Monocrystalline thin film, periodically poled waveguide device and preparation method thereof, solar blind ultraviolet light detector and detection method

Abstract

The application provides a single crystal thin film, a preparation method of a periodic polarization waveguide device, a solar blind ultraviolet light detector and a detection method. The single crystal thin film is formed by forming a functional layer on a substrate, and the material of the functional layer is near-stoichiometric lithium tantalate or magnesium-doped near-stoichiometric lithium tantalate, which can provide solar blind ultraviolet band transparent characteristics and solve the problem of solar blind ultraviolet transparency. In addition, the thickness of the functional layer is set to be between 100 nm and 1000 nm. In this thickness range, the polarization reversal voltage can be reduced to tens of volts, the low voltage can inhibit the lateral expansion of the domain wall, and then a uniform sub-micron periodic polarization structure is obtained.

Description

Technical Field

[0001] This application relates to the fields of integrated optics, nonlinear optics and photoelectric detection technology, and in particular to a single-crystal thin film, a periodically polarized waveguide device and its fabrication method, a solar-blind ultraviolet detector and its detection method. Background Technology

[0002] Solar-blind ultraviolet (UV) communication offers advantages such as low background noise and strong interference resistance, making it suitable for secure communication applications. The solar-blind UV detector is a core component of the communication system, converting UV signals into electrical signals; its performance directly determines the communication distance and quality. UV detectors primarily consist of semiconductor photodiodes and photomultiplier tubes. Semiconductor detectors are small and inexpensive but have extremely low UV responsivity, while photomultiplier tubes offer superior performance but are bulky and expensive.

[0003] To improve the ultraviolet responsivity of semiconductor detectors, some solutions employ fluorescent down-conversion materials to convert ultraviolet light into visible light. However, the long decay lifetime of fluorescent conversion materials leads to poor dynamic response, and organic encapsulation adhesives are prone to aging and deterioration under ultraviolet irradiation. Besides fluorescent conversion materials, nonlinear optical crystals can also achieve high-efficiency frequency conversion. For example, lithium niobate crystals have excellent performance, but their ultraviolet absorption edge is located at 326 nm, resulting in significant absorption loss in the solar-blind ultraviolet band. Another example is lithium tantalate crystals, which have an even shorter ultraviolet absorption edge. After near-stoichiometric modification and magnesium doping, they can be blue-shifted to below 266 nm, and also exhibit low coercivity and high resistance to photodamage.

[0004] However, bulk lithium tantalate has a low Curie temperature, making it impossible to fabricate waveguides at high temperatures. It is also difficult to fabricate submicron-scale periodic polarization structures uniformly over a large area, thus failing to combine the transparency characteristics of solar-blind ultraviolet bands with the ability to fabricate uniform submicron-scale periodic polarization structures. Summary of the Invention

[0005] This application provides a single-crystal thin film, a periodically polarized waveguide device and its fabrication method, a solar-blind ultraviolet detector and its detection method, to solve the problem of not being able to simultaneously possess the transparency characteristics of the solar-blind ultraviolet band and be able to fabricate a uniform submicron periodically polarized structure.

[0006] In a first aspect, a single-crystal thin film is provided, comprising: a substrate, a buffer layer, and a functional layer sequentially stacked; The material of the functional layer is near-stoichiometric lithium tantalate or magnesium-doped near-stoichiometric lithium tantalate, and the thickness of the functional layer is 100nm-1000nm.

[0007] Secondly, a periodically polarized waveguide device is provided, comprising: The single-crystal thin film as described in any one of the first aspects; A periodic polarization structure is formed in the functional layer of the single-crystal thin film; A ridge waveguide structure is formed on the functional layer, and the extension direction of the ridge waveguide structure is parallel to the arrangement direction of the periodic polarization structure.

[0008] Thirdly, a solar-blind ultraviolet light detector is provided, comprising: The periodically polarized waveguide device described in any one of the second aspects; A silicon detector connected to the optical path of the periodically polarized waveguide device.

[0009] Fourthly, a method for detecting solar-blind ultraviolet light includes: The solar-blind ultraviolet signal light to be tested and the pump light are coupled into the periodically polarized waveguide device described in any one of the second aspects; In the periodically polarized waveguide device, the solar-blind ultraviolet signal light and the pump light undergo a difference frequency effect to generate difference frequency light, and the intensity of the difference frequency light is proportional to the intensity of the solar-blind ultraviolet signal light. The difference frequency light is detected using a silicon detector, and the intensity information of the solar-blind ultraviolet signal light is obtained based on the intensity of the difference frequency light.

[0010] Fifthly, a method for preparing a single-crystal thin film is provided, for preparing the single-crystal thin film according to any one of the first aspects, comprising: Provide near-stoichiometric lithium tantalate or magnesium-doped near-stoichiometric lithium tantalate single crystals as donor wafers; Ion implantation is performed on the donor wafer to form an implantation layer inside the donor wafer; A substrate is provided on which a buffer layer is formed; Bond the injection layer to the buffer layer; Heat treatment is performed to peel the donor wafer along the implantation layer and form a functional layer on the substrate; The functional layer is subjected to surface planarization and annealing to obtain a single-crystal thin film.

[0011] Sixthly, a method for fabricating a periodically polarized waveguide device is provided, for fabricating the periodically polarized waveguide device as described in any one of the second aspects, comprising: Periodic electrodes are fabricated on the functional layer of a single-crystal thin film and polarized by an external electric field to form a periodic polarization structure in the functional layer. Remove the periodic electrode; A ridge waveguide structure is etched on the functional layer, and the extension direction of the ridge waveguide structure is parallel to the arrangement direction of the periodic polarization structure.

[0012] As can be seen from the above technical solutions, this application provides a single-crystal thin film, a periodically polarized waveguide device and its fabrication method, a solar-blind ultraviolet detector and its detection method. The single-crystal thin film forms a functional layer on a substrate, and the material of the functional layer is near-stoichiometric lithium tantalate or magnesium-doped near-stoichiometric lithium tantalate, which can provide transparency characteristics in the solar-blind ultraviolet band and solve the problem of solar-blind ultraviolet transparency. Furthermore, the thickness of the functional layer is set between 100nm and 1000nm. Within this thickness range, the polarization reversal voltage can be reduced to tens of volts. The low voltage can suppress the lateral widening of the domain walls, thereby obtaining a uniform submicron periodically polarized structure. Attached Figure Description

[0013] To more clearly illustrate the technical solution of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0014] Figure 1 This is a schematic diagram of the structure of the single-crystal thin film provided in the embodiments of this application; Figure 2 A schematic diagram illustrating the method for preparing a single-crystal thin film according to an embodiment of this application; Figure 3 This is a schematic diagram of the structure of a periodically polarized waveguide device provided in an embodiment of this application; Figure 4 A schematic diagram illustrating the fabrication process of the X-near-stoichiometric lithium tantalate periodically polarized waveguide device provided in the embodiments of this application; Figure 5 A schematic diagram illustrating the fabrication process of the Z-cut magnesium-doped near-stoichiometric lithium tantalate periodically polarized waveguide device provided in this application embodiment; Figure 6 This is a schematic diagram of the structure of a solar-blind ultraviolet detector provided in an embodiment of this application. Detailed Implementation

[0015] The embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following examples do not represent all embodiments consistent with this application.

[0016] The electromagnetic spectrum of ultraviolet light ranges from 10nm to 400nm. When ultraviolet radiation from the sun passes through the atmosphere, it exhibits the following characteristics: oxygen in the upper atmosphere strongly absorbs ultraviolet radiation with wavelengths less than 200nm, and this band of ultraviolet radiation only exists in outer space. The ozone layer in the stratosphere strongly absorbs ultraviolet radiation with wavelengths around 250nm, and this band of ultraviolet radiation is almost non-existent in the near-Earth atmosphere, known as the solar blind zone, with a wavelength range of 200nm-300nm. The near-ultraviolet component of solar radiation, with wavelengths of 300nm-400nm, can pass through the Earth's atmosphere in greater quantities; this band is known as the atmospheric ultraviolet window.

[0017] Ultraviolet (UV) communication utilizes the scattering of UV light in the atmosphere for information transmission. When UV communication systems operate in the 200nm-300nm wavelength band, there is virtually no atmospheric background noise interference during signal transmission. The energy loss from Rayleigh scattering of UV radiation in the atmosphere is more than 1000 times that of infrared radiation, and the energy attenuation is rapid. Therefore, even UV detectors struggle to eavesdrop on signals beyond a limited distance. The transmission characteristics of UV light in the near-ground atmosphere give UV communication advantages such as low eavesdropping rate, anti-interference capability, omnidirectional and all-weather capability, and non-line-of-sight communication, making it suitable for short-range, anti-interference, and secure communication in complex environments.

[0018] Solar-blind ultraviolet (UV) photodetectors in the 200nm-300nm band are core components of UV communication systems. Their main function is to convert UV light signals into electrical signals. The performance of UV photodetectors directly affects the transmission distance and code generation rate of UV communication. Internationally used UV photodetectors include photodiodes (PIN), avalanche photodiodes (APD), and photomultiplier tubes (PMT). Semiconductor photodetectors such as photodiodes and avalanche photodiodes typically have response wavelengths in the visible and near-infrared light bands. Their responsivity in the UV band is very low, only 0.05-0.1 amperes per watt, and their low cutoff frequency severely affects the detection of UV signals in the solar-blind zone.

[0019] Solar-blind photomultiplier tube detectors have high responsivity in the ultraviolet band, as well as large detection area, high gain and bandwidth, and extremely low dark current. Power consumption can be reduced to about 100 milliwatts. However, even with the latest technology, photomultiplier tube detectors are still much larger than semiconductor detectors and cost thousands of times more, which severely limits their practical application in ultraviolet communication systems.

[0020] To improve the responsivity of semiconductor photodetectors such as photodiodes and avalanche photodiodes in the ultraviolet band, two approaches can be adopted. The first approach is to directly improve the responsivity of ultraviolet light detection using wide-bandgap semiconductor photodiodes, such as gallium nitride and gallium nitride / aluminum gallium nitride heterojunctions. This method has significant advantages in terms of the electron mobility, cutoff frequency, and thermal conductivity of the material. However, the semiconductor material needs to be grown on expensive substrates, and the high defect density caused by the lattice mismatch between heterojunctions has not yet been well resolved.

[0021] The second approach is to indirectly improve the responsivity of ultraviolet light detection by using frequency conversion. For example, fluorescent downconversion materials, such as fluorescent quantum dots and rare-earth phosphors, can be modified in the detector window to convert incident ultraviolet light into visible light, thereby indirectly changing the spectral response curve of the semiconductor photodetector and improving the responsivity of ultraviolet light detection. However, due to the long decay lifetime of phosphors, the dynamic performance of the detector is not ideal. The organic adhesives used for phosphor encapsulation and protection are prone to deterioration under high temperature or ultraviolet irradiation, which leads to a decrease in the performance of the frequency converter.

[0022] Besides fluorescent conversion materials, frequency conversion can also be achieved using nonlinear optical crystals. Lithium niobate is the most widely used, possessing excellent nonlinear optical properties. Lithium niobate crystals are chemically and mechanically stable, heat-resistant, corrosion-resistant, and easy to grow, making it easy to obtain large-size, high-quality optical-grade crystals. By periodically polarizing lithium niobate crystals, quasi-phase matching techniques can be used to compensate for the phase mismatch between interacting light waves caused by material dispersion, thereby achieving high conversion efficiency. By fabricating optical waveguide structures on periodically polarized lithium niobate crystals and strictly confining the beam propagation inside the waveguide, the interaction length can be increased, the spot mode size can be reduced, and the optical power density can be improved, further increasing the conversion efficiency by 2-3 orders of magnitude. However, the ultraviolet absorption edge of lithium niobate crystals is approximately 326 nm, resulting in significant absorption loss in the solar-blind ultraviolet region.

[0023] In comparison, the ultraviolet absorption edge of lithium tantalate crystal is approximately 273 nm. By increasing the lithium-tantalum ratio of the crystal to near stoichiometry and doping with a small amount of magnesium, the ultraviolet absorption edge of the crystal can be further blue-shifted to 266 nm and 262 nm. Therefore, it is more suitable for fabricating frequency conversion devices in solar-blind semiconductor photodetectors. In terms of other performance aspects, the coercivity fields of near-stoichiometric lithium tantalate crystal and magnesium-doped near-stoichiometric lithium tantalate crystal are 2.1 kV / mm and 0.6 kV / mm, respectively, which are much lower than the 21 kV / mm of lithium niobate and lithium tantalate crystals of the same composition. Therefore, it is easier to achieve periodic polarization. At the same time, both materials have higher resistance to light damage thresholds and are more suitable for applications in high-power and short-wavelength devices.

[0024] However, the quasi-phase matching period for nonlinear frequency conversion of ultraviolet light in the solar blind zone is usually on the submicron scale. Due to limitations in crystal polarization technology, it is difficult to obtain a uniform periodic polarization structure over a large area. At the same time, since the Curie temperature of lithium tantalate crystal is low, about 610°C, it is impossible to form an optical waveguide through the high-temperature titanium diffusion process. Therefore, it is difficult to achieve high-efficiency frequency conversion of ultraviolet light signals in the solar blind zone to visible light.

[0025] The development of lithium niobate single-crystal thin film materials has provided a new approach to solving the above problems. Since the thickness of the lithium niobate layer is very thin, about a few hundred nanometers, the polarization reversal voltage is significantly reduced from several thousand volts to tens of volts. This can effectively suppress the lateral broadening effect of the reverse domains, making it possible to prepare submicron periodic and uniform periodic polarization structures over a large area.

[0026] Furthermore, due to the presence of a low-refractive-index silicon dioxide buffer layer beneath the lithium niobate layer, optical waveguide structures with strong confinement and low transmission loss can be fabricated using standard semiconductor precision processing techniques. The processing temperature is typically below 350°C, which is far lower than the Curie temperature (~1142°C) of lithium niobate crystals.

[0027] As an isomeric heterostructure of lithium niobate crystals, lithium tantalate crystals can also be prepared into lithium tantalate single-crystal thin films through techniques such as ion slicing, wafer bonding, thermal exfoliation, and chemical mechanical polishing. Then, high-conversion-efficiency, low-transmission-loss nonlinear frequency conversion devices can be prepared through periodic polarization and semiconductor precision processing techniques.

[0028] To improve the responsivity of semiconductor photodetectors in the ultraviolet band of the solar blind zone, the technical solution of this application will be further described in detail below with reference to the accompanying drawings.

[0029] This application provides a single-crystal thin film in some embodiments, including: a substrate, a buffer layer and a functional layer stacked in sequence, wherein the substrate is located at the bottom layer and provides mechanical support. Since the functional layer is extremely thin, it cannot exist and be used independently without the support of the substrate.

[0030] The buffer layer is located between the substrate and the functional layer. On the one hand, it serves as the lower cladding layer in optics, forming a refractive index difference with the functional layer and providing a basis for the subsequent fabrication of the optical waveguide. On the other hand, the buffer layer serves as a bonding interface during the fabrication process, used to bond with the donor wafer and realize the transfer of the functional layer.

[0031] The functional layer, located above the buffer layer, is the core layer of the entire single-crystal thin film. Subsequent periodic polarization structures and waveguide structures are formed in this layer to achieve optical frequency conversion functions, such as... Figure 1As shown, for example, the substrate is a Si substrate, the buffer layer is a SiO2 buffer layer, and the material of the functional layer is near-stoichiometric lithium tantalate (SLT) or magnesium-doped near-stoichiometric lithium tantalate (MgO:SLT).

[0032] Near-stoichiometric lithium tantalate has a lithium to tantalum molar ratio close to 1:1. Compared with lithium tantalate of the same composition, it has fewer intrinsic defects. By increasing the lithium-tantalum ratio of the crystal to near stoichiometry and doping with a small amount of magnesium, the ultraviolet absorption edge of the crystal can be shifted to 266nm and 262nm, which can solve the problem of transparency in the solar-blind ultraviolet band.

[0033] The ultraviolet absorption edge is usually defined as an absorption coefficient of 20 cm⁻¹. -1 The wavelength corresponding to the time is the wavelength threshold at which the material begins to strongly absorb ultraviolet light. The shorter the absorption edge, the better the material's transmittance to the solar-blind ultraviolet band. The ultraviolet absorption edge of lithium tantalate of the same composition is about 273nm, and it still absorbs solar-blind ultraviolet light with wavelengths less than 273nm.

[0034] In one embodiment, this application shortens the ultraviolet absorption edge to 266 nm by using near-stoichiometric lithium tantalate; in another embodiment, by doping magnesium into near-stoichiometric lithium tantalate, the ultraviolet absorption edge can be further shortened to 262 nm, thereby broadening the transparency range in the solar-blind ultraviolet band, which can significantly reduce the absorption loss of signal light before frequency conversion and provide a low-loss optical transmission medium for subsequent efficient frequency conversion.

[0035] When the functional layer material is near-stoichiometric lithium tantalate doped with magnesium, the magnesium doping concentration is 1 mol.%. Magnesium doping not only further shortens the ultraviolet absorption edge but also reduces the coercive field and increases the resistance to photodamage. The coercive field is the minimum electric field strength required to reverse the polarization direction of a ferroelectric material. The lower the coercive field, the lower the voltage required to achieve periodic polarization, and the easier it is to control the polarization process.

[0036] The 1 mol.% doping concentration (doping threshold) is an optimized ratio. At this concentration, the coercive field can be reduced to 0.6 kV / mm, far lower than the 21 kV / mm of lithium tantalate of the same composition, making periodic polarization easier to achieve. Simultaneously, the magnesium doping also improves the light damage threshold, making the material more suitable for operation under high optical power or short wavelength conditions. Therefore, the 1 mol.% magnesium doping concentration is an optimized ratio, at which the material exhibits the best overall performance.

[0037] Based on this, the thickness of the functional layer in this embodiment is 100nm-1000nm. This thickness range is related to the subsequent preparation of submicron periodic polarization structures. In bulk materials, polarization reversal requires the application of a high voltage of several thousand volts. High voltage can easily cause the domain walls to widen laterally, causing adjacent reversal domains to merge, making it difficult to obtain high-quality submicron periodic polarization structures over a large area.

[0038] By thinning the functional layer to 100nm-1000nm, the polarization reversal voltage can be reduced to tens of volts. The low voltage can effectively suppress the lateral broadening effect of the domain walls, and uniform submicron periodic polarization structures can be prepared over a large area.

[0039] Furthermore, in some embodiments, the thickness of the functional layer is 300nm-900nm. Within this thickness range, the functional layer can be guaranteed to have sufficient mechanical strength to facilitate operation and processing during the fabrication process, while maintaining a low polarization voltage to ensure a uniform periodic polarization structure. Therefore, this range can achieve a better balance between operability and polarization effect.

[0040] In some embodiments, the diameter of the functional layer is 3 inches, 4 inches, 6 inches, 8 inches, or 12 inches, which are standard wafer sizes in the semiconductor industry. Using a standard-sized single-crystal thin film means that existing semiconductor processing equipment can be used for subsequent processes such as electrode preparation, photolithography, and etching, without the need to customize special fixtures or adjust equipment parameters for each thin film. This facilitates large-scale mass production at the wafer level, thereby reducing the manufacturing cost of devices and improving the market competitiveness of products.

[0041] For the substrate, in some embodiments, the substrate is a silicon substrate, a quartz substrate, a lithium niobate substrate, or a lithium tantalate substrate. Among them, silicon substrates are low in cost and compatible with semiconductor processes, quartz substrates have good light transmittance, and lithium niobate and lithium tantalate substrates have thermal expansion coefficients that match the functional layers. This application does not impose any restrictions and the substrate can be selected according to the specific application scenario.

[0042] The buffer layer is a silicon dioxide layer. For example, a layer of silicon dioxide is thermally oxidized and grown on a silicon substrate to serve as the optical lower cladding. The refractive index of silicon dioxide is about 1.45, while that of lithium tantalate is about 2.1. The two form a high refractive index difference. This high refractive index difference allows for the fabrication of strongly constrained optical waveguide structures without the need for subsequent high-temperature diffusion processes. This avoids the problem that lithium tantalate has a low Curie temperature and cannot be processed at high temperatures.

[0043] The crystal tangent of the functional layer is X-shaped, Y-shaped, or Z-shaped. Functional layers with different tangents are suitable for optical signals with different polarization states. In subsequent periodically polarized waveguide devices, in order to achieve high-efficiency frequency conversion, it is necessary to utilize the largest nonlinear optical coefficient of lithium tantalate crystal. d 33.

[0044] For Z-cut crystals d 33 The polarization direction corresponding to the coefficient is the vertical direction, meaning the electric field vector of light needs to vibrate along the z-axis of the crystal. For X-cut or Y-cut crystals, d 33 The polarization direction corresponding to the coefficient is horizontal. Therefore, choosing different crystal tangents lays the foundation for polarization control, so that the signal light and pump light can be adjusted to the correct polarization state to excite the maximum nonlinear coefficient.

[0045] Understandably, regardless of whether it's an X, Y, or Z cut, to maximize the nonlinear optical coefficient, the rule is that "the electric field vector of the light needs to be parallel to the z-axis direction of the crystal."

[0046] Single-crystal thin films can provide transparency in the solar-blind ultraviolet band by forming a functional layer on a substrate. The material of the functional layer is near-stoichiometric lithium tantalate or magnesium-doped near-stoichiometric lithium tantalate. This solves the problem of transparency in the solar-blind ultraviolet band. Furthermore, the thickness of the functional layer is set between 100nm and 1000nm. Within this thickness range, the polarization reversal voltage can be reduced to tens of volts. The low voltage can suppress the lateral widening of domain walls, thereby obtaining a uniform submicron periodic polarization structure.

[0047] Figure 2 This is a schematic diagram illustrating the method for preparing a single-crystal thin film according to an embodiment of this application.

[0048] This application also provides a method for preparing a single-crystal thin film, which involves transferring high-quality single-crystal material onto a substrate with a buffer layer through steps such as ion implantation, bonding, thermal stripping, and surface treatment to form a single-crystal thin film with controllable thickness and a smooth surface.

[0049] The method includes the following steps S201-S206: S201: Provides near-stoichiometric lithium tantalate or magnesium-doped near-stoichiometric lithium tantalate single crystals as donor wafers.

[0050] The near-stoichiometric lithium tantalate or magnesium-doped near-stoichiometric lithium tantalate materials have been described in the above embodiments and will not be repeated in this embodiment.

[0051] Donor wafers are high-quality single-crystal materials. During the preparation of donor wafers, their crystal quality determines the crystal quality of the functional layers. Double-sided polished X-cut lithium tantalate single crystal wafers can be selected as donor wafers, or Z-cut 1 mol.% magnesium-doped near-stoichiometric lithium tantalate single crystal wafers can be selected as donor wafers.

[0052] S202: Ion implantation is performed on the donor wafer to form an implantation layer inside the donor wafer.

[0053] Ion implantation involves accelerating high-energy ions and bombarding them into a donor wafer. As the ions penetrate the wafer, they collide with lattice atoms, gradually losing energy and eventually settling at a certain depth inside the wafer. Near this depth, the ions damage the lattice, forming a fragile region known as the implantation layer. This implantation layer becomes the peeling interface during subsequent heat treatment, and the donor wafer will crack along this layer.

[0054] In some embodiments, the ions implanted are hydrogen ions (H+). + The ions used are helium ions, nitrogen ions, oxygen ions, or argon ions. Different types of ions have different masses in the crystal lattice and different interaction mechanisms with lattice atoms. Therefore, the depth and degree of damage caused by these ions vary. Among them, hydrogen ions are the lightest and have the deepest implantation depth, and are often used to prepare thicker films. Helium ions are slightly heavier and have higher damage efficiency. Nitrogen, oxygen, and argon ions have even greater masses and can be used to prepare ultrathin films or in situations where specific damage morphologies are required. In this embodiment, the appropriate type of ion can be selected according to the required thickness and quality requirements of the functional layer, without any restrictions.

[0055] The ion implantation energy is 30keV-5MeV. The implantation energy determines the penetration depth of ions in the wafer. The higher the energy, the deeper the ions penetrate, the farther the implanted layer is from the surface of the donor wafer, and the thicker the functional layer.

[0056] For example, taking hydrogen ions as an example, to obtain a thin film of approximately 500 nm, the implantation energy is typically 150 keV-200 keV. In this embodiment, the correspondence between a specific energy and the implantation depth can be determined through simulation or experimentation, thereby selecting an appropriate implantation energy based on the target thin film thickness.

[0057] The injection dose is 1×10 15 ions / cm 2 -1×10 17 ions / cm 2 The implantation dose is the number of ions implanted per unit area. If the dose is too low, the damage in the implanted layer is insufficient, and a continuous bubble layer cannot be formed in the subsequent heat treatment, resulting in difficult or uneven peeling. If the dose is too high, the damage in the implanted layer is too severe, which may cause blistering on the surface of the donor wafer or the formation of an excessively thick damage layer. These damages are difficult to completely repair in the subsequent annealing and will affect the crystal quality of the functional layer. Therefore, it is necessary to select an appropriate dose within this range to ensure smooth peeling while minimizing damage to the functional layer.

[0058] S203: Provides a substrate on which a buffer layer is formed.

[0059] S204: Bond the injection layer to the buffer layer.

[0060] Before bonding, the surfaces of the donor wafer and the substrate are subjected to RCA cleaning and hydrophilic treatment to remove surface contaminants and suspend hydroxyl groups on the surface. Then, the two surfaces are activated by plasma, for example, oxygen plasma or nitrogen plasma treatment, to generate a large number of suspended bonds on the surface, which greatly enhances the surface activity. The two activated wafers are then brought into face-to-face contact, and due to the intermolecular van der Waals forces, they will spontaneously combine together to form an initial bond.

[0061] After the initial bonding, further bonding is carried out. In some embodiments, the bonding is low-temperature plasma-activated bonding. After bonding, annealing is performed at 200℃-400℃ to strengthen the bonding. During this process, the hydroxyl groups (-OH) at the contact interface undergo a polymerization reaction to form covalent bonds, which greatly improves the bonding strength. Low-temperature annealing can avoid the additional impact of high temperature on the implanted layer and crystal structure, while ensuring that the bonding strength is sufficient to withstand the mechanical stress in the subsequent peeling process.

[0062] S205: Perform heat treatment to peel off the donor wafer along the implantation layer and form a functional layer on the substrate.

[0063] After bonding is completed, heat treatment is performed. During the heat treatment process, the implanted ions gather and combine at the implantation layer to form bubbles. The bubbles gradually expand and generate huge pressure, causing the donor wafer to crack along the implantation layer. After natural cooling, a part of the donor wafer (i.e. the part above the implantation layer) is bonded to the substrate to form a functional layer. The remaining part of the donor wafer (the scrap layer) can be removed and reused, which can reduce material costs.

[0064] In some embodiments, the heat treatment temperature is 300℃-500℃ and the time is 30 minutes-10 hours. The selection of temperature and time needs to take into account both the peeling effect and the thermal budget. If the temperature is too low or the time is too short, the ion aggregation will be insufficient and the bubble pressure will be insufficient, which may lead to incomplete peeling or a rough peeling surface. If the temperature is too high or the time is too long, it may cause thermal damage to the crystal quality of the functional layer. Optimizing the parameters within this range can minimize the adverse effects on the functional layer while ensuring the peeling effect.

[0065] S206: The functional layer is planarized and annealed to obtain a single-crystal thin film.

[0066] The surface of the functional layer obtained after stripping is usually quite rough and requires surface planarization. This method performs surface planarization and annealing on the functional layer to obtain a single-crystal thin film. Chemical mechanical polishing is then used for thinning and global planarization to obtain an atomically smooth surface. The combination of chemical mechanical polishing and chemical etching and mechanical grinding can effectively remove surface undulations and damaged layers caused by stripping, making the functional layer uniform in thickness and smooth in surface. The surface roughness of the planarized functional layer can reach the nanometer or even sub-nanometer level, meeting the stringent surface quality requirements of optical waveguide devices.

[0067] After planarization, annealing is performed. During ion implantation, high-energy ions damage the crystal lattice, generating defects such as dislocations and vacancies. These defects affect the optical and electrical properties of the functional layer. High-temperature annealing can provide enough energy for atoms to migrate to the correct positions, repair the lattice damage, and restore the crystal quality and optical properties of the functional layer. The annealing temperature can be 500℃-600℃. On the one hand, it needs to be high enough to activate atomic migration and achieve repair. On the other hand, it needs to be lower than the Curie temperature of lithium tantalate, 610℃, to avoid phase transitions or depolarization of the crystal structure due to excessively high temperatures.

[0068] In some embodiments, surface planarization is achieved by chemical mechanical polishing, and the annealing temperature is 500℃-600℃. Chemical mechanical polishing can precisely control the final thickness and surface roughness of the functional layer, enabling high-quality optical waveguides. The annealing temperature range of 500℃-600℃ can effectively repair lattice damage without destroying the crystal structure and polarization characteristics of the functional layer.

[0069] Through the above steps, a single-crystal thin film is prepared. High-quality single-crystal material is then transferred to the target substrate using ion implantation and bond-stripping techniques, avoiding lattice mismatch problems that may occur with direct film growth. Furthermore, since thinning is performed after bonding, the thickness of the functional layer can be precisely controlled, and surface quality can be ensured through chemical mechanical polishing. The prepared single-crystal thin film can be directly used for the fabrication of subsequent periodically polarized waveguide devices, providing a material basis for the realization of solar-blind ultraviolet detectors.

[0070] The method will be described below with reference to specific embodiments.

[0071] Example 1: Preparation of lithium tantalate single-crystal thin films with X-close stoichiometric ratio A donor wafer is provided, which is a double-sided polished, optical-grade X-tangent near stoichiometric lithium tantalate single-crystal. Ion implantation is performed on the donor wafer to form an implantation layer inside the donor wafer. In this embodiment, hydrogen ions are used for implantation. To obtain a thin film of approximately 500 nm, the implantation energy is selected as 150 keV-200 keV, and the implantation dose is selected as 1 × 10⁻⁶. 16 ions / cm 2The implantation process is carried out at room temperature. After ion implantation, a fragile region, namely the implantation layer, is formed inside the donor wafer. This layer will serve as the lift-off interface in subsequent heat treatment.

[0072] During or after ion implantation, a silicon substrate is prepared. A silicon dioxide layer, approximately 1 μm thick, is grown on the silicon substrate as a buffer layer through thermal oxidation. The substrate surface is then cleaned and hydrophilized to obtain a clean, hydrophilic surface. The donor wafer is then bonded to the substrate. Before bonding, the implantation side of the donor wafer and the surface of the buffer layer of the substrate are activated by oxygen plasma to generate a large number of dangling bonds on the surface. The two activated surfaces are then brought into face-to-face contact, and the two wafers spontaneously form an initial bond under the action of van der Waals forces. The bonded wafer pair is then placed in an annealing furnace and annealed at 300°C for 2 hours to allow the hydroxyl groups at the interface to polymerize and form covalent bonds, thereby strengthening the bond strength.

[0073] After bonding, heat treatment is performed to achieve peeling. The bonded wafer pair is heat-treated at 400°C for 2 hours. During the heat treatment, the injected hydrogen ions accumulate at the injection layer to form hydrogen gas and expand, generating huge pressure, causing the donor wafer to precisely crack along the injection layer. After natural cooling, a portion of the donor wafer, i.e., the thin film layer, is transferred to the substrate to form a functional layer on the substrate. The remaining portion of the donor wafer, i.e., the surplus material layer, can be removed and reused.

[0074] Finally, the functional layer formed after peeling is subjected to surface planarization and annealing. Chemical mechanical polishing is used to planarize the surface of the functional layer, remove the surface undulations and damaged layers caused by peeling, and obtain an atomically smooth surface. Then, high-temperature annealing at 550℃ is carried out in an oxygen-rich environment to repair the lattice damage caused by ion implantation and restore the crystal quality and optical properties of the functional layer.

[0075] Through the above steps, a single-crystal thin film is prepared in this embodiment. The thin film includes a silicon substrate, a silicon dioxide buffer layer, and an X-tangential stoichiometric lithium tantalate functional layer with a thickness of approximately 500 nm.

[0076] Example 2: Preparation of Z-cut magnesium-doped near-stoichiometric lithium tantalate single-crystal thin films This embodiment provides a method for preparing a Z-cut magnesium-doped near-stoichiometric lithium tantalate single crystal thin film. The main difference from Embodiment 1 lies in the requirements for the donor wafer material, substrate, and some process parameters.

[0077] A donor wafer is provided, which is a double-sided polished, optical-grade Z-cut 1 mol.% magnesium-doped near-stoichiometric lithium tantalate single crystal wafer. The uniformity of magnesium doping concentration is confirmed by secondary ion mass spectrometry or X-ray fluorescence spectroscopy to ensure the consistency of material properties. Ion implantation is performed on the donor wafer. In this embodiment, hydrogen ions are used for implantation. To obtain a thin film with a thickness of approximately 600 nm, the implantation energy is selected as 180 keV and the implantation dose is selected as 1 × 10⁻⁶. 16 ions / cm 2 The implantation process is carried out at room temperature. After implantation is completed, an implantation layer is formed inside the donor wafer.

[0078] Prepare a silicon substrate with good conductivity. Then, thermally oxidize and grow a layer of silicon dioxide on the silicon substrate as a buffer layer. The thickness of the silicon dioxide layer must be controlled within 2 μm, for example, 1 μm. This is because electrodes need to be prepared on the back side of the substrate in the subsequent periodic polarization step. If the silicon dioxide layer is too thick, it will hinder the electric field penetration and affect the polarization effect. Clean and hydrophilize the substrate surface.

[0079] Next, the donor wafer is bonded to the substrate. Before bonding, oxygen plasma activation treatment is performed on the injection side of the donor wafer and the surface of the buffer layer of the substrate. The two activated surfaces are brought into face-to-face contact to form an initial bond. The bonding strength is enhanced by annealing at 300°C for 2 hours. After bonding, heat treatment is performed. The bonded wafer pair is heat treated at 400°C for 2 hours to peel the donor wafer along the injection layer and form a functional layer on the substrate. After natural cooling, the excess material layer is removed.

[0080] Finally, the functional layer is planarized and annealed. Planarization is performed by chemical mechanical polishing to obtain an atomically smooth surface, and then high-temperature annealing at 550°C is carried out in an oxygen-rich environment to repair lattice damage.

[0081] Through the above steps, a single-crystal thin film was prepared in this embodiment. The thin film includes a conductive silicon substrate, a silicon dioxide buffer layer with a thickness of ≤2μm, and a Z-cut 1mol.% magnesium-doped near stoichiometric lithium tantalate functional layer with a thickness of approximately 600nm.

[0082] The single-crystal thin film prepared by the above method can be directly used for the subsequent fabrication of periodically polarized waveguide devices.

[0083] Figure 3 This is a schematic diagram of the structure of a periodically polarized waveguide device provided in an embodiment of this application.

[0084] like Figure 3 As shown, some embodiments of this application provide a periodically polarized waveguide device, including: The single-crystal thin film described in any of the above claims; Periodic polarization structures are formed in the functional layers of single-crystal thin films; A ridge waveguide structure is formed on the functional layer, and the extension direction of the ridge waveguide structure is parallel to the arrangement direction of the periodic polarization structure.

[0085] Since the specific structure and materials of single-crystal thin films have been described in detail in the previous embodiments, they will not be repeated here.

[0086] A periodic polarization structure is formed in the functional layer of the single-crystal thin film. The periodic polarization structure is a structure in which the spontaneous polarization direction of the functional layer is periodically reversed along a specific direction. In this embodiment, the periodic polarization structure is formed in the lithium tantalate thin film by the external electric field polarization method. The periodic polarization structure is used to achieve quasi-phase matching.

[0087] In the nonlinear frequency conversion process, when the signal light and pump light propagate in the crystal, the phase mismatch between the two beams due to material dispersion reduces the energy conversion efficiency. The periodic polarization structure can compensate for the phase mismatch by periodically reversing the spontaneous polarization direction and periodically modulating the nonlinear coefficient, so that the two beams can continuously and effectively interact nonlinearly during propagation, thereby obtaining a higher frequency conversion efficiency.

[0088] In some embodiments, the polarization period of the periodically polarized structure is 0.5 μm-1.5 μm. The quasi-phase-matching period for nonlinear frequency conversion of solar-blind ultraviolet light is typically in the submicron range, with the polarization period between 0.5 and 1.5 μm. The choice of polarization period depends on the wavelengths of the signal light and the pump light. For the conversion of solar-blind ultraviolet light to visible light, the signal light wavelength is approximately 280 nm, and the pump light wavelength is 430 nm-525 nm. The corresponding polarization period falls within this range. By adjusting the period length, light of a specific wavelength can satisfy the quasi-phase-matching condition, achieving efficient frequency conversion.

[0089] In some embodiments, the periodic polarization structure is formed by polarization with an applied electric field. The direction of the applied electric field is opposite to the crystal polarization direction of the functional layer. The intensity of the applied electric field is greater than the coercive field of the functional layer material. The direction of the applied electric field must be parallel to and opposite to the +z axis of the crystal. The electric field intensity must be higher than the coercive field of the crystal. For near-stoichiometric lithium tantalate crystals, the coercive field is about 2.1 kV / mm; for magnesium-doped near-stoichiometric lithium tantalate crystals, the coercive field is about 0.6 kV / mm. Applying a reverse and sufficiently strong electric field can reverse the spontaneous polarization direction in the functional layer.

[0090] By fabricating periodically patterned electrodes on the surface of the functional layer and applying an electric field to the electrode region, a periodic domain inversion structure can be formed in the corresponding region, while the region not covered by the electrode retains its original polarization direction, thus forming a periodic polarization structure.

[0091] Ridge waveguide structures are also formed on the functional layer. For example, ridge waveguide structures can be fabricated on periodically polarized lithium tantalate single crystal thin films using electron beam lithography and dry etching techniques. The ridge waveguide structure strictly confines the beam to propagate within the waveguide core layer at the micrometer scale. This confinement can increase the interaction length between the signal light and the pump light, while reducing the spot mode size and increasing the optical power density. Through these two effects, the frequency conversion efficiency can be greatly improved, providing a foundation for realizing high-sensitivity solar-blind ultraviolet light detection.

[0092] In some embodiments, the ridge waveguide structure is fabricated by a dry etching process. Dry etching has good anisotropy and can etch a ridge structure with steep sidewalls, precisely controlling the width and height of the waveguide, thereby obtaining a waveguide with low transmission loss. The process temperature of dry etching is relatively low, usually below 350°C, which is much lower than the Curie temperature of lithium tantalate. Therefore, the already formed periodic polarization structure will not be destroyed during the etching process.

[0093] The end face of the ridge waveguide structure is polished, and an anti-reflection film is formed on the polished surface, which can improve the end face coupling efficiency of optical signals. End face polishing can remove the rough end face formed by mechanical cutting, reduce the scattering loss of light at the end face, and the anti-reflection film can reduce end face reflection, allowing more light energy to be coupled into the waveguide or output from the waveguide, thereby improving the overall device efficiency.

[0094] The extension direction of the ridge waveguide structure is parallel to the arrangement direction of the periodic polarization structure. During the quasi-phase matching process, the periodic polarization structure provides periodic nonlinear coefficient modulation along a specific direction. Only when the propagation direction of the optical waveguide is consistent with this modulation direction can the light experience the correct periodic sequence and achieve phase matching during propagation. If the two are not parallel, the light will experience changing periods or invalid modulation, the phase matching condition will be destroyed, and the conversion efficiency will drop sharply.

[0095] In some embodiments, when the crystal tangent of the functional layer is X-shaped, the extension direction of the ridge waveguide structure is parallel to the y-axis of the functional layer; when the crystal tangent of the functional layer is Z-shaped, the extension direction of the ridge waveguide structure is parallel to the x-axis of the functional layer. The correspondence between the waveguide direction and the crystal axis is determined by the nonlinear coefficient tensor and the quasi-phase matching condition. Choosing the corresponding axis as the waveguide direction under a specific tangent ensures that the maximum nonlinear optical coefficient of the crystal is fully utilized during light propagation. d 33 This allows for accurate periodic modulation, thereby achieving the most efficient frequency conversion.

[0096] In the waveguide device of this embodiment, the functional layer ensures transparency to solar-blind ultraviolet light, making it possible to fabricate uniform submicron periodic polarized structures at low voltage. The periodic polarized structure provides a quasi-phase matching mechanism, and the ridge waveguide structure provides strong optical field confinement and a long interaction length. The extension direction of the ridge waveguide is parallel to the arrangement direction of the periodic polarized structure, ensuring that the quasi-phase matching condition is met throughout the waveguide. This enables the device to efficiently convert solar-blind ultraviolet light into visible light, laying the foundation for subsequent detection using silicon detectors.

[0097] This application provides a method for fabricating a periodically polarized waveguide device, which includes the following steps S401-S403: S401: Periodic electrodes are fabricated on the functional layer of a single-crystal thin film and polarized by an external electric field to form a periodic polarization structure in the functional layer.

[0098] Periodic electrodes are used to apply a local electric field, causing the polarization direction of the corresponding region to reverse. The pattern of the electrodes determines the period and shape of the periodic polarization structure. The material, thickness, and period length of the periodic electrodes can be selected and adjusted as needed.

[0099] Then, polarization is achieved by applying an external electric field, forming a periodic polarization structure in the functional layer. The direction of the external electric field is opposite to the crystal polarization direction of the functional layer. The electric field strength must be greater than the coercive field of the functional layer material. In the area covered by the periodic electrode, the polarization direction is reversed, while the area not covered by the electrode retains the original direction, thus forming a periodic domain inversion structure.

[0100] S402: Remove the periodic electrode.

[0101] After polarization is completed, the periodic electrodes are removed. The method for removing the electrodes must be selected according to the electrode material, and the surface of the functional layer must not be damaged. After the electrodes are removed, the surface of the functional layer is restored to a clean and smooth state, which is ready for subsequent waveguide fabrication.

[0102] S403: A ridge waveguide structure is etched on the functional layer, and the extension direction of the ridge waveguide structure is parallel to the arrangement direction of the periodic polarization structure.

[0103] The etching process needs to be able to precisely control the width and height of the waveguide to obtain a waveguide with low transmission loss. Then, the end face of the waveguide structure can be polished and coated to improve the coupling efficiency of optical signals.

[0104] In some embodiments, the periodic electrode is a metal electrode made of gold, aluminum, or chromium, with a thickness of 100 nm to 1000 nm. The selection of the electrode material must take into account conductivity, adhesion to the functional layer, and ease of subsequent removal. The electrode thickness must ensure the continuity and conductivity of the electrode, while facilitating photolithography and lift-off processes. The period length of the electrode is set according to the target wavelength and is consistent with the period of the final formed periodic polarization structure.

[0105] The preparation method will be described in detail below with reference to specific embodiments.

[0106] Example 3: Fabrication of a periodically polarized waveguide device with X-near-stoichiometric ratio of lithium tantalate like Figure 4 As shown, this embodiment provides a method for fabricating an X-near stoichiometric lithium tantalate periodically polarized waveguide device, which is based on the X-near stoichiometric lithium tantalate single crystal thin film prepared in the aforementioned embodiment 1.

[0107] like Figure 4 As shown in (a) and (b), periodic electrodes are fabricated on the functional layer of a single-crystal thin film. The functional layer is lithium tantalate with a near-stoichiometric ratio of X and a thickness of about 500 nm. Photoresist is coated on the upper surface of the functional layer by photolithography and exposed and developed to form openings of the electrode pattern. The electrode pattern is designed as periodically arranged stripes with a period length of 1 μm.

[0108] Then, an electron beam evaporation process is used to deposit metal electrodes. Gold is selected as the electrode material, and the thickness is about 200 nm. After deposition, a lift-off process is used to remove the photoresist and the metal layer on it, leaving only periodic electrodes in the opening area. The positive and negative electrodes of the periodic electrodes are located on the upper surface of the functional layer, and the distance between the positive and negative electrodes is about 5 μm, which is greater than the bottom width of the subsequent ridge waveguide.

[0109] Polarization is achieved by applying an external electric field. The periodic electrode is used as the positive electrode, and the negative electrode is set at the edge or back of the functional layer. An external electric field is applied, and the direction of the electric field is opposite to the crystal polarization direction of near-stoichiometric lithium tantalate (X-axis), that is, parallel to and opposite to the +z axis. The electric field strength is set to 3 kV / mm, which is higher than the coercive field of near-stoichiometric lithium tantalate (2.1 kV / mm). Under the action of the electric field, the polarization direction of the area covered by the periodic electrode is reversed, forming a periodic domain inversion structure. The polarization time is determined according to the electric field strength and the thickness of the functional layer, and is usually from several minutes to tens of minutes.

[0110] like Figure 4As shown in (c), after polarization, the wafer with periodic electrodes is immersed in a mixed etching solution of potassium iodide and iodine. This etching solution has a selective etching effect on gold, which can quickly dissolve the gold electrodes without damaging the surface of the lithium tantalate functional layer. After etching, the wafer is cleaned with deionized water and dried, and the surface of the functional layer is restored to a clean and smooth state.

[0111] like Figure 4 As shown in (d), a ridge waveguide structure is etched onto the functional layer. Specifically, electron beam lithography (EBL) is used to define the ridge waveguide pattern on the upper surface of the functional layer. The waveguide width is set to 2 μm, and the waveguide direction must be strictly parallel to the arrangement direction of the periodic polarization structure. For X-cut crystals, the waveguide direction is parallel to the y-axis of the functional layer. Ar + Ion-assisted dry etching technology is used for etching, with Ar as the etching gas. The etching power and gas pressure are optimized, and the etching depth is controlled at about 400nm to form a ridge waveguide structure. After etching, the residual photoresist is removed.

[0112] Finally, the end face of the ridge waveguide structure formed by etching is processed by cutting the waveguide chip into individual devices and mechanically polishing the incident and exit end faces to obtain smooth end faces. An antireflection film is then deposited on the polished surface. The antireflection film material is silicon dioxide, and the thickness is designed according to the target wavelength to reduce end face reflection and improve the coupling efficiency of optical signals.

[0113] Through the above steps, this embodiment prepares a periodically polarized waveguide device with an X-close stoichiometric ratio of lithium tantalate.

[0114] Example 4: Fabrication of Z-cut magnesium-doped near-stoichiometric lithium tantalate periodically polarized waveguide device like Figure 5 As shown, this embodiment provides a method for fabricating a Z-cut magnesium-doped near-stoichiometric lithium tantalate periodically polarized waveguide device. The device is based on a Z-cut 1 mol.% magnesium-doped near-stoichiometric lithium tantalate single crystal thin film prepared in the aforementioned embodiment 2. The substrate of the single crystal thin film is a conductive silicon substrate, the buffer layer is silicon dioxide, and the functional layer is Z-cut magnesium-doped near-stoichiometric lithium tantalate with a thickness of approximately 600 nm.

[0115] like Figure 5As shown in (a) and (b), a periodic electrode is fabricated on the functional layer. Unlike Example 3, this example requires the fabrication of a periodic electrode as the positive electrode on the surface of the functional layer, and the fabrication of a full-coverage electrode as the negative electrode on the back side of the substrate. The periodic electrode is fabricated on the surface of the functional layer by ultraviolet lithography and lift-off process. The electrode material is aluminum with a thickness of about 200 nm and the period length is set to 0.8 μm. A full-coverage aluminum electrode with a thickness of about 200 nm is deposited on the back side of the conductive silicon substrate by electron beam evaporation as the negative electrode. Alternatively, the back side of the conductive silicon substrate can be used directly as the negative electrode without the need for additional electrode deposition.

[0116] Polarization is achieved by applying an external electric field. The periodic electrode on the upper surface of the functional layer is the positive electrode, and the electrode on the back side of the substrate is the negative electrode. An external electric field is applied with the direction of the electric field opposite to the crystal polarization direction of the Z-cut magnesium-doped near-stoichiometric lithium tantalate, that is, parallel to and opposite to the +z direction. The electric field strength is set to 1 kV / mm, which is higher than the coercive field of magnesium-doped near-stoichiometric lithium tantalate of 0.6 kV / mm. Under the action of the electric field, the polarization direction of the area covered by the periodic electrode is reversed, forming a periodic domain inversion structure.

[0117] like Figure 5 As shown in (c), after polarization is completed, the periodic electrode is removed, and the aluminum electrode is removed by selective wet etching process. The etching solution is a mixed solution of phosphoric acid, nitric acid and acetic acid. This solution has a selective etching effect on aluminum, which can quickly dissolve the aluminum electrode without damaging the surface of the lithium tantalate functional layer and the electrode on the back of the silicon substrate. After etching, the wafer is cleaned with deionized water and dried.

[0118] like Figure 5 As shown in (d), a ridge waveguide structure is etched onto the functional layer. The ridge waveguide pattern can be defined on the surface of the functional layer using electron beam lithography. The waveguide width is set to 2 μm, and the waveguide direction must be strictly parallel to the arrangement direction of the periodic polarization structure. For Z-cut crystals, the waveguide direction is parallel to the x-axis of the functional layer. Ar... + Ion-assisted dry etching technology is used for etching, with the etching depth controlled at around 400nm, to form a ridge waveguide structure. After etching, the residual photoresist is removed.

[0119] Finally, the end face of the ridge waveguide structure was polished and coated with an antireflection film, the same as in Example 3. Through the above steps, this example successfully fabricated a Z-cut magnesium-doped near-stoichiometric lithium tantalate periodically polarized waveguide device.

[0120] The two embodiments described above illustrate the fabrication process of periodically polarized waveguide devices based on X-cut and Z-cut crystals, respectively. Those skilled in the art can optimize and adjust the parameters within the above range according to actual needs.

[0121] Figure 6This is a schematic diagram of the structure of a solar-blind ultraviolet detector provided in an embodiment of this application.

[0122] This application provides a solar-blind ultraviolet detector in some embodiments. The detector includes a periodically polarized waveguide device as described in any of the foregoing embodiments, and a silicon detector optically connected to the periodically polarized waveguide device. The specific structure and fabrication method of the periodically polarized waveguide device have been described in detail in the foregoing embodiments and will not be repeated here.

[0123] Periodically polarized waveguide devices are used to convert solar-blind ultraviolet light signals into visible light signals. Silicon detectors are used to detect the converted visible light signals. The silicon detector can be a silicon avalanche photodiode, which has the advantages of high detection efficiency, low noise and low cost in the 600nm-800nm ​​visible light band, but its responsivity to solar-blind ultraviolet light is extremely low. By converting solar-blind ultraviolet light into visible light through periodically polarized waveguide devices and then detecting it with a silicon detector, high-sensitivity detection of solar-blind ultraviolet light can be indirectly achieved.

[0124] In some embodiments, the solar-blind ultraviolet detector is used to detect ultraviolet light signals with wavelengths of 266nm-300nm. This band is a solar-blind zone with extremely low background noise in the atmosphere, making it suitable for secure communication. For example, the wavelength of the signal light source can be set to 280nm.

[0125] Furthermore, if magnesium-doped near-stoichiometric lithium tantalate is used, the ultraviolet absorption edge of the functional layer can be further shortened to 262 nm, thereby extending the detection wavelength range to 262 nm-300 nm.

[0126] The detector also includes a pump source connected to a periodically polarized waveguide device. The output wavelength of the pump source is 430nm-525nm. The pump light and the signal light undergo a difference frequency effect in the waveguide to generate difference frequency light. The wavelength of the difference frequency light is determined by the wavelength of the signal light and the wavelength of the pump light. Specifically, the wavelength of the difference frequency light is equal to the difference between the reciprocal of the wavelength of the signal light and the wavelength of the pump light. By selecting the pump light wavelength, the wavelength of the difference frequency light can be made to fall within the 600nm-800nm ​​range where the silicon detector has the highest detection efficiency, thereby maximizing the responsivity of the detector.

[0127] The detector also includes two polarization controllers, one for adjusting the polarization state of the solar-blind ultraviolet signal light and the other for adjusting the pump light. In periodically polarized lithium tantalate thin-film waveguides, to achieve efficient difference-frequency conversion, the crystal's maximum nonlinear optical coefficient needs to be utilized. d 33 , d 33 The corresponding polarization matching condition requires the signal light and pump light to have specific polarization states, and the polarization controller is used to ensure that the two beams of light meet this condition.

[0128] In some embodiments, the polarization controller adjusts the polarization state of the signal light and pump light according to the crystal tangent of the functional layer. When the crystal tangent is Z-cut, the polarization controller is used to adjust the solar-blind ultraviolet signal light and pump light to be measured to a vertical polarization state. The maximum nonlinear optical coefficient of the Z-cut crystal... d 33 The corresponding polarization direction is vertical, meaning the electric field vector of the light vibrates along the z-axis of the crystal. Effective excitation is only possible when both the signal light and pump light are vertically polarized. d 33 The coefficient enables high-efficiency difference-frequency conversion.

[0129] When the crystal is X-shaped or Y-shaped, the polarization controller is used to adjust the solar-blind ultraviolet signal light and pump light to be horizontally polarized. (X-shaped or Y-shaped crystal...) d 33 The polarization direction corresponding to the coefficient is horizontal, so the two beams need to be adjusted to be horizontally polarized to meet the eee-type phase matching condition.

[0130] The detector also includes a beam-combining coupling structure, which is used to combine the solar-blind ultraviolet signal light to be measured and the pump light and then couple them into a periodically polarized waveguide device. The beam-combining coupling structure combines two beams of light with different wavelengths into the same optical path and efficiently couples them into the waveguide, which is a prerequisite for ensuring the occurrence of the difference frequency effect. In some embodiments, the beam-combining coupling structure is a wavelength division multiplexer or a focusing lens.

[0131] The detector also includes a filtering structure, which is placed between the periodically polarized waveguide device and the silicon detector to filter out residual solar-blind ultraviolet signal light and pump light after passing through the periodically polarized waveguide device.

[0132] The difference frequency conversion efficiency cannot reach 100%. In addition to the target difference frequency light, the waveguide output end also has some unconverted signal light and pump light. If these residual lights directly enter the silicon detector, they will generate background noise and reduce the detection signal-to-noise ratio. The filtering structure filters them out, which can ensure that only the difference frequency light enters the silicon detector, thereby improving the detection accuracy. In some embodiments, the filtering structure is a filter or filter sheet.

[0133] Through the above structure, the solar-blind ultraviolet detector of this application combines a periodically polarized waveguide device with a silicon detector. The periodically polarized waveguide device converts the solar-blind ultraviolet signal light to be measured into visible light, and the silicon detector efficiently detects the converted visible light, enabling the detector to achieve high sensitivity and low noise detection of solar-blind ultraviolet light. At the same time, it utilizes the advantages of low cost and small size of silicon detector to overcome the defects of large size and high price of traditional photomultiplier tubes, and also avoids the shortcomings of slow dynamic response and easy aging of fluorescent conversion materials.

[0134] This application provides a method for detecting solar-blind ultraviolet light in some embodiments. This method is based on the aforementioned periodically polarized waveguide device to detect solar-blind ultraviolet light signals. The method includes the following steps S701-S703: S701: Couple the solar-blind ultraviolet signal light and pump light to be tested into the aforementioned periodically polarized waveguide device.

[0135] The signal light is the target light to be detected, and its wavelength is located in the solar blind ultraviolet band. The pump light is the auxiliary light, which is used to generate a difference frequency effect with the signal light. Both beams need to be input into the waveguide at the same time. The coupling process can be achieved by a beam-combining coupling structure, which combines two beams of different wavelengths into the same optical path and efficiently couples them into the waveguide.

[0136] S702: In a periodically polarized waveguide device, the solar-blind ultraviolet signal light and the pump light undergo a difference frequency effect to generate difference frequency light.

[0137] The difference frequency effect is a three-wave mixing process in nonlinear optics. Two input beams are generated by the nonlinear polarization of a crystal to produce a third beam, the frequency of which is equal to the difference between the frequencies of the two input beams. The periodic polarization structure compensates for the phase mismatch through quasi-phase matching, so that the two beams can continuously and effectively interact nonlinearly during propagation, thus achieving a high conversion efficiency.

[0138] The intensity of the difference frequency light is directly proportional to the intensity of the solar-blind ultraviolet signal light. Under the condition that the pump light intensity and conversion efficiency are constant, the intensity of the difference frequency light is linearly proportional to the intensity of the signal light. Therefore, the intensity of the signal light can be inferred by detecting the difference frequency light.

[0139] S703: Utilizes a silicon detector to detect difference frequency light, and obtains intensity information of solar-blind ultraviolet signal light based on the intensity of the difference frequency light.

[0140] The silicon detector outputs an electrical signal that is proportional to the intensity of the incident light. By measuring the electrical signal, the intensity of the difference frequency light can be obtained, and then the intensity of the original solar-blind ultraviolet signal light can be inferred, thus completing the indirect detection of solar-blind ultraviolet light.

[0141] The method utilizes the high frequency conversion capability of periodically polarized waveguide devices and the high detection efficiency of silicon detectors in the visible light band to achieve high-sensitivity detection of solar-blind ultraviolet light. Simultaneously, polarization matching is ensured through polarization control, effective input of two beams is guaranteed through beam combining coupling, and the signal-to-noise ratio is improved through filtering.

[0142] This application leverages the low absorption characteristics of SLT / MgO:SLT thin films in the solar-blind ultraviolet band, along with the high optical field confinement and long interaction length of the waveguide structure, to achieve a UV-Vis difference frequency conversion efficiency far exceeding that of fluorescent material and bulk crystal solutions. This significantly improves the detector's responsivity and signal-to-noise ratio in the ultraviolet band. The all-inorganic crystal materials (SLT thin film, SiO2, silicon substrate) and stable periodic polarization domain structure enable the device to withstand high temperatures, resist ultraviolet radiation, and have a long lifespan, overcoming the problems of easy aging and performance degradation of organic phosphor materials. The ion implantation, wafer bonding, and semiconductor micro / nano fabrication processes employed are highly compatible with existing mature silicon-based processes, facilitating wafer-level large-scale manufacturing, reducing costs, and easily integrating with back-end electronic devices such as readout circuits. This lays the foundation for realizing miniaturized, low-power, and low-cost ultraviolet detection modules. By selecting different crystal orientations (X, Y, Z), adjusting the film thickness, and designing different waveguide cross-sections and polarization periods, the device can be flexibly optimized to meet the application requirements of different ultraviolet wavelengths, bandwidths, and dynamic ranges.

[0143] Similar parts between the embodiments provided in this application can be referred to mutually. The specific implementation methods provided above are only a few examples under the overall concept of this application and do not constitute a limitation on the scope of protection of this application. For those skilled in the art, any other implementation methods extended from the solution of this application without creative effort shall fall within the scope of protection of this application.

Claims

1. A single-crystal thin film, characterized in that, include: A substrate, a buffer layer, and a functional layer are stacked sequentially. The material of the functional layer is near-stoichiometric lithium tantalate or magnesium-doped near-stoichiometric lithium tantalate, and the thickness of the functional layer is 100nm-1000nm.

2. The single-crystal thin film according to claim 1, characterized in that, The substrate is a silicon substrate, a quartz substrate, a lithium niobate substrate, or a lithium tantalate substrate; The buffer layer is a silicon dioxide layer; The crystal tangent of the functional layer is X-cut, Y-cut, or Z-cut.

3. The single-crystal thin film according to claim 1, characterized in that, The ultraviolet absorption edge of the functional layer is less than or equal to 266 nm.

4. The single-crystal thin film according to claim 1, characterized in that, The diameter of the functional layer is 3 inches, 4 inches, 6 inches, 8 inches, or 12 inches.

5. The single-crystal thin film according to claim 1, characterized in that, When the material of the functional layer is magnesium-doped near-stoichiometric lithium tantalate, the magnesium doping concentration is 1 mol.

6. A periodically polarized waveguide device, characterized in that, include: The single-crystal thin film according to any one of claims 1-5; A periodic polarization structure is formed in the functional layer of the single-crystal thin film; A ridge waveguide structure is formed on the functional layer, and the extension direction of the ridge waveguide structure is parallel to the arrangement direction of the periodic polarization structure.

7. The periodically polarized waveguide device according to claim 6, characterized in that, The polarization period of the periodic polarization structure is 0.5 μm-1.5 μm.

8. The periodically polarized waveguide device according to claim 6, characterized in that, When the crystal tangent of the functional layer is X-cut, the extension direction of the ridge waveguide structure is parallel to the y-axis of the functional layer; When the crystal tangent of the functional layer is Z-cut, the extension direction of the ridge waveguide structure is parallel to the x-axis of the functional layer.

9. A solar-blind ultraviolet light detector, characterized in that, include: The periodically polarized waveguide device according to any one of claims 6-8; A silicon detector connected to the optical path of the periodically polarized waveguide device.

10. The solar-blind ultraviolet detector according to claim 9, characterized in that, The solar-blind ultraviolet detector is used to detect ultraviolet light signals with wavelengths of 266nm-300nm.

11. The solar-blind ultraviolet detector according to claim 9, characterized in that, The detector also includes: A pump light source is connected to the periodically polarized waveguide device; A polarization controller is used to adjust the polarization state of the solar-blind ultraviolet signal light and the pump light to be measured, respectively. The wavelength range of the difference frequency light output by the periodically polarized waveguide device is set based on the wavelength of the pump light.

12. The solar-blind ultraviolet detector according to claim 11, characterized in that, When the crystal tangent is Z-cut, the polarization controller is used to adjust the solar-blind ultraviolet signal light to be measured and the pump light to be vertically polarized. When the crystal is X-shaped or Y-shaped, the polarization controller is used to adjust the solar-blind ultraviolet signal light to be measured and the pump light to be horizontally polarized.

13. The solar-blind ultraviolet detector according to claim 9, characterized in that, Also includes: A beam-combining coupling structure, which is a wavelength division multiplexer or a focusing lens, is used to combine the solar-blind ultraviolet signal light to be measured and the pump light, and then couple them into the periodically polarized waveguide device.

14. The solar-blind ultraviolet detector according to claim 9, characterized in that, Also includes: A filtering structure is disposed between the periodically polarized waveguide device and the silicon detector. The filtering structure is used to filter out the residual solar-blind ultraviolet signal light and pump light after passing through the periodically polarized waveguide device.

15. A method for detecting solar-blind ultraviolet light, characterized in that, include: The solar-blind ultraviolet signal light to be tested and the pump light are coupled into the periodically polarized waveguide device according to any one of claims 6-8; In the periodically polarized waveguide device, the solar-blind ultraviolet signal light and the pump light undergo a difference frequency effect to generate difference frequency light, and the intensity of the difference frequency light is proportional to the intensity of the solar-blind ultraviolet signal light. The difference frequency light is detected using a silicon detector, and the intensity information of the solar-blind ultraviolet signal light is obtained based on the intensity of the difference frequency light.

16. A method for preparing a single-crystal thin film, characterized in that, For preparing the single-crystal thin film according to any one of claims 1-5, comprising: Provide near-stoichiometric lithium tantalate or magnesium-doped near-stoichiometric lithium tantalate single crystals as donor wafers; Ion implantation is performed on the donor wafer to form an implantation layer inside the donor wafer; A substrate is provided on which a buffer layer is formed; Bond the injection layer to the buffer layer; Heat treatment is performed to peel the donor wafer along the implantation layer and form a functional layer on the substrate; The functional layer is subjected to surface planarization and annealing to obtain a single-crystal thin film.

17. A method for fabricating a periodically polarized waveguide device, characterized in that, For fabricating the periodically polarized waveguide device according to any one of claims 6-8, comprising: Periodic electrodes are fabricated on the functional layer of a single-crystal thin film and polarized by an external electric field to form a periodic polarization structure in the functional layer. Remove the periodic electrode; A ridge waveguide structure is etched on the functional layer, and the extension direction of the ridge waveguide structure is parallel to the arrangement direction of the periodic polarization structure.

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