Method for manufacturing an optical phase modulation device

Abstract

The application provides a preparation method of an optical signal phase modulation device. The preparation method of the optical signal phase modulation device comprises the following steps: providing a substrate and forming a first dielectric layer on one side surface of the substrate; forming a patterned optical waveguide layer on the side of the first dielectric layer away from the substrate, the optical waveguide layer being used for transmitting an optical signal; forming a second dielectric layer on the side of the first dielectric layer away from the substrate, the second dielectric layer covering the optical waveguide layer; forming an isolation layer on the side of the second dielectric layer away from the first dielectric layer, the crystal direction consistency of the isolation layer being greater than that of the second dielectric layer; and forming a piezoelectric control unit on the side of the isolation layer away from the second dielectric layer, the piezoelectric control unit being capable of exerting pressure on the optical waveguide layer to adjust the refractive index of the optical waveguide layer to the optical signal. According to the application, the preparation difficulty of the piezoelectric control unit can be effectively reduced, so that the overall preparation yield is improved.

Description

Technical Field

[0001] This application relates to the field of integrated optical sensing technology, and in particular to a method for fabricating an optical signal phase modulation device. Background Technology

[0002] Fiber optic gyroscopes play a crucial role in fields such as autonomous driving, aerial navigation, and geographic surveying because they can accurately measure the angular displacement of objects. Furthermore, compared to traditional mechanical gyroscopes, optical gyroscopes are unaffected by shocks and vibrations, thus offering advantages such as ease of installation and a wider range of applications.

[0003] The rapid development of integrated optics technology has pointed the way for miniaturization, low cost, and low power consumption in fiber optic gyroscopes. The initial concept for integrated optical gyroscopes was to integrate all discrete optical components, such as light sources, detectors, beam splitters, phase modulators, and interference rings, onto a single chip using a monolithic integration approach. Chip-based optical gyroscopes can significantly reduce system size and, like integrated circuits, continuously reduce chip costs through mass production as shipments increase. Furthermore, the already fully automated chip manufacturing process can further replace the complex fiber optic component assembly and debugging processes of fiber optic gyroscopes, further improving the mass production and standardization capabilities of gyroscopes. However, researchers quickly discovered that, constrained by the limitations of integrated optical materials and processes, achieving light output, detection, modulation, and low-loss transmission on a single chip still faces numerous material compatibility and manufacturing challenges.

[0004] As a crucial component of optical gyroscopes, phase modulation devices are essential for their stable and reliable operation. Therefore, they require high modulation responsivity, modulation linearity, and large modulation bandwidth. Recent in-depth research on phase modulation devices has revealed that the inverse piezoelectric effect of piezoelectric materials can alter the stress applied to a waveguide, generating strain, which in turn changes the equivalent refractive index of the optical transmission mode through the photoelastic effect. Compared to other effects used to change the refractive index of optical media, such as thermo-optical effects or injected carrier dispersion, the photoelastic effect produces relatively strong birefringence, resulting in higher phase modulation efficiency.

[0005] However, in current phase modulation devices based on piezoelectric materials, the fabrication of the piezoelectric control unit is challenging and yields low success rates, thus impacting the product's economic viability. Therefore, effectively reducing the fabrication difficulty of the piezoelectric control unit is a pressing issue that needs to be addressed. Summary of the Invention

[0006] In view of the above problems, this application provides a method for fabricating an optical signal phase modulation device, which can effectively reduce the fabrication difficulty of the piezoelectric control unit and improve the overall fabrication yield.

[0007] This application provides a method for fabricating an optical signal phase modulation device. The method includes: providing a substrate and forming a first dielectric layer on one side surface of the substrate; forming a patterned optical waveguide layer on the side of the first dielectric layer facing away from the substrate, the optical waveguide layer being used to transmit optical signals; forming a second dielectric layer on the side of the first dielectric layer facing away from the substrate, the second dielectric layer covering the optical waveguide layer; forming an isolation layer on the side of the second dielectric layer facing away from the first dielectric layer, the isolation layer having a higher crystal orientation uniformity than the second dielectric layer; and forming a piezoelectric control unit on the side of the isolation layer facing away from the second dielectric layer, the piezoelectric control unit being capable of applying pressure to the optical waveguide layer to adjust the refractive index of the optical waveguide layer for optical signals.

[0008] In some embodiments, before the step of forming an isolation layer on the side of the second dielectric layer opposite to the first dielectric layer, the method further includes: polishing the surface of the second dielectric layer on the side opposite to the first dielectric layer to form a polished surface.

[0009] In some embodiments, forming a second dielectric layer on the side of the first dielectric layer facing away from the substrate includes: depositing a dielectric material on the side of the first dielectric layer facing away from the substrate to form a dielectric film, the dielectric film covering the optical waveguide layer; further depositing a dielectric material on the portion of the dielectric film covering the optical waveguide layer so that the portion of the dielectric film covering the optical waveguide layer protrudes beyond the portion of the dielectric film covering the first dielectric layer, to obtain a second dielectric layer with protrusions.

[0010] In some embodiments, providing a substrate and forming a first dielectric layer on one side surface of the substrate includes: grooving a substrate substrate to form a groove to obtain a substrate with a groove; and forming a first dielectric layer on one side surface of the substrate having a groove opening.

[0011] In some embodiments, forming a patterned optical waveguide layer on the side surface of the first dielectric layer facing away from the substrate includes: depositing an optical waveguide material on the side surface of the first dielectric layer facing away from the substrate to form an optical waveguide thin film; and performing photolithography on the optical waveguide thin film to form a patterned optical waveguide layer.

[0012] In some embodiments, the method of forming an isolation layer on the side of the second dielectric layer opposite to the first dielectric layer includes at least one of chemical vapor deposition, atomic layer deposition, free radical assisted film formation, and supercritical fluid film formation.

[0013] In some embodiments, forming a piezoelectric control unit on the side of the isolation layer opposite to the second dielectric layer includes: forming a piezoelectric material layer on the side of the isolation layer opposite to the second dielectric layer; forming a first electrode and a second electrode on the side of the piezoelectric material layer opposite to the isolation layer, wherein the first electrode and the second electrode are spaced apart along a first direction, and the first direction intersects the transmission direction of the optical signal.

[0014] In some embodiments, forming a piezoelectric control unit on the side of the isolation layer opposite to the second dielectric layer includes: forming a first electrode on the side of the isolation layer opposite to the second dielectric layer; forming a piezoelectric material layer on the side of the first electrode opposite to the isolation layer; and forming a second electrode on the side of the piezoelectric material layer opposite to the first electrode.

[0015] In some embodiments, the method for fabricating an optical signal phase modulation device further includes: etching a piezoelectric control unit to divide the piezoelectric control unit into two independent sub-piezoelectric control units, the two sub-piezoelectric control units being spaced apart along a first direction, the first direction intersecting the direction of optical signal transmission.

[0016] In some embodiments, the method for forming a piezoelectric material layer includes at least one of magnetron sputtering, sol-gel method, and pulsed laser deposition.

[0017] The method for fabricating an optical signal phase modulation device provided in this application involves first forming an isolation layer on a second dielectric layer, and then forming a piezoelectric control unit on the isolation layer. Because the crystal orientation uniformity of the isolation layer is greater than that of the second dielectric layer, the isolation layer has higher density. On one hand, the isolation layer can further reduce the impact of the flatness and density of the surface of the second dielectric layer facing away from the first dielectric layer on the fabrication of the piezoelectric control unit, thereby effectively reducing the fabrication difficulty of the piezoelectric control unit. On the other hand, the isolation layer can also improve the piezoelectric efficiency of the piezoelectric control unit and reduce its modulation power consumption. Simultaneously, the isolation layer can also prevent the diffusion of piezoelectric material in the piezoelectric control unit into the second dielectric layer, thereby reducing the absorption of light transmitted in the optical waveguide layer by the second dielectric layer, and thus effectively reducing the modulation loss of the optical signal phase modulation device.

[0018] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0019] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0020] Figure 1 This is a schematic flowchart of a method for fabricating an optical signal phase modulation device according to some embodiments of this application;

[0021] Figure 2 This is a schematic diagram of the structure of an integrated optical gyroscope chip provided in some embodiments of this application;

[0022] Figure 3 for Figure 2 Schematic diagram of the cross-sectional structure along the middle AA;

[0023] Figures 4 to 8 The following are schematic diagrams showing the structure of each stage of a method for fabricating an optical signal phase modulation device according to some embodiments of this application;

[0024] Figure 9 This is a schematic diagram of the structure of another optical signal phase modulation device provided in some embodiments of this application;

[0025] Figure 10 This is a schematic diagram of the structure of another optical signal phase modulation device provided in some embodiments of this application;

[0026] Figure 11 This is a schematic diagram of the structure of another optical signal phase modulation device provided in some embodiments of this application;

[0027] Figure 12 This is a schematic diagram of the structure of another optical signal phase modulation device provided in some embodiments of this application.

[0028] The reference numerals in the detailed embodiments are as follows:

[0029] 100. Integrated optical gyroscope chip; 110. Optical signal phase modulation device; 120. Mode converter; 130. Beam splitter; 140. Polarizer;

[0030] 10. Substrate; 11. Groove; 20. First dielectric layer; 30. Optical waveguide layer; 40. Second dielectric layer; 41. Protrusion; 50. Isolation layer; 60. Piezoelectric control unit; 60a. First sub-control unit; 60b. Second sub-control unit; 61. Piezoelectric material layer; 611. First piezoelectric material; 612. Second piezoelectric material; 62. First electrode; 63. Second electrode; 64. Third electrode; 65. Fourth electrode; 66. Fifth electrode; 67. Sixth electrode; X, First direction. Detailed Implementation

[0031] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0032] It should be noted that, unless otherwise stated, the technical or scientific terms used in the embodiments of this application should have the ordinary meaning understood by those skilled in the art to which the embodiments of this application pertain.

[0033] In the description of the embodiments in this application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", and "bottom" are used.

[0034] The orientations or positional relationships indicated by terms such as "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", and "circumferential" are based on the orientations or positional relationships shown in the accompanying drawings. They are only for the purpose of facilitating the description of the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0035] Furthermore, technical terms such as "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. In the description of the embodiments of this application, "a plurality of" means two or more, unless otherwise explicitly defined.

[0036] In the description of the embodiments of this application, unless otherwise expressly specified and limited, the technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0037] In the description of the embodiments of this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0038] Fiber optic gyroscopes play a crucial role in fields such as autonomous driving, aerial navigation, and geographic surveying because they can accurately measure the angular displacement of objects. Furthermore, compared to traditional mechanical gyroscopes, optical gyroscopes are unaffected by shocks and vibrations, thus offering advantages such as ease of installation and a wider range of applications.

[0039] The rapid development of integrated optics technology has pointed the way for miniaturization, low cost, and low power consumption in fiber optic gyroscopes. The initial concept for integrated optical gyroscopes was to integrate all discrete optical components, such as light sources, detectors, beam splitters, phase modulators, and interference rings, onto a single chip using a monolithic integration approach. Chip-based optical gyroscopes can significantly reduce system size and, like integrated circuits, continuously reduce chip costs through mass production as shipments increase. Furthermore, the already fully automated chip manufacturing process can further replace the complex fiber optic component assembly and debugging processes of fiber optic gyroscopes, further improving the mass production and standardization capabilities of gyroscopes. However, researchers quickly discovered that, constrained by the limitations of integrated optical materials and processes, achieving light output, detection, modulation, and low-loss transmission on a single chip still faces numerous material compatibility and manufacturing challenges.

[0040] For interferometric optical gyroscopes, stable phase modulation is crucial for achieving high sensitivity and accuracy in extracting phase difference signals within the system. This necessitates phase shifters with high modulation responsivity, modulation linearity, and large modulation bandwidth. Currently, integrated phase shifters widely used in fiber optic gyroscope systems are primarily based on the electro-optic effect in bulk lithium niobate waveguides. These are used to achieve closed-loop feedback of the interferometric phase in fiber optic gyroscopes at different accuracy levels, reducing the impact of device drift and achieving high precision. However, the modulation challenges of using lithium niobate thin films are also significant in the chip-based integration of integrated optical gyroscopes.

[0041] On the one hand, the low-cost dry etching problem of lithium niobate materials remains a challenge. Dry etching is the preferred method for integrated photonics, but unlike most other integrated photonics platforms, lithium niobate lacks suitable reactive ion etching formulations. Fluorine-based reactive ion etching can effectively remove lithium by forming volatile niobium fluoride. However, it also forms non-volatile lithium fluoride, leading to severe redeposition problems. In thin-film lithium niobate waveguides, the lithium fluoride formed by redeposition exhibits extremely high resistivity to further etching, thereby increasing sidewall roughness and scattering loss.

[0042] On the other hand, lithium niobate and silicon photonics materials require interlayer coupling structures to achieve light transmission between different materials. The alignment accuracy of the interlayer coupling structure is high, and misalignment can easily excite multimode. The energy coupled into the base film by multimode modulation will cause non-reciprocal errors that are difficult for the system to eliminate.

[0043] In recent years, in-depth research on phase modulation devices has revealed that the inverse piezoelectric effect of piezoelectric materials can be used to alter the stress applied to a waveguide, thereby generating strain and subsequently changing the equivalent refractive index of the optical transmission mode through the elasto-optical effect. Compared to other effects used to change the refractive index of optical media, such as the thermo-optical effect or injected carrier dispersion, the elasto-optical effect can produce relatively strong birefringence, resulting in higher phase modulation efficiency.

[0044] The phase modulation device, as a crucial component of the optical gyroscope, is essential for its stable and reliable operation. Therefore, the phase modulation device needs to possess performance characteristics such as high modulation response, modulation linearity, and large modulation bandwidth. However, the fabrication of the piezoelectric control unit in current phase modulation devices based on piezoelectric thin film materials is challenging, resulting in low yields and consequently impacting the product's economic viability.

[0045] Current phase modulation devices typically involve depositing a silicon oxide layer after fabricating an optical waveguide layer, followed by chemical mechanical polishing (CMP) to achieve the desired thickness, and then fabricating a piezoelectric control unit on the surface of the polished silicon oxide layer. However, direct CMP results in poor controllability of the silicon oxide layer thickness. Furthermore, the presence of the optical waveguide layer creates an uneven surface on the deposited silicon oxide, which remains undulating even after CMP. This leads to significant thickness variations, poor density, and poor surface smoothness, making the subsequent fabrication of the piezoelectric control unit extremely difficult.

[0046] Based on the above considerations, this application provides a method for fabricating an optical signal phase modulation device. The method includes: providing a substrate and forming a first dielectric layer on one side surface of the substrate; forming a patterned optical waveguide layer on the side of the first dielectric layer facing away from the substrate, the optical waveguide layer being used to transmit optical signals; forming a second dielectric layer on the side of the first dielectric layer facing away from the substrate, the second dielectric layer covering the optical waveguide layer; forming an isolation layer on the side of the second dielectric layer facing away from the first dielectric layer, the isolation layer having a higher crystal orientation uniformity than the second dielectric layer; and forming a piezoelectric control unit on the side of the isolation layer facing away from the second dielectric layer, the piezoelectric control unit being capable of applying pressure to the optical waveguide layer to adjust the refractive index of the optical waveguide layer for optical signals.

[0047] Thus, by first forming an isolation layer on the second dielectric layer and then forming a piezoelectric control unit on the isolation layer, the isolation layer exhibits higher density due to its greater crystal orientation uniformity compared to the second dielectric layer. On one hand, the isolation layer can further reduce the impact of the flatness and density of the surface of the second dielectric layer facing away from the first dielectric layer on the fabrication of the piezoelectric control unit, thereby further reducing the fabrication difficulty. On the other hand, the piezoelectric efficiency of the piezoelectric control unit largely depends on the crystal orientation and density of the isolation material. Higher crystal orientation uniformity and density result in a superior piezoelectric effect and lower modulation power consumption of the piezoelectric control unit. Therefore, the isolation layer can also improve the piezoelectric efficiency and reduce the modulation power consumption of the piezoelectric control unit. Simultaneously, the isolation layer can also prevent the diffusion of piezoelectric material from the piezoelectric control unit into the second dielectric layer, reducing the absorption of light transmitted in the optical waveguide layer by the second dielectric layer, thereby effectively reducing the modulation loss of the optical signal phase modulation device.

[0048] The fabrication method of the optical signal phase modulation device provided in the embodiments of this application is described below with reference to the accompanying drawings.

[0049] Figure 1 This is a schematic flowchart illustrating a method for fabricating an optical signal phase modulation device according to some embodiments of this application. Figure 2 This is a schematic diagram of the structure of an integrated optical gyroscope chip provided in some embodiments of this application. Figure 3 for Figure 2 A schematic diagram of the cross-sectional structure along the middle AA line. Figures 4 to 8 The diagram shows the structure of each stage of a method for fabricating an optical signal phase modulation device according to some embodiments of this application.

[0050] like Figures 1 to 8 As shown, an embodiment of this application provides a method for fabricating an optical signal phase modulation device 110, the method comprising:

[0051] Step 110: Provide a substrate 10 and form a first dielectric layer 20 on one side surface of the substrate 10;

[0052] Step 120: A patterned optical waveguide layer 30 is formed on the side of the first dielectric layer 20 facing away from the substrate 10. The optical waveguide layer 30 is used to transmit optical signals.

[0053] Step 130: A second dielectric layer 40 is formed on the side of the first dielectric layer 20 facing away from the substrate 10, and the second dielectric layer 40 covers the optical waveguide layer 30.

[0054] Step 140: An isolation layer 50 is formed on the side of the second dielectric layer 40 opposite to the first dielectric layer 20. The crystal orientation uniformity of the isolation layer 50 is greater than that of the second dielectric layer 40.

[0055] Step 150: A piezoelectric control unit 60 is formed on the side of the isolation layer 50 facing away from the second dielectric layer 40. The piezoelectric control unit 60 can apply pressure to the optical waveguide layer 30 to adjust the refractive index of the optical waveguide layer 30 for optical signals.

[0056] For example, continue to refer to Figure 2 and Figure 3 The integrated optical gyroscope chip 100 includes an optical signal phase modulation device 110, a mode converter 120, a beam splitter 130, and a polarizer 140, wherein the optical signal phase modulation device 110 is used to realize the phase modulation of the optical signal.

[0057] Continue to refer to Figure 4 As an example, the substrate 10 may be, but is not limited to, a silicon substrate 10, and a first dielectric layer 20 is formed on one side surface of the substrate 10.

[0058] Optionally, the thickness of the substrate 10 can be controlled between 0.2 mm and 1 mm. As an example, the thickness of the substrate 10 can be, but is not limited to, 0.2 mm, 0.25 mm, 0.3 mm, 0.35 mm, 0.4 mm, 0.45 mm, 0.5 mm, 0.55 mm, 0.65 mm, 0.7 mm, 0.75 mm, 0.8 mm, 0.85 mm, 0.9 mm, 0.95 mm, 1 mm, etc.

[0059] Optionally, the first dielectric layer 20 can be prepared using materials such as silicon dioxide, but is not limited to this method. The method for forming the first dielectric layer 20 can be, but is not limited to, thermal oxidation or deposition. The first dielectric layer 20 formed by the above-mentioned thermal oxidation or deposition methods has high strength and high yield, resulting in higher stability and reliability of the first dielectric layer 20 in subsequent processes.

[0060] Optionally, the thickness of the first dielectric layer 20 can be controlled between 1000nm and 5000nm. As an example, the thickness of the first dielectric layer 20 can be, but is not limited to, 1000nm, 1500nm, 2000nm, 2500nm, 3000nm, 3500nm, 4000nm, 4500nm, and 5000nm.

[0061] Continue to refer to Figure 5 As an example, the optical waveguide layer 30 can transmit optical signals, and the optical waveguide layer 30 is patterned so that the optical signals can be transmitted along the extension direction of the optical waveguide layer 30.

[0062] Optionally, the optical waveguide layer 30 can be fabricated using materials such as silicon nitride or silicon, but is not limited to these methods. The method for forming the optical waveguide layer 30 can be, but is not limited to, deposition or photolithography.

[0063] Optionally, the thickness of the optical waveguide layer 30 can be controlled between 100nm and 1000nm. As an example, the thickness of the optical waveguide layer 30 can be, but is not limited to, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 550nm, 600nm, 650nm, 700nm, 7500nm, 800nm, 850nm, 900nm, 950nm, 1000nm, etc.

[0064] Continue to refer to Figure 6 As an example, the second dielectric layer 40 can cover the optical waveguide layer 30 so that the first dielectric layer 20, the second dielectric layer 40 and the optical waveguide layer 30 form a sandwich structure, that is, the first dielectric layer 20 and the second dielectric layer 40 are the outer cladding layers of the sandwich structure, and the optical waveguide layer 30 is the core layer of the sandwich structure. In other words, the first dielectric layer 20 and the second dielectric layer 40 surround the outer periphery of the optical waveguide layer 30.

[0065] Optionally, the refractive index of the optical waveguide layer 30 is greater than that of the first dielectric layer 20, and the refractive index of the optical waveguide layer 30 is greater than that of the second dielectric layer 40, so that the optical signal can be confined to propagate in the optical waveguide layer 30, which can effectively reduce the transmission loss of the optical waveguide layer 30.

[0066] Optionally, the second dielectric layer 40 can be prepared using materials such as silicon dioxide, but is not limited to this method. The method for forming the second dielectric layer 40 can be, but is not limited to, thermal oxidation or deposition. For example, the first dielectric layer 20 and the second dielectric layer 40 can be prepared using the same material and the same method to simplify the overall preparation complexity and reduce costs.

[0067] Optionally, the thickness of the portion of the second dielectric layer 40 that extends beyond the optical waveguide layer 30 can be controlled within the range of 10 nm to 3000 nm. As an example, the thickness of the portion of the second dielectric layer 40 that extends beyond the optical waveguide layer 30 can be, but is not limited to, 10 nm, 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 1000 nm, 1100 nm, 1200 nm, 1300 nm, 1400 nm, 1500 nm, 2000 nm, 2500 nm, 3000 nm, etc.

[0068] Continue to refer to Figure 7As an example, during the formation of the isolation layer 50, a solution containing the isolation material is first coated on the surface of the second dielectric layer 40 facing away from the first dielectric layer 20. After preheating, annealing is performed. The above steps are repeated multiple times to form the isolation layer 50.

[0069] Optionally, the insulating material may be, but is not limited to, at least one of nitrate compounds containing strontium titanate, silicon dioxide, lanthanides, or ytterbium. All of the above materials exhibit high crystal orientation uniformity and most can be well grown on the first dielectric layer 20, making them excellent insulating materials.

[0070] Optionally, the method for forming the isolation layer 50 on the side of the second dielectric layer 40 opposite to the first dielectric layer 20 can be, but is not limited to, at least one of chemical vapor deposition (CVD), atomic layer deposition (ALD), free radical-assisted film formation, and supercritical fluid film formation. The CVD method can be, but is not limited to, plasma-enhanced CVD, pulsed CVD, low-pressure CVD, sub-atmospheric pressure CVD, or atmospheric pressure CVD; the ALD method can be, but is not limited to, plasma-enhanced ALD. The above methods can be selected according to actual needs. Similarly, other techniques known in the art can also be used to prepare the isolation layer 50, without limitation.

[0071] Optionally, the thickness of the isolation layer 50 can be controlled between 5nm and 100nm. As an example, the thickness of the optical waveguide layer 30 can be, but is not limited to, 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, 95nm, 100nm, etc.

[0072] Continue to refer to Figure 8 The piezoelectric control unit 60 can deform under voltage control. The deformation of the piezoelectric control unit 60 induces strain in the optical waveguide layer 30, causing the refractive index of the optical waveguide layer 30 to change due to the photoelastic effect, thereby achieving phase modulation of the light. The fabrication of the piezoelectric control unit 60 is the final step in the fabrication of the entire optical signal phase modulation device 110. Therefore, the quality of the piezoelectric control unit 60 is less affected by the preceding processes, thus improving the fabrication yield of the piezoelectric control unit 60.

[0073] As an example, the isolation layer 50 includes an isolation material, the crystal orientation of which is greater than that of the first dielectric layer 20. It should be noted that higher crystal orientation consistency indicates higher material density, and growing on a material with high crystal orientation consistency can improve the control efficiency of the piezoelectric control unit 60. The piezoelectric efficiency of the piezoelectric control unit 60 depends largely on the crystal orientation and density of the isolation material. Higher crystal orientation consistency and density of the isolation material result in a superior piezoelectric effect and lower modulation power consumption of the piezoelectric control unit 60.

[0074] On the other hand, the isolation layer 50 can also prevent the piezoelectric material in the piezoelectric control unit 60 from diffusing into the second dielectric layer 40. It should be noted that after the piezoelectric material diffuses into the second dielectric layer 40, it will have a strong absorption effect on the light transmitted in the optical waveguide layer 30, resulting in extremely high transmission loss, which will affect the performance of the fiber optic gyroscope.

[0075] In the above technical solution, by first forming an isolation layer 50 on the second dielectric layer 40, and then forming a piezoelectric control unit 60 on the isolation layer 50, the isolation layer 50 has higher density due to its greater crystal orientation uniformity than that of the second dielectric layer 40. On one hand, the isolation layer 50 can further reduce the impact of the flatness and density of the surface of the second dielectric layer 40 facing away from the first dielectric layer 20 on the fabrication of the piezoelectric control unit 60, thereby effectively reducing the fabrication difficulty of the piezoelectric control unit 60. On the other hand, the piezoelectric efficiency of the piezoelectric control unit 60 largely depends on the crystal orientation and density of the isolation material. Higher crystal orientation uniformity and density of the isolation material result in a better piezoelectric effect and lower modulation power consumption of the piezoelectric control unit 60. Therefore, the isolation layer 50 can also improve the piezoelectric efficiency of the piezoelectric control unit 60 and reduce its modulation power consumption. Meanwhile, the isolation layer 50 can also block the piezoelectric material in the piezoelectric control unit 60 from diffusing into the second dielectric layer 40, thereby reducing the absorption of light transmitted in the optical waveguide layer 30 by the second dielectric layer 40, and thus effectively reducing the modulation loss of the optical signal phase modulation device 110.

[0076] In some embodiments, prior to step 140 above, before forming the isolation layer 50 on the side of the second dielectric layer 40 opposite to the first dielectric layer 20, the method further includes:

[0077] The step of polishing the surface of the second dielectric layer 40 facing away from the first dielectric layer 20 to form a polished surface.

[0078] As an example, a chemical mechanical polishing method can be used to polish the surface of the second dielectric layer 40 facing away from the first dielectric layer 20 to form a polished surface. Then, an isolation layer 50 is formed on the side of the second dielectric layer 40 facing away from the first dielectric layer 20. It should be noted that other techniques known in the art can also be used to polish the surface of the second dielectric layer 40 facing away from the first dielectric layer 20; this is not a limitation.

[0079] The above technical solution polishes the surface of the second dielectric layer 40 facing away from the first dielectric layer 20, which can improve the flatness and density of the surface of the second dielectric layer 40 facing away from the first dielectric layer 20. This can effectively reduce the difficulty of fabricating the isolation layer 50 and improve the surface flatness and density of the isolation layer 50, thereby further reducing the difficulty of fabricating the subsequent piezoelectric control unit 60.

[0080] Figure 9 This is a schematic diagram of the structure of another optical signal phase modulation device 110 provided in some embodiments of this application.

[0081] Continue to refer to Figure 9 In some embodiments, step 130 above, forming a second dielectric layer 40 on the side of the first dielectric layer 20 facing away from the substrate 10, may specifically include the following steps:

[0082] Step 1301: Deposit dielectric material on the side of the first dielectric layer 20 facing away from the substrate 10 to form a dielectric thin film, the dielectric thin film covering the optical waveguide layer 30;

[0083] Step 1302: Further deposit dielectric material on the portion of the dielectric film covering the optical waveguide layer 30, so that the portion of the dielectric film covering the optical waveguide layer 30 protrudes beyond the portion of the dielectric film covering the first dielectric layer 20, to obtain a second dielectric layer 40 with protrusions 41.

[0084] As an example, a dielectric material is first deposited on the side of the first dielectric layer 20 facing away from the substrate 10 to form a dielectric film capable of covering the optical waveguide layer 30. Then, a further dielectric material is deposited on the portion of the dielectric film covering the optical waveguide layer 30, where protrusions 41 have been formed. Optionally, the dielectric material may be, but is not limited to, silicon dioxide.

[0085] A portion of the protrusion 41 protrudes toward the piezoelectric control unit 60 and compresses the insulating layer 50 and the piezoelectric control unit 60 to form an upward protrusion. Thus, when the piezoelectric control unit 60 applies deformation stress to the optical waveguide layer 30, the protrusion 41 can increase the stress concentrated on the optical waveguide layer 30 to a certain extent, thereby improving the efficiency of phase modulation and reducing driving power consumption.

[0086] The above technical solution can form the protrusion 41 during the preparation of the second dielectric layer 40. On the one hand, the protrusion 41 and the second dielectric layer 40 are made using the same method and the same material, resulting in a high degree of smoothness in the preparation process and improving the preparation efficiency. On the other hand, by directly forming the protrusion by further depositing dielectric material in the portion of the optical waveguide layer 30 covered by the dielectric film, compared with other methods (such as forming the protrusion in the non-removed area by excavation), material waste can be effectively reduced, which is beneficial to reducing production costs.

[0087] Figure 10 This is a schematic diagram of the structure of another optical signal phase modulation device 110 provided in some embodiments of this application.

[0088] Continue to refer to Figure 10 In some embodiments, step 110 above, which involves providing a substrate 10 and forming a first dielectric layer 20 on one side surface of the substrate 10, may specifically include the following steps:

[0089] Step 1101: Groove the substrate 10 base material to form a groove 11, so as to obtain a substrate 10 with groove 11;

[0090] Step 1102: A first dielectric layer 20 is formed on the side surface of the substrate 10 where the groove 11 opening is located.

[0091] As an example, the substrate 10 can be, but is not limited to, made of silicon. The groove 11 can be formed by machining the substrate 10 through a groove-cutting process, or by chemical etching.

[0092] It is understandable that during the phase modulation of the optical waveguide layer 30 by the piezoelectric control unit 60, the optical waveguide layer 30 will deform, and the deformation stress will be transmitted to the first dielectric layer 20, thereby causing the first dielectric layer 20 to also deform.

[0093] Thus, the groove 11 can accommodate the first dielectric layer 20 that is squeezed by the deformation of the substrate 10, thereby increasing the movable space of the optical waveguide layer 30, thereby increasing the equivalent mode refractive index difference of the optical waveguide layer 30 under the same stress and improving the phase modulation efficiency of the piezoelectric control unit 60.

[0094] Optionally, the orthographic projection of the optical waveguide layer 30 on the substrate 10 at least partially coincides with the groove 11, or the orthographic projection of the optical waveguide layer 30 on the substrate 10 completely coincides with the groove 11. In this way, by setting the groove 11 to correspond to the optical waveguide layer 30, the sensitivity of the optical waveguide layer 30 to generate strain can be improved, and the phase modulation accuracy of the piezoelectric control unit 60 can be further improved.

[0095] It is understandable that if the first dielectric layer 20 is formed on one side surface of the substrate 10, and then the substrate 10 is grooved to form a groove 11, the first dielectric layer 20 is easily damaged during the grooving process, which will affect the quality of the product and the preparation yield.

[0096] The above technical solution, by first forming a groove 11 on the substrate 10 and then forming a first dielectric layer 20 on the side surface of the substrate 10 with the opening of the groove 11, can effectively reduce the impact of the formation process of the groove 11 on the first dielectric layer 20, thereby improving the quality of the product and the preparation yield.

[0097] In some embodiments, step 120, which involves forming a patterned optical waveguide layer 30 on the surface of the first dielectric layer 20 facing away from the substrate 10, may specifically include the following steps:

[0098] Step 1201: Deposit optical waveguide material on the side of the first dielectric layer 20 facing away from the substrate 10 to form an optical waveguide thin film;

[0099] Step 1202: The optical waveguide thin film is subjected to photolithography to form a patterned optical waveguide layer 30.

[0100] As an example, an optical waveguide material is first deposited on the surface of the first dielectric layer 20 facing away from the substrate 10 to form an optical waveguide thin film. Then, photoresist is coated onto the optical waveguide thin film, and the photoresist is patterned using a photolithography machine. The photoresist pattern is then used to mask the optical waveguide thin film. Finally, the optical waveguide thin film is etched to form a patterned optical waveguide layer 30. The optical waveguide material can be, but is not limited to, silicon nitride or silicon.

[0101] The above technical solution combines deposition and photolithography methods to form a patterned optical waveguide layer 30, which can further improve the fabrication yield and quality of the optical waveguide layer 30.

[0102] Continue to refer to Figure 8 In some embodiments, step 150 above, forming a piezoelectric control unit 60 on the side of the insulating layer 50 facing away from the second dielectric layer 40, may specifically include the following steps:

[0103] Step 1501: A piezoelectric material layer 61 is formed on the side of the isolation layer 50 facing away from the second dielectric layer 40;

[0104] Step 1502: A first electrode 62 and a second electrode 63 are formed on the side of the piezoelectric material layer 61 facing away from the isolation layer 50. The first electrode 62 and the second electrode 63 are spaced apart along a first direction X, which intersects with the direction of optical signal transmission.

[0105] As an example, electrode material can be deposited on the surface of the piezoelectric material layer 61 on the side opposite to the isolation layer 50 to form an electrode material film, and then the electrode material film can be etched to form the first electrode 62 and the second electrode 63.

[0106] Optionally, the piezoelectric material layer 61 can be prepared using, but is not limited to, at least one of barium titanate, lead zirconate titanate, zinc oxide, aluminum nitride, or scandium-doped aluminum nitride. It should be noted that other compound materials with inverse piezoelectric effects known in the art can also be used to prepare the piezoelectric material layer 61, and this is not a limitation.

[0107] Optionally, the method for forming the piezoelectric material layer 61 on the side of the isolation layer 50 facing away from the second dielectric layer 40 can be, but is not limited to, at least one of magnetron sputtering, sol-gel method, and pulsed laser deposition. The above methods can be selected according to actual needs. Similarly, other techniques known in the art can also be used to prepare the piezoelectric material layer 61, without limitation.

[0108] Optionally, the method for forming the first electrode 62 can be, but is not limited to, at least one of deposition or etching methods, and the method for forming the second electrode 63 can be, but is not limited to, at least one of deposition or etching methods. Exemplarily, the first electrode 62 and the second electrode 63 can be made of the same material and prepared using the same method to simplify the overall preparation complexity and reduce costs.

[0109] As an example, by energizing the first electrode 62 and the second electrode 63, a voltage can be applied to the piezoelectric material layer 61, causing it to deform. The deformation of the piezoelectric control unit 60 induces strain in the optical waveguide layer 30, causing the refractive index of the optical waveguide layer 30 to change due to the photoelastic effect, thereby achieving phase modulation of the light. Thus, by applying a voltage to the piezoelectric material layer 61 through two electrodes to induce deformation, an electrical signal is converted into a compressive force on the optical waveguide layer 30, exhibiting high modulation efficiency and low optical transmission loss.

[0110] Furthermore, the first electrode 62 and the second electrode 63 are spaced apart on both sides of the piezoelectric material layer 61 along the first direction X, and the orthographic projection of the optical waveguide layer 30 onto the substrate 10 is located between the orthographic projections of the first electrode 62 and the second electrode 63 onto the substrate 10. The optical signal is transmitted in the optical waveguide layer 30 along its extension direction (axial direction), where the first direction X can be understood as the radial direction of the optical waveguide layer 30. This allows for better utilization of the space above the optical waveguide layer 30, alters the electric field application method of the piezoelectric control unit 60, and to a certain extent ensures that the distance between the first electrode 62 and the second electrode 63 is sufficiently large, thereby increasing the electrical bandwidth of the piezoelectric control unit 60 and improving modulation efficiency.

[0111] After the piezoelectric material layer 61 is formed on the side of the isolation layer 50 facing away from the second dielectric layer 40, the first electrode 62 and the second electrode 63 can be formed directly on the side of the piezoelectric material layer 61 facing away from the isolation layer 50. This reduces the fabrication steps of the piezoelectric control unit 60, which is beneficial to improving fabrication efficiency and reducing fabrication costs.

[0112] Figure 11 This is a schematic diagram of the structure of another optical signal phase modulation device 110 provided in some embodiments of this application.

[0113] Continue to refer to Figure 11 In some embodiments, step 150 above, forming a piezoelectric control unit 60 on the side of the insulating layer 50 facing away from the second dielectric layer 40, may specifically include the following steps:

[0114] Step 1503: Form a first electrode 62 on the side of the isolation layer 50 facing away from the second dielectric layer 40;

[0115] Step 1504: A piezoelectric material layer 61 is formed on the side of the first electrode 62 facing away from the isolation layer 50;

[0116] Step 1505: A second electrode 63 is formed on the side of the piezoelectric material layer 61 facing away from the first electrode 62.

[0117] Optionally, the piezoelectric material layer 61 can be prepared using, but is not limited to, at least one of barium titanate, lead zirconate titanate, zinc oxide, aluminum nitride, or scandium-doped aluminum nitride. It should be noted that other compound materials with inverse piezoelectric effects known in the art can also be used to prepare the piezoelectric material layer 61, and this is not a limitation.

[0118] Optionally, the method for forming the piezoelectric material layer 61 on the side of the isolation layer 50 facing away from the second dielectric layer 40 can be, but is not limited to, at least one of magnetron sputtering, sol-gel method, and pulsed laser deposition. The above methods can be selected according to actual needs. Similarly, other techniques known in the art can also be used to prepare the piezoelectric material layer 61, without limitation.

[0119] Optionally, the method for forming the first electrode 62 can be, but is not limited to, at least one of deposition or etching methods, and the method for forming the second electrode 63 can be, but is not limited to, at least one of deposition or etching methods. Exemplarily, the first electrode 62 and the second electrode 63 can be made of the same material and prepared using the same method to simplify the overall preparation complexity and reduce costs.

[0120] In the above technical solution, the piezoelectric material layer 61 is located between the first electrode 62 and the second electrode 63. The first electrode 62 and the second electrode 63 apply a voltage to the piezoelectric material layer 61, which enables the piezoelectric material layer 61 to undergo a more uniform deformation in a direction parallel to the plane where the piezoelectric material layer 61 is located. This results in a more uniform deformation stress on the optical waveguide layer 30, thereby improving the reliability of the optical signal phase modulation device 110. Furthermore, by first forming the first electrode 62 on the side of the isolation layer 50 facing away from the second dielectric layer 40, and then forming the piezoelectric material layer 61 on the side of the first electrode 62 facing away from the isolation layer 50, the influence of the flatness and density of the surface of the second dielectric layer 40 facing away from the first dielectric layer 20 on the fabrication of the piezoelectric material layer 61 can be further reduced, thereby effectively reducing the overall fabrication difficulty of the piezoelectric control unit 60.

[0121] Figure 12 This is a schematic diagram of the structure of another optical signal phase modulation device 110 provided in some embodiments of this application.

[0122] Continue to refer to Figure 12 In some embodiments, after forming the second electrode 63 on the side of the piezoelectric material layer 61 opposite to the first electrode 62 in step 1505, the following steps may be further included:

[0123] Step 1506: The piezoelectric control unit 60 is etched to divide it into two independent sub-piezoelectric control units 60. The two sub-piezoelectric control units 60 are spaced apart along the first direction X, which intersects the direction of optical signal transmission.

[0124] As an example, after sequentially forming a first electrode 62, a piezoelectric material layer 61, and a second electrode 63 to obtain a piezoelectric control unit 60, the piezoelectric control unit 60 is then etched to divide it into two independent sub-piezoelectric control units. Optionally, etching can be performed along the central axis of the piezoelectric control unit 60 to obtain two sub-piezoelectric control units of the same size, thereby improving the performance uniformity between the two sub-piezoelectric control units.

[0125] In this way, the two sub-piezoelectric control units can apply deformation stress to the optical waveguide layer 30 on both sides of the first direction X, which changes the electric field application mode of the piezoelectric control unit 60 and ensures that the distance between the two sub-piezoelectric control units 60 is large enough to a certain extent, thereby increasing the electrical bandwidth of the piezoelectric control unit 60 and improving the modulation efficiency.

[0126] To more clearly describe the embodiments of this application, the following description uses two independent sub-piezoelectric control units, namely the first sub-control unit 60a and the second sub-control unit 60b, as an example.

[0127] For example, the piezoelectric control unit 60 includes a first sub-control unit 60a and a second sub-control unit 60b. The first sub-control unit 60a and the second sub-control unit 60b are spaced apart on both sides of the optical waveguide layer 30 along a first direction X. The optical signal is transmitted in the optical waveguide layer 30 along the extension direction (axial direction) of the optical waveguide layer 30, and the first direction X can be understood as the radial direction of the optical waveguide layer 30. In this way, the space on the upper side of the optical waveguide layer 30 can be better utilized, the electric field application mode of the piezoelectric control unit 60 is changed, and the distance between the first sub-control unit 60a and the second sub-control unit 60b is large enough to a certain extent, thereby increasing the electrical bandwidth of the piezoelectric control unit 60 and improving the modulation efficiency.

[0128] Specifically, the first sub-control unit 60a includes a third electrode 64, a fourth electrode 65, and a first piezoelectric material 611. The third electrode 64 is disposed on the isolation layer 50, the fourth electrode 65 is located on the side of the third electrode 64 away from the isolation layer 50, and the first piezoelectric material 611 is located between the third electrode 64 and the fourth electrode 65.

[0129] The second sub-control unit 60b includes a fifth electrode 66, a sixth electrode 67, and a second piezoelectric material 612. The fifth electrode 66 is disposed on the isolation layer 50, the sixth electrode 67 is located on the side of the fifth electrode 66 away from the isolation layer 50, and the second piezoelectric material 612 is located between the fifth electrode 66 and the sixth electrode 67.

[0130] Compared with the method of forming a first electrode 62, a piezoelectric material layer 61, and a second electrode 63 in two separate steps to obtain two independent sub-piezoelectric control units, the above-mentioned technical solution can effectively simplify the preparation process, improve preparation efficiency, and reduce costs. On the other hand, it can reduce the structural differences between the two sub-piezoelectric control units, which is beneficial to improving the performance uniformity between the two sub-piezoelectric control units.

[0131] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0132] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for fabricating an optical signal phase modulation device, characterized in that, include: A substrate is provided and a first dielectric layer is formed on one side surface of the substrate; A patterned optical waveguide layer is formed on the side of the first dielectric layer facing away from the substrate, and the optical waveguide layer is used to transmit optical signals; A second dielectric layer is formed on the side of the first dielectric layer facing away from the substrate, and the second dielectric layer covers the optical waveguide layer; An isolation layer is formed on the side of the second dielectric layer opposite to the first dielectric layer, and the crystal orientation uniformity of the isolation layer is greater than that of the second dielectric layer. A piezoelectric control unit is formed on the side of the isolation layer opposite to the second dielectric layer. The piezoelectric control unit is capable of applying pressure to the optical waveguide layer to adjust the refractive index of the optical waveguide layer for the optical signal.

2. The method for fabricating the optical signal phase modulation device according to claim 1, characterized in that, Before the step of forming an isolation layer on the side of the second dielectric layer opposite to the first dielectric layer, the method further includes: The step of polishing the side surface of the second dielectric layer facing away from the first dielectric layer to form a polished surface.

3. The method for fabricating the optical signal phase modulation device according to claim 1, characterized in that, The step of forming a second dielectric layer on the side of the first dielectric layer facing away from the substrate includes: A dielectric material is deposited on the side of the first dielectric layer facing away from the substrate to form a dielectric thin film, the dielectric thin film covering the optical waveguide layer; The dielectric material is further deposited on the portion of the dielectric film covering the optical waveguide layer, such that the portion of the dielectric film covering the optical waveguide layer protrudes beyond the portion of the dielectric film covering the first dielectric layer, to obtain a second dielectric layer with protrusions.

4. The method for fabricating the optical signal phase modulation device according to claim 1, characterized in that, The provision of a substrate and the formation of a first dielectric layer on one side surface of the substrate includes: Grooves are formed by grooving the substrate material to obtain a substrate with grooves; The first dielectric layer is formed on the side surface of the substrate having the groove opening.

5. The method for fabricating the optical signal phase modulation device according to claim 1, characterized in that, The formation of a patterned optical waveguide layer on the side surface of the first dielectric layer facing away from the substrate includes: Optical waveguide material is deposited on the side of the first dielectric layer facing away from the substrate to form an optical waveguide thin film; The optical waveguide thin film is subjected to photolithography to form a patterned optical waveguide layer.

6. The method for fabricating the optical signal phase modulation device according to claim 1, characterized in that, Methods for forming an isolation layer on the side of the second dielectric layer opposite to the first dielectric layer include at least one of chemical vapor deposition, atomic layer deposition, free radical-assisted film formation, and supercritical fluid film formation.

7. The method for fabricating the optical signal phase modulation device according to claim 1, characterized in that, The piezoelectric control unit formed on the side of the insulating layer opposite to the second dielectric layer includes: A piezoelectric material layer is formed on the side of the insulating layer opposite to the second dielectric layer; A first electrode and a second electrode are formed on the side of the piezoelectric material layer opposite to the insulating layer. The first electrode and the second electrode are spaced apart along a first direction, which intersects the transmission direction of the optical signal.

8. The method for fabricating the optical signal phase modulation device according to claim 1, characterized in that, The piezoelectric control unit formed on the side of the insulating layer opposite to the second dielectric layer includes: A first electrode is formed on the side of the isolation layer opposite to the second dielectric layer; A piezoelectric material layer is formed on the side of the first electrode opposite to the insulating layer; A second electrode is formed on the side of the piezoelectric material layer opposite to the first electrode.

9. The method for fabricating the optical signal phase modulation device according to claim 8, characterized in that, Also includes: The piezoelectric control unit is etched to divide it into two independent sub-piezoelectric control units. The two sub-piezoelectric control units are spaced apart along a first direction, which intersects the direction of optical signal transmission.

10. The method for fabricating the optical signal phase modulation device according to any one of claims 7-9, characterized in that, The method for forming the piezoelectric material layer includes at least one of magnetron sputtering, sol-gel method and pulsed laser deposition.

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