Method for manufacturing optical connection component

Abstract

This method for manufacturing an optical connection component comprises a preparation step, a laser irradiation step, and a light condensing point movement step. In the preparation step, a glass member is prepared. In the laser irradiation step, a plurality of branch beams branching off from femtosecond laser light using a beam shaping element are condensed and applied to the glass member via a condensing lens. In the light condensing point movement step, the light condensing point position of each of the branch beams is relatively moved with respect to the glass member. The ratio of a beam spot to the diffraction grating period of the beam shaping element is set to 0.6-0.9, and a continuous refractive index changing region is formed on the glass member.

Description

Manufacturing method of optical connection parts

[0001] This disclosure relates to a method for manufacturing an optical connecting component. This application claims priority from Japanese Patent Application No. 2023-026348, filed February 22, 2023, the contents of which are incorporated herein by reference in their entirety.

[0002] Optical connecting components are generally used as optical signal transmitting and receiving components in optical communications. Non-Patent Documents 1 to 5, for example, disclose techniques for forming optical waveguides by drawing using a femtosecond laser light source as manufacturing methods for such optical connecting components. Specifically, Non-Patent Document 1 discloses a technique for forming a core serving 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 (composition rearrangement) by irradiation with femtosecond laser light. Furthermore, 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).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).Y.Shi, Optics Express, vol.28(2020)38733.

[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, laser light is branched and irradiated. The laser light is femtosecond laser light with 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. Multiple branched beams are generated from the femtosecond laser light using a beam shaping element having a diffraction grating. The multiple branched beams are then focused and irradiated into the glass member via a focusing lens. In the focal point movement step, the focal point positions of each of the multiple branched beams are moved relative to the glass member. In particular, the mode field diameter (hereinafter referred to as "MFD") of the beam spot at the focal point position of each of the multiple branched beams is set to a ratio MFD / L of the beam spot MFD to the diffraction grating period L of the beam shaping element such that the ratio is 0.6 to 0.9. By linking the laser irradiation step and the focal point moving step, a continuous refractive index change region is formed inside the glass member.

[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 a structure 1 of beam spots arranged one-dimensionally. FIG. 5 is a diagram illustrating the light intensity distribution of an input beam of a first modified example based on the light intensity distribution of the input beam of FIG. 4 and the light intensity distribution of diffracted light converted from the input beam. FIG. 6 is a diagram illustrating the light intensity distribution of an input beam of a second modified example based on the light intensity distribution of the input beam of FIG. 4 and the light intensity distribution of diffracted light converted from the input beam.

[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 has succeeded in forming an optical waveguide by 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 one optical waveguide is 20 times longer than that required for single-scan writing, which poses a problem of significantly reducing the productivity of optical connection components including optical waveguides.

[0008] The present disclosure provides a method for manufacturing an optical connecting component that makes it easy to control the shape of an optical waveguide provided in the optical connecting component and that allows for a 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, laser light is branched and irradiated. The laser light is femtosecond laser light with a pulse width of 500 fs or less, which has enough energy to cause a photo-induced refractive index change in the glass member. Multiple branched beams are generated from the femtosecond laser light using a beam shaping element having a diffraction grating. The multiple branched beams are then focused and irradiated into the glass member via a focusing lens. In the focal point movement step, the focal point positions of each of the multiple branched beams are moved relative to the glass member. In particular, the MFD of the beam spot at the focal point position of each of the multiple branched beams is set to a ratio MFD / L of the beam spot MFD to the diffraction grating period L of the beam shaping element such that the ratio is 0.6 or more and 0.9 or less. By linking the laser irradiation step and the focal point movement step, a continuous refractive index change region is formed inside the glass member.

[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 the productivity of optical connecting parts.

[0013] (2) In the above (1), the beam shaping element may be a DOE (Diffractive Optical Element). DOEs include LCoS (Liquid Crystal on Silicon). Hereinafter, a DOE with a non-variable refractive index modulation will be referred to as a bulk DOE or glass DOE, and a variable refractive index modulation will be referred to as an LCoS. The use of such a beam shaping element enables the emission of multiple branched beams that form any beam arrangement pattern using a simple optical system.

[0014] (3) In (1) or (2) above, for each of the multiple branched beams, the phase difference between adjacent diffracted beams among the diffracted beams constituting one branched beam may be within a range of −95° to +95°, i.e., a range in which the lower limit is set to a value of −5° to +5° with −90° as the reference and the upper limit is set to a value of −5° to +5° with +90° as the reference. In this case, it is possible to shape the light intensity distribution of each branched beam into a flat-top shape, and it is easy to control the thickness of the optical waveguide provided in the glass member in the depth direction of the glass member.

[0015] (4) In (1) or (2), one of the plurality of branch beams is composed of a plurality of diffracted beams. Furthermore, for a reference branch beam designed so that the phase difference between adjacent diffracted beams among the plurality of diffracted beams falls within a range of −95° to +95°, i.e., a range with a lower limit of −5° to +5° relative to −90° and an upper limit of −5° to +5° relative to +90°, when the position X / L of the reference branch beam relative to the diffraction grating period L is defined on coordinate axes with the center position X0 / L as the origin, the center position X0 / L of the plurality of branch beams may be −0.2 to +0.2. This is because a complex light intensity distribution is formed when the center position X0 / L of the plurality of branch beams is outside the range of −0.2 to +0.2.

[0016] (5) In any of (1) to (4) above, the number of the multiple branch beams may be 2 or more and 100 or less. In this case, it becomes possible to configure any beam arrangement pattern in accordance with the width of the optical waveguide to be formed in the glass member.

[0017] (6) In any of (1) to (5) above, the MFD of the beam spot of each of the plurality of branched beams may be 0.5 μm or more and 6.0 μm or less. In this case, too, it is possible to configure any beam arrangement pattern in accordance with the width of the optical waveguide to be formed in the glass member.

[0018] 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.

[0019] [Details of the embodiments of the present disclosure] Specific structures of the manufacturing method 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. In addition, in the description of the drawings, the same elements are given the same reference numerals, and duplicate explanations will be omitted.

[0020] 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.

[0021] 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.

[0022] 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 ２This is effective because it can achieve a refractive index of 100 kHz or more. Furthermore, the 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 that can produce a refractive index change Δnp due to pressure, and a refractive index change Δnd due to both Δnp and structure, when irradiated with laser light. Silica-based glass is a material that can produce a refractive index change Δnd due to pressure, such as silicon dioxide (SiO ２ ) as the main component, and SiO ２ The glass may be undoped glass, germanium (Ge)-doped glass, or glass co-doped with Ge and boron (B). 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 inside the glass member 10 placed on the XYZ stage 40, i.e., on the YZ plane. This results in a refractive index change region 15 being formed as an optical waveguide inside the glass member 10, thereby obtaining the optical connecting component 100.

[0023] 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.

[0024] 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 where a three-dimensional optical waveguide device having an optical waveguide (refractive index changing region 15) with an arbitrary pattern is manufactured will be described.

[0025] 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 glass member 10 (e.g., parallel plate glass) to become the optical connecting part 100 is prepared (step ST10).

[0026] 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.

[0027] 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.

[0028] FIG. 3 is a diagram illustrating various beam shaping optical systems and beam spot shapes (denoted as "beam shaping optical system" and "beam spot shape" in FIG. 3, respectively). The beam shaping optical system 30 is composed of a beam shaping element and a condenser lens. Examples of the beam shaping element include a DOE and a hologram optical element using an LCoS. The upper part of FIG. 3 (denoted as "DOE" in FIG. 3) shows the configuration of an optical system including a DOE 131 as a beam shaping element. The lower part of FIG. 3 (denoted as "hologram optical element" in FIG. 3) shows the configuration of an optical system including an LCoS 141 as a beam shaping element.

[0029] In the example disclosed herein, a femtosecond laser beam is combined with a beam shaping element such as a hologram optical element to generate multiple branched beams, each composed of diffracted light, from the femtosecond laser beam. The multiple branched beams are focused inside the glass member 10 via a focusing lens, and a refractive index change region 15 serving as an optical waveguide is formed inside the glass member 10 by moving the XYZ stage 40. The laser beam wavelength is in the range of −10 nm to +10 nm relative to 1030 nm, or in the range of −10 nm to +10 nm relative to 1060 nm, or second harmonic generation (SHG) or third harmonic generation (THG) within each wavelength range. The pulse width is 500 fs or less. The repetition rate is 100 kHz to 5 MHz. The femtosecond laser beam is split using a DOE 131, an LCoS 141, or the like.

[0030] The "DOE" optical system shown in the upper part of FIG. 3 includes a DOE 131, which is a beam shaping element, and a condenser lens 132. The DOE 131 receives femtosecond laser light from the femtosecond laser 20 and outputs a group of branched beams with various beam arrangement patterns. The condenser lens 132 focuses the multiple branched beams output from the DOE 131 inside the glass member 10 while maintaining the beam arrangement pattern. The focusing point 35 is set at the position of the beam waist BW. The "hologram optical element" optical system shown in the lower part of FIG. 3 includes an LCoS 141, which is a beam shaping element, and a condenser lens 142. The LCoS 141 receives femtosecond laser light from the femtosecond laser 20 and outputs a group of branched beams with various beam arrangement patterns. The condenser lens 142 focuses the multiple branched beams output from the LCoS 141 inside the glass member 10 while maintaining the beam arrangement pattern. In this example, the focal point 35 is also set at the position of the beam waist BW, and the shape of the beam irradiation area 350 can be set to, for example, an area with a maximum width Zd along the Z-axis direction and a maximum width Yd (≧Zd) along the Y-axis direction. For example, when five branch beams are output from the DOE 131 or LCoS 141 having a diffraction grating period L, each branch beam is composed of multiple diffracted beams, and the beam spots #1 to #5 of these branch beams may be spatially separated so that their spot centers are located along the Y-axis direction, as shown in Figure 3 (pattern A shown in Figure 3). In this pattern A, the beam spots #1 to #5 of the overlapping branch beams correspond to the beam irradiation area 350 on the beam waist BW. In pattern A, Yd is 1 / e 2where ΔY is the beam diameter in the Y-axis direction of the light intensity distribution of branched beams arranged in the Y-axis direction such that adjacent beam spots of the branched beams having beam diameters of ΔZ and ΔY are partially overlapping. Zd is the beam diameter in the Z-axis direction in this case. Furthermore, as shown in FIG. 3, beam spots #1 to #5 of the branched beams may be spatially separated to form an M-shaped beam arrangement pattern along both the Y-axis and the Z-axis (pattern B shown in FIG. 3). Alternatively, beam arrangements may be applied in which each of the spatially separated branched beams is shifted by a variation ΔY along the Y-axis, by a variation ΔZ along the Z-axis, or by both a variation ΔY and a variation ΔZ along both the Y-axis and the Z-axis so that the optical waveguide has a predetermined width. ΔY is the closest distance between the beam centers in the Y-axis direction. ΔZ is the closest distance between the beam centers in the Z-axis direction. The combined light intensity distribution of beam spots #1 to #5 of the branched beams of pattern A has a flat-top shape.

[0031] In particular, when some of the beam spots of the branched beams are spatially separated along the Z axis, a correction beam spot obtained by rearranging the beam spots of the branched beams so that the center-to-center distance between the beam spots of the branched beams along the Z axis is zero corresponds to the beam irradiation area 350. Furthermore, the light intensity distribution of such a correction beam spot (the total light intensity distribution obtained by superimposing the partial light intensity distributions of the branched beams) also has a flat-top shape. In the case of pattern B, the beam spots #1 to #5 of the branched beams move on the YZ plane while maintaining the M-shaped beam arrangement pattern. That is, after beam spots #1 and #2 pass through the beam irradiation area 350 indicated by the dashed line, beam spots #3 to #5 pass through t seconds later. Therefore, pattern B is a beam arrangement pattern that is spatially separated along the Y axis but temporally separated along the Z axis.

[0032] Fig. 4 is a diagram for explaining structure 1 (spatial separation) of beam spots arranged one-dimensionally. Fig. 5 is a diagram showing the light intensity distribution of an input beam of a first modified example based on the light intensity distribution of the input beam of Fig. 4 and the light intensity distribution of diffracted light converted from the input beam (in Fig. 5, this is labeled "Light Intensity Distribution of Input Beam (Modification 1)"). Fig. 6 is a diagram showing the light intensity distribution of an input beam of a second modified example based on the light intensity distribution of the input beam of Fig. 4 and the light intensity distribution of diffracted light converted from the input beam (in Fig. 5, this is labeled "Light Intensity Distribution of Input Beam (Modification 2)").

[0033] The upper part of Fig. 4 (labeled "Beam Arrangement Pattern" in Fig. 4) shows an example of a beam arrangement pattern formed by beam spots #1 to #5 of a plurality of branched beams output from the DOE 131. The middle part of Fig. 4 (labeled "DOE Phase" in Fig. 4) shows the correspondence between the light intensity distribution of the femtosecond laser beam input to the DOE 131 and the phase pattern formed on the DOE 131, with the positions X / L of the branched beams relative to the diffraction grating period L as a common axis with the center position X0 / L as the origin. The lower part of Fig. 4 (labeled "Light Intensity Distribution of Diffracted Light" in Fig. 4) shows the light intensity distribution (flat-top light intensity distribution) of the diffracted light constituting the branched beams having beam spots #1 to #5 output from the DOE 131. The upper part of Fig. 5 (labeled "DOE phase" in Fig. 5) shows the correspondence between the light intensity distribution of the femtosecond laser beam input to the DOE 131 and the phase pattern formed on the DOE 131. The lower part of Fig. 5 (labeled "diffracted beam intensity distribution" in Fig. 5) shows the light intensity distribution of the diffracted beams constituting the branched beams having beam spots #1 to #5 output from the DOE 131. The upper part of Fig. 6 (labeled "DOE phase" in Fig. 6) shows the correspondence between the light intensity distribution of the femtosecond laser beam input to the DOE 131 and the phase pattern formed on the DOE 131. The lower part of Fig. 6 (labeled "diffracted beam intensity distribution" in Fig. 6) shows the light intensity distribution of the diffracted beams constituting the branched beams having beam spots #1 to #5 output from the DOE 131.

[0034] As shown in the upper part of Fig. 4, beam spots #1 to #5 of the five branched beams form a beam arrangement pattern in which they are arranged so as to partially overlap along the Y-axis direction, which is orthogonal to the scanning direction (i.e., the Z-axis direction). This beam arrangement pattern corresponds to a beam irradiation area 350 having a maximum width Zd along the Z-axis direction and a maximum width Yd (≥ Zd) along the Y-axis direction. When femtosecond laser light is input to the DOE 131 having the phase distribution shown in the middle part of Fig. 4, five branched beams are obtained, each having a partial light intensity distribution obtained by -2nd order diffraction, -1st order diffraction, 0th order diffraction, +1st order diffraction, and +2nd order diffraction. The MFD of the beam spot of the input laser light is 1 / e with respect to the intensity peak. ２ The ratio MFD / L of the beam spot MFD to the diffraction grating period L of DOE 131 is 0.78. Each of these five branched beams is diffracted light having a flat-top light intensity distribution as shown in the lower part of FIG. 4 . By moving the beam spots #1 to #5 of the five branched beams together along the Z-axis direction, a refractive index change region 15 serving as an optical waveguide is formed in glass member 10. The total diffraction efficiency from the above-mentioned −2nd order diffraction to +2nd order diffraction is 92.1%, and the diffraction efficiency of each branched beam is 18.4%, confirming by calculation that the branched beams are branched with the same diffraction efficiency. Here, the phase distribution of DOE 131 shown in the lower part of the middle part of FIG. 4 is designed so that the phase difference between adjacent diffracted beams falls within a range with a lower limit of −95° to −85° and an upper limit of 85° to +95°. This reduces abrupt changes in light intensity due to interference between overlapping diffracted beams. If the phase difference between adjacent diffracted beams is 180°, the light intensity in the overlap region will drop sharply to 0 due to interference. This is generally not effective in forming an optical waveguide because a flat-top light intensity distribution is not formed. When the phase difference between adjacent diffracted beams is 0°, the impact is not as great as when it is 180°, but it makes it difficult to design a flat light intensity distribution.

[0035] The upper part of Figure 5 shows the calculation results when the center position of the light intensity distribution of the input laser relative to the phase distribution of the DOE 131 shown in the middle part of Figure 4 is intentionally shifted to X0 / L = -0.25. In the example shown in the upper part of Figure 5, it can be seen that due to interference between adjacent branch beams, the diffracted light constituting each branch beam forms a complex light intensity distribution, as shown in the lower part of Figure 5. For reference, the lower part of Figure 5 shows the light intensity distribution of the diffracted light constituting each branch beam shown in the lower part of Figure 4 with a dashed line. Thus, there is an appropriate range for the position X / L of the branch beam relative to the diffraction grating period L, and it is important that the center position X0 / L be between -0.20 and +0.20, based on the branch beam shown in the middle part of Figure 4.

[0036] Furthermore, the example in the upper part of Figure 6 shows the calculation results for an input laser with an MFD / L ratio of 1.27, compared to the input laser with an MFD / L ratio of 0.78 shown in the upper part of Figure 4. Even in this example in the upper part of Figure 6, the diffracted light constituting each branched beam forms a flat-top shape, as shown in the lower part of Figure 6, but large valleys appear between the diffracted light, and the ratio of the MFD of the beam spot of the input laser to the diffraction grating period L must also be incorporated into the design. For reference, the lower part of Figure 6 also shows the light intensity distribution of the diffracted light constituting each branched beam shown in the lower part of Figure 4 with dashed lines.

[0037] As described above, considering the shape changes in the light intensity distribution of the diffracted light shown in the lower rows of Figures 4 to 6, in order for the diffracted light constituting each branch beam to have a flat-top light intensity distribution, the ratio MFD / L is 0.6 to 0.9. Furthermore, with respect to the reference branch beam shown in the middle row of Figure 4, the central position X0 / L is -0.20 to +0.20. The beam spot diameter of each branch beam, defined by the beam waist BW, is 0.5 μm to 6.0 μm. Note that Non-Patent Documents 6 and 7 do not describe the ratios MFD / L and X0 / L related to the beam spot diameter or the phase of adjacent diffracted light.

[0038] 10...Glass member 15...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 131...DOE 132...Converging lens 141...LCoS 142...Converging lens 350...Beam irradiation area #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 generating a plurality of branched beams using a beam shaping element having a diffraction grating from femtosecond laser light having a pulse width of 500 fs or less, the femtosecond laser light having an energy amount sufficient to cause a photoinduced refractive index change in the glass member, and then condensing and irradiating the plurality of branched beams onto the interior of the glass member via a condenser lens; a focusing point moving step of moving focusing points of the plurality of branched beams relative to the glass member; Equipped with an MFD of a beam spot of each of the plurality of branched beams at the focal point position is set such that a ratio MFD / L of the MFD to a diffraction grating period L of the beam shaping element is set to be 0.6 or more and 0.9 or less; The laser irradiation step and the focusing point moving step are performed in conjunction with each other to form a continuous refractive index change region inside the glass member. A manufacturing method for optical connection components.

2. the beam shaping element is an LCoS or bulk DOE; The method for manufacturing the optical connecting component according to claim 1 .

3. For each of the plurality of branched beams, a phase difference between adjacent diffracted beams among the diffracted beams constituting one branched beam is not less than −95° and not more than +95°. The method for manufacturing the optical connecting component according to claim 1 or 2.

4. one of the plurality of branched beams is composed of a plurality of diffracted beams, Regarding a reference branch beam designed so that the phase difference between adjacent diffracted beams among the plurality of diffracted beams is between −95° and +95°, when a position X / L of the reference branch beam with respect to the diffraction grating period L is defined on a coordinate axis having a center position X0 / L as the origin, a central position X0 / L of the plurality of branch beams is equal to or greater than −0.20 and equal to or less than +0.20; The method for manufacturing the optical connecting component according to claim 1 or 2.

5. the number of the plurality of branch beams is 2 or more and 100 or less; The method for manufacturing the optical connecting component according to claim 1 or 2.

6. The MFD of the beam spot of each of the plurality of branched beams is 0.5 μm or more and 6.0 μm or less. The method for manufacturing the optical connecting component according to claim 1 or 2.