Method for producing optical coupling component, and optical coupling component

Abstract

A production method according to the present disclosure comprises: a preparation step; a laser irradiation step; and a focal point movement step. The light intensity distribution of an emitted femtosecond laser beam is specified by a coordinate axis having the origin at the center of the laser beam. The shape of the light intensity distribution is such that the diameter of the beam is given in the range of -0.5 to +0.5 on the coordinate axis, and that an average light intensity AV0 in the range of -0.1 to +0.1 on the coordinate axis is 70-99% of both an average light intensity AV- in the range of -0.3 to -0.1 on the coordinate axis and an average light intensity AV+ in the range of +0.1 to +0.3 on the coordinate axis.

Description

Optical connection component manufacturing method and optical connection component

[0001] This disclosure relates to a method for manufacturing an optical connecting component and an optical connecting component. This application claims priority from Japanese Patent Application No. 2023-026425, filed February 22, 2023, the contents of which are relied upon and incorporated herein by reference in their entirety.

[0002] Optical connecting components are generally used as optical signal transmitting and receiving components in optical communications. Regarding manufacturing methods for such optical connecting components, for example, Non-Patent Documents 1 to 5 disclose techniques for forming optical waveguides by drawing using a femtosecond laser light source. Specifically, Non-Patent Document 1 discloses a technique for forming a core that serves as a waveguide by single-scan drawing with femtosecond laser light. Non-Patent Document 2 discloses a technique for forming a core having a square cross-sectional shape by multi-scan drawing with femtosecond laser light. Non-Patent Document 3 also introduces a mechanism for increasing the refractive index (compression) by irradiation with femtosecond laser light, Non-Patent Document 4 introduces a mechanism for increasing the refractive index by irradiation with femtosecond laser light (composition rearrangement), and Non-Patent Document 5 introduces a mechanism for forming a nanograting periodic structure by irradiation with femtosecond laser light.

[0003] Dezhi Tan, et al., “Femtosecond laser writing low-loss waveguides in silica glass: highly symmetrical mode field and mechanism of refractive index change,” Optical Materials Express, Vol.11, No.3 pp.848-857.Y.Nasu, et al., " Low-loss waveguides written with a femtosecond laser for flexible interconnection in a planar light-wave circuit", Optics Letters, Vol.30, pp.723-725 (2005).E. N. Glezer and E. Mazur, “Ultrafast-laser driven micro-explosions in transparent materials,” Appl. Phys. Lett. Vol.71, No.7, pp.882-884 (1997).Y. Liu, et al., “Micromodification of element distribution in glass using femtosecond laser irradiation,” OPTICS LETTERS, Vol.34, No.2, pp.136-138 (2009).Y. Shimotsuma, et al., “Self-organized nanogratings in glass irradiated by ultrashort light pulses,” PHYSICAL REVIEW LETTERS, Vol.91, No.24, pp.247405-1 to 247405-4 (2003).S. Masaaki, et al., “Improved phase hologram design for generating symmetric light spots and its application for laser writing of waveguides,” OPTICS LETTERS, Vol.36, No.7, April 1, 2011, pp.1065-1067.Keiji Fuse, “Beam Shaping for Advanced Laser Materials Processing,” Laser Technik Journal, pp.19-22 (2015).S. Hasegawa, et al., “Holographic vector wave femtosecond laser processing,” International Journal of Optomechatronics, p.73(2014)Payne. F. P., et al., “A theoretical analysis of scattering loss from planar optical waveguides, “Optical and Quantum Electronics, vol.26 (1994) pp.977-986.

[0004] The manufacturing method of an optical connecting component disclosed herein includes a preparation step, a laser irradiation step, and a focal point movement step. In the preparation step, a silica-based glass member is prepared. In the laser irradiation step, femtosecond laser light having an energy amount sufficient to cause a photo-induced refractive index change in the glass member and a shaped beam having a pulse width of 500 fs or less is focused and irradiated onto the interior of the glass member via a focusing lens. In the focal point movement step, the focal point position of the femtosecond laser light is moved relative to the glass member. Furthermore, by linking the laser irradiation step and the focal point movement step, a continuous refractive index change region functioning as an optical waveguide is formed within the glass member. The light intensity distribution of the irradiated femtosecond laser light is specified by coordinate axes that pass through the center of gravity of the beam irradiation region of the femtosecond laser light at the focal point position, extend along a direction perpendicular to the movement direction of the focal point position relative to the glass member, and have the center of the femtosecond laser light as their origin. The shape of the light intensity distribution satisfies the following three conditions: The first condition is that the beam diameter of the femtosecond laser beam is given in the range of -0.5 to +0.5 on the coordinate axis. The second condition is that the light intensity of the femtosecond laser beam is increased compared to the light intensity of a Gaussian beam of the same laser light amount in the range of -∞ to -0.1 on the coordinate axis and in the range of +0.1 to +∞ on the coordinate axis. The third condition is that the average light intensity AV0 in the range of -0.1 to +0.1 on the coordinate axis is 70% to 99% of both the average light intensity AV- in the range of -0.3 to -0.1 on the coordinate axis and the average light intensity AV+ in the range of +0.1 to +0.3 on the coordinate axis.

[0005] Fig. 1 is a flowchart illustrating an example of a manufacturing method for an optical connecting component according to the present disclosure. Fig. 2 is a diagram illustrating a configuration example of a manufacturing apparatus for implementing the manufacturing method for an optical connecting component according to the present disclosure, and is also a diagram illustrating laser light scanning. Fig. 3 is a diagram illustrating various beam shaping optical systems and beam spot shapes. Fig. 4 is a diagram illustrating the beam shape of a Gaussian beam used to form an optical waveguide and the cross section of the formed optical waveguide. Fig. 5 is a diagram illustrating the relationship between the beam shape of laser light applied to the manufacturing method according to the present disclosure and the cross-sectional shape of the formed optical waveguide.

[0006] [Problem to be Solved by the Present Disclosure] As a result of examining the above-mentioned conventional techniques, the inventors discovered the following problem. That is, the technique disclosed in Non-Patent Document 1 succeeds in forming an optical waveguide by single-scan drawing with femtosecond laser light, but the width of the optical waveguide is not controlled. That is, the shape of the obtained optical waveguide is long with respect to the laser irradiation axis, but the lateral dimension of the optical waveguide is narrow, at approximately 2 μm or less. This results in a large coupling loss of light propagating within the optical waveguide.

[0007] In contrast, the technology of Non-Patent Document 2 successfully forms an optical waveguide using multi-scan writing with femtosecond laser light. In multi-scan writing, the femtosecond laser light irradiated along the beam irradiation axis is scanned 20 times while being shifted in a direction perpendicular to the beam irradiation axis, thereby controlling the width of the optical waveguide. However, the time required to form a single optical waveguide is 20 times longer than that required for single-scan writing. Non-Patent Document 6 also introduces a technology that uses hologram technology to generate multiple branch beams from femtosecond laser light, each of which is a diffracted light beam, and then simultaneously creates multiple optical waveguides within a glass member by irradiating these branch beams. As such, the technology of Non-Patent Document 6 forms optical waveguides with only one scan, making it difficult to maintain the required width of the optical waveguide, resulting in a significant decrease in productivity of optical connection components including optical waveguides.

[0008] The present disclosure provides an optical connecting component and a method for manufacturing an optical connecting component that facilitates control of the shape of an optical waveguide provided in the optical connecting component and enables significant increase in productivity of the optical connecting component.

[0009] Effect of the Present Disclosure According to the method for manufacturing an optical connecting component of the present disclosure, it becomes easier to control the shape of the optical waveguide provided in the glass member, and it becomes possible to significantly increase productivity.

[0010] [Description of Embodiments of the Present Disclosure] First, the contents of the embodiments of the present disclosure will be individually listed and described.

[0011] The manufacturing method of an optical connecting component disclosed herein includes (1) a preparation step, a laser irradiation step, and a focal point movement step. In the preparation step, a silica-based glass member is prepared. In the laser irradiation step, femtosecond laser light having an energy amount sufficient to cause a photo-induced refractive index change in the glass member and a shaped beam having a pulse width of 500 fs or less is focused and irradiated onto the interior of the glass member via a focusing lens. In the focal point movement step, the focal point position of the femtosecond laser light is moved relative to the glass member. Furthermore, by linking the laser irradiation step and the focal point movement step, a continuous refractive index change region functioning as an optical waveguide is formed within the glass member. The light intensity distribution of the irradiated femtosecond laser light is specified by coordinate axes that pass through the center of gravity of the beam irradiation region of the femtosecond laser light at the focal point position, extend along a direction perpendicular to the movement direction of the focal point position relative to the glass member, and have the center of the femtosecond laser light as the origin. The shape of the light intensity distribution satisfies the following three conditions: The first condition is that the beam diameter of the femtosecond laser beam is given in the range of -0.5 to +0.5 on the coordinate axis. The second condition is that the light intensity of the femtosecond laser beam is increased compared to the light intensity of a Gaussian beam of the same laser light amount in the range of -∞ to -0.1 on the coordinate axis and in the range of +0.1 to +∞ on the coordinate axis. The third condition is that the average light intensity AV0 in the range of -0.1 to +0.1 on the coordinate axis is 70% to 99% of both the average light intensity AV- in the range of -0.3 to -0.1 on the coordinate axis and the average light intensity AV+ in the range of +0.1 to +0.3 on the coordinate axis.

[0012] This configuration makes it easier to control the shape of the optical waveguide provided in the glass member, and also makes it possible to significantly increase productivity.

[0013] (2) In the above (1), the light intensity of the femtosecond laser beam may be increased in the range of −∞ to −0.1 on the coordinate axis and in the range of +0.1 to +∞ on the coordinate axis compared to the light intensity of a Gaussian beam of the same laser light amount. This configuration makes it easier to control the shape of the optical waveguide provided in the glass member and enables a significant increase in productivity.

[0014] (3) In the above (1) or (2), the shape of the beam irradiation area at the focal point position may have a first maximum width Zd along the movement direction and a second maximum width Yd along a direction perpendicular to the movement direction, and the ratio Yd / Zd of the second maximum width Yd to the first maximum width Zd may be equal to or greater than 2 and equal to or less than 15. In this case, it is easy to control the width of the optical waveguide formed in one scan.

[0015] (4) In any of (1) to (3) above, the optical system used for beam shaping may be any element selected from the group consisting of an LCoS, a DOE, an aspherical lens, and a cylindrical lens, or a combination of multiple elements selected from the group. In this case, the shape of the beam irradiation area at the focal point can be shaped into any shape.

[0016] (5) In any of (1) to (4) above, the refractive index change region may have a rectangular shape in a plane perpendicular to the direction of movement of the focal point position relative to the glass member, thereby making the light intensity distribution of the propagation mode circular and improving the coupling efficiency with a single-mode fiber (SMF).

[0017] The optical connection component of the present disclosure is (6) an optical connection component manufactured by any one of the manufacturing methods (1) to (5) above, wherein the shape of the refractive index change region may be quadrangular in a plane perpendicular to the direction of movement of the focal point position relative to the glass member.

[0018] (7) In the above (6), the refractive index inside the rectangle may be uniform, thereby reducing propagation loss.

[0019] As described above, each aspect listed in the [Description of Embodiments of the Present Disclosure] section can be applied to all of the remaining aspects individually or to all combinations of these remaining aspects.

[0020] [Details of the embodiments of the present disclosure] The manufacturing method of the optical connecting component and the specific structure of the optical connecting component of the present disclosure will be described in detail below with reference to the accompanying drawings. Note that the present disclosure is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims. Furthermore, in the description of the drawings, the same elements are given the same reference numerals, and duplicate explanations will be omitted.

[0021] Fig. 1 is a flowchart for explaining an example of a manufacturing method for an optical connecting part 100 of the present disclosure. Fig. 2 is a diagram for explaining laser light scanning, showing an example of the configuration of a manufacturing apparatus for carrying out the manufacturing method for an optical connecting part 100 of the present disclosure (denoted as "manufacturing apparatus" in Fig. 2). The upper part of Fig. 2 (denoted as "configuration" in Fig. 2) shows an example of the configuration of the manufacturing apparatus. The lower part of Fig. 2 (denoted as "laser light scanning" in Fig. 2) shows laser light scanning in the laser light irradiation step.

[0022] The manufacturing apparatus shown in the upper part of Figure 2 includes a femtosecond laser 20, a laser driver 25 for driving the femtosecond laser 20, a beam shaping optical system 30 for shaping the beam spot of the femtosecond laser light into an arbitrary shape, an XYZ stage 40, a stage driver 45 for driving the XYZ stage 40, and a controller 50 for controlling the operation of each of these components.

[0023] The laser driver 25 controls the power and repetition frequency of the pulsed laser light (hereinafter referred to as "femtosecond laser light") output from the femtosecond laser 20 in accordance with instructions from the controller 50. This allows the femtosecond laser 20 to output femtosecond laser light having a pulse width of several hundred femtoseconds or less. In particular, the femtosecond laser light having a pulse width set to several hundred femtoseconds or less has a peak power of 10 ５ W / cm ２The repetition frequency of the output femtosecond laser light may be 10 kHz or more in order to smooth the refractive index and structure of the optical waveguide formed inside the glass material. A glass member 10 to be the main body of the optical component is placed on the device mounting surface of the XYZ stage 40. The glass member 10 is glass, such as silica-based glass, that can generate a pressure-induced refractive index change Δnp, or both Δnp and a structure-induced refractive index change Δnd, when irradiated with laser light. Silica-based glass is a material containing silicon dioxide (SiO ２ ) as the main component, and SiO ２ The glass member 10 includes 50% or more of the above-mentioned elements. The glass member 10 may be undoped with impurities, germanium (Ge)-doped glass, or glass co-doped with Ge and boron (B). More specifically, the glass member 10 may include no dopants other than Ge, or glass co-doped with B and Ge. These glasses may also be silica-based glass, phosphate-based glass, halide glass, or sulfide glass. The femtosecond laser light output from the femtosecond laser 20 is focused by the beam shaping optical system 30 onto a focusing point 35 located within the glass member 10 mounted on the XYZ stage 40, i.e., on the YZ plane. This results in a refractive index change region 15 serving as an optical waveguide within the glass member 10, resulting in the optical connecting component 100. The axis along the scanning direction of the laser light is defined as the Z-axis. The axis perpendicular to the Z-axis and perpendicular to the laser irradiation surface of the glass member 10 is defined as the X-axis. The Y axis is set as an axis perpendicular to the scanning direction and perpendicular to both the Z axis and the X axis.

[0024] In accordance with instructions from the control unit 50, the stage driver 45 drives the XYZ stage 40 so that the device mounting surface of the XYZ stage 40 moves along the X-axis, Y-axis, and Z-axis directions. This configuration enables laser scanning as shown in the lower part of FIG. 2 , and the position of the focal point 35 of the femtosecond laser light moves relative to the glass member 10. The control unit 50 controls the operations of the laser driver 25 and the stage driver 45 as described above, thereby creating a refractive index change region 15 of an arbitrary pattern inside the glass member 10. Note that the arbitrary pattern corresponds to the shape of the optical waveguide projected onto the YZ plane taking into account depth direction information along the X-axis. Through the above processes, an optical connecting part 100 is manufactured as an optical component.

[0025] Next, an optical connecting part 100 provided with an optical waveguide is manufactured using a manufacturing apparatus having the above-described structure. A manufacturing method for the optical connecting part 100 of the present disclosure will be described with reference to the flowchart in Fig. 1. In the following description, as an example of a manufacturing method for the optical connecting part 100, a case will be described in which a three-dimensional optical waveguide device is manufactured in which a refractive index change region 15 of an arbitrary pattern to become an optical waveguide is formed.

[0026] The manufacturing method of the optical connecting part 100 of the present disclosure comprises a preparation step and an optical waveguide manufacturing step. First, in the preparation step, a parallel plate glass, for example, is prepared as the glass member 10 to become the optical connecting part 100 (step ST10).

[0027] In the optical waveguide manufacturing process, a refractive index change region 15 of an arbitrary pattern that will become an optical waveguide is fabricated inside a prepared glass member 10. Specifically, after completing step ST10, the prepared glass member 10 is immediately placed on the device mounting surface of the XYZ stage 40 and irradiated with femtosecond laser light (step ST20). The control unit 50 controls the laser driver 25 so that the femtosecond laser 20 outputs femtosecond laser light having an energy amount sufficient to cause a photoinduced refractive index change inside the glass member 10 and a repetition rate of 10 kHz or more. The femtosecond laser light output from the femtosecond laser 20 is focused inside the glass member 10 by the beam shaping optical system 30. The beam shaping optical system 30 shapes the beam spot of the input femtosecond laser light into a predetermined shape. A photoinduced refractive index change is formed in the beam irradiation region at the focal point 35 of the femtosecond laser light. When laser irradiation of a predetermined portion of glass member 10 is completed, control unit 50 controls stage driving unit 45 to move the position of glass member 10 placed on the device mounting surface of XYZ stage 40 (step ST30). In this way, in the focal point moving step (step ST30), as shown in the lower part of Figure 2, the installation position of glass member 10, the position of focal point 35 of the femtosecond laser beam, or both the installation position and the focal point position are continuously or intermittently changed, thereby moving the position of focal point 35 of the femtosecond laser beam inside glass member 10.

[0028] The laser irradiation process of step ST20 and the focal point movement process of step ST30, i.e., the control of the operation of laser driver 25 and stage driver 45 by controller 50, are repeated (step ST40) while changing the irradiation conditions or maintaining the same conditions, starting from the point C in Fig. 1, until the pre-designed optical waveguide pattern is formed inside glass member 10. Once the formation of refractive index change region 15 into glass member 10 is complete (step ST40), glass member 10 is annealed for aging or other purposes to prevent the refractive index from changing over a long period of time (step ST50). Through these steps, an optical connecting component having an optical waveguide therein is obtained.

[0029] The beam shaping optical system 30 may be, for example, an optical system including an aspherical lens, an optical system combining a condenser lens and a cylindrical lens, or a DOE (diffractive optical element), as shown in FIG. 3 . DOEs include liquid crystal on silicon (LCoS). Here, a glass-type DOE with non-variable refractive index modulation is referred to as a DOE, and an LCoS with variable refractive index modulation is referred to as a holographic optical element. The top row of FIG. 3 (labeled "aspherical lens" in FIG. 3 ) shows the configuration of an optical system including an aspherical lens 110. The second row of FIG. 3 (labeled "cylindrical lens + condenser lens" in FIG. 3 ) shows the configuration of an optical system combining a cylindrical lens and a condenser lens. The third row of FIG. 3 (labeled "DOE" in FIG. 3 ) shows the configuration of an optical system including a DOE. The bottom row of FIG. 3 (labeled "holographic optical element" in FIG. 3 ) shows the configuration of an optical system including a holographic optical element.

[0030] The first optical system using an aspherical lens shown in the top row of Fig. 3 includes an aspherical lens 110. If necessary, a beam shaper 111 may be provided upstream or downstream of the aspherical lens 110. The total light intensity distribution of the femtosecond laser beam output from the aspherical lens 110 (hereinafter simply referred to as "light intensity distribution") is defined on a beam waist BW where a focal point 35 is located and which is included in the YZ plane. The beam spot of the femtosecond laser beam corresponds to a beam irradiation area 350 having a first maximum width Zd along the Z-axis direction and a second maximum width Yd (≥ Zd) along the Y-axis direction.

[0031] The second optical system shown in the second row of Figure 3, which is composed of a focusing lens and a cylindrical lens, includes a focusing lens 121 and a cylindrical lens 122, and similar to the above-mentioned ``aspherical lens'' optical system, outputs femtosecond laser light having a beam spot corresponding to a beam irradiation area 350 having a width Yd along the Y-axis direction and a width Zd (≦Yd) along the Z-axis direction.

[0032] The third optical system shown in the third row of FIG. 3 , which is composed of a condenser lens and a DOE, includes DOE 131 and condenser lens 132. DOE 131 receives femtosecond laser light from femtosecond laser 20 and outputs a group of branched beams having various beam arrangement patterns. The condenser lens 132 focuses the multiple branched beams output from DOE 131 inside glass member 10 while maintaining the beam arrangement pattern. The fourth optical system shown in the bottom row of FIG. 3 , which is composed of a condenser lens and a holographic optical element, includes LCoS 141, which is a holographic optical element, and condenser lens 142. LCoS 141 receives femtosecond laser light from femtosecond laser 20 and outputs a group of branched beams having various beam arrangement patterns. The condenser lens 142 focuses the multiple branched beams output from LCoS 141 inside glass member 10 while maintaining the beam arrangement pattern. For example, when five branch beams are output from the DOE 131 or the LCoS 141, the beam spots #1 to #5 of these branch beams may be spatially separated so that the spot centers are arranged along the Y-axis direction, as shown on the right side of the third and bottom rows of Fig. 3. In this case, the beam spots #1 to #5 form a beam irradiation area 350.

[0033] As mentioned above, it is known that a refractive index change region that serves as an optical waveguide can be formed in a glass member by a drawing method using a femtosecond laser light source (Non-Patent Documents 3 and 4). It has also been proposed to improve productivity by splitting femtosecond laser light into multiple diffracted beams using a hologram diffraction element or the like, and simultaneously forming multiple optical waveguides using each of the multiple branched beams composed of these diffracted beams (Non-Patent Document 6).

[0034] On the other hand, in the embodiment of the present disclosure, the beam irradiation area 350 is defined on a beam waist BW included in the YZ plane where the focusing point 35 exists. In this beam irradiation area 350, the focusing power in the Z-axis direction is set to be at or near the diffraction limit. In contrast, the focusing power in the Y-axis direction is set to be weaker than the focusing power in the Z-axis direction. For example, if the beam diameter in the Z-axis direction is 1, the beam diameter in the Y-axis is 2 or more and 15 or less, i.e., the ratio Yd / Zd is 2 or more and 15 or less. The beam diameter defined along the Y-axis direction on the beam waist BW, i.e., the beam width, is 1 / e of the maximum light intensity existing on either side of the beam center. ２ is the distance between the positions where

[0035] Specifically, femtosecond laser light is focused inside the glass member 10 by the beam shaping optical system 30 shown in FIG. 3 , and a refractive index change region 15 is formed inside the glass member 10 by driving the XYZ stage 40. The wavelength of the laser light is, for example, in the range of −10 nm or more and +10 nm or less relative to 1030 nm, or in the range of −10 nm or more and +10 nm or less relative to 1060 nm, second harmonic generation (SHG) for each wavelength range, or third harmonic generation (THG) for each wavelength range. The pulse width of the laser light is 500 fs or less. The repetition rate is 100 kHz or more and 5 MHz or less. Below, FIG. 4 shows an example of Gaussian beam irradiation as a comparative example, while FIG. 5 shows an example of an embodiment of the present disclosure.

[0036] FIG. 4 is a diagram showing the beam shape of a Gaussian beam used to form an optical waveguide and the cross section of the formed optical waveguide (denoted as "Formation of Optical Waveguide (Gaussian Beam)" in FIG. 5). The upper part of FIG. 4 (denoted as "Beam Shape" in FIG. 4) shows a beam irradiation area 350 of the Gaussian beam defined on the YZ plane, a light intensity distribution 350Y along the central axis of the beam irradiation area 350 parallel to the Y axis, and a light intensity distribution 350Z along the central axis of the beam irradiation area 350 parallel to the Z axis. The lower part of FIG. 4 (denoted as "Cross Section of Optical Waveguide" in FIG. 4) shows a cross section of the optical waveguide taken along line II shown in the lower part of FIG. 2, formed by irradiation with a beam having the light intensity distribution shown in the upper part of FIG. 4.

[0037] As shown in the upper part of Figure 4, the beam irradiation region 350 defined by the beam waist BW is shaped by the beam shaping optical system 30 shown in Figure 3. That is, the femtosecond laser light irradiated into the interior of the glass member 10 is a Gaussian beam with a beam diameter along the Z-axis direction of approximately 1 μm or less and a beam diameter along the Y-axis direction of 2 μm to 10 μm. The Gaussian beam itself has a light intensity distribution 350Y along the Y-axis direction and a light intensity distribution 350Z along the Z-axis direction. The light intensity distribution 350Y is a light intensity distribution centered on an axis AXz parallel to the Z-axis, one of two axes that intersect at right angles at the center of gravity of the beam irradiation region 350. The light intensity distribution 350Z is a light intensity distribution centered on an axis AXy parallel to the Y-axis. Irradiation of this Gaussian beam results in a refractive index change region 150 having the cross-sectional shape shown in the lower part of Figure 4. The refractive index change region 150 functions as an optical waveguide. In the example shown in the lower part of Figure 4, the NA of the focusing lens applied to the beam shaping optical system 30 is 0.40 or more and 0.55 or less. The wavelength of the incident beam is 1030 nm, or 515 nm for its SHG. The pulse width is 100 fs or more and 450 fs or less. The scanning speed is 0.01 mm / sec or more and 10 mm / sec or less. The pulse energy is 30 nJ or more and 1000 nJ or less. The repetition frequency is 100 kHz or more and 5 MHz or less. The position of the focusing point 35 is set at a depth of 50 μm or more and 250 μm or less from the surface of the glass member 10.

[0038] As can be seen from the cross-sectional shape of the refractive index change region 150 shown in the lower part of Figure 4, a 9.2 μm optical waveguide width was obtained with a single beam scan. It was found that this optical waveguide width could be controlled to between 3 μm and 10 μm by adjusting the laser light power. For reference, the outline of the refractive index change region 150 formed by Gaussian beam irradiation is shown by a dashed line in the Y-axis direction light intensity distribution 350Y shown in the upper part of Figure 4. In other words, the outline of this refractive index change region 150 is superimposed on the Y-axis direction light intensity distribution 350Y to match the scale. This indicates that there is a modification threshold within the glass member 10 at which a modified region that becomes the refractive index change region 150 is formed, and that the cross-sectional shape of the refractive index change region 150 generally matches the shape of the light intensity distribution 350Y, except for the central portion extending along the X-axis direction. Meanwhile, the cross-sectional shape of the refractive index change region 150 shown in the lower part of Figure 4 is elongated in the X-axis direction. Therefore, a higher-order mode occurs in the X-axis direction, making it impossible to use this for a single-mode propagation optical waveguide. Therefore, it is necessary to set an appropriate laser light intensity taking into account this modified shape.

[0039] Furthermore, as described above, the central portion of the refractive index change region 150 has a shape that is more modified than the shape of the light intensity distribution 350Y. In particular, on the side irradiated with laser light, it is known that electrons excited due to multiphoton absorption increase the number of excited electrons through nonlinear absorption, as described in Non-Patent Documents 3 and 4. In this way, it is presumed that the absorption of the irradiated laser light causes the region with a high light intensity distribution in the central region to be further modified.

[0040] When laser light is irradiated into the interior of the glass member 10 under the above-described conditions, an irradiation-side modified region separate from the refractive index change region 150 is generated on the side irradiated with the laser light. It is known that a nanograting of several hundred nanometers is formed in this irradiation-side modified region, and that this nanograting is formed perpendicular to the polarization of the irradiated laser light (Non-Patent Document 5). Non-Patent Document 7 discloses a beam shaping technique, and Non-Patent Document 8 points out that the nanograting is formed depending on the polarization of multiple branched beams. Therefore, the refractive index change region 150 can be considered an optical waveguide, and the irradiation-side modified region located on the side irradiated with the laser light can be regarded as an optical cladding. The nanograting, which has periodic refractive index fluctuations in this optical cladding, increases propagation loss. The relationship between propagation loss and the periodicity of the different refractive indices is disclosed in Non-Patent Document 9.

[0041] 5 shows the relationship between the beam shape of laser light applied to the manufacturing method of the present disclosure and the cross-sectional shape of the formed optical waveguide (denoted as "Formation of optical waveguide (present embodiment)" in FIG. 5). The upper part of FIG. 5 (denoted as "Light intensity distribution in the Y-axis direction" in FIG. 5) shows a light intensity distribution 350P of laser light applied to the manufacturing method of an optical waveguide of the present disclosure, which corresponds to the light intensity distribution 350Y shown in the upper part of FIG. 4. The lower part of FIG. 5 (denoted as "Cross section of optical waveguide" in FIG. 5) shows a cross section of the optical waveguide taken along line II shown in the lower part of FIG. 2, formed by irradiation with a beam having the light intensity distribution shown in the upper part of FIG. 5.

[0042] 4, the shape of refractive index change region 150 formed by laser light irradiation coincides with the shape of light intensity distribution 350Y in the Y-axis direction, except for the central portion. This means that by adjusting the shape of the intensity distribution of the irradiated femtosecond laser light, it is possible to control the cross-sectional shape of refractive index change region 15 formed inside glass member 10 by laser light irradiation to a desired shape.

[0043] In an embodiment of the present disclosure, the femtosecond laser beam irradiated onto the glass member 10 has a light intensity distribution 350P in the Y-axis direction, as shown in the upper part of Fig. 5. The light intensity distribution 350P of the femtosecond laser beam is defined by a coordinate axis that passes through the center of gravity of the beam irradiation area 350 of the femtosecond laser beam at the position of the focal point 35 and extends along the Y-axis direction perpendicular to the scanning direction, and has its origin at the position of the axis AXz indicating the center of the femtosecond laser beam. Furthermore, on the coordinate axis along the Y-axis, the beam diameter of the femtosecond laser beam is given in the range of -0.5 to +0.5. That is, 1 / e of the maximum light intensity of the beam ２ The beam width at the position where is 1. Furthermore, using light intensity distribution 350Y of the Gaussian beam in the Y-axis direction indicated by the dashed line as a reference, light intensity distribution 350P expands in the direction indicated by arrow S2 in the range of -∞ to -0.1, concaves in the direction indicated by arrow S1 in the range of -0.1 to +0.1, and expands in the direction indicated by arrow S2 in the range of +0.1 to +∞.

[0044] More specifically, in the light intensity distribution 350P, the light intensity of the femtosecond laser beam is increased in the range of −∞ to −0.1 and the range of +0.1 to +∞ compared to the light intensity of a Gaussian beam of the same laser light amount. In addition, the average light intensity AV0 in the range of −0.1 to +0.1 may be within a range of 70% to 99% of both the average light intensity AV− in the range of −0.3 to −0.1 and the average light intensity AV+ in the range of +0.1 to +0.3.

[0045] By setting the light intensity distribution 350P of the irradiated femtosecond laser within the above-mentioned range, it is possible to change the cross-sectional shape of the refractive index change region 15 formed inside the glass member 10 from the shape of the refractive index change region 150 shown on the left side of the cross-sectional shapes shown in the lower part of FIG. 5 to the cross-sectional shape of the refractive index change region 15B shown on the right side. That is, the refractive index change region 150 shown on the left side forms a shaded region 150A extending along the X-axis direction. This causes the generation of higher-order modes in the X-axis direction. On the other hand, if the average light intensity AV0 in the range of -0.1 to +0.1 is set to 99% or less of both the average light intensity AV- in the range of -0.3 to -0.1 and the average light intensity AV+ in the range of +0.1 to +0.3, it is possible to reduce the portion of the refractive index change region 150 on the left side corresponding to the shaded region 150A, as in the refractive index change region 15A shown in the center of the lower part of FIG. 5. Furthermore, when the average light intensity AV0 is set to 99% or less of the average light intensity AV － If both AV+ and AV+ are low, it becomes possible to reduce the formation of the portion corresponding to the shaded region 150A of the refractive index change region 150 on the left side, as shown in the refractive index change region 15B in the lower right section of Figure 5 . In other words, an optical waveguide with a rectangular cross-sectional shape of the refractive index change region 15 can be manufactured. This circularizes the light intensity distribution of the propagation mode, improving the coupling efficiency with SMF. Furthermore, the required width of the cross-sectional shape of the refractive index change region 15 can be maintained, thereby increasing the productivity of optical waveguides. In the multi-scan lithography method, when the core is scanned laterally, the etching shape reflecting the modified layer inside the core appears as a comb-tooth shape parallel to the beam irradiation axis. In this method, the etching shape inside the core does not appear as a comb-tooth shape, but rather reveals a boundary between the modified and unmodified layers, and the refractive index is uniformly etched within. This reduces propagation loss.

[0046] 10...Glass member 15, 15A, 15B...Refractive index change region 20...Femtosecond laser 25...Laser driving unit 30...Beam shaping optical system 35...Converging point 40...XYZ stage 45...Stage driving unit 50...Control unit 100...Optical connecting part 110...Aspheric lens 111...Beam shaper 121...Converging lens 122...Cylindrical lens 131...DOE 132...Converging lens 141...LCoS 142...Converging lens 350...Beam irradiation area 350Y, 350Z, 350P...Light intensity distribution #1 to #5...Beam spot BW...Beam waist.

Claims

1. a preparation step of preparing a silica-based glass member; a laser irradiation step of irradiating the interior of the glass member with femtosecond laser light having a pulse width of 500 fs or less, which has an energy amount sufficient to cause a photoinduced refractive index change in the glass member and is beam-shaped, via a focusing lens; a focal point moving step of moving a focal point position of the femtosecond laser beam relative to the glass member; Equipped with the laser irradiation step and the focusing point moving step are linked to form a continuous refractive index change region inside the glass member; the light intensity distribution of the femtosecond laser beam is specified by a coordinate axis that passes through a center of gravity of a beam irradiation area of ​​the femtosecond laser beam at the focal point position, extends along a direction perpendicular to a moving direction of the focal point position relative to the glass member, and has a center of the femtosecond laser beam as its origin; the shape of the light intensity distribution is given on the coordinate axis in which the beam diameter of the femtosecond laser beam is in the range of −0.5 to +0.5, an average light intensity AV0 in the range of -0.1 to +0.1 on the coordinate axis is 70% to 99% of both an average light intensity AV- in the range of -0.3 to -0.1 on the coordinate axis and an average light intensity AV+ in the range of +0.1 to +0.3 on the coordinate axis; A manufacturing method for optical connection components.

2. the light intensity of the femtosecond laser beam is increased in a range of −∞ to −0.1 on the coordinate axis and in a range of +0.1 to +∞ on the coordinate axis as compared with the light intensity of a Gaussian beam of the same laser light amount; The method for manufacturing the optical connecting component according to claim 1 .

3. The shape of the beam irradiation area at the focal point position is a first maximum width Zd along the movement direction; a second maximum width Yd along a direction perpendicular to the movement direction; a ratio Yd / Zd of the second maximum width Yd to the first maximum width Zd is equal to or greater than 2 and equal to or less than 15; The method for manufacturing the optical connecting component according to claim 1 or 2.

4. the optical system used for beam shaping includes at least one of a DOE, an aspherical lens, and a cylindrical lens; The method for manufacturing the optical connecting component according to claim 1 or 2.

5. the refractive index change area has a rectangular shape in a plane perpendicular to the direction of movement of the focal point position relative to the glass member; The method for manufacturing the optical connecting component according to claim 1 or 2.

6. An optical connecting part manufactured by the method for manufacturing an optical connecting part according to claim 1 or 2, the refractive index change area has a rectangular shape in a plane perpendicular to the direction of movement of the focal point position relative to the glass member; Optical connection parts.

7. 7. The optical connecting part according to claim 6, wherein the refractive index inside the quadrangle is uniform.