Laser processing device, method for manufacturing optical device, and laser processing method

Abstract

A laser processing device 1A comprising: a light generation unit 20A that generates laser light L3 that is radially polarized light or azimuthally polarized light and has a spiral phase distribution; a condensing optical system 30 that condenses the laser light L3 at a condensing position in a uniaxial birefringent crystal body; and a control unit 40A that shifts the condensing position in the uniaxial birefringent crystal body and forms an optical structure.

Description

Laser processing apparatus, optical device manufacturing method, and laser processing method

[0001] This application claims priority to Japanese Patent Application No. 2024-146336 filed on August 28, 2024, and Japanese Patent Application No. 2025-007069 filed on January 17, 2025, and incorporates all of the contents of the aforementioned Japanese applications by reference.

[0002] Non-Patent Document 1 discloses the formation of an optical waveguide in a dielectric crystal using a femtosecond laser. Non-Patent Document 2 discloses a technique for writing into a uniaxial birefringent crystal (lithium niobate) using an ultrashort pulse laser beam. Non-Patent Document 3 discloses the formation of an optical waveguide in a uniaxial birefringent crystal (lithium niobate) using a femtosecond laser. ３ A technique for forming an intensity modulator is disclosed.

[0003] Lingqi Li, Weijin Kong, and Feng Chen, "Femtosecond laser-inscribed optical waveguides in dielectric crystals: a concise review and recent advances," Advanced Photonics, SPIE, Vol. 4(2), 024002 (2022)P. Karpinski, V. Shvedov, W. Krolikowski, and C. Hnatovsky, "Laser-writing inside uniaxially birefringent crystals: fine morphology of ultrashort pulseinduced changes in lithium niobate," Optics Express, Optica Publishing Group, Vol. 24, No. 7, pp.7456-7476 (2016)D.A. Presti et al., "Intensity modulator fabricated in LiNbO3 by femtosecond laser writing," Optics and Lasers in Engineering, ELSEVIER SCI LTD, 111, pp.222-226 (2018)Sjoerd Stallinga, "Light distribution close to focus in biaxially birefringent media," Journal of the Optical Society of America A, Optical Society of America, Vol. 21, No. 9, pp.1785-1798 (2004)Satoshi Hasegawa and Yoshio Hayasaki, "Polarization distribution control of parallel femtosecond pulses with spatial light modulators," Optics Express, Optica Publishing Group, Vol. 21, No. 11, pp.12987-12995 (2013).

[0004] Birefringent crystals are used in many optical devices due to their optical characteristics. In particular, lithium niobate (LiNbO ３ ) has excellent properties in electro-optic coefficient, acousto-optic coefficient, piezoelectric coefficient, nonlinear optical coefficient, etc. In uniaxial birefringent crystals such as lithium niobate, the refractive index of one axis (here, the z-axis) is different from the refractive index of the other two axes (the x-axis and the y-axis). A birefringent crystal having a principal surface perpendicular to the z-axis is called a z-cut crystal, and a birefringent crystal having a principal surface perpendicular to the x-axis or y-axis is called an x-cut crystal or a y-cut crystal, respectively. Compared to x-cut crystals and y-cut crystals, z-cut crystals can significantly lower the driving voltage of optical devices, contributing to lower power consumption of optical devices.

[0005] When fabricating optical devices using birefringent crystals, some optical structures (e.g., optical waveguides) may be formed by focusing laser light inside the birefringent crystal. However, when forming an optical structure deep in a z-cut crystal, the effect of birefringence causes the focused spot of the laser light to split into two along the optical axis. Therefore, in the past, it was difficult to form an optical structure deep in a z-cut crystal, and it was common to form the optical structure shallower in the z-cut crystal or to use an x-cut crystal or y-cut crystal.

[0006] The present disclosure aims to provide a laser processing apparatus, an optical device manufacturing method, and a laser processing method that can form an optical structure without separating the focused spot of laser light even at a deep position in a Z-cut crystal.

[0007] [1A] A laser processing apparatus according to an embodiment of the present disclosure includes a light generation unit, a focusing optical system, and a focusing position control unit. The light generation unit generates radially polarized or azimuthal polarized laser light having a helical phase distribution. The focusing optical system focuses the laser light at a focusing position within a uniaxial birefringent crystal. The focusing position control unit moves the focusing position within the uniaxial birefringent crystal to form an optical structure.

[0008] [1B] A method for manufacturing an optical device according to an embodiment of the present disclosure is a method for manufacturing an optical device having a uniaxial birefringent crystal and an optical structure formed within the uniaxial birefringent crystal, and includes a light generating step, a light focusing step, and a forming step. In the light generating step, radially polarized or azimuthal polarized laser light having a helical phase distribution is generated. In the focusing step, the laser light is focused at a focusing position within the uniaxial birefringent crystal. In the forming step, the focusing position is moved within the uniaxial birefringent crystal to form the optical structure.

[0009] [1C] A laser processing method according to an embodiment of the present disclosure includes a light generating step, a light focusing step, and a forming step. In the light generating step, radially polarized or azimuthal polarized laser light having a helical phase distribution is generated. In the focusing step, the laser light is focused at a focusing position within a uniaxial birefringent crystal. In the forming step, the focusing position is moved within the uniaxial birefringent crystal to form an optical structure.

[0010] The inventor's research has revealed the following phenomenon: When radially or azimuthally polarized laser light is focused within a uniaxial birefringent crystal, a single focused spot is formed without separation, even at deep positions in the z-cut crystal. However, in this case, the focused spot becomes annular with a hole, which may prevent the energy required for processing from being sufficiently concentrated in the processing area. In contrast, when a spiral phase distribution is imparted to radially or azimuthally polarized light, the hole in the focused spot closes, allowing the energy to be sufficiently concentrated in the processing area. In other words, according to the laser processing apparatus described in [1A] above, the manufacturing method described in [1B] above, and the laser processing method described in [1C] above, an optical structure can be formed without separation of the focused spot of laser light, even at deep positions in the z-cut crystal.

[0011] [2A] In the laser processing apparatus of [1A] above, the light generation unit may have a phase control unit and a polarization control unit. The phase control unit imparts a helical phase distribution to the laser light. The polarization control unit radially polarizes or azimuthally polarizes the laser light after the helical phase distribution has been imparted to the laser light or before the helical phase distribution has been imparted to the laser light. Similarly, [2B] in the manufacturing method of [1B] above and the laser processing method of [1C] above, the light generation step may include a step of imparting a helical phase distribution to the laser light and a step of radially polarizing or azimuthally polarizing the laser light after the helical phase distribution has been imparted to the laser light or before the helical phase distribution has been imparted to the laser light. For example, these configurations or methods can suitably generate radially polarized or azimuthally polarized laser light having a helical phase distribution.

[0012] [3A] In the laser processing apparatus of [2A] above, the phase control unit may include a phase plate, and the polarization control unit may include a vector polarizer. Alternatively, [4A] in the laser processing apparatus of [2A] above, the phase control unit may include a first spatial light modulator, and the polarization control unit may include a vector polarizer. Alternatively, [5A] in the laser processing apparatus of [2A] above, the phase control unit may include a phase plate, and the polarization control unit may include a second spatial light modulator. Alternatively, [6A] in the laser processing apparatus of [1A] above, the light generation unit may have a quarter-wave plate, a half-wave plate, and a spatial light modulator arranged on the optical path between the quarter-wave plate and the half-wave plate, and the quarter-wave plate, the half-wave plate, and the spatial light modulator may cooperate to generate radially polarized or azimuthally polarized laser light having a spiral phase distribution. For example, any of the configurations of [3A] to [6A] above can suitably generate radially polarized or azimuthally polarized laser light having a spiral phase distribution.

[0013] [7A] In the laser processing apparatuses of [1A] to [6A] above, the light generation unit may alternately generate radially polarized laser light having a spiral phase distribution and azimuthally polarized laser light having a spiral phase distribution. Similarly, [3B] in the manufacturing methods of [1B] and [2B] above and the laser processing methods of [1C] and [2B] above, the light generation step may alternately generate radially polarized laser light having a spiral phase distribution and azimuthally polarized laser light having a spiral phase distribution. Optical structures formed by radially polarized light and optical structures formed by azimuthally polarized light have different shape characteristics due to differences in polarization direction. By alternately irradiating a uniaxial birefringent crystal with radially polarized laser light and azimuthally polarized laser light, an optical structure having the characteristics of both (e.g., compensating for each other's shortcomings) can be formed.

[0014] [8A] In the laser processing apparatus of [7A] above, the focusing position control unit may overlap at least a portion of the range of the focused spot of the radially polarized laser light having a spiral phase distribution with at least a portion of the range of the focused spot of the azimuthally polarized laser light having a spiral phase distribution. Similarly, [4B] in the manufacturing method and laser processing method of [3B] above, in the forming step, at least a portion of the range of the focused spot of the radially polarized laser light having a spiral phase distribution may overlap at least a portion of the range of the focused spot of the azimuthally polarized laser light having a spiral phase distribution. When the same focusing optical system is used for radially polarized light and azimuthally polarized light, the depths of the focused spots are different. By at least partially overlapping the ranges of the focused spots of both the radially polarized light and the azimuthally polarized light using the focusing position control unit, both the radially polarized light and the azimuthally polarized light can be applied to a single point.

[0015] [5B] In the manufacturing methods of the above [1B] to [4B] and the laser processing methods of the above [1C] and [2B] to [4B], the uniaxial birefringent crystal is GaN, SiC, LiNbO ３ , LiTaO ３ , β-BBO, sapphire, polyimide, Nd:YVO ４ , Nd:GdVO ４ , α-Quartz, AlN, ZnO, 4H—SiC, 6H—SiC, and Nd:YCOB.

[0016] [6B] In the optical device manufactured by the manufacturing methods [1B] to [5B] above, the optical structure may constitute at least one optical element selected from the group consisting of an optical waveguide, a quasi-phase matching structure, a diffraction grating, a splitter, a directional coupler, an amplitude modulation structure, a polarization control structure, a wavelength conversion structure, and a voxel. In this case, an optical element with excellent optical properties can be obtained.

[0017] [7B] The optical device manufactured by the manufacturing methods [1B] to [5B] above may include a substrate that is a uniaxial birefringent crystal, and an optical integrated circuit including an optical structure formed on the substrate. In this case, an optical integrated circuit with excellent optical properties can be obtained.

[0018] [9A] In the laser processing apparatuses described above in [1A] to [8A], the focusing optical system may include an objective lens, and the numerical aperture of the objective lens may be 0.04 or more and 3.0 or less. Similarly, [8B] in the manufacturing methods and laser processing methods described above in [1B] to [7B], in the focusing step, the laser light may be focused using an objective lens, and the numerical aperture of the objective lens may be 0.04 or more and 3.0 or less. Typically, the peak intensity of laser light obtained by imparting a spiral phase distribution to radially polarized or azimuthally polarized light is smaller than the peak intensity of circularly polarized laser light. However, because circularly polarized light is affected by birefringence in birefringent crystals, the deeper the focusing position, the lower the peak intensity at the focusing spot. On the other hand, the peak intensity at the focusing spot of laser light obtained by imparting a spiral phase distribution to radially polarized or azimuthally polarized light does not depend on the depth of the focusing position, and therefore, when the depth of the focusing position exceeds a certain depth, the peak intensity at the focusing spot of the circularly polarized light becomes greater than the peak intensity at the focusing spot of the circularly polarized light. The "certain depth" depends on the numerical aperture of the objective lens, and the greater the numerical aperture of the objective lens, the shallower the depth becomes. By using an objective lens with a numerical aperture of 0.04 or greater, the effects of the laser processing apparatus of [1A] above, the manufacturing method of [1B] above, and the laser processing method of [1C] above can be obtained even if the depth of the focusing position is relatively shallow.

[0019] According to the present disclosure, it is possible to provide a laser processing apparatus, an optical device manufacturing method, and a laser processing method that can form an optical structure without separating the focused spot of laser light even at a deep position in a Z-cut crystal.

[0020] FIG. 1 is a perspective view schematically illustrating a process for fabricating an optical device 10 using a laser processing apparatus according to an embodiment of the present disclosure. FIG. 2 is a block diagram illustrating a configuration of the laser processing apparatus according to an embodiment. FIG. 3 is a diagram illustrating a helical phase distribution imparted to laser light by a phase plate. FIG. 4 is a flowchart illustrating a method for manufacturing an optical device and a laser processing method according to an embodiment. FIG. 5 is a schematic diagram illustrating a process for irradiating a uniaxial birefringent crystal with laser light. FIG. 6 is a diagram illustrating a phase distribution and a polarization direction distribution of an ordinary light component. FIG. 7 is a diagram illustrating a phase distribution and a polarization direction distribution of an extraordinary light component. FIG. 8 is a diagram illustrating a simulation result regarding the shape of a focused spot when laser light is focused within a Z-cut crystal. FIG. 9 is a diagram illustrating a simulation result regarding the shape of a focused spot when laser light is focused within a Z-cut crystal. FIG. 10 is a diagram illustrating another simulation result. FIG. 11 is a graph illustrating the relationship between the position of the focused spot in the optical axis direction and the peak intensity of the focused spot for each numerical aperture of the objective lens. FIG. 12 is a graph showing the relationship between the position of the focused spot in the optical axis direction and the peak intensity of the focused spot for each numerical aperture of the objective lens. FIG. 13 is a graph showing the relationship between the position of the focused spot in the optical axis direction and the peak intensity of the focused spot. FIG. 14 is a graph showing the relationship between the position of the focused spot in the optical axis direction and the peak intensity of the focused spot. FIG. 15 is a graph showing the relationship between the position of the focused spot in the optical axis direction and the peak intensity of the focused spot for each numerical aperture of the objective lens. FIG. 16 is a diagram schematically showing the configuration of a laser processing apparatus according to a first modified example. FIG. 17 is a diagram schematically showing the configuration of a laser processing apparatus according to a second modified example. FIG. 18 is an example of a phase distribution for converting laser light into radially polarized or azimuthally polarized light having a helical phase. FIG. 19 is an example of a phase distribution displayed on a spatial light modulator. FIG. 20 is a diagram schematically showing the configuration of a laser processing apparatus according to a third modified example. 21 and 22 are diagrams showing simulation results for simultaneously forming a plurality of focused spots aligned in a direction intersecting the optical axis direction.Fig. 23 is a diagram showing a simulation result, Fig. 24 is a diagram showing a schematic configuration of a laser processing apparatus according to a sixth modified example, and Fig. 25 is a diagram showing a result of verification using Stokes parameters.

[0021] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are designated by the same reference numerals, and duplicated explanations will be omitted.

[0022] FIG. 1 is a perspective view schematically illustrating the fabrication of an optical device 10 using a laser processing apparatus according to an embodiment of the present disclosure. The laser processing apparatus of this embodiment forms an optical structure 12 by focusing laser light L3 into a uniaxial birefringent crystal 11 (hereinafter simply referred to as the crystal 11) using a focusing optical system 30. In the crystal 11, the refractive index of one axis (here, the z-axis) is different from the refractive indexes of the other two axes (the x-axis and the y-axis). The crystal 11 is a so-called z-cut crystal having a principal surface 11a perpendicular to the z-axis. The laser light L3 enters the crystal 11 from the principal surface 11a of the crystal 11.

[0023] For example, the optical device 10 includes a substrate as a crystal body 11 and an optical integrated circuit formed on the substrate, the optical integrated circuit including an optical structure 12. The crystal body 11 has uniaxial birefringence characteristics and is made of, for example, gallium nitride (GaN), silicon carbide (SiC), or LiNbO ３ , LiTaO ３ , β-BBO, sapphire, polyimide, Nd:YVO ４ , Nd:GdVO ４The optical structure 12 includes at least one material selected from the group consisting of α-Quartz, aluminum nitride (AlN), zinc oxide (ZnO), 4H-SiC, 6H-SiC, and Nd:YCOB. The optical structure 12 is, for example, a refractive index change region whose refractive index differs from that of its surroundings. For example, the refractive index of the optical structure 12 is greater or smaller than that of its surroundings. Such a change in refractive index can be adjusted by the intensity of the irradiated light. In the optical device 10, the optical structure 12 constitutes, for example, at least one optical element selected from the group consisting of an optical waveguide, a quasi-phase matching structure, a diffraction grating, a splitter, a coupler, a branching / directional coupler, an amplitude modulation structure, a polarization control structure, a wavelength conversion structure, and a voxel.

[0024] 2 is a block diagram showing the configuration of a laser processing apparatus 1A according to this embodiment. The laser processing apparatus 1A includes a light generating unit 20A, a focusing optical system 30, and a control unit 40A.

[0025] The light generation unit 20A generates laser light L3. The laser light L3 is radially polarized or azimuthally polarized and has a spiral phase distribution. The light generation unit 20A of this embodiment is configured to be able to generate both radially polarized laser light L3 having a spiral phase distribution and azimuthally polarized laser light L3 having a spiral phase distribution.

[0026] Specifically, the light generating unit 20A includes a laser light source 21, a phase plate 22, a double-telecentric relay lens system 23, a vector polarizer 24, and a double-telecentric relay lens system 25. The laser light source 21 outputs linearly polarized laser light L1. The laser light L1 has a uniform phase distribution in a cross section perpendicular to the optical axis. The laser light source 21 includes, for example, a semiconductor laser element. The wavelength of the laser light L1 is, for example, 350 nanometers or more and 2000 nanometers or less. The laser light L1 is, for example, pulsed light, and in this case, the pulse width is, for example, 15 femtoseconds or more and 200 picoseconds or less.

[0027] The phase plate 22 is optically coupled to the laser light source 21. The phase plate 22 is a phase control unit in this embodiment, and generates laser light L2 by imparting a helical phase distribution to the laser light L1. That is, the laser light L2 is linearly polarized light including a helical phase distribution. FIG. 3 is a diagram showing the helical phase distribution imparted to the laser light L1 by the phase plate 22. In FIG. 3, the magnitude of the phase is indicated by a shade of color, which changes from white to black as the phase approaches 0 (rad) to 2π (rad). As shown in FIG. 3, the helical phase distribution is a phase distribution in which the phase changes from 0 (rad) to 2π (rad) in the azimuthal direction around the optical axis. The phase plate 22 may impart to the laser light L1 a phase distribution obtained by superimposing the helical phase distribution on a phase distribution different from the helical phase distribution.

[0028] The double telecentric relay lens system 23 is optically coupled to the phase plate 22. The double telecentric relay lens system 23 has a focal length (f １ +f ２ ) and a set of lenses 231 (focal length f １ ) and lens 232 (focal length f ２ ) and optically couples the phase plate 22 and the vector polarizer 24. If the distance between the phase plate 22 and the vector polarizer 24 is short, the double-telecentric relay lens system 23 may be omitted. An aperture may be disposed on the optical path between the lens 231 and the lens 232 to modulate the intensity of the laser light L2.

[0029] The vector polarizer 24 is a polarization control unit in this embodiment. The vector polarizer 24 converts the polarization of the laser light L2 after the helical phase distribution has been imparted from linear polarization to radial polarization or azimuthal polarization, thereby generating the laser light L3. That is, the laser light L3 is radially polarized or azimuthal polarization containing a helical phase distribution. When the vector polarizer 24 forms a predetermined first angle around the optical axis with respect to the polarization direction of the laser light L2, the laser light L3 becomes radially polarized. When the vector polarizer 24 forms a predetermined second angle around the optical axis with respect to the polarization direction of the laser light L2, the laser light L3 becomes azimuthal polarization. The difference between the first angle and the second angle is 90°.

[0030] In the illustrated example, the vector polarizer 24 is provided after the phase plate 22, and the vector polarizer 24 controls the polarization of the laser light L2 after it has been given a spiral phase distribution. This configuration is not limiting, and the vector polarizer 24 may be provided before the phase plate 22. In this case, the vector polarizer 24 controls the polarization of the laser light L1 before it has been given a spiral phase distribution. The phase plate 22 then gives a spiral phase distribution to the laser light that is radially polarized or azimuthally polarized.

[0031] The double telecentric relay lens system 25 is optically coupled to the vector polarizer 24. The double telecentric relay lens system 25 has a distance from each other equal to a focal length (f ３ +f ４ ) and a set of lenses 251 (focal length f ３ ) and lens 252 (focal length f ４ ) and optically couples the vector polarizer 24 and the focusing optical system 30. If the distance between the vector polarizer 24 and the focusing optical system 30 is short, the double-telecentric relay lens system 25 may be omitted. An aperture may be disposed on the optical path between the lens 251 and the lens 252 to modulate the intensity of the laser light L3.

[0032] The focusing optical system 30 focuses the laser light L3 at a focusing position within the crystal body 11. The focusing optical system 30 includes an objective lens. The focusing optical system 30 is configured to be movable relative to the crystal body 11, which is the processing target. The position of the crystal body 11 may be fixed and the focusing optical system 30 may be movable, or the position of the focusing optical system 30 may be fixed and the crystal body 11 may be movable. Alternatively, both the crystal body 11 and the focusing optical system 30 may be movable.

[0033] The control unit 40A is a focusing position control unit in this embodiment, and moves the focusing position within the crystal 11. The control unit 40A moves the focusing position within the crystal 11 by controlling the relative positional relationship between the focusing optical system 30 and the crystal 11. If the focusing optical system 30 is movable, the control unit 40A drives an actuator attached to the focusing optical system 30. If the crystal 11 is movable, the control unit 40A drives a stage on which the crystal 11 is mounted. The optical structure 12 is formed by moving the focusing position within the crystal 11. In FIG. 1 , the optical structure 12 is formed by moving the focusing position in a direction along the main surface 11a, so that the optical structure 12 extends along the direction of movement.

[0034] The control unit 40A may further control the angle around the optical axis of the vector polarizer 24. In other words, the angle around the optical axis of the vector polarizer 24 may be switchable. In this case, the control unit 40A controls the angle around the optical axis of the vector polarizer 24 to a first angle at which the laser light L3 becomes radially polarized, or to a second angle at which the laser light L3 becomes azimuthal polarized.

[0035] The control unit 40A may control the angle around the optical axis of the vector polarizer 24 so that the first angle and the second angle alternate. In this case, the light generation unit 20A alternately generates radially polarized laser light L3 having a spiral phase distribution and azimuthally polarized laser light L3 having a spiral phase distribution. At this time, the control unit 40A controls the relative positional relationship between the focusing optical system 30 and the crystal 11 so that at least a portion of the range of the focused spot of the radially polarized laser light L3 having a spiral phase distribution overlaps at least a portion of the range of the focused spot of the azimuthally polarized laser light L3 having a spiral phase distribution.

[0036] The control unit 40A may be configured by a computer. The computer physically includes memory such as RAM and ROM, a processor (arithmetic circuit) such as a CPU, a communication interface, a storage unit such as a hard disk, and a display unit such as a display. The computer is, for example, a personal computer, a cloud server, or a smart device (smartphone, tablet terminal, etc.). The computer functions as the control unit 40A by executing a program stored in the memory in the CPU of the computer system.

[0037] Next, a method for manufacturing the optical device 10 and a laser processing method according to this embodiment will be described. The method for manufacturing the optical device 10 and the laser processing method can be performed, for example, by the laser processing apparatus 1A described above. Figure 4 is a flowchart showing the method for manufacturing the optical device 10 and the laser processing method according to this embodiment.

[0038] First, in the light generation step ST1, a radially or azimuthally polarized laser beam L3 having a helical phase distribution is generated. The light generation step ST1 includes a step ST11 of imparting a helical phase distribution to the laser beam L1 and a step ST12 of converting the laser beam L2 after the helical phase distribution has been imparted to the radially or azimuthally polarized laser beam L2. However, in the light generation step ST1, the order of steps ST11 and ST12 may be reversed, and the laser beam L1 before the helical phase distribution is imparted may be radially or azimuthally polarized. Then, in the focusing step ST2, the laser beam L3 is focused at a focusing position within the crystal 11. Then, in the forming step ST3, the focusing position is moved within the crystal 11. Thereafter, the above-described focusing step ST2 and forming step ST3 are repeated to form the optical structure 12.

[0039] In the light generating step ST1, radially polarized laser light L3 having a spiral phase distribution and azimuthally polarized laser light L3 having a spiral phase distribution may be alternately generated. In this case, in the forming step ST3, at least a part of the range of the focused spot of the radially polarized laser light L3 having a spiral phase distribution is overlapped with at least a part of the range of the focused spot of the azimuthally polarized laser light L3 having a spiral phase distribution.

[0040] The effects obtained by the laser processing apparatus 1A, the manufacturing method for the optical device 10, and the laser processing method according to the present embodiment described above will now be described. When fabricating an optical device using a birefringent crystal, some optical structure (e.g., an optical waveguide) may be formed by focusing laser light inside the birefringent crystal. Part (a) of FIG. 5 is a schematic diagram showing how laser light L is irradiated onto a z-cut crystal 14. Part (b) of FIG. 5 is a schematic diagram showing how laser light L is irradiated onto a y-cut crystal 15. Conventionally, when an optical structure is formed by focusing light deep within a z-cut crystal 14 using a lens or objective lens, the focused spot of the laser light L splits into two along the optical axis due to the influence of birefringence. Specifically, when the lens numerical aperture is low or the focusing position is shallow, the focused spot does not split. However, when the lens numerical aperture is large or the focusing position is deep, the ideal elliptical focused shape in the xz plane (or yz plane) gradually changes and eventually splits into two. Therefore, in the past, it was difficult to form the optical structure 12 at a deep position in the z-cut crystal 14, and it was common to form the optical structure 12 at a shallow position in the z-cut crystal 14, or to focus the light using a lens with a small numerical aperture, or to use a y-cut crystal 15 (or x-cut crystal).

[0041] The splitting of the focused spot into two along the optical axis direction is caused by the inclusion of an ordinary light component and an extraordinary light component in the laser light L. Part (a) of FIG. 6 is a graph showing the phase distribution of the ordinary light component. Part (a) of FIG. 7 is a graph showing the phase distribution of the extraordinary light component. In Parts (a) of FIG. 6 and (a) of FIG. 7, axes A1 and A2 represent coordinates in a plane perpendicular to the optical axis, and axis A3 represents phase values ​​(both normalized values). Part (b) of FIG. 6 is a diagram showing the distribution of the polarization direction of the ordinary light component in a plane perpendicular to the optical axis. Part (b) of FIG. 7 is a diagram showing the distribution of the polarization direction of the extraordinary light component in a plane perpendicular to the optical axis. As shown in these figures, the ordinary light component and the extraordinary light component have significantly different characteristics in their phase distribution and polarization distribution. That is, in the phase distribution, the ordinary light component and the extraordinary light component have defocusing in opposite directions, and in the polarization distribution, the ordinary light component is azimuthally polarized, while the extraordinary light component is radially polarized.

[0042] Therefore, the inventors considered focusing radially polarized or azimuthally polarized laser light within the Z-cut crystal 14. In this case, it was confirmed that a single focused spot could be formed without separation even at a deep position in the Z-cut crystal 14. However, it became clear that in this case, the focused spot would be annular with a hole, and there was a risk that the energy required for processing would not be sufficiently focused on the processing area.

[0043] Parts (a) to (e) of Fig. 8 and parts (a) and (b) of Fig. 9 are diagrams showing the results of a simulation of the shape of the focused spot when the laser light L is focused in the z-cut crystal 14. In this simulation, the z-cut crystal 14 is made of lithium niobate (LiNbO ３ ), the wavelength of the laser light L was 1030 nm, the numerical aperture (NA) of the objective lens was 0.9, the depth of the light-focusing position was 335 μm, and only the influence due to birefringence was taken into consideration.

[0044] Part (a) of Figure 8 shows the case where the laser light L is linearly polarized and the polarization direction is parallel to the x-axis of the z-cut crystal 14. Part (b) of Figure 8 shows the case where the laser light L is linearly polarized and the polarization direction is parallel to the y-axis of the z-cut crystal 14. Part (c) of Figure 8 shows the case where the laser light L is circularly polarized. Referring to parts (a) to (c) of Figure 8, it can be seen that when the laser light L is linearly polarized or circularly polarized, the focused spot is separated into two along the optical axis direction (depth direction). In contrast, part (d) of Figure 8 shows the case where the laser light L is radially polarized. Part (e) of Figure 8 shows the case where the laser light L is azimuthally polarized. Referring to parts (d) and (e) of Figure 8, it can be seen that the focused spot is formed as a single spot without separation. However, as is clear from part (f) of FIG. 8, which is a cross section taken along line BB of part (e) of FIG. 8, the focused spot is annular with a hole.

[0045] In contrast, part (a) of Figure 9 shows the case where the laser light L is radially polarized and has a helical phase distribution. Part (b) of Figure 9 shows the case where the laser light L is azimuthally polarized and has a helical phase distribution. Referring to parts (a) and (b) of Figure 9, it can be seen that the hole in the focused spot is closed. This allows energy to be sufficiently concentrated in the processing area. It is presumed that the hole in the focused spot is closed because the polarization direction rotates over time due to the helical phase, causing opposing polarized light to have the same direction. In other words, according to the laser processing apparatus 1A, the manufacturing method for the optical device 10, and the laser processing method of this embodiment, the optical structure 12 can be efficiently formed without separating the focused spot of the laser light L3, even deep in the crystalline body 11, which is a Z-cut crystal.

[0046] FIG. 10 shows a z-cut crystal 14 made of LiNbO ３10 is a diagram showing a simulation result of the focused spot shape when the wavelength of the laser light L is 400 nm, the numerical aperture (NA) of the objective lens is 0.1, and the depth of the focused position is 2230 μm. As shown in FIG. 10 , even when the numerical aperture of the objective lens is small, the laser processing apparatus 1A, the manufacturing method of the optical device 10, and the laser processing method of the present embodiment can efficiently form the optical structure 12 without separating the focused spot of the laser light L3 at a deep position in the crystal body 11.

[0047] As in the present embodiment, the light generation unit 20A may include a phase control unit and a polarization control unit. The phase control unit imparts a helical phase distribution to the laser light L3. The polarization control unit radially polarizes or azimuthally polarizes the laser light L3 after the helical phase distribution has been imparted to the laser light L3 or before the helical phase distribution has been imparted to the laser light L3. Similarly, the light generation step ST1 may include a step ST11 of imparting a helical phase distribution to the laser light L3 and a step ST12 of radially polarizing or azimuthally polarizing the laser light L3 after the helical phase distribution has been imparted to the laser light L3 or before the helical phase distribution has been imparted to the laser light L3. For example, these configurations or methods can suitably generate radially polarized or azimuthally polarized laser light L3 having a helical phase distribution.

[0048] As in the present embodiment, the phase control section may include a phase plate 22, and the polarization control section may include a vector polarizer 24. For example, with such a configuration, it is possible to suitably generate laser light L3 that is radially polarized or azimuthally polarized and has a spiral phase distribution.

[0049] As in this embodiment, the light generating unit 20A may be configured to generate both radially polarized laser light L3 having a spiral phase distribution and azimuthally polarized laser light L3 having a spiral phase distribution, and these laser lights L3 may be generated alternately. Similarly, in the light generating step ST1, radially polarized laser light L3 having a spiral phase distribution and azimuthally polarized laser light L3 having a spiral phase distribution may be generated alternately. The optical structure 12 formed by radial polarization and the optical structure 12 formed by azimuth polarization have different shape characteristics due to differences in polarization direction. By alternately irradiating the crystalline body 11 with radially polarized laser light L3 and azimuthally polarized laser light L3, it is possible to form an optical structure 12 having both characteristics (e.g., compensating for each other's shortcomings), or an optical structure 12 in which both characteristics are reduced or eliminated (e.g., nanostructures due to the polarization state are reduced or eliminated). This can reduce light propagation loss, for example, when forming an optical waveguide as the optical structure 12.

[0050] In this case, the control unit 40A may cause at least a portion of the range of the focused spot of the radially polarized laser light L3 having a spiral phase distribution to overlap with at least a portion of the range of the focused spot of the azimuthally polarized laser light L3 having a spiral phase distribution. Similarly, in the forming step ST3, at least a portion of the range of the focused spot of the radially polarized laser light L3 having a spiral phase distribution may overlap with at least a portion of the range of the focused spot of the azimuthally polarized laser light L3 having a spiral phase distribution. When the same focusing optical system 30 is used for the radially polarized light and the azimuthally polarized light, the depths of the focused spots are different, as is clear from comparing parts (a) and (b) of Figure 9. The control unit 40A may move the focusing position so that the ranges of the focused spots of both the radially polarized light and the azimuthally polarized light overlap at least partially, thereby allowing both the radially polarized light and the azimuthally polarized light to act on a single point.

[0051] Here, we consider the numerical aperture (NA) of the objective lens of the focusing optical system 30. FIGS. 11 to 15 are graphs showing the relationship between the position of the focused spot in the optical axis direction (depth direction) (hereinafter referred to as the "formation position") and the peak intensity (normalized intensity) of the focused spot for each numerical aperture of the objective lens. In FIGS. 11 to 15, the dashed line Q indicates the peak intensity of the focused spot when the laser light L3 is azimuthally polarized or radially polarized and has a spiral phase distribution, i.e., in this embodiment. The peak intensity of the focused spot in this embodiment is constant regardless of the formation position. In FIGS. 11 to 15, plots P1 to P11 indicate the peak intensity of the focused spot when the laser light is circularly polarized.

[0052] FIG. 11 shows a crystal 11 made of z-cut LiNbO ３ The plots P1 to P4 in Fig. 11 show the relationship when the numerical aperture of the objective lens is 0.1, 0.3, 0.5, and 0.9, respectively. Fig. 12 shows the relationship when the crystal 11 is a z-cut LiNbO ３ The graph shows the relationship when the wavelength of the laser light L3 is 800 nm and the objective lens is a water-immersion objective lens. Plots P5 to P7 shown in Fig. 12 show the cases where the numerical aperture of the objective lens is 0.8, 1.0, and 1.2, respectively. Fig. 13 shows the relationship when the crystal 11 is a z-cut LiNbO ３ The graph shows the relationship when the wavelength of the laser light L3 is 800 nm and the objective lens is a silicone immersion objective lens. Plot P8 shown in Fig. 13 shows the case where the numerical aperture of the objective lens is 1.3. Fig. 14 shows the relationship when the crystal 11 is a z-cut LiNbO ３ The graph shows the relationship when the crystal mass 11 is made of z-cut 4H—SiC, the wavelength of the laser light L3 is 515 nm, and the objective lens is an oil-immersion objective lens. Plot P9 in Fig. 14 shows the relationship when the numerical aperture of the objective lens is 1.5. Fig. 15 shows the relationship when the crystal mass 11 is made of z-cut 4H—SiC, the wavelength of the laser light L3 is 515 nm, and the objective lens is a dry objective lens. Plots P10 and P11 in Fig. 15 show the relationships when the numerical apertures of the objective lens are 0.2 and 0.6, respectively.

[0053] In this embodiment, when the laser light L3 is azimuthally polarized or radially polarized, the light intensity of the laser light L3 irradiated onto the crystal body 11 is lower than when the laser light is circularly polarized. Therefore, when the optical structure 12 is formed at a shallow position, the peak intensity of the focused spot in this embodiment is lower than the peak intensity of the focused spot when the laser light is circularly polarized. However, when the laser light is circularly polarized, the influence of birefringence is significant, so the peak intensity of the focused spot decreases as the formation depth of the optical structure 12 increases. In contrast, the peak intensity of the focused spot in this embodiment is constant regardless of depth, and therefore, at a certain depth, the peak intensity of the focused spot in this embodiment becomes greater than the peak intensity of the focused spot when the laser light is circularly polarized.

[0054] The "certain depth" depends on the numerical aperture of the objective lens. As shown in Figures 11, 12, and 15, when the laser light is circularly polarized, the position where the peak intensity of the focused spot begins to decrease becomes shallower as the numerical aperture of the objective lens increases. Therefore, the "certain depth" also becomes shallower as the numerical aperture of the objective lens increases. Therefore, the effect of this embodiment becomes more pronounced as the numerical aperture of the objective lens increases.

[0055] As described above, the numerical aperture of the objective lens may be 0.1 or more and 3.0 or less. By using an objective lens with a numerical aperture of 0.1 or more, the effect of the laser processing apparatus 1A of this embodiment can be obtained even if the depth of the focused spot is relatively shallow.

[0056] The numerical aperture of the objective lens may be 0.04 or more and 3.0 or less. Even if the depth of the focused spot is relatively shallow, the effect of the laser processing apparatus 1A of this embodiment can be obtained by using an objective lens with a numerical aperture of 0.04 or more.

[0057] As described above, the optical structure 12 may be at least one optical element selected from the group consisting of an optical waveguide, a quasi-phase matching structure, a diffraction grating, a splitter, a coupler, a branching device and a directional coupler, an amplitude modulation structure, a polarization control structure, a wavelength conversion structure, and a voxel. According to this embodiment, energy is sufficiently concentrated in the processed region, so that these optical elements with excellent optical properties can be obtained.

[0058] As described above, optical device 10 may include a substrate that is a crystalline body 11 and an optical integrated circuit (e.g., a waveguide laser, a beam shaping element such as an optical vortex generator, a quantum memory, or a frequency conversion element) formed on the substrate and including optical structure 12. According to this embodiment, energy is sufficiently concentrated in the processed region, thereby obtaining an optical integrated circuit with excellent optical properties.

[0059] 16 is a diagram schematically illustrating the configuration of a laser processing apparatus 1B according to a first modification of the present disclosure. Laser processing apparatus 1B includes a light generation unit 20B and a control unit 40B instead of light generation unit 20A and control unit 40A of the above embodiment. Light generation unit 20B includes a spatial light modulator (SLM) 26 and a mirror 271 as a phase control unit instead of phase plate 22 of the above embodiment.

[0060] In addition to the functions of the control unit 40A in the above embodiment, the control unit 40B also has the function of controlling the phase distribution displayed on the SLM 26. The control unit 40B causes the SLM 26 to display a spiral phase distribution. The SLM 26 is a first spatial light modulator in this disclosure. The spiral phase distribution displayed on the SLM 26 is the same as the spiral phase distribution possessed by the phase plate 22 in the above embodiment (see FIG. 3 ). The control unit 40B may also cause the SLM 26 to display a phase distribution obtained by superimposing the spiral phase distribution on a phase distribution different from the spiral phase distribution. The SLM 26 receives the laser light L1 output from the laser light source 21 and reflected by the mirror 271, and generates the laser light L2 by phase-modulating the laser light L1. The SLM 26 is optically coupled to the vector polarizer 24 via the double-telecentric relay lens system 23 (or directly), and provides the laser light L2 having a spiral phase distribution to the vector polarizer 24.

[0061] According to the configuration of this modified example, it is possible to obtain the same effects as in the above embodiment. In addition, as in this modified example, the phase control unit may include an SLM 26, and the polarization control unit may include a vector polarizer 24. Even with this configuration, it is possible to preferably generate laser light L3 that is radially polarized or azimuthally polarized and has a spiral phase distribution.

[0062] When radially polarized laser light L3 and azimuthally polarized laser light L3 are alternately irradiated, the depth of the focused spots differs between the radially polarized light and the azimuthally polarized light, as described above. In this modification, in order to overlap the range of the focused spots of the radially polarized light and the range of the focused spots of the azimuthally polarized light, the control unit 40B may adjust the defocus component in the SLM 26 instead of, or in addition to, controlling the relative positional relationship between the focusing optical system 30 and the crystal 11.

[0063] If the SLM 26 is a polarization-dependent SLM, such as a liquid crystal type, the laser light must be converted into radially polarized light or azimuthally polarized light after being given a helical phase by the SLM 26. Therefore, in this case, in this modified example, the SLM 26 is placed before the vector polarizer 24. However, if the SLM 26 is a polarization-independent SLM, such as a MEMS (Micro Electro Mechanical Systems) type, the SLM 26 may be placed either before or after the vector polarizer 24.

[0064] [Second Modification] FIG. 17 is a diagram schematically illustrating the configuration of a laser processing apparatus 1C according to a second modification of the present disclosure. The laser processing apparatus 1C includes a light generation unit 20C and a control unit 40C instead of the light generation unit 20A and the control unit 40A of the above embodiment. The light generation unit 20C includes a spatial light modulator (SLM) 26 and a mirror 271 as a phase control unit instead of the phase plate 22 of the above embodiment. Furthermore, the light generation unit 20C includes a spatial light modulator (SLM) 28, a mirror 272, a half-wave plate 291, and a quarter-wave plate 292 as a polarization control unit instead of the vector polarizer 24 of the above embodiment. The SLM 28 is a second spatial light modulator according to the present disclosure. The configurations of the SLM 26 and the mirror 271 are the same as those of the first modification described above.

[0065] In addition to the functions of the control unit 40A in the above embodiment, the control unit 40C has a function of controlling the phase distribution displayed on the SLM 26 and the phase distribution displayed on the SLM 28. The control unit 40C causes the SLM 28 to display a phase distribution for converting the laser light L2 into radially polarized or azimuthally polarized light having a spiral phase to generate the laser light L3. Part (a) of Figure 18 is an example of a phase distribution displayed on the SLM 28 for converting the laser light L2 into radially polarized light having a spiral phase. Part (b) of Figure 18 is an example of a phase distribution displayed on the SLM 28 for converting the laser light L2 into azimuthally polarized light having a spiral phase. In these figures, the magnitude of the phase is indicated by a shade of color, which changes from white to black as the phase approaches 0 (rad) to 2π (rad). 18(a) and 18(b), the control unit 40C causes the SLM 28 to display a phase distribution in which a phase change from 0 (rad) to 2π (rad) around the optical axis is repeated twice (in other words, the phase changes from 0 (rad) to 4π (rad) around the optical axis). The circumferential position at which the phase becomes 0 (rad) differs by 90° between the phase distribution for converting the laser light L2 into radially polarized light (part (a) of FIG. 18) and the phase distribution for converting the laser light L2 into azimuthal polarization (part (b) of FIG. 18).

[0066] The control unit 40C causes the SLM 26 to display a phase correction pattern such as that shown in part (a) of Fig. 19 or an unmodulated pattern such as that shown in part (b) of Fig. 19. The laser light L2 modulated by the SLM 26 is guided to the SLM 28 by the double telecentric relay lens system 23 and the mirror 27 via the half-wave plate 291.

[0067] The half-wave plate 291 is disposed on the optical path of the laser light L2 between the SLM 26 and the SLM 28. The quarter-wave plate 292 is disposed on the optical path of the laser light between the SLM 28 and the focusing optical system 30. The half-wave plate 291 and the quarter-wave plate 292 cooperate with the SLM 28 to convert the laser light L2 into radially polarized or azimuthally polarized light having a helical phase, thereby generating laser light L3.

[0068] The configuration of this modification can achieve the same effects as the above embodiment. In addition, as in this modification, the SLM 28 functions as a phase control unit and a polarization control unit. Even with this configuration, it is possible to preferably generate radially polarized or azimuthally polarized laser light L3 having a spiral phase distribution.

[0069] When radially polarized laser light L3 and azimuthally polarized laser light L3 are alternately irradiated, it is preferable to overlap the range of the focused spot of the radially polarized laser light with the range of the focused spot of the azimuthally polarized laser light L3. To achieve this, the control unit 40C may adjust the defocus component in one or both of the SLMs 26 and 28, instead of or in addition to controlling the relative positional relationship between the focusing optical system 30 and the crystal 11.

[0070] [Third Modification] Figure 20 is a diagram schematically illustrating the configuration of a laser processing apparatus 1D according to a third modification of the present disclosure. The laser processing apparatus 1D includes a light generation unit 20D and a control unit 40D instead of the light generation unit 20A and the control unit 40A of the above embodiment. The light generation unit 20D includes an SLM 28, a mirror 272, a half-wave plate 291, and a quarter-wave plate 292 as a polarization control unit instead of the vector polarizer 24 of the above embodiment. The SLM 28 is the second spatial light modulator of the present disclosure. The configurations of the SLM 28, the mirror 272, the half-wave plate 291, and the quarter-wave plate 292 are the same as those of the second modification described above.

[0071] According to the configuration of this modified example, it is possible to obtain the same effects as in the above embodiment. In addition, as in this modified example, the phase control section may include a phase plate 22, and the polarization control section may include an SLM 28. Even with this configuration, it is possible to suitably generate laser light L3 that is radially polarized or azimuthally polarized and has a spiral phase distribution.

[0072] When radially polarized laser light L3 and azimuthally polarized laser light L3 are alternately irradiated, it is preferable to overlap the range of the focused spot of the radially polarized laser light L3 with the range of the focused spot of the azimuthally polarized laser light L3. To achieve this, the control unit 40D may adjust the defocus component of the SLM 28 instead of or in addition to controlling the relative positional relationship between the focusing optical system 30 and the crystal 11.

[0073] [Fourth Modification] As described above, the phase plate 22 and the SLM 26 may provide the laser light L1 with a phase distribution obtained by superimposing a phase distribution different from the spiral phase distribution on the spiral phase distribution. Fig. 21 shows a simulation result in which a plurality of (for example, two) focused spots aligned in a direction intersecting with the optical axis direction are simultaneously formed by superimposing a phase distribution representing a grating on the spiral phase distribution. In this example, the z-cut crystal 14 is made of LiNbO ３The wavelength of the laser light L is 1030 nm, the numerical aperture (NA) of the objective lens is 0.4, and the depth of the focusing position is 669 μm. Part (a) of Figure 21 shows a case where a phase distribution representing a certain grating is superimposed on a spiral phase distribution. Part (b) of Figure 21 shows a case where a phase distribution representing a different grating from that shown in Part (a) of Figure 21 is superimposed on a spiral phase distribution.

[0074] For example, if the refractive index of each focused spot is smaller than the refractive index of its surroundings, multiple focused spots aligned in a direction intersecting the optical axis direction constitute a Type-II optical waveguide. Light is guided between the multiple focused spots. According to the laser processing apparatus, optical device manufacturing method, and laser processing method of the above-described embodiment and each modification, multiple focused spots can be formed simultaneously, thereby enabling the fabrication of a Type-II optical waveguide to be completed more quickly. Additionally, the distance between the two focused spots shown in part (b) of FIG. 21 is shorter than the distance between the two focused spots shown in part (a) of FIG. 21. In this way, by changing the superimposed phase distribution, the distance between the focused spots (in other words, the lateral width of the Type-II optical waveguide) can be freely changed.

[0075] 22 shows the results of a simulation in which a phase distribution representing a Fresnel lens is superimposed on a spiral phase distribution to simultaneously form multiple (for example, two) focused spots aligned in the optical axis direction. In this example, the z-cut crystal 14 is also made of LiNbO ３The laser beam L has a wavelength of 1030 nm, the objective lens has a numerical aperture (NA) of 0.4, and the focal position is at a depth of 669 μm. Part (a) of FIG. 17 shows a case where a phase distribution representing a certain Fresnel lens is superimposed on a spiral phase distribution. Part (b) of FIG. 22 shows a case where a phase distribution representing a different Fresnel lens from that shown in Part (a) of FIG. 22 is superimposed on a spiral phase distribution. According to the laser processing apparatus, optical device manufacturing method, and laser processing method of the above embodiment and each modification, it is also possible to simultaneously form multiple focal spots aligned in the optical axis direction. In addition, the distance between the two focal spots shown in Part (b) of FIG. 22 is shorter than the distance between the two focal spots shown in Part (a) of FIG. 22. While the distance between the vertically separated focal spots (see Part (c) of FIG. 8) formed when the laser beam L3 is circularly polarized cannot be changed, according to the above embodiment and each modification, the distance between the focal spots can be freely changed by changing the superimposed phase distribution.

[0076] [Fifth Modification] As described above, the phase plate 22 and the SLM 26 may provide the laser light L1 with a phase distribution obtained by superimposing a phase distribution different from the helical phase distribution on the helical phase distribution. Part (c) of Figure 23 shows the simulation results when a phase distribution for correcting spherical aberration is superimposed on the helical phase distribution when the numerical aperture (NA) of the objective lens is large. For comparison, part (a) of Figure 23 shows the case where the laser light L3 is circularly polarized, no helical phase is imparted, and no spherical aberration is corrected. Part (b) of Figure 23 shows the case where the laser light L3 is circularly polarized, no helical phase is imparted, and spherical aberration is corrected. Part (d) of Figure 23 shows the case where the laser light L3 is azimuthally polarized, no helical phase is imparted, and no spherical aberration is corrected. In this example, the z-cut crystal 14 is made of LiNbO ３ The wavelength of the laser light L is 1030 nm, the numerical aperture (NA) of the objective lens is 0.9, and the depth of the light-condensing position is 335 μm.

[0077] 23(a) and 23(b), when the laser beam L3 is circularly polarized, even if the spherical aberration is corrected, the focused spot will still be separated into upper and lower parts. As shown in 23(c) of FIG. 23(c), according to the above embodiment and each modified example, by superimposing a phase distribution for correcting spherical aberration on a spiral phase distribution, it is possible to form a single focused spot without separation, and to reduce the spherical aberration, thereby further shortening the dimension of the focused spot in the optical axis direction and further concentrating energy on the processed area.

[0078] [Sixth Modification] FIG. 24 is a diagram schematically illustrating the configuration of a laser processing apparatus 1E according to a sixth modification of the present disclosure. The laser processing apparatus 1E includes a light generation unit 20E and a controller 40E instead of the light generation unit 20A and the controller 40A of the above embodiment. The light generation unit 20E includes an SLM 28, a half-wave plate 291, and a quarter-wave plate 292 as phase and polarization controllers, instead of the phase plate 22 and the vector polarizer 24 of the above embodiment. The laser light L1 output from the laser light source 21 is reflected by mirrors 271 and 273 and reaches the half-wave plate 291. In addition to the functions of the controller 40A of the above embodiment, the controller 40E has a function of controlling the phase distribution displayed on the SLM 28. The controller 40E converts the laser light L1 into radially polarized or azimuthally polarized light having a helical phase to generate laser light L3, and causes the SLM 28 to display a phase distribution.

[0079] The SLM 28 is disposed on the optical path between the half-wave plate 291 and the quarter-wave plate 292. The half-wave plate 291 is disposed so that its fast axis forms an angle of π / 8 (rad) with respect to the polarization direction of the incident light, and the quarter-wave plate 292 is disposed so that its fast axis forms an angle of π / 4 (rad) with respect to the polarization direction of the incident light. Thus, the half-wave plate 291 and the quarter-wave plate 292, in cooperation with the SLM 28, generate laser light L3 that is radially polarized or azimuthally polarized and has a spiral phase distribution.

[0080] 25 is a diagram showing the results of verifying, using Stokes parameters, whether or not radially polarized or azimuthal polarized laser light L3 having a spiral phase distribution can be generated even when the light generation unit 20E includes an SLM 28, a half-wave plate 291, and a quarter-wave plate 292 as phase and polarization control units. Parts (a) to (c) of FIG. 25 show Stokes parameters when the laser light is radially polarized and does not have a spiral phase distribution. Parts (d) to (f) of FIG. 25 show Stokes parameters when radially polarized laser light L3 having a spiral phase distribution is generated using a vector polarizer and a phase plate (i.e., in the above embodiment). Parts (g) to (i) of FIG. 25 show Stokes parameters when laser light L3 is generated using the light generation unit 20E according to this modification. In Fig. 25, parts (a), (d), and (g) show the Stokes parameter S0, parts (b), (e), and (h) show the Stokes parameter S1, and parts (c), (f), and (i) show the Stokes parameter S2. Since the Stokes parameters S0 to S2 shown in parts (g) to (i), respectively, of Fig. 25 are the same as the Stokes parameters S0 to S2 shown in parts (d) to (f), respectively, it can be seen that even when the light generation unit 20E of this modified example is used, it is possible to generate laser light L3 that is radially polarized or azimuthally polarized and has a spiral phase distribution, as in the above embodiment.

[0081] According to the configuration of this modification, the SLM 28, the half-wave plate 291, and the quarter-wave plate 292 function as a phase control unit and a polarization control unit. Therefore, the same effects as those of the above embodiment can be obtained. That is, even with the configuration of this modification, it is possible to preferably generate laser light L3 that is radially polarized or azimuthally polarized and has a spiral phase distribution.

[0082] When radially polarized laser light L3 and azimuthally polarized laser light L3 are alternately irradiated, it is preferable to overlap the range of the focused spot of the radially polarized light with the range of the focused spot of the azimuthally polarized light. To achieve this, the control unit 40E may adjust the defocus component in the SLM 28 instead of, or in addition to, controlling the relative positional relationship between the focusing optical system 30 and the crystal 11.

[0083] The laser processing apparatus, optical device manufacturing method, and laser processing method according to the present disclosure are not limited to the above-described embodiments and may be modified in various ways. For example, in the above-described embodiments, the light generation unit includes a phase control unit that imparts a helical phase distribution to the laser light and a polarization control unit that radially or azimuthally polarizes the laser light. This configuration is not limited to this, and the phase control unit may be omitted from the light generation unit. That is, the laser processing apparatus may include a light generation unit that generates radially or azimuthally polarized laser light, a focusing optical system that focuses the laser light at a focusing position within a uniaxial birefringent crystal, and a focusing position control unit that moves the focusing position within the uniaxial birefringent crystal to form an optical structure. In this case, the light generation unit may include a polarization control unit that radially or azimuthally polarizes the laser light. The configuration example of the polarization control unit is the same as that of the above-described embodiments or each modified example. However, in the second modified example shown in Figure 17, the phase distribution displayed on the SLM 26 is different from that shown in Figure 18, and is a phase distribution (see Figure 3) in which the phase changes from 0 (rad) to 2π (rad) in the azimuthal direction centered on the optical axis.

[0084] In some birefringent crystals, such as sapphire, the axis whose refractive index differs from the other two axes is sometimes referred to as the c-axis rather than the z-axis. The birefringent crystals to be processed in the present invention also include birefringent crystals having a principal plane perpendicular to the c-axis, such as c-plane sapphire and SiC.

[0085] While the principles of the present invention have been illustrated and described in preferred embodiments, it will be recognized by those skilled in the art that the present invention can be modified in arrangement and detail without departing from such principles. The present invention is not limited to the particular constructions disclosed herein. We therefore claim all modifications and variations that come within the scope and spirit of the following claims.

[0086] 1A to 1E...laser processing apparatus, 10...optical device, 11...crystal (uniaxial birefringent crystal), 11a...main surface, 12...optical structure, 14...z-cut crystal, 15...y-cut crystal, 20A to 20E...light generation unit, 21...laser light source, 22...phase plate, 23, 25...double telecentric relay lens system, 24...vector polarizer, 26, 28...spatial light modulator (SLM), 30...focusing optical system, 40A to 40E...control unit, 231, 232, 251, 252...lenses, 271, 272, 273...mirrors, 291...half wave plate, 292...quarter wave plate, A1 to A3...axis, L, L1 to L3...laser light, ST1...light generation step, ST2...focusing step, ST3...forming step, ST11, ST12...steps.

Claims

a light generating unit that generates radially polarized or azimuthal polarized laser light having a spiral phase distribution; a focusing optical system that focuses the laser light at a focusing position within a uniaxial birefringent crystal; a focus position control unit that moves the focus position within the uniaxial birefringent crystal to form an optical structure; A laser processing device comprising: 　 The light generating unit a phase control unit that imparts the helical phase distribution to the laser light; a polarization control unit that converts the laser light after being given the spiral phase distribution or before being given the spiral phase distribution into the radially polarized light or the azimuthal polarized light; The laser processing device according to claim 1 , further comprising: 　 The laser processing apparatus according to claim 2 , wherein the phase control section includes a phase plate, and the polarization control section includes a vector polarizer. 　 The laser processing apparatus according to claim 2 , wherein the phase control section includes a first spatial light modulator, and the polarization control section includes a vector polarizer. 　 The laser processing apparatus according to claim 2 , wherein the phase control section includes a phase plate, and the polarization control section includes a second spatial light modulator. 　 the light generating unit has a quarter-wave plate, a half-wave plate, and a spatial light modulator arranged on an optical path between the quarter-wave plate and the half-wave plate, 2. The laser processing device according to claim 1, wherein the quarter-wave plate, the half-wave plate, and the spatial light modulator cooperate to generate the laser light that is radially polarized or azimuthally polarized and has a spiral phase distribution. 　 The laser processing apparatus according to any one of claims 1 to 6, wherein the light generating unit alternately generates the radially polarized laser light having the spiral phase distribution and the azimuthally polarized laser light having the spiral phase distribution.

8. The laser processing apparatus according to claim 7, wherein the focusing position control unit overlaps at least a portion of a range of a focusing spot of the radially polarized laser light having the spiral phase distribution with at least a portion of a range of a focusing spot of the azimuthally polarized laser light having the spiral phase distribution. 　 the focusing optical system includes an objective lens; 9. The laser processing device according to claim 1, wherein the numerical aperture of the objective lens is 0.04 or more and 3.0 or less. A method for manufacturing an optical device having a uniaxial birefringent crystal and an optical structure formed in the uniaxial birefringent crystal, comprising: a light generating step of generating a laser beam that is radially polarized or azimuthal polarized and has a spiral phase distribution; a focusing step of focusing the laser light at a focusing position within the uniaxial birefringent crystal; a forming step of moving the focusing position in the uniaxial birefringent crystal to form the optical structure; A method for manufacturing an optical device, comprising: 　 The light generating step includes: imparting the spiral phase distribution to laser light; a step of radially polarizing the laser light after the helical phase distribution has been imparted or before the helical phase distribution has been imparted, or the step of azimuthal polarizing the laser light; The method for manufacturing an optical device according to claim 10 , comprising:

12. The method for manufacturing an optical device according to claim 10, wherein the laser light that is radially polarized and has the spiral phase distribution and the laser light that is azimuthal polarized and has the spiral phase distribution are alternately generated in the light generating step.

13. The method for manufacturing an optical device according to claim 12, wherein in the forming step, at least a portion of a range of a focused spot of the radially polarized laser light having the spiral phase distribution is overlapped with at least a portion of a range of a focused spot of the azimuthal polarized laser light having the spiral phase distribution. 　 The uniaxial birefringent crystal is made of GaN, SiC, LiNbO ３ , LiTaO ３ , β-BBO, sapphire, polyimide, Nd:YVO ４ , Nd:GdVO ４ 14. The method for manufacturing an optical device according to claim 10, wherein the optical device comprises at least one material selected from the group consisting of α-Quartz, AlN, ZnO, 4H—SiC, 6H—SiC, and Nd:YCOB.

15. The method for manufacturing an optical device according to any one of claims 10 to 14, wherein in the optical device, the optical structure constitutes at least one optical element selected from the group consisting of an optical waveguide, a quasi-phase matching structure, a diffraction grating, a splitter, a directional coupler, an amplitude modulation structure, a polarization control structure, a wavelength conversion structure, and a voxel. 　 The optical device comprises: a substrate that is the uniaxial birefringent crystal; an optical integrated circuit formed on the substrate and including the optical structure; The method for manufacturing an optical device according to any one of claims 10 to 14, comprising: 　 In the focusing step, the laser light is focused using an objective lens, 17. The method for manufacturing an optical device according to claim 10, wherein the numerical aperture of the objective lens is 0.04 or more and 3.0 or less. 　 a light generating step of generating a laser beam that is radially polarized or azimuthal polarized and has a spiral phase distribution; a focusing step of focusing the laser light at a focusing position within a uniaxial birefringent crystal; a forming step of forming an optical structure by moving the focusing position within the uniaxial birefringent crystal; A laser processing method comprising:

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