Aluminum oxide surface waveguide and surface sensor based on structural deformation and preparation method of aluminum oxide surface waveguide and surface sensor

Abstract

The invention discloses an aluminum oxide surface waveguide based on structural deformation, a surface sensor and a preparation method, and the method comprises the steps: carrying out the structural deformation of an aluminum oxide internal waveguide which is composed of a linear modification region and has a circular end surface, specifically, enabling the aluminum oxide internal waveguide to move to an aluminum oxide surface, a linear modification area above the aluminum oxide surface is removed from the circular ring aluminum oxide internal waveguide, a U-shaped ring structure formed on the aluminum oxide surface serves as an aluminum oxide surface waveguide, the end face is perpendicular to the aluminum oxide surface, and the inner radius of the circular ring is 10-25 microns; the distance from the top of the U-shaped ring structure to the surface of the aluminum oxide is 1-10 microns, and when the linear modification area above the surface of the aluminum oxide is removed to form the U-shaped ring structure, the distance from the bottom of the U-shaped ring structure to the surface of the aluminum oxide is also limited to be 1 / 2-3 / 2 of the inner radius of a circular ring. By optimizing laser parameters and process conditions of laser direct writing, high-precision and high-stability aluminum oxide surface optical waveguide preparation is realized, and a new technical means is provided for integration and miniaturization of photonic devices.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical devices and laser processing, and in particular relates to an aluminum oxide surface waveguide and surface sensor based on structural deformation and a preparation method thereof. Background Art

[0002] Optical waveguides are important basic components in optical devices, and their preparation technology and performance optimization have received widespread attention. They play a key role in application fields such as optical communications and integrated optics. In recent years, laser direct writing technology has become a highly efficient method for preparing optical waveguides due to its advantages such as high precision, flexible controllability, and non-contact processing. Laser direct writing technology can be used as an effective alternative, especially in areas where traditional micro-nano processing technologies have difficulty achieving ideal results. Laser direct writing technology uses methods such as objective lens focusing to focus a high-energy density laser beam, achieving local modification of the target material near the focus of the laser beam. By structurally designing the modified area, the desired waveguide structure is formed. This technology can achieve patterning and structuring with precise controllability at the micro-nano scale, is applicable to a variety of materials, and has broad application prospects.

[0003] Optical waveguides fabricated using laser direct writing technology can be divided into three main categories based on material classification: glass, polymers, and crystals. The effects of laser interaction with different materials differ fundamentally. Glass and polymers, as amorphous materials, have a low threshold laser power for modification. Laser focus modifies the material, resulting in a positive change in the refractive index (i.e., an increase) in the modified area. Furthermore, these two types of materials are susceptible to external conditions, and glass and polymers exhibit poor stability in environments such as high temperatures and corrosion. Regarding the third category: crystalline materials, due to their lattice structure, the threshold laser power for modification is relatively high, resulting in a negative change in the refractive index (i.e., a decrease) in the modified area. The advantages of crystalline materials include greater material stability, greater reliability in temperature and corrosive environments, and some crystalline materials also possess superior hardness and wear resistance. However, their disadvantage is that crystalline materials are prone to cracking when using laser direct writing technology to fabricate micro-nanooptical components such as optical waveguides. Due to the hard and brittle material properties of crystals, laser processing requires precise control of laser optical parameters and mechanical parameters included in the processing conditions. At the same time, special structural designs can also be used to ultimately produce optical waveguide components with excellent performance and realize applications in different fields.

[0004] When using laser direct writing technology to prepare optical waveguides for crystal materials, the location of the optical waveguide is also distinguished, including two types: inside the crystal material and on the surface. In existing inventions and literature reports, laser direct writing technology can realize waveguide structures inside the crystal, but it cannot directly modify the material on the crystal surface. This is because the laser power threshold for laser modification of the crystal surface is low, and as the interface between the crystal and the environment (such as air), it is more susceptible to thermal effects. Therefore, when the laser modifies the crystal surface, cracks are inevitably generated, which is a difficulty in preparing crystal surface waveguides.

[0005] Alumina, a typical crystalline material, has a high melting point, adapts to high-temperature environments, possesses excellent mechanical properties with high hardness, and exhibits chemical stability and corrosion resistance. It also exhibits high transmittance across a wide spectrum encompassing the ultraviolet, visible, near-infrared, and mid-infrared, making it a versatile material with excellent performance. Traditional methods for processing alumina primarily include micro-nanofabrication techniques such as ion beam etching and photolithography. While these methods can achieve the fabrication of optical waveguides to a certain extent, they suffer from complex processes, high costs, and long fabrication cycles, limiting their widespread adoption in practical applications. Accordingly, laser direct writing, as a novel technology, offers a precise and efficient fabrication method for fabricating waveguide structures in alumina crystals. Currently, research on the fabrication of alumina surface waveguides based on laser direct writing still faces challenges, including laser parameter optimization, waveguide structure design, and surface quality control. Therefore, developing an efficient and controllable method for fabricating alumina waveguides, particularly alumina surface waveguides, based on laser direct writing is of great significance for promoting the development of photonic integrated technology. Summary of the Invention

[0006] In view of the above, the purpose of the present invention is to provide an alumina surface waveguide and surface sensor based on structural deformation and a preparation method. By designing an alumina surface waveguide with a special structure based on structural deformation and optimizing the laser parameters and process conditions of laser direct writing, high-precision and high-stability alumina surface optical waveguide preparation is achieved, providing new technical means for the integration and miniaturization of photonic devices.

[0007] To achieve the above-mentioned purpose of the invention, an embodiment provides an aluminum oxide surface waveguide based on structural deformation, comprising: The alumina internal waveguide, which has a circular end face and is composed of linear modified regions, is structurally deformed. Specifically, the alumina internal waveguide is moved toward the alumina surface, and the linear modified regions near or above the alumina surface are removed from the circular alumina internal waveguide. The resulting U-shaped ring structure serves as the alumina surface waveguide, where the end face is perpendicular to the alumina surface and the inner radius of the ring is 10-25 μm. The distance from the top of the U-shaped ring structure to the alumina surface is 1-10um, and when the linear modified area above the alumina surface is removed to form the U-shaped ring structure, the distance from the bottom of the U-shaped ring structure to the alumina surface is also limited to 1 / 2-3 / 2 of the inner radius of the ring.

[0008] In response to the problem that cracks will inevitably appear on the surface of alumina crystals after laser modification, in order to meet the needs of laser direct writing of alumina crystal surface waveguides, alumina surface waveguides are designed based on structural deformation. Specifically, waveguides are prepared at different depths inside the crystal from the surface. The distance between the structure and the surface is reduced until the waveguide structure is close to the surface. The above-mentioned U-shaped ring structure is formed as the alumina surface waveguide. In this way, when implementing the laser direct writing technology, the straight modified area directly on the crystal surface is eliminated, thereby avoiding the occurrence of cracks. However, since the designed U-shaped ring structure is composed of straight modified areas, it can achieve the effect of binding the mode field during light transmission, and thus can be used as a crystal surface waveguide.

[0009] To achieve the above-mentioned object of the invention, an embodiment of the present invention further provides a method for preparing an alumina surface waveguide, wherein the alumina surface waveguide is the above-mentioned U-shaped ring structure formed on the alumina surface, and the preparation method comprises the following steps: Laser direct writing is used to process a U-shaped ring structure on the alumina surface. During processing, the laser beam focusing depth in the alumina, which determines the shape of the structure, the laser repetition frequency and the lateral movement speed of the translation stage, as well as the laser single pulse energy, which determines the degree of modification, are controlled.

[0010] The laser repetition frequency and the lateral movement speed of the translation stage simultaneously determine the shape of the U-shaped ring structure. The laser repetition frequency is set to be adjustable from 1Hz to 2MHz, and the lateral movement speed of the translation stage is set to 1um / s-2000um / s. Multiple laser pulse points form a linear modification zone along the movement direction of the translation stage at a certain interval. Since the interval between laser pulse points directly affects the laser modification performance of alumina, in order to improve the laser modification performance of alumina, when maintaining the laser repetition frequency at 5kHz, the acceptable lateral movement speed is 500-1500um / s, and the interval distance of the laser pulses is required to be 0.1-0.3um. In the experimental investigation, considering the stability of the translation stage movement and the laser processing efficiency, a laser repetition frequency f of 5kHz and a translation stage lateral movement speed v of 900um / s can be used, and the interval distance between the laser pulse points is x=v / f=0.18um. When the spot diameter D after focusing by the objective lens is estimated to be 2um, the number of laser pulses acting on the spot coverage area is approximately N=D / x=11 times. It can be considered that the laser modification effect on alumina is achieved by multiple pulses.

[0011] The energy of a single laser pulse determines the degree of modification of the alumina, specifically the length and width of the linear modified zone. After focusing the objective lens, measurements show that laser pulse energies reaching the alumina in the hundreds of nanojoules (nJ) achieve excellent modification. The specific laser pulse energy fluctuates within a certain range, depending on the depth and effectiveness of the laser modification. Research has also found that the deeper the internal waveguide, the greater the laser pulse energy required for material modification. At a greater depth with the same laser pulse energy, if the laser pulse energy does not reach the modification threshold, the waveguide structure will be incomplete. For surface waveguides, the laser pulse energy must be reduced because cracks are more likely to form near the crystal surface. Cracks are a major challenge and difficulty in fabricating surface waveguides. Therefore, in the present invention, when fabricating alumina surface waveguides, laser pulse energies are in the hundreds of nJ. As the distance from the linear modified zone to the alumina surface decreases, the laser pulse energy used decreases, ensuring both modification and crack-free U-shaped ring-shaped alumina surface waveguides.

[0012] According to the distance between each linear modified area in the U-shaped ring structure and the aluminum oxide surface, the focusing depth of the laser beam in the aluminum oxide is controlled and regulated to achieve different depths of modification of the aluminum oxide to form each linear modified area.

[0013] The laser wavelength can achieve the effect of modifying the alumina crystal. When using laser direct writing to process the U-shaped ring structure on the alumina surface, the laser band range is also limited to the visible to near-infrared range. Combined with common laser wavelengths and the use of frequency doubling accessories, the wavelength range includes 515nm, 532nm, 635nm, 808nm, 1030nm, 1064nm, etc.

[0014] Laser pulse widths of fs are preferred because the fs timescale is shorter than the ps timescale of the heat-affected zone (HAZ) generated by laser absorption in alumina. Therefore, when modifying alumina with an fs laser, the HAZ can be minimized or avoided. This HAZ can lead to uneven stress distribution within the alumina, thus affecting the performance of the fabricated waveguide. Specifically, when fabricating U-shaped ring structures on the alumina surface using laser direct writing, the laser pulse width is limited to 130 fs to 1 ps. To minimize the HAZ and keep it below 1 ps, the laser pulse width is further limited to 130 fs.

[0015] To achieve the above-mentioned object of the invention, an embodiment of the present invention further provides a surface sensor, which adopts the above-mentioned aluminum oxide surface waveguide based on structural deformation.

[0016] To achieve the above-mentioned object of the invention, an embodiment of the present invention further provides a surface sensor, wherein the surface sensor adopts the aluminum oxide surface waveguide prepared by the above-mentioned method.

[0017] Compared with the prior art, the present invention has the following beneficial effects: The present invention uses an ultrafast laser to focus on an incident alumina crystal to achieve local modification of the alumina, and the refractive index of the modified area is reduced. By regulating the optical parameters of the ultrafast laser, including the laser pulse width, laser wavelength, and laser single pulse energy, the concentrated laser is used to act on the alumina to cause material modification. At the same time, the mechanical parameters such as the lateral movement speed of the displacement stage and the laser repetition frequency are regulated to cause relative displacement between the laser beam and the alumina sample, so that the laser beam can form a modified area with a specific trajectory inside and / or on the surface of the alumina sample. The optical parameters and mechanical parameters are synergistically regulated to form a controllable modification result for the alumina crystal while avoiding the generation of cracks. The focusing depth of the laser beam in the alumina is controlled to achieve different depths of modification of the alumina, forming each linear modified area, forming a U-shaped ring structure on the alumina surface, and thus obtaining an alumina surface waveguide that prevents the generation of cracks. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0019] Figure 1 1 is a schematic structural diagram of an alumina surface waveguide based on structural deformation provided in an embodiment; Figure 2 This is a light field simulation diagram of an aluminum oxide surface waveguide based on structural deformation provided in an embodiment; Figure 3 is a cross-sectional view of an alumina surface waveguide prepared experimentally provided in an embodiment; Figure 4 3 is a light field simulation diagram of the surface sensor provided in the embodiment. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not limit the scope of protection of the present invention.

[0021] The inventive concept of the present invention is as follows: when using laser direct writing technology to prepare waveguides from crystal materials, cracks are easily generated due to the material properties of the crystal, making it difficult to obtain optical devices with good performance. At the same time, due to the technical problem that cracks will inevitably be generated when the laser modifies the surface of the crystal, it is impossible to directly prepare the surface waveguide of the crystal. The present invention provides an alumina surface waveguide based on structural deformation and a preparation method thereof. By optimizing the laser optical parameters and the mechanical condition parameters during processing, the laser modification effect on the alumina crystal is regulated, and the laser modification of the alumina is achieved without cracks. By designing a special waveguide structure to prepare an alumina surface optical waveguide and testing its optical properties, the obtained alumina surface waveguide can be used for device applications in extreme environments, such as surface sensors in high temperature environments and corrosive gas environments.

[0022] The alumina surface waveguide provided in the embodiment is obtained by structural deformation of the alumina internal waveguide, that is, the alumina internal waveguide with a circular end face composed of a linear modified area is structurally deformed, specifically, the alumina internal waveguide is moved to the alumina surface, and the linear modified area close to the alumina surface is removed from the circular alumina internal waveguide, such as Figure 1 As shown in the middle left figure, or remove the linear modified area above the aluminum oxide surface, such as Figure 1 As shown in the middle and right figures, the U-shaped ring structure formed serves as an alumina surface waveguide, where the end face is perpendicular to the alumina surface.

[0023] In such Figure 1 In the U-shaped ring structure shown in FIG. Figure 2 The simulation study shown found that Figure 1 In any of the U-shaped ring structures, the enclosed area of ​​the U-shaped ring structure can form a bound light field, acting as a waveguide for surface-transmitted light. By limiting the distance from the top of the U-shaped ring structure to 1-10 μm, specifically 2 μm, the bound light field formed by the U-shaped ring structure exhibits surface waveguide properties without causing cracks on the alumina surface. Furthermore, by limiting the inner radius of the ring to 10-25 μm, specifically 15 μm, the bound light field formed by the U-shaped ring structure exhibits stronger confinement and waveguide properties.

[0024] In the embodiments, it is also explored that when the linear modified area above the aluminum oxide surface is removed to form a U-shaped ring structure, the distance from the bottom of the U-shaped ring structure to the aluminum oxide surface is constrained to 1 / 2-3 / 2 of the inner radius of the ring. The bound light field formed in this way has the transmission characteristics of a surface waveguide. When this distance is exceeded, the U-shaped ring structure can no longer transmit light on the surface, and the central area of ​​the U-shaped ring structure can no longer bind the light field.

[0025] The alumina surface waveguide of the above structure eliminates direct modification of the crystal surface by laser during preparation, thus avoiding cracks, while still maintaining the integrity of the waveguide and the property of efficient light transmission.

[0026] An embodiment also provides a method for preparing the above-mentioned structural deformation-based alumina surface waveguide, specifically using laser direct writing processing to process a U-shaped ring structure in alumina. During processing, the laser repetition frequency and the lateral movement speed of the translation stage that determine the structural shape, the laser single pulse energy that determines the degree of modification, the focusing depth of the laser beam in the alumina, the laser wavelength, and the laser pulse width are controlled.

[0027] The specific steps include: S1. Set the optical parameters and platform processing parameters. The optical parameters include a laser wavelength of 1030 nm, a laser pulse width of 130 fs, a repetition rate of f = 5 kHz, and a single pulse energy of E = 192 nJ. The platform processing parameters include a lateral movement speed of v = 900 μm / s and an initial laser beam focus depth of Z = 0.

[0028] S2: Confirm the U-shaped ring structure and dimensional parameters to be processed. This structure refers to a 1 / 2-circle U-shaped ring structure, but also includes structures that are nearly complete and 3 / 4-circle. The U-shaped ring dimensional parameters include an inner radius of r = 15 μm, the total number of straight lines N = 11 that make up the modified 1 / 2-circle area, and the distance Z0 = 2 μm from the top of the U-shaped ring structure to the alumina surface.

[0029] S3, start from the line with the greatest depth of the U-shaped ring inside the alumina material, and process the lines one by one in the order of decreasing depth. The specific operations include: In step S3-1, first set the laser beam's focal depth to Z1 = Z0 + r, meaning the target line will be the line with the greatest depth within the alumina. Turn on the laser and simultaneously move the stage laterally a certain distance (5mm). Turn off the laser to complete the processing of the first line. S3-2, then set the focal depth of the laser beam to Z2=Z0+ , corresponding to the two lines with the second-greatest depth in the U-shaped ring. Since the U-shaped ring is a symmetrical circular structure, except for the line with the greatest depth, there are two symmetrical lines at all other depths. First, process the left line at that depth. Turn on the laser, move the stage horizontally a certain distance (5mm), and then turn off the laser. Then, process the right line at that depth. S3-3, then set the focus depth of the laser beam to Z3=Z0+ , corresponding to the two lines with the third largest depth in the U-shaped ring. First, process the left line at this depth, turn on the laser, and at the same time move the translation stage a certain distance (5mm) horizontally, then turn off the laser. Then, process the right line at this depth; S3-4, then set the focal depth of the laser beam to Z4 = Z0 + , corresponding to the two straight lines with the fourth largest depth in the U-shaped ring. First, process the left straight line at this depth, turn on the laser, and at the same time move the translation stage a certain distance (5mm) horizontally, then turn off the laser. Then process the right straight line at this depth; S3-5, then set the focus depth of the laser beam to Z5 = Z0 + , corresponding to the two lines with the fifth largest depth in the U-shaped ring. First, process the left line at this depth, turn on the laser, and at the same time move the translation stage a certain distance (5mm) horizontally, then turn off the laser. Then, process the right line at this depth; In step S3-6, set the laser beam's focal depth to Z6 = Z0, corresponding to the two lines closest to the aluminum oxide surface in the U-shaped ring. First, machine the left line at this depth. Turn on the laser, then move the stage laterally a certain distance (5 mm), then turn off the laser. Then, machine the right line at this depth.

[0030] Through the above steps, the Figure 3 Alumina surface waveguide shown.

[0031] The present embodiment also provides a surface sensor based on the aforementioned alumina surface waveguide. In this surface sensor, based on the surface waveguide structure designed according to the present invention, the waveguide core confines the optical mode field of the transmitted light, allowing the transmitted light to be extremely close to the interface between the alumina material and the environment. Due to the differences in the interaction of environmental materials with the transmitted light, a clear comparison can be made between the results of the waveguide transmission of the light.

[0032] For example, the environment is set to air and water, and the transmitted light is set to a mid-infrared wavelength of 2.85um. At this wavelength, water has a strong absorption and air has a weak absorption. When the input light is TM mode, the electric field of the TM mode has a longitudinal component (E z ), will penetrate the waveguide-environment interface more strongly, enhancing the interaction between light and the surrounding matter. As a result, when the environment is water, the light transmitted in the waveguide is more easily absorbed by the environment, making it difficult to detect at the output end. When the environment is air, the light transmitted in the waveguide is less susceptible to environmental influences and can be detected at the output end.

[0033] The embodiment also conducted a simulation, with the inner ring radius of the waveguide structure being 15 μm, the outer ring radius being 28 μm, the transmitted light wavelength being 2.85 μm, and the TM mode. The left and right figures show the mode field distribution of the transmitted light in ambient water (non-transmittable) and air (transmittable). The simulation results are shown in Figure 1. Figure 4 As shown, analysis Figure 4 It can be seen that the aluminum oxide surface waveguide of the present invention has a confinement effect on light.

[0034] The specific implementation methods described above provide a detailed description of the technical solutions and beneficial effects of the present invention. It should be understood that the above is only the most preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, supplements and equivalent substitutions made within the scope of the principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An alumina surface waveguide based on structural deformation, characterized in that: include: The alumina internal waveguide, which has a circular end face and is composed of linear modified regions, is structurally deformed. Specifically, the alumina internal waveguide is moved toward the alumina surface, and the linear modified regions near or above the alumina surface are removed from the circular alumina internal waveguide. The resulting U-shaped ring structure serves as the alumina surface waveguide, where the end face is perpendicular to the alumina surface and the inner radius of the ring is 10-25 μm. The distance from the top of the U-shaped ring structure to the alumina surface is 1-10um, and when the linear modified area above the alumina surface is removed to form the U-shaped ring structure, the distance from the bottom of the U-shaped ring structure to the alumina surface is also limited to 1 / 2-3 / 2 of the inner radius of the ring.

2. A method for preparing an alumina surface waveguide, characterized in that: The alumina surface waveguide is a U-shaped ring structure formed on the alumina surface as claimed in claim 1, and the preparation method includes the following steps: Laser direct writing is used to process a U-shaped ring structure in alumina. During processing, the focusing depth of the laser beam in alumina, which determines the shape of the structure, the laser repetition frequency and the lateral movement speed of the translation stage, and the laser single pulse energy, which determines the degree of modification, are controlled.

3. The method for preparing an aluminum oxide surface waveguide according to claim 2, wherein: The laser repetition frequency is 1 Hz-2 MHz, the lateral movement speed of the translation stage is 1 um / s-2000 um / s, and the interval distance between the laser pulses is 0.1-0.3 um.

4. The method for preparing an aluminum oxide surface waveguide according to claim 2, wherein: The energy of the single laser pulse is on the order of hundreds of nJ, and as the distance from the linear modified area to the alumina surface becomes shorter, the energy of the single laser pulse used becomes smaller, thereby ensuring that the U-shaped ring structure alumina surface waveguide does not have cracks while ensuring modification.

5. The method for preparing an aluminum oxide surface waveguide according to claim 2, wherein: According to the distance between each linear modified area in the U-shaped ring structure and the aluminum oxide surface, the focusing depth of the laser beam in the aluminum oxide is adjusted to achieve different depths of modification of the aluminum oxide to form each linear modified area.

6. The method for preparing an aluminum oxide surface waveguide according to claim 2, wherein: When laser direct writing is used to process a U-shaped ring structure on an alumina surface, the laser wavelength range is limited to visible to near-infrared, specifically 515 nm, 532 nm, 635 nm, 808 nm, 1030 nm, and 1064 nm.

7. The method for preparing an aluminum oxide surface waveguide according to claim 2, wherein: When using laser direct writing to process a U-shaped ring structure on an alumina surface, the laser pulse width is also limited to 130fs-1ps.

8. A surface sensor, characterized in that: The surface sensor adopts the aluminum oxide surface waveguide based on structural deformation as claimed in claim 1.

9. A surface sensor, characterized in that: The surface sensor adopts the aluminum oxide surface waveguide prepared by the method according to any one of claims 2 to 7.

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