JPH02236505A - Incident tapered optical waveguide and wavelength converting element and manufacture of incident tapered optical waveguide - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to optical information processing using a coherent light source.
The present invention relates to an input tapered optical waveguide, a wavelength conversion element, and a method for manufacturing an input tapered optical waveguide that enable high-refraction coupling between an optical waveguide, a laser, and a fiber used in the field of optical measurement and control.

Conventional technology An optical waveguide was formed on LINbO3 using a proton exchange method, and a TE/TM mode splitter, a wavelength conversion element, etc. were manufactured. The optical waveguide has a refractive index difference (Δrle>
0. If I) was large and only a single mode was to be propagated, the thickness would be extremely thin at 0.4 to 0.6 μm. Therefore, in order to improve the coupling efficiency to the optical waveguide, it is conceivable to make the light incidence part tapered.

As a conventional input taper optical waveguide, for example, there is an optical waveguide whose input portion is widened in a tapered shape.

FIG. 5 shows a basic configuration diagram of this conventional input tapered optical waveguide, in which 1' is a dielectric substrate, 2' is an optical waveguide, 3' is a tapered waveguide, and 4° is an input section.

In the conventional input tapered optical waveguide configured as described above, the shape and area of the input part are changed to match the wavefront distribution of coherent light excited in the waveguide and the waveguide mode distribution propagating in the waveguide, and guide the waveguide. This is an input tapered waveguide that achieves high coupling efficiency between the waveguide and coherent light. In addition, as a method for manufacturing this input tapered optical waveguide (Abrid Optics (Human pplled Opt1cs) 1979
March issue, Vol. 18, P900-902) J. C. C
According to Mr. Ampbel1, as shown in FIG. 6, an incident tapered optical waveguide is formed by gradually immersing a substrate 1° into a silver nitrate solution 4° to change the diffusion depth. When forming an optical waveguide in LjNbO31', a tapered optical waveguide is produced using benzoic acid as the solution 4' at a temperature of about 200°C. 6 in Figure 6
゜ is a heater 7 1 is a beaker.

Problems to be Solved by the Invention In the above configuration, it is difficult to partially change the refractive index of the tapered optical waveguide, and in the tapered portion of the optical waveguide, there are It is likely that several propagation modes exist, and therefore coupling occurs between the propagation modes, resulting in considerable propagation loss in the tapered optical waveguide.

In addition, in the above-described method for manufacturing an input tapered optical waveguide, there is a problem in that since the heat treatment is performed at a high temperature, the temperature of the portion not immersed in the liquid decreases due to the steam, making it impossible to form the input section as designed.

In view of the above points, the present invention controls the propagation mode by controlling the refractive index distribution of the input tapered optical waveguide by providing a cladding layer around the input tapered optical waveguide,
In a tapered optical waveguide, it is possible to widen the width of the waveguide mode while keeping the waveguide mode at the fundamental mode. The purpose of this invention is to provide an input tapered waveguide with low propagation loss and high coupling efficiency. Another object of the present invention is to form a wavelength conversion element using the above optical waveguide and provide a wavelength conversion element with high conversion efficiency. A further object of the present invention is to provide a method for manufacturing an input tapered optical waveguide, which allows the above-mentioned input tapered optical waveguide to be manufactured homogeneously with good controllability.

Means for Solving the Problems In order to solve the above problems, the present invention uses a substrate with a refractive index n1 and a refractive index n2 (n 1 < n2) formed on the substrate.
an optical waveguide, a tapered entrance part formed in the waveguide, and a refractive index n3 (nl<n3
The present invention is an input tapered optical waveguide characterized by having a cladding portion of <n2).

Further, a substrate made of a nonlinear optical material with a refractive index of n1, an optical waveguide with a refractive index of n2 (nl<n2) formed on the substrate, a tapered entrance part formed on the waveguide, and a tapered entrance part formed around the entrance part. A wavelength conversion element characterized by comprising a cladding portion with a refractive index of n3 (nl<n3<n2) and at least one semiconductor laser directly connected to the tapered optical waveguide.

In addition, as a method for manufacturing the above-mentioned input taper optical waveguide, an ionization-resistant mask material other than the dielectric material is formed on the surface of the dielectric material to prevent the underlying dielectric material from ionization and to form a thick one. A first mask is formed by locally depositing an ionization-resistant mask layer that is thinner than the width of the optical waveguide, and the first mask layer has a substantially flat surface and a layer made of a material that is thinner than the ionization-resistant mask material. A substrate capable of preventing ionization of the underlying dielectric material is crimped as a mask to form a second mask that locally covers the body, and then the body of dielectric material is subjected to a first ion exchange treatment to remove the non-masked material. The ions in the dielectric are exchanged with the treated ions to change the refractive index in the dielectric to form a leading wave, and then the second ion exchange is performed immediately after removing the second mask. This is a method for manufacturing an input tapered optical waveguide, characterized by performing a step of changing the thickness and refractive index distribution of an ion exchange layer.

In addition, as a method for manufacturing the above-mentioned incident taper optical waveguide with good mass productivity, Tag OsP is added as an ionization-resistant mask material to the surface of the LiNbxTa1-m03 (0≦x≦1) substrate.
IN: is locally deposited to form a first mask, and a chloride film is locally deposited as an ionization-resistant mask material on the surface of the first mask to form a second mask. Then, after performing a first proton exchange on the substrate to form a high refractive index layer on the non-masked portion, the second mask is removed and a second proton exchange is performed on the substrate.
This method of manufacturing an input tapered optical waveguide is characterized by performing a step of performing proton exchange and partially changing the thickness and refractive index distribution of the proton exchange layer.

Effect The present invention has the above-described configuration, and includes a substrate having a refractive index n1, an optical waveguide having a refractive index n2 (n1<n2) formed on the substrate, a tapered entrance portion formed in the waveguide, and a surrounding area around the entrance portion. refractive index n3 (n 1<n3<n2)
By controlling the thickness and refractive index distribution of the cladding part, the propagation mode in the tapered entrance part can be controlled. This makes it possible to expand the width of the propagation mode by widening the input section while keeping the propagation mode guided in the input section as the fundamental mode, and it is possible to couple the propagation mode to the waveguide while keeping the propagation mode as the fundamental mode. can.

If the above method is adopted, a substrate with a refractive index of n1, an optical waveguide with a refractive index of n2 (nl<n2) formed on the substrate, a tapered entrance part formed on the waveguide, and an optical waveguide formed around the entrance part are formed. With the cladding portion having a refractive index n3 (nl<n3<n2), an input tapered waveguide with low propagation loss and high coupling efficiency can be constructed.

Example (Example 1) FIG. 1 shows a diagram of the structure of the input tapered waveguide in the first example. ), a tapered entrance part formed in the waveguide, and a cladding part with a refractive index n3 (nl<n3<n2) formed around the entrance part. 1 is a substrate made of LINbO3 with a +2 plate (tenth side of the substrate cut out perpendicular to the Z axis) with a refractive index of 2.1, and 2 is a substrate with a refractive index of 2.1 formed by proton exchange treatment in phosphoric acid. 3 has a tapered entrance part, and 3 has a refractive index of 2.2 formed around the entrance part by proton exchange treatment in phosphoric acid followed by annealing treatment.
The cladding portion 5 is also tapered, and 4 is a waveguide formed by proton exchange.

The operation of the input tapered waveguide of the first embodiment configured as described above will be described below.

A substrate 1 made of LINb03 with a refractive index of 2.1 was subjected to heat treatment (proton exchange treatment) at 300°C for 5 minutes with birophosphoric acid, which is a type of phosphoric acid, and then annealed at 300°C for 1 hour to obtain refraction. Rate 2. 25, width 10 μm 1 depth 2
A cladding portion 3 of μm was formed. On this cladding part 3, a proton exchange treatment is performed at 230°C with pyrophosphoric acid to form a waveguide 4 with a refractive index of 2, 3, a width of 2 μm1 and a depth of 0.4 μm, and a tapered waveguide 4 with a width of 5 μm1 and a depth of 1 μm. Part 2 was formed. This input tapered optical waveguide has a length of 0
．． The propagation loss of the waveguide was measured by exciting 8 μm semiconductor laser light. The measurement method is to focus the semiconductor laser light 21 using a focusing optical system consisting of a collimator lens with a numerical aperture of 0.3, a λ/2 plate, and a focusing lens with a numerical aperture of 06, and taper the light 21 with a minimum focused spot diameter of 5Xlμm. The light was focused on the waveguide. A phosphor was coated on the waveguide, and the scattered light from the waveguide surface was observed with a strike IJ camera, and the waveguide propagation mode and waveguide propagation loss were measured based on the intensity of the scattered light from the waveguide. As a result, by providing a cladding part in the input tapered optical waveguide part, the difference in refractive index between the waveguide, the cladding, and the end part was reduced, and it was possible to prevent the waveguide mode from becoming a multi-mode in the tapered part. As a result, the propagation loss due to the multi-mode waveguide has been greatly reduced, so the propagation loss at the tapered portion has decreased. An IdB input tapered waveguide was obtained. This value is very small compared to the 1 dB propagation loss of the conventional input tapered optical waveguide. As described above, according to this example, it was possible to construct an input tapered waveguide with little propagation loss.

In addition, in this implementation order, LINb03 was used as the substrate, but LINb03 doped with MgO, LI
Ferroelectric materials such as TaOa and KNb03. Any substrate that can form an optical waveguide can be used, such as a dielectric material such as SiO2, an organic material such as MNA, or a compound semiconductor such as ZnS.

(Example 2) FIG. 2 shows a configuration diagram of a wavelength conversion element in the second and third examples, in which a substrate made of a nonlinear optical material with a refractive index n1 and a substrate with a refractive index n2 (n 1<n
2), the optical waveguide, the tapered entrance part formed in the waveguide, and the refractive index n3 (nL<
The wavelength conversion element is characterized in that a semiconductor laser for exciting light is provided in the cladding portion of n3<n2 and the tapered waveguide. In FIG. 2, 5 is a substrate made of LiNb03, which is a +Z plate (the + side of the substrate cut perpendicular to the Z axis), which is a nonlinear optical material with a refractive index of 2.1, and 6 is a substrate formed by proton exchange treatment in phosphoric acid. 7 is a tapered entrance part with a refractive index of 2 or 3; 7 is a cladding part with a refractive index of 2.25 formed by annealing after proton exchange;
8 is a waveguide formed by proton exchange, and 9 is a semiconductor laser.

The operation of the wavelength conversion elements of the second and third embodiments configured as described above will be described below.

An input tapered waveguide 8 having an incidence 6 similar to that in Example 1 was formed on a nonlinear optical material LINbO3 substrate 5, and a semiconductor laser 5 with a wavelength of 0.8 μm and a light emitting area of 5×1 μm was aligned with this waveguide using a fine adjustment device. It was fixed with ultraviolet curing resin. Next, when the coupling efficiency between the semiconductor laser and the waveguide was measured, the coupling efficiency was 50%. This value is 1.6 times higher than the conventional coupling efficiency of 30% through a condensing optical system of a tapered waveguide and a semiconductor laser. Furthermore, a second harmonic with a wavelength of 0.4 μm is generated due to the nonlinear optical effect, and the second harmonic wave is 0.4 μm with respect to the semiconductor laser output of 80 mW.
A second harmonic component of mW could be obtained. This is 2.5 times the conventional value (second harmonic component 0.11 mW for semiconductor laser output 80 mW). Also, according to this configuration, a GX2X2mm LINb03 board and a length of 2
By directly connecting and integrating O0 μm semiconductor lasers, it was possible to form a small wavelength conversion element of 10×5×5 mm. As described above, according to this example, it was possible to form a small-sized, high-output wavelength conversion element.

In this implementation order, LINbOa is used as a substrate made of a nonlinear optical material, but LINbCh doped with MgO, LITa03. Ferroelectric materials such as KNbO3. Any substrate having a large nonlinear optical constant, such as an organic material such as MNA or a compound semiconductor such as ZnS, can be used.

(Example 3) FIG. 3 is a process perspective view of a method for manufacturing an input tapered waveguide in a fourth example. In this example, as a method for manufacturing an input taper waveguide, a case will be described in which an input taper waveguide is manufactured by proton exchange on a dielectric LINbOa substrate. In FIG. 3(a), Ta is applied to the LINbO3 substrate 11 of the +Z board (the tenth side of the board cut out perpendicular to the Z axis).
A protective mask was deposited at 300A by electron beam deposition. Next, a 0.5 μm thick photoresist was patterned on the protective mask by a normal photo process, and then the CF
4, the Ta protective mask was etched. Next, the photoresist was removed, and a Ta protective mask 12 serving as an ionization-resistant mask was formed. Next, as a second protective mask, a LiNbOs film with a thickness of I mm and both end faces optically polished was used.
The substrate 13 was crimped onto the Ta mask and fixed with a jig.

This substrate 11 was subjected to proton exchange in pyrophosphoric acid, a type of phosphoric acid, at a temperature of 230°C for 20 minutes to form a high refractive index layer with a refractive index of 2.3, and then annealed at 190°C for 1 hour. The refractive index of the proton exchange layer is lowered to 2.25 and the volume is increased to form a cladode layer 14 having a thickness of 2 μm. (b) shows the incident part 15 with a refractive index of 2.3 and a thickness of 1 μm after proton exchange in pyrophosphoric acid for 230″CIO minutes.
form. In (C), after removing the substrate 13, the substrate 11 is subjected to proton exchange in phosphoric acid at a temperature of 230°C for 5 minutes to form a high refractive index layer 16 with a refractive index of 2.3 and a thickness of 0.4 μm.
form. In (d), after removing the Ta mask 12, the surface perpendicular to the optical waveguide is optically polished. By this method, it is possible to manufacture an optical waveguide with partially different thicknesses and refractive indexes of ion exchange layers and a cladding layer in the input taper portion.

In addition, in this implementation order, after performing the first ion exchange with birophosphoric acid and then performing an annealing treatment to form the cladding layer 14,
Although the second ion exchange was performed with birophosphoric acid to form the entrance part and the refractive index of the entrance part and the cladding was changed, the acids used for the first ion exchange and the second ion exchange may also be changed. For example, the first ion exchange is performed with stearic acid, which has a refractive index of 2.
After forming the cladding part No. 2, a second ion exchange may be performed with pyrophosphoric acid to form an entrance part with a refractive index of 2.3, thereby changing the refractive index of the cladding part and the entrance part.

In addition, in this implementation order, LiNbOs was used as the substrate, but in addition, LINbO3 doped with MgO, LI
Any substrate that can form an optical waveguide by ion exchange can be used, such as a ferroelectric material such as TaO3 or KNb03, a dielectric material such as SL02, or an organic material such as MNA.

(Example 4) FIG. 4 is a process perspective view of a method for manufacturing an input tapered waveguide in a fifth example. In this example, as a method for manufacturing an input taper waveguide, a case will be described in which an input taper waveguide is manufactured by proton exchange on a dielectric LINbO3 substrate. In Figure 4 (a-), the +Z board (the tenth side of the board cut out perpendicular to the Z axis). A Ta2O6 protective mask was applied to the LiNb03 substrate 18 of 150A by electron beam evaporation.
Next, a 0.5 μm thick photoresist was patterned on the protective mask by a conventional photo process, and then the Ta206 protective mask was etched with CF4. Next, the photoresist is removed and Ta, 2O. A protective mask 19 was formed.

In (b), a Ta mask 2O was formed as a second protective mask on the Ta2O% protective mask by electron beam evaporation. This substrate 18 was subjected to proton exchange for 20 minutes at a temperature of 230'C in pyrophosphoric acid, a type of phosphoric acid, to form a high refractive index layer with a refractive index of 2.3, and then annealed at 190°C for 1 hour. and set the refractive index of the proton exchange layer to 2.2.
5 and the volume is increased to form a cladding layer 21 with a thickness of 2 μm. (C) shows the entrance part 22 with a thickness of 1 μm after proton exchange in pyrophosphoric acid for 230° CIO minutes.
form. In (d), after removing the Ta protective mask 19, the substrate 18 is subjected to proton exchange in phosphoric acid at a temperature of 230° C. for 5 minutes to form a high refractive index layer 23 with a refractive index of 2.3 and a thickness of 0.4 μm. .

(e) is °Ta2 0. After removing the protective mask 19, the surface 24 perpendicular to the optical waveguide is optically polished. By this method, it is possible to manufacture optical waveguides having partially different ion exchange layer thicknesses and refractive indexes with good mass productivity.

In addition, in this implementation order, after performing the first ion exchange with pyrophosphoric acid and then annealing to form the cladding layer 14, the second ion exchange is performed with pyrophosphoric acid to form the incident part. Although the refractive index of the cladding was changed, the acids used for the first ion exchange and the second ion exchange may also be changed. For example, the first ion exchange is performed with stearic acid and the refractive index is 2.
．． After forming the second cladding part, a second ion exchange may be performed with pyrophosphoric acid to form an entrance part with a refractive index of 2.3, thereby changing the refractive index of the cladding part and the entrance part.

In this implementation order, T.NbOa was used as the substrate, but MgO-doped LINbOa, T.T. t
Any substrate that can form an optical waveguide by ion exchange can be used, such as ferroelectric materials such as Taoa and KNbO3, dielectric materials such as SiO2, and organic materials such as gate NA.

In addition, in this enforcement order, T is used as an ionization-resistant protective mask.
a2 0. was used as the first protective mask and Ta as the second protective mask, SiO2 was used as the second mask, stearic acid was used as the first ion exchange, and Ta2O5 was used as the second ion exchange mask. By using pyrophosphoric acid as a replacement, an input tapered optical waveguide similar to Temo can be formed.

In addition, in this enforcement order, as an ionization-resistant protective mask,
Ta2O. However, a similar incident tapered optical waveguide can be formed using a Ta/Ta2Oa double mask as the first protective mask.

Effects of the Invention As explained above, a substrate with a refractive index of n1, an optical waveguide with a refractive index of n2 (nl<n2) formed on the substrate, a tapered entrance portion formed on the waveguide, and the area around the entrance portion By controlling the thickness and refractive index distribution of the cladding portion having a refractive index n3 (nl<n3<n2) formed in the cladding portion, the propagation mode in the tapered incident portion can be controlled. This makes it possible to expand the width of the propagation mode by widening the input section while keeping the propagation mode guided in the input section as the fundamental mode, and it is possible to couple the propagation mode to the waveguide while keeping the propagation mode as the fundamental mode. It is possible to construct an input tapered waveguide with little propagation loss, and its practical effects are great.

Further, a substrate with a refractive index n1 made of a nonlinear optical material, an optical waveguide with a refractive index n2 (nl<n2) formed on the substrate, a tapered entrance part formed on the waveguide, and a tapered entrance part formed around the entrance part. refractive index n3 (n 1<n3<n2)
By providing a semiconductor laser directly connected to the cladding portion and the tapered waveguide, it becomes possible to couple the light from the semiconductor laser to the single mode waveguide with high efficiency. This made it possible to increase the power density of light propagating through the waveguide, and greatly increase the wavelength conversion efficiency due to nonlinear optical effects. Further, by integrating the input tapered optical waveguide and the semiconductor laser, a condensing optical system is no longer required, so a compact and high-output wavelength conversion element can be constructed, and its practical effects are great.

In addition, as a method for manufacturing the above-mentioned input taper optical waveguide, an ionization-resistant mask material other than the dielectric material is formed on the surface of the dielectric material to prevent the underlying dielectric material from ionization and to form a thick one. A first mask is formed by locally covering an ionization-resistant mask layer that is thinner than the width of the optical waveguide to be used, and the first mask layer has a substantially flat surface and a layer of ionization-resistant mask material that is thinner than the width of the optical waveguide. A substrate capable of preventing ionization of the underlying dielectric material is crimped as a mask to form a second mask that locally covers the body, and then the body of dielectric material is subjected to a first ion exchange treatment to remove the non-masked material. The ions in the dielectric are exchanged with the treated ions to change the refractive index in the dielectric to form an optical waveguide, and then the second mask is removed and a second ion exchange is performed to partially remove the ions. This is an input taper optical waveguide manufacturing method characterized by performing a step of changing the thickness and refractive index distribution of the exchange layer.By using this force method, it is possible to easily and stably create a waveguide taper using a double mask, which was previously difficult. It became possible to create. Furthermore, when forming a cladding layer with a different refractive index from the waveguide at the entrance taper, the processing procedure is simplified by appropriately changing the substrate that forms the mask when performing annealing or ion exchange by changing the exchange ions. and its practical effects are great.

In addition, as a method for manufacturing the above-mentioned input taper optical waveguide with good mass productivity, a TaeOs film is locally deposited as an ionization-resistant mask material on the surface of the LiNbxTa1-xOs (0≦x≦1) substrate to form the first mask. A second mask is formed by locally depositing a Ta film as an ionization-resistant mask material on the surface of the first mask, and then a first proton exchange is performed on the substrate to make the non-mask area highly ionized. An input tapered optical waveguide characterized in that, after forming a refractive index layer, a step of removing the second mask and performing a second proton exchange to partially change the thickness and refractive index distribution of the proton exchange layer is performed. The manufacturing method makes it possible to form a double mask for ion exchange performed with a strong acid, and also to manufacture an input tapered optical waveguide having partially different refractive indexes with good mass production, which has great practical effects.

[Brief explanation of drawings]

FIG. 1 is a perspective view of the structure of an input tapered optical waveguide according to the present invention, FIG. 2 is a perspective view of the structure of a wavelength conversion element according to the present invention, and FIG. FIG. 4 is a perspective view of the steps in the method for manufacturing an input tapered waveguide according to the present invention, FIG. 5 is a perspective view of the basic configuration of a conventional input taper waveguide, and FIG. 6 is a basic configuration diagram of the conventional method for manufacturing an input taper optical waveguide. It is. 1 ●●● board. 2●●●Incidence part. 3●●-Clad part,
4*@● waveguide, 5●●● substrate made of nonlinear optical material, 6●●● incidence section, 7●●● cladding section, 8●-φ waveguide, 9●● tatami semiconductor laser. Name of agent: Patent attorney Shigetaka Awano Haka 1 person i&l@1&2 Figure 84' JR Route Map Tomomi Map

Claims (11)

[Claims] (1) A substrate with a refractive index n1, an optical waveguide with a refractive index n2 (n1<n2) formed on the substrate, a tapered entrance part formed on the waveguide, and a refractive index n3 formed around the entrance part An input tapered optical waveguide characterized by having a cladding portion (n1<n3<n2). (2) A substrate with a refractive index n1 made of a nonlinear material, an optical waveguide with a refractive index n2 (n1<n2) formed on the substrate, a tapered entrance part formed on the optical waveguide, and a tapered entrance part formed around the entrance part. A wavelength conversion element comprising: a cladding portion having a refractive index n3 (n1<n3<n2); a coherent light source; and a condensing optical system for exciting light from the coherent light source in the incident tapered optical waveguide. (3) A substrate with a refractive index n1 made of a nonlinear material, an optical waveguide with a refractive index n2 (n1<n2) formed on the substrate, a tapered entrance part formed in the waveguide, and a tapered entrance part formed around the entrance part. 1. A wavelength conversion element comprising a cladding portion having a refractive index n3 (n1<n3<n2) and at least one semiconductor laser directly connected to the incident tapered optical waveguide. (4) An ionization-resistant mask layer made of an ionization-resistant mask material other than the dielectric material on the surface of the dielectric material, capable of preventing the underlying dielectric material from ionization, and having a thickness thinner than the width of the optical waveguide to be formed. is locally deposited to form a first mask, and the first mask layer has a substantially flat surface and is made of an ionization-resistant mask material to prevent the underlying dielectric material from being ionized. a substrate that can be used as a mask is crimped to form a locally covering second mask, and the body of dielectric material is then subjected to a first ion exchange treatment to exchange ions in the dielectric with treated ions from the non-masked portions. forming an optical waveguide by changing the refractive index within the dielectric, and then removing the second mask and further performing a second ion exchange to partially change the thickness and refractive index distribution of the ion exchange layer. A method for manufacturing an input tapered optical waveguide, the method comprising: (5) LiNb_xTa_1_−_xO_3 (0≦x≦
1) Ta_2O on the substrate surface as an ionization-resistant mask material
A first mask is formed by locally depositing a _5 film, a Ta film is locally deposited as an ionization-resistant mask material on the surface of the first mask, and a second mask is then formed. After performing a first proton exchange on the substrate and forming a high refractive index layer on the non-masked portion, the second mask is removed and a second proton exchange is performed on the substrate.
1. A method for manufacturing an incident tapered optical waveguide, comprising performing a step of partially changing the thickness and refractive index distribution of a proton exchange layer by performing proton exchange. (6) LiNb_xTa_1_-_xO_3 as a substrate
(0≦x≦1) or MgO-doped LiNb
The wavelength conversion element according to any one of claims 2 and 3 to 5, characterized in that _xTa_1_-_xO_3 (0≦x≦1) is used. (7) LiNb_xTa_1_-_xO_3(0
5. The method for manufacturing an input tapered optical waveguide according to claim 4, characterized in that ≦x≦1) is used. (8) LiNb_xT with MgO doped on the substrate
The method for manufacturing an input tapered optical waveguide according to claims 4 and 5, characterized in that a_1_-_xO_3 (0≦x≦1) is used. (9) The method for manufacturing an input tapered optical waveguide according to claim 5, characterized in that SiO_2 is used as the second mask. (10) The method for manufacturing an input tapered optical waveguide according to claim 5, characterized in that a double mask of Ta_2O_5 film and Ta film is used as the first mask, and SiO_2 is used as the second mask. (11) The method for manufacturing an input tapered optical waveguide according to claim 5, wherein the first and second proton exchanges are performed using different acids.