure is made of silicon nitride or silicon oxynitride material, and the cladding is made of silicon dioxide material. The operating wavelength can support any band of 850nm, 1310nm or 1550nm;

[0062] The minimum bending radius of the first S-bend waveguide 1-2, the second S-bend waveguide 1-7 and the loop waveguide is greater than a certain value, so that the bending loss is less than 0.1 dB / m;

[0063] The vertically integrated on-chip ultra-long waveguide ring structure has the following manufacturing process:

[0064] (1) First, a silicon dioxide cladding layer is grown on the substrate layer 4 by using a plasma enhanced chemical vapor deposition (PECVD) or a low pressure chemical vapor deposition (LPCVD) process, and then the silicon dioxide cladding layer is flattened and uniformly processed by using a metal chemical polishing process (CMP);

[0065] (2) growing a silicon nitride or silicon oxynitride core layer by an LPCVD process and annealing it, and planarizing the core layer by a CMP process;

[0066] (3) Using photolithography and etching processes to complete the waveguide core structure processing;

[0067] (4) Based on step 3, a silicon dioxide cladding layer is grown by plasma enhanced chemical vapor deposition (PECVD) or low pressure chemical vapor deposition (LPCVD) process, and then the silicon dioxide cladding layer is flattened and uniformly processed by metal chemical polishing process (CMP) to obtain a bottom waveguide layer 3;

[0068] (5) Repeat the above process on the bottom waveguide layer 3 to obtain the intermediate waveguide layer 2;

[0069] (6) Repeat the above process on the middle waveguide layer 2 to obtain the top waveguide layer 1.

[0070] The three-dimensional integrated chip ultra-long waveguide ring structure proposed in the present invention adopts a vertically integrated multi-layer waveguide ring, which can double the length of the waveguide ring under the same chip size; the spatial coupling structure is used to achieve efficient coupling of adjacent layers, and the waveguide ring loss is greatly reduced in combination with the low-loss optical waveguide structure design. At the same time, the vertically integrated waveguide ring is prepared with the help of mature CMOS technology and can be mass-produced at low cost. Using the vertically integrated waveguide ring to replace the traditional optical fiber ring can greatly improve the full-temperature performance of the gyroscope, and can eliminate the optical fiber interconnection of the optical path device. The complexity of the gyroscope assembly process is significantly reduced, and the consistency and long-term reliability of the gyroscope performance are effectively improved, which provides a feasible solution for realizing a small-volume, high-precision monolithic integrated optical gyroscope, and meets the low-cost and miniaturization requirements of future weapon systems.

Claims

1. A three-dimensional integrated on-chip ultra-long waveguide ring structure, characterized in that: The ultra-long waveguide ring structure is integrated on a single silicon-based chip, and the structure comprises: A top waveguide layer (1), a plurality of intermediate waveguide layers (2), a bottom waveguide layer (3), and a substrate layer (4); the top waveguide layer (1), a plurality of intermediate waveguide layers (2), a bottom waveguide layer (3), and a substrate layer (4) are parallel to each other, and the top waveguide layer (1), a plurality of intermediate waveguide layers (2), a bottom waveguide layer (3), and a substrate layer (4) are stacked in sequence in a vertical direction and are symmetrical about the mid-vertical plane of the ultra-long waveguide ring structure; Light is interconnected between adjacent waveguide layers through vertical coupling to form an optical circuit.

2. The three-dimensional integrated on-chip ultra-long waveguide ring structure according to claim 1, characterized in that: The top waveguide layer (1) comprises: an input straight waveguide (1-1), a first S-bend waveguide (1-2), a first loop waveguide (1-3), a first coupling structure (1-4), a second coupling structure (1-5), a second loop waveguide (1-6), a second S-bend waveguide (1-7), and an output straight waveguide (1-8); One end of the input straight waveguide (1-1) is flush with the end surface of the silicon-based chip, and the other end is connected to one end of a first loop waveguide (1-3) through a first S-bend waveguide (1-2), and the other end of the first loop waveguide (1-3) is connected to a first coupling structure (1-4); the second coupling structure (1-5) is connected to one end of a second loop waveguide (1-6), and the other end of the second loop waveguide (1-6) is connected to an output straight waveguide (1-8) through a second S-bend waveguide (1-7).

3. The three-dimensional integrated on-chip ultra-long waveguide ring structure according to claim 2, characterized in that: An intermediate waveguide layer (2) comprises: a third coupling structure (2-1), a third loop waveguide (2-2), a fourth coupling structure (2-3), a fifth coupling structure (2-4), a fourth loop waveguide (2-5), a sixth coupling structure (2-6), a seventh coupling structure (2-7), a fifth loop waveguide (2-8), an eighth coupling structure (2-9), a ninth coupling structure (2-10), a sixth loop waveguide (2-11), and a tenth coupling structure (2-12); The third coupling structure (2-1) and the fourth coupling structure (2-3) are connected via a third loop waveguide (2-2); the fifth coupling structure (2-4) and the sixth coupling structure (2-6) are connected via a fourth loop waveguide (2-5); the seventh coupling structure (2-7) and the eighth coupling structure (2-9) are connected via a fifth loop waveguide (2-8); and the ninth coupling structure (2-10) and the tenth coupling structure (2-12) are connected via a sixth loop waveguide (2-11).

4. The three-dimensional integrated on-chip ultra-long waveguide ring structure according to claim 3, characterized in that: The bottom waveguide layer (3) comprises: an eleventh coupling structure (3-1), a seventh loop waveguide (3-2), a connecting straight waveguide (3-3), an eighth loop waveguide (3-4), and a twelfth coupling structure (3-5); The eleventh coupling structure (3-1) is connected to one end of the straight waveguide (3-3) through the seventh loop waveguide (3-2), and the other end of the straight waveguide (3-3) is connected to the twelfth coupling structure (3-5) through the eighth loop waveguide (3-4).

5. The three-dimensional integrated on-chip ultra-long waveguide ring structure according to claim 4, characterized in that: The incident light enters the first ring waveguide (1-3) through the input straight waveguide (1-1) and the first S-bend waveguide (1-2), is transmitted from the top waveguide layer to the middle waveguide layer through the vertical coupling effect of the first coupling structure (1-4) and the third coupling structure (2-1), enters the third ring waveguide (2-2), enters the fourth ring waveguide (2-5) through the vertical coupling effect of the fourth coupling structure (2-3) and the fifth coupling structure (2-4), and further enters the seventh ring waveguide (3-2) of the bottom waveguide layer through the vertical coupling effect of the sixth coupling structure (2-6) and the eleventh coupling structure (3-1); The light continues to be transmitted along the connecting straight waveguide (3-3) and the eighth ring waveguide (3-4), and is transmitted from the bottom waveguide layer to the fifth ring waveguide (2-8) of the middle waveguide layer through the vertical coupling effect of the twelfth coupling structure (3-5) and the seventh coupling structure (2-7), and is further transmitted to the sixth ring waveguide (2-11) through the vertical coupling effect of the eighth coupling structure (2-9) and the ninth coupling structure (2-10), and further enters the second ring waveguide (1-6) of the top waveguide layer through the vertical coupling effect of the tenth coupling structure (2-12) and the second coupling structure (1-5), and is finally output through the second S-bend waveguide (1-7) and the output straight waveguide (1-8).

6. The three-dimensional integrated on-chip ultra-long waveguide ring structure according to claim 3, characterized in that: The intermediate waveguide layer (2) can be repeatedly added, and the number of layers of the intermediate waveguide layer (2) is N (N=0, 1, 2...), so under the same silicon-based chip area, the length of the waveguide ring on the vertical integrated chip can be increased by 2N times.

7. The three-dimensional integrated on-chip ultra-long waveguide ring structure according to claim 1, characterized in that: The input straight waveguide (1-1) and the output straight waveguide (1-8) are both arranged on the top waveguide layer (1) and are parallel to each other; The waveguide structures of each layer in the ultra-long waveguide ring structure do not cross each other; The spiral directions of the ring waveguides in adjacent waveguide layers are opposite, ensuring that when light is transmitted in the ultra-long waveguide ring, it is always transmitted in the same direction relative to the axial direction of the ring waveguide; the axial direction of the ring waveguide is a direction perpendicular to the plane of the waveguide layer, and the same direction is a clockwise direction or a counterclockwise direction.

8. The three-dimensional integrated on-chip ultra-long waveguide ring structure according to claim 1, characterized in that: The input straight waveguide (1-1), the output straight waveguide (1-8), the first S-bend waveguide (1-2), the second S-bend waveguide (1-7), the connecting straight waveguide (3-3) and the ring waveguide have the same size structure and adopt a flat silicon nitride or silicon oxynitride waveguide structure with a cross-sectional aspect ratio of >10.

9. The three-dimensional integrated on-chip ultra-long waveguide ring structure according to claim 1, characterized in that: All coupling structures adopt the same inverted cone structure that gradually narrows linearly from wide; The two coupling structures that produce vertical coupling should be placed in opposite directions according to the narrowing direction of the inverted cone, and the two coupling structures should be aligned in a direction perpendicular to the plane of the waveguide layer.

10. A process for preparing an ultra-long waveguide ring structure on a three-dimensional integrated chip, characterized in that: The preparation process is used to prepare the ultra-long waveguide ring structure as described in any one of claims 1 to 9; The top waveguide layer (1) further comprises: a first waveguide cladding (1-9); each intermediate waveguide layer (2) further comprises: a second waveguide cladding (2-13) and a third waveguide cladding (2-14); the bottom waveguide layer (3) further comprises: a fourth waveguide cladding (3-6); and the first waveguide cladding (1-9), the second waveguide cladding (2-13), the third waveguide cladding (2-14) and the fourth waveguide cladding (3-6) are all made of silicon dioxide material; The preparation process is as follows: (1) firstly, a silicon dioxide cladding layer is grown on the substrate layer (4) by using a plasma enhanced chemical vapor deposition (PECVD) or a low pressure chemical vapor deposition (LPCVD) process, and then the silicon dioxide cladding layer is flattened and uniformly processed by using a metal chemical polishing process (CMP); (2) growing a silicon nitride or silicon oxynitride core layer by an LPCVD process and annealing it, and planarizing the core layer by a CMP process; (3) Using photolithography and etching processes to complete the waveguide core structure processing; (4) Based on (3), a silicon dioxide cladding layer is grown by a plasma enhanced chemical vapor deposition (PECVD) or a low pressure chemical vapor deposition (LPCVD) process, and then the silicon dioxide cladding layer is flattened and uniformly processed by a metal chemical polishing process (CMP) to obtain a bottom waveguide layer (3); (5) Repeating the above process on the bottom waveguide layer (3) to obtain the middle waveguide layer (2); (6) Repeat the above process on the middle waveguide layer (2) to obtain the top waveguide layer (1).

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