Method for manufacturing wavelength conversion element, wavelength conversion element

Abstract

This manufacturing method for a wavelength conversion element that has a periodical polarization inversion structure includes: a step of forming the periodical polarization inversion structure by forming a polarization inversion section and a non-polarization inversion section in an alternating manner on a ferroelectric substrate; a step of etching a surface of the ferroelectric substrate on which the periodical polarization inversion structure is formed and forming a step between the polarization inversion section and the non-polarization inversion section; a step of forming a bonding layer, of a first thickness, on the ferroelectric substrate on which the step is formed; a step of polishing the surface of the bonding layer such that the thickness of the bonding layer becomes a second thickness; and a step of bonding a support substrate to the polished surface of the bonding layer.

Description

[Technical Field]

[0001] The present invention relates to a wavelength conversion element having a periodically poled structure and a method for manufacturing the same. [Background technology]

[0002] Conventionally, as a light source realizing, for example, a blue or green laser, a structure that combines a laser that oscillates using red light as a fundamental wave with a wavelength conversion element that functions as a second harmonic generation element is known. In the wavelength conversion element used in such a light source, wavelength conversion is performed by a QPM (Quasi-Phase Matching) structure that is realized using a periodically poled structure in which poled parts and non-poled parts are periodically alternately formed.

[0003] Patent Document 1 describes a wavelength conversion element in which a periodic polarization inversion structure formed in an optical waveguide has first polarization inversion sections and second polarization inversion sections with different design widths arranged alternately, the difference between the design width of the first polarization inversion section and the design width of the second polarization inversion section is an odd multiple of the accuracy of the mask used to form the electrodes, and the design width of the non-polarization inversion sections is approximately constant. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent No. 4100937 Summary of the Invention [Problem to be solved by the invention]

[0005] In the manufacturing process of wavelength conversion elements such as those described in Patent Document 1, the substrate surface is etched to observe the formation of periodic steps in the polarization inversion portions, thereby confirming that the periodic polarization inversion structure is properly formed on the substrate. However, if a bonding layer such as SiO2 is formed on a substrate on which a periodic polarization inversion structure has been confirmed to be formed in this manner for bonding to a support substrate, the bonding layer is formed on the steps formed by etching, resulting in similar steps on the surface of the bonding layer. In this state, if a wavelength conversion element is fabricated by bonding the substrate to the support substrate via the bonding layer, a gap is formed between the bonding layer and the support substrate due to the steps on the surface of the bonding layer. If air bubbles are trapped in this gap, they can become trapped inside the wavelength conversion element, causing problems such as poor appearance.

[0006] The present invention has been made in consideration of the above, and its main object is to provide a wavelength conversion element and a manufacturing method thereof that can prevent air bubbles from being trapped inside even when the formation of a periodic polarization inversion structure is confirmed by etching. [Means for solving the problem]

[0007] The manufacturing method of a wavelength conversion element according to the present invention is a manufacturing method of a wavelength conversion element having a periodic polarization inversion structure, and includes the steps of: forming the periodic polarization inversion structure by alternately forming polarization inversion parts and non-polarization inversion parts on a ferroelectric substrate; etching the surface of the ferroelectric substrate on which the periodic polarization inversion structure is formed to form steps between the polarization inversion parts and the non-polarization inversion parts; forming a bonding layer with a first thickness on the ferroelectric substrate on which the steps are formed; and forming a bonding layer with a second thickness. and in the step of forming the bonding layer, a step formed in the bonding layer corresponding to the step of the ferroelectric substrate is eliminated, so that the surface of the bonding layer becomes flat. The method includes polishing the surface of the bonding layer, and bonding a support substrate to the polished surface of the bonding layer. The wavelength conversion element according to the present invention has a periodic polarization inversion structure, in which polarization inversion sections and non-polarization inversion sections are alternately arranged on a ferroelectric substrate, the periodic polarization inversion structure having a step between the polarization inversion sections and the non-polarization inversion sections, a bonding layer provided on the ferroelectric substrate having the step, and a support substrate bonded onto the bonding layer, the step being 10 to 40 nm, and the surface roughness of the bonding layer on the support substrate side being 2 nm or less. [Effects of the Invention]

[0008] According to the present invention, it is possible to realize a wavelength conversion element and a manufacturing method thereof that can prevent bubbles from being trapped inside even when the formation of a periodic domain inversion structure is confirmed by etching. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic cross-sectional view showing a schematic configuration of a wavelength conversion element according to one embodiment of the present invention. [Figure 2A] 10A and 10B are diagrams illustrating a process of forming a periodically poled structure in the manufacturing process of a wavelength conversion element according to a comparative example. [Figure 2B] 10A and 10B are diagrams illustrating an etching step in the manufacturing process of a wavelength conversion element according to a comparative example. [Figure 2C] 10A and 10B are diagrams illustrating a bonding layer forming step in the manufacturing process of a wavelength conversion element according to a comparative example. [Figure 2D] 10A and 10B are diagrams illustrating a bonding step of a support substrate in the manufacturing process of a wavelength conversion element according to a comparative example. [Figure 3A] 3A to 3C are diagrams illustrating a step of forming a periodically poled structure in the manufacturing process of a wavelength conversion element according to one embodiment of the present invention. [Figure 3B] 3A to 3C are diagrams illustrating an etching step in the manufacturing process of a wavelength conversion element according to one embodiment of the present invention. [Figure 3C] 5A to 5C are diagrams illustrating a step of forming a bonding layer in the manufacturing process of a wavelength conversion element according to one embodiment of the present invention. [Figure 3D]10A to 10C are diagrams illustrating a polishing step of a bonding layer in the manufacturing process of a wavelength conversion element according to one embodiment of the present invention. [Figure 3E] 5A to 5C are diagrams illustrating a step of bonding a support substrate in the manufacturing process of a wavelength conversion element according to one embodiment of the present invention. [Figure 4] 10A and 10B are diagrams showing the results of observation of the surface of the bonding layer before, during and after the polishing step. [Figure 5A] 10 is an image of a bonding layer of a wavelength conversion element according to a comparative example, observed with a dark-field microscope. [Figure 5B] 1 is an image of a bonding layer of a wavelength conversion element according to an embodiment of the present invention, observed with a dark-field microscope. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to these embodiments. In addition, in order to clarify the description, the drawings may show the width, thickness, shape, etc. of each part more schematically than in the embodiments, but these are merely examples and do not limit the interpretation of the present invention.

[0011] (Structure of wavelength conversion element) 1 is a schematic cross-sectional view showing the general configuration of a wavelength conversion element according to one embodiment of the present invention. The wavelength conversion element 100 has a structure in which a ferroelectric substrate 10 is bonded to a support substrate 40 via a bonding layer 20 and an adhesive layer 30.

[0012] The ferroelectric substrate 10 is a substrate made of a ferroelectric material. Examples of the ferroelectric material that constitutes the ferroelectric substrate 10 include MgO:LN (MgO-added lithium niobate) and MgO:LT (MgO-added lithium tantalate). The ferroelectric substrate 10 has polarization inversion parts 11 formed in the opposite polarization direction to other parts, which are periodically arranged at regular intervals. That is, the ferroelectric substrate 10 has polarization inversion parts 11 and other parts (non-polarization inversion parts) periodically alternately formed. This forms a periodic polarization inversion structure in the ferroelectric substrate 10.

[0013] The bonding layer 20 is used to form a bonding surface when bonding the ferroelectric substrate 10 to the support substrate 40. By bonding the ferroelectric substrate 10 to the support substrate 40 via the bonding layer 20, a bonding surface suitable for bonding is formed on the bonding layer 20, and the ferroelectric substrate 10 can be firmly bonded to the support substrate 40. In addition, since the periodically poled structure formed on the ferroelectric substrate 10 can be bonded to the support substrate 40 via the bonding layer 20 rather than directly to the support substrate 40, the periodically poled structure can also be protected.

[0014] The bonding layer 20 is made of, for example, an amorphous material such as SiO2. By making the bonding layer 20 of an amorphous material, for example, polishing, which will be described later, becomes easier, and it becomes easier to obtain a suitable surface roughness for the bonding surface.

[0015] The bonding layer 20 can be formed by any suitable method, such as physical vapor deposition (e.g., sputtering, vacuum deposition, or ion beam assisted deposition (IAD)), chemical vapor deposition, or atomic layer deposition (ALD). The bonding layer 20 can be formed at a temperature between room temperature (25°C) and 300°C.

[0016] The adhesive layer 30 bonds the ferroelectric substrate 10 to the support substrate 40 via the bonding layer 20. The adhesive layer 30 is made of, for example, a resin, and is interposed between the bonding layer 20 and the support substrate 40 to bond them together. That is, in the wavelength conversion element 100, the surface of the bonding layer 20 and the support substrate 40 are bonded via the adhesive layer 30.

[0017] The support substrate 40 supports the ferroelectric substrate 10. Any appropriate substrate can be used as the support substrate 40. The support substrate 40 may be made of a single crystal or a polycrystalline material. It may also be made of a metal. The material constituting the support substrate 40 is preferably selected from the group consisting of silicon, sialon, sapphire, cordierite, mullite, glass, quartz, crystal, alumina, SUS, iron-nickel alloy (42 alloy), LN (LiNbO3: lithium niobate), LT (LiTaO3: lithium tantalate), and brass. Any appropriate thickness can be adopted for the support substrate 40.

[0018] The silicon may be single crystal silicon, polycrystalline silicon, or high resistance silicon, and the support substrate 40 may be SOI (Silicon on Insulator).

[0019] Typically, the sialon is a ceramic obtained by sintering a mixture of silicon nitride and alumina, and has a composition represented by, for example, Si6-wAlwOwN8-w. Specifically, the sialon has a composition in which alumina is mixed into silicon nitride, where w represents the alumina mixing ratio. w is preferably 0.5 or more and 4.0 or less.

[0020] Typically, the sapphire is a single crystal having a composition of Al2O3, and the alumina is a polycrystalline material having a composition of Al2O3. The alumina is preferably translucent alumina.

[0021] Typically, the cordierite is a ceramic having a composition of 2MgO·2Al2O3·5SiO2, and the mullite is a ceramic having a composition in the range of 3Al2O3·2SiO2 to 2Al2O3·SiO2.

[0022] The wavelength conversion element 100 described above is used as a second harmonic generation element for converting the wavelength of red laser light to obtain blue or green laser light, for example. Although not shown, the wavelength conversion element 100 may further include any layer. The type, function, number, combination, arrangement, etc. of such layers can be appropriately set depending on the purpose.

[0023] The wavelength conversion element 100 can be manufactured in any suitable shape, and the size of the wavelength conversion element 100 can be appropriately set depending on the purpose.

[0024] (Comparative Manufacturing Method) Before describing the manufacturing method of the wavelength conversion element 100, a manufacturing method of a wavelength conversion element according to a comparative example to which the present invention is not applied will be described below with reference to FIGS. 2A to 2D.

[0025] 2A shows a process for forming a periodically poled structure in the manufacturing process of a wavelength conversion element 110 according to a comparative example. In this process, predetermined voltages are applied to the poled portions 11 and other portions of a ferroelectric substrate 10 made of MgO:LN or MgO:LT, thereby forming the poled portions 11 and non-poled portions alternately in a periodic manner. This forms a periodically poled structure in the ferroelectric substrate 10.

[0026] 2B shows an etching step in the manufacturing process of the wavelength conversion element 110 according to the comparative example. In this step, a mixed solution of hydrofluoric acid and nitric acid is applied to the surface of the ferroelectric substrate 10 on which the periodically poled structure has been formed in the manufacturing process of FIG. 2A, and etching is performed. At this time, since the etching rates of the poled portions 11 and the non-poled portions are different, the poled portions 11 are eroded more deeply than the non-poled portions, and a step 12 is formed between the poled portions 11 and the non-poled portions on the surface of the ferroelectric substrate 10. By observing this step 12, it can be confirmed that a periodically poled structure has been formed in the ferroelectric substrate 10.

[0027] 2C shows a bonding layer deposition step in the manufacturing process of the wavelength conversion element 110 according to the comparative example. In this step, a bonding layer 20 is formed by depositing an amorphous material such as SiO2 on the ferroelectric substrate 10 on which the steps 12 have been formed in the etching step of FIG. 2B. As described above, in this deposition step, various deposition methods can be used to form the bonding layer 20 so that the thickness from the surface of the ferroelectric substrate 10 becomes a predetermined thickness according to the deposition time. Therefore, steps 21 are formed on the surface of the bonding layer 20 corresponding to the steps 12 on the surface of the ferroelectric substrate 10.

[0028] 2D shows a bonding process of a support substrate in the manufacturing process of the wavelength conversion element 110 according to the comparative example. In this process, a resin or the like is applied to the surface of the bonding layer 20 formed in the film formation process of FIG. 2C to form an adhesive layer 30, and a support substrate 40 is placed on this adhesive layer 30. As a result, the bonding layer 20 and the support substrate 40 are bonded by the adhesive layer 30, and the ferroelectric substrate 10 and the support substrate 40 are bonded via the bonding layer 20 and the adhesive layer 30.

[0029] The wavelength conversion element 110 of the comparative example is manufactured by carrying out the steps of FIGS. 2A to 2D described above in order.

[0030] In the wavelength conversion element 110 according to the comparative example, as shown in FIG. 2D , a gap 31 is formed between the adhesive layer 30 and the support substrate 40. This gap 31 is formed because, in the bonding step shown in FIG. 2D , the adhesive layer 30 is formed along the step 21 present on the surface of the bonding layer 20, and the bonding layer 20 and the support substrate 40 are bonded together via the adhesive layer 30. That is, in the manufacturing method of the wavelength conversion element according to the comparative example described with reference to FIGS. 2A to 2D , a step 12 is formed on the surface of the ferroelectric substrate 10 in the etching step shown in FIG. 2B , and then, in the subsequent film formation step shown in FIG. 2C , a step 21 corresponding to the step 12 is formed on the surface of the formed bonding layer 20, thereby forming the gap 31 between the adhesive layer 30 and the support substrate 40. If air bubbles are trapped in this gap 31 in the bonding step shown in FIG. 2D , the wavelength conversion element 110 is manufactured with the air bubbles trapped inside.

[0031] The wavelength conversion element 110 must transmit the laser light that performs wavelength conversion, and therefore at least a portion of the element is made of a transparent material. Air bubbles trapped inside the wavelength conversion element 110 can be seen from the outside through this transparent portion, which may cause poor appearance. In addition, expansion and contraction of the air bubbles due to temperature changes may lead to problems such as poor bonding. That is, in the wavelength conversion element 110 according to the comparative example, the formation of a gap 31 between the adhesive layer 30 and the support substrate 40 may cause these problems.

[0032] (Production method of the present invention) A method for manufacturing a wavelength conversion element according to the present invention for solving the problems in the above comparative example will be described below with reference to FIGS. 3A to 3E.

[0033] 3A shows a process for forming a periodically poled structure in the manufacturing process of the wavelength conversion element 100 according to one embodiment of the present invention. In this process, the periodically poled structure is formed in the ferroelectric substrate 10 by periodically alternately forming poled portions 11 and non-poled portions in the ferroelectric substrate 10 by a method similar to that of the process for forming a periodically poled structure in the comparative example described in FIG. 2A.

[0034] Fig. 3B shows an etching step in the manufacturing process of the wavelength conversion element 100 according to one embodiment of the present invention. In this step, similar to the etching step in the comparative example described with reference to Fig. 2B, a step 12 is formed between the polarization inversion portion 11 and the non-polarization inversion portion by etching the surface of the ferroelectric substrate 10 on which the periodic polarization inversion structure has been formed in the manufacturing process of Fig. 3A. The height of the step 12 is, for example, 10 to 40 nm.

[0035] 3C shows a bonding layer deposition step in the manufacturing process of the wavelength conversion element 100 according to one embodiment of the present invention. In this step, similar to the etching step in the comparative example described with reference to FIG. 2C, a bonding layer 20 is deposited on the ferroelectric substrate 10 on which the step 12 has been formed in the etching step of FIG. 3B. At this time, it is preferable to make the thickness of the bonding layer 20 larger (first thickness) than that in the etching step in the comparative example so that a sufficient thickness of the bonding layer 20 after polishing is ensured even when the bonding layer 20 is polished in the polishing step described later. Note that, similar to the comparative example, a step 21 is formed on the surface of the bonding layer 20 corresponding to the step 12 on the surface of the ferroelectric substrate 10. The first thickness is, for example, 480 to 700 nm.

[0036] FIG. 3D shows a polishing step of the bonding layer in the manufacturing process of the wavelength conversion element 100 according to one embodiment of the present invention. In this step, the bonding layer 20 formed in the film-forming step of FIG. 3C is subjected to processes such as grinding and polishing until the bonding layer 20 reaches a predetermined thickness (second thickness). This eliminates the step 21 present on the surface of the bonding layer 20 at the end of the film-forming step of FIG. 3C, thereby forming a flat surface, for example, so that the unevenness of the surface of the bonding layer 20 (the surface bonded to the support substrate 40) is 2 nm or less. The difference in thickness of the bonding layer 20 before and after polishing (the difference between the first thickness and the second thickness) can be, for example, 5 to 15 times the height of the step 12 (step 21), more preferably 5 to 10 times. This range allows the surface of the bonding layer 20 to be sufficiently flattened while maintaining the required thickness of the polished bonding layer 20. The second thickness is, for example, 380 to 500 nm.

[0037] 3E shows a bonding step of the support substrate in the manufacturing process of the wavelength conversion element 100 according to one embodiment of the present invention. In this step, a resin or the like is applied to the surface of the bonding layer 20 polished in the polishing step of FIG. 2D in the same manner as in the bonding step of the comparative example described with reference to FIG. 2D to form an adhesive layer 30, and the support substrate 40 is placed on this adhesive layer 30. As a result, the bonding layer 20 and the support substrate 40 are bonded by the adhesive layer 30, and the ferroelectric substrate 10 and the support substrate 40 are bonded via the bonding layer 20 and the adhesive layer 30.

[0038] The wavelength conversion element 100 of this embodiment is manufactured by carrying out the steps of FIGS. 3A to 3E described above in order.

[0039] The wavelength conversion element 100 of this embodiment can solve the problems that occur in the wavelength conversion element 110 of the comparative example described above. Specifically, since the step 21 is removed from the surface of the bonding layer 20 in the polishing step of Fig. 3D, when the adhesive layer 30 is formed in the subsequent bonding step of Fig. 3E, the gap 31 as shown in Fig. 2D is not formed between the adhesive layer 30 and the support substrate 40. Therefore, the wavelength conversion element 100 can suppress the trapping of air bubbles inside, and can avoid problems such as poor appearance and poor bonding caused by air bubbles.

[0040] During the bonding step, it is preferable to clean the surfaces of the bonding layer 20 and the support substrate 40, for example, to remove abrasive residue. Examples of cleaning methods include wet cleaning, dry cleaning, and scrub cleaning. Among these, scrub cleaning is preferable because it is simple and efficient. A specific example of scrub cleaning is a method in which a cleaning agent (e.g., Sunwash series manufactured by Lion Corporation) is used, followed by cleaning in a scrub cleaner using a solvent (e.g., a mixed solution of acetone and isopropyl alcohol (IPA)). [Example]

[0041] An example of the method for manufacturing the wavelength conversion element 100 according to the present invention will be described below. Unless otherwise specified, the following procedures were carried out at room temperature.

[0042] A ferroelectric substrate 10 was prepared using MgO:LN, a lithium niobate single crystal doped with 5% magnesium, with a diameter of 4 inches and a thickness of 0.3 mm. Multiple electrodes were placed at predetermined intervals on this ferroelectric substrate 10 and connected to a power supply. A pulsed voltage of 1.4 kV (pulse width 20 msec, 25 Hz, 4 pulses, maximum applied current 2 mA) was generated from the power supply, thereby carrying out the process of forming the periodically poled structure shown in Fig. 3A, and a periodically poled structure was formed.

[0043] Next, the etching step of Fig. 3B was performed by etching the surface of the ferroelectric substrate 10 using a mixed solution of hydrofluoric acid (aqueous solution of hydrogen fluoride) and nitric acid, thereby forming a step 12 between the polarization inversion portion 11 and the non-polarization inversion portion. Note that the etching step of Fig. 3B may be performed using an aqueous solution of hydrogen fluoride with a concentration of 50 wt% instead of the mixed solution of hydrofluoric acid and nitric acid.

[0044] Next, a 540 nm thick SiO2 film was formed by sputtering on the surface of the ferroelectric substrate 10 on which the step 12 was formed, thereby performing the film formation process shown in Fig. 3C, and a bonding layer 20 was formed on the ferroelectric substrate 10. A predetermined area on the surface of this bonding layer 20 was then observed with an atomic force microscope (AFM), and it was confirmed that a step 21 had been formed.

[0045] 4(a) is a diagram showing the results of observing the surface of the bonding layer 20 after the film formation process (before the polishing process). In this state, it was confirmed that a step 21 with a height of about 13 nm was formed on the surface of the bonding layer 20.

[0046] Next, the surface of bonding layer 20 was polished by chemical mechanical polishing (CMP), thereby performing the polishing step shown in Fig. 3D. In this polishing step, the surface of bonding layer 20 was polished by about 100 nm until the thickness of bonding layer 20 became 440 nm from 540 nm, so that the surface of bonding layer 20 became uniform. Then, a predetermined area of ​​the surface of bonding layer 20 at this time was observed with an atomic force microscope (AFM), and it was confirmed that the steps 21 had been removed and the surface had become flat.

[0047] 4(b) is a diagram showing the observation result of the surface of the bonding layer 20 during the polishing process. Fig. 4(b) shows the observation result after the surface of the bonding layer 20 has been polished by 50 nm. In this state, the height of the step 21 has been reduced to about 3 nm, but it was confirmed that the step 21 has not yet been completely removed.

[0048] Fig. 4(c) is a diagram showing the observation result of the surface of the bonding layer 20 after the polishing process. Fig. 4(c) shows the observation result in a state where the surface of the bonding layer 20 has been polished by 100 nm. In this state, it was confirmed that the step 21 had almost completely disappeared (less than 2 nm), and the surface of the bonding layer 20 had become flat.

[0049] Finally, a resin (e.g., epoxy resin) was applied to the surface of the bonding layer 20 after 100 nm polishing to form an adhesive layer 30, and the support substrate 40 was placed on the adhesive layer 30 and dried to perform the bonding step shown in Fig. 3E. As a result, the wavelength conversion element 100 having the structure shown in Fig. 1 was obtained.

[0050] (Observation of bubbles) The wavelength conversion element 110 according to the comparative example and the wavelength conversion element 100 according to the present embodiment fabricated as described above were each observed using a dark-field microscope from the side of the ferroelectric substrate 10. The observed images are shown in Figures 5A and 5B, respectively.

[0051] In the observation image shown in Fig. 5A, the air bubbles trapped inside the wavelength conversion element 110 appear brighter than other parts. This shows that a large number of air bubbles are trapped inside the wavelength conversion element 110. On the other hand, in the observation image shown in Fig. 5B, it is clear that no air bubbles exist inside the wavelength conversion element 110, and that trapping of air bubbles inside the element is suppressed.

[0052] According to the embodiment of the present invention described above, the following advantageous effects are achieved.

[0053] (1) A method for manufacturing a wavelength conversion element 100 having a periodic polarization inversion structure includes forming a periodic polarization inversion structure by alternately forming polarization inversion portions 11 and non-polarization inversion portions on a ferroelectric substrate 10 (FIG. 3A: periodic polarization inversion structure forming process), etching the surface of the ferroelectric substrate 10 on which the periodic polarization inversion structure has been formed to form a step 12 between the polarization inversion portions 11 and the non-polarization inversion portions (FIG. 3B: etching process), forming a bonding layer 20 with a first thickness on the ferroelectric substrate 10 on which the step 12 has been formed (FIG. 3C: bonding layer forming process), polishing the surface of the bonding layer 20 so that the thickness of the bonding layer 20 becomes a second thickness (FIG. 3D: bonding layer polishing process), and bonding a support substrate 40 to the polished surface of the bonding layer 20 (FIG. 3E: support substrate bonding process). This method achieves a wavelength conversion element manufacturing method that can prevent air bubbles from being trapped inside, even when the formation of a periodic polarization inversion structure is confirmed by etching.

[0054] (2) The difference between the first thickness and the second thickness of bonding layer 20 is preferably 5 to 15 times the height of step 12. In this way, the surface of bonding layer 20 can be sufficiently flattened while maintaining the thickness of bonding layer 20 after polishing.

[0055] (3) In the step of bonding the support substrate, the surface of the bonding layer 20 and the support substrate 40 are bonded via the adhesive layer 30. This adhesive layer 30 is made of, for example, a resin. This allows the surface of the bonding layer 20 and the support substrate 40 to be bonded easily and firmly.

[0056] (4) The ferroelectric substrate 10 can be made of either MgO:LN or MgO:LT, which allows the ferroelectric substrate 10 to be made of any material depending on the application.

[0057] The present invention is not limited to the above-described embodiment, and can be implemented using any components without departing from the spirit of the present invention.

[0058] The above-described embodiments and modifications are merely examples, and the present invention is not limited to these details as long as the features of the invention are not impaired. Furthermore, although various embodiments and modifications have been described above, the present invention is not limited to these details. Other aspects that can be considered within the scope of the technical idea of ​​the present invention are also included within the scope of the present invention. [Explanation of symbols]

[0059] 10: Ferroelectric substrate 11: Polarization inversion section 12: Step 20: Bonding layer 21: Step 30: Adhesive layer 40: Support substrate 100, 110: Wavelength conversion element

Claims

1. A method for manufacturing a wavelength conversion element having a periodic polarization inversion structure, forming the periodically poled structure by alternately forming poled portions and non-poled portions on a ferroelectric substrate; a step of etching the surface of the ferroelectric substrate on which the periodically poled structure is formed, to form a step between the poled portion and the non-poled portion; forming a bonding layer with a first thickness on the ferroelectric substrate on which the step is formed; a step of polishing a surface of the bonding layer so that the thickness of the bonding layer becomes a second thickness and the step formed in the bonding layer corresponding to the step of the ferroelectric substrate in the step of forming the bonding layer is eliminated, thereby making the surface of the bonding layer flat; and bonding a support substrate to the polished surface of the bonding layer.

2. 2. The method for manufacturing a wavelength conversion element according to claim 1, a difference between the first thickness and the second thickness being 5 to 15 times the height of the step;

3. 3. The method for manufacturing a wavelength conversion element according to claim 1, A method for manufacturing a wavelength conversion element, comprising bonding a surface of the bonding layer to the support substrate via an adhesive layer.

4. 4. The method for manufacturing a wavelength conversion element according to claim 3, The adhesive layer is made of a resin.

5. 3. The method for manufacturing a wavelength conversion element according to claim 1, The method for manufacturing a wavelength conversion element, wherein the ferroelectric substrate is made of either MgO:LN or MgO:LT.

6. A wavelength conversion element having a periodic polarization inversion structure, a periodically poled structure in which poled portions and non-poled portions are alternately provided on a ferroelectric substrate, and a step is formed between the poled portions and the non-poled portions; a bonding layer provided on the ferroelectric substrate having the step; and a support substrate bonded onto the bonding layer; the step is 10 to 40 nm; A wavelength conversion element, wherein the surface of the bonding layer facing the support substrate has a surface roughness of 2 nm or less.

7. The wavelength conversion element according to claim 6 , further comprising an adhesive layer that bonds the bonding layer and the support substrate together.

8. The wavelength conversion element according to claim 7 , wherein the adhesive layer is made of a resin.

9. 9. The wavelength conversion element according to claim 6, wherein the ferroelectric substrate is made of either MgO:LN or MgO:LT.

10. 9. The wavelength conversion element according to claim 6, wherein the bonding layer is made of an amorphous material of SiO2.

Images