A method for preparing an optical waveguide with focusing capability, an optical waveguide and a frequency converter

Abstract

The present invention discloses a method for preparing an optical waveguide with focusing capability, the method comprising steps S1: processing preparation, S2: high-energy ion irradiation, S3: sub-high-energy ion irradiation, S4: surface patterning processing, etc. The present invention also provides an optical waveguide and a frequency converter. The optical waveguide structure prepared by the method provided by the present invention has a focusing capability, which constrains the light field to converge to the center of the optical waveguide without reducing the cross-sectional size of the optical waveguide core, thereby improving the frequency conversion efficiency of the optical waveguide itself, so as to facilitate its application as a frequency converter in a specific optical path, and help improve the optical frequency conversion efficiency of the overall optical path.

Description

Technical Field

[0001] The invention relates to the fields of optical materials and integrated optical technology, and in particular to an optical waveguide. Background Art

[0002] Nonlinear optical crystals have the characteristics of second-order nonlinear polarization response. When light passes through a nonlinear optical crystal, the frequency of a part of the light will change and propagate forward at a new vibration frequency. Therefore, nonlinear optical crystals are widely used as optical frequency converters, prepared into optical waveguides, and applied to specific integrated optical circuit components to expand the wavelength range of light and modulate parameters such as the intensity and phase of light.

[0003] In the above-mentioned nonlinear conversion process of light, 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, and the light conversion efficiency is also proportional to the power density of the fundamental frequency light in the nonlinear optical crystal, while 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 nonlinear optical crystals as a matrix to prepare optical waveguides and applying them in specific integrated optical circuits as optical frequency converters can help the optical circuits obtain better nonlinear performance, facilitate the acquisition of small-sized and compact optical devices, and make them easier to integrate on-chip.

[0004] In order to further improve the frequency conversion efficiency of optical waveguides prepared with nonlinear optical crystals, a method often used in the prior art is to further reduce the size of the core of the optical waveguide in order to further reduce the area of ​​the transmission cross section of the optical waveguide. However, the method of reducing the cross-sectional area of ​​the optical waveguide to improve the frequency conversion efficiency of the optical waveguide not only puts forward higher requirements on the preparation technology of the optical waveguide, but also the optical waveguide prepared has a small core cross section, and the existing optical waveguide end coupling device has a large output spot size and is difficult to match it. The coupling efficiency between the end coupling device and the optical waveguide is low, and there is serious loss of light here. Summary of the invention

[0005] Based on this, it is necessary to provide a method for preparing an optical waveguide with a nonlinear optical crystal as a matrix. The optical waveguide structure prepared by this preparation method has a focusing capability, which can constrain the light field to converge to the center of the optical waveguide without reducing the cross-sectional size of the optical waveguide core, thereby improving the frequency conversion efficiency of the optical waveguide itself, so as to facilitate its application as a frequency converter in a specific optical path, and help improve the optical frequency conversion efficiency of the overall optical path.

[0006] The technical solution of the present invention is as follows:

[0007] The present invention provides a method for preparing an optical waveguide with focusing capability, the method comprising the following steps:

[0008] S1: Processing preparation: prepare the nonlinear optical crystals required for processing, determine the types of heavy ions required for processing and the size of the relevant parameters of the irradiation process;

[0009] S2: High-energy ion irradiation: Accelerate heavy ions to make them carry high energy, use the high-energy heavy ions to bombard the nonlinear optical crystal, form a first refractive index decrease peak at a first depth of the nonlinear optical crystal along the depth direction, and obtain a primary processed crystal;

[0010] S3: Sub-high energy ion irradiation: accelerating heavy ions to carry sub-high energy, using the sub-high energy heavy ions to bombard the primary processed crystal, forming a second refractive index decrease peak at a second depth of the primary processed crystal along the depth direction; obtaining a secondary processed crystal;

[0011] S4: Surface patterning: The secondary processed crystal is split from top to bottom along the beam propagation direction to obtain a formed optical waveguide.

[0012] Select appropriate heavy ions and accelerate them to a suitable speed level. At this time, the heavy ion beam will carry a certain amount of energy. Use this energetic ion beam to bombard the nonlinear optical crystal. The energetic ion beam interacts with the nonlinear optical crystal. The electron energy damage of the irradiated ions plays a major role in the change of the material structure and the refractive index of the material. The refractive index of the bombarded part of the nonlinear optical crystal will change significantly.

[0013] For some irradiated ions, the electron stopping ability Se of optical crystal materials has an amorphous threshold Se th , the electron blocking ability Se exceeds the amorphous threshold Se th , the irradiated ions will form a quasi-continuous amorphous track in the optical crystal, and the cross-sectional radius r of the track is related to the size of Se. After fast heavy ion irradiation, the dielectric constant ε of the optical crystal is macroscopically expressed as the weighted average of the amorphous track and the original dielectric constant:

[0014]

[0015] Among them, the amorphous weight coefficient f is proportional to the current heavy ion irradiation dose Φ and the cross-sectional area of ​​the amorphous track:

[0016] f∝Φπr 2

[0017] It is not difficult to see from the above formula that the formed amorphous track has a significant impact on the refractive index of the material, so only an extremely low irradiation dose is required to cause a refractive index change equivalent to high-dose ion implantation.

[0018] Adjust the energy load of the ion beam so that the ion beam carries high energy. If high-energy ion irradiation is used alone on the nonlinear optical crystal, the ion beam carrying high energy will cause electronic damage to the nonlinear optical crystal. After the nonlinear optical crystal is irradiated with high-energy ions, the refractive index of the irradiated part changes, and the first refractive index decrease peak appears at the first depth. The specific value of the first depth is directly related to the energy carried by the ion beam during this high-energy irradiation process. The influence of high-energy ion irradiation processing on the refractive index of nonlinear optical crystals is as follows: Figure 1 .

[0019] Figure 1 This is a schematic diagram of the refractive index change of the irradiated nonlinear optical crystal along its depth direction after the S1 processing preparation and S2 high-energy ion irradiation processing. The horizontal axis in the figure is the depth value of the nonlinear optical crystal processed specifically, and the vertical axis is the relative refractive index of the nonlinear optical crystal. Figure 1 It can be clearly seen that under the influence of high-energy ion beam irradiation, the refractive index of the nonlinear optical crystal changes. From the surface of the nonlinear optical crystal to its depth, the refractive index of the crystal shows a trend of gradually decreasing and then gradually increasing, and a first refractive index decrease peak appears at the first depth d1.

[0020] Similarly, the energy load of the ion beam is adjusted to be lower than the energy load of the ion beam during high-energy ion irradiation; when the sub-high-energy ion beam is used to irradiate the nonlinear optical crystal, the ion beam carrying the sub-high energy will also cause electron damage to the nonlinear optical crystal, and the refractive index of the irradiated part of the nonlinear optical crystal will also change, with a second refractive index drop peak appearing at a second depth. The specific value of the second depth is also directly related to the energy carried by the ion beam during this sub-high-energy irradiation process. The effect of sub-high-energy ion irradiation on the refractive index of nonlinear optical crystals is as follows: Figure 2 .

[0021] Figure 2 This is a schematic diagram of the refractive index change of the irradiated nonlinear optical crystal along its depth direction after the S1 processing preparation and S3: sub-high energy ion irradiation processing of the nonlinear optical crystal. The horizontal axis in the figure is the depth value of the nonlinear optical crystal being processed, and the vertical axis is the relative refractive index of the nonlinear optical crystal. Figure 2 It can be clearly seen that under the influence of the sub-high energy ion beam irradiation, the refractive index of the nonlinear optical crystal changes. From the surface of the nonlinear optical crystal to its depth, the refractive index of the crystal shows a trend of gradually decreasing and then gradually increasing, and a second refractive index decrease peak appears at the second depth d2.

[0022] By superimposing the above-mentioned high-energy ion irradiation and sub-high-energy ion irradiation processes, the two ion irradiation processes will respectively cause electron damage to the nonlinear optical crystal, and each electron damage will cause a corresponding change in the refractive index of the nonlinear optical crystal. Since the depth of the crystal refractive index decrease peak after ion irradiation is directly related to the energy carried by the ion beam, after superimposing the above-mentioned high-energy ion irradiation and sub-high-energy ion irradiation, the refractive index decrease peak of the nonlinear crystal in the high-energy ion irradiation process and the refractive index decrease peak of the nonlinear crystal in the sub-high-energy ion irradiation process are staggered, and two decrease peaks coexist in the nonlinear optical crystal. The influence of superimposing the above-mentioned high-energy ion irradiation and sub-high-energy ion irradiation on the refractive index of the nonlinear optical crystal is as follows: Figure 3 .

[0023] Figure 3 This is a schematic diagram of the refractive index change of the nonlinear optical crystal along its depth direction after the S1-S3 processing in the method for preparing an optical waveguide with focusing capability provided in the invention content is performed on the nonlinear optical crystal alone. The horizontal axis in the figure is the depth value of the nonlinear optical crystal that is specifically processed, and the vertical axis is the relative refractive index of the crystal. Figure 3 It can be clearly seen that under the influence of the two ion irradiations, the relative refractive index of the nonlinear optical crystal first decreases continuously along the surface of the nonlinear optical crystal toward its depth, and a second refractive index decrease peak appears at the second depth d2. Then the relative refractive index of the crystal gradually rises and then gradually decreases, and a first refractive index decrease peak appears at the first depth d1, and then gradually rises again. Along the surface of the nonlinear optical crystal toward its depth, the relative refractive index of the crystal changes roughly in a "w" type.

[0024] After light is coupled into the optical waveguide prepared in this way along the light input surface of the optical waveguide, since the relative refractive index of the crystal continuously decreases before reaching the first depth d1 and continuously increases after crossing the second depth d2, the light coupled into the optical waveguide can only be transmitted 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 can be regarded as the waveguide core WG. core ; The light coupled into the optical waveguide is in the waveguide core WG core When transmitting in the waveguide core WG, the relative refractive index between the first depth d1 and the second depth d2 of the nonlinear optical crystal gradually increases and then gradually decreases. core During transmission, it will present a waveguide core WG core The crystal refractive index is higher at the convergence point; thus, when the optical waveguide prepared by the preparation method provided by the present invention is used in a specific application, the light coupled into the optical waveguide naturally flows along the waveguide core WG core Transmission, and in the waveguide core WG coreWhen light is transmitted in the crystal, the light also exhibits a focusing effect; without artificially reducing the core size of the optical waveguide, the power density of the fundamental frequency light when the light is transmitted in the crystal can be greatly improved, thereby effectively improving the light frequency conversion efficiency of the optical waveguide prepared by the preparation method, avoiding the problems of high manufacturing difficulty and low end face coupling efficiency caused by reducing the core size of the optical waveguide in the prior art.

[0025] Optionally, S2: high energy ion irradiation specifically includes the following sub-steps:

[0026] S21: placing the nonlinear optical crystal in the irradiation target chamber;

[0027] S22: Use high-energy ion accelerators to accelerate heavy ions to carry high energy;

[0028] S23: bombarding the nonlinear optical crystal with heavy ions having energy E1 to form a first optical barrier along the depth direction of the nonlinear optical crystal. The first optical barrier has a first refractive index decrease peak at a first depth d1 of the nonlinear optical crystal. After the irradiation is completed, a processed crystal is obtained.

[0029] Optionally, S3: sub-high energy ion irradiation specifically includes the following sub-steps:

[0030] S31: placing the primary processed crystal in the irradiation target chamber;

[0031] S32: Use high energy ion accelerator to accelerate heavy ions to carry sub-high energy;

[0032] S33: bombarding the primary processed crystal with a sub-high energy ion beam to form a second optical barrier along the depth direction of the primary processed crystal. The second optical barrier has a second refractive index decrease peak at a second depth d2 of the primary processed crystal. After the irradiation is completed, a secondary processed crystal is obtained.

[0033] Optionally, the type of heavy ions used in the S2 high-energy ion irradiation and the S3 high-energy ion irradiation is the same.

[0034] The heavy ion species will determine the width of the descending peak w b , the same heavy ions are used in S2 high-energy ion irradiation and S3 high-energy ion irradiation, then Figure 1 The width w of the first optical barrier b1 presented in b1 Will be with Figure 2 The width w of the second optical barrier b2 presented in b2 After the nonlinear optical crystal is processed by superimposed high-energy ion irradiation and sub-high-energy ion irradiation processes, the first optical barrier b1 and the second optical barrier b2 existing on an optical waveguide will be roughly symmetrically distributed, so as to obtain high-quality optical transmission effect.

[0035] Optionally, the high energy ion beam carries an energy greater than the energy carried by the next highest energy ion beam.

[0036] Optionally, S1: processing preparation specifically includes the following sub-steps:

[0037] S11: Cutting regular-shaped blocks from the original stone as the original nonlinear optical crystal;

[0038] S12: performing surface polishing on the upper surface, the light input end face and the light output end face of the original nonlinear optical crystal to obtain the nonlinear optical crystal required for processing;

[0039] S13: selecting the type of heavy ions according to the light guiding requirements for the formed optical waveguide;

[0040] S14: analyzing the first optical barrier b1 required by the shaped optical waveguide, and determining the size of the high energy E1 according to the depth position d1 of the first refractive index drop peak;

[0041] S15: Analyze the second optical barrier b2 required by the shaped optical waveguide, and determine the size of the second highest energy E2 according to the depth d2 of the second refractive index drop peak.

[0042] Optionally, S4: surface patterning processing specifically includes the following sub-steps:

[0043] S41: etching a first optical waveguide side on the upper surface of the secondary processed crystal using a surface etching device;

[0044] S42: etching a second optical waveguide side on the upper surface of the secondary processed crystal using a surface etching device, and using the enclosed portion of the first optical waveguide side and the second optical waveguide side as a formed optical waveguide.

[0045] Optionally, the first and second optical waveguide sides extend from the light input end face of the secondary processed crystal to the light output end face; along the light input end face of the secondary processed crystal to its light output end face, the first optical waveguide side includes a first input section, a first transition section and a first output section in sequence, and the second optical waveguide side includes a second input section, a second transition section and a second output section in sequence; along the light input end face of the secondary processed crystal to its light output end face, the first input section and the second input section are equal in length and parallel to each other, the first transition section and the second transition section are equal in length and the spacing gradually decreases, and the first output section and the second output section are equal in length and parallel to each other.

[0046] When the optical waveguide prepared by the preparation method provided by the present invention is applied in practice, since the lengths of the first transition section and the second transition section are equal and the spacing gradually decreases, the spacing between the first input section and the second input section will be significantly wider than the spacing between the first output section and the second output section. The end face coupling device is arranged on the light input surface side of the optical waveguide. After the light is coupled into the optical waveguide, it will first be transmitted between the wider first input section and the second input section. When passing through the first transition section and the second transition section, the light transmission channel is laterally narrowed, and the light is gradually focused in the width direction, and finally output from between the first output section and the second output section, and transmitted to the next-level optical path device.

[0047] The present invention also provides an optical waveguide, which is prepared by using the above method for preparing an optical waveguide with focusing capability.

[0048] The present invention also provides a frequency converter, which includes the above optical waveguide.

[0049] The beneficial effects of the technical solution of the present invention are as follows: the heavy ion irradiation process will change the refractive index of the nonlinear optical crystal at the bombarded location, adjust the energy carried by the heavy ions during the two irradiation treatments, and form two obvious optical barriers on the nonlinear optical crystal by using the two heavy ion irradiations with different energies. The refractive index of the crystal between the two optical barriers gradually changes and relatively increases, forming an obvious sandwich-type optical waveguide structure. When light is transmitted in the sandwich-type waveguide structure, it will converge between the two optical barriers under the influence of the crystal refractive index. Therefore, it can be said that the above-mentioned preparation method constructs a new refractive index distribution in the nonlinear optical crystal. The optical waveguide structure prepared by this method will have focusing ability, which can constrain the light field to converge to the center of the optical waveguide, greatly improving the power density of the fundamental frequency light when the light is transmitted in the crystal, thereby effectively improving the conversion efficiency of the optical waveguide frequency converter prepared by the preparation method. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0051] Figure 1The present invention is a schematic diagram of the refractive index variation of the irradiated nonlinear optical crystal along its depth direction after S1: processing preparation and S2: high-energy ion irradiation processing in the method for preparing an optical waveguide with focusing capability provided in the invention content are separately implemented for a nonlinear optical crystal. The horizontal axis in the figure is the depth value of the nonlinear optical crystal being processed, and the vertical axis is the relative refractive index of the nonlinear optical crystal.

[0052] Figure 2 The present invention is a schematic diagram of the refractive index variation of the irradiated nonlinear optical crystal along its depth direction after S1: processing preparation and S3: sub-high energy ion irradiation processing in the method for preparing an optical waveguide with focusing capability provided in the invention content are separately implemented for a nonlinear optical crystal. The horizontal axis in the figure is the depth value of the nonlinear optical crystal being processed, and the vertical axis is the relative refractive index of the nonlinear optical crystal.

[0053] Figure 3 The present invention is a schematic diagram of the refractive index variation of a nonlinear optical crystal along its depth direction after the S1-S3 processing in the method for preparing an optical waveguide with focusing capability provided in the invention content is performed on the nonlinear optical crystal. The horizontal axis in the figure is the depth value of the nonlinear optical crystal that is specifically processed, and the vertical axis is the relative refractive index of the crystal.

[0054] Figure 4 The flowchart of the method for preparing an optical waveguide with focusing capability provided in a specific embodiment is shown.

[0055] Figure 5 This is a schematic diagram of irradiating a KTP crystal with a high-energy chloride ion beam when performing steps S21-S23 of the method for preparing an optical waveguide with focusing capability provided in a specific embodiment on the KTP crystal.

[0056] Figure 6 It is a refractive index distribution diagram of a KTP processed crystal along the depth direction after processing in steps S21-S23 of the method for preparing an optical waveguide with focusing capability provided in a specific embodiment. The horizontal axis in the figure is the depth value of the crystal, and the vertical axis is the refractive index of the crystal.

[0057] Figure 7 A schematic diagram of irradiating a primary KTP processed crystal with a chloride ion beam carrying the second highest energy when performing steps S31-S33 of the method for preparing an optical waveguide with focusing capability provided in a specific embodiment on a primary KTP processed crystal.

[0058] Figure 8 This is a refractive index distribution diagram of the secondary processed KTP crystal along the depth direction after processing in steps S31-S33 of the method for preparing an optical waveguide with focusing capability provided in a specific embodiment. The horizontal axis in the figure is the depth value of the crystal, and the vertical axis is the refractive index of the crystal.

[0059] Fig. 9 This is a schematic diagram of S4: surface patterning processing in the method for preparing an optical waveguide with focusing capability provided in this specific embodiment.

[0060] Fig.10 Schematic diagram of the local structure of an optical waveguide manufactured by the method for preparing an optical waveguide with focusing capability provided in this specific embodiment, and a light intensity distribution diagram of a tapered transition section in the optical waveguide when incident light in the 1.55 micron band is introduced therein. In the figure, the horizontal axis is along the propagation direction of the light, the vertical axis is along the width direction of the optical waveguide, and the color represents the light intensity.

[0061] Fig.11 The optical waveguide prepared by the method for preparing an optical waveguide with focusing capability provided in this specific embodiment is a distribution diagram of the z component of the optical electric field in the optical waveguide when incident light in the 1.55 micron band is introduced therein. In the diagram, the horizontal axis is along the propagation direction of the light, the vertical axis is along the depth direction of the optical waveguide, and the color represents the value of the z component of the optical electric field.

[0062] Fig.12 The figure is a schematic diagram of the power density distribution of the optical waveguide along the depth direction when the incident light in the 1.55 micron band is introduced into the optical waveguide prepared by the method for preparing an optical waveguide with focusing capability provided in the present specific embodiment. In the figure, the horizontal axis is the depth of the optical waveguide, and the vertical axis is the power density in the optical waveguide.

[0063] Fig.13 This is the refractive index distribution diagram of the step-index KTP optical waveguide along the depth direction. The horizontal axis in the figure is the depth value of the KTP crystal, and the vertical axis is the relative refractive index of the crystal.

[0064] Fig.14 This is a step-refractive index KTP optical waveguide. When 1.55-micron incident light is introduced into it, the z component distribution diagram of the optical electric field in the optical waveguide. The horizontal axis in the figure is along the propagation direction of light, and the vertical axis is along the depth direction of the optical waveguide. The color represents the z component value of the optical electric field.

[0065] Fig.15 It is a step-refractive index KTP optical waveguide. When 1.55 micron band incident light is passed into it, the power density distribution along the depth direction of the optical waveguide is schematically shown. The power density distribution along the depth direction of the optical waveguide is schematically shown. In the figure, the horizontal axis is the depth of the optical waveguide, and the vertical axis is the power density in the optical waveguide. DETAILED DESCRIPTION

[0066] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0067] It should be noted that all directional indications in the embodiments of the present invention (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0068] In addition, the descriptions of "first", "second", etc. in the present invention are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, "and / or" in the full text includes three solutions. Taking A and / or B as an example, it includes technical solution A, technical solution B, and technical solution that satisfies both A and B. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in this field to implement. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0069] See also Figure 4-12 .

[0070] In this specific embodiment, a method for preparing an optical waveguide with focusing capability is provided, the method comprising the following steps:

[0071] S1: Processing preparation: prepare the nonlinear optical crystals required for processing, determine the types of heavy ions required for processing and the size of the relevant parameters of the irradiation process;

[0072] S2: High-energy ion irradiation: Accelerate heavy ions to make them carry high energy E1, use the high-energy heavy ions to bombard the nonlinear optical crystal, form a first refractive index decrease peak at a first depth Δy1 of the nonlinear optical crystal along the depth direction, and obtain a primary processed crystal;

[0073] S3: Sub-high energy ion irradiation: accelerating heavy ions to carry sub-high energy, using the sub-high energy heavy ions to bombard the primary processed crystal, forming a second refractive index decrease peak at a second depth Δy2 of the primary processed crystal along the depth direction; obtaining a secondary processed crystal;

[0074] S4: Surface patterning: The secondary processed crystal is split along the width direction to obtain a shaped optical waveguide.

[0075] Specifically, in this specific embodiment, the method for preparing the optical waveguide with focusing capability includes the following sub-steps:

[0076] S11: Select a KTP (potassium titanyl phosphate) crystal rough stone, and cut a required 10 mm (length) × 8 mm (width) × 2 mm (height) rectangular block from the KTP crystal rough stone as an original KTP crystal;

[0077] S12: performing surface polishing on the upper surface, the light input end face and the light output end face of the KTP crystal to obtain a crystal block as the KTP crystal C0 required for processing;

[0078] S13: After irradiating the nonlinear optical crystal with fluorine, chlorine and argon ions, the refractive index of the crystal can all change gradually, and the main difference between the effects of the three ions is that the width of the descending peak Wb formed is different, wherein the width of the descending peak formed by fluorine ions is about 1 μm, the width of the descending peak formed by chlorine ions is about 2 μm, and the width of the descending peak formed by argon ions is about 3 μm. In this specific embodiment, chlorine ions are selected as heavy ions for irradiation treatment.

[0079] S14: Based on a Monte Carlo algorithm, the energy E1 carried by the heavy ions in the high-energy ion irradiation step is determined according to the depth Δy1 of the first refractive index drop peak required for processing;

[0080] S15: Similarly, based on the Monte Carlo algorithm, the energy E2 carried by the heavy ions in the next high energy ion irradiation step is determined according to the depth Δy2 of the second refractive index drop peak required by the processing.

[0081] S21: placing the KTP crystal C0 in the irradiation target chamber;

[0082] S22: Use a high energy ion accelerator to accelerate chloride ions to have energy E1;

[0083] S23: Bombarding the KTP crystal C0 with chloride ions having energy E1, forming a first refractive index decrease peak P1 at a depth Δy1 on the KTP crystal C0, and obtaining a primary KTP processed crystal C1.

[0084] S31: placing a KTP-processed crystal C1 in an irradiation target chamber;

[0085] S32: using a high-energy ion accelerator to accelerate heavy ions to have energy E2, and adjusting the ion beam energy load so that the energy E2 is less than the energy E1;

[0086] S33: bombarding the primary KTP processed crystal C1 with ions having energy E2, forming a second refractive index drop peak P2 at a depth Δy2 on the primary KTP processed crystal C1, and obtaining a secondary KTP processed crystal C2. After the above two ion irradiations of S2-S3, with high energy first and low energy later, the secondary KTP processed crystal C2 has formed a sandwich-type optical waveguide structure with two optical barriers in the depth direction, and has a focusing effect in the depth direction, and can effectively constrain the light field to converge to the center of the optical waveguide structure in the depth direction.

[0087] S41: In order to constrain the light field in the width direction and minimize the divergence of light in the width direction, in this specific embodiment, the secondary KTP processed crystal C2 is placed on a three-axis electric workbench, and a titanium sapphire femtosecond laser processing system is used to ablate the upper surface of the secondary KTP processed crystal C2 along the light beam propagation direction to form a first optical waveguide side L1;

[0088] S42: using a titanium sapphire femtosecond laser processing system FLS to ablate the upper surface of the secondary KTP processed crystal C2 along the beam propagation direction to form a second optical waveguide side L2, with the enclosed portion of the first optical waveguide side L1 and the second optical waveguide side L2 serving as a formed optical waveguide.

[0089] The titanium sapphire femtosecond laser processing system FLS uses linearly polarized light with a wavelength of 796 nanometers as the light source. Its polarization direction is parallel to the height direction of the KTP nonlinear optical crystal. The laser pulse duration of the processing system is adjusted to 120 femtoseconds and the repetition frequency is 1 kHz. The laser beam is focused through a microscope objective and scans the sample placed on the three-axis electric worktable along a specific route. The scanning speed and pulse energy are set to 50 microns / second and 0.7 microjoules, respectively.

[0090] After two scans, the first light guide side L1 and the second light guide side L2 divide the upper surface of the secondary KTP processed crystal C2 into three areas. The part enclosed by the first light guide side L1 and the second light guide side L2 is selected. This part is a sandwich waveguide structure along the depth direction, separated from other parts along the width direction, and extends from the light input end face to the light output end face. Such a crystal structure can be used as a mature optical waveguide in a specific optical path.

[0091] In one specific embodiment, along the light input end face to the light output end face of the secondary KTP processed crystal C2, the first optical waveguide side L1 includes a first input section L11, a first transition section L12 and a first output section L13 in sequence, and the second optical waveguide side L2 includes a second input section L21, a second transition section L22 and a second output section L23 in sequence; the first input section L11 and the second input section L21 are equal in length and parallel to each other, the first transition section L12 and the second transition section L22 are equal in length and the spacing gradually decreases, and the first output section L13 and the second output section L13 are equal in length and parallel to each other.

[0092] From the light input end face of the secondary KTP processed crystal C2 to its light output end face, the first optical waveguide side L1 and the second optical waveguide side L2 will roughly enclose a conical or trumpet-shaped surface shape. Such a shape makes the transmission cross-sectional width of the light beam in the optical waveguide continuously reduce, which plays a role in lateral focusing of the light beam; and when the end face coupling device is set at the light input end face of the optical waveguide, the light is coupled to the current optical waveguide structure through the end face coupling device. Since the entire optical waveguide structure partially presents a cone that gradually narrows along the light propagation direction from the light input end face to its light output end face, the cross-sectional size at the light input end face is relatively large, which can be easily adapted to the end face coupling device, thereby minimizing the coupling loss.

[0093] In this specific embodiment, an optical waveguide is also provided. The optical waveguide is prepared by using the above method for preparing an optical waveguide with focusing capability.

[0094] In this specific embodiment, a frequency converter is also provided. The frequency converter includes the above optical waveguide.

[0095] The above are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. All equivalent structural changes made using the contents of the present invention's specification and drawings, or directly / indirectly applied in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A method for preparing an optical waveguide with focusing capability, characterized in that: The method comprises the following steps: S1: Processing preparation: prepare the nonlinear optical crystals required for processing, determine the types of heavy ions required for processing and the size of the relevant parameters of the irradiation process; S2: high energy ion irradiation: accelerating heavy ions to make them have high energy, bombarding the nonlinear optical crystal with the high energy heavy ions, forming a first refractive index decrease peak at a first depth of the nonlinear optical crystal along the depth direction, and obtaining a primary processed crystal; S3: Sub-high energy ion irradiation: accelerating heavy ions to make them have sub-high energy, using the sub-high energy heavy ions to bombard the primary processed crystal, forming a second refractive index decrease peak at a second depth of the primary processed crystal along the depth direction; obtaining a secondary processed crystal; S4: surface patterning processing: dividing the secondary processed crystal to obtain a formed optical waveguide; Wherein, the S4: surface patterning process specifically includes the following sub-steps: S41: etching a first optical waveguide side on the upper surface of the secondary processed crystal using a surface etching device; S42: etching a second optical waveguide side on the upper surface of the secondary processed crystal using a surface etching device, and using the enclosed portion of the first optical waveguide side and the second optical waveguide side as a formed optical waveguide; The first and second optical waveguide sides extend from the light input end face of the secondary processed crystal to the light output end face; Along the light input end face to the light output end face of the secondary processed crystal, the first optical waveguide side includes a first input section, a first transition section and a first output section in sequence, and the second optical waveguide side includes a second input section, a second transition section and a second output section in sequence; Along the light input end face to the light output end face of the secondary processed crystal, the first input section and the second input section are equal in length and parallel to each other, the first transition section and the second transition section are equal in length and the spacing gradually decreases, and the first output section and the second output section are equal in length and parallel to each other; Wherein, in S4, a femtosecond laser processing system is used as a surface etching device to divide the secondary processed crystal.

2. The method for preparing an optical waveguide with focusing capability according to claim 1, characterized in that: The S2: high energy ion irradiation specifically includes the following sub-steps: S21: placing the nonlinear optical crystal in an irradiation target chamber; S22: Use high-energy ion accelerators to accelerate heavy ions to carry high energy; S23: bombarding the nonlinear optical crystal with a high-energy ion beam to form a first optical barrier along the depth direction of the nonlinear optical crystal, wherein the first optical barrier has a first refractive index decrease peak at a first depth position of the nonlinear optical crystal; and obtaining the once-processed crystal after the irradiation is completed.

3. The method for preparing an optical waveguide with focusing capability according to claim 2, characterized in that: The S3: sub-high energy ion irradiation specifically includes the following sub-steps: S31: placing the primary processed crystal in an irradiation target chamber; S32: Use high energy ion accelerator to accelerate heavy ions to carry sub-high energy; S33: bombarding the primary processed crystal with a sub-high energy ion beam to form a second optical barrier along the depth direction of the primary processed crystal, wherein the second optical barrier has a second refractive index decrease peak at a second depth position of the primary processed crystal, and the secondary processed crystal is obtained after the irradiation is completed.

4. The method for preparing an optical waveguide with focusing capability as claimed in claim 3, characterized in that: The type of heavy ions used in the S2 high-energy ion irradiation is the same as that used in the S3 high-energy ion irradiation.

5. The method for preparing an optical waveguide with focusing capability according to claim 4, characterized in that: The energy carried by the high-energy ion beam is greater than the energy carried by the sub-high-energy ion beam.

6. The method for preparing an optical waveguide with focusing capability according to claim 5, characterized in that: The S1: processing preparation specifically includes the following sub-steps: S11: Cutting a block with a regular shape from the original stone as the original nonlinear optical crystal; S12: performing surface polishing on the upper surface, the light input end face and the light output end face of the original nonlinear optical crystal to obtain the nonlinear optical crystal required for processing; S13: selecting a type of heavy ions according to the light guiding requirements of the molded optical waveguide; S14: analyzing the first optical barrier required by the molded optical waveguide, and determining the energy carried by the high-energy ion beam according to the first depth of the first refractive index drop peak; S15: Analyze the second optical barrier required by the molded optical waveguide, and determine the energy carried by the sub-high energy ion beam according to the second depth of the first refractive index drop peak.

7. An optical waveguide, characterized in that: The optical waveguide is prepared by the method for preparing an optical waveguide with focusing capability as claimed in any one of claims 1 to 6.

8. A frequency converter, characterized in that: The frequency converter comprises the optical waveguide as claimed in claim 7.

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