Optical connection member and method for manufacturing optical connection member

Abstract

The optical connection member includes a glass member and an optical waveguide. In a cross section of the glass member, one or more modified regions (15A) having a refractive index lower than the refractive index of the optical waveguide and lower than the refractive index of the glass member other than the optical waveguide are formed in an upper layer region of the glass member located between the optical waveguide and the laser irradiation surface of the glass member. The average correlation length of the nanograting in the layer constituted by the modified region is shorter than 100 nm.

Description

Technical Field

[0001] The present disclosure relates to an optical connecting component and a method for manufacturing the optical connecting component.

[0002] This application claims priority based on Japanese Patent Application No. 2023-026423 filed on February 22, 2023 and Japanese Patent Application No. 2023-197462 filed on November 21, 2023, the contents of which are incorporated herein by reference in their entirety. Background Art

[0003] Generally speaking, optical connection components are used as optical signal transceiver components in optical communications. Regarding the manufacturing method of the optical connection component, for example, non-patent documents 1 to non-patent documents 5 disclose a technology for forming an optical waveguide based on a drawing method using a femtosecond laser light source. Specifically, non-patent document 1 discloses a technology for forming a core that becomes a waveguide by a single scan drawing of a femtosecond laser. In addition, non-patent document 2 discloses a technology for forming a core with a square cross-sectional shape by multiple scan drawings of a femtosecond laser. Non-patent document 3 discloses a technology for forming a core that becomes an optical waveguide using multiple branched light beams with the same polarization. In addition, non-patent document 4 introduces a refractive index increase mechanism (compression) based on irradiation of a femtosecond laser, non-patent document 5 introduces a refractive index increase mechanism (rearrangement of composition) based on irradiation of a femtosecond laser, and non-patent document 6 introduces a mechanism for forming a nano-grating periodic structure based on irradiation of a femtosecond laser.

[0004] Furthermore, Non-Patent Document 7 describes a technique for simultaneously fabricating three optical waveguides using multi-point irradiation of a hologram. It should be noted that beam shaping can utilize the technique of Non-Patent Document 8, and Non-Patent Document 9 reports the use of two LCoS sheets to control the polarization of multi-branched beams and form polarization-dependent nanogratings.

[0005] Prior art literature

[0006] Non-patent literature

[0007] Non-Patent Literature 1: 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.

[0008] Non-patent document 2: Y. Nasu, et al., “Low-loss waveguides written with femtosecond laser for flexible interconnection in a planar light-wave circuit”, Optics Letters, Vol. 30, pp. 723-725 (2005).

[0009] Non-patent document 3: Henk van Wolferen, et al., Lithography: Principles, Processes and Materials ISBN: 978-1-61761-837-6, Editor: Theodore C. Hennessy, pp. 133-148 “LASER INTERFERENCE LITHOGRAPHY”.

[0010] Non-patent document 4: ENG Lezer and E. Mazur, “Ultrafast-laser driven micro-explosions in transparent materials”, Appl. Phys. Lett. Vol. 71, No. 7, pp. 882-884 (1997).

[0011] Non-patent document 5: Y. Liu, et al., “Micromodification of element distribution in glass using femtosecond laser irradiation”, OPTICS LETTERS, Vol. 34, No. 2, pp. 136-138 (2009).

[0012] Non-patent document 6: 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).

[0013] Non-Patent Document 7: 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.

[0014] Non-Patent Document 8: Keiji Fuse, “Beam Shaping for Advanced Laser Materials Processing”, Laser Technik Journal, pp. 19-22 (2015).

[0015] Non-Patent Literature 9: S. Hasegawa, et al., “Holographic vector wave femtosecond laser processing”, International Journal of Optomechatronics, p. 73 (2014).

[0016] Non-Patent Document 10: Payne FP, et al., “A theoretical analysis of scattering loss from planar optical waveguides”, Optical and Quantum Electronics, vol. 26 (1994) pp. 977-986.

[0017] Non-Patent Document 11: Weijia Yang, et al., “Self-assembled periodic sub-wavelength structures by femtosecond laser direct writing”, Vol. 14, No. 21 / OPTICS EXPRESS (2006) 10117. Summary of the Invention

[0018] The optical connecting component disclosed herein comprises: a silica-based glass member; and an optical waveguide disposed within the glass member and having a refractive index higher than that of the glass member. Furthermore, one or more modified regions are formed within an upper region of the glass member, each having a refractive index lower than that of the glass member excluding the optical waveguide. The average correlation length of the nanograting formed within the layer comprising the one or more modified regions is shorter than 100 nm. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a flowchart for explaining an example of a method for manufacturing the optical connecting component of the present disclosure.

[0020] Figure 2 This is a diagram showing a configuration example of a manufacturing apparatus for implementing the manufacturing method of the optical connecting component disclosed herein.

[0021] Figure 3 These are diagrams used to explain various beam shaping optical systems.

[0022] Figure 4 This is a diagram for explaining laser scanning for forming an optical waveguide and a configuration example of the manufactured optical connecting component.

[0023] Figure 5 It is a diagram showing the observation results of the modified shape in the cross section of the optical waveguide.

[0024] Figure 6This is a diagram showing calculation results for evaluating the side surface roughness of the optical waveguide. DETAILED DESCRIPTION

[0025] [Problems to be Solved by the Present Disclosure]

[0026] The inventors and others studied the above-mentioned prior art and found the following problems. That is, the technology disclosed in non-patent document 1 has successfully formed an optical waveguide by single-shot scanning of a femtosecond laser, but the width of the optical waveguide is not controlled. In other words, the shape of the resulting optical waveguide is long relative to the laser irradiation axis, and the lateral direction of the optical waveguide is narrow to less than 2μm. Therefore, the coupling loss of the light propagating in the optical waveguide increases. It should be noted that non-patent document 7 discloses a technology that combines a femtosecond laser with holographic technology to split a laser beam into multiple diffracted light beams and use these multiple diffracted light beams to write to multiple optical waveguides simultaneously. However, in this case, it is also impossible to maintain a sufficient width of the optical waveguide, so the coupling loss of the light propagating in the optical waveguide increases.

[0027] In contrast, the technology in Non-Patent Document 2 has successfully formed an optical waveguide using multiple-scanning femtosecond laser patterns. In this method, the femtosecond laser beam, directed along the beam irradiation axis, is scanned 20 times in a staggered pattern perpendicular to the beam irradiation axis, thereby controlling the width of the optical waveguide. However, this method takes 20 times longer to form a single optical waveguide than a single-scan pattern, significantly reducing the productivity of optical connector components containing optical waveguides.

[0028] The present disclosure provides an optical connecting component that effectively reduces propagation loss in an optical waveguide, and provides a method for manufacturing the optical connecting component that facilitates control of the shape of an optical waveguide provided in the optical connecting component and can significantly increase productivity of the optical connecting component.

[0029] [Effects of the Present Disclosure]

[0030] According to the present disclosure, an optical connection component can be obtained that effectively reduces propagation loss in an optical waveguide. Furthermore, the shape of the optical waveguide provided in the optical glass member can be easily controlled, and productivity can be greatly increased.

[0031] [Description of Embodiments of the Present Disclosure]

[0032] First, the contents of the embodiments of the present disclosure will be individually listed and described.

[0033] The optical connection components disclosed herein are as follows:

[0034] (1) The optical connecting component comprises: a silica-based glass member; and an optical waveguide, which is provided inside the glass member and has a refractive index higher than that of the glass member. In addition, one or more modified regions are formed in the upper region of the glass member, wherein the modified region has a refractive index lower than that of the glass member other than the optical waveguide, and the average correlation length of the nanograting formed in the layer composed of the one or more modified regions is controlled to be shorter than 100 nm. It should be noted that the upper region of the glass member is defined as the region between the optical waveguide and the laser irradiation surface of the glass member irradiated with a laser used to form the optical waveguide, such as a femtosecond laser, in a cross section of the glass member perpendicular to the long dimension of the optical waveguide. In addition, the correlation length of the nanograting refers to the period length of the periodic refractive index fluctuation relative to the propagation axis aligned with the long dimension of the optical waveguide in one or more modified regions.

[0035] In a structure in which an optical waveguide is formed within a glass component by generating multiple branched beams using a laser and focusing these multiple branched beams into the glass component, it is difficult to completely avoid the formation of one or more modified regions in the upper region of the glass component. In this case, the layer composed of one or more modified regions is generated in a region that can essentially be regarded as an optical cladding. Various nanogratings and nanostructures with periodicity along the long dimension of the optical waveguide, in a direction perpendicular to the long dimension, and in a direction inclined relative to the long dimension are formed within this optical cladding. The presence of nanogratings and nanostructures in the layer composed of such modified regions significantly affects the increase in propagation loss of the optical waveguide in the optical connecting component. In contrast, in the optical connecting component disclosed herein, the average correlation length of the nanogratings formed in the layer of modified regions is controlled to be less than 100 nm. This structure can effectively reduce the increase in propagation loss of the optical waveguide formed in the glass component. It should be noted that one or more modified regions may be generated in the upper layer of the substantial optical cladding, and the aforementioned various nano-gratings and periodic, randomly oriented nanostructures may also exist in a portion of the inner layer.

[0036] (2) In the above (1), the number of reformed regions that can be identified in the cross section of the glass member may be less than 100. In this case, the increase in propagation loss of the optical waveguide formed in the glass member can also be effectively reduced.

[0037] The manufacturing method of the optical connecting component disclosed in the present invention is as follows:

[0038] (3) The method for manufacturing an optical connecting component includes a preparation step, a laser irradiation step, and a light-converging point moving step. In the preparation step, a silica-based glass component is prepared. In the laser irradiation step, a femtosecond laser having energy that causes a light-induced refractive index change in the glass component and a pulse width of 500 fs or less is used. After generating a plurality of branch beams from the femtosecond laser using one or more beam shaping elements, the plurality of branch beams are focused and irradiated into the interior of the glass component via a focusing lens. In the light-converging point moving step, the light-converging point positions of the plurality of branch beams are moved relative to the glass component. In addition, the polarizations of adjacent diffracted lights in the diffracted lights that constitute the plurality of branch beams are different. By linking the laser irradiation step and the light-converging point moving step, a continuous refractive index change region that functions as an optical waveguide is formed inside the glass component. In this case, the average correlation length of the nanograting in the modified region layer formed near the optical waveguide is controlled to be less than 100 nm, thereby effectively reducing the increase in the propagation loss of the optical waveguide formed in the glass component.

[0039] (4) In (3) above, the beam shaping element may be a DOE (Diffractive Optical Element). The DOE includes LCoS (Liquid Crystal on Silicon). Here, the glass type with fixed refractive index modulation is referred to as DOE, and the glass type with variable refractive index modulation is referred to as LCoS. The use of such a beam shaping element enables the emission of multiple branched beams forming an arbitrary beam configuration pattern using a simple optical system.

[0040] (5) In the above (3), the beam shaping element may be composed of a plurality of LCoS or a plurality of glass-type DOEs. This configuration enables selectively changing the polarization state of the diffracted light of the plurality of branched beams.

[0041] Each aspect listed above in the [Description of Embodiments of the Present Disclosure] column can be applied to each of all the remaining aspects, or can be applied to all combinations of the remaining aspects.

[0042] [Details of the embodiments of the present disclosure]

[0043] The specific structure of the manufacturing method of the optical connecting component disclosed herein is described in detail below with reference to the accompanying drawings. It should be noted that the present disclosure is not limited to these examples but is set forth in the claims, which are intended to encompass all modifications within the meaning and scope equivalent to the claims. In the description of the drawings, identical elements are denoted by the same reference numerals, and duplicate descriptions are omitted.

[0044] Figure 1This is a flowchart for explaining an example of a method for manufacturing the optical connecting component 100 of the present disclosure. Figure 2 1 is a diagram showing a configuration example of a manufacturing apparatus for implementing the manufacturing method of the optical connecting component 100 disclosed herein.

[0045] Figure 2 The manufacturing apparatus shown includes a femtosecond laser 20, a laser driving unit 25 for driving the femtosecond laser 20, a beam shaping optical system 30 for shaping the beam spot of the femtosecond laser into an arbitrary shape, an XYZ stage 40, a stage driving unit 45 for driving the XYZ stage 40, and a control unit 50 for controlling the operation of these parts.

[0046] The laser driving unit 25 controls the power and repetition frequency of the pulsed laser (hereinafter referred to as "femtosecond laser") output from the femtosecond laser 20 according to the instructions from the control unit 50. As a result, the femtosecond laser 20 can output a femtosecond laser having a pulse width of several hundred femtoseconds or less. In particular, the femtosecond laser with a pulse width of several hundred femtoseconds or less can have a peak power of 10 5 W / cm 2 Above. In addition, in order to make the refractive index and structure of the optical waveguide formed inside the glass material smooth, the repetition frequency of the output femtosecond laser can be above 10kHz. The glass component 10 to be the main body of the optical component is placed on the device mounting surface of the XYZ stage 40. The glass component 10 is a glass or silica-based glass that can produce a refractive index change Δnp caused by pressure or both Δnp and a refractive index change Δnd caused by structure by laser irradiation. Silica-based glass refers to glass with silicon dioxide (SiO2) as the main component and contains more than 50% SiO2. For example, it can be undoped glass, germanium (Ge)-doped glass, co-doped glass of Ge and boron (B), etc. In addition, these glasses can also be quartz glass, phosphate glass, halide glass and sulfide glass. The femtosecond laser output from the femtosecond laser 20 is focused by the beam shaping optical system 30 to the interior of the glass component 10 set on the XYZ stage 40, that is, to the focal point 35 located on the YZ plane. As a result, the refractive index change region 15 serving as an optical waveguide is formed inside the glass member 10 , thereby obtaining the optical connecting component 100 .

[0047] The stage driving unit 45 drives the XYZ stage 40 according to the instructions from the control unit 50, so that the device mounting surface of the XYZ stage 40 moves along the X-axis direction, the Y-axis direction and the Z-axis direction respectively. Through this structure, laser scanning can be performed, and the position of the focal point 35 of the femtosecond laser will move relative to the glass component 10. The control unit 50 controls the various actions of the laser driving unit 25 and the stage driving unit 45 as described above to produce a refractive index change area 15 of an arbitrary pattern inside the glass component 10. It should be noted that the arbitrary pattern is consistent with the shape of the optical waveguide projected onto the YZ plane taking into account the depth direction information of the X-axis. After the above steps, the optical connecting component 100 as an optical component is manufactured.

[0048] Next, the optical connecting component 100 provided with an optical waveguide is manufactured using the manufacturing apparatus having the above-described structure. Figure 1 The flowchart of FIG. 1 illustrates the manufacturing method of the optical connecting component 100 of the present disclosure. It should be noted that in the following description, as an example of the manufacturing method of the optical connecting component 100, the case of manufacturing a three-dimensional optical waveguide device having a refractive index change region 15 with an arbitrary pattern serving as an optical waveguide is described.

[0049] The manufacturing method of the optical connecting component 100 of the present disclosure comprises a preparation step and an optical waveguide manufacturing step. First, in the preparation step, a glass member 10 to be the optical connecting component 100, for example, parallel plate glass, is prepared (step ST10).

[0050] In the optical waveguide manufacturing process, a refractive index change region 15 of an arbitrary pattern forming an optical waveguide is formed inside the prepared glass component 10. Specifically, after step ST10 is completed, the prepared glass component 10 is immediately placed on the device mounting surface of the XYZ stage 40 and irradiated with a femtosecond laser (step ST20). The control unit 50 controls the laser driving unit 25 so that a femtosecond laser having energy that causes a light-induced refractive index change inside the glass component 10 and a repetition frequency of 10 kHz or more is output from the femtosecond laser 20. The femtosecond laser output from the femtosecond laser 20 is focused into the interior of the glass component 10 by the beam shaping optical system 30. It should be noted that the beam shaping optical system 30 shapes the beam spot of the input femtosecond laser into a predetermined shape. A light-induced refractive index change is formed in the beam irradiation area at the focal point 35 of the femtosecond laser. When laser irradiation of a predetermined portion of glass member 10 is completed, control unit 50 controls stage drive unit 45 to move the position of glass member 10, which is mounted on the device mounting surface of XYZ stage 40 (step ST30). In this manner, in the light-converging point moving step (step ST30), the position of glass member 10, the position of light-converging point 35 of the femtosecond laser beam, or both are continuously or intermittently changed, thereby moving the position of light-converging point 35 of the femtosecond laser beam within glass member 10.

[0051] It should be noted that the laser irradiation process of step ST20 and the light-converging point moving process of step ST30, that is, the operation control of the laser driving unit 25 and the stage driving unit 45 by the control unit 50, are returned to the state in which the laser irradiation process of step ST20 and the light-converging point moving process of step ST30 are returned to the state in which the laser irradiation process of step ST20 and the light-converging point moving process of Figure 1 At the time indicated by point C in FIG, the irradiation conditions are changed or repeated under the same conditions until the pre-designed optical waveguide pattern is formed within the glass member 10 (step ST40). When the refractive index change region 15 of the glass member 10 is formed (step ST40), the glass member 10 is annealed to perform an aging treatment, etc., to ensure that the relative refractive index difference Δn remains constant over a long period of time (step ST50). Through the above steps, an optical connecting component having an internal optical waveguide is obtained.

[0052] Figure 3 This is a diagram used to illustrate various beam shaping optical systems (in Figure 3 The beam shaping optical system 30 is composed of a beam shaping element and a focusing lens. As the beam shaping element, DOE, a holographic optical element using LCoS, etc. can be listed. It should be noted that in Figure 3 The upper part (in Figure 3 In FIG, “DOE” is shown as a beam shaping element in an optical system. Figure 3 The lower part (in Figure 3 , referred to as "holographic optical element" in the figure, shows the structure of an optical system including a holographic optical element as a beam shaping element.

[0053] It should be noted that in the examples disclosed herein, a beam shaping element such as a holographic optical element is combined with a femtosecond laser, and a plurality of branch beams each consisting of diffracted light is generated by the femtosecond laser. The plurality of branch beams are focused to the interior of the glass component 10 via a focusing lens, and a refractive index change region 15 serving as an optical waveguide is formed inside the glass component 10 by the movement of the XYZ stage. Regarding the laser wavelength, the range of -10 nm to +10 nm based on 1030 nm, the range of -10 nm to +10 nm based on 1060 nm, or the second harmonic generation (SHG) and third harmonic generation (THG) within each wavelength range are effective. Regarding the pulse width, 500 fs or less is effective. Regarding the repetition frequency, 100 kHz or more and 5 MHz or less is effective. It should be noted that the femtosecond laser light is split by a pair of beam shaping elements that generate diffracted lights of mutually different polarizations, for example, a pair of DOE 131A and DOE 131B or a pair of LCoS 141A and LCoS 141B.

[0054] exist Figure 3 In the example shown in the upper section, a pair of PBS (Polarization Beam Splitter) 133A and PBS 133B, a pair of DOE 131A and DOE 131B as beam shaping elements, a pair of mirrors 134A and 134B for optical path deflection, and a focusing lens 132 are provided. PBS 133A converts 45-degree linear polarization into a 0-degree polarization component and a 90-degree polarization component. The 0-degree polarization component is input from PBS 133A to DOE 131A, and the 90-degree polarization component is input from PBS 133B to DOE 131B via mirror 134A. DOE 131A, which receives the 0-degree polarization component, produces diffracted light L0 consisting solely of the 0-degree polarization component. This diffracted light L0 then travels from DOE 131A to PBS 133B. On the other hand, DOE 131B, which receives the 90-degree polarization component, produces diffracted light L90, which contains only the 90-degree polarization component. Diffracted light L90 travels from DOE 131B through reflector 134B and reaches PBS 133B. PBS 133B combines diffracted light L0 and diffracted light L90, ultimately generating multiple diffracted light groups, or branched light beams, with adjacent diffracted light beams differing in polarization state by 90 degrees. These combined branched light beams are then focused by condenser lens 132 onto focal point 35 on beam waist BW.

[0055] On the other hand, Figure 3 In the example shown in the lower section of FIG, a group of LCoS141A and LCoS141B and a focusing lens 142 are prepared as beam shaping elements. When a laser beam having a linear polarization of 45 degrees is input to LCoS141A, a 0-degree polarization component and a 90-degree polarization component are generated from LCoS141A. In LCoS141A, in order to convert only the 0-degree polarization component among the output polarization components into diffracted light L0, the phase distribution of LCoS141A is formed by controlling the liquid crystal orientation, thereby only the 0-degree polarization component is converted into diffracted light L0, and the 90-degree polarization component is directly reflected. Moreover, in LCoS141B, the diffracted light L0 of 0-degree polarization is directly reflected, while only the 90-degree polarization component is converted into diffracted light L90, ultimately generating a plurality of diffracted lights, i.e., a plurality of branched light beams, whose polarization states differ by 90 degrees between adjacent diffracted lights. The plurality of branched light beams from the LCoS 141B are focused by the condenser lens 142 to a focal point 35 on the beam waist BW.

[0056] As described above, the diffraction gratings of each element constituting the beam shaping element are adjusted so that the multiple branched beams generated from a single input laser beam are converted into diffracted light with linear polarizations of 0 and 90 degrees. This allows the polarization states of the diffracted light constituting each of the multiple branched beams to be controlled so that adjacent diffracted light has different polarization states of 0 and 90 degrees.

[0057] In addition, Non-Patent Document 11 reports that inserting a λ / 2 wave plate between the first LCoS and the second LCoS and inserting a λ / 4 wave plate between the second LCoS and the focusing lens can control the inclination of radial polarization and linear polarization. Figure 3 The combination of LCoS141A and LCoS141B shown in the lower section of the figure is combined with the LCoS group of non-patent document 11. If the number of LCoS sheets included in the beam shaping optical system increases, the degree of freedom of polarization selection of the diffracted light after branching can be increased accordingly. In this case, even in the upper region 150 of the glass member 10 (see Figure 4) produces an overlap of the diffracted light constituting the generated branch light beams, and can also achieve non-interference or reduce the interference effect in a manner below the damage threshold. This means that the area to be the optical waveguide can be irradiated with the desired energy. In addition, regarding the irradiation of the diffracted light group with different polarization states between adjacent diffracted lights as multiple branch light beams, the electron wave and electric field vector generated by the induced surface plasmon in the overlapping area are different. Therefore, the irradiation of multiple branch light beams of the present invention with different polarization states between adjacent branch light beams acts on the direction of the periodic destruction of the nano grating formed in the upper region 150 adjacent to the optical waveguide, which can reduce the propagation loss in the optical waveguide. Alternatively, the beam irradiation of the present invention will form periodicities with different angles in the upper region 150 adjacent to the optical waveguide, which is actually effective in shortening the correlation length of the nano grating.

[0058] Figure 4 This is a diagram for explaining laser scanning for forming an optical waveguide and a configuration example of the manufactured optical connecting component (in Figure 4 In Figure 4 The upper part (in Figure 4 In FIG, “laser scanning” is indicated as “laser scanning”) showing a structure in which a refractive index change region 15 serving as an optical waveguide is drawn in the glass member 10 by scanning the glass member 10 with laser light. Figure 4 The lower part (in Figure 4 The structure of the optical connecting component 100 obtained by laser scanning is shown in FIG. Figure 3 DOE, LCoS, etc. shown.

[0059] exist Figure 4 In the example in the upper section, in the laser irradiation process, a plurality of branched light beams are irradiated to the interior of the glass component 10 via the laser irradiation surface 10A in a state where the plurality of branched light beams are staggered at intervals Δy in the Y-axis direction. The plurality of branched light beams move relatively along a scanning direction that is consistent with the Z-axis direction or a direction that deviates from the Z-axis by a predetermined angle, thereby obtaining an optical connection component 100 having a refractive index change region 15 that serves as an optical waveguide. This method is effective because it can obtain the width of the optical waveguide that corresponds to the design. It should be noted that in Figure 4The lower section shows an example of an XY cross-section of the refractive index change region 15 formed within the glass member 10 by the laser irradiation step. In the example shown in this XY cross-section, multiple modified regions 15A are formed near the refractive index change region 15, which is formed by irradiating the glass member 10 with multiple branched light beams having the same polarization state, that is, within the refractive index change region 15 and the upper region 150 adjacent to the refractive index change region 15. Furthermore, it is assumed that multiple modified regions 15B, different from the modified region 15A, are formed in a portion closer to the laser irradiation surface 10A than the modified region 15A due to the influence of interference between adjacent branched light beams.

[0060] When the interval Δy between the multiple branched beams irradiated on the laser irradiation surface 10A of the glass member 10 is wide enough, a light intensity distribution corresponding to the design can be obtained. On the contrary, it can be understood from, for example, non-patent document 3 that when the interval Δy is narrowed, since the polarizations are the same, the overlapping areas of the multiple branched beams will cause interference. Figure 5 The influence of interference generated in the overlapping area will be described in detail. Figure 5 The upper region 150 excluding the modified region 15A is a modified layer affected by this interference. Therefore, when forming the refractive index change region 15 to serve as an optical waveguide within the glass member 10, in addition to focusing on the light intensity distribution near the focal point 35 that directly contributes to the structure of the optical waveguide, it is also necessary to observe the interference in the overlapping region of the multiple branched light beams in the upper region 150 between the laser irradiation surface 10A and the focal point 35.

[0061] Figure 5 This is a diagram showing the observation results of the modified shape in the cross section of the optical waveguide caused by laser scanning (in Figure 5 In , it is referred to as "modified shape of waveguide cross section"). Figure 5 The upper part (in Figure 5 In the figure, "Δy1 = 1.3 μm" is shown as a beam shaping element. Figure 3 The observation results of the reformed region 15A when the interval Δy1 of the 13 branched light beams branched from the combination of LCoS141A and LCoS141B is set to 1.3 μm are shown in the lower section. Figure 5 The middle part (in Figure 5 In the figure, "Δy2 = 2.2 μm" is shown as a beam shaping element. Figure 3 The observation results of the reformed region 15A when the interval Δy2 of the 13 branched light beams branched from the combination of LCoS141A and LCoS141B is set to 2.2 μm are shown in the lower section. Figure 5 The lower part (in Figure 5In the figure, "Δy3 = 4.4 μm" is shown as a beam shaping element. Figure 3 The lower section shows observation results of the reformed region 15A when the interval Δy3 between the 13 branched light beams branched from the combination of LCoS 141A and LCoS 141B is set to 4.4 μm.

[0062] The NA (Numerical Aperture) of the prepared focusing lens is greater than or equal to 0.40 and less than or equal to 0.55. The wavelength of each branched beam is 515 nm, and the pulse width is greater than or equal to 100 fs and less than or equal to 450 fs. The scanning speed is greater than or equal to 0.01 mm / sec and less than or equal to 10 mm / sec. The pulse energy is greater than or equal to 30 nJ and less than or equal to 1000 nJ. The repetition frequency is greater than or equal to 100 kHz and less than or equal to 5 MHz. The depth from the laser irradiation surface 10A to the interior of the glass member 10 (the distance to the focal point 35) is greater than or equal to 5 μm and less than or equal to 500 μm.

[0063] like Figure 5 As shown in the upper and lower sections, when the interval between the branched beams (Δy1<Δy2<Δy3) is large, the two types of modified regions corresponding to the multiple branched beams can be more clearly confirmed. The modified region corresponding to the refractive index change region 15 that becomes the optical waveguide has a refractive index higher than the refractive index of the glass component 10. A modified region 15A having a refractive index lower than the refractive index of the glass component 10 other than the refractive index change region 15 is formed between the refractive index change region 15 and the laser irradiation surface 10A. When the modified region constituting a part of the refractive index change region 15 is joined along the Y-axis direction, an optical waveguide is formed. However, when the interval between the multiple branched beams is narrowed, the sizes of the modified region constituting a part of the refractive index change region 15 and the modified region 15A become uneven, and it can be seen that a complex modified structure is formed in the upper region 150 located between the laser irradiation surface 10A and the refractive index change region 15. For example, in Figure 5 In the example shown in the upper and middle sections of , there is a modified region 15B that is different from the modified region 15A, which can be considered to be enhanced by the interference of multiple branched light beams, thereby reflecting a state of exceeding the modification threshold. It should be noted that the modified region 15B has a refractive index that is the same as that of the modified region 15A, that is, it has a refractive index lower than the refractive index of the glass component 10 except for the refractive index change region 15. In addition, in the case where the modified region 15B is formed away from the modified region 15A and is located close to the laser irradiation surface 10A, between the modified region 15B and the refractive index change region 15, a region that is brighter than both the modified region 15A and the modified region 15B and has the same degree of brightness as the refractive index change region 15 can be confirmed. In Figure 5In the upper and middle sections of the laser beam, the high-brightness region has a refractive index approximately equal to that of the refractive index change region 15, that is, a refractive index higher than that of the glass member 10. Therefore, when the beam spacing is simply narrowed, in the upper region 150 between the refractive index change region 15 and the laser irradiation surface 10A, in addition to the modified region 15A and the modified region 15B, a region having a refractive index approximately equal to that of the refractive index change region 15 is mixed.

[0064] In the upper region 150 of the glass member 10, a Figure 5 The complex modified structure shown in the upper section (Δy1=1.3μm) means that the energy of each branch light beam is consumed in the upper region 150. In this case, it is difficult to perform the required energy depiction on the modified region constituting the refractive index change region 15. In addition, even in the modified region 15A and the modified region 15B between the laser irradiation surface 10A and the modified region constituting the refractive index change region, refractive index modulation occurs, thereby hindering light scattering and light focusing. As a method for eliminating this problem, there is a method of controlling the polarization states of adjacent diffracted lights in the diffracted lights that respectively constitute a plurality of branch light beams in an orthogonal manner to avoid interference between the plurality of branch light beams. For example, it is effective to make the polarization states of adjacent diffracted lights orthogonal at 0 degrees and 90 degrees, to combine radially polarized light and angularly polarized light, etc., so that the polarization states of adjacent branch light beams are orthogonal.

[0065] It should be noted that the modified regions constituting the refractive index change region 15 function as optical waveguides. However, portions of the modified regions 15A and 15B form a layer approximately 5 μm thick in the upper region 150, directly above the refractive index change region 15, which serves as the optical waveguide. Within this layer, various nanogratings are formed that have a periodic pattern along the long dimension of the refractive index change region 15 and in directions intersecting the long dimension. Alternatively, a nanostructure with a random periodic pattern is formed. By shortening the period of the nanogratings in the modified region 15A, propagation loss is reduced. The smaller the nanogratings and nanostructures in the upper region 150, excluding the modified region 15A, the more effectively the desired energy mapping of the refractive index change region 15, which constitutes the optical waveguide, can be achieved, thereby obtaining the desired optical waveguide structure. Furthermore, the number of modified regions 15A and 15B formed directly above the refractive index change region 15 that can be identified in an XY cross-section may be 10 or more and 100 or less, 1 or more and 9 or less, or zero. Modified regions 15A and 15B are identified by microscopic observation while illuminating the XY cross-section of the refractive index change region 15 provided in the glass member 10 with transmitted light. Specifically, modified regions 15A and 15B are defined as regions having a brightness that is 10% or more lower than the brightness of unmodified regions in the glass member 10 excluding the refractive index change region 15, modified regions 15A, and modified regions 15B, and having a maximum diameter of 0.5 μm or greater. The total number of modified regions 15A and 15B is determined by counting the number of regions identified by the aforementioned microscopic observation in the XY cross-section.

[0066] Figure 6 is a graph showing the calculation results for evaluating the side roughness of the optical waveguide (in Figure 6 In the , it is recorded as "roughness evaluation of waveguide side surface"). Figure 6 The upper part (in Figure 6 In the example, the specifications of Type 1 to Type 3 are shown as "evaluation samples". Figure 6 The lower part (in Figure 6 The relationship between the correlation length Lc and the roughness σ of the optical waveguide side is shown as "correlation length dependence of roughness σ". Figure 6 The graph G610 shown in the lower section indicates Figure 6 The upper portion of FIG6 shows the calculation result of type 1, graph G620 shows the calculation result of type 2, and graph G630 shows the calculation result of type 3.

[0067] As described above, it is known that when interference between multiple branched light beams occurs, a nano-grating having a correlation length of several hundred nanometers is formed in the layer consisting of the modified region 15A and a portion of the modified region 15B in the upper region 150 of the glass member 10. However, it is known that this nano-grating is formed perpendicular to the incident polarization (Non-Patent Document 6). The relationship between the light propagation loss and the period of the refractive index difference is shown in the calculation results based on the description of Non-Patent Document 10. Figure 6 That is, according to equations (1), (2), and (5) of non-patent document 10, only the scattering on the side of the optical waveguide is considered, and the roughness σ with a propagation loss of 0.1 dB / cm is calculated. Here, the calculation of the roughness σ focuses only on the modified region 15A in the upper region 150, which is directly related to the transmission loss. The wavelength is 1.55 μm, and the cladding refractive index, which is equivalent to the refractive index of the glass member 10, is 1.45. In addition, as Figure 6 As shown in the upper part of , d [μm] is the waveguide width, Δn [%] is the relative refractive index difference of the optical waveguide with respect to the refractive index of the cladding, b is the normalized propagation constant of the optical waveguide, λc [μm] is the cutoff wavelength of the optical waveguide, and MFD [μm] is the mode field diameter of the optical waveguide.

[0068] In addition, Figure 6 In the lower section, the horizontal axis is the correlation length Lc, which refers to the period length when there is a random periodicity of the fluctuation component or the period length when there is a roughly fixed periodicity of the fluctuation component. The following results are shown: Figure 6 The roughness σ required to reduce the propagation loss to below 0.1 dB / cm varies for each condition shown in the upper section. However, the trends are generally consistent, showing that the propagation loss is most sensitive to fluctuations in the roughness σ around 100 μm. In other words, as the correlation length Lc decreases below 100 μm, the smaller the periodicity, the more insensitive the transmission loss is to fluctuations in the roughness σ. If the roughness required to reduce the propagation loss to below 0.1 dB / cm when the nanograting period is 100 nm is set to σ_100 nm, then reducing the period of the nanograting—that is, controlling the average correlation length to less than 100 nm—can achieve lower optical waveguide loss.

[0069] Here, assuming that the refractive index change region 15 is the core, a portion of the modified region 15A surrounding it can be considered an optical cladding. Due to the periodic refractive index fluctuations of the optical cladding, the propagation loss increases. It is known that the nanograting is formed perpendicular to the incident polarization, and when multiple branch beams have the same polarization, the nanograting will grow. In addition, it is reported that the periodic length of the nanograting formed in the optical cladding region, the so-called correlation length Lc, varies depending on the wavelength of each branch beam, pulse energy, scanning speed, etc., but is greater than 100nm and less than 700nm (Non-Patent Document 11). Nanogratings appear periodically in the optical cladding region, so it can be inferred that the propagation loss in the core includes propagation loss that depends on the correlation length Lc of the nanograting. In order to achieve low core loss, it is effective to shorten the correlation length Lc of all nanogratings formed around the core. Non-Patent Document 11 shows the laser drawing conditions for shortening the correlation length Lc of the nanograting, but even with the minimum correlation length, a period of at least 100nm is produced, which is insufficient to reduce the propagation loss. Alternatively, even with a controlled periodicity of 100 nm, the required relative refractive index difference Δn between the core and cladding cannot be maintained due to limitations on pulse energy, or there are limitations on scanning speed, which is directly related to productivity, causing problems. Therefore, the manufacturing method disclosed herein controls the average correlation length of various nanogratings formed near the core to be shorter than 100 nm by varying the polarization states of adjacent diffracted light beams that constitute the multiple branched beams.

[0070] Description of Reference Numerals

[0071] 10: Glass components;

[0072] 10A: laser irradiation surface;

[0073] 15: refractive index change region (optical waveguide);

[0074] 15A, 15B: modified region;

[0075] 20: Femtosecond laser;

[0076] 25: laser driver;

[0077] 30: beam shaping optical system;

[0078] 35: Spotlight;

[0079] 40: XYZ stage;

[0080] 45: stage driving unit;

[0081] 50: Control Department;

[0082] 100: optical connection components;

[0083] 131A, 131B: DOE;

[0084] 132: focusing lens;

[0085] 133A, 133B: PBS;

[0086] 134A, 134B: reflectors;

[0087] 141A, 141B: LCoS;

[0088] 142: focusing lens;

[0089] 150: Upper area;

[0090] BW: waistband.

Claims

1. An optical connecting component comprising: Silica-based glass components; and an optical waveguide provided inside the glass member and having a refractive index higher than that of the glass member, In a cross section of the glass member perpendicular to the longitudinal direction of the optical waveguide, one or more modified regions are formed in an upper region of the glass member located between the optical waveguide and a laser irradiated surface of the glass member irradiated with laser light for forming the optical waveguide, the modified regions having a refractive index lower than that of the glass member excluding the optical waveguide. The average correlation length of the nanograting as the periodic refractive index fluctuation formed in the layer consisting of the one or more modified regions is shorter than 100 nm.

2. The optical connecting component according to claim 1, wherein The number of the reformed regions that can be identified in the cross section of the glass member is 100 or less.

3. A method for manufacturing an optical connecting component, comprising: A preparation step of preparing a silica-based glass component; a laser irradiation step of generating a plurality of branched beams using a beam shaping element from a femtosecond laser having energy that causes a light-induced refractive index change in the glass member and a pulse width of 500 fs or less, and then focusing the plurality of branched beams through a focusing lens and irradiating the interior of the glass member; and a light-converging point moving step of moving the light-converging point positions of the plurality of branched light beams relative to the glass member; The polarizations of adjacent diffracted lights in the diffracted lights constituting the plurality of branch light beams are different. By linking the laser irradiation step and the light-converging point movement step, a continuous refractive index change region is formed in the interior of the glass member.

4. The method for manufacturing an optical connecting component according to claim 3, wherein: The beam shaping element is a liquid crystal on silicon (LCoS) or a glass-type diffractive optical element (DOE).

5. The method for manufacturing an optical connecting component according to claim 3, wherein: The beam shaping element is composed of a plurality of silicon-based liquid crystals (LCoS) or a plurality of glass-type diffractive optical elements (DOE).

Images