Single-mode microdisk resonator device, method of making and use thereof

Abstract

The application discloses a single-mode micro-disk resonator device and a preparation method and application thereof. The single-mode micro-disk resonator device based on amorphous gallium oxide comprises an optical coupler for coupling input and output light, a half-circular pulley type coupling waveguide structure and a gallium oxide micro-disk resonant cavity structure; the design of the half-circular pulley type coupling waveguide is adopted, the width and the bending radius of the coupling waveguide are designed so that the phase matching condition is met between the coupling waveguide and the micro-disk, the light in different radial modes of the micro-disk is selected, and finally the single-mode output is realized; meanwhile, by adjusting and controlling the proportion of the etching mixed gas, the etching rate of the amorphous gallium oxide coupling waveguide can be higher, the sidewall angle of the coupling waveguide can be improved, and the surface morphology of the gallium oxide coupling waveguide can be improved; the preparation method of the amorphous gallium oxide coupling waveguide is developed for the first time, and the application has important application value in the field of integrated photon chip technology.

Description

Technical Field

[0001] This invention specifically relates to a single-mode microdisk resonant device, its fabrication method, and its application, belonging to the field of integrated photonic chip technology. Background Technology

[0002] In recent years, the rapid development of emerging technologies such as 5G, artificial intelligence, cloud computing, and the Internet of Things has posed significant technical challenges to current signal processing speed, transmission bandwidth, and chip power consumption. However, various optoelectronic chips and coupled waveguide devices, as carriers for communication signal transmission and processing, will face even higher performance requirements. Traditional silicon-based optoelectronic chips face performance bottlenecks and limitations in active chips, thus driving the development of numerous novel optoelectronic materials and devices, such as lithium niobate, silicon nitride, silicon carbide, III-V semiconductors, gallium nitride, tantalum oxide, and gallium oxide. Integrated optoelectronic chips developed based on these material platforms each have their own advantages and suitable application scenarios.

[0003] Gallium oxide (Ga2O3), as a representative of fourth-generation semiconductor materials, has gained widespread attention in fields such as power devices for new energy vehicles, radio frequency chips, artificial intelligence, and high-speed optical communication, compared to third-generation semiconductors, due to its advantages such as better control of carrier concentration, high thermal stability, ultra-wide bandgap (4.2-4.9 eV), solar blind wavelength (200-300 nm), ultra-high critical breakdown field strength (8 MV / cm), ultra-strong transparent conductivity, and lower power consumption (loss is 1 / 3000 of silicon under the same conditions). It is expected to enable my country to achieve a "leapfrog development" in the semiconductor chip field within the next decade. Therefore, the development of integrated optoelectronic devices and coupled waveguide processes based on Ga2O3 has become a key link in high-performance chip development.

[0004] Currently, Ga2O3 devices used in the communication field are all based on crystal structures. Their fabrication involves complex processes such as epitaxial growth of high-quality single-crystal materials, etching problems caused by different crystal phases, and bonding with silicon-based semiconductor devices, which increases the fabrication cost of Ga2O3 coupled waveguide devices. However, amorphous Ga2O3 materials also possess most of the characteristics of crystalline Ga2O3. Moreover, the fabrication technology of amorphous Ga2O3 thin film materials is simple, and they can be easily grown on any substrate using sputtering and evaporation methods. They are also easy to integrate heterogeneously with silicon-based chips, and are widely used in the current photonic chip technology field. For example, direct-coupled waveguides, microdisks, microrings, and MZI structures are all core components in photonic chips. However, there are very few reports on photonic devices developed based on amorphous Ga2O3 and their fabrication methods. Summary of the Invention

[0005] The main objective of this invention is to provide a single-mode microdisk resonant device, its fabrication method, and its application, thereby overcoming the shortcomings of the prior art.

[0006] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0007] The first aspect of this invention provides a single-mode microdisk resonant device, comprising:

[0008] A first optical coupler, a coupling waveguide, a second optical coupler, and a microdisk resonant cavity are disposed on the same working plane. The coupling waveguide includes a first waveguide, a second waveguide, and a third waveguide connected in sequence. The first optical coupler and the second optical coupler are respectively connected to the first waveguide and the third waveguide. The second waveguide is spaced on one side of the microdisk resonant cavity and has an arc-shaped structure surrounding the microdisk resonant cavity.

[0009] The coupling coefficient κ between the coupled waveguide and the microdisk resonant cavity is:

[0010]

[0011] Where, n wg R wg =n disk R disk θ0 is the coupling angle of the second waveguide around the microdisk resonant cavity, θ is a variable representing the range of the coupling angle, from -θ0 to θ0, i represents the direction of integration, S is a constant determined by the dimensions of the coupling waveguide, and E disk and E wg Let represent the normalized electric field intensity in the microdisk resonant cavity and the coupled waveguide, respectively; ε(r,z) represent the dielectric constant corresponding to the mode perturbation at different positions in the microdisk resonant cavity when coupling occurs; ε0 represents the dielectric constant corresponding to the microdisk resonant cavity without coupling; κ0=2π / λ0, where κ0 is the wave number in free space, λ0 is the input wavelength, m is the azimuth mode order of the microdisk resonant cavity, and n wg R is the effective refractive index of the coupled waveguide. wg Let n be the radius of curvature of the second waveguide. disk R is the effective refractive index of the microdisk resonant cavity. disk R is the radius of the microdisk resonant cavity. wg =R disk +g+w / 2, where g is the coupling distance between the second waveguide and the microdisk resonant cavity, and w is the width of the second waveguide.

[0012] A second aspect of this invention provides a method for fabricating the single-mode microdisk resonant device, comprising:

[0013] An amorphous gallium oxide thin film is formed on an optical substrate, wherein the refractive index of the optical substrate is lower than the refractive index of the amorphous gallium oxide thin film;

[0014] A patterned mask is deposited on the amorphous gallium oxide thin film. The amorphous gallium oxide thin film not covered by the mask is etched using a plasma dry etching process. The etching gas used in the plasma dry etching process is a mixture of BCl3 and Ar, thereby forming the first optical coupler, the coupling waveguide, the second optical coupler, and the micro disk resonant cavity. The sidewalls of the coupling waveguide and the micro disk resonant cavity are made smooth and perpendicular to the working surface of the optical substrate.

[0015] The coupling waveguide includes a first waveguide, a second waveguide, and a third waveguide connected in sequence. The first optical coupler and the second optical coupler are respectively connected to the first waveguide and the third waveguide. The second waveguide is spaced out on one side of the microdisk resonant cavity and has an arc-shaped structure surrounding the microdisk resonant cavity.

[0016] The coupling coefficient κ between the coupled waveguide and the microdisk resonant cavity is:

[0017]

[0018] Where, n wg R wg =n disk R disk θ0 is the coupling angle of the second waveguide around the microdisk resonant cavity, θ is a variable representing the range of the coupling angle, from -θ0 to θ0, i represents the direction of integration, S is a constant determined by the dimensions of the coupling waveguide, and E disk and E wg Let represent the normalized electric field intensity in the microdisk resonant cavity and the coupled waveguide, respectively; ε(r,z) represent the dielectric constant corresponding to the mode perturbation at different positions in the microdisk resonant cavity when coupling occurs; ε0 represents the dielectric constant corresponding to the microdisk resonant cavity without coupling; κ0=2π / λ0, where κ0 is the wave number in free space, λ0 is the input wavelength, m is the azimuth mode order of the microdisk resonant cavity, and n wg R is the effective refractive index of the coupled waveguide. wg Let n be the radius of curvature of the second waveguide. disk R is the effective refractive index of the microdisk resonant cavity. disk R is the radius of the microdisk resonant cavity. wg =R disk +g+w / 2, where g is the coupling distance between the second waveguide and the microdisk resonant cavity, and w is the width of the second waveguide.

[0019] A third aspect of the present invention is an optoelectronic device comprising the single-mode microdisk resonator described above.

[0020] Compared with the prior art, the advantages of the present invention include:

[0021] (1) This invention realizes a gallium oxide resonator structure with single-mode output by adjusting the phase matching condition between the coupled waveguide and the micro disk resonator. It can achieve the same function as the micro ring resonator and realize a single mode selection. However, the micro ring resonator will interact with light on both sides, which increases light scattering and reduces the transmission performance of the entire device. The micro disk resonator will only scatter light on one side, so under the same manufacturing conditions, the optical performance will be better.

[0022] (2) Most existing microdisk resonant cavities use external single-mode optical fibers for coupling, which generates multiple higher-order modes during the coupling process. At the same time, they cannot be integrated with on-chip optical chips (i.e., silicon-based optoelectronic chips). In this invention, the coupling waveguide and the microdisk resonant cavity are fabricated simultaneously, which can achieve efficient single-mode transmission and increase the integration of on-chip photonic devices (i.e., silicon-based optoelectronic devices), thereby reducing the footprint and power consumption of the chip system using this invention (e.g., the large-scale on-chip silicon photonic integrated chip system formed by the application of this invention on silicon photonic chips).

[0023] (3) This invention obtains a coupled waveguide and micro disk resonant cavity with vertical and smooth sidewalls by optimizing the ratio of BCl3 and Ar gases;

[0024] (4) Previous technologies have been used to prepare optoelectronic devices in single-crystal Ga2O3 thin films. This invention is the first to develop a complete coupled waveguide preparation process in amorphous Ga2O3 thin films, and also provides potential application value for amorphous Ga2O3 coupled waveguides in current photonic chip technology. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of a single-mode microdisk resonator based on amorphous gallium oxide in Embodiment 1 of the present invention;

[0026] Figure 2 This is a cross-sectional view of a single-mode microdisk resonant device based on amorphous gallium oxide in Embodiment 1 of the present invention;

[0027] Figure 3 This is a top view of a single-mode microdisk resonator based on amorphous gallium oxide in Embodiment 1 of the present invention;

[0028] Figure 4a , Figure 4b These are the electric field distribution diagrams of TE mode and TM mode in a single-mode microdisk resonator based on amorphous gallium oxide in Embodiment 1 of the present invention.

[0029] Figure 5 This is a flowchart illustrating the fabrication process of a single-mode microdisk resonant device based on amorphous gallium oxide in Embodiment 1 of the present invention.

[0030] Figure 6 This is a cross-sectional SEM image of a single-mode microdisk resonator based on amorphous gallium oxide in Embodiment 1 of the present invention;

[0031] Figure 7 This describes the relationship between the etching rate and RF power of an amorphous gallium oxide thin film in Embodiment 1 of the present invention.

[0032] Figure 8 This describes the relationship between the etching rate of an amorphous gallium oxide thin film and the flow rate of BCl3 gas in Embodiment 1 of the present invention. Detailed Implementation

[0033] In view of the shortcomings of the prior art, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention. The following will further explain and illustrate this technical solution, its implementation process, and its principles.

[0034] This invention proposes a single-mode microdisk resonator based on amorphous gallium oxide (Ga2O3) and its fabrication method. Compared with conventional microdisk resonators, which mostly use fiber coupling or single-point coupling waveguide coupling, multimode resonance spectra are inevitable, reducing the working efficiency of microdisks in applications such as on-chip light sources and filters. This invention designs the coupling waveguide as a pulley structure, which can increase the fabrication tolerance of the coupling region and achieve the phase matching condition of single-mode coupling, thus realizing the single-mode resonance microdisk resonator structure. At the same time, it presents for the first time a fabrication method of single-mode microdisk resonator based on amorphous gallium oxide, which mainly obtains a single-mode microdisk resonator with collimated and smooth sidewalls by controlling the dynamic balance of gas flow rate and ratio and combining it with substrate heating.

[0035] The first aspect of this invention provides a single-mode microdisk resonant device, comprising:

[0036] A first optical coupler, a coupling waveguide, a second optical coupler, and a microdisk resonant cavity are disposed on the same working plane. The coupling waveguide includes a first waveguide, a second waveguide, and a third waveguide connected in sequence. The first optical coupler and the second optical coupler are respectively connected to the first waveguide and the third waveguide. The second waveguide is spaced on one side of the microdisk resonant cavity and has an arc-shaped structure surrounding the microdisk resonant cavity.

[0037] The coupling coefficient κ between the coupled waveguide and the microdisk resonant cavity is:

[0038]

[0039] Where, n wg R wg =n disk R disk θ0 is the coupling angle of the second waveguide around the microdisk resonator, θ is a variable representing the range of the coupling angle, from -θ0 to θ0, i represents the direction of integration, S is a constant determined by the size of the coupling waveguide, and S mainly corresponds to the change in mode perturbation in the microdisk resonator introduced by the coupling between the coupling waveguide and the microdisk resonator. For a given coupling condition and microdisk size, the value of S is fixed, E disk and E wg Let represent the normalized electric field intensity in the microdisk resonant cavity and the coupled waveguide, respectively; ε(r,z) represent the dielectric constant corresponding to the mode perturbation at different positions in the microdisk resonant cavity when coupling occurs; ε0 represents the dielectric constant corresponding to the microdisk resonant cavity without coupling; κ0=2π / λ0, where κ0 is the wave number in free space, λ0 is the input wavelength, m is the azimuth mode order of the microdisk resonant cavity, and n wg R is the effective refractive index of the coupled waveguide. wg Let n be the radius of curvature of the second waveguide. disk R is the effective refractive index of the microdisk resonant cavity. disk R is the radius of the microdisk resonant cavity. wg =R disk +g+w / 2, where g is the coupling distance between the second waveguide and the microdisk resonant cavity, and w is the width of the second waveguide.

[0040] Furthermore, the phase mismatch between the coupled waveguide and the microdisk resonant cavity is (κ0n) wg R wg -m)θ0, which makes the coupling waveguide in this invention more difficult to couple compared to a single-point coupled waveguide, if the phase matching condition κ0n is satisfied. wg R wg =m, and the coupling coefficient is a linear function of the coupling length, i.e., proportional to θ0. The phase matching condition is highly dependent on the radial modes excited within the microdisk resonant cavity, and the effective refractive index of each radial mode is n. disk ≡m / κ0R disk Therefore, when n wg R wg =n disk R disk Only when the phase matching condition is met can the width, bending radius and radius of the microdisk resonator be selected according to the effective refractive index of different modes under the phase matching condition, so as to further enable the microdisk resonator to couple a single-mode optical field, thereby realizing a microdisk resonator device with single-mode optical field output.

[0041] Furthermore, both the first optical coupler and the second optical coupler are one of the following structures: a focused Bragg grating, a subwavelength Bragg grating, and an inverted conical coupler.

[0042] Furthermore, the height of the focusing Bragg grating is 300nm to 600nm.

[0043] Furthermore, the focusing Bragg grating corresponds to a TE mode polarization grating with a period of 1.1 μm to 1.3 μm, a duty cycle of 0.5 to 0.7, and a coupling efficiency of 25% to 40%.

[0044] Furthermore, the microdisk resonant cavity has a circular structure, and the second waveguide has an arc-shaped structure.

[0045] Furthermore, the second waveguide has a semi-circular structure.

[0046] Furthermore, the coupling spacing g between the second waveguide and the microdisk resonant cavity is equal.

[0047] Furthermore, the straight-line width of the second waveguide is 700nm to 1200nm, and the radius of curvature R of the second waveguide is... wg The radius R of the microdisk resonant cavity is 40μm to 60μm. disk The coupling distance g between the second waveguide and the microdisk resonant cavity is 35μm to 55μm, and the coupling distance g between the second waveguide and the microdisk resonant cavity is 500nm to 900nm.

[0048] Furthermore, the coupled waveguide is a pulley-type coupled waveguide.

[0049] Furthermore, the first optical coupler, the coupling waveguide, the second optical coupler, and the microdisk resonant cavity are made of the same material.

[0050] Furthermore, the first optical coupler, the coupling waveguide, the second optical coupler, and the microdisk resonant cavity are integrally formed.

[0051] Furthermore, the first optical coupler, the coupling waveguide, the second optical coupler, and the microdisk resonant cavity are integrally formed from an amorphous gallium oxide thin film.

[0052] Furthermore, at least the sidewalls of the coupling waveguide and the microdisk resonator are perpendicular to the working surface, and the sidewalls of the coupling waveguide are smooth. This reduces the coupling loss of the single-mode microdisk resonator and improves its quality factor. In nonlinear optical applications, waveguide dispersion can be flexibly controlled by changing the dimensions of the coupling waveguide and the microdisk resonator.

[0053] Specifically, the design of having the sidewalls of the coupling waveguide and the microdisk resonator perpendicular to the working surface and the sidewalls of the coupling waveguide being smooth has at least the following advantages: First, in nonlinear optics applications, the dispersion of a single-mode microdisk resonator can be precisely controlled by adjusting the size of the coupling waveguide and the microdisk resonator; second, in on-chip nonlinear light source applications, the pump threshold of the device can be reduced, thus reducing power consumption.

[0054] In a more specific implementation, the single-mode microdisk resonator further includes: an optical substrate, wherein the first optical coupler, the coupling waveguide, the second optical coupler, and the microdisk resonator cavity are disposed on the optical substrate, and the working surface is the surface of the optical substrate.

[0055] Furthermore, the refractive index of the material forming the optical substrate is lower than the refractive index of the material forming the first optical coupler, the coupling waveguide, the second optical coupler, and the microdisk resonant cavity.

[0056] Furthermore, the optical substrate includes a substrate and a thermally oxidized silicon layer stacked on the substrate, the working surface being the surface of the thermally oxidized silicon layer facing away from the substrate, and the substrate being made of at least one of silicon wafer, sapphire, calcium oxide, and magnesium oxide.

[0057] Furthermore, the thickness of the optical substrate is 300μm to 500μm.

[0058] A second aspect of this invention provides a method for fabricating the single-mode microdisk resonant device, comprising:

[0059] An amorphous gallium oxide thin film is formed on an optical substrate, wherein the refractive index of the optical substrate is lower than the refractive index of the amorphous gallium oxide thin film;

[0060] A patterned mask is deposited on the amorphous gallium oxide thin film. The amorphous gallium oxide thin film not covered by the mask is etched using a plasma dry etching process. The etching gas used in the plasma dry etching process is a mixture of BCl3 and Ar, thereby forming the first optical coupler, the coupling waveguide, the second optical coupler, and the micro disk resonant cavity. The sidewalls of the coupling waveguide and the micro disk resonant cavity are made smooth and perpendicular to the working surface of the optical substrate.

[0061] The coupling waveguide includes a first waveguide, a second waveguide, and a third waveguide connected in sequence. The first optical coupler and the second optical coupler are respectively connected to the first waveguide and the third waveguide. The second waveguide is spaced out on one side of the microdisk resonant cavity and has an arc-shaped structure surrounding the microdisk resonant cavity.

[0062] The coupling coefficient κ between the coupled waveguide and the microdisk resonant cavity is:

[0063]

[0064] Where, n wg R wg =n disk R disk θ0 is the coupling angle of the second waveguide around the microdisk resonator, θ is a variable representing the range of the coupling angle, from -θ0 to θ0, i represents the direction of integration, S is a constant determined by the size of the coupling waveguide, and S mainly corresponds to the change in mode perturbation in the microdisk resonator introduced by the coupling between the coupling waveguide and the microdisk resonator. For a given coupling condition and microdisk size, the value of S is fixed, E disk and E wg Let represent the normalized electric field intensity in the microdisk resonant cavity and the coupled waveguide, respectively; ε(r,z) represent the dielectric constant corresponding to the mode perturbation at different positions in the microdisk resonant cavity when coupling occurs; ε0 represents the dielectric constant corresponding to the microdisk resonant cavity without coupling; κ0=2π / λ0, where κ0 is the wave number in free space, λ0 is the input wavelength, m is the azimuth mode order of the microdisk resonant cavity, and n wg R is the effective refractive index of the coupled waveguide. wg Let n be the radius of curvature of the second waveguide. disk R is the effective refractive index of the microdisk resonant cavity. disk R is the radius of the microdisk resonant cavity. wg =R disk +g+w / 2, where g is the coupling distance between the second waveguide and the microdisk resonant cavity, and w is the width of the second waveguide.

[0065] Furthermore, the volume ratio of BCl3 to Ar in the etching gas is (20-50):(5-20).

[0066] Furthermore, during plasma dry etching of amorphous gallium oxide thin films, the gas flow rate of BCl3 is 20 sccm to 50 sccm, the gas flow rate of Ar is 2 sccm to 20 sccm, the power of RF is 50 W to 300 W, the power of ICP is 200 W to 1000 W, and the pressure of the etching chamber is 5 mTorr to 15 mTorr.

[0067] Specifically, amorphous gallium oxide thin films lack the fixed crystal orientation of crystalline thin films. During etching, the isotropic etching rate and the formation rate of byproducts need to be dynamically balanced; otherwise, difficult-to-remove residues will form on the surface of the single-mode microdisk resonator, resulting in a rough surface. This invention controls the generation of BCl3 in the plasma by adjusting parameters such as the ratio and flow rate of the BCl3 / Ar mixed gas. 2+ The ion rate is controlled, and oxygen is then removed from Ga2O3 to form volatile B3Cl3O3. Simultaneously, by combining substrate heating, a dynamic balance is achieved between the formation rates of the etching products and the etch passivation layer, thus obtaining a smooth-morphological structure.

[0068] In a more specific implementation, during the etching process of the amorphous gallium oxide thin film not covered by the mask using plasma dry etching, the temperature of the optical substrate is maintained at 80°C to 120°C. The main purpose is to bring the surface temperature of the optical substrate to the boiling point of the etching products. This allows the products generated during the etching process to be quickly pumped away by a mechanical pump, making them less likely to adhere to the device surface, which would otherwise affect the etching rate and the morphology of the device.

[0069] In a more specific implementation, the method for fabricating the single-mode microdisk resonator further includes: first annealing the amorphous gallium oxide film at 500℃~700℃ in an oxygen atmosphere, and then etching the amorphous gallium oxide film. Through annealing, the gallium element in the amorphous gallium oxide film can be more fully oxidized, resulting in better film quality and more stable optical performance.

[0070] In a more specific implementation, a method for fabricating a single-mode microdisk resonator based on amorphous gallium oxide may include the following steps:

[0071] Provide an optical substrate, which may be one of a silicon wafer with a silicon dioxide cladding, sapphire, magnesium oxide or calcium oxide substrate;

[0072] An amorphous gallium oxide thin film with a thickness of 200 nm to 600 nm was grown on an optical substrate using ion beam evaporation.

[0073] A mask layer is grown on a gallium oxide thin film using plasma-enhanced chemical vapor deposition (PECVD). The mask layer can be made of SiN, SiO2, or a metal mask. The thickness of the SiO2 mask layer can be 0.6 μm to 1 μm.

[0074] UV photoresist is spin-coated onto the mask layer. The UV photoresist includes positive photoresist and can be AZ5214 with a thickness of 1μm to 1.5μm.

[0075] The pattern is transferred onto the ultraviolet photoresist using ultraviolet exposure and development techniques.

[0076] The mask layer is fully etched using plasma dry etching technology to further transfer the pattern on the photoresist onto the mask layer to serve as a hard mask. At the same time, the temperature of the optical substrate is maintained at 80°C to 120°C.

[0077] N-methylpyrrolidone (NMP) and oxygen plasma were used to remove residual photoresist from the surface of the hard mask after etching.

[0078] The gallium oxide thin film is annealed in an oxygen atmosphere at a temperature of 500℃~700℃. The gallium oxide thin film is then etched again using an ICP-RIE machine and substrate heating to transfer the pattern on the hard mask onto the gallium oxide thin film, forming an optically coupled waveguide structure.

[0079] The gallium oxide optically coupled waveguide structure containing a hard mask is immersed in BOE solution to remove the hard mask, and finally a complete amorphous gallium oxide coupled waveguide device is obtained.

[0080] Furthermore, in the fabrication process of the amorphous gallium oxide coupled waveguide, all thin film substrates include substrate cleaning and baking steps before spin coating with photoresist.

[0081] Furthermore, in the fabrication process of the amorphous gallium oxide coupled waveguide, the photoresist needs to undergo pre-baking and post-baking steps before exposure and after development.

[0082] A third aspect of the present invention is an optoelectronic device comprising the single-mode microdisk resonator described above.

[0083] The following will further explain the technical solution, its implementation process and principle in conjunction with the accompanying drawings and specific implementation examples. Unless otherwise specified, the etching equipment and other equipment used in the embodiments of the present invention are known in the art.

[0084] Example 1

[0085] This embodiment 1 provides a single-mode microdisk resonator device (also known as a single-mode microdisk resonator device, etc.) based on amorphous gallium oxide. A coupling waveguide and a microdisk resonator are simultaneously fabricated on an amorphous gallium oxide thin film. The coupling waveguide is designed as a semi-circular pulley structure. The phase matching condition between the coupling waveguide and the microdisk resonator is strictly controlled, enabling the single-mode microdisk resonator device to achieve single selection of optical field modes. By adjusting the width and radius of the coupling waveguide and the radius of the microdisk resonator, the single-mode output of the single-mode microdisk resonator device can be achieved. At the same time, compared with the conventional single-mode fiber coupling, this structure is more conducive to the integration of current optical chips, reducing the chip area and power consumption.

[0086] Please see Figure 1 As shown, this embodiment of a single-mode microdisk resonator based on amorphous gallium oxide includes an optical substrate 1, a silicon dioxide layer 2, a first grating coupler 3 for coupling the light field into the coupling waveguide, an amorphous gallium oxide microdisk resonator cavity (hereinafter referred to as the microdisk resonator cavity) 4, a pulley-type gallium oxide coupling waveguide (hereinafter referred to as the coupling waveguide) 5, and a second grating coupler 7 for outputting the resonated light. The pulley-type gallium oxide coupling waveguide 5 and the amorphous gallium oxide microdisk resonator cavity 4 have a coupling spacing 6. Specifically, the optical substrate 1 is a silicon wafer, the silicon dioxide layer 2 is deposited on the optical substrate 1 to form a low refractive index lower cladding layer, an amorphous gallium oxide thin film is deposited on the silicon dioxide layer 2, and the first grating coupler 3, the amorphous gallium oxide microdisk resonator cavity 4, the pulley-type gallium oxide coupling waveguide 5, and the second grating coupler 7 are fabricated using micro-nano fabrication technology.

[0087] The pulley-type gallium oxide coupling waveguide 5 includes a first waveguide, a second waveguide, and a third waveguide connected in sequence. The first optical coupler 3 and the second optical coupler 7 are respectively connected to the first waveguide and the third waveguide. The second waveguide is spaced on one side of the amorphous gallium oxide microdisk resonant cavity 4, and the second waveguide is an arc-shaped structure surrounding the amorphous gallium oxide microdisk resonant cavity.

[0088] The coupling coefficient κ between the pulley-type gallium oxide coupled waveguide 5 and the amorphous gallium oxide microdisk resonant cavity 4 is:

[0089]

[0090] Where, n wg R wg =n disk R diskθ0 is the coupling angle of the second waveguide around the microdisk resonator, θ is a variable representing the range of the coupling angle, from -θ0 to θ0, i represents the direction of integration, S is a constant determined by the size of the coupling waveguide, and S mainly corresponds to the change in mode perturbation in the microdisk resonator introduced by the coupling between the coupling waveguide and the microdisk resonator. For a given coupling condition and microdisk size, the value of S is fixed, E disk and E wg Let represent the normalized electric field intensity in the microdisk resonant cavity and the coupled waveguide, respectively; ε(r,z) represent the dielectric constant corresponding to the mode perturbation at different positions in the microdisk resonant cavity when coupling occurs; ε0 represents the dielectric constant corresponding to the microdisk resonant cavity without coupling; κ0=2π / λ0, where κ0 is the wave number in free space, λ0 is the input wavelength, m is the azimuth mode order of the microdisk resonant cavity, and n wg R is the effective refractive index of the coupled waveguide. wg Let n be the radius of curvature of the second waveguide. disk R is the effective refractive index of the microdisk resonant cavity. disk R is the radius of the microdisk resonant cavity. wg =R disk +g+w / 2, where g is the coupling distance between the second waveguide and the microdisk resonant cavity, and w is the width of the second waveguide.

[0091] The principle behind the selection of resonant optical field modes by this single-mode microdisk resonator during operation is as follows: the coupling between the coupled waveguide and the microdisk resonator needs to meet stricter phase matching conditions. Multiple radial modes will have resonance peaks within the microdisk resonator. When the product of the effective refractive index of a specific radial mode and the bending radius of the coupled waveguide is equal to the product of the effective refractive index of the microdisk resonator and the corresponding radius, a better phase matching condition can be achieved. This ensures that the optical field of this specific radial mode in the microdisk is coupled and has a uniform free spectral range (FSR), thus realizing the output of a single-mode optical field. During this process, the width and bending radius of the coupled waveguide can be adjusted to select a specific radial mode.

[0092] See Figure 2 As shown in the figure, this embodiment provides a cross-sectional view of a single-mode microdisk resonator based on amorphous gallium oxide, wherein the thickness of the optical substrate 1 is 0.5mm-1mm, the thickness of the silicon dioxide layer 2 is 2μm-10μm, and the thickness of the amorphous gallium oxide thin film is 300nm-600nm.

[0093] See Figure 3 As shown, Figure 3This is a top view of a single-mode microdisk resonator based on amorphous gallium oxide. Here, both the first grating coupler 3 and the second grating coupler 7 are TE-mode polarization-focusing Bragg grating couplers with a grating period of 1.1-1.3 μm, a duty cycle of 0.5-0.7, a grating coupling efficiency of 25-40%, and a total etching depth of 300-600 nm. The pulley-type gallium oxide coupling waveguide 5 has a width of 700-1200 nm and a bending radius of 40-60 μm, corresponding to a radius of 35-55 μm for the amorphous gallium oxide microdisk resonator 4. The coupling spacing 6 is 500-900 nm. The coupling waveguide dimensions can be designed according to phase matching conditions to achieve single-mode output by enabling single-mode selection.

[0094] See Figure 4a , Figure 4b As shown, the single-mode microdisk resonator described in Embodiment 1 of this invention was simulated using Mode Solution software in TE mode at a wavelength of 1550nm. Figure 4a ) and TM mode ( Figure 4b Simulations were performed, and it can be seen that most of the electric field is confined to the central region of the pulley-type gallium oxide coupled waveguide 5, which fully demonstrates that the amorphous gallium oxide coupled waveguide prepared by the method of the present invention has a good ability to confine light in the communication band.

[0095] This embodiment 1 provides a fabrication process for a single-mode microdisk resonator based on amorphous gallium oxide. For the first time, a coupled waveguide with vertical and smooth sidewalls was obtained on an amorphous gallium oxide thin film by dry etching using a mixture of BCl3 and Ar gases.

[0096] See Figure 5 As shown, a fabrication process for a single-mode microdisk resonator based on amorphous gallium oxide includes the following steps:

[0097] Step 1) Deposit a 500 nm thick amorphous gallium oxide thin film on an optical substrate using magnetron sputtering or ion beam evaporation.

[0098] Step 2) The amorphous gallium oxide film is annealed in an annealing furnace filled with oxygen at a temperature of 600°C for 10 hours. This step is mainly used to further reduce defects inside the amorphous gallium oxide film.

[0099] Step 3) A layer of 800 nm thick amorphous silicon dioxide film is deposited on top of the amorphous gallium oxide film using plasma-enhanced chemical vapor deposition, which mainly serves as a hard mask.

[0100] Step 4) Spin-coat a 1300nm thick AZ5214 photoresist over the amorphous silicon dioxide film.

[0101] Step 5) Expose AZ5214 photoresist using a contact ultraviolet lithography device. After development, the coupled waveguide pattern on the layout is transferred to the photoresist.

[0102] Step 6) Use an inductively coupled plasma etching device (CF4 and O2 mixed gas) to fully etch the silicon dioxide film, transferring the coupled waveguide pattern on the photoresist onto the silicon dioxide hard mask. This process requires an over-etching time of 10 seconds to ensure that the silicon dioxide is completely etched.

[0103] Step 7) The sample from step 6 is immersed in NMP solution at 75°C for 20 minutes, and then treated with oxygen plasma for 10 minutes to remove residual adhesive on the surface of the hard mask, finally obtaining a hard mask with coupled waveguide pattern. The thickness of the hard mask is 800 nm.

[0104] Step 8) The temperature of the optical substrate is maintained at 80℃~120℃, and the amorphous gallium oxide thin film is etched again using an inductively coupled plasma etching machine. Specifically, the BCl3 gas flow rate is 30 sccm, the Ar gas flow rate is 10 sccm, the RF power is 100W, the ICP power is 750W, the cavity gas pressure is 10mTorr, the substrate heating temperature is 90℃, and the etching time is 120s. Finally, a single-mode microdisk resonant device based on amorphous gallium oxide with an etching depth of 500nm is obtained.

[0105] The BCl3 and Ar mixed gas selected in this embodiment 1 makes full use of their respective properties. The BCl3 gas enhances the chemical reaction in the etching process, which can provide a greater etching rate, while Ar can enhance the physical bombardment ability, remove the non-volatile substances produced in the etching process, and help improve the smoothness of the coupled waveguide surface.

[0106] Step 9) The etched single-mode microdisk resonator was immersed in BOE solution for a period of time to remove the remaining silicon dioxide mask, and finally a single-mode microdisk resonator with a silicon-silicon dioxide-gallium oxide structure was obtained.

[0107] Please see Figure 6 , Figure 6 The image shows a physical diagram of the single-mode microdisk resonator device prepared in Example 1. It can be seen that the sidewalls of the coupled waveguide are vertical and have a good morphology, indicating that the preparation method of the single-mode microdisk resonator device developed in this invention can obtain a single-mode microdisk resonator device with excellent morphology.

[0108] Please see Figure 7 , Figure 7The relationship between the etching rate and RF power of the single-mode microdisk resonant device in Example 1 shows that as the RF power increases from 100W to 250W, the etching rate of the gallium oxide film gradually increases. This is mainly because increasing the RF power enhances the combined effect of physical etching and chemical etching. Moreover, the increased proportion of physical etching effectively removes the non-volatile products generated during the etching process, exposing the unetched gallium oxide film. At this point, the enhanced chemical etching will continue to etch.

[0109] join Figure 8 The figure shows the relationship between the etching rate of the amorphous gallium oxide thin film and the BCl3 gas flow rate in Example 1. It can be seen that increasing the BCl3 gas flow rate gradually increases the etching rate of the gallium oxide thin film. When the gas flow rate exceeds 30 sccm, the etching rate weakens. This is mainly because before the BCl3 flow rate reaches 30 sccm, the ratio of BCl3 to Ar is moderate. Increasing the amount of products generated by chemical etching will also remove them through physical etching by Ar, thus increasing the etching rate accordingly. However, when the gas flow rate increases to 35 sccm, chemical etching becomes dominant, causing the rate at which products are removed by physical etching to be less than the rate at which products are generated by chemical etching. Therefore, the etching rate then shows a decreasing trend.

[0110] It should be understood that the above embodiments are merely illustrative of the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A single-mode microdisk resonant device, characterized in that, include: A first optical coupler, a coupling waveguide, a second optical coupler, and a microdisk resonant cavity are disposed on the same working plane. These components are integrally formed from an amorphous gallium oxide thin film. The coupling waveguide comprises a first waveguide, a second waveguide, and a third waveguide connected sequentially. The first optical coupler and the second optical coupler are respectively connected to the first waveguide and the third waveguide. The second waveguide is spaced apart on one side of the microdisk resonant cavity and has an arc-shaped structure surrounding the microdisk resonant cavity. The coupling coefficient κ between the coupled waveguide and the microdisk resonant cavity is: Where, n wg R wg =n disk R disk θ0 is the coupling angle of the second waveguide around the microdisk resonant cavity, θ is a variable representing the range of the coupling angle, from -θ0 to θ0, i represents the direction of integration, S is a constant determined by the dimensions of the coupling waveguide, and E disk and E wg Let represent the normalized electric field intensity in the microdisk resonant cavity and the coupled waveguide, respectively; ε(r,z) represent the dielectric constant corresponding to the mode perturbation at different positions in the microdisk resonant cavity when coupling occurs; ε0 represents the dielectric constant corresponding to the microdisk resonant cavity without coupling; κ0=2π / λ0, where κ0 is the wave number in free space, λ0 is the input wavelength, m is the azimuth mode order of the microdisk resonant cavity, and n wg R is the effective refractive index of the coupled waveguide. wg Let n be the radius of curvature of the second waveguide. disk R is the effective refractive index of the microdisk resonant cavity. disk R is the radius of the microdisk resonant cavity. wg =R disk +g+w / 2, where g is the coupling distance between the second waveguide and the microdisk resonant cavity, and w is the width of the second waveguide.

2. The single-mode microdisk resonant device according to claim 1, characterized in that: Both the first optical coupler and the second optical coupler are one of the following structures: a focused Bragg grating, a subwavelength Bragg grating, and an inverted conical coupler.

3. The single-mode microdisk resonant device according to claim 2, characterized in that: The height of the focused Bragg grating is 300nm to 600nm.

4. The single-mode microdisk resonant device according to claim 2, characterized in that: The focused Bragg grating has a TE mode polarization grating period of 1.1 μm to 1.3 μm, a duty cycle of 0.5 to 0.7, and a coupling efficiency of 25% to 40%.

5. The single-mode microdisk resonant device according to claim 1, characterized in that: The microdisk resonant cavity has a circular structure, and the second waveguide has an arc-shaped structure.

6. The single-mode microdisk resonant device according to claim 4, characterized in that: The second waveguide has a semi-circular structure.

7. The single-mode microdisk resonant device according to claim 4, characterized in that: The coupling spacing g between the second waveguide and the microdisk resonant cavity is equal.

8. The single-mode microdisk resonant device according to claim 1, characterized in that: The straight width of the second waveguide is 700nm to 1200nm, and the radius of curvature R of the second waveguide is... wg The radius R of the microdisk resonant cavity is 40μm to 60μm. disk The coupling distance g between the second waveguide and the microdisk resonant cavity is 35μm to 55μm, and the coupling distance g between the second waveguide and the microdisk resonant cavity is 500nm to 900nm.

9. The single-mode microdisk resonant device according to claim 1, characterized in that: At least the sidewalls of the coupling waveguide and the microdisk resonant cavity are perpendicular to the working surface, and the sidewalls of the coupling waveguide and the microdisk resonant cavity are smooth.

10. The single-mode microdisk resonant device according to claim 1, characterized in that, Also includes: An optical substrate, wherein the first optical coupler, the coupling waveguide, the second optical coupler, and the microdisk resonant cavity are disposed on the optical substrate, and the working surface is the surface of the optical substrate.

11. The single-mode microdisk resonant device according to claim 10, characterized in that: The refractive index of the material forming the optical substrate is lower than that of the material forming the first optical coupler, the coupling waveguide, the second optical coupler, and the microdisk resonant cavity.

12. The single-mode microdisk resonant device according to claim 10, characterized in that: The optical substrate includes a base and a thermally oxidized silicon layer stacked on the base. The working surface is the surface of the thermally oxidized silicon layer facing away from the base. The base is made of at least one of silicon wafer, sapphire, calcium oxide, and magnesium oxide.

13. The method for fabricating a single-mode microdisk resonant device as described in any one of claims 1-12, characterized in that, include: An amorphous gallium oxide thin film is formed on an optical substrate, wherein the refractive index of the optical substrate is lower than the refractive index of the amorphous gallium oxide thin film; A patterned mask is deposited on the amorphous gallium oxide thin film. The amorphous gallium oxide thin film not covered by the mask is etched using a plasma dry etching process. The etching gas used in the plasma dry etching process is a mixture of BCl3 and Ar, thereby forming the first optical coupler, the coupling waveguide, the second optical coupler, and the micro disk resonant cavity. The sidewalls of the coupling waveguide and the micro disk resonant cavity are made smooth and perpendicular to the working surface of the optical substrate. The coupling waveguide includes a first waveguide, a second waveguide, and a third waveguide connected in sequence. The first optical coupler and the second optical coupler are respectively connected to the first waveguide and the third waveguide. The second waveguide is spaced out on one side of the microdisk resonant cavity and has an arc-shaped structure surrounding the microdisk resonant cavity. The coupling coefficient κ between the coupled waveguide and the microdisk resonant cavity is: Where, n wg R wg =n disk R disk θ0 is the coupling angle of the second waveguide around the microdisk resonant cavity, θ is a variable representing the range of the coupling angle, from -θ0 to θ0, i represents the direction of integration, S is a constant determined by the dimensions of the coupling waveguide, and E disk and E wg Let represent the normalized electric field intensity in the microdisk resonant cavity and the coupled waveguide, respectively; ε(r,z) represent the dielectric constant corresponding to the mode perturbation at different positions in the microdisk resonant cavity when coupling occurs; ε0 represents the dielectric constant corresponding to the microdisk resonant cavity without coupling; κ0=2π / λ0, where κ0 is the wave number in free space, λ0 is the input wavelength, m is the azimuth mode order of the microdisk resonant cavity, and n wg R is the effective refractive index of the coupled waveguide. wg Let n be the radius of curvature of the second waveguide. disk R is the effective refractive index of the microdisk resonant cavity. disk R is the radius of the microdisk resonant cavity. wg =R disk +g+w / 2, where g is the coupling distance between the second waveguide and the microdisk resonant cavity, and w is the width of the second waveguide.

14. The method for fabricating a single-mode microdisk resonant device according to claim 13, characterized in that: The volume ratio of BCl3 to Ar in the etching gas is (20-50):(5-20).

15. The method for fabricating a single-mode microdisk resonant device according to claim 13, characterized in that: When dry etching amorphous gallium oxide thin films using plasma, the gas flow rate of BCl3 is 20 sccm to 50 sccm, the gas flow rate of Ar is 2 sccm to 20 sccm, the power of RF is 50 W to 300 W, the power of ICP is 200 W to 1000 W, and the pressure of the etching chamber is 5 mTorr to 15 mTorr.

16. The method for fabricating a single-mode microdisk resonant device according to claim 13, characterized in that, The preparation method further includes maintaining the temperature of the optical substrate at 80°C to 120°C during the etching process of the amorphous gallium oxide thin film not covered by the mask using a plasma dry etching process.

17. The method for fabricating a single-mode microdisk resonant device according to claim 13, characterized in that: The preparation method further includes: first annealing the amorphous gallium oxide film at 500℃~700℃ in an oxygen atmosphere, and then etching the amorphous gallium oxide film.

18. An optoelectronic device, characterized in that, include: The single-mode microdisk resonator device according to any one of claims 1-12.

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