A quartz crystal Y-type optical beam splitter capable of deep ultraviolet waveband nonlinear frequency conversion

Abstract

This invention discloses a quartz crystal Y-type optical beamsplitter capable of nonlinear frequency conversion in the deep ultraviolet band, belonging to the field of optoelectronic device technology. It includes a quartz crystal with a Y-type ridge waveguide structure on its surface. The Y-type ridge waveguide structure includes an input arm, the end of which is connected to the beginning of two branch arms. Each branch arm is connected to an output arm parallel to the input arm. One output arm contains a periodic phase grating structure arranged along the light transmission direction of the quartz crystal. The periodic phase grating structure is composed of several single-cycle femtosecond laser-modified regions and several unmodified regions arranged periodically. The Y-type optical beamsplitter disclosed in this invention integrates optical beam splitting and nonlinear frequency conversion functions, allowing for the low-loss output of both a fundamental ultraviolet beam and a deep ultraviolet frequency-doubled beam from an input fundamental ultraviolet light beam.

Description

Technical Field

[0001] This invention relates to the field of optoelectronic device technology, and more specifically to a quartz crystal Y-type optical beam splitter capable of realizing nonlinear frequency conversion in the deep ultraviolet band. Background Technology

[0002] In laser technology, ultraviolet light typically refers to lasers with wavelengths between 10 nm and 400 nm, while deep ultraviolet light refers to lasers with wavelengths between 100 nm and 280 nm. Ultraviolet and deep ultraviolet lasers are indispensable key tools in modern high-end precision manufacturing and cutting-edge industries. In the field of ultra-precision machining, thanks to the extremely high photon energy and minimal diffraction limit brought by their short wavelengths, lasers in this band can achieve high-precision processing, cutting, and surface treatment, and are widely used in key processes in laser processing and semiconductor chip manufacturing. In the field of advanced scientific instrument fabrication, ultraviolet and deep ultraviolet lasers are their core light sources, determining the performance limits of equipment such as high-resolution photoelectron spectrometers and laser-induced breakdown spectrometers, and providing ultra-high sensitivity detection capabilities for materials analysis and environmental monitoring. Therefore, developing technologies and devices that can efficiently generate, stably control, and reliably transmit lasers in this band is a key technological foundation supporting the upgrading of high-end manufacturing and empowering cutting-edge scientific research, possessing significant application value and strategic importance.

[0003] Currently, common techniques for generating deep ultraviolet lasers include using nonlinear optical crystals to perform nonlinear frequency conversions such as frequency doubling, sum-frequency conversion, or fourth-frequency conversion on near-infrared or visible fundamental light. Typical deep ultraviolet nonlinear crystals include β-BaB₂O₄ and CsLiB₆O₄. 10 While materials like KBe2BO3F2 (KBBF) possess high nonlinear coefficients, they generally suffer from practical problems such as limited lower limits of transmission bands, susceptibility to deliquescence, and difficulties in processing or limited crystal growth size due to their layered structure. Furthermore, traditional nonlinear frequency conversion devices based on bulk crystals rely on birefringent phase-matching or quasi-phase-matching (QPM) techniques, resulting in complex optical path structures, large volumes, and significant absorption or scattering of the converted deep ultraviolet light during long-distance transmission within the crystal, leading to low output efficiency.

[0004] Furthermore, integrated optics technology offers new insights into miniaturized nonlinear frequency conversion devices. Among these, the Y-type optical beamsplitter, as a fundamental passive optical device, is widely used for optical power distribution. However, traditional Y-type beamsplitters only possess beam splitting capabilities and lack nonlinear frequency conversion capabilities. To integrate beam splitting and frequency conversion functions, it is typically necessary to cascade devices made of different materials, which introduces additional coupling losses, interface reflections, and packaging complexity, hindering improvements in system integration and stability.

[0005] Recent studies have shown significant progress in fabricating three-dimensional optical waveguides and microstructures within transparent media using femtosecond laser direct writing technology. However, most existing quasi-phase-matched devices based on femtosecond laser direct writing operate in the visible or near-infrared bands and typically employ ferroelectric crystals such as lithium niobate (PPLN achieved through periodic polarization). For centrosymmetric nonferroelectric materials like quartz crystals (SiO2), the periodic reversal of the second-order nonlinear coefficient cannot be achieved through conventional electric field polarization methods, making conventional quasi-phase-matching methods difficult to apply. Furthermore, the second-order nonlinear coefficient of quartz crystals is relatively small, making it difficult to obtain efficient deep-ultraviolet frequency doubling output using traditional methods.

[0006] In summary, how to achieve monolithic integration of beam splitting and nonlinear frequency conversion functions on a crystal material platform that combines wide light transmission range (covering deep ultraviolet), low intrinsic loss, high stability, and easy integration, and effectively reduce the loss of deep ultraviolet frequency-doubled light during transmission, is a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0007] In view of the above problems, the present invention is proposed to provide a quartz crystal Y-type optical beam splitter that can realize nonlinear frequency conversion in the deep ultraviolet band to overcome or at least partially solve the above problems.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] In a first aspect, embodiments of the present invention provide a quartz crystal Y-type optical beam splitter capable of realizing nonlinear frequency conversion in the deep ultraviolet band, comprising: Quartz crystal, The surface of the quartz crystal is provided with a Y-shaped ridge waveguide structure. The Y-shaped ridge waveguide structure includes an input arm, the end of which is connected to the beginning of two branch arms respectively. The end of each branch arm is connected to an output arm parallel to the input arm. Among them, one output arm is provided with a periodic phase grating structure arranged along the light transmission direction of the quartz crystal. The periodic phase grating structure is composed of several femtosecond laser modified regions and several unmodified regions arranged periodically within a single period.

[0010] Preferably, the light transmission direction of the quartz crystal is the y-direction of the quartz crystal.

[0011] Preferably, in the periodic phase grating structure provided in one output arm, the width ratio of the femtosecond laser-modified region to the unmodified region within a single cycle is 1:1.

[0012] Preferably, the horizontal angle between each branch arm and the line containing the input arm is 1 degree.

[0013] Preferably, in the Y-shaped ridge waveguide structure, the width of the input arm is 24 μm, and the width of each branch arm and each output arm is 12 μm.

[0014] Preferably, the quartz crystal is z Cut quartz crystals.

[0015] Preferably, the bottom of the Y-shaped ridge waveguide structure is provided with several femtosecond laser-induced refractive index reduction modification grooves with a width of 2 μm and a depth of 4 μm.

[0016] Secondly, embodiments of the present invention provide a method for fabricating a quartz crystal Y-type optical beam splitter capable of nonlinear frequency conversion in the deep ultraviolet band, comprising the following steps: S1. Using a femtosecond laser Gaussian beam to scan along the y-direction of a quartz crystal, two parallel air slots are prepared by ablation, and the quartz crystal structure between the two parallel air slots is used as the input arm of the Y-shaped ridge waveguide structure. S2. With the center point of the end of the input arm as the center, rotate the quartz crystal by the same set angle in both clockwise and counterclockwise directions. After each rotation, two parallel air grooves are ablated and prepared, and the quartz crystal structure between the two parallel air grooves is used as the branch arm of the Y-shaped ridge waveguide structure. S3. Scan along the y-direction of the quartz crystal at the end of each branch arm, and re-prepare two parallel air slots by ablation. Use the quartz crystal structure between the two parallel air slots as the output arm of the Y-shaped ridge waveguide structure. S4. In the input arm, branch arm and output arm of the Y-shaped ridge waveguide structure, along the direction parallel to their respective air slots, a number of refractive index reduction type modified grooves are prepared by scanning with a femtosecond laser Gaussian beam parallel to their respective air slots. S5. Select any output arm with a refractive index reduction modified groove, perform a through scan on the selected output arm using a femtosecond laser Bessel beam, and translate the femtosecond laser irradiation area along the y-direction of the quartz crystal of the selected output arm to obtain a periodic phase grating structure arranged along the y-direction, which consists of several femtosecond laser modified regions and several unmodified regions arranged periodically in a single cycle.

[0017] Furthermore, the above method also includes: S6. Perform optical polishing on the two end faces of the quartz crystal that are perpendicular to the y-direction of the quartz crystal.

[0018] Furthermore, in steps S1, S2, and S3, each air trough has a depth of 16 μm and a width of 2 μm.

[0019] As can be seen from the above technical solution, compared with the prior art, the present invention discloses a quartz crystal Y-type optical beam splitter that can realize nonlinear frequency conversion in the deep ultraviolet band, which has the following beneficial effects:

[0020] This invention proposes a quartz crystal Y-type optical beamsplitter capable of nonlinear frequency conversion in the deep ultraviolet band. One output arm of the Y-type ridge waveguide contains a periodic phase grating structure directly written with a femtosecond laser Bessel beam. The distribution of this periodic structure meets the requirements of APP phase matching technology. Within a single cycle, the ratio of the femtosecond laser modified region to the unmodified region is 1:1, effectively achieving nonlinear optical frequency conversion within the quartz crystal. This splits the input ultraviolet fundamental frequency light into the original ultraviolet fundamental frequency light and a deep ultraviolet frequency-doubled light, with the deep ultraviolet frequency-doubled light being output immediately after generation, significantly reducing its transmission loss. Furthermore, this invention utilizes a z-cut quartz crystal material platform. This nonlinear optical crystal material possesses characteristics such as a wide transmission range (from deep ultraviolet to near-infrared), low intrinsic optical loss, strong resistance to optical damage, excellent material homogeneity, and high chemical and physical stability. These features facilitate efficient and stable deep ultraviolet laser output, making it an excellent material carrier for integrating the functions of a beamsplitter and a nonlinear frequency conversion device.

[0021] This invention utilizes a Y-shaped ridge waveguide structure to construct a Y-shaped optical beamsplitter. Through femtosecond laser ablation and modification, it can achieve strong optical field confinement in both horizontal and vertical directions and can be integrated on-chip. By effectively reducing the mode field area, the power density in the optical waveguide is increased. At the Y-shaped branch, the ridge waveguide structure, with its excellent mode confinement characteristics, can suppress radiation loss and mode perturbation, ensuring that the optical power is efficiently and stably distributed to each output arm.

[0022] The quartz crystal Y-type optical beam splitter disclosed in this invention, which can realize nonlinear frequency conversion in the deep ultraviolet band, has the characteristics of simple preparation method, high preparation efficiency, high nonlinear frequency conversion efficiency, stable beam distribution capability, low transmission loss and high integration. Furthermore, it can achieve efficient integration of nonlinear frequency converter and beam splitter functions in the deep ultraviolet band, and will have wide applications in integrated optics, nonlinear optics and quantum optics. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0024] Figure 1This is a top view of a quartz crystal Y-type optical beam splitter capable of nonlinear frequency conversion in the deep ultraviolet band, provided in an embodiment of the present invention. Figure 2 A front view of a quartz crystal Y-type optical beam splitter capable of nonlinear frequency conversion in the deep ultraviolet band, provided in an embodiment of the present invention; Figure 3 A left view of a quartz crystal Y-type optical beam splitter capable of nonlinear frequency conversion in the deep ultraviolet band, provided in an embodiment of the present invention; Figure 4 This is a schematic diagram illustrating a method for fabricating a quartz crystal Y-type optical beam splitter capable of nonlinear frequency conversion in the deep ultraviolet band, provided by an embodiment of the present invention. In the figure, 1- the waveguide region of the Y-type ridge waveguide, 2- the air groove near the crystal surface etched by femtosecond laser, 3- the periodic phase grating structure, 4- the z-cut quartz crystal, and 5- the refractive index reduction modified groove of the quartz crystal induced by femtosecond laser. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Terminology Explanation: Frequency doubling: A nonlinear frequency conversion process that increases the frequency of fundamental light by two times.

[0027] Grating period: A phase grating structure with a periodic refractive index is formed inside the crystal by processing it with femtosecond laser direct writing technology. The grating period is the sum of the width of the laser-induced modified region and the width of the unmodified region along the light transmission direction of the crystal.

[0028] Example 1 Embodiment 1 of this invention discloses a quartz crystal Y-type optical beamsplitter capable of nonlinear frequency conversion in the deep ultraviolet band, such as... Figures 1-3 ,include: z A platform for cutting quartz crystal materials, the light transmission direction of which is along the crystal. y Towards; z A Y-shaped ridge waveguide structure is provided on the surface of a quartz crystal to serve as a Y-type optical beamsplitter. This Y-type optical beamsplitter includes one input arm, two branch arms, and two output arms, with the light transmission direction along the quartz crystal. y The direction, and in one of the output arms, there is a femtosecond laser Bessel beam directly written along the crystal.y A periodic phase grating structure arranged in a specific direction.

[0029] In this embodiment, the width ratio of the modified region induced by the femtosecond laser to the unmodified region in a single cycle of the periodic phase grating structure is 1:1. The closer this width ratio is to 1:1, the higher the frequency conversion efficiency. When the width ratio of the modified region to the unmodified region in a single cycle is 1:1, the frequency conversion efficiency reaches its maximum.

[0030] At room temperature, the grating period for APP phase matching during nonlinear frequency conversion is:

[0031] Where Λ is the quasi-phase matching period size, λ 2ω It is the wavelength of the emitted frequency-doubled light. n ω and n 2ω These are the refractive index values ​​of the material under fundamental and second-harmonic light conditions, respectively; the dispersion equation is used to calculate the refractive index of a quartz crystal at a certain incident fundamental light wavelength λ. z The refractive index in the direction is as follows: .

[0032] To further implement the above technical solution, the femtosecond laser Gaussian beam is directed along the quartz crystal. z The incident light is used to ablate the near-surface of the quartz crystal to prepare a Y-shaped ridge waveguide structure.

[0033] To further implement the above technical solution, the width of the two branch arms and the two output arms (perpendicular to the direction of light transmission) is 12 μm, and the width of the input arm is 24 μm.

[0034] To further implement the above technical solution, the angle between the two branch arms of the Y-type optical beam splitter and the straight line containing the input arm is 1 degree, that is, the angle between the two branch arms of the Y-type ridge waveguide is 2 degrees.

[0035] To further implement the above technical solution, femtosecond laser Bessel beam direct writing along the crystal... y The number of periods in the periodically arranged phase grating structure is ≥300.

[0036] To further implement the above technical solution, a periodic phase grating structure directly written by a femtosecond laser Bessel beam is constructed along the quartz crystal. z The length of the direction is 30 μm.

[0037] To further implement the above technical solution, the six faces of the quartz crystal are optically polished, and a femtosecond laser Bessel beam is applied along the quartz crystal. zAn incident periodic phase grating structure is used, where the incident fundamental ultraviolet light and the split-beam emitted frequency-doubled deep ultraviolet and fundamental ultraviolet lasers all follow the direction of the quartz crystal. y Transmission.

[0038] Furthermore, the component has a size of 5 ( x ) 10 ( y ) 2 ( z ) mm 3 tangential direction z Cut, light transmission direction along y Towards.

[0039] In this embodiment, the working principle of a quartz crystal Y-type optical beamsplitter capable of nonlinear frequency conversion in the deep ultraviolet band is as follows: a Y-type optical beamsplitter is constructed using a Y-type ridge waveguide structure directly written by a femtosecond laser (combining an air groove formed by femtosecond laser ablation with a refractive index reduction modification induced by a femtosecond laser). Furthermore, a periodic phase grating structure conforming to the APP phase matching theory is fabricated in one output arm of the beamsplitter. The combination of the Y-type ridge waveguide structure and the periodic phase grating structure achieves the functional integration of optical beam splitting and frequency conversion in the deep ultraviolet band.

[0040] The advantages of this invention are mainly reflected in the following three aspects: First, the combination of the Y-shaped ridge waveguide structure and the periodic phase grating structure can realize the integration of optical beam splitting and frequency conversion functions; second, based on the z-cut quartz crystal material platform, its wide light transmission range and combined with APP phase matching technology can efficiently transmit and generate deep ultraviolet lasers; finally, the time required for direct writing of the Y-shaped ridge waveguide structure using femtosecond laser and processing of the periodic phase grating structure using the shaped femtosecond laser Bessel beam is relatively short, enabling rapid and efficient fabrication.

[0041] Specifically, optical beam splitting and nonlinear frequency conversion work synergistically. The beam splitter splits the incident light in two, with one arm generating a new wavelength through a nonlinear effect, while the other arm retains the original wavelength. This design allows the same chip to perform wavelength conversion while maintaining the natural phase-locked relationship between the two output beams, providing an integrated dual-wavelength coherent light source for quantum information processing and precision measurement.

[0042] Furthermore, the core value of the Y-bifurcation ridge waveguide beamsplitter design disclosed in this invention lies in its ability to achieve the collaborative operation and functional partitioning of two different wavelength beams on a single integrated photonic chip. Specifically, this beamsplitter can split the incident ultraviolet fundamental frequency light into two paths with low loss. One output arm efficiently generates deep ultraviolet frequency-doubled light, while the other output arm directly outputs the original fundamental frequency light. In this way, on the same chip-level platform, short-wavelength deep ultraviolet light is obtained for high-resolution detection or material processing, while the original wavelength fundamental frequency light is retained for atomic manipulation or as a coherent reference source. Since the two light sources originate from the same coherent source and can be integrated on the same waveguide chip, they have natural phase locking and excellent spatial overlap, greatly simplifying the optical system and providing a compact, stable, and powerful dual-wavelength photonic source for cutting-edge applications such as quantum computing, precision measurement, and on-chip spectral analysis.

[0043] Example 2 like Figure 4 As shown in Example 2, a method for fabricating a quartz crystal Y-type optical beam splitter capable of nonlinear frequency conversion in the deep ultraviolet band is disclosed, comprising the following steps: A femtosecond laser Gaussian beam is focused onto a quartz crystal using a microscope objective. Based on the processing parameters for ablation of near-surface air grooves in the quartz crystal using femtosecond laser, a first set (two) of parallel air grooves is first prepared by scanning along the y-axis of the quartz crystal. Then, the quartz crystal is rotated clockwise and counterclockwise, and a second set (two) of parallel air grooves are prepared by scanning along the two rotated directions starting from the end of the first set of air grooves. Finally, a second set (two) of parallel air grooves are prepared by scanning along the y-axis of the quartz crystal starting from the end of the first two sets of air grooves, keeping them parallel to the first set of air grooves. Subsequently, using a femtosecond laser, several refractive index reduction modified grooves are prepared between the two parallel air grooves in each of the above five sets of parallel air grooves, along a direction parallel to the corresponding air grooves, forming the waveguide region of a Y-shaped ridge waveguide and constructing a Y-shaped optical beam splitter.

[0044] In this step, the refractive index-reducing modified grooves are set at the bottom of the middle area between the two parallel air slots in each group. Each groove is 4 micrometers deep and 2 micrometers wide. There are 11 grooves at the bottom of the middle area between the air slots on both sides of the output arm, with an interval of 0.2 micrometers. There are 5 grooves at the bottom of the middle area between the air slots on both sides of the branch arm and the output arm, with an interval of 0.5 micrometers. This perfectly fills the bottom gap between the two parallel air slots in each group.

[0045] In this step, the refractive index reduction modification groove is located at the bottom, thus forming a structure similar to a cladding waveguide. The refractive index of the area surrounding the light-guiding region is lower than that of the light-guiding region, allowing light to propagate better within the light-guiding region of the ridge waveguide and effectively reducing transmission loss. By selecting the appropriate femtosecond laser processing parameters, a femtosecond laser Gaussian beam is incident perpendicularly along the z-direction, focused by the objective lens to the bottom (the modification groove induced by the femtosecond laser Gaussian beam will only occur at and near the focal point), and then translated along other directions, the refractive index modification groove can be obtained.

[0046] A femtosecond laser Gaussian beam is shaped into a femtosecond laser Bessel beam using a femtosecond laser shaping system based on a conical lens. After being focused by a microscope objective, the beam is incident perpendicularly onto a quartz crystal along the z-axis. A through-scan is performed along the x-axis of the crystal on one output arm of a Y-type optical beam splitter, generating a periodic phase grating structure unit. The width ratio of the femtosecond laser-modified region to the unmodified region within a single period is adjusted to 1:1, and the femtosecond laser irradiation area is translated along the y-axis of the quartz crystal. Finally, a periodic phase grating structure arranged along the y-axis is obtained in one output arm of the Y-type optical beam splitter. Unlike the femtosecond laser Gaussian beam, the refractive index modification indentation induced by the femtosecond laser Bessel beam can be several hundred micrometers long along the z-axis (laser incident direction). Therefore, during the fabrication of the periodic phase grating structure unit, the scanning depth of the femtosecond laser Bessel beam is usually higher than the air groove depth obtained by scanning with the femtosecond laser Gaussian beam.

[0047] Optical polishing is performed on the two y-end faces of the quartz crystal, that is, the two end faces perpendicular to the y-direction of the quartz crystal, to finally obtain a quartz crystal Y-type optical beam splitter that can realize nonlinear frequency conversion in the deep ultraviolet band.

[0048] For a laser of a specific wavelength, this invention theoretically calculates the corresponding period width and adjusts the width ratio of the modified region to the unmodified region within the periodic structural unit to 1:1. By preparing a phase grating structure with hundreds or thousands of periods along the transmission direction of the "laser of a specific wavelength", efficient frequency conversion can be achieved.

[0049] In practical applications, the microscope objective has a magnification of 50 and a numerical aperture of 0.67.

[0050] To further implement the above technical solutions, the processing parameters for femtosecond laser ablation of near-surface air grooves in quartz crystals are as follows: femtosecond laser pulse width of 400 fs, wavelength of 1030 nm, repetition rate of 250 kHz, single pulse energy of 8 μJ, and femtosecond laser scanning speed of 4 mm / s. The processing parameters for femtosecond laser-induced refractive index reduction modification inside quartz crystals are as follows: femtosecond laser pulse width of 400 fs, wavelength of 1030 nm, repetition rate of 25 kHz, single pulse energy of 0.5 μJ, and femtosecond laser scanning speed of 5 mm / s. In the fabrication step of the periodic phase grating structure, the femtosecond laser pulse width is 400 fs, the wavelength is 1030 nm, the repetition frequency is 2.5 MHz, the single pulse energy is 1.92 μJ, and the femtosecond laser scanning speed is 10 mm / s.

[0051] The femtosecond laser direct writing technology used in Example 2 is an advanced manufacturing method that utilizes ultrashort pulse lasers to process materials at the microscale. It leverages femtosecond (10^6) lasers... - ¹ 5 The nonlinear interaction between a femtosecond laser pulse and a transparent optical material allows for highly localized energy deposition within the material, overcoming the limitations of traditional optical diffraction and enabling the fabrication of sub-micron precision three-dimensional structures within transparent media. Furthermore, due to the extremely short duration of the femtosecond laser pulse, the energy injection rate far exceeds the rate of heat diffusion, virtually eliminating the formation of a heat-affected zone. This makes femtosecond laser direct writing a "cold processing" precision fabrication technique. Femtosecond laser direct writing technology truly realizes the direct construction of three-dimensional micro / nano structures within transparent media and has been widely applied in the fabrication of precision instruments such as micro-optical components, photonic integrated circuits, and microfluidic chips.

[0052] Added periodic phased (APP) phase matching is a novel method that introduces periodic ordered and disordered structures within nonlinear optical crystals using processing techniques such as femtosecond laser direct writing, thereby providing additional phase to compensate for phase mismatch. The core advantage of this phase matching method lies in its complete elimination of the dependence on the natural birefringence of the crystal in traditional birefringent phase matching, and it also overcomes the limitation that quasi-phase matching is only applicable to ferroelectric crystals. It greatly enriches the types of crystal materials suitable for phase matching, enabling many non-centrosymmetric crystals that were previously discarded due to insufficient birefringence or lack of ferroelectricity to be used in efficient frequency conversion. APP phase matching technology opens up a universal and flexible new avenue for the utilization of nonlinear optical crystal materials, and initiates a new universal material paradigm for efficient nonlinear optical frequency conversion.

[0053] Example 3 A quartz crystal Y-type optical beam splitter capable of achieving 320 nm frequency doubling is fabricated, specifically as follows: (1) Z-cut quartz crystal was selected, and a femtosecond laser Gaussian beam was focused onto the quartz crystal using a microscope objective. Based on the processing parameters of the femtosecond laser ablation of the air grooves near the surface of the quartz crystal (femtosecond laser pulse width of 400 fs, wavelength of 1030 nm, repetition frequency of 25 kHz, single pulse energy of 8 μJ, and femtosecond laser scanning speed of 4 mm / s) and the conditions for femtosecond laser to induce refractive index reduction modification in the quartz crystal (femtosecond laser pulse width of 400 fs, wavelength of 1030 nm, repetition frequency of 25 kHz, single pulse energy of 0.5 μJ, and femtosecond laser scanning speed of 5 mm / s), a Y-shaped ridge waveguide structure was prepared according to the operation described in step S1 of Example 2 to construct a Y-shaped optical beam splitter, and the structural parameters of the Y-shaped optical beam splitter were kept consistent with the parameters listed in Example 1. (2) A femtosecond laser Gaussian beam (400 fs, wavelength 1030 nm, repetition frequency 2.5 MHz, single pulse energy 1.92 μJ, femtosecond laser scanning speed 10 mm / s) is shaped into a femtosecond laser Bessel beam using a beam shaping system based on a conical lens. After being focused by a microscope objective (magnification 50, numerical aperture 0.67), it is incident perpendicularly along the z-axis of the quartz crystal. A periodic phase grating structure is fabricated in one output arm of a Y-shaped ridge waveguide. The theoretical calculated value of the APP phase matching period corresponding to a wavelength of 320 nm is 0.46 μm. Therefore, the grating period is set to 0.46 μm. The width ratio of the femtosecond laser modified region to the unmodified region is adjusted to 1:1 to obtain a periodic phase grating structure based on APP phase matching. This periodic structure can be used to realize the frequency doubling process of 320 nm and output deep ultraviolet frequency-doubled light of 160 nm. (3) The two y-end faces of the quartz crystal (i.e. the two end faces perpendicular to the y-direction of the quartz crystal) are optically polished, with about 0.5 mm removed from each face. Then the sample is cleaned with a mixed solution of ethanol and acetone to obtain the polished surface.

[0054] A quartz crystal Y-type optical beam splitter capable of achieving 355 nm frequency doubling is fabricated, specifically as follows: (1) Z-cut quartz crystal was selected, and a femtosecond laser Gaussian beam was focused onto the quartz crystal using a microscope objective. Based on the processing parameters of the femtosecond laser ablation of the air grooves near the surface of the quartz crystal (femtosecond laser pulse width of 400 fs, wavelength of 1030 nm, repetition frequency of 25 kHz, single pulse energy of 8 μJ, and femtosecond laser scanning speed of 4 mm / s) and the conditions for femtosecond laser to induce refractive index reduction modification in the quartz crystal (femtosecond laser pulse width of 400 fs, wavelength of 1030 nm, repetition frequency of 25 kHz, single pulse energy of 0.5 μJ, and femtosecond laser scanning speed of 5 mm / s), a Y-shaped ridge waveguide structure was prepared according to the operation described in step S1 of Example 2 to construct a Y-shaped optical beam splitter, and the structural parameters of the Y-shaped optical beam splitter were kept consistent with the parameters listed in Example 1. (2) A femtosecond laser Gaussian beam (400 fs, wavelength 1030 nm, repetition frequency 2.5 MHz, single pulse energy 1.92 μJ, femtosecond laser scanning speed 10 mm / s) is shaped into a femtosecond laser Bessel beam using a beam shaping system based on a conical lens. After being focused by a microscope objective (magnification 50, numerical aperture 0.67), it is incident perpendicularly along the z-axis of the quartz crystal. A periodic phase grating structure is fabricated in one output arm of a Y-shaped ridge waveguide. The theoretical calculated value of the APP phase matching period corresponding to a wavelength of 320 nm is 0.7 μm. Therefore, the grating period is set to 0.7 μm. The width ratio of the femtosecond laser modified region to the unmodified region is adjusted to 1:1 to obtain a periodic phase grating structure based on APP phase matching. This periodic structure can be used to realize the frequency doubling process of 355 nm and output deep ultraviolet frequency-doubled light of 177.5 nm. (3) The two y-end faces of the quartz crystal (i.e. the two end faces perpendicular to the y-direction of the quartz crystal) are optically polished, with about 0.5 mm removed from each face. Then the sample is cleaned with a mixed solution of ethanol and acetone to obtain the polished surface.

[0055] In this embodiment, a comparative experiment is conducted using two comparatively assembled optical beam splitters and the quartz crystal Y-type optical beam splitter prepared in Example 3: Comparative Example 1 differs from Example 3 in that no periodic phase grating structure is fabricated in the beam output arm; Comparative Example 2 differs from Example 3 in that the ratio of the width of the femtosecond laser modified region to the width of the unmodified region in a single cycle of the periodic phase grating structure is 1:4.

[0056] In Comparative Example 1, due to the lack of a periodic phase grating, nonlinear frequency conversion in the deep ultraviolet band cannot be achieved, meaning it can only split the input light but cannot output deep ultraviolet frequency-doubled laser; in Comparative Example 2, the intensity of the output ultraviolet frequency-doubled laser is significantly weakened.

[0057] Experiments show that this invention innovatively utilizes a Y-shaped ridge waveguide on the surface of a z-cut quartz crystal to construct an optical beamsplitter capable of nonlinear frequency conversion in the deep ultraviolet band. A periodic phase grating structure is fabricated in one output arm of the beamsplitter using a shaped femtosecond laser Bessel beam, thus achieving the integration of optical beam splitting and nonlinear frequency conversion functions. An input ultraviolet fundamental frequency light beam can output a primary ultraviolet light beam and a deep ultraviolet frequency-doubled light beam with low loss.

[0058] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0059] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A quartz crystal Y-type optical beam splitter capable of nonlinear frequency conversion in the deep ultraviolet band, characterized in that, include: Quartz crystal, The surface of the quartz crystal is provided with a Y-shaped ridge waveguide structure. The Y-shaped ridge waveguide structure includes an input arm, the end of which is connected to the beginning of two branch arms respectively. The end of each branch arm is connected to an output arm parallel to the input arm. Among them, one output arm is provided with a periodic phase grating structure arranged along the light transmission direction of the quartz crystal. The periodic phase grating structure is composed of several femtosecond laser modified regions and several unmodified regions arranged periodically within a single period.

2. The quartz crystal Y-type optical beamsplitter capable of nonlinear frequency conversion in the deep ultraviolet band according to claim 1, characterized in that, The light transmission direction of the quartz crystal is the y-direction of the quartz crystal.

3. The quartz crystal Y-type optical beamsplitter capable of nonlinear frequency conversion in the deep ultraviolet band according to claim 1, characterized in that, In the periodic phase grating structure set in an output arm, the width ratio of the femtosecond laser-modified region to the unmodified region is 1:1 within a single cycle.

4. The quartz crystal Y-type optical beam splitter capable of nonlinear frequency conversion in the deep ultraviolet band according to claim 1, characterized in that, The horizontal angle between each branch arm and the line containing the input arm is 1 degree.

5. The quartz crystal Y-type optical beamsplitter capable of nonlinear frequency conversion in the deep ultraviolet band according to claim 1, characterized in that, In the Y-shaped ridge waveguide structure, the width of the input arm is 24 μm, and the width of each branch arm and each output arm is 12 μm.

6. The quartz crystal Y-type optical beamsplitter capable of nonlinear frequency conversion in the deep ultraviolet band according to claim 1, characterized in that, The quartz crystal is a Z-cut quartz crystal.

7. The quartz crystal Y-type optical beam splitter capable of nonlinear frequency conversion in the deep ultraviolet band according to claim 1, characterized in that, The bottom of the Y-shaped ridge waveguide structure is provided with several femtosecond laser-induced refractive index reduction modification grooves with a width of 2 μm and a depth of 4 μm.

8. The method for fabricating a quartz crystal Y-type optical beam splitter capable of nonlinear frequency conversion in the deep ultraviolet band according to any one of claims 1-7, characterized in that, Includes the following steps: S1. Using a femtosecond laser Gaussian beam to scan along the y-direction of a quartz crystal, two parallel air slots are prepared by ablation, and the quartz crystal structure between the two parallel air slots is used as the input arm of the Y-shaped ridge waveguide structure. S2. With the center point of the end of the input arm as the center, rotate the quartz crystal by the same set angle in both clockwise and counterclockwise directions. After each rotation, two parallel air grooves are ablated and prepared, and the quartz crystal structure between the two parallel air grooves is used as the branch arm of the Y-shaped ridge waveguide structure. S3. Scan along the y-direction of the quartz crystal at the end of each branch arm, and re-prepare two parallel air slots by ablation. Use the quartz crystal structure between the two parallel air slots as the output arm of the Y-shaped ridge waveguide structure. S4. In the input arm, branch arm and output arm of the Y-shaped ridge waveguide structure, along the direction parallel to their respective air slots, a number of refractive index reduction type modified grooves are prepared by scanning with a femtosecond laser Gaussian beam parallel to their respective air slots. S5. Select any output arm with a refractive index reduction modified groove, perform a through scan on the selected output arm using a femtosecond laser Bessel beam, and translate the femtosecond laser irradiation area along the y-direction of the quartz crystal of the selected output arm to obtain a periodic phase grating structure arranged along the y-direction, which consists of several femtosecond laser modified regions and several unmodified regions arranged periodically in a single cycle.

9. The method for fabricating a quartz crystal Y-type optical beam splitter capable of nonlinear frequency conversion in the deep ultraviolet band according to claim 8, characterized in that, Also includes: S6. Perform optical polishing on the two end faces of the quartz crystal that are perpendicular to the y-direction of the quartz crystal.

10. The method for fabricating a quartz crystal Y-type optical beam splitter capable of nonlinear frequency conversion in the deep ultraviolet band according to claim 8, characterized in that, In steps S1, S2, and S3, each air trough has a depth of 16 μm and a width of 2 μm.

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