A silicon-based erbium-doped tantalum pentoxide micro-ring composite cavity single-mode laser and a preparation method thereof

Abstract

The application belongs to the field of integrated photonics, and discloses a silicon-based erbium-doped tantalum pentoxide micro-ring composite cavity single-mode laser and a preparation method thereof. The laser comprises a monocrystalline silicon substrate, a silicon dioxide buffer layer and an erbium-doped tantalum pentoxide composite resonant cavity embedded in the buffer layer, the composite resonant cavity is composed of a micro-ring resonator and a U-shaped waveguide through evanescent wave coupling, and the top surface is an air cladding structure. The application adopts a photonic damascene process, forms smooth inclined sidewalls through a heat reflow process, and realizes pore-free filling by combining magnetron sputtering and chemical mechanical polishing. The laser has the advantages of low transmission loss, high quality factor and high side mode suppression ratio, and can realize stable single-mode laser output in a wide temperature range.

Description

Technical Field

[0001] This invention belongs to the field of integrated photonics, specifically relating to a silicon-based erbium-doped tantalum oxide microring composite cavity single-mode laser and its fabrication method. Background Technology

[0002] In integrated photonics technology, on-chip light sources are the core components supporting various photonic applications. Their miniaturization, low loss, high energy conversion efficiency, and single-mode output stability directly determine the performance ceiling of integrated photonic systems. Silicon-based photonic platforms, with their mature large-scale manufacturing processes and high integration advantages, have become the preferred carrier for on-chip light sources. Erbium-doped tantalum oxide (Er:Ta2O5) is considered an ideal gain medium for constructing silicon-based integrated lasers due to its excellent photoluminescence properties in the 1500-1577 nm optical communication band, as well as its high refractive index (n ≈ 2.11), low nonradiative multiphonon relaxation, and good compatibility with silicon-based processes. However, existing erbium-doped tantalum oxide lasers still face multiple performance bottlenecks, severely restricting their practical applications: 1. Scattering loss due to poor process adaptability: Due to the chemical inertness of erbium-doped tantalum oxide, direct dry etching of its active thin film easily leads to severe sidewall roughness. To reduce this scattering loss, existing solutions have to adopt wide waveguide designs with large mode area (LMA), which severely limits the construction and high-density integration of compact high-Q resonant cavities; 2. Insufficient single-mode output performance: Due to the structural design of relying on a single micro-ring or straight waveguide cavity, it is impossible to achieve "narrow linewidth and high side-mode rejection ratio" single-mode output through efficient mode selection, resulting in poor mode stability; Therefore, developing an erbium-doped tantalum oxide on-chip laser that combines excellent single-mode performance, low loss, and good integration compatibility has become a key requirement for promoting the practical application of integrated photonic systems. Summary of the Invention

[0003] The purpose of this invention is to provide a silicon-based erbium-doped tantalum oxide microring composite cavity single-mode laser and its fabrication method. The aim is to solve the problem of high scattering loss caused by direct etching through innovative photonic damascus technology and composite cavity design, and to achieve low threshold, high side-mode suppression ratio, and stable single-mode laser output over a wide temperature range.

[0004] This invention is achieved through the following technical solution: This invention discloses a silicon-based erbium-doped tantalum oxide microring composite cavity single-mode laser, comprising a single-crystal silicon substrate and a silicon dioxide buffer layer stacked sequentially from bottom to top, and an erbium-doped tantalum oxide composite resonant cavity embedded inside the silicon dioxide buffer layer; the top surface of the erbium-doped tantalum oxide composite resonant cavity has no upper cladding material and has an air cladding structure; The erbium-doped tantalum oxide composite resonant cavity is composed of a microring resonator and a U-shaped waveguide. The U-shaped waveguide is coupled to the microring resonator at two symmetrical positions via evanescent waves, and a physical gap is maintained at the coupling point.

[0005] Furthermore, the width of the physical gap is 200-800 nm.

[0006] Furthermore, the waveguide cross-section of the erbium-doped tantalum oxide composite resonant cavity has an inverted trapezoidal structure that is wider at the top and narrower at the bottom, and the waveguide sidewall is a smooth inclined surface with an angle greater than 90° formed by thermal reflow treatment.

[0007] Furthermore, the angle between the smooth inclined surface and the horizontal direction is 110°.

[0008] Furthermore, the waveguide width of the microring resonator is 2-5 μm, and the diameter is 50-250 μm; the waveguide width of the U-shaped waveguide is 1-2 μm; and the thickness of the silicon dioxide buffer layer is 5-10 μm.

[0009] This invention also discloses a method for fabricating the silicon-based erbium-doped tantalum oxide microring composite cavity single-mode laser, specifically including the following steps: S1. Select a monocrystalline silicon wafer as the monocrystalline silicon substrate and grow a silicon dioxide buffer layer on its surface through a thermal oxidation process. S2. A composite structure pattern of microring resonator and U-shaped waveguide is prepared on the surface of the silicon dioxide buffer layer. The pattern is transferred by etching process to form a trench structure of predetermined depth. S3. The sample with the groove structure is subjected to thermal reflux treatment in an atmospheric environment, which causes the vertical sidewalls of the groove structure to flow viscously and form a smooth trapezoidal inclined surface. S4. Erbium-doped tantalum oxide material is deposited into the trench using a magnetron sputtering process. The erbium-doped tantalum oxide material is overgrown to a thickness greater than the depth of the trench structure to achieve complete filling without pores. S5. Remove excess erbium-doped tantalum oxide material from the outside of the trench through chemical mechanical polishing process, so that the material embedded in the silicon dioxide buffer layer forms the erbium-doped tantalum oxide composite resonant cavity composed of micro-ring resonators and U-shaped waveguides, and the surface is kept as an air cladding. S6. The polished sample is annealed in an oxygen atmosphere at a temperature of 500-700℃ for 5-15 hours to activate erbium ions and obtain the silicon-based erbium-doped tantalum oxide microring composite cavity single-mode laser.

[0010] Furthermore, in S4, the target material used in the magnetron sputtering process has a composition of Ta2O5: Er2O3 = 99:1 (wt%).

[0011] Furthermore, in S4, the deposition conditions for magnetron sputtering are limited to: substrate temperature of 100-200℃, chamber pressure of 0.2-0.3 Pa, Ar flow rate of 10-20 sccm, O2 flow rate of 5-10 sccm, and RF power of 50-100 W.

[0012] Furthermore, the trench structure formed in S2 has a depth of 400-500 nm; In S4, the erbium-doped tantalum oxide material is overgrown to a thickness of 550-700 nm.

[0013] Furthermore, in S3, the conditions for hot reflux treatment are: treatment temperature of 1000-1200℃ and time of 5-10 hours.

[0014] Compared with the prior art, the present invention has the following beneficial technical effects: This invention discloses a silicon-based erbium-doped tantalum oxide microring composite cavity single-mode laser, using a single-crystal silicon substrate as the base. A silicon dioxide buffer layer embeds the resonant cavity within it, providing optical isolation to prevent light field leakage to the silicon substrate and thus avoiding additional losses, while also providing a structural basis for subsequent planarization processes. The top surface of the resonant cavity uses an air cladding instead of an upper cladding material. Due to the significant refractive index difference between air and erbium-doped tantalum oxide, the light field is strongly confined within the waveguide core, enhancing light-matter interaction and thus helping to lower the laser threshold and improve pumping efficiency. The optical efficiency is improved; the micro-ring resonator and the U-shaped waveguide form a composite cavity, and the energy exchange of the optical field between the two is realized through evanescent wave coupling. The physical gap at the coupling point avoids the additional scattering loss caused by direct contact and ensures that the intrinsic quality factor of the micro-ring is not destroyed. The U-shaped waveguide is coupled to the micro-ring at two symmetrical positions to form a dual coupling point structure. This allows the longitudinal modes of the composite resonator to obtain the maximum gain when they simultaneously meet the resonance condition in frequency. Thus, the vernier effect is used to achieve preliminary mode selection, laying the foundation for subsequent single-mode output.

[0015] Furthermore, the width of the physical gap was limited to 200-800 nm. The evanescent wave coupling strength decreases exponentially with the gap width. Too small a gap leads to excessive coupling, significantly reducing the intrinsic quality factor of the microring resonator and increasing the laser's linewidth and threshold. Too large a gap results in weak coupling, preventing effective pump light injection from the U-shaped waveguide into the microring, and hindering laser signal coupling. The 200-800 nm gap range falls precisely within the effective range of evanescent wave coupling, ensuring sufficient coupling efficiency for pump light injection and signal extraction while avoiding excessive coupling that degrades the Q-value of the microring resonator. This allows the device to maintain low-loss resonance while achieving sufficient gain, a crucial structural guarantee for achieving low-threshold lasing.

[0016] Furthermore, the waveguide cross-section of the erbium-doped tantalum oxide composite resonator is defined as an inverted trapezoidal structure, wider at the top and narrower at the bottom, with the waveguide sidewalls being smooth inclined surfaces greater than 90° formed through thermal reflow treatment. By transforming the rough vertical sidewalls (90°) formed by etching into smooth inclined surfaces (greater than 90°) through thermal reflow treatment, the sidewall roughness introduced by dry etching is eliminated, significantly suppressing the scattering loss of light waves propagating through the sidewalls. This allows the intrinsic quality factor of the microring resonator to reach 5.03 × 10⁻⁶ within the band. 5 The transmission loss is as low as 0.73 dB / cm. On the other hand, the inverted trapezoidal opening structure, which is wider at the top and narrower at the bottom, provides a larger receiving angle during magnetron sputtering deposition, allowing sputtered particles to be uniformly deposited to the bottom of the trench. This completely avoids the pinch-off effect caused by premature closure of the top during the deposition process of traditional vertical trenches, achieving void-free dense filling. This further ensures the optical uniformity of the waveguide structure and avoids the formation of pore scattering centers.

[0017] This invention discloses a method for fabricating a silicon-based erbium-doped tantalum oxide microring composite cavity single-mode laser, comprising six key steps. S1 involves thermally oxidizing and growing a silicon dioxide buffer layer to obtain a high-quality, controllable-thickness insulating layer. S2 involves etching to form a trench structure, determining the waveguide geometry for subsequent filling. S3 involves thermal reflow treatment in an atmospheric atmosphere, transforming the vertical sidewalls into smooth, inclined surfaces through viscous flow; this step directly leads to a significant reduction in sidewall scattering loss. S4 employs magnetron sputtering to deposit erbium-doped tantalum oxide material; this process is compatible with semiconductor processes, enabling large-area uniform deposition, and overgrowth ensures complete trench filling. S5 involves chemical mechanical polishing to achieve planarization, completely embedding the resonant cavity within the buffer layer with the top surface exposed as an air cladding, providing process assurance for low-loss optical transmission and the air cladding structure. S6 involves annealing and activating erbium ions in an oxygen atmosphere, a crucial thermal treatment step to ensure erbium ions are in an optically active state. The above steps together constitute a complete photonic damascus process, avoiding the sidewall roughness problem caused by directly etching erbium-doped tantalum oxide films. This fundamentally solves the bottleneck of high scattering loss caused by dry etching of chemically inert materials in existing technologies, while also achieving compatibility with silicon-based CMOS processes. Attached Figure Description

[0018] Figure 1 This is a topological diagram of the silicon-based erbium-doped tantalum oxide microring composite cavity based on the damascus process in an embodiment of the present invention. Figure 2 This is a planar layout diagram and schematic diagram of key structural parameters of the composite resonant cavity in an embodiment of the present invention; Figure 3The transmission spectrum and quality factor (Q value) fitting curve of the erbium-doped tantalum oxide waveguide in the embodiment of the present invention are shown. Figure 4 The photoluminescence spectrum and fluorescence lifetime curve of erbium-doped tantalum oxide material under 980 nm pump are shown in Figure a; where Figure a is the photoluminescence spectrum and Figure b is the fluorescence lifetime curve. Figure 5 Figure a shows the wideband output spectrum and the magnified narrow linewidth spectrum of the single-mode laser in Embodiment 1 of the present invention; wherein, Figure a is the wideband output spectrum of the single-mode laser; and Figure b is the magnified narrow linewidth spectrum. Figure 6 This is the curve showing the relationship between the single-end on-chip output power and the coupled pump power of the laser in Embodiment 1 of the present invention. Figure 7 A diagram showing the three-dimensional evolution of the laser output spectrum and mode hopping phenomenon at different temperatures; Figure 8 This is a schematic cross-sectional view of the photonic damascus process in an embodiment of the present invention; Figure 9 These are comparison images of the trench sidewall morphology before and after hot reflow in an embodiment of the present invention; wherein Figure a shows the cross-sectional morphology of the trench waveguide before thermal reflow treatment; Figure b shows the cross-sectional morphology of the trench waveguide after thermal reflow treatment; Figure c shows a local magnified morphology of the trench sidewall before thermal reflow treatment; Figure d shows a local magnified morphology of the trench sidewall after thermal reflow treatment.

[0019] Among them, 1. silicon substrate; 2. silicon dioxide buffer layer; 3. erbium-doped tantalum oxide composite resonant cavity; 31. micro-ring resonator; 32. U-shaped waveguide. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the present invention clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention; that is, the described embodiments are only a part of the embodiments of the present invention, and not all of them.

[0021] The detailed description of the embodiments of the present invention provided in the following figures is not intended to limit the scope of the claimed invention, but merely to illustrate one selected embodiment of the invention. All other embodiments obtained by those skilled in the art based on the figures and embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0022] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0023] like Figure 1 and Figure 2As shown, this invention discloses a silicon-based erbium-doped tantalum oxide microring composite cavity single-mode laser, comprising a single-crystal silicon substrate 1 and a silicon dioxide buffer layer 2 stacked sequentially from bottom to top, and an erbium-doped tantalum oxide composite resonant cavity 3 embedded inside the silicon dioxide buffer layer 2; the top surface of the erbium-doped tantalum oxide composite resonant cavity 3 has no upper cladding material and has an air cladding structure; the erbium-doped tantalum oxide composite resonant cavity 3 is composed of a microring resonator 31 and a U-shaped waveguide 32, the U-shaped waveguide 32 being coupled to the microring resonator 31 at two symmetrical points via evanescent waves, and a physical gap is maintained at the coupling point.

[0024] Evanescent wave coupling and physical gap design: To maintain extremely low transmission loss of the microring and achieve optimal pump light injection, a precise physical gap is maintained between the U-shaped waveguide 32 and the microring resonator 31, preferably in the range of 200-800 nm.

[0025] Non-resonant pumping and gain clamping: Introducing 1480 nm pump light, at this wavelength, the system remains non-resonant due to structural parameter mismatch, making it insensitive to the spectral purity of the pump source. Once the master vernier mode oscillates in the 1550 nm band, Er... 3+ The global gain clamping effect will significantly reduce the ASE noise baseline to approximately -74 dBm.

[0026] Example 1: Fabrication of Laser Devices like Figure 8 As shown, this embodiment provides a method for fabricating a silicon-based erbium-doped tantalum oxide microring composite cavity single-mode laser, employing a photonic damascene process, including the following steps: S1. Substrate pretreatment: Select a single crystal silicon wafer as silicon substrate 1, and grow a 10 μm thick silicon dioxide buffer layer 2 on its surface by thermal oxidation. S2. Patterning of the composite resonant cavity: A pattern is fabricated on the surface of the buffer layer using electron beam lithography, and a trench structure with a depth of 450 nm is formed by inductively coupled plasma etching. The micro-ring waveguide has a width of 3 μm, the U-shaped waveguide has a width of 1 μm, and the coupling gap is 500 nm. S3. Hot reflux smoothing treatment: The sample is placed in an atmospheric tube furnace and treated at 1050℃ for 5 hours. At high temperature, viscous flow occurs on the vertical sidewalls of the groove, transforming it into a trapezoidal inclined surface with an angle of approximately 110°; S4. Gain Dielectric Deposition: Erbium-doped tantalum oxide was deposited using magnetron sputtering. The target composition was Ta₂O₅:Er₂O₃ = 99:1 (wt%). The substrate temperature was 200℃, chamber pressure was 0.3 Pa, Ar / O₂ flow rate was 20 / 5 sccm, and RF power was 100 W. To avoid planarization defects, the erbium-doped tantalum oxide was overgrown to approximately 600 nm. S5. Planarization: Excess thickness is removed through chemical mechanical polishing (CMP) to expose the upper surface of silicon dioxide, so that the waveguide material is completely flush with and embedded in the trench, with an air cladding at the top; S6. Activation Annealing: The sample is placed in an oxygen atmosphere and annealed at 600℃ for 10 hours to completely activate the erbium ions, thereby obtaining the silicon-based erbium-doped tantalum oxide microring composite cavity single-mode laser.

[0027] The laser prepared in Example 1 was optically characterized.

[0028] like Figure 4 As shown in Figure a, the photoluminescence spectrum of erbium-doped tantalum oxide material in the C+L band under 980nm excitation has a center wavelength of 1530nm.

[0029] like Figure 4 As shown in Figure b, its fluorescence lifetime is 1.89 ms under 980 nm excitation.

[0030] like Figure 3 As shown, the microring resonator 31 has an intrinsic quality factor of 5.03 × 10⁻⁶ within its absorption band (1542.45 nm). 5 The transmission loss is as low as 0.73 dB / cm, demonstrating that the thermal reflow process greatly suppresses sidewall scattering.

[0031] A 1480 nm single-mode fiber-coupled laser was used as the pump source. Figure 5 As shown in Figure a, the device exhibits single-longitudinal-mode lasing at 1556.37 nm within the 1520-1580 nm range, with a side-mode suppression ratio (SMSR) as high as 53.5 dB; Figure 5 As shown in Figure b, the full width at half maximum (FWHM) measured by the instrument is 9.5 pm.

[0032] like Figure 6 As shown, the laser threshold is 3.3 mW. When the coupled pump power reaches 29.24 mW, the single-end on-chip output power reaches 72.14 μW, and the slope efficiency is 0.3%.

[0033] Wide-temperature-range tuning and mode competition testing: With a pump power of 30 mW, the device temperature is regulated using a thermoelectric cooler (18-68℃, in 10℃ increments).

[0034] Test results are as follows Figure 7 As shown, with increasing temperature, the micro-ring envelope and the comb resonance peak of the U-shaped waveguide 32 undergo asynchronous thermal drift. Within the 18-38℃ (low temperature region) and 58-68℃ (high temperature region) ranges, the device maintains stable single-mode output (SMSR > 40 dB), and the lasing peak exhibits a continuous linear redshift driven by the thermal expansion of the tantalate matrix and thermo-optic effects. At 48℃, the thermal drift of the global vernier envelope promotes net gain equalization across different frequency bands, triggering intense mode competition, macroscopically exhibiting macroscopic mode-hopping behavior from the 1529 nm band to the 1556 nm band.

[0035] Figure 9 Figure a shows the cross-sectional morphology of the trench waveguide before thermal reflow treatment, revealing the steep sidewalls (approximately 90°) formed after inductively coupled plasma etching. Figure 9 Figure b shows the cross-sectional morphology of the trench waveguide after thermal reflow treatment (corresponding to 1050℃ and 5 hours). It shows that the vertical sidewall has undergone viscous flow and transformed into an outward inclined surface, with the sidewall tilting to a certain degree (about 110°). Figure 9 Figure c shows a local magnified morphology of the trench sidewall before the hot reflow treatment. There are obvious etching stripes and rough undulations on the sidewall surface. This rough morphology will cause strong scattering loss when light waves are transmitted through the waveguide sidewall. Figure 9 Figure d shows a magnified view of the sidewall of the trench after the hot reflow treatment, which shows the smooth transition at the corner. This proves that the viscous flow occurs uniformly throughout the entire trench cross section, without local stress concentration or abrupt changes in morphology. This avoids additional radiation loss of the optical field at the waveguide corner, significantly reduces the sidewall roughness, and results in a uniform and continuous morphology. This greatly suppresses sidewall scattering loss and forms the structural basis for achieving a high quality factor.

[0036] Example 2 The difference from Example 1 is as follows: In S2, the micro-ring waveguide has a width of 2 μm and a diameter of 50 μm; the U-shaped waveguide has a width of 1.5 μm; the coupling gap is 200 nm; and the trench depth is 400 nm. In S3, the reflux temperature is 1000℃ and the time is 10 h; In S4, erbium-doped tantalum oxide material is overgrown to 550 nm.

[0037] The remaining steps and parameters are the same as in Example 1.

[0038] Example 3 (Changes: microring diameter, waveguide width, buffer layer thickness) The difference from Example 1 is as follows: In S1, the thickness of the silica buffer layer (2) is 5 μm; In S2, the micro-ring waveguide has a width of 5 μm and a diameter of 250 μm; the U-shaped waveguide has a width of 2 μm; the coupling gap is 800 nm; and the trench depth is 500 nm. In S3, the reflux temperature is 1200℃ and the time is 5 h; In S4, erbium-doped tantalum oxide material is overgrown to 700 nm; The remaining steps and parameters are the same as in Example 1.

[0039] Example 4 (Modification: Magnetron sputtering deposition conditions) The difference from Example 1 is as follows: In S4, the magnetron sputtering deposition conditions are: substrate temperature 100℃, chamber pressure 0.2 Pa, Ar flow rate 10 sccm, O2 flow rate 5 sccm, and RF power 50 W; In S6, annealing is performed at 500℃ for 15 hours.

[0040] The remaining steps and parameters are the same as in Example 1.

[0041] Example 5 (Modification: Combination of magnetron sputtering deposition conditions) The difference from Example 1 is as follows: In S4, the magnetron sputtering deposition conditions are: substrate temperature 150℃, chamber pressure 0.25 Pa, Ar flow rate 15 sccm, O2 flow rate 10 sccm, and RF power 80 W; In S6, annealing is performed at 700℃ for 5 hours.

[0042] The remaining steps and parameters are the same as in Example 1.

[0043] Example 6 (Modification: Combination of microring diameter and waveguide width) The difference from Example 1 is as follows: In S2, the micro-ring waveguide has a width of 4 μm and a diameter of 150 μm; the U-shaped waveguide has a width of 1.2 μm; the coupling gap is 300 nm; and the trench depth is 420 nm. In S4, erbium-doped tantalum oxide material is overgrown to 580 nm; The remaining steps and parameters are the same as in Example 1.

[0044] Example 7 (Modification: Combination of microring diameter and waveguide width) The difference from Example 1 is as follows: In S2, the microring waveguide has a width of 2.5 μm and a diameter of 200 μm; the U-shaped waveguide has a width of 1.8 μm; the coupling gap is 600 nm; and the trench depth is 480 nm. In S4, erbium-doped tantalum oxide material is overgrown to 650 nm; The remaining steps and parameters are the same as in Example 1.

[0045] The present invention has the following advantages: 1. Extremely low transmission loss and high quality factor: This invention employs a photonic damascus process, using a 1050° thermal reflow treatment to transform the 90° vertical sidewalls of the pre-fabricated trench into a smooth trapezoidal inclined surface of approximately 110°. This morphological evolution not only smooths the etching roughness but also increases the receiving angle during sputtering deposition, completely avoiding the pinch-off effect and achieving void-free dense filling. The device achieves an intrinsic quality factor of 9.35 × 10⁻⁶ outside the band (1599.15 nm). 5 The quality factor reaches 5.03 × 10⁻⁶ within the band (1542.45 nm). 5 The transmission loss is as low as 0.73dB / cm.

[0046] 2. Excellent single-mode selection mechanism and high side-mode suppression ratio: A composite cavity structure combining a micro-ring resonator and a long-path U-shaped waveguide is employed, and the global vernier effect caused by structural mismatch achieves strict longitudinal mode selection. Simultaneously, combined with Er... 3+ The strong global gain clamping effect of the dielectric effectively suppresses adjacent modes and amplified spontaneous emission (ASE) baselines, resulting in a device side-mode rejection ratio (SMSR) of up to 53.5 dB and a linewidth of only 9.5 pm.

[0047] 3. Wide-temperature operating stability and tunability: Thanks to the air cladding structure, the device maintains a stable single-mode output with an SMSR > 40 dB in both the 18-38℃ and 58-68℃ ranges. Within a single steady-state range, the lasing peak exhibits a continuous linear redshift; at the envelope mismatch critical point caused by thermal drift (e.g., 48℃), it exhibits macroscopic mode-hopping behavior, demonstrating excellent wavelength tuning potential.

Claims

1. A silicon-based erbium-doped tantalum oxide microring composite cavity single-mode laser, characterized in that, It includes a single-crystal silicon substrate (1) and a silicon dioxide buffer layer (2) stacked sequentially from bottom to top, and an erbium-doped tantalum oxide composite resonant cavity (3) embedded inside the silicon dioxide buffer layer (2); the top surface of the erbium-doped tantalum oxide composite resonant cavity (3) has no upper cladding material and has an air cladding structure; The erbium-doped tantalum oxide composite resonant cavity (3) is composed of a micro-ring resonator (31) and a U-shaped waveguide (32). The U-shaped waveguide (32) is coupled to the micro-ring resonator (31) at two symmetrical positions via evanescent waves, and a physical gap is maintained at the coupling point.

2. The silicon-based erbium-doped tantalum oxide microring composite cavity single-mode laser according to claim 1, characterized in that: The width of the physical gap is 200-800 nm.

3. The silicon-based erbium-doped tantalum oxide microring composite cavity single-mode laser according to claim 1, characterized in that: The waveguide cross-section of the erbium-doped tantalum oxide composite resonant cavity (3) is an inverted trapezoidal structure with a wider top and a narrower bottom, and the waveguide sidewall is a smooth inclined surface with a slope greater than 90° formed by heat reflow treatment.

4. The silicon-based erbium-doped tantalum oxide microring composite cavity single-mode laser according to claim 3, characterized in that: The angle between the smooth inclined surface and the horizontal direction is 110°.

5. The silicon-based erbium-doped tantalum oxide microring composite cavity single-mode laser according to claim 1, characterized in that: The waveguide width of the microring resonator (31) is 2-5 μm and the diameter is 50-250 μm; the waveguide width of the U-shaped waveguide (32) is 1-2 μm; and the thickness of the silicon dioxide buffer layer (2) is 5-10 μm.

6. A method for fabricating a silicon-based erbium-doped tantalum oxide microring composite cavity single-mode laser as described in any one of claims 1-5, characterized in that, Specifically, the following steps are included: S1. Select a single crystal silicon wafer as a single crystal silicon substrate (1), and grow a silicon dioxide buffer layer on its surface through a thermal oxidation process (2). S2. A composite structure pattern of micro-ring resonator (31) and U-shaped waveguide (32) is prepared on the surface of the silicon dioxide buffer layer (2). The pattern is transferred by etching process to form a trench structure of predetermined depth. S3. The sample with the groove structure is subjected to thermal reflux treatment in an atmospheric environment, which causes the vertical sidewalls of the groove structure to flow viscously and form a smooth trapezoidal inclined surface. S4. Erbium-doped tantalum oxide material is deposited into the trench using a magnetron sputtering process. The erbium-doped tantalum oxide material is overgrown to a thickness greater than the depth of the trench structure to achieve complete filling without pores. S5. Remove excess erbium-doped tantalum oxide material outside the trench through chemical mechanical polishing process, so that the material embedded in the silicon dioxide buffer layer (2) forms the erbium-doped tantalum oxide composite resonant cavity (3) composed of micro-ring resonator (31) and U-shaped waveguide (32), and the surface is kept as an air cladding. S6. The polished sample is annealed in an oxygen atmosphere at a temperature of 500-700℃ for 5-15 hours to activate erbium ions and obtain the silicon-based erbium-doped tantalum oxide microring composite cavity single-mode laser.

7. The preparation method according to claim 6, characterized in that: In S4, the target material composition used in the magnetron sputtering process is Ta2O5: Er2O3 = 99:1 (wt%).

8. The preparation method according to claim 6, characterized in that: In S4, the deposition conditions for magnetron sputtering are limited to: substrate temperature of 100-200℃, chamber pressure of 0.2-0.3 Pa, Ar flow rate of 10-20 sccm, O2 flow rate of 5-10 sccm, and RF power of 50-100 W.

9. The preparation method according to claim 6, characterized in that: The trench structure formed in S2 has a depth of 400-500 nm; In S4, the erbium-doped tantalum oxide material is overgrown to a thickness of 550-700 nm.

10. The preparation method according to claim 6, characterized in that: In S3, the conditions for hot reflux treatment are: treatment temperature of 1000-1200℃ and time of 5-10 hours.

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