JP3999736B2 - Wavelength conversion element and manufacturing method thereof - Google Patents

Description

  The present invention relates to a wavelength conversion element and a method for manufacturing the same, and more specifically, converts the wavelength of signal light to a different wavelength using a second harmonic generation, difference frequency generation, or sum frequency generation effect generated in a nonlinear optical medium. The present invention relates to a wavelength conversion element and a manufacturing method thereof.

  Conventionally, laser light sources are used in optical communication systems using wavelength division multiplexing or time division multiplexing, high-density recording media such as magneto-optical disks, and measuring instruments in the medical and measurement fields. The wavelengths required for these laser light sources are in a wide range from infrared to visible light. Therefore, in order to realize a laser light source having a wavelength that cannot be obtained by a semiconductor laser, a solid-state laser, or a gas laser, a wavelength conversion element using a nonlinear optical effect of a crystal has been developed (for example, see Patent Document 1).

  In a wavelength conversion element, phase matching between signal light and control light is important for efficient wavelength conversion. Therefore, a quasi-phase matching technique using a periodic domain-inverted structure that has a degree of design freedom and can be expected to have high conversion efficiency is widely used. On the other hand, a bulk type and a waveguide type are known as the structure of the wavelength conversion element. The waveguide type is easy to miniaturize and is widely used due to the progress of efficiency improvement by efficient confinement of light. A ridge-type waveguide structure is used as a typical waveguide-type structure.

As shown in FIG. 1, the ridge-type waveguide has a core 12 formed on the substrate 11 in accordance with the waveguide pattern, and has a step-type refractive index distribution. The core 12 has three side surfaces not in contact with the substrate 11 in contact with the air layer. For example, the substrate 11 is manufactured as follows using LiNbO ₃ (hereinafter abbreviated as LN) or LiTaO ₃ (hereinafter abbreviated as LT).

  First, the core layer is formed by any of the following four methods. (1) A core layer is formed on a LN or LT single crystal substrate by a liquid phase epitaxial (LPE) method. (2) A core layer having a refractive index higher than that of the substrate is formed by a Ti diffusion technique to the LN and LT single crystal substrates. (3) A core layer having a higher refractive index than that of the substrate is formed by performing proton exchange on the LN and LT single crystal substrates. (4) A thin LN / LT crystal substrate is bonded to and bonded to a dissimilar material substrate (material having a refractive index smaller than that of LN / LT) to form a core layer. Next, a waveguide pattern is formed on the core layer by photolithography, and the side surface of the core layer is processed by a dry etching method to produce a ridge-type waveguide.

  However, the LPE method (1) has a problem that the group V element contained in the flux used for the liquid phase crystal growth of the core layer causes optical damage and deteriorates device characteristics. Also in the Ti diffusion method (2), the Ti element causes optical damage and deteriorates the device characteristics. Accordingly, the proton exchange method (3) and the substrate bonding technique (4) have been used to fabricate a ridge-type waveguide for wavelength conversion elements using LN and LT crystals.

JP 2002-328405 A

  In the ridge-type optical waveguide, as described above, the under cladding layer is a single crystal substrate (refractive index is about 2), and the over cladding layer is air (refractive index is 1). Therefore, the refractive index in the depth direction (vertical direction in FIG. 1) is asymmetric, and the optical electric field distributions of the signal light and the control light are also asymmetric. For this reason, there is a problem that the wavelength conversion efficiency proportional to the overlap integral of the optical electric fields of the signal light and the control light does not increase because the overlap of the optical electric fields of the two is poor.

In order to increase the conversion efficiency of the wavelength conversion element, an over clad layer close to the refractive index of the under clad layer is formed on the core layer, the optical electric field distribution shape of the guided light is kept in a perfect circle, and the overlap integral is increased. It is necessary to. As a material of the over clad layer, for example, when LN or LT crystal is used for a substrate (under clad layer), LiNb _(x) Ta _(1-x) O ₃ (0 <x <1 ₎ having the same composition. ) Is an optimal material, and it is desirable to perform epitaxial growth by the LPE method.

However, high temperature growth of 1,000 ° C. or higher is necessary, and technical difficulty is high. Since the LPE method has a problem of optical damage due to mixing of flux components, the over clad layer is formed by the method described above. This method has not been put to practical use. In the case of forming a _{LiNb (x) Ta (1-} x) O 3 in other ways, this material include easily evaporated Li element, is difficult composition control by including three elements other than an oxygen element It has not been put into practical use due to the fact that it cannot be obtained and a practical film forming speed for obtaining a cladding thickness of 1 μm or more. The materials other than LN and LT have the same problems when the LPE method is not applied.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide a wavelength conversion element including an optical waveguide in which the refractive index in the depth direction is symmetric and optical damage due to impurity contamination does not occur. It is in providing the manufacturing method.

In order to achieve such an object, the present invention provides a ridge type in which a core made of a material having a nonlinear optical effect and having a periodically poled structure is formed on a substrate. In the wavelength conversion element including the optical waveguide, an amorphous structure having a composition made of Ta _(x) Nb _(2-x) O ₅ ( 0 <x <2 ) is provided on a surface of the core that is not in contact with the substrate. And an over clad layer having a thickness of 1 μm or more and 20 μm or less .

According to a second aspect of the present invention, the material having the nonlinear optical effect according to the first aspect is LiNbO ₃ , KNbO ₃ , LiTaO ₃ , KTaO ₃ , LiNb _(x) Ta _(1-x) O ₃ (0 <X <1), KNb _(x) Ta _(1-x) O ₃ (0 <x <1), Ba ₂ NaNb ₅ O ₁₅ , BaTiO ₃ , or Mg, Zn, Sc It is characterized by containing at least one selected from the group as an additive.

  According to a third aspect of the present invention, the composition (x) of the over clad layer according to the first or second aspect is constant so that a refractive index of the over clad layer is smaller than a refractive index of the core. It is controlled by a value.

  According to a fourth aspect of the present invention, in the composition (x) of the overcladding layer according to the first or second aspect, the refractive index of the overcladding layer is smaller than the refractive index of the core, and the outer periphery from the core It is characterized by being controlled to become gradually smaller toward the part.

The invention according to claim 5 is a method of manufacturing a wavelength conversion element including a ridge-type optical waveguide made of a material having a nonlinear optical effect and having a core having a periodic domain-inverted structure. A first step of bonding the first substrate having the periodic domain-inverted structure and the second substrate by diffusion bonding by heat treatment; and A second step of polishing to a predetermined thickness for forming; a third step of cutting the first substrate to form the core to produce a ridge-type optical waveguide; An amorphous structure having a composition made of Ta _(x) Nb _(2-x) O ₅ ( 0 <x <2 ) on the surface not in contact with the first substrate, and having a thickness of 1 μm or more and 20 μm or less Form a cladding layer Characterized by comprising a fourth step.

According to a sixth aspect of the present invention, the fourth step according to the fifth aspect includes a sputtering method, a physical vapor deposition method of an ion plating method, a thermal decomposition CVD method, and a chemical vapor deposition method of a sol-gel method. The over clad layer is formed by any of the above.

According to a seventh aspect of the present invention, in the fourth step of the fifth or sixth aspect , the ridge-type optical waveguide is heated to 600 ° C. or higher and 900 ° C. or lower to crystallize the over clad layer, It is characterized by reducing internal stress.

According to an eighth aspect of the present invention, in the fourth step according to the fifth, sixth or seventh aspect , the over clad layer is configured such that the refractive index of the over clad layer is smaller than the refractive index of the core. The composition (x) is controlled to a constant value.

According to a ninth aspect of the present invention, in the fourth step according to the fifth, sixth or seventh aspect , the refractive index of the over clad layer is smaller than the refractive index of the core, and from the core to the outer peripheral portion. The composition (x) of the over-cladding layer is controlled so as to become gradually smaller.

As described above, according to the present invention, since the over clad layer having the composition of Ta _(x) Nb _(2-x) O ₅ (0 ≦ x ≦ 2) is included, the refractive index in the depth direction is symmetric. Thus, it is possible to form a stable overcladding layer in which optical damage due to impurities is not caused.

  In addition, according to the present invention, since the refractive index can be easily controlled, it is possible to manufacture a small-sized and highly efficient wavelength conversion element and a single-mode propagation wavelength conversion element.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the present invention, an over cladding layer having a composition made of Ta _(x) Nb _(2-x) O ₅ (0 ≦ x ≦ 2) is formed around the core of the ridge-type optical waveguide used for the wavelength conversion element. The over clad layer having such a composition has a refractive index of 2.1 to 2.4. In addition, since it is composed of stable oxides Ta ₂ O ₅ and Nb ₂ O ₅ , there is no evaporation during film formation, and composition control is easy. Further, since no chemical reaction and interdiffusion occur with the core layer material, the optical properties of the core are not deteriorated.

  The thickness of the over clad layer is desirably 1 μm or more and 20 μm or less. This is because the protrusion of the optical electric field distribution of the guided light can be ignored if it is 1 μm or more, and the ridge type optical waveguide can be processed by a dicing saw if it is 20 μm or less.

Materials having nonlinear optical effects are LiNbO ₃ , KNbO ₃ , LiTaO ₃ , KTaO ₃ , LiNb _(x) Ta _(1-x) O ₃ (0 <x <1), KNb _(x) Ta _(1-x) O ₃ (0 <x <1), Ba ₂ NaNb ₅ O ₁₅ , or BaTiO ₃ , or contains at least one selected from the group consisting of Mg, Zn, and Sc as an additive . The core using such a nonlinear optical crystal has a refractive index of 2.0 to 2.5. Therefore, a stable over clad layer can be formed on this core.

The clad layer made of Ta _(x) Nb _(2-x) O ₅ (0 ≦ x ≦ 2) has an amorphous structure at a relatively low temperature of 200 to 600 ° C., and can be formed at high speed. Since the structure of the cladding layer is amorphous, the anisotropy of the refractive index can be eliminated. Further, the inside of the cladding layer can be crystallized by post-processing this cladding layer at a high temperature, or by forming a single crystal by forming a film at a temperature of 600 ° C. Stress can be reduced to improve mechanical strength.

  FIG. 2 shows a method for manufacturing a ridge-type waveguide according to an embodiment of the present invention. The LT single crystal plate 21 having a thickness of 500 μm is overlaid with the LN single crystal plate 22 having a thickness of 300 μm and having a Z-axis orientation, heat-treated in a vacuum at 400 ° C. for 1 hour, and bonded by diffusion bonding (FIG. 2A). The LN single crystal plate 22 functions as a core layer and the LT single crystal plate 21 undercladding layer. Note that the LN crystal plate 22 is formed with a periodic domain-inverted structure so that wavelength conversion is possible in a communication wavelength band having a wavelength of 1.5 μm. Next, the LN crystal plate 22 is polished to a thickness of 10 μm or less (FIG. 2B). Further, a waveguide pattern is formed by a dry etching process and processed into a ridge waveguide having a waveguide width of 10 μm or less (FIG. 2C).

A Ta ₂ O ₅ film (x = 1) is formed as an overcladding layer on the upper and side surfaces of this ridge-type waveguide by magnetron sputtering. FIG. 3 shows the configuration of the sputtering apparatus according to the first example. A substrate 32 on which a ridge-type waveguide is formed is placed on a substrate holder 31 with a heater. The sputter target 33 is a high-purity Ta metal disk having a diameter of 120 mm and a thickness of 5 mm, and is disposed so as to face the ridge waveguide substrate 32.

Magnets 34 a and 34 b are fixed on the back side of the sputter target 33, and a cycloid motion of electrons is generated by a magnetic field penetrating the sputter target 33. By increasing the plasma density on the front surface of the sputtering target 33, high-speed sputtering film formation is performed. The ridge waveguide substrate 32 is heated to 300 ° C. and oxygen gas is added to the argon sputtering gas to form a Ta ₂ O ₅ film at a rate of 0.1 μm / min in a sputtering mode in which the target is oxidized. In this manner, an amorphous Ta ₂ O ₅ film that is transparent, has a refractive index of 2.10 (wavelength of 1.5 μm), and a thickness of 10 μm or more is formed.

FIG. 4 shows a wavelength conversion element according to an embodiment of the present invention. The refractive index of the Ta ₂ O ₅ film 23 serving as the over cladding layer is close to the refractive index of the LT single crystal plate 21 of the under cladding layer. Moreover, since it has an amorphous structure, it is possible to form a good cladding film having no refractive index anisotropy. Furthermore, by making the diameter of the opposing sputter target 33 sufficiently larger than the waveguide cross-sectional width (10 μm or less), a thick Ta ₂ O ₅ film 23 adheres to the side surface of the ridge waveguide, and the cover ridge wraps around the waveguide. Will also be good.

According to Example 1, the refractive index at a wavelength of 1.5 μm is as follows: Ta ₂ O ₅ film 23 (over clad layer) = 2.10, core made of LN crystal plate 22 = 2.2, LT single crystal plate 21 (Under clad layer) = 2.14, so that a satisfactory buried optical waveguide can be manufactured.

  In Example 2, an optical waveguide is formed by bonding single crystal plates having different refractive indexes by impurity doping. A Zn-doped LN single crystal plate 22 having a thickness of 300 μm and having a Z-axis orientation is directly bonded to the Mg-doped LT single crystal plate 21 having a thickness of 500 μm in a vacuum (FIG. 2A). The Zn-doped LN crystal plate 22 is formed with a periodic domain-inverted structure so that wavelength conversion is possible in a communication wavelength band having a wavelength of 1.5 μm. Next, the LN crystal plate 22 is polished to a thickness of 10 μm or less (FIG. 2B). Further, a waveguide pattern is formed by a dry etching process and processed into a ridge waveguide having a waveguide width of 10 μm or less (FIG. 2C).

A Ta ₂ O ₅ film (x = 1) is formed as an overcladding layer on the upper and side surfaces of this ridge-type waveguide by magnetron sputtering. The configuration of the sputtering apparatus is the same as that shown in FIG. The ridge waveguide substrate 32 is formed by heating to 500 ° C. In this manner, an amorphous Ta ₂ O ₅ film that is transparent, has a refractive index of 2.10 (wavelength of 1.5 μm), and a thickness of 10 μm or more is formed.

  According to Example 2, since the same type of substrates having the same thermal expansion coefficient were bonded together, the temperature at the time of forming the over clad layer (500 ° C.) was higher than the temperature at which the substrates were directly bonded (400 ° C.). Regardless, it can be manufactured without causing damage or the like in the joint portion of the substrate.

  In Example 3, an LN single crystal plate 22 having a thickness of 300 μm and a Z-axis orientation is directly bonded to an LT single crystal plate 21 having a thickness of 500 μm in a vacuum (FIG. 2A). The LN crystal plate 22 is formed with a periodic domain-inverted structure so that wavelength conversion is possible in a communication wavelength band having a wavelength of 1.5 μm. Next, the LN crystal plate 22 is polished to a thickness of 10 μm or less (FIG. 2B). Further, a waveguide pattern is formed by a dry etching process and processed into a ridge waveguide having a waveguide width of 10 μm or less (FIG. 2C).

A Ta ₂ O ₅ film is formed as an overcladding layer on the upper and side surfaces of the ridge-type waveguide by a thermal decomposition CVD method. The ridge waveguide substrate is fixed in the reaction container by a carbon holder. As starting materials, Ta (OC ₂ H ₅ ) ₅ (including C ₂ H ₅ OH) and oxygen gas are used and supplied from an evaporator and a cylinder outside the reaction vessel. The ridge waveguide substrate was heated to 350 ° C. to form a film based on the following thermal decomposition reaction.
2Ta (OC ₂ H ₅ ) ₅ → Ta ₂ O ₅ + 5C ₂ H ₅ OH + 5C ₂ H ₄
The film formation rate is controlled by the evaporation temperature of Ta (OC ₂ H ₅ ) ₅ , the amount of C ₂ H ₅ OH added, and the oxygen gas flow rate, and is formed at a rate of 0.01 μm / min or more.

In this manner, an amorphous Ta ₂ O ₅ film 23 that is transparent, has a refractive index of 2.10 (wavelength of 1.5 μm), and a thickness of 10 μm or more is formed (FIG. 4). A thick Ta ₂ O ₅ film 23 is also attached to the side surface of the ridge waveguide, and the cover ridge surrounding the waveguide is also good. According to Example 3, the refractive index at a wavelength of 1.5 μm is as follows: Ta ₂ O ₅ film 23 (over clad layer) = 2.10, core made of LN crystal plate 22 = 2.2, LT single crystal plate 21 (Under clad layer) = 2.1, and a satisfactory buried optical waveguide can be manufactured.

In Example 4, a periodic domain-inverted structure is formed on a ZN-oriented LN single crystal plate so that wavelength conversion is possible in a communication wavelength band of 1.5 μm, and then diffusion-conducted by a proton exchange method. A crystal substrate on which a waveguide is formed is used. The side wall of the waveguide was exposed by a dry etching process to form a ridge waveguide. A Ta ₂ O ₅ film is formed as an overcladding layer on the upper and side surfaces of the ridge-type waveguide by magnetron sputtering. As the sputtering target, a Ta metal disk having a diameter of 120 mm and a thickness of 5 mm is used and disposed so as to face the ridge-type waveguide.

By heating the ridge waveguide substrate to 300 ° C. and adding oxygen gas to the argon sputtering gas, a Ta ₂ O ₅ film is formed at a rate of 0.1 μm / min in a sputtering mode in which the target is oxidized. In this manner, an amorphous Ta ₂ O ₅ film 23 that is transparent, has a refractive index of 2.10 (wavelength of 1.5 μm), and a thickness of 10 μm or more is formed (FIG. 4). By making the diameter of the opposing sputter target sufficiently larger than the waveguide cross-sectional width (10 μm or less), a thick Ta ₂ O ₅ film 23 is attached to the side surface of the ridge waveguide, and the cover ridge surrounding the waveguide is also good. Become.

According to Example 4, the refractive index at a wavelength of 1.5 μm is as follows: Ta ₂ O ₅ film 23 (over clad layer) = 2.10, core made of LN crystal plate 22 = 2.2, LT single crystal plate 21 (Under clad layer) = 2.14, so that a satisfactory buried optical waveguide can be manufactured.

In Example 5, a periodic domain-inverted structure is formed on a ZN-oriented LN single crystal plate so that wavelength conversion is possible in the communication wavelength band of 1.5 μm, and then diffusion-conducted by a proton exchange method. A crystal substrate on which a waveguide is formed is used. The side wall of the waveguide was exposed by a dry etching process to form a ridge waveguide. An Nb _(x) Ta _(2-x) O ₅ (0 ≦ x ≦ 2) film is formed as an overcladding layer on the upper and side surfaces of the ridge-type waveguide by a magnetron sputtering method.

In Example 5, the composition is selected so that the refractive index of the film is 2.15. Considering the refractive index of Ta ₂ O ₅ = 2.1 and the refractive index of Nb ₂ O ₅ = 2.3, the composition of x = 0.25, that is, Nb _0.25 Ta _1.75 O ₅ is selected. . A Ta / Nb alloy plate whose composition is adjusted is used as the sputtering target, and is arranged so as to face the ridge-type waveguide.

The ridge waveguide substrate is heated to 300 ° C. to form a film at a rate of 0.1 μm / min in an atmosphere of argon sputtering gas and oxygen gas. In this way, an amorphous Nb _0.25 Ta _1.75 O ₅ film having a thickness of 10 μm or more is formed. By making the diameter of the facing sputtering target sufficiently larger than the waveguide cross-sectional width (10 μm or less), a thick film adheres also to the side surface of the ridge waveguide, and the cover ridge that wraps the waveguide becomes good.

According to Example 5, the refractive index at a wavelength of 1.5 μm is as follows: Nb _0.25 Ta _1.75 O ₅ film (over clad layer) = 2.15, core made of LN crystal plate = 2.2, LT Single crystal plate (under clad layer) = 2.14, and a satisfactory buried optical waveguide can be manufactured. According to Example 5, single mode light propagation can be realized by adjusting the refractive index of the over cladding layer to a value close to the refractive index of the LT single crystal plate.

In Example 6, after forming a periodic domain-inverted structure on a ZN-oriented LN single crystal plate so that desired wavelength conversion is possible, a crystal substrate on which a diffusion waveguide is formed by a proton exchange method is used. Use. The side wall of the waveguide was exposed by a dry etching process to form a ridge waveguide. An Nb _(x) Ta _(2-x) O ₅ (0 ≦ x ≦ 2) film is formed as an overcladding layer on the upper and side surfaces of the ridge-type waveguide by a magnetron sputtering method.

In Example 6, x = 0.25 at the initial stage of film formation is continuously changed to x = 0. That is, the composition of the over clad is a gradient composition that changes from Nb _0.25 Ta _1.25 O ₅ to Ta ₂ O ₅ . FIG. 5 shows the configuration of the sputtering apparatus according to Example 6. A substrate 32 on which a ridge-type waveguide is formed is placed on a substrate holder 31 with a heater. A Ta metal disc having a diameter of 120 mm and a thickness of 5 mm is used for the sputter target 33 and is disposed so as to face the ridge waveguide substrate 32. Further, the Nb metal targets 36a and 36b divided into two are used independently, and are arranged directly above or obliquely above the ridge waveguide substrate 32.

The power supplied from the sputtering power source 35 to the sputtering target 33 (Ta metal target) is kept constant, and the power supplied from the sputtering power source 37 to the Nb metal targets 36a and 36b is Nb _0.25 Ta _1.75 O ₅ . The composition control was performed by continuously decreasing the power value to zero. The ridge waveguide substrate 32 is heated to 300 ° C. and formed at a rate of 0.1 μm / min in an atmosphere of argon sputtering gas and oxygen gas.

In this way, an amorphous Nb _(x) Ta _(2-x) O ₅ (0 ≦ x ≦ 0.25) film having a thickness of 2 μm or more is formed. The refractive index of the over clad layer decreases from the core of the ridge-type waveguide toward the outer peripheral portion, and continuously changes from 2.15 to 2.10 (wavelength: 1.5 μm). By using such an overcladding layer, although it is an overcladding layer thinner than those of Examples 1 to 5, light confinement, improvement in overlap integral of optical fields of signal light and control light, and single mode An equivalent effect can be obtained in light propagation. In addition, the thickness of the over clad layer for obtaining the same effect is at least 1 μm or more.

  In Example 7, the ridge waveguide manufactured in Examples 1 to 6 is heat-treated in a higher temperature environment than during film formation. The treatment atmosphere is vacuum or air, and the treatment temperature is 600 ° C. or higher. In any film formation method such as sputtering, ion plating, or thermal decomposition CVD, the substrate temperature is raised and the high temperature treatment is performed without removing the substrate from the chamber or reaction vessel after film formation. The over clad layer is amorphous at the time of film formation, but is crystallized by heating at 600 ° C. or higher for 1 hour or longer. Further, in the sputtering method, argon gas is taken into the film at the time of film formation, but there is an effect that the argon gas is released from the film by external diffusion by the high temperature treatment.

  Due to the densification and gas release due to the structural change of the film, the internal stress of the over clad layer is reduced and the mechanical strength is increased. In general, when a clad is formed on a waveguide substrate, the substrate tends to warp due to a bimetallic effect caused by a difference in thermal expansion coefficient between the film and the substrate and a volume expansion effect due to gas occlusion. However, according to Example 7, warpage of the substrate can be significantly reduced by densification and gas release, and an optical waveguide of 50 mm or more can be manufactured.

  In Example 8, an LN single crystal plate 22 having a thickness of 300 μm and a Z-axis orientation is directly bonded to an LT single crystal plate 21 having a thickness of 500 μm in a vacuum (FIG. 2A). The LN single crystal plate 22 is formed with a periodic domain-inverted structure so that wavelength conversion is possible at a specific wavelength from visible to mid-infrared. Next, the LN crystal plate 22 is polished to a thickness of 10 μm or less (FIG. 2B). Further, a waveguide pattern is formed by a dry etching process and processed into a ridge waveguide having a waveguide width of 10 μm or less (FIG. 2C).

A Ta ₂ O ₅ film is formed as an overcladding layer on the upper and side surfaces of the ridge-type waveguide by a sol-gel method. As a starting material, a stabilized alkoxide obtained by reacting Ta (OC ₂ H ₅ ) ₅ and ethanolamine is used. Water is added to this to produce a sol liquid that is hydrolyzed and polymerized. A ridge type waveguide fixed to a turntable using a spinner is coated with a sol solution and dried. Further, the ridge-type waveguide was heated to 600 ° C. in the atmosphere, and the film was baked to obtain a single crystallized film of Ta ₂ O ₅ film.

The film thickness in this process is about 0.1 μm. This process is repeated to form a transparent Ta ₂ O ₅ film 23 having a refractive index of 2.2 to 2.1 (wavelength of 633 nm to 1.5 μm) and a thickness of 5 μm or more (FIG. 4). By repeatedly forming a thin single crystal film, the internal stress of the over clad layer can be relaxed and densified, so that a clad having high mechanical strength without warping of the substrate can be formed. A thick Ta ₂ O ₅ film 23 is also attached to the side surface of the ridge waveguide, and the cover ridge surrounding the waveguide is also good. In this way, an optically and structurally high quality cladding can be formed.

  A compact and highly efficient wavelength converter capable of providing a wavelength converter capable of single-mode light propagation, and being applied to a laser light source with a wide range of output light wavelengths from infrared to visible light. Can do.

It is sectional drawing which shows the structure of the conventional ridge type waveguide. It is a figure which shows the manufacturing method of the ridge type waveguide concerning one Embodiment of this invention. It is a figure which shows the structure of the sputtering device concerning Example 1. FIG. It is sectional drawing which shows the wavelength conversion element concerning one Embodiment of this invention. It is a figure which shows the structure of the sputtering device concerning Example 6. FIG.

Explanation of symbols

11 Substrate 12 Core 21 LT Single Crystal Plate 22 LN Single Crystal Plate 23 Ta ₂ O ₅ Film 31 Substrate Holder 32 Ridge Waveguide Substrate 33 Sputter Target 34a, 34b Magnet 35, 37 Sputtering Power Supply 36a, 36b Nb Metal Target

Claims (9)

In a wavelength conversion element including a ridge type optical waveguide in which a core made of a material having a nonlinear optical effect and having a periodically domain-inverted structure is formed on a substrate,
The surface of the core that is not in contact with the substrate has an amorphous structure composed of Ta _(x) Nb _(2-x) O ₅ ( 0 <x <2 ) and has a thickness of 1 μm or more and 20 μm or less. A wavelength conversion element comprising an over cladding layer. The material having the nonlinear optical effect is LiNbO ₃ , KNbO ₃ , LiTaO ₃ , KTaO ₃ , LiNb _(x) Ta _(1-x) O ₃ (0 <x <1), KNb _(x) Ta _{(1-x )} O ₃ (0 <x <1), Ba ₂ NaNb ₅ O ₁₅ , BaTiO ₃ , or at least one selected from the group consisting of Mg, Zn, and Sc as an additive The wavelength conversion element according to claim 1, wherein:   The composition (x) of the over clad layer is controlled to a constant value so that the refractive index of the over clad layer is smaller than the refractive index of the core. The wavelength conversion element as described.   The composition (x) of the over clad layer is controlled such that the refractive index of the over clad layer is smaller than the refractive index of the core and gradually decreases from the core toward the outer peripheral portion. The wavelength conversion element according to claim 1 or 2. In a method of manufacturing a wavelength conversion element including a ridge-type optical waveguide made of a material having a nonlinear optical effect and having a core having a periodically poled structure,
A first step of bonding the first substrate and the second substrate made of a material having the nonlinear optical effect and having the periodic domain-inverted structure by diffusion bonding by heat treatment;
A second step of polishing the first substrate to a predetermined thickness for forming the core;
A third step of cutting the first substrate to form the core and producing a ridge-type optical waveguide;
The surface of the core that is not in contact with the first substrate has an amorphous structure having a composition of Ta _(x) Nb _(2-x) O ₅ ( 0 <x <2 ), and has a thickness of 1 μm or more and 20 μm. And a fourth step of forming an overcladding layer as described below . A method for manufacturing a wavelength conversion element, comprising:   The fourth step is characterized in that the over clad layer is formed by any one of a sputtering method, a physical vapor deposition method of an ion plating method, a thermal decomposition CVD method, and a chemical vapor deposition method of a sol-gel method. The manufacturing method of the wavelength conversion element of Claim 5.   7. The fourth step according to claim 5, wherein the ridge type optical waveguide is heated to 600 ° C. or higher and 900 ° C. or lower to crystallize the over clad layer and reduce internal stress. Manufacturing method of the wavelength conversion element. The fourth step is characterized in that the composition (x) of the over clad layer is controlled to a constant value so that the refractive index of the over clad layer is smaller than the refractive index of the core. The method for producing a wavelength conversion element according to 5, 6 or 7 . In the fourth step, the composition (x) of the over clad layer is set so that the refractive index of the over clad layer is smaller than the refractive index of the core and gradually decreases from the core toward the outer peripheral portion. The method of manufacturing a wavelength conversion element according to claim 5, 6 or 7 , wherein control is performed.

Images