阅读说明：本技术 光波长转换器及光波长转换器的制造方法 (Optical wavelength converter and method for manufacturing optical wavelength converter ) 是由 长能重博 藤原巧 高桥仪宏 寺门信明 于 2019-02-07 设计创作，主要内容包括：根据实施例的光波长转换器包括：由晶体材料或非晶体材料构成的基板；多个第一结晶区域,其具有放射状第一极化有序结构；以及多个第二结晶区域,其具有放射状第二极化有序结构。在该基板上限定有第一区域和第二区域,当从与虚拟轴线正交的基准方向观察基板时,第一区域和第二区域在夹着虚拟轴线的情况下彼此直接相邻。位于第一区域中的第一极化有序结构的放射中心和位于第二区域中的第二极化有序结构的放射中心沿着虚拟轴线交替地布置。多个第一结晶区域的一部分地突出到第二区域。多个第二结晶区域的一部分地突出到第一区域。(An optical wavelength converter according to an embodiment includes: a substrate composed of a crystalline material or an amorphous material; a plurality of first crystalline regions having a radially first poled ordered structure; and a plurality of second crystalline regions having a radially second polarization ordered structure. A first region and a second region are defined on the substrate, and the first region and the second region are directly adjacent to each other with the virtual axis therebetween when the substrate is viewed from a reference direction orthogonal to the virtual axis. The radial centers of the first polarized ordered structures located in the first region and the radial centers of the second polarized ordered structures located in the second region are alternately arranged along the virtual axis. A portion of the plurality of first crystalline regions protrudes partially into the second region. A portion of the plurality of second crystallization regions partially protrudes into the first region.)

1. An optical wavelength converter comprising:

a substrate comprised of a crystalline material or an amorphous material, the substrate having a first region and a second region, the first region and the second region defined as such: the first region and the second region are directly adjacent to each other with the virtual axis interposed therebetween when the substrate is viewed from a reference direction orthogonal to the virtual axis set in the substrate;

a plurality of first crystalline regions respectively having a radial first polarization ordered structure in which radial centers of the radial first polarization ordered structures are arranged along the virtual axis in the first region of the substrate, each of the plurality of first crystalline regions partially protruding to the second region across the virtual axis when the substrate is viewed from the reference direction; and

a plurality of second crystal regions respectively having a radial second polarization order structure in which radial centers of the radial second polarization order structures are arranged along the virtual axis in the second region of the substrate, each of the plurality of second crystal regions partially protruding to the first region across the virtual axis in a state in which the radial centers of the radial second polarization order structures and the radial centers of the radial first polarization order structures are alternately arranged along the virtual axis when the substrate is viewed from the reference direction.

2. The optical wavelength converter of claim 1,

the substrate has a channel optical waveguide structure with the virtual axis as an optical axis.

3. The optical wavelength converter of claim 1,

the substrate comprises a crystalline body of a Titanite type, BaO-TiO₂-GeO₂-SiO₂Glass series and SrO-TiO₂-SiO₂Is at least one kind of glass.

4. The optical wavelength converter of claim 3,

the substrate comprises BaO-TiO₂-GeO₂-SiO₂Glass series and SrO-TiO₂-SiO₂Is at least one of a group glass, and further includes, as an additive, a metal contained in lanthanides, actinides, and any of groups 4 to 12.

5. A method of manufacturing an optical wavelength converter, comprising:

a preparation step of preparing a substrate composed of a crystalline material or an amorphous material, the substrate having a first region and a second region defined as follows: the first region and the second region are directly adjacent to each other with the virtual axis interposed therebetween when the substrate is viewed from a reference direction orthogonal to the virtual axis set in the substrate; and

a first processing step of providing, in the substrate, a plurality of first crystal regions and a plurality of second crystal regions, the plurality of first crystal regions respectively having a radial first polarization ordered structure in which radial centers of the radial first polarization ordered structures are arranged along the virtual axis, the plurality of second crystal regions respectively having a radial second polarization ordered structure in which radial centers of the radial second polarization ordered structures are arranged along the virtual axis, each of the plurality of first crystal regions partially protruding to the second region across the virtual axis when the substrate is viewed from the reference direction, and when the substrate is viewed from the reference direction, in a state in which the radial centers of the radial second polarization ordered structures and the radial centers of the radial first polarization ordered structures are alternately arranged Each of the plurality of second crystallization regions partially protruding to the first region across the virtual axis, and

wherein the first processing step includes a laser irradiation step, and

the laser irradiation step includes irradiating each of a plurality of first convergence points corresponding to the radial center of the radial first polarized ordered structure of the plurality of first crystal regions and each of a plurality of second convergence points corresponding to the radial center of the radial second polarized ordered structure of the plurality of second crystal regions with laser light to form the radial first polarized ordered structure and the radial second polarized ordered structure.

6. The method of manufacturing an optical wavelength converter according to claim 5,

the laser has a wavelength contained in an absorption band of the substrate.

7. The method of manufacturing an optical wavelength converter according to claim 5,

the laser includes a first laser for generating a high-density excited electron region on a surface of the substrate or inside the substrate and a second laser for heating the high-density excited electron region, and

the laser irradiation step includes irradiating each of the plurality of first convergence points and each of the plurality of second convergence points with the first laser light and the second laser light in a state where a convergence region of the second laser light overlaps a convergence region of the first laser light.

8. The method of manufacturing an optical wavelength converter according to claim 7,

the first laser includes an fs laser having a pulse width of less than 1ps and having a wavelength outside an absorption band of the substrate or a wavelength that suppresses an amount of light absorbed by the substrate to be low.

9. The method of manufacturing an optical wavelength converter according to claim 7,

the second laser light includes a pulse laser light having a pulse width of 1ps or more and having a wavelength outside an absorption band of the substrate or a wavelength suppressing an amount of light absorbed by the substrate to be low in a region other than the condensing region of the first laser light.

10. The method of manufacturing an optical wavelength converter according to claim 7,

the second laser light includes CW laser light having a wavelength outside an absorption band of the substrate or a wavelength that suppresses an amount of light absorbed by the substrate to be low in a region other than the condensing region of the first laser light.

11. The method of manufacturing an optical wavelength converter of claim 5, further comprising:

a second processing step of forming a channel optical waveguide structure on the substrate with the virtual axis as an optical axis before or after the laser irradiation step.

12. The method of manufacturing an optical wavelength converter according to claim 11,

the channel optical waveguide structure is formed by dicing or dry etching.

13. The method of manufacturing an optical wavelength converter according to claim 5,

the laser irradiation step includes irradiating the substrate with the laser light via an optical member configured to shape a light intensity distribution of the laser light into a top hat shape.

14. The method of manufacturing an optical wavelength converter according to claim 13,

the optical member includes a diffractive optical element or an aspheric lens.

15. The method of manufacturing an optical wavelength converter according to claim 5,

the light source of the laser comprises CO₂A laser.

16. The method of manufacturing an optical wavelength converter according to claim 5,

the laser irradiation step includes irradiating the substrate with the laser in a state where a light absorbing material is disposed on a surface of the substrate.

17. The method of manufacturing an optical wavelength converter according to claim 16,

the light absorption material is carbon paste.

Technical Field

The present invention relates to an optical wavelength converter and a method for manufacturing the optical wavelength converter.

This application claims priority from japanese patent application No.2018-021281, filed on 8.2.2018, the entire contents of which are incorporated herein by reference.

Background

Materials for optical devices utilizing second-order nonlinear optical phenomena mainly include ferroelectric optical crystals such as LiNbO₃(LN) crystal, KTiOPO₄(KTP) crystal and LiB₃O₅(LBO) crystals and β -BaB₂O₄(BBO) crystal. Optical devices using these crystals have been developed in a wide range of application fields with wavelength conversion as a main application. In the field of laser processing, for example, Second Harmonic Generation (SHG) of fiber lasers is used to shorten the wavelength of optical devices using these crystals. Such an optical device is used in fine processing since the diameter of the beam spot can be reduced. In the field of optical communications, in order to effectively utilize wavelength resources in Wavelength Division Multiplexing (WDM) optical communications, optical devices using these crystals are used as optical wavelength converters that perform simultaneous wavelength conversion from C-band WDM signals to L-band signals. Further, in the field of measurement, attention is paid to terahertz spectrum that allows observation of intermolecular vibration caused by hydrogen bond or the like, and an optical device using these crystals is used as a light source for generating terahertz light.

Recently, compound semiconductor crystals such as GaAs, GaP, GaN, CdTe, ZnSe, and ZnO have also been used as materials for optical devices utilizing second-order nonlinear optical phenomena. Due to significant advances in the technology of manufacturing periodic spatially polarized structures, these materials have attracted attention as materials for second-order nonlinear optical devices, for which periodic spatially polarized structures are essential, in addition to having large second-order nonlinear optical constants.

Schemes of wavelength conversion can be classified as angular phase matching and periodically poled quasi-phase matching (QPM). Among them, quasi-phase matching enables various phase matching wavelengths to be generated and wavelength-converted in all transparent regions of a material by appropriately designing a polarization pitch. In addition, quasi-phase matching has no walk-off angle caused by angular phase matching, beam quality is excellent, and the interaction length can be made long. Therefore, the quasi-phase matching is a method suitable for improving efficiency and suppressing coupling loss, and is effective in processing, measurement, and the like.

CITATION LIST

Patent document

Patent document 1: PCT International application publication No.2017/110792

Non-patent document

Non-patent document 1: r.gatass and e.mazur, Nature Photonics 2, p.219(2008)

Non-patent document 2: ito et al, "ultrasonic and precision drilling of glass substrate absorption of fiber-laser inter-ferromagnetic-induced filing", Applied Physics Letters, Vol.113,2018, pp.061101-1

Disclosure of Invention

The optical wavelength converter of the present disclosure includes: a substrate composed of a crystalline material or an amorphous material; a plurality of first crystalline regions having a radial first polarization ordered structure, respectively; and a plurality of second crystalline regions having radially second polarization-ordered structures, respectively. In the substrate, the first region and the second region are defined as follows: when the substrate is viewed from a reference direction orthogonal to a certain virtual axis set in the substrate, the first region and the second region are directly adjacent to each other with the virtual axis sandwiched therebetween. In a first region of the substrate, the radial centers of the first polarization ordered structures are arranged along a virtual axis. When the substrate is viewed from the reference direction, each of the plurality of first crystalline regions partially protrudes to the second region across the virtual axis. In a second region of the substrate, the radial centers of the second polarization ordered structures are arranged along the virtual axis, and the radial centers of the second polarization ordered structures alternate with the radial centers of the first polarization ordered structures along the virtual axis. Each of the plurality of second crystallization regions partially protrudes to the first region across the virtual axis when the substrate is viewed from the reference direction.

The method for manufacturing the optical wavelength converter according to the present invention comprises: a preparation step of preparing a substrate; and a first processing step of providing, in the substrate, a plurality of first crystal regions each having a radial first polarization ordered structure and a plurality of second crystal regions each having a radial second polarization ordered structure. The substrate is composed of a crystalline material or an amorphous material. In addition, in the substrate, a first region and a second region are defined, and the first region and the second region are directly adjacent to each other with the virtual axis therebetween when the substrate is viewed from a reference direction orthogonal to a certain virtual axis set in the substrate. In the first region of the substrate, radial centers of the first polarization ordered structures of the plurality of first crystalline regions are arranged along the virtual axis. In addition, each of the plurality of first crystal regions partially protrudes to the second region across the virtual axis when the substrate is viewed from the reference direction. On the other hand, in the second region of the substrate, the radiation centers of the second polarization ordered structures of the plurality of second crystal regions are arranged along the virtual axis. In addition, each of the plurality of second crystalline regions partially protrudes to the first region across the virtual axis in a state where the radiation center of the second polarization ordered structure and the radiation center of the first polarization ordered structure are alternately arranged along the virtual axis when the substrate is viewed from the reference direction. The first processing step includes a laser irradiation step of irradiating each of a plurality of first convergence points corresponding to radial centers of the first polarized ordered structures of the plurality of first crystal regions and each of a plurality of second convergence points corresponding to radial centers of the second polarized ordered structures of the plurality of second crystal regions with laser light to form the first polarized ordered structures and the second polarized ordered structures.

Drawings

Fig. 1 is a sectional view showing the structure of an optical wavelength converter 1A according to one embodiment of the present invention.

Fig. 2 is an enlarged plan view of the crystalline regions 10A and 10B.

FIG. 3 is a flow chart illustrating a method of manufacturing according to one embodiment.

Fig. 4 is a view showing a state where a plurality of convergence points P1 and a plurality of convergence points P2 are set on the substrate 2.

Fig. 5 is a graph illustrating an example of a light intensity distribution of laser light according to an embodiment.

Fig. 6 is a sectional view showing the configuration of an optical wavelength converter 1B according to a first modification.

Fig. 7 is a graph showing an example of the light intensity distribution of the laser light for forming the crystallization regions 10A and 10B of the first modification.

Fig. 8 is a diagram showing an example of an optical system configured to obtain the light intensity distribution shown in fig. 7.

Fig. 9A is a sectional view showing the configuration of an optical wavelength converter 1C according to a second modification.

Fig. 9B is a graph showing the electric field distribution in the wavelength converting region B1.

Fig. 9C is a graph showing the electric field distribution in the wavelength converting region B2.

Fig. 10A is a plan view showing the configuration of an optical wavelength converter 1D according to a third modification of the above-described embodiment.

Fig. 10B is a sectional view taken along line IXb-IXb of fig. 10A.

Fig. 10C is a cross-sectional view taken along line IXc-IXc of fig. 10A.

Fig. 11 is a sectional view showing one step of a method for manufacturing an optical wavelength converter according to the fourth modification of the above-described embodiment.

Fig. 12 is a sectional view showing one step of a method for manufacturing an optical wavelength converter according to a fifth modification.

Fig. 13A is a schematic diagram for describing the polarization orientation in the crystallized region formed using the laser having the light intensity distribution shown in fig. 5.

Fig. 13B is a schematic diagram for describing the polarization orientation in the crystalline region formed by the method for manufacturing an optical wavelength converter according to the fifth modification.

FIG. 14A is a schematic diagram showing the use of a catalyst derived from CO₂Laser irradiation of SrO-TiO with laser₂-SiO₂Optical microscope image of the state after glass attachment.

Fig. 14B is a partially enlarged view of fig. 14A.

FIG. 15A is a schematic diagram showing the use of a catalyst derived from CO₂Laser irradiation of SrO-TiO with laser₂-SiO₂Optical microscope image of the state after glass attachment.

Fig. 15B is a partially enlarged view of fig. 15A.

FIG. 16A is a schematic diagram showing the use of a catalyst derived from CO₂Laser irradiation of SrO-TiO with laser₂-SiO₂Optical microscope image of the state after glass attachment.

Fig. 16B is a partially enlarged view of fig. 16A.

Fig. 17 is an image showing the measurement result of the second harmonic generation.

Detailed Description

[ problem to be solved by the invention ]

As a result of examining the conventional optical wavelength converter, the inventors found the following problems. That is, as an optical wavelength converter that performs quasi-phase matching, an optical device obtained by combining in-situ molding of glass and a wavelength conversion technique has been proposed (for example, see patent document 1). Such an optical wavelength converter has an advantage that since the base material is glass, the glass can be processed into various shapes such as a fiber shape and a film shape, and a wavelength conversion function can be imparted to the shape. Patent document 1 describes a method of forming a polarization ordered structure defined by polarization orientation by irradiating laser light in a state where an electric field is applied. Meanwhile, the polarized ordered structures achieving quasi-phase matching are fine, and the interval between adjacent polarized ordered structures is extremely short. In such a structure, the interval between the positive electrode and the negative electrode configured to apply an electric field is narrowed, and therefore, there is a problem that the process step is complicated in order to avoid dielectric breakdown when a high voltage is applied.

The present invention has been made to solve such problems, and an object thereof is to provide an optical wavelength converter capable of forming a polarization-ordered structure for realizing quasi-phase matching by a simple method, and a method for manufacturing the same.

[ Effect of the present disclosure ]

According to the optical wavelength converter and the manufacturing method thereof of the present invention, the crystal regions having the radially polarized ordered structure are alternately formed along the virtual axis in the pair of regions sandwiching the virtual axis.

[ description of various embodiments of the present disclosure ]

First, the contents of the various embodiments of the present disclosure will be separately listed and described.

(1) As one aspect, an optical wavelength converter according to one embodiment of the present disclosure includes: a substrate composed of a crystalline material or an amorphous material; a plurality of first crystalline regions having a radial first polarization ordered structure, respectively; and a plurality of second crystalline regions having radially second polarization-ordered structures, respectively. In the substrate, the first region and the second region are defined as follows: the first region and the second region are directly adjacent to each other with the virtual axis therebetween when the substrate is viewed from a reference direction orthogonal to a certain virtual axis set in the substrate. In a first region of the substrate, the radial centers of the first polarization ordered structures are arranged along a virtual axis. When the substrate is viewed from the reference direction, each of the plurality of first crystal regions partially protrudes to the second region across the virtual axis. In a second region of the substrate, the radial centers of the second polarization ordered structures are disposed along the virtual axis, and the radial centers of the second polarization ordered structures alternate with the radial centers of the first polarization ordered structures along the virtual axis. Each of the plurality of second crystallization regions partially protrudes to the first region across the virtual axis when the substrate is viewed from the reference direction.

In the optical wavelength converter having the above structure, the radially polarized ordered structures are alternately arranged on both sides of the virtual axis. Therefore, polarization orientations that are opposite to each other and intersect the virtual axis alternately occur on the virtual axis. Thus, quasi-phase matching of periodic polarization can be performed on light propagating on the virtual axis. Further, by irradiating the substrate with a laser beam having a wavelength included in the absorption wavelength of the substrate or by forming a heat source on the surface of the substrate or inside the substrate, each crystal region of the optical wavelength converter can be easily formed.

(2) As an aspect of the present embodiment, the substrate preferably has a channel optical waveguide structure with the virtual axis as an optical axis. The channel optical waveguide structure can improve the light propagation efficiency on the virtual axis. As an aspect of this embodiment, the substrate preferably includes a fresnoite-type crystal (crystal), BaO-TiO₂-GeO₂-SiO₂Glass series and SrO-TiO₂-SiO₂Is at least one kind of glass. For example, by irradiating laser light on these substrates, the above-described radially polarized ordered structure can be easily formed. Further, as an aspect of the embodiment, the substrate may include BaO-TiO₂-GeO₂-SiO₂Glass series and SrO-TiO₂-SiO₂Is at least one of the group glasses, and may further include, as an additive, a metal contained in any of the lanthanoid elements, the actinoid elements, and the groups 4 to 12. In this case, the absorption of laser light in the substrate can be enhanced, and the above-described radially polarized ordered structure can be formed more efficiently.

(3) As one aspect, a method of manufacturing an optical wavelength converter according to one embodiment of the present disclosure includes: a preparation step of preparing a substrate; and a first processing step of providing a plurality of first crystal regions and a plurality of second crystal regions in the substrate, each of the first crystal regions having a radial first polarization ordered structure, and each of the second crystal regions having a radial second polarization ordered structure. The substrate is composed of a crystalline material or an amorphous material. In addition, in the substrate, a first region and a second region are defined, and the first region and the second region are directly adjacent to each other with the virtual axis therebetween when the substrate is viewed from a reference direction orthogonal to a certain virtual axis set in the substrate. In the first region of the substrate, radial centers of the first polarization ordered structures of the plurality of first crystalline regions are arranged along the virtual axis. In addition, each of the plurality of first crystal regions partially protrudes to the second region across the virtual axis when the substrate is viewed from the reference direction. On the other hand, in the second region of the substrate, the radiation centers of the second polarization ordered structures of the plurality of second crystal regions are arranged along the virtual axis. In addition, each of the plurality of second crystalline regions partially protrudes to the first region across the virtual axis in a state where the radiation center of the second polarization ordered structure and the radiation center of the first polarization ordered structure are alternately arranged along the virtual axis when the substrate is viewed from the reference direction.

In particular, the first processing step comprises a laser irradiation step. In the laser irradiation step, each of a plurality of first convergence points corresponding to the radiation centers of the first polarized ordered structures of the plurality of first crystal regions and each of a plurality of second convergence points corresponding to the radiation centers of the second polarized ordered structures of the plurality of second crystal regions are irradiated with laser light to form the first polarized ordered structures and the second polarized ordered structures. Each crystal region of the optical wavelength converter can be easily formed by irradiating the substrate with a laser beam having a wavelength included in the absorption wavelength of the substrate or by forming a heat source on the surface of the substrate or in the substrate. That is, according to this manufacturing method, a polarization ordered structure for realizing quasi-phase matching can be formed in a simple manner.

(4) As an aspect of the present embodiment, the laser light for forming the polarization ordered structure preferably has a wavelength included in an absorption band of the substrate. In this case, the substrate can be directly heated by irradiation with laser light. In addition, as one mode of the present embodiment, the laser light for forming the polarization ordered structure may include a first laser light for generating a high-density excited electron region on the surface of the substrate or inside the substrate and a second laser light for heating the high-density excited electron region. In this configuration, in the laser light irradiation step, each of the plurality of first convergence points and each of the plurality of second convergence points are irradiated with the first laser light and the second laser light in a state where a convergence region of the second laser light overlaps with a convergence region of the first laser light. In this case, a heat source configured to form a polarization ordered structure may be formed at an arbitrary position on the surface of the substrate or inside the substrate.

(5) Incidentally, various types of laser light may be applied to the first laser light and the second laser light. For example, as one aspect of the present embodiment, it is preferable that the first laser includes an fs (femtosecond) laser whose pulse width is less than 1ps and has a wavelength outside an absorption band of the substrate or a wavelength that suppresses the amount of light absorbed by the substrate to be low. In addition, as one aspect of the present embodiment, it is preferable that the second laser light includes a pulse laser light having a pulse width of 1ps or more and preferably 1ns or more and having a wavelength outside an absorption band of the substrate or a wavelength suppressing an amount of light absorbed by the substrate to be low in a region other than a convergence region of the first laser light. As one aspect of the present embodiment, the second laser light may include a Continuous Wave (CW) laser light having a wavelength outside an absorption band of the substrate or a wavelength that suppresses an amount of light absorbed by the substrate to be low in a region other than a convergence region of the first laser light.

The convergence region of the first laser light refers to a region where excited electrons are generated at a high density (high-density excited electron region) centered on the convergence point of the first laser light, and is defined as a density of the number of excited electrons of 10¹⁹/cm³The above region. In addition, a state in which the convergence region of the first laser light and the convergence region of the second laser light overlap each other (hereinafter, referred to as an overlapping state) includes not only a state in which the convergence point of the first laser light and the convergence point of the second laser light coincide with each other but also a state in which the convergence points do not coincide with each other. Specifically, even if the second laser beam is not present at the converging point of the second laser beam, the second laser beam does not exist at a high densityIn the case of the laser region (the region where the first laser light is condensed), the overlap state also includes a state where the spot diameter of the second laser light is narrowed so that the high-density excited electron region exists entirely or at least partially in the irradiation region of the second laser light. When a first laser light (fs laser light) is condensed within an amorphous substrate (e.g., precursor glass), a high-density excited electron region is temporarily generated in a region where the fs laser light is condensed. If the second laser light (pulse laser light or CW laser light) is emitted so as to overlap the condensed region with the high-density excited electron region (the condensed region of the first laser light) while generating the high-density excited electron region, light absorption can be preferentially and selectively generated only in a local region of the high-density excited electron region. At this time, heat is generated in the light absorption region (a convergence region where the first laser light and the second laser light overlap each other), and a crystalline region is formed. By three-dimensionally scanning a convergence region where the first laser light and the second laser light overlap each other on the surface of the substrate or inside the substrate, a high-efficiency optical wavelength converter having various forms such as a block shape and an optical fiber shape can be realized.

(6) As one aspect of the present embodiment, the manufacturing method may further include a second processing step of forming the tunnel optical waveguide structure having the virtual axis as the optical axis on the substrate before or after the laser irradiation step. As a result, the light propagation efficiency on the virtual axis can be improved. In addition, as an aspect of the present embodiment, the channel optical waveguide structure is preferably formed by dicing or dry etching. As a result, the channel optical waveguide structure can be easily formed on the substrate composed of a crystalline material or an amorphous material.

(7) As one aspect of the present embodiment, in the laser irradiation step, the substrate is preferably irradiated with the laser light via an optical member configured to shape the light intensity distribution of the laser light into a top hat shape. As a result, melting of the substrate at the central portion of each crystallization region is suppressed, and generation of voids at the center of each crystallization region can be suppressed. In addition, as an aspect of the present embodiment, the above-mentioned optical member preferably includes a diffractive optical element or an aspherical lens. As a result, laser light having a top-hat-shaped light intensity distribution can be easily generated.

(8) As an aspect of this embodiment, the light source of the laser may comprise CO₂A laser. As a result, the substrate can be irradiated with laser light in the infrared region included in the absorption wavelengths of many substrates at a relatively high light intensity.

(9) As an aspect of the embodiment, in the laser irradiation step, the substrate may be irradiated with the laser in a state where the light absorbing material is disposed on the surface of the substrate. As a result, the absorption of laser light in the substrate can be enhanced, and the above-described radially-polarized ordered structure can be formed more efficiently. Further, as an aspect of one embodiment of the present invention, the light absorbing material is preferably carbon paste. As a result, a light absorbing material that effectively absorbs laser light can be easily arranged on the substrate.

As described above, each aspect listed in [ description of embodiments of the present disclosure ] may be applied to each of the remaining aspects or all combinations of these remaining aspects.

[ detailed description of the embodiments of the present disclosure ]

Hereinafter, specific examples of the optical wavelength converter and the method of manufacturing the optical wavelength converter of the present disclosure will be described in detail with reference to the accompanying drawings. Incidentally, the present disclosure is not limited to these examples, but is shown by the claims, and equivalents and any modifications within the scope of the claims are intended to be included therein. In addition, the same elements in the description of the drawings will be denoted by the same reference numerals, and redundant description will be omitted. Further, in the following description, unless otherwise specified, the positional relationship between the respective elements (regions, axes, etc.) means the positional relationship on the substrate surface.

Fig. 1 is a sectional view showing the structure of an optical wavelength converter 1A according to one embodiment of the present disclosure, and shows a section of the optical wavelength converter 1A along an optical waveguide direction D1. As shown in fig. 1, the optical wavelength converter 1A according to the present embodiment includes a substrate 2 composed of a crystalline material or an amorphous material. The substrate 2 is a substrate having a flat plate face (surface), and has a pair of end faces 2a and 2b arranged opposite to each other along the optical waveguide direction D1. In this implementationIn the example, the end faces 2a and 2b are orthogonal to the optical waveguide direction D1 and parallel to each other. The substrate 2 has a characteristic of transmitting at least light of a predetermined wavelength. The predetermined wavelength is, for example, a wavelength in the range of 400nm to 4500 nm. Examples of the constituent material of the substrate 2 include a crystalline of the Titanite type, BaO-TiO₂-GeO₂-SiO₂Glass series and SrO-TiO₂-SiO₂Is at least one kind of glass.

The substrate 2 includes: a plurality of crystal regions 10A (first crystal regions) each having a ring-like planar shape (a shape substantially defined on the surface of the substrate 2) when the substrate 2 is viewed from a reference direction orthogonal to the optical waveguide direction D1, and a plurality of crystal regions 10B (second crystal regions) each having a ring-like planar shape. Fig. 2 is an enlarged plan view of the crystalline regions 10A and 10B. The crystalline regions 10A and 10B are regions each having a radially polarized ordered structure. The polarization ordered structure refers to a structure in which spontaneous polarization is oriented in a specific manner. The crystal region 10A of the present embodiment has a radially polarized ordered structure in which the spontaneous polarization a1 extends radially from the radial center O1 of the crystal region 10A toward the outer periphery. Similarly, the crystal region 10B of the present embodiment has a radially polarized ordered structure in which the spontaneous polarization a2 extends radially from the radial center O2 of the crystal region 10B toward the outer periphery. As will be described later, the polarization ordered structure is formed by irradiating the substrate 2 with, for example, laser light in the infrared region. When the substrate 2 comprises BaO-TiO₂-GeO₂-SiO₂Glass series and SrO-TiO₂-SiO₂When at least one of the glasses is used, the substrate 2 may include a metal included in any of lanthanoid elements, actinoid elements, and group 4 to 12 elements as an additive to enhance absorption of laser light having a specific wavelength in the infrared region. Examples of lanthanide or actinide metals include Yb, Tm, and Er. In addition, examples of the metals belonging to groups 4 to 12 include Ti, Cr, and Zn.

As shown in fig. 1, the substrate 2 has a pair of regions 2c and 2d sandwiching a certain virtual axis AX set on the substrate 2. The pair of regions 2c and 2d are regions directly adjacent to each other with the virtual axis sandwiched therebetween when the substrate 2 is viewed from a reference direction orthogonal to the virtual axis. Then, the radiation centers O1 of the plurality of crystal regions 10A (which coincide with the radiation centers of the polarization ordered structures) are located in the region 2c of one of the two regions, and are arranged in a line at equal intervals along the virtual axis AX. In addition, the radiation centers O2 (which coincide with the radiation center of the polarization ordered structure) of the plurality of crystal regions 10B are located in another region 2d and are arranged in a line at equal intervals along the virtual axis AX. The radial centers O1 of the plurality of crystal regions 10A and the radial centers O2 of the plurality of crystal regions 10B are alternately arranged along the extending direction of the virtual axis AX (the optical waveguide direction D1). In other words, when the surface of the substrate 2 is viewed from the direction D2 intersecting the extending direction of the virtual axis AX, the radiation centers O1 and O2 are alternately arranged on the surface of the substrate 2. Therefore, a straight line connecting the radiation centers O1 and O2 adjacent to each other intersects the virtual axis AX at an angle greater than 0 ° and less than 90 ° on the surface of the base plate 2. Further, a first straight line connecting the plurality of radiation centers O1 and a second straight line connecting the plurality of radiation centers O2 are parallel to the virtual axis AX, respectively. The virtual axis AX is located between these first and second straight lines. That is, the distance between each of the plurality of radiation centers O1 and the virtual axis AX is equal, and the distance between each of the plurality of radiation centers O2 and the virtual axis AX is equal. In addition, the distance between the radiation center O1 and the virtual axis AX and the distance between the radiation center O2 and the virtual axis AX are equal to each other. In other words, the axis (line defined by the surface of the base plate 2) corresponding to the virtual axis AX is parallel to such a straight line: the straight line connects midpoints of line segments connecting the radiation centers O1 and O2 adjacent to each other on the surface of the substrate 2.

Each crystal region 10A partially protrudes to the region 2d side across the virtual axis AX. That is, each crystal region 10A has a portion overlapping with the virtual axis AX. In addition, each crystal region 10B partially protrudes to the region 2c across the virtual axis AX. That is, each crystal region 10B has a portion overlapping with the virtual axis AX. On the virtual axis AX, the crystal regions 10A and the crystal regions 10B are alternately arranged.

The substrate 2 also has a void (laser processing mark) 12A in each of the crystalline regions 10A. The planar shape of the aperture 12A (the shape defined on the surface of the substrate 2) is a circle centered on the radiation center O1. The outer periphery of the void 12A is in contact with the inner periphery of the crystallization region 10A. In addition, the substrate 2 also has a void (laser processing mark) 12B in each of the crystal regions 10B. The planar shape of the aperture 12B is a circle centered on the radiation center O2. The outer periphery of the void 12B is in contact with the inner periphery of the crystallization region 10B. These voids 12A and 12B are holes (recesses or voids) generated when a part of the substrate 2 is melted by laser irradiation.

In the optical wavelength converter 1A having the above-described structure, the wavelength conversion region B1 is formed inside the substrate 2. The wavelength conversion region B1 is an optical waveguide extending along the optical waveguide direction D1 with the virtual axis AX as the optical axis. One end B1a of the wavelength converting region B1 reaches the end face 2a of the substrate 2, and the other end B1B of the wavelength converting region B1 reaches the end face 2B of the substrate 2. Light of a predetermined wavelength incident from the one end B1a propagates in the wavelength conversion region B1, and then exits from the other end B1B.

Next, an example of a method for manufacturing the optical wavelength converter 1A of the present embodiment having the above-described structure will be described. Fig. 3 is a flowchart showing the manufacturing method of the present embodiment. First, in the preparation step of preparing the substrate 2, a raw material (in SrO-TiO) of the substrate 2 is weighed₂-SiO₂Sr in the case of glass series₂CO₃、TiO₂And SiO₂) Then, these raw materials are mixed (step S1). The above-mentioned metal for enhancing laser absorption may be added to the mixed raw materials, if necessary. Next, the raw materials are heated and melt-mixed, and the molten raw materials are poured into a flat plate-like mold, cooled and molded to finally obtain the substrate 2 (step S2). The melting temperature is, for example, 1500 ℃, and the melting time is, for example, one hour. Subsequently, heat treatment is performed on the substrate 2 to eliminate deformation of the substrate 2 (step S3). At this time, the heat treatment temperature is, for example, 760 ℃, and the heat treatment time is, for example, one hour. Thereafter, mirror polishing is performed on both plate surfaces (obverse and reverse surfaces) of the substrate 2 (step S4).

Next, a first processing step of providing the plurality of crystal regions 10A and the plurality of crystal regions 10B on the substrate 2 is performed. The first processing step includes a laser irradiation step. As an example of the laser irradiation step, when a laser having a wavelength included in the absorption wavelength of the substrate 2 is used, the plurality of crystal regions 10A and the plurality of crystal regions 10B are formed by irradiating the plate surface of the substrate 2 with the laser. Specifically, as shown in fig. 4, a plurality of convergence points P1 (first convergence points) and a plurality of convergence points P2 (second convergence points) are set on the substrate 2. That is, the plurality of convergence points P1 are located in one region 2c of the regions sandwiching the virtual axis AX, and are arranged in a line along the virtual axis AX on the surface of the base plate 2. In addition, a plurality of convergence points P1 are located in another region 2d and arranged in a line along the virtual axis AX. Further, the plurality of convergence points P1 and the plurality of convergence points P2 are alternately arranged in the extending direction of the virtual axis AX (i.e., in the optical waveguide direction D1). In other words, when the surface of the substrate 2 is viewed from the direction D2 intersecting the extending direction of the virtual axis AX, the convergence point P1 and the convergence point P2 are alternately arranged. A first straight line connecting the plurality of convergence points P1 and a second straight line connecting the plurality of convergence points P1 are parallel to the virtual axis AX. The virtual axis AX is located between these first and second straight lines. That is, the distance between each of the plurality of convergence points P1 and the virtual axis AX is equal, and the distance between each of the plurality of convergence points P1 and the virtual axis AX is equal. In addition, the distance between the convergence point P1 and the virtual axis AX is equal to the distance between the convergence point P2 and the virtual axis AX. In other words, the axis corresponding to the virtual axis AX (the line defined on the surface of the base plate 2) is parallel to such a straight line: the straight line connects the midpoints of line segments connecting the convergence points P1 and P2 adjacent to each other on the surface of the substrate 2 together.

Then, the laser light is sequentially emitted to the plurality of convergence points P1 and P2 (step S5). As a result, the substrate 2 is locally crystallized, and a plurality of crystal regions 10A having radial spontaneous polarization with the plurality of convergence points P1 as the radial center are formed (see fig. 1), and a plurality of crystal regions 10B each having a radial polarized ordered structure with the plurality of convergence points P2 as the radial center are formed (see fig. 1). In this step, the power density and irradiation time of the laser light are adjusted so that each crystal region 10A protrudes to the region 2d side across the virtual axis AX, and each crystal region 10B protrudes to the region across the virtual axis AXThe side of the domain 2c protrudes. Incidentally, in the example of the laser light irradiation step described above, the wavelength of the laser light is an arbitrary wavelength contained in an absorption band (for example, far infrared region) of the material forming the substrate 2. In this step, the laser light is condensed by a condensing lens as necessary to increase the power density so that the temperature of the region locally heated by the absorbed energy becomes 800 ℃ or higher. As a light source of the laser, for example, CO capable of outputting high-intensity far infrared light₂A laser is preferred. When the substrate 2 is made of SrO-TiO₂-SiO₂When made of glass, CO₂The transmission of the laser light in the 10.6 μm band is about a few percent. Thus, CO may be used₂A laser is used to make the substrate 2 absorb a large amount of laser light, thereby forming the crystallization regions 10A and 10B appropriately. Incidentally, the light source is not limited to CO₂A laser as long as heat required for crystallization can be locally applied.

Fig. 5 is a graph showing an example of the light intensity distribution of the laser light in the present embodiment. In fig. 5, the horizontal axis represents the radial position, and the vertical axis represents the light intensity. In addition, a broken line E1 is a crystallization threshold of the substrate 2, and a broken line E2 is a processing (melting) threshold of the substrate 2. As shown in fig. 5, in the present embodiment, the laser light emitted toward the substrate 2 has a light intensity distribution such as a gaussian distribution. That is, the light intensity at the center is highest, and the light intensity gradually decreases as the distance from the center increases. Then, the light intensity at the center exceeds the processing (melting) threshold of the substrate 2. According to the laser light having such a light intensity distribution, the power density in the vicinity of the convergence points P1 and P2 becomes high, and therefore, the substrate 2 is locally melted to form the apertures 12A and 12B. In addition, the power density has a magnitude between the crystallization threshold and the processing (melting) threshold in the vicinity of the pores 12A and 12B, thereby forming crystallized crystalline regions 10A and 10B.

At the end of the first processing step, heat treatment is performed on the substrate 2 to eliminate the deformation of the substrate 2 again (step S6). At this time, the heat treatment temperature is, for example, 760 ℃, and the heat treatment time is, for example, one hour. The light wavelength converter 1A according to the present embodiment is manufactured by the above-described manufacturing step and the first processing step (including the laser irradiation step).

Effects obtained by the optical wavelength converter 1A and the manufacturing method thereof according to the above-described present embodiment will be described. In the light wavelength converter 1A and the manufacturing method thereof according to the present embodiment, when the surface (laser irradiated surface) of the substrate 2 is observed, the radial polarization ordered structures are alternately arranged on both sides of the virtual axis AX. Therefore, in the wavelength conversion region B1 including the virtual axis AX, polarization orientations that intersect the virtual axis AX and are opposite to each other (180 degrees reversed) periodically and alternately occur. Thus, quasi-phase matching of the periodic polarization can be performed on the light propagating in the wavelength converting region B1. In addition, each of the crystal regions 10A, 10B of the optical wavelength converter 1A of the present embodiment can be easily formed by irradiating the substrate 2 with laser light having a wavelength included in the absorption band of the substrate 2. In the manufacturing method of the present embodiment, the crystal regions 10A and 10B can be formed by irradiating the substrate 2 with laser light having a wavelength included in the absorption band of the substrate 2. That is, according to the optical wavelength converter 1A and the manufacturing method thereof of the present embodiment, a polarization-ordered structure configured to realize quasi-phase matching can be formed with a simple method.

In addition, as in the present embodiment, the substrate 2 may include a crystalline of the titanosilicate type, BaO-TiO₂-GeO₂-SiO₂Glass series and SrO-TiO₂-SiO₂Is at least one kind of glass. For example, the above-described radially polarized ordered structure can be easily formed in these substrates 2 by irradiation of laser light. Furthermore, when the substrate 2 comprises BaO-TiO₂-GeO₂-SiO₂Glass series and SrO-TiO₂-SiO₂When at least one of the glasses is used, the substrate 2 may include the following metals as additives: the metal is included in the lanthanides, actinides, and any of groups 4 to 12. As a result, absorption of laser light in the substrate 2 is enhanced, and the above-described radially polarized ordered structure can be formed more efficiently.

In addition, CO₂A laser may be used as a light source of the laser as in the present embodiment. As a result, absorption with a large number of substrates can be used in a state having a relatively high light intensityThe substrate 2 is irradiated with laser light in the infrared region in the wavelength band.

(first modification)

Fig. 6 is a sectional view showing the configuration of an optical wavelength converter 1B according to a first modification of the above-described embodiment. The difference between this modification and the above-described embodiment is the shape of the crystalline regions 10A and 10B. In other words, the crystal regions 10A and 10B of the present modification are not annular but circular with the radial centers O1 and O2 of the radially polarized ordered structure as the center. The crystal regions 10A and 10B include emission centers O1 and O2, respectively. Therefore, the light wavelength converter 1B of the present modification does not include the apertures 12A and 12B.

Fig. 7 is a graph showing an example of the light intensity distribution of the laser light used to form the crystallization regions 10A and 10B of the present modification. In fig. 7, the horizontal axis represents the radial position, and the vertical axis represents the light intensity. The broken line E1 is the crystallization threshold of the substrate 2, and the broken line E2 is the processing (melting) threshold of the substrate 2. As shown in fig. 7, in the present modification, the laser light emitted toward the substrate 2 has a top hat (flat top) shaped light intensity distribution. That is, the light intensity is substantially constant in the region within a certain radius from the center, and the light intensity gradually decreases with increasing distance from the center in the outer region. Then, the light intensity in a region within a certain radius from the center is higher than the crystallization threshold of the substrate 2 and lower than the processing (melting) threshold. According to such light intensity distribution, the power density in the vicinity of the convergence points P1 and P2 becomes lower than the melting threshold, and therefore, the substrate 2 does not melt, and the voids 12A and 12B are not formed. In addition, in the regions within a certain radius from the convergence points P1 and P2, the watt density becomes a magnitude between the crystallization threshold and the processing (melting) threshold, thereby forming the crystalline regions ( crystalline regions 10A and 10B).

According to the optical wavelength converter 1B of the present modification, the same effects as those of the above-described embodiment can be obtained. In addition, since the light intensity distribution of the laser light has a top hat shape as in the present modification, melting of the substrate 2 in the central portion of each of the crystal regions 10A and 10B can be suppressed, and formation of the voids 12A and 12B at the centers of the respective crystal regions 10A and 10B can be suppressed. As a result, deterioration of device performance due to cracks or the like caused by the pores 12A and 12B can be suppressed.

In manufacturing the optical wavelength converter 1B of the present modification, the substrate 2 may be irradiated with laser light via the following optical members: the optical member changes the intensity distribution of the laser light into a top hat shape as shown in fig. 7. Examples of such optical members include Diffractive Optical Elements (DOEs), aspherical lenses, and the like. With such an optical member, laser light having a top-hat-shaped light intensity distribution can be easily generated.

Fig. 8 is a diagram showing an example of an optical system configured to obtain the light intensity distribution shown in fig. 7. In the example shown in fig. 8, an optical member OP1 is disposed between a laser light source (which may also include an optical system configured to collimate the laser light La) 30 that outputs collimated laser light La and the convergence point. The condensing lens 40A and the diffractive optical element 50 are arranged as the optical member OP1 in this order from the laser light source 30 toward the convergence point. In this configuration, the light intensity distribution I1 of the laser light La between the laser light source 30 and the condenser lens 40A has a gaussian distribution shape shown in fig. 5. On the other hand, the light intensity distribution I2 at the converging point of the laser light La having passed through the condenser lens 40A and the diffractive optical element 50 has a top-hat shape shown in fig. 7. Incidentally, the optical member OP1 may also be replaced with an optical member OP2 including an aspherical lens 40B. Even when the optical member OP2 is arranged between the laser light source 30 of the laser light La and the convergence point, the shape of the light intensity distribution I2 at the convergence point is a top hat shape.

(second modification)

Fig. 9A is a sectional view showing the configuration of an optical wavelength converter 1C according to a second modification of the above-described embodiment. This modification is different from the above-described embodiment in that, similarly to the first modification, the crystalline regions 10A, 10B include the radial centers O1, O2 of the radially polarized ordered structure but do not have the pores 12A, 12B, and the crystalline regions 10A, 10B are alternately arranged even in the direction D2 intersecting with the optical waveguide direction D1. In this configuration, the same wavelength conversion region B1 as in the above-described embodiment can be formed by the crystal regions 10A and 10B located on both sides of a certain virtual axis AX. In addition, the wavelength converting region B2 may be formed of the crystal regions 10A and 10B located on both sides of one virtual axis AX1 and the crystal regions 10B and 10A located on both sides of a virtual axis AX2 adjacent to the virtual axis AX1 (the crystal region 10B is common to the crystal region 10B on the virtual axis AX1 side). That is, the wavelength conversion region B2 is a region that includes two virtual axes AX1 and AX2 and extends along the optical waveguide direction D1. The width of the wavelength converting region B2 along the direction D2 is substantially equal to the period of the radiation center O1 along the direction D2 (i.e., the period of the convergence point P1).

Fig. 9B and 9C are graphs showing electric field distributions that can effectively perform wavelength conversion in the wavelength conversion regions B1 and B2, respectively. The horizontal axis represents the electric field intensity, and the vertical axis represents the position in the direction D2. As shown in FIG. 9B, in the wavelength conversion region B1, the electric field intensity distribution is at LP₀₁Mode (fundamental mode). On the other hand, as shown in fig. 9C, in the wavelength conversion region B2, the electric field intensity distribution is at LP₁₁Mode(s). Even in such an electric field mode, wavelength conversion is appropriately performed. Incidentally, in the wavelength conversion region B2, the electric field intensity distribution is at LP before and after wavelength conversion₁₁Mode(s).

(third modification)

Fig. 10A is a plan view showing the configuration of an optical wavelength converter 1D according to a third modification of the above-described embodiment. Fig. 10B is a sectional view taken along a line IXb-IXb of fig. 10A, and shows a section intersecting with the optical waveguide direction D1. Fig. 10C is a sectional view taken along line IXc-IXc of fig. 10A, and shows a section intersecting optical waveguide direction D1. In the optical wavelength converter 1D according to the present modification, the substrate 2 has a channel optical waveguide structure 21 having the virtual axis AX as an optical axis. The channel optical waveguide structure 21 has a pair of side surfaces 21a and 21b extending along the virtual axis AX. In one example, in a cross section of the substrate 2 along the line IXb-IXb, one side face 21a is located between the virtual axis AX and the radiation center O1. In a cross section of the base plate 2 along the line IXc-IXc, the other side face 21b is located between the virtual axis AX and the radiation center O2. The side faces 21a and 21b are obtained, for example, by a second processing step before or after step S5 (step equivalent to the laser light irradiation step) shown in fig. 3. In this second processing step, the portion of the substrate 2 located outside the channel optical waveguide structure 21 is removed by dry etching, so that the side faces 21a and 21b can be easily formed.

As in the present modification, the optical wavelength converter according to the present embodiment may also be provided with the substrate 2 having the channel optical waveguide structure 21 with the virtual axis AX as the optical axis. In addition, the manufacturing method of the optical wavelength converter may further include the second processing step of forming the channel optical waveguide structure 21 in the substrate 2 as described above. As a result, the light propagation efficiency on the virtual axis AX (wavelength conversion region B1) can be improved.

Incidentally, as a method for forming the channel optical waveguide structure in the substrate 2 (second processing step), various methods other than the above-described method are conceivable. Examples of such methods include, for example: a method of cutting the substrate 2 with a dicing saw while leaving a portion as a channel optical waveguide structure, a method of locally changing the refractive index by diffusing additives such as Ge and Ti into the substrate 2, a method of forming a channel optical waveguide structure inside the substrate 2 by a proton (H +) exchange method, and the like.

(fourth modification)

Fig. 11 is a sectional view showing a step in the manufacturing method of the optical wavelength converter according to the fourth modification of the above-described embodiment, and shows a section of the substrate 2 intersecting the optical waveguide direction D1. In the present modification, in step S5 (step corresponding to the laser light irradiation step) shown in fig. 3, the substrate 2 on which the light absorbing material 31 is disposed is irradiated with the laser light La. The light absorbing material 31 contains a material having absorption in a wavelength band including the wavelength of the laser La. Methods of disposing the light absorbing material 31 on the surface of the substrate 2 include coating, sputtering, vapor deposition, and the like. The light absorbing material 31 is composed of, for example, a carbonaceous material, and in one example, a carbon paste (a conductive paste obtained by adding carbon particles as a filler to a resin).

According to the method of the present modification, absorption of the laser light La in the substrate 2 is enhanced, and the radially polarized ordered structure can be formed more efficiently. In addition, in this case, a carbon paste may be appliedIs a light absorbing material 31. Thereby, the light absorbing material 31 that effectively absorbs laser power is easily arranged on the substrate 2. In addition, the carbon paste has a wide absorption band, and thus can absorb CO₂And light of a wavelength band of oscillation such as a fiber laser, a solid laser, and a semiconductor laser other than the laser. Further, after laser irradiation, the carbon paste can be easily removed by washing or the like.

Incidentally, various methods other than the above-described method may be considered as a method of improving the laser light absorption efficiency. For example, there is a method of: the light absorption rate of the substrate 2 is increased in advance by a reduction reaction before laser irradiation, and the light absorption rate is recovered by an oxidation reaction after laser irradiation.

(fifth modification)

Fig. 12 is a diagram showing one step of a method of manufacturing a light wavelength converter according to the fourth modification of the above-described embodiment, and is a diagram for describing a laser irradiation step corresponding to step S5 of fig. 3. Although the laser light La having a wavelength included in the absorption band of the substrate 2 is used in the above modification, in the present modification, the first laser light Lb1 and the second laser light Lb2 are emitted as laser light for forming a polarization ordered structure, the first laser light Lb1 is used for generating a high-density excited electron region on the substrate surface or in the substrate, and the second laser light Lb2 is used for heating the high-density excited electron region. That is, in the laser light irradiation step, each of the plurality of convergence points P1 and each of the plurality of convergence points P2 are irradiated with the first laser light Lb1 and the second laser light Lb2 in a state where the convergence region of the second laser light Lb2 overlaps with the convergence region of the first laser light Lb 1.

Incidentally, the first laser light Lb1 is suitably an fs laser whose pulse width is less than 1ps and has a wavelength outside the absorption band of the substrate 2, or has a wavelength that can suppress the amount of light absorbed by the substrate 2 to be low. In addition, the second laser light Lb2 is suitably a pulsed laser light having a pulse width of 1ps or more, and preferably 1ns or more, and having a wavelength outside the absorption band of the substrate 2, or having a wavelength that suppresses the amount of light absorbed by the substrate 2 to be low in a region other than the region where the first laser light Lb1 converges. The second laser light Lb2 may be a CW laser light having a wavelength outside the absorption band of the substrate 2, or a wavelength that can suppress the amount of light absorbed by the substrate 2 to be low in a region other than the region where the first laser light Lb1 converges. As a light source for irradiating the second laser light Lb2, a laser light source such as the above-described CO2 laser, fiber laser, semiconductor laser, and solid-state laser is suitable.

It is known that a high-density excited electron region is instantaneously generated in a convergence region of fs laser light applicable to the first laser light Lb1 according to irradiation conditions (non-patent document 1). In addition, laser light having a pulse width of 1ns or more (e.g., 1070nm wavelength) applicable to the second laser light Lb2 is emitted so as to overlap with a high-density excited electron region (the convergence region of the first laser light Lb 1) in which light energy of the emitted laser light is preferentially and selectively absorbed only. As a result, the above-mentioned non-patent document 2 discloses that the region that has absorbed the optical energy (the high-density excited electron region is a region temporarily generated by irradiation of the first laser light Lb 1) efficiently generates heat as a hot filament. The amount of heat generated in the region (hot filament) that has absorbed the optical energy of the second laser light Lb2 depends on the irradiation time of the second laser light Lb 2. That is, as the amount of heat generated increases, the temperature in the surrounding area centered on the hot filament also increases (the area exceeding the crystallization threshold E1 shown in fig. 5 and 7). At this time, by controlling the amount of heat generated in the absorption region so that the temperature of the surrounding region becomes equal to or lower than the processing (melting) threshold E2, crystallization of the surrounding region becomes possible.

Specifically, as shown in fig. 12, in the laser irradiation step (step S5 of fig. 3) of the present modification, the substrate 2 having the channel optical waveguide structure 21 is prepared. Each of a convergence point P1 (coinciding with the radiation center O1) and a convergence point P2 (coinciding with the radiation center O2) shown in fig. 4 and 9A is irradiated with a first laser light Lb1(fs laser) from a first light source 30A for generating a high-density excited electron region on the surface of the substrate 2 or inside the substrate. On the other hand, the substrate 2 is irradiated with a second laser beam Lb2 (a pulsed laser or CW laser having a pulse width of 1ps or more, preferably 1ns or more) from the second light source 30B to heat the high-density excited electron region temporarily generated by the irradiation with the first laser beam Lb 1. In the example of fig. 12, the first laser light Lb1 and the second laser light Lb2 are emitted coaxially. That is, the common optical member OP3 (including the condenser lens 40A) and the half mirror 60 are arranged in each of the optical path of the first laser light Lb1 from the first light source 30A to the substrate 2 and the optical path of the second laser light Lb2 from the second light source 30B to the substrate 2. Such an illumination system has the advantage of being easy to construct. However, the optical path of the first laser light Lb1 and the optical path of the second laser light Lb2 may be different.

The substrate 2 is irradiated with the first laser light Lb1 and the second laser light Lb2 synchronized with each other. During laser irradiation, the first laser light Lb1 output from the first light source 30A is reflected by the half mirror 60 and travels to the condenser lens 40A. Further, the first laser light Lb1 passing through the condenser lens 40A is condensed near the surface of the substrate 2. A high-density excited electron region is generated in the convergence region of the first laser light Lb 1. Meanwhile, the second laser light Lb2 output from the second light source 30B passes through the half mirror 60 and travels to the condenser lens 40A. Further, the second laser light Lb2 passing through the condenser lens 40A is condensed so as to overlap with the high-density excited electron region. The light energy of the second laser light Lb2 is efficiently absorbed in the high-density excited electron region, and the high-density excited electron region functions as the hot filament 110 at this time. As a result, the crystallization regions 10A and 10B oriented perpendicular to the temperature contour in the peripheral region of the hot filament 110 are formed in the substrate 2.

Incidentally, fig. 13A is a schematic diagram for describing the polarization orientation in the crystallized region formed using the laser light having the light intensity distribution shown in fig. 5. In addition, fig. 13B is a schematic diagram for describing the polarization orientation in the crystalline region formed by the method for manufacturing the light wavelength converter according to the fifth modification.

In the above-described embodiment and the first to fourth modifications to which fs laser is not applied, as shown in fig. 13A, the orientation of the irradiated material (substrate 2) in the depth direction is not completely parallel to the surface of the substrate 2, but is slightly inclined in the depth direction.

On the other hand, when the fs laser and the pulse laser are emitted in a state where the convergence region of the fs laser and the convergence region of the pulse laser having a pulse width of 1ns or more overlap each other, the temperature is selectively increased in the depth direction of the irradiation material (substrate 2) due to the hot filament effect. Therefore, as shown in fig. 13B, in the region α, the orientation of the irradiated material in the depth direction is parallel to the surface of the substrate 2. Although the shapes of the apertures (laser processing marks) 12A and 12B depend on the convergence condition of the fs laser, a shape having a high aspect ratio of about 10 μm in diameter and 100 μm or more in depth can also be processed according to the irradiation conditions (see the above-mentioned non-patent document 2). Since the shape of the hot filament 110 depending on the processing shape is formed perpendicular to the depth direction and is polarized perpendicular to the temperature contour line, the polarization of the region α shown in fig. 13B is oriented as parallel as possible to the surface of the substrate 2. As a result, highly efficient wavelength conversion can be performed according to the polarization of incident light. Incidentally, as a light source configured to output fs laser light, a Ti: S laser, a1 μm-band fiber laser, or SHG of such a light source is effective.

(examples)

FIGS. 14A, 15A and 16A are optical microscope images showing images taken from CO₂Laser irradiation of SrO-TiO with laser₂-SiO₂The state after glass attachment. Fig. 14A shows a state where the laser output is 7.8W and the irradiation time is 2 seconds. Fig. 15A shows a state where the laser output is 7.8W and the irradiation time is 1 second. Fig. 16A shows a state where the laser output is 3.28W and the irradiation time is 2 seconds. Incidentally, fig. 14B, 15B, and 16B are partial enlarged views of fig. 14A, 15A, and 16A, respectively. Under all irradiation conditions, pores (laser-processed marks) 12 are generated, and crystalline regions, i.e., crystalline regions 10 (corresponding to the crystalline regions 10A and 10B), are formed around the pores 12.

In order to clarify the orientation of the optical axis of the crystal region 10, the present inventors performed a measurement of the generation of the second harmonic wave using a laser having a wavelength of 1.06 μm and an optical diameter of about 2 mm. Fig. 17 is an image showing a measurement result of Second Harmonic Generation (SHG). Incidentally, fig. 17 also shows the polarization direction of the laser light used for measurement. SrO-TiO₂-SiO₂The second-order nonlinear optical constant (d constant) of the glass has d₃₁＞d₃₃And is preferentially observed to have d in the measurement₃₁SH light of (1). As shown in fig. 17, in this experiment, a pair of SH beams was observed in the crystal region 10 formed in a ring shape. Incidentally, these SH beams are generated on a straight line passing through the center of the crystallization area 10 and extending in a direction perpendicular to the polarization direction.

SH light is composed of₃₁Component induced SH light, and the polarization direction of the SH light is perpendicular to the incident wavefront. That is, it should be understood that the polarization direction extends along a straight line connecting the generation region of SH light and the center of the crystal region 10, and is radial. This shows that by irradiating the substrate 2 with laser light, the crystalline region 10 having a radially polarized ordered structure can be formed.

The optical wavelength converter of the present disclosure is not limited to the above-described embodiments (including modifications), and various other modifications may be made. For example, the above-described embodiment and each modification can be combined with each other according to the intended purpose and effect. In the above-described embodiments and modifications, the substrate material is exemplified by a crystalline structure of a perovskite type, BaO-TiO₂-GeO₂-SiO₂Glass series and SrO-TiO₂-SiO₂Glass, however, various materials that are crystalline or amorphous and transparent to the desired wavelength may be applied to the substrate of the present disclosure.

List of reference numerals

1A, 1B, 1C, 1D … … optical wavelength converters; 2 … … a substrate; 2a, 2b … … end faces; 2c, 2d … … area; 10. 10A, 10B … … crystalline regions; 12A, 12B … … pores (laser machining marks); 21 … … channel optical waveguide structure; 21a, 21b … … side; 30 … … laser light source; 30a … … first light source; 30B … … second light source; 31 … … light absorbing material; 40a … … condenser lens; 40B … … aspheric lens; a 50 … … diffractive optical element; 60 … … half mirror; a1, a2 … … spontaneous polarization; AX, AX1, AX2 … … virtual axis; b1, B2 … … wavelength conversion region; b1a … … one end; the other end of B1B … …; d1 … … optical waveguide direction; the direction D2 … …; la … … laser; lb1 … … first laser; lb2 … … second laser; o1, O2 … … radial centers; p1, P2 … … convergence points; and OP1, OP2, OP3 … … optical members.