WO2024105765A1 - Optical module and method for producing optical module - Google Patents

Abstract

An optical fiber module 100 equipped with one or more optical fibers 101, a planar lightwave circuit 102 which is optically connected to the one or more optical fibers 101, a fiber block 103 into which the one or more optical fibers 101 are inserted and secured, a glass layer 104 for adhering and securing the optical fiber 101 and the planar lightwave circuit 102 to one another, and an adhesive layer 105 for adhering and securing the fiber block 103 and the planar lightwave circuit 102 to one another, said optical fiber module 100 being characterized in that: the glass layer 104 is only provided between the end surface section of the optical fiber 101 and the planar lightwave circuit; and the fiber block 103 is provided with an opening section 110 where the optical fiber 101 and the planar lightwave circuit 102 are exposed.

Description

Optical module and method for manufacturing the optical module

The present disclosure relates to an optical module in which a planar lightwave circuit is optically connected to an optical fiber, and which is resistant to high-energy light such as visible light used in optical sensing, and a method for manufacturing the optical module.

In recent years, there has been a demand for optical devices that have been used in communications to be applied to non-communications fields. In particular, optical devices based on waveguide-type optical elements such as quartz-based planar lightwave circuits (PLCs) are expected to have the potential to exceed the performance of existing Vasque-Optics-type optical elements, and are expected to be applied to fields such as displays, life sciences, quantum computers, and space. Important issues include making quartz-based PLCs compatible with visible wavelengths, increasing their output, making them smaller, and reducing the cost.

Quartz-based PLCs use semiconductor process techniques such as photolithography and dry etching to form optical waveguides consisting of cores and cladding on quartz or silicon substrates. In the broad sense, PLCs can also be realized as splitters that branch light, optical switches that change the path of optical signals, and lasers and modulators that serve as light sources. PLCs are usually used with optical fibers connected to the optical input and output terminals rather than used alone.

An example of a method for connecting a PLC and an optical fiber will be described with reference to FIG. 1. FIG. 1 shows an optical module 10 including a laser light source (LD) 11, an optical fiber 12 connected to the LD, a PLC 13 that propagates and outputs light input from the optical fiber 12, a fiber block 14 for fixing the optical fiber 12 to the PLC 13, and a photodiode 16 for receiving light emitted from the PLC 13. The PLC 13 and the fiber block 14 are usually bonded together with a UV-curable resin adhesive 15. UV-curable resin adhesives are generally used because they have a short curing time, can connect the optical fiber and the PLC while maintaining their relative positions, and can fix the optical fiber to the PLC with precise relative positions. The fiber block is placed at the tip of the optical fiber to obtain an adhesive area for the PLC. A glass member such as a V-groove substrate or a capillary is generally used as the fiber block.

The relative position of the optical fiber and the PLC is determined by fixing the PLC and the optical fiber to a fine adjustment device, applying a UV-curable resin adhesive to the connection gap while bringing the fiber block with the optical fiber inserted close to the PLC, and then adjusting with sub-micron precision so that the light receiving intensity of the PD is maximized. The optical fiber and PLC are then fixed by irradiating them with UV light to harden the UV-curable resin adhesive. In this way, it is common to use a UV-curable resin adhesive to connect the optical fiber and the PLC (for example, Patent Document 1: JP 2014-048628 A).

However, this UV-curing resin adhesive is known to deteriorate as it absorbs high-energy visible light. To prevent this deterioration, a connection method is used in which only the parts of the adhesive at the PLC and optical fiber through which light does not pass are fixed with UV-curing resin adhesive, leaving gaps in the parts through which light passes. However, this connection method has the problem that dust can collect in the gaps through which light passes, increasing connection loss.

As a result, a method has been proposed in which glass is filled into the part of the adhesive through which light passes, as shown in Patent Document 2 (JP Patent Publication 2018-194802).

2 shows an optical module 20 described in Patent Document 2. The optical module 20 includes an optical fiber 21, a PLC 22 connected to the optical fiber 21, a fiber block 23 into which the optical fiber 21 is inserted and fixed, a UV-curable resin adhesive layer 24 that bonds and fixes a portion between the connection end faces of the PLC 22 and the fiber block 23 through which light input and output between the optical fiber 21 and the PLC 22 does not pass, and a glass layer 25 that bonds and fixes a portion between the connection end faces of the PLC 22 and the fiber block 23 through which light input and output between the optical fiber 21 and the PLC 22 passes. The glass layer 25 of the optical module 20 is generated, for example, by a liquid phase synthesis method. One of the simple methods of liquid phase synthesis is a method in which polysilazane is used as a glass precursor. Polysilazane is a polymer material whose basic unit is [( _R1 )( _R2 )Si-N( _R3 )] ( _R1 , _R2 , _R3 = hydrogen, alkyl group, vinyl group), and is resistant to high-energy light because it converts to _SiO2 glass when it reacts with water.

However, depending on the type of polysilazane, the material of the fiber or fiber block may not wet well and may be repelled, making it difficult to stably perform the work of dropping polysilazane into a gap of several micrometers wide as shown in Patent Document 2 and filling the optical axis part. Even if it is possible to fill it, as shown in Patent Document 3 (JP Patent Publication 2013-001721), the curing shrinkage rate of polysilazane is large, and air gaps and voids are generated after curing, making it difficult to form a SiO ₂ glass layer in the optical axis part. Even if the amount of polysilazane dropped is increased to fill it sufficiently, polysilazane penetrates into areas other than the optical axis part, so there is a problem that stress is applied due to curing shrinkage and the optical axis is shifted after curing.

Furthermore, in order to lower the conversion temperature to _SiO2 glass, polysilazane is often doped with Pb compounds, which are dehydrogenation and oxidation catalysts, and amine-based catalysts that promote reactions with moisture, but these catalysts often absorb high-energy visible light and need to be sufficiently volatilized after curing. However, it takes time to volatilize the catalyst in the polysilazane between the fiber block including the optical axis part (fiber part) and the PLC. The reason for this is that the polysilazane in the optical axis part (fiber part) that needs to be volatilized is located in a position that is difficult to volatilize, near the center of the polysilazane filling area between the fiber block and the PLC. Here, even if a catalyst that promotes the reaction is added to polysilazane, it is difficult to cure in a short time like UV-curable resin adhesives, so it goes without saying that it is difficult to use polysilazane as a substitute for UV-curable resin adhesives.

As described above, with conventional optical connection technology, when high-energy light such as visible light is transmitted, the UV-curable resin adhesive used in the optical connection section deteriorates, and if there is a gap in the optical connection section, dust collection occurs, and as mentioned above, even if you try to fill the gap with glass, it is actually difficult to do so. Therefore, the optical connection technology of conventional optical modules has the problem of being unable to achieve stable optical connections that are reliable over the long term.

This disclosure has been made in consideration of the above problems, and aims to provide an optical module that is resistant to high-energy visible light and a method for manufacturing the optical module.

JP 2014-048628 A JP 2018-194802 A JP 2013-001721 A

In order to achieve this objective, an optical module according to one embodiment of the present disclosure is an optical module comprising one or more optical fibers, a planar lightwave circuit optically connected to the one or more optical fibers, a fiber block into which the one or more optical fibers are inserted and fixed, a glass layer that bonds and fixes the optical fiber and the planar lightwave circuit, and an adhesive layer that bonds and fixes the fiber block and the planar lightwave circuit, wherein the glass layer is provided only between the end face of the optical fiber and the planar lightwave circuit, and the fiber block is provided with an opening so that the connection between the optical fiber and the planar lightwave circuit is exposed.

In addition, a manufacturing method of an optical module according to one embodiment of the present disclosure is a manufacturing method of an optical module in which one or more optical fibers inserted and fixed in a fiber block are optically connected to a planar lightwave circuit, and is characterized by including the steps of: inserting an optical fiber into the fiber block; applying a glass precursor material to an end surface of the optical fiber; adjusting the positions of the optical fiber and the planar lightwave circuit using a fine alignment device and bringing the glass precursor material applied to the end surface of the optical fiber into contact with the planar lightwave circuit; semi-curing the glass precursor material and temporarily bonding and fixing the optical fiber and the planar lightwave circuit; bonding and fixing the fiber block to the end surface of the planar lightwave circuit and bonding and fixing the fiber block and the optical fiber at the same time; and fully curing the glass precursor material between the optical fiber and the planar lightwave circuit.

FIG. 1 is a diagram for explaining a conventional method for connecting a PLC and an optical fiber. FIG. 2 is a diagram for explaining another conventional example of a method for connecting a PLC and an optical fiber. FIG. 3 is a cross-sectional view of an optical module according to a first embodiment of the present disclosure. FIG. 4 is a perspective view of the optical module according to the first embodiment of the present disclosure in a state in which the PLC and the fiber block are separated. FIG. 5 is a flowchart showing a process of connecting an optical fiber and a PLC in a manufacturing method for an optical module according to each embodiment of the present disclosure. FIG. 6 is a diagram illustrating an example of a method for applying a glass precursor material to an end face of an optical fiber in a connection process of an optical module according to each embodiment of the present disclosure. FIG. 7 is a cross-sectional view of an optical module according to a second embodiment of the present disclosure. FIG. 8 is a perspective view of an optical module according to a second embodiment of the present disclosure in a state in which the PLC and the fiber block are separated. FIG. 9 is a cross-sectional view of an optical module according to a third embodiment of the present invention.

Below, an embodiment of the present disclosure will be described in detail with reference to the drawings.

(Example)
Fig. 3 is a cross-sectional view of an optical module 100 according to a first embodiment of the present disclosure. Fig. 3 shows the optical module 100 including an optical fiber 101, a PLC 102 optically connected to the optical fiber 101, a fiber block 103 into which the optical fiber is inserted and fixed, a glass layer 104 that bonds and fixes the optical fiber 101 and the PLC 102, and an adhesive layer 105 that bonds and fixes the fiber block and the PLC. For simplification, Fig. 3 shows a configuration in which the optical fiber is connected only to the input side of the PLC.

As shown in FIG. 4, the fiber block 103 is composed of a V-groove plate 106 in which a V-groove 108 for placing the optical fiber is formed, an upper plate 107, and an adhesive layer 109 that fixes them in place. The fiber block is provided with a 50 μm-long opening 110 so that the connection between the optical fiber and the PLC is exposed. The fiber insertion section on the opposite side of the opening 110 also has the same structure. By making the front and rear shapes of the fiber block the same in this way, the fiber block can be connected without worrying about the front-to-rear direction. The PLC 102 has an embedded waveguide structure in which a core 112 layer is embedded in a cladding 113 layer on a Si substrate 111.

As shown in FIG. 3, in the embodiment of the present disclosure, the glass layer 104 is provided only between the optical fiber end surface and the PLC, and the glass layer 104 is generated by a liquid phase synthesis method. Examples of the liquid phase synthesis method include a sol-gel method in which a liquid raw material is polymerized to form a gel, which is then left at room temperature or baked to harden to form glass, a polysilazane method, which is a type of sol-gel method, in which polysilazane is left at room temperature or baked to harden to form glass, and a liquid phase deposition method in which a liquid raw material is hydrolyzed to harden to form glass. In this embodiment, polysilazane is used as the precursor material of the glass layer. In addition to inorganic polymer materials such as polysilazane that have SiH ₂ NH as a basic unit, for example, materials that have silicon alkoxide (Si(OC ₂ H ₅ ) ₄ ) as the main component or hydrogen silicofluoride (H ₂ SiF ₆ ) as the main component can be used. The adhesive layer 105 can be formed using adhesives with a short hardening time, such as UV-curable resin adhesives, thermosetting adhesives, and two-liquid adhesives.

The manufacturing method of the optical module according to each embodiment of the present disclosure will be described below.

(Preparation of PLC)
The PLC can be fabricated, for example, by the following procedure. An undercladding layer made of quartz glass with a thickness of 20 μm and a core layer made of quartz glass with a thickness of 3 μm and with a high refractive index due to Ge doping are sequentially deposited on a Si substrate. The core layer is shaped into an optical waveguide pattern by general exposure and development techniques and etching techniques. After that, an overcladding layer made of quartz glass is laminated to a thickness of 20 μm to form an optical waveguide, and then the wafer is cut to cut out chips with a size of 10.0 mm×10.0 mm, thereby fabricating a quartz-based PLC.

(Fabrication of Fiber Block)
The fiber block can be fabricated, for example, by the following procedure. A V-groove of φ125 μm for fixing the fiber is formed by machining a glass plate having a thickness of 1.0 mm and a size of 5.0 mm×5.0 mm to fabricate a V-groove plate. Next, a glass plate having a thickness of 0.5 mm and a size of 5.0 mm×4.9 mm is prepared and fixed to the center of the previously fabricated V-groove plate with adhesive. If an adhesive with oxygen inhibition properties is used at this time, the adhesive will not harden even if it flows into the V-groove portion, so that the adhesive that has flowed into the V-groove portion can be removed by washing with ethanol after hardening.

(Connection process between PLC and optical fiber)
5 is a flowchart showing a process of connecting an optical fiber and a PLC in a manufacturing method of an optical module according to each embodiment of the present disclosure. The process of connecting an optical fiber and an optical waveguide of a PLC will be described with reference to FIG.

First, insert the optical fiber into the fiber block (201). After that, the PLC and the optical fiber are fixed to the fine adjustment device (202).

A glass precursor material (polysilazane in this example) is applied to the end face of the tip of the optical fiber (203). Note that after applying the glass precursor material to the end face of the optical fiber (203), the optical fiber may be inserted into the fiber block (201), and then the PLC and the optical fiber may be fixed to the fine adjustment device (202).

The application of glass precursor material (polysilazane) to the end face of the tip of the optical fiber can be performed, for example, by the procedure shown in FIG. 6. FIG. 6 is a diagram showing an example of a method for applying glass precursor material to the end face of an optical fiber. A glass precursor material 302, specifically, for example, polysilazane, is dropped onto a glass plate 301, and the glass plate 301 is preheated to volatilize the catalyst contained in the glass precursor material 302 to a certain extent. Here, the guideline is that the polysilazane 302 dropped onto the glass plate 301 does not drip even when the glass plate is placed vertically. After that, the glass plate 301 is fixed to a fine adjustment device, and the optical fiber 303, which has been fixed to the fine adjustment device in advance, is butted against the polysilazane 302 on the glass plate 301, so that polysilazane can be applied to the end face of the optical fiber 303. In FIG. 6, one optical fiber 303 is shown inserted into the fiber block 304, but even if multiple optical fibers are inserted into the fiber block, the glass precursor material can be applied to the end face of the optical fiber at once using a similar method.

Returning to Figure 5, after applying polysilazane, a glass precursor material, to the end face of the tip of the optical fiber (203), a fine adjustment device is used to adjust the positions of the PLC and the optical fiber, so that the glass precursor material applied to the end face of the optical fiber comes into contact with the PLC (204). Specifically, the positions of the PLC and the optical fiber are adjusted on the fine adjustment device to align their optical axes, the distance between the PLC and the optical fiber is reduced to about 1 μm, and the polysilazane applied to the end face of the optical fiber comes into contact with the PLC.

Then, a heater capable of localized heating is used to semi-cure the glass precursor material, and the PLC and the optical fiber are temporarily bonded and fixed (205). Here, for example, the polysilazane is semi-cure by heating at 150°C for about 5 minutes.

Then, the fiber block and the PLC are bonded and fixed together, and at the same time, the fiber block and the optical fiber are bonded and fixed together (206). Specifically, a UV-curable resin adhesive is applied to the fiber block, the fiber block into which the optical fiber has already been inserted is moved to the connection with the PLC, the fiber block is brought into contact with the PLC, and UV light is applied to harden it. At this time, the UV-curable resin adhesive spreads into the V-groove of the fiber block due to capillary action, so that the PLC and fiber block are fixed together, and the optical fiber and fiber block are fixed together.

After the bonded and fixed PLC, optical fiber, and fiber block were removed from the fine adjustment device, the glass precursor material was fully cured using an electric furnace (207). Here, the polysilazane was fully cured by heating at 150° C. for 48 hours. Even if a glass layer was not formed on the optical axis portion due to the cure shrinkage of polysilazane, in each embodiment of the present disclosure, the connection portion between the optical fiber and the PLC is largely exposed due to the opening provided in the fiber block, so that a glass layer can be formed by dropping polysilazane from the opening of the fiber block and heating it again.
In this manner, the optical module according to each embodiment of the present disclosure can be manufactured.

In this manner, in the manufacturing method of the present disclosure, first, a glass precursor material is applied only to the end surface of the optical fiber, and then the end surface of the optical fiber and the PLC are brought into contact and semi-cured to temporarily bond and fix the optical fiber, and the fiber block and the PLC and the fiber block and the optical fiber are simultaneously bonded and fixed with a UV-curable resin adhesive, after which the glass precursor material is fully cured by heat treatment. As a result, the glass layer that bonds and fixes the optical fiber and the PLC is formed only between the end surface of the optical fiber and the PLC. Therefore, in all of the optical modules of this embodiment, the connection portion between the optical fiber and the PLC is formed of a glass layer, making the optical module resistant to high-energy visible light.

In addition, the glass precursor is applied to only the end surface of the optical fiber in the optical module of each embodiment of the present disclosure. As a result, for example, in the case of a standard optical fiber, the application area of the glass driver can be limited to a very small area of about φ125 μm, which makes it possible to suppress optical axis misalignment caused by stress resulting from curing shrinkage.

In addition, the glass precursor material is locally heated from the outside during pre-curing and heated in an electric furnace during final curing, but the fiber blocks in each embodiment of the present disclosure are provided with an opening that exposes the connection between the optical fiber and the PLC, allowing for effective heating. Also, because the connection between the optical fiber and the PLC is exposed through the opening, the catalyst added to the glass precursor material can be efficiently volatilized during heating and after curing.

In the above, the glass precursor material is hardened by heating both during the semi-hardening and the full hardening stages, but either or both of the hardening stages may be performed by leaving the glass precursor material at room temperature.

Furthermore, when using the method of applying glass precursor material to the end of the optical fiber shown in Figure 6, the glass precursor material applied to the optical fiber is used in a state in which the catalyst has been volatilized to a certain extent, further reducing the occurrence of air gaps and voids due to cure shrinkage.

Second Example
In the first embodiment of the present disclosure, a fiber block consisting of a V-groove plate and an upper plate is used, but as shown in Figs. 7 and 8, the fiber block can also use a capillary.

Figure 7 is a cross-sectional view of an optical module 400 using a capillary as a fiber block according to a second embodiment of the present invention. Figure 7 shows an optical module 400 that includes an optical fiber 401, a PLC 402 that is optically connected to the optical fiber 401, a fiber block 403 into which the optical fiber is inserted and fixed, a glass layer 404 that bonds and fixes the optical fiber 401 and the PLC 402, and an adhesive layer 405 that bonds and fixes the fiber block and the PLC. For simplicity, Figure 7 also shows the configuration when the optical fiber is connected only to the input side of the PLC.

As shown in FIG. 8, the fiber block 403 has a hole 408 through which the optical fiber 401 passes. The fiber block 403 also has an opening 410 of 50 μm length to expose the connection between the optical fiber and the PLC. This opening can be manufactured by removing the upper half of the capillary's fiber insertion port by machining. The fiber insertion portion on the opposite side to the opening 410 has the same structure. The PLC 402 has an embedded waveguide structure in which a core 412 layer is embedded in a cladding 413 layer on a Si substrate 411, similar to the first embodiment in FIG. 5.

In this second embodiment, as shown in FIG. 7, the glass layer 404 is provided only between the optical fiber end face and the PLC.

(Third Example)
Next, an optical module according to a third embodiment of the present disclosure will be described with reference to FIG.

9 shows an optical module 500 including an optical fiber 501, a PLC 502 optically connected to the optical fiber 501, a fiber block 503 for inserting and fixing the optical fiber, a glass layer 504 for bonding and fixing the optical fiber 501 and the PLC 502, and an adhesive layer 505 for bonding and fixing the fiber block and the PLC. For simplification, FIG. 9 also shows a configuration for connecting the optical fiber only to the input side of the PLC. As in the first embodiment, the fiber block 503 is composed of a V-groove plate 506 in which a V-groove is formed for arranging the optical fiber, an upper plate 507, and an adhesive layer for fixing them. The fiber block is provided with an opening 510 of 50 μm length so that the connection between the optical fiber and the PLC is exposed. The fiber insertion portion on the opposite side to the opening 510 has the same structure. In this embodiment, as shown in FIG. 9, the glass layer 504 is provided only between the end surface of the optical fiber and the PLC. In this embodiment, an adhesive reinforcing plate 515 is provided to bond the upper surface of the PLC 502 to the upper plate 507. This improves the adhesive strength between the fiber block and the PLC.

The optical modules according to the second and third embodiments can also be manufactured by the manufacturing method for the optical module according to the first embodiment described above.

In the manufacturing method of the optical module according to the embodiment of the present disclosure described above, the glass precursor material is semi-cured to temporarily connect the optical fiber to the PLC, and then the fiber block and the PLC and the fiber block and the optical fiber are simultaneously fixed with a UV-curable resin adhesive, and then the glass precursor material is fully cured by heat treatment. Among these, the fixing with the UV-curable resin adhesive and the fully cured are performed after the optical axis adjustment using the fine adjustment device is completed, so there is no need for optical axis adjustment using the fine adjustment device, and it can be performed on multiple optical fibers at once, so mass productivity is not significantly reduced.
Therefore, the manufacturing method of the optical module disclosed herein makes it possible to realize stable manufacturing of optical connections that are resistant to high-energy light by taking advantage of the advantages of glass precursor materials. Therefore, the present disclosure will greatly contribute to expanding the range of applications of PLC.

For the sake of simplicity, the optical module in each of the above embodiments of the present disclosure is exemplified as a configuration in which one optical fiber is connected to the input end of the PLC, but the present invention is not limited to this, and the optical fiber can also be connected to the output end of the PLC. In addition, a configuration in which multiple V-grooves or insertion holes for inserting and fixing multiple optical fibers in the fiber block and multiple optical waveguides are formed in the PLC, with multiple optical fibers connected to each of the input and output ends of the PLC can be used. Furthermore, multiple fiber blocks can be used to connect multiple optical fibers to each of the input and output ends of the PLC.

This disclosure makes it possible to provide an optical module that is resistant to high-energy visible light and a method for manufacturing the optical module.

Claims (8)

one or more optical fibers;
a planar lightwave circuit optically connected to the one or more optical fibers;
a fiber block into which the one or more optical fibers are inserted and fixed;
a glass layer for bonding and fixing the optical fiber and the planar lightwave circuit;
an adhesive layer for bonding and fixing the fiber block and the planar lightwave circuit;
An optical module comprising:
the glass layer is provided only between the end face of the optical fiber and the planar lightwave circuit,
the fiber block is provided with an opening so that a connection portion between the optical fiber and the planar lightwave circuit is exposed.
1. An optical module comprising: The optical module according to claim 1, characterized in that the fiber block is composed of a V-groove plate having a V-groove in which the optical fiber is arranged, an upper plate, and an adhesive layer that fixes the V-groove plate and the upper plate. The optical module according to claim 1, characterized in that the fiber block is composed of an integrated capillary having a hole for inserting the optical fiber. The optical module according to any one of claims 1 to 3, characterized in that the fiber block has the same structure as the opening in the fiber insertion section opposite the opening. The optical module according to any one of claims 1 to 3, characterized in that the opening of the fiber block is open from the end of the fiber block to 50 μm or more in the longitudinal direction of the fiber block. A method for manufacturing an optical module in which one or more optical fibers inserted and fixed in a fiber block are optically connected to a planar lightwave circuit, comprising the steps of:
inserting the optical fiber into the fiber block;
applying a glass precursor material to an end surface of the optical fiber;
a step of adjusting the positions of the optical fiber and the planar lightwave circuit using a fine adjustment device, and bringing the glass precursor material applied to the end surface of the optical fiber into contact with the planar lightwave circuit;
a step of semi-curing the glass precursor material and temporarily bonding and fixing the optical fiber and the planar lightwave circuit;
a step of adhering and fixing the fiber block to an end face of the planar lightwave circuit and at the same time adhering and fixing the fiber block and the optical fiber;
permanently curing the glass precursor material between the optical fiber and the planar lightwave circuit;
A method for manufacturing an optical module comprising the steps of: applying the glass precursor material to an end surface of the optical fiber;
Dropping the glass precursor material onto a glass plate;
preheating the glass plate onto which the glass precursor material has been dropped;
attaching the glass plate to the fine alignment device and using the fine alignment device to bring the optical fiber into contact with the glass precursor material applied to the glass plate;
7. The method for manufacturing an optical module according to claim 6, further comprising: The method for manufacturing an optical module according to claim 6, characterized in that the semi-curing and/or the full curing of the glass precursor material is carried out by leaving the glass precursor material at room temperature or by heating the glass precursor material.

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