Method for manufacturing a nonlinear optical waveguide having a self-focusing effect

Abstract

To provide a method for fabricating an optical waveguide with a focusing capability in order to improve the frequency conversion efficiency of an optical waveguide itself.SOLUTION: A method for fabricating an optical waveguide with a focusing capability comprises steps such as S1 of processing preparation, S2 of high-energy ion irradiation, S3 of secondary high-energy ion irradiation, S4 of surface patterning processing. The invention further provides an optical waveguide and a frequency converter. The optical waveguide structure fabricated by the fabrication method provided herein has a focusing capability, constrains a light field to converge to a center of the optical waveguide without reducing the cross-sectional size of an optical waveguide core, improves the frequency conversion efficiency of the optical waveguide itself, facilitates application to a specific optical path as a frequency converter, and contributes to improvement in the optical frequency conversion efficiency of the entire optical path.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to the technical fields of optical materials and integrated optics, and in particular to optical waveguides. [Background technology]

[0002] Nonlinear optical crystals have second-order nonlinear polarization response characteristics. When light passes through a nonlinear optical crystal, the frequency of some of the light changes and propagates forward at a new vibration frequency. Therefore, nonlinear optical crystals are widely used as optical frequency converters, fabricated as optical waveguides, and applied to specific integrated optical path assemblies to expand parameters such as the wavelength range of light, the intensity and phase of modulated light, etc.

[0003] In the above-mentioned nonlinear optical conversion process, the intensity of the frequency-converted light in the nonlinear optical crystal is proportional to the square of the power density of the fundamental frequency light, the optical conversion efficiency is also proportional to the power density of the fundamental frequency light in the nonlinear optical crystal, and the power density of the fundamental frequency light in the optical waveguide is proportional to the fundamental frequency light power and inversely proportional to the transmission cross-sectional area of ​​the optical waveguide. Therefore, using a nonlinear optical crystal as a substrate to fabricate an optical waveguide and applying it to a specific integrated optical path to form an optical frequency converter contributes to the optical path achieving better nonlinear performance, and makes it easy to obtain an optical device with a small volume and compact structure, making on-chip integration easier.

[0004] In order to further improve the frequency conversion efficiency of an optical waveguide made of a nonlinear optical crystal, a commonly used method in the prior art is to further reduce the core size of the optical waveguide to further reduce the transmission cross-sectional area of ​​the optical waveguide. However, reducing the cross-sectional area of ​​the optical waveguide to improve the frequency conversion efficiency of the optical waveguide not only places higher requirements on the optical waveguide manufacturing technology, but also makes it difficult for the manufactured optical waveguide to match with a conventional optical waveguide end-face coupling device due to the large output spot size, resulting in low coupling efficiency between the end-face coupling device and the optical waveguide and serious light loss. Summary of the Invention

[0005] In view of the above circumstances, it is necessary to provide a method for manufacturing an optical waveguide using a nonlinear optical crystal as a substrate, which has a light-focusing ability and can constrain the light field to converge to the center of the optical waveguide without reducing the cross-sectional dimensions of the optical waveguide core, thereby improving the frequency conversion efficiency of the optical waveguide itself, facilitating its application as a frequency converter in a specific optical path, and contributing to improving the optical frequency conversion efficiency of the entire optical path.

[0006] The technical means of the present invention are as follows: According to the present invention, there is provided a method for manufacturing an optical waveguide having light-gathering capabilities, the method comprising the steps of: S1 Processing preparation: Prepare the nonlinear optical crystal required for processing, and determine the type of heavy ions required for processing and the magnitude of parameters related to the irradiation process. S2 High-energy ion irradiation: Heavy ions are accelerated to have high energy, and the high-energy heavy ions are collided with a nonlinear optical crystal, thereby forming a first refractive index reduction peak at a first depth in the nonlinear optical crystal along the depth direction, thereby obtaining a primary processed crystal. S3 Secondary high energy ion irradiation: Heavy ions are accelerated to have secondary high energy, and the heavy ions with secondary high energy are collided with the primary processed crystal, thereby forming a second refractive index reduction peak at a second depth in the primary processed crystal along the depth direction, thereby obtaining a secondary processed crystal. S4 Surface patterning: The secondary processing crystal is divided along the light beam propagation direction from the top to the bottom to obtain a shaped optical waveguide.

[0007] Appropriate heavy ions are selected and accelerated to an appropriate velocity level. At this time, the heavy ion beam has a specific amount of energy. When this energetic ion beam is collided with a nonlinear optical crystal, the energetic ion beam interacts with the nonlinear optical crystal, and damage caused by the electron energy of the irradiated ions plays a major role in changing the material structure and refractive index of the material, resulting in a significant change in the refractive index of the impacted part of the nonlinear optical crystal.

[0008] For a specific ion beam, the electronic stopping power of the optical crystal material Se is compared with the amorphous threshold Se. th When the electronic stopping power Se exceeds this amorphous threshold Seth, the irradiated ions form a quasi-continuous amorphous track in the optical crystal. The cross-sectional radius r of this track is related to the size of Se. After swift heavy ion irradiation, the dielectric constant ε of the optical crystal is expressed as a weighted average of the dielectric constants of the amorphous track and the original dielectric constant.

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[0009] By adjusting the energy of the ion beam so that it has high energy and irradiating only high-energy ions onto a nonlinear optical crystal, the high-energy ion beam causes electronic damage to the nonlinear optical crystal. After the nonlinear optical crystal is irradiated with high-energy ions, the refractive index of the irradiated area changes, and a first refractive index decrease peak appears at a first depth. The specific value of this first depth is directly related to the amount of energy possessed by the ion beam during the high-energy irradiation process. Figure 1 shows the effect of high-energy ion irradiation processing on the refractive index of a nonlinear optical crystal.

[0010] Figure 1 is a schematic diagram of the refractive index change along the depth direction of an irradiated nonlinear optical crystal after S1 processing preparation and S2 high-energy ion irradiation processing are performed separately. In Figure 1, the abscissa is the depth value of the processed nonlinear optical crystal, and the ordinate is the relative refractive index of the nonlinear optical crystal. As can be seen from Figure 1, the refractive index of the nonlinear optical crystal changes due to irradiation with a high-energy ion beam. As the depth direction increases from the surface of the nonlinear optical crystal, the refractive index of the crystal tends to gradually decrease and then gradually increase, with a first refractive index decrease peak appearing at a first depth d1.

[0011] Similarly, by adjusting the energy carried by the ion beam, it is made smaller than the energy carried by the ion beam in the high-energy ion irradiation process, and this secondary high-energy ion beam is irradiated onto the nonlinear optical crystal. As a result, the ion beam with secondary high energy similarly causes electronic damage to the nonlinear optical crystal. A similar change in refractive index occurs in the irradiated portion of the nonlinear optical crystal, and a second refractive index decrease peak appears at the second depth. The specific value of this second depth is also directly related to the magnitude of the energy carried by the ion beam in the secondary high-energy irradiation process. Figure 2 shows the effect of secondary high-energy ion irradiation processing on the refractive index of the nonlinear optical crystal.

[0012] Figure 2 is a schematic diagram of the refractive index change along the depth direction of the irradiated nonlinear optical crystal after S1 (processing preparation) and S3 (secondary high-energy ion irradiation processing) are performed on the nonlinear optical crystal separately. In Figure 2, the abscissa is the depth value of the processed nonlinear optical crystal, and the ordinate is the relative refractive index of the nonlinear optical crystal. As can be seen from Figure 2, the refractive index of the nonlinear optical crystal changes due to irradiation with the secondary high-energy ion beam, and as the depth direction increases from the surface of the nonlinear optical crystal, the refractive index of the crystal tends to gradually decrease and then gradually increase, with a second refractive index decrease peak appearing at a second depth d2.

[0013] When both the high-energy ion irradiation and the secondary high-energy ion irradiation processes are performed, the two ion irradiation processes each cause electronic damage to the nonlinear optical crystal, and each electronic damage causes a corresponding change in the refractive index of the nonlinear optical crystal. Because the depth of the refractive index decrease peak of the crystal after ion irradiation is directly related to the energy of the ion beam, after both the high-energy ion irradiation and the secondary high-energy ion irradiation are performed, the refractive index decrease peak of the nonlinear optical crystal caused by the high-energy ion irradiation process and the secondary high-energy ion irradiation are offset, and two decrease peaks exist in the nonlinear optical crystal. The effects of both the high-energy ion irradiation and the secondary high-energy ion irradiation on the refractive index of the nonlinear optical crystal are shown in Figure 3.

[0014] 3 is a schematic diagram of the change in refractive index along the depth direction of a nonlinear optical crystal after the S1-S3 processing in the manufacturing method of an optical waveguide with light-collecting ability provided in the Summary of the Invention is performed on the nonlinear optical crystal. In FIG. 3, the abscissa is the depth value of the processed nonlinear optical crystal, and the ordinate is the relative refractive index of the crystal. As can be seen from FIG. 3, after two ion irradiations, as the nonlinear optical crystal deepens from its surface in its depth direction, the relative refractive index of the crystal first decreases, and a second refractive index decrease peak appears at a second depth d2. The relative refractive index of the crystal then gradually increases, then decreases again, and a first refractive index decrease peak appears at a first depth d1, and then gradually increases again. As the nonlinear optical crystal deepens in its depth direction from its surface, the change in the relative refractive index of the crystal roughly exhibits a "w" shape.

[0015] In the optical waveguide manufactured in this manner, after light is coupled into the optical waveguide along the light input surface, the relative refractive index of the crystal decreases before reaching the first depth d1 and increases after passing through the second depth d2. Therefore, the light coupled into the optical waveguide can be transmitted only between the first depth d1 and the second depth d2 of the nonlinear optical crystal. The region between the first depth d1 and the second depth d2 of the nonlinear optical crystal is called the waveguide core WG. core The light coupled into the optical waveguide passes through the waveguide core WG coreWhen light is transmitted through the waveguide core WG, the relative refractive index between the first depth d1 and the second depth d2 of the nonlinear optical crystal increases and then decreases. core When transmitted through the waveguide core WG core As a result, when an optical waveguide manufactured by the manufacturing method provided by the present invention is actually used, the light coupled into the optical waveguide is focused on the waveguide core WG core and is transmitted along the waveguide core WG core The crystal exhibits a focusing effect when light is transmitted within the crystal. Without artificially reducing the core size of the optical waveguide, the power density of the fundamental frequency light can be significantly increased when the light is transmitted through the crystal, thereby effectively improving the optical frequency conversion efficiency of the optical waveguide manufactured by this manufacturing method and avoiding the problems of the prior art, such as the difficulty of manufacturing and low end-face coupling efficiency caused by reducing the core size of the optical waveguide.

[0016] Optionally, S2: High energy ion irradiation specifically includes the following substeps: S21: Place the nonlinear optical crystal in the irradiation target chamber. S22: Heavy ions are accelerated to high energy by a high energy ion accelerator. S23: Heavy ions having energy E1 are collided with the nonlinear optical crystal to form a first optical barrier along the depth direction of the nonlinear optical crystal, and the first optical barrier has a first refractive index reduction peak at a first depth d1 of the nonlinear optical crystal, and after the irradiation is completed, a primary processed crystal is obtained.

[0017] Optionally, S3: secondary high energy ion irradiation specifically includes the following substeps: S31: The primary processed crystal is placed in the irradiation target chamber. S32: Heavy ions are accelerated to secondary high energy by a high energy ion accelerator. S33: A secondary high-energy ion beam is collided with the primary processed crystal to form a second optical barrier along the depth direction of the primary processed crystal, and the second optical barrier has a second refractive index reduction peak at a second depth d2 of the primary processed crystal, and after the irradiation is completed, a secondary processed crystal is obtained.

[0018] Optionally, the type of heavy ions used in the S2 high energy ion bombardment and the S3 secondary high energy ion bombardment are the same.

[0019] The type of heavy ion is determined by the width of the decline peak, w b Since the same type of heavy ions are used in the S2 high-energy ion irradiation and the S3 secondary high-energy ion irradiation, the width w of the first optical barrier b1 shown in FIG. b1 is the width w of the second light barrier b2 shown in FIG. b2 After processing the nonlinear optical crystal through high-energy ion irradiation and secondary high-energy ion irradiation processes, the first optical barrier b1 and the second optical barrier b2 that exist simultaneously in one optical waveguide have an almost symmetrical distribution, which makes it easy to achieve excellent optical transmission effects.

[0020] Optionally, the high energy ion beam has an energy higher than the energy of the second high energy ion beam.

[0021] Optionally, the S1 processing preparation specifically includes the following substeps: S11: A block having a regular shape is cut out from the raw stone to be used as a raw material nonlinear optical crystal. S12: The upper surface, the optical input end surface, and the optical output end surface of the raw material nonlinear optical crystal are polished to obtain the nonlinear optical crystal required for processing. S13: The type of heavy ion is selected according to the light guiding demand for the molded optical waveguide. S14: Analyze the first optical barrier b1 required for the molded optical waveguide, and determine the magnitude of the high energy E1 based on the depth position d1 of the first refractive index-decreasing peak. S15: Analyze the second optical barrier b2 required for the molded optical waveguide, and determine the magnitude of the secondary high energy E2 based on the depth d2 of the second refractive index-decreasing peak.

[0022] Optionally, the S4 surface patterning process specifically includes the following sub-steps: S41: The upper surface of the secondary processed crystal is etched using a surface etching device to form the first optical waveguide sidewall. S42: The upper surface of the secondary processed crystal is etched using a surface etching device to form a second optical waveguide sidewall, and the portion surrounded by the first optical waveguide sidewall and the second optical waveguide sidewall is made into a molded optical waveguide.

[0023] Optionally, the first and second optical waveguide sidewalls extend from the optical input end face of the secondary processed crystal to the optical output end face. From the optical input end face of the secondary processed crystal to its optical output end face, the first optical waveguide sidewall sequentially includes a first input region, a first transition region, and a first output region, and the second optical waveguide sidewall includes a second input region, a second transition region, and a second output region. From the optical input end face of the secondary processed crystal to its optical output end face, the first input region and the second input region have the same length and are parallel to each other, the first transition region and the second transition region have the same length and the distance between them gradually decreases, and the first output region and the second output region have the same length and are parallel to each other.

[0024] In practical use of the optical waveguide manufactured by the manufacturing method provided by the present invention, the first transition region and the second transition region have the same length, but the distance between them gradually decreases, so that the distance between the first input region and the second input region is significantly greater than the distance between the first output region and the second output region. By providing an end-face coupling device on the light input surface side of the optical waveguide, after light is coupled into the optical waveguide, it first transmits between the relatively wide first input region and the second input region, and after passing through the first transition region and the second transition region, the optical transmission path narrows in the horizontal direction, and the light is gradually concentrated in the width direction, finally outputting from between the first output region and the second output region and transmitting to the next optical path device.

[0025] The present invention further provides an optical waveguide manufactured by the above-described method for manufacturing an optical waveguide having light-collecting ability.

[0026] The present invention further provides a frequency converter including the optical waveguide described above.

[0027] The beneficial effects of the present invention are as follows: The heavy ion irradiation process changes the refractive index of the nonlinear optical crystal at the impact point, adjusting the energy of the heavy ions during the two irradiation processes. The two rounds of heavy ion irradiation with different energies create two distinct optical barriers in the nonlinear optical crystal. The refractive index of the crystal between the two optical barriers gradually changes and becomes relatively higher, forming a distinct sandwich-type optical waveguide structure. When light is transmitted through this sandwich-type waveguide structure, it is focused between the two optical barriers due to the influence of the crystal refractive index. Therefore, the above fabrication method can be said to create a new refractive index profile in the nonlinear optical crystal. The optical waveguide structure fabricated using this method has the ability to focus light, constraining the light field to converge at the center of the optical waveguide. This significantly increases the power density of fundamental frequency light as it propagates through the crystal, effectively improving the conversion efficiency of optical waveguide frequency converters fabricated using this method. [Brief explanation of the drawings]

[0028] In order to more clearly describe the embodiments of the present invention or the technical solutions of the prior art, the following briefly introduces drawings necessary for describing the embodiments or the prior art. It is obvious that the following drawings are only some embodiments of the present invention, and those skilled in the art can obtain other drawings based on the structures shown in these drawings without creative efforts.

[0029] [Figure 1] 1 is a schematic diagram showing the change in refractive index along the depth direction of an irradiated nonlinear optical crystal after performing S1 (processing preparation) and S2 (high-energy ion irradiation processing) separately in the manufacturing method of an optical waveguide having light-collecting ability provided in the Summary of the Invention for the nonlinear optical crystal. In Fig. 1, the abscissa is the depth value of the nonlinear optical crystal subjected to processing, and the ordinate is the relative refractive index of the nonlinear optical crystal. [Figure 2]2 is a schematic diagram showing the change in refractive index along the depth direction of an irradiated nonlinear optical crystal after performing S1 (processing preparation) and S3 (secondary high-energy ion irradiation processing) alone in the manufacturing method of an optical waveguide having light-collecting ability provided in the Summary of the Invention for a nonlinear optical crystal. In FIG. 2, the abscissa is the depth value of the processed nonlinear optical crystal, and the ordinate is the relative refractive index of the nonlinear optical crystal. [Figure 3] 3 is a schematic diagram of the refractive index change along the depth direction of a nonlinear optical crystal after the S1-S3 processing is performed on the nonlinear optical crystal in the manufacturing method of an optical waveguide having light-collecting ability provided in the Summary of the Invention. In FIG. 3, the abscissa is the depth value of the nonlinear optical crystal after the processing is performed, and the ordinate is the relative refractive index of the nonlinear optical crystal. [Figure 4] 1 is a flowchart of a method for manufacturing an optical waveguide having light-collecting ability provided in an embodiment. [Figure 5] 10 is a schematic diagram illustrating irradiation of a KTP crystal with a high-energy chlorine ion beam when performing steps S21-S23 in the method for manufacturing an optical waveguide with light-collecting ability provided in an embodiment of the present invention. [Figure 6] 6 is a graph showing the refractive index distribution along the depth direction of a primary KTP processed crystal after processing by steps S21-S23 in the manufacturing method of an optical waveguide with light-collecting ability provided in an embodiment. In FIG. 6, the abscissa is the depth value of the crystal, and the ordinate is the refractive index of the crystal. [Figure 7] FIG. 1 is a schematic diagram illustrating the irradiation of a primary KTP processed crystal with a secondary high-energy chloride ion beam when performing steps S31-S33 in the method for manufacturing an optical waveguide with light-collecting ability provided in an embodiment on the primary KTP processed crystal. [Figure 8] 6 is a graph showing the refractive index distribution along the depth direction of a secondary KTP processed crystal after processing by steps S31-S33 in the manufacturing method of an optical waveguide with light-collecting ability provided in an embodiment. In FIG. 6, the abscissa is the depth value of the crystal, and the ordinate is the refractive index of the crystal. [Figure 9]FIG. 10 is a schematic diagram of S4 (surface patterning) in the manufacturing method of the optical waveguide having light-collecting ability provided in the embodiment. [Figure 10] 10 is a schematic diagram of the local structure of an optical waveguide manufactured by a method for manufacturing an optical waveguide with light-collecting ability provided in an embodiment. It is also a diagram of the light intensity distribution in the tapered transition region of the optical waveguide when incident light in the 1.55 μm wavelength band is incident thereon. In FIG. 10, the abscissa is the light propagation direction, the ordinate is the width direction of the optical waveguide, and the color indicates the magnitude of the light intensity. [Figure 11] 11 is a diagram showing the distribution of the z-component of the optical field in an optical waveguide manufactured by the method for manufacturing an optical waveguide having light-collecting ability provided in an embodiment when incident light in the 1.55 μm wavelength band is incident on the optical waveguide. In Fig. 11, the abscissa is the propagation direction of the light, the ordinate is the width direction of the optical waveguide, and the color indicates the z-component value of the optical field. [Figure 12] 12 is a schematic diagram showing the distribution of power density along the depth direction of an optical waveguide manufactured by the method for manufacturing an optical waveguide with light-collecting ability provided in an embodiment when incident light in the 1.55 μm wavelength band is incident on the optical waveguide. In Fig. 12, the abscissa is the depth of the optical waveguide and the ordinate is the power density in the optical waveguide. [Figure 13] 13 is a refractive index profile diagram along the depth direction of a step-index KTP optical waveguide, in which the abscissa is the depth value of the KTP crystal and the ordinate is the relative refractive index of the crystal. [Figure 14] This is a diagram showing the distribution of the z component of the optical electric field in a step-index KTP optical waveguide when incident light in the 1.55 μm wavelength band is incident on the optical waveguide. In Figure 14, the abscissa is the light propagation direction, the ordinate is the depth direction of the optical waveguide, and the color is the z component value of the optical electric field. [Figure 15] 15 is a diagram showing the power density distribution along the depth direction of a step-index KTP optical waveguide when incident light in the 1.55 μm wavelength band is incident on the optical waveguide. In Fig. 15, the abscissa is the depth of the optical waveguide and the ordinate is the power density in the optical waveguide. DETAILED DESCRIPTION OF THE INVENTION

[0030] Hereinafter, the technical solutions in the embodiments of the present invention will be clearly and completely described with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only some embodiments of the present invention, not all embodiments, and all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without any creative work fall within the protection scope of the present invention.

[0031] It should be noted that all directional indications (e.g., up, down, left, right, front, back, etc.) in the embodiments of the present invention are merely intended to explain the relative positional relationships and movement conditions between each component in a specific posture (as shown in the drawings), and when the specific posture changes, the directional indications also change accordingly.

[0032] Furthermore, in the present invention, descriptions such as "first," "second," etc., are for explanatory purposes only and should not be understood as indicating or implying the relative importance or the number of technical features described. Accordingly, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the feature. Furthermore, "and / or" in the entire text includes three solutions, such as technical solution A, technical solution B, and a solution satisfying both A and B, for example. Furthermore, technical solutions in each embodiment may be combined with each other, but this should be based on what a person skilled in the art can achieve. If a combination of technical solutions contradicts or is not feasible, such a combination of technical solutions should be considered as not existing and not within the scope of protection of the present invention.

[0033] Please refer to Figure 4-12.

[0034] In a specific embodiment of the present invention, a method for manufacturing an optical waveguide with light-collecting ability is provided, which includes the following steps S1 to S4. S1: Preparation for processing: Prepare the nonlinear optical crystal required for processing, and confirm the type of heavy ions required for processing and the magnitude of parameters related to the irradiation process. S2: High-energy ion irradiation: Heavy ions are accelerated to have high energy E1, and these high-energy heavy ions are collided with the nonlinear optical crystal to form a first refractive index reduction peak at a first depth Δy1 in the nonlinear optical crystal along the depth direction, thereby obtaining a primary processed crystal. S3: Secondary high-energy ion irradiation: Heavy ions are accelerated to have a secondary high energy E2, and these secondary high-energy heavy ions are collided with the primary processed crystal to form a second refractive index reduction peak at a second depth Δy2 in the depth direction of the primary processed crystal, thereby obtaining a secondary processed crystal. S4: Surface patterning: The secondary processed crystal is divided along the width direction to obtain a molded optical waveguide.

[0035] Specifically, in a specific embodiment of the present invention, the method for manufacturing an optical waveguide with light-collecting ability includes the following substeps: S11: KTP (potassium phosphate titanate) crystal raw ore is selected, and a rectangular parallelepiped block of the desired size of 10 mm (length) x 8 mm (width) x 2 mm (height) is cut from this KTP crystal raw ore as the starting KTP crystal. S12: The upper surface, the optical input end face, and the optical output end face of the KTP crystal are polished to obtain a crystal block as the KTP crystal C0 required for processing. S13: By irradiating a nonlinear optical crystal with two types of ions, fluorine, chlorine, and argon, a gradient change in the refractive index of the crystal can be generated. The main difference in the effect of these ions is the width Wb of the depression peak formed. The width of the depression peak formed by fluorine ions is about 1 μm, the width Wb of the depression peak formed by chlorine ions is about 2 μm, and the width of the depression peak formed by argon ions is about 3 μm. In a specific embodiment, chlorine ions are selected as the heavy ions for irradiation treatment. S14: Based on the Monte Carlo algorithm, the magnitude of the energy E1 of the heavy ions in the high-energy ion irradiation step is determined according to the depth Δy1 of the first refractive index-decreasing peak required for processing. S15: Similarly, based on the Monte Carlo algorithm, the magnitude of the energy E2 of the heavy ions in the high-energy ion irradiation step is determined according to the depth Δy2 of the second refractive index-decreasing peak required for processing. S21: A KTP crystal C0 is placed in the irradiation target chamber. S22: The chloride ions are accelerated by a high-energy ion accelerator to have energy E1. S23: Chlorine ions having energy E1 are collided with the KTP crystal C0 to form a first refractive index-decreasing peak P1 at a depth Δy1 of the KTP crystal C0, thereby obtaining a primary KTP processed crystal C1. S31: Place the primary KTP processed crystal C1 in the irradiation target chamber. S32: Heavy ions are accelerated by a high-energy ion accelerator to have energy E2, and the energy carried in the ion beam is adjusted so that the energy E2 is smaller than the energy E1. S33: Ions with energy E2 are collided with the primary KTP processed crystal C1 to form a second refractive index-decreasing peak P2 at a depth Δy2 of the primary KTP processed crystal C1, thereby obtaining a secondary KTP processed crystal C2. In the above S2-S3, by irradiating the primary KTP processed crystal C1 with ions of relatively high energy and then with ions of relatively low energy, the secondary KTP processed crystal C2 forms a sandwich-type optical waveguide structure with two optical barriers in the depth direction, which has a light-focusing effect in the depth direction and can effectively constrain the light field in the depth direction to focus toward the center of the optical waveguide structure. S41: Constrain the light field in the width direction and minimize the divergence of light in the width direction. In a specific embodiment of the present invention, the secondary KTP processed crystal C2 is placed on a three-axis motorized worktable, and the top surface of the secondary KTP processed crystal C2 is ablated along the light beam propagation direction using a Ti:sapphire femtosecond laser processing system to form the first optical waveguide sidewall L1. S42: Using the titanium sapphire femtosecond laser processing system FLS, the upper surface of the secondary KTP processed crystal C2 is ablated along the beam propagation direction to form the second optical waveguide sidewall L2. The area surrounded by the first optical waveguide sidewall L1 and the second optical waveguide sidewall L2 is defined as a molded optical waveguide.

[0036] A titanium sapphire femtosecond laser processing system (FLS) was used. The light source was linearly polarized light with a wavelength of 796 nm, and its polarization direction was parallel to the height direction of the KTP nonlinear optical crystal. The laser pulse duration of the processing system was adjusted to 120 fs and the repetition rate to 1 kHz. The laser beam was focused by a single microscope objective lens and scanned along a specific path across the sample placed on a three-axis motorized worktable. The scanning speed and pulse energy were set to 50 μm / s and 0.7 μJ, respectively.

[0037] After two scans, the first and second waveguide sidewalls L1 and L2 divided the top surface of the secondary KTP processed crystal C2 into three sections. The section surrounded by the first and second waveguide sidewalls L1 and L2 was selected. This section had a sandwich-type waveguide structure in the depth direction, was separated from the other sections in the width direction, and had a crystal structure extending from the optical input end face to the optical output end face. This crystal structure could be used as a mature optical waveguide for specific optical paths.

[0038] In a specific embodiment, from the optical input end face of the secondary KTP processed crystal C2 to its optical output end face, the first optical waveguide sidewall L1 sequentially includes a first input region L11, a first transition region L12, and a first output region L13. The second optical waveguide sidewall L2 sequentially includes a second input region L21, a second transition region L22, and a second output region L23. The first input region L11 and the second input region L21 have the same length and are parallel to each other. The first transition region L12 and the second transition region L22 have the same length and the distance between them gradually decreases. The first output region L13 and the second output region L13 have the same length and are parallel to each other.

[0039] The secondary KTP processed crystal C2 is surrounded by a first optical waveguide sidewall L1 and a second optical waveguide sidewall L2, forming a tapered or horn-shaped surface shape from the optical input end face to its optical output end face. This shape allows the width of the light beam's transmission cross section in the optical waveguide to decrease, focusing the light beam laterally. Furthermore, by providing an end-face coupling device at the optical input end face of this optical waveguide, light is coupled into the current optical waveguide structure via the end-face coupling device. The optical waveguide structure as a whole tapers in the direction of light propagation from the optical input end face to its optical output end face, and the relatively large cross section at the optical input end face makes it easy to fit into the end-face coupling device, minimizing coupling loss.

[0040] In a specific embodiment of the present invention, there is further provided an optical waveguide manufactured by the above-mentioned method for manufacturing an optical waveguide having light-collecting ability.

[0041] In a specific embodiment of the present invention, there is further provided a frequency converter including the optical waveguide described above.

[0042] The above is a preferred embodiment of the present invention, and does not limit the scope of protection of the present invention. Any equivalent structural transformation made based on this specification and drawings within the scope of the concept of the present invention, or direct or indirect application to other related technical fields, is also included in the scope of protection of the present invention.

Claims

1. A method for manufacturing an optical waveguide having a light-collecting ability, comprising the following steps S1 to S4: S1 Processing preparation: Prepare the nonlinear optical crystal required for processing, and determine the type of heavy ions required for processing and the magnitude of irradiation process related parameters. The nonlinear optical crystal is KTP (potassium titanate phosphate) crystal, and the heavy ions are chloride ions. S2 high-energy ion irradiation: Accelerating heavy ions to have high energy, and colliding the high-energy heavy ions with the nonlinear optical crystal to form a first refractive index reduction peak at a first depth of the nonlinear optical crystal along the depth direction, thereby obtaining a primary processed crystal; S3 secondary high energy ion irradiation: heavy ions are accelerated to have secondary high energy, and the heavy ions having secondary high energy are collided with the primary processed crystal, thereby forming a second refractive index reduction peak at a second depth of the primary processed crystal along the depth direction, thereby obtaining a secondary processed crystal; S4 surface patterning: the secondary processed crystal is divided to obtain a shaped optical waveguide; The S4 surface patterning process includes the following sub-steps S41 and S42: S41: Etching the top surface of the secondary processed crystal using a surface etching device to form a first optical waveguide sidewall; S42: Etching the upper surface of the secondary processed crystal using a surface etching device to form a second optical waveguide sidewall, and forming a portion surrounded by the first optical waveguide sidewall and the second optical waveguide sidewall as a molded optical waveguide; the first and second optical waveguide sidewalls extend from the optical input end face to the optical output end face of the fabricated crystal; From the optical input end face of the fabricated crystal to its optical output end face, the first optical waveguide sidewall sequentially includes a first input region, a first transition region, and a first output region, and the second optical waveguide sidewall sequentially includes a second input region, a second transition region, and a second output region; From the light input end face of the secondary processed crystal to its light output end face, the first input region and the second input region have the same length and are parallel to each other, the first transition region and the second transition region have the same length and the distance between them gradually decreases, and the first output region and the second output region have the same length and are parallel to each other; Here, in step S4, the secondary processed crystal is divided using an fs laser processing system as a surface etching device.

2. The S2 high energy ion irradiation includes the following substeps S21 to S23: S21: Place the nonlinear optical crystal in an irradiation target chamber; S22: Accelerating heavy ions to have high energy by a high-energy ion accelerator; S23: A high-energy ion beam is collided with the nonlinear optical crystal to form a first optical barrier along the depth direction of the nonlinear optical crystal, and the first optical barrier has a first refractive index reduction peak at a first depth position of the nonlinear optical crystal, and the primary processed crystal is obtained after the irradiation is completed.

3. The S3 secondary high-energy ion irradiation includes the following substeps S31 to S33: S31: Place the primary processed crystal in an irradiation target chamber; S32: Accelerating heavy ions to have secondary high energy by a high energy ion accelerator; S33: A secondary high-energy ion beam is collided with the primary processed crystal to form a second light barrier along the depth direction of the primary processed crystal, and the second light barrier has a second refractive index reduction peak at a second depth position of the primary processed crystal, and the secondary processed crystal is obtained after irradiation is completed.

4. 4. The method of claim 3, wherein the heavy ions used in the S2 high-energy ion irradiation and the S3 secondary high-energy ion irradiation are of the same type.

5. 5. The manufacturing method according to claim 4, wherein the energy of the high-energy ion beam is greater than the energy of the secondary high-energy ion beam.

6. The S1 processing preparation includes the following sub-steps S11 to S15: S11: A block having a regular shape is cut out from the raw stone to be used as a raw material nonlinear optical crystal; S12: The upper surface, the optical input end face, and the optical output end face of the raw nonlinear optical crystal are surface-polished to obtain the nonlinear optical crystal required for processing; S13: Selecting the type of heavy ion as required for guiding light through the molded optical waveguide; S14: Analyzing the first optical barrier required for the molded optical waveguide, and determining the magnitude of the energy of the high-energy ion beam based on the first depth of the first refractive index-decreasing peak; S15: Analyzing the second optical barrier required for the molded optical waveguide, and determining the magnitude of energy of the secondary high-energy ion beam based on the second depth of the first refractive index reduction peak.

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