JP7846423B2 - Optical module and method for manufacturing an optical module - Google Patents

Description

This disclosure relates to an optical module in which a planar light wave circuit and an optical fiber are optically connected, and to an optical module, which is resistant to high-energy light such as visible light used in optical sensing, etc.

In recent years, there has been a growing demand for applications of optical devices, previously used in communications, in non-communications fields. In particular, optical devices based on waveguide-type optical elements such as silica-based planar lightwave circuits (PLCs) are expected to surpass the performance of existing bass optics-type optical elements, and are anticipated to be applied in fields such as displays, life sciences, quantum mechanics, and space. Key challenges for silica-based PLCs include achieving visible wavelength compatibility, high power output, miniaturization, and cost reduction.

Silica-based PLCs utilize semiconductor process technologies such as photolithography and dry etching to form optical waveguides consisting of a core and cladding on a quartz or silicon substrate. Splitters that branch light, optical switches that switch the path of optical signals, and even lasers and modulators that serve as light sources are all realized using PLCs in a broad sense. Typically, PLCs are used with optical fibers connected to their optical input and output terminals rather than being used alone.

An example of a method for connecting a PLC and an optical fiber will be explained using Figure 1. Figure 1 shows an optical module 10 comprising 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 that receives the light emitted from the PLC 13. The PLC 13 and the fiber block 14 are usually bonded together with a UV-curing resin adhesive 15. UV-curing resin adhesives are commonly used because they have a short curing time, can be connected while maintaining the relative position of the optical fiber and the PLC, and allow the optical fiber to be fixed to the PLC with high precision by aligning the relative position. The fiber block is placed at the end of the optical fiber to obtain a bonding area with respect to the PLC. As the fiber block, glass materials such as V-groove substrates or capillaries are generally used.

The relative position between the optical fiber and the PLC is determined by fixing the PLC and the optical fiber to a fine-adjustment device, applying UV-curing resin adhesive to the connection gap with the fiber block containing the inserted optical fiber close to the PLC, and then adjusting it to a sub-micron order precision so that the light reception intensity of the photodiode (PD) is maximized. Subsequently, the optical fiber and PLC are fixed by curing the UV-curing resin adhesive by irradiating it with UV light. Thus, it is common to use UV-curing resin adhesive for connecting optical fibers and PLCs (for example, Patent Document 1: Japanese Patent Application Publication No. 2014-048628).

However, it is known that this UV-curing resin adhesive degrades by absorbing high-energy visible light. To suppress this degradation, a connection method is used in which only the parts where light does not pass through are fixed with UV-curing resin adhesive at the bonding point between the PLC and the optical fiber, leaving the parts where light passes through as an air gap. However, this connection method has the problem that dust accumulation occurs in the air gap through which light passes, increasing connection loss.

Therefore, as shown in Patent Document 2 (Japanese Patent Application Publication No. 2018-194802), a method has been proposed in which glass is filled into the portion of the adhesive joint through which light passes.

Figure 2 shows an optical module 20 described in Patent Document 2. The optical module 20 comprises 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-curing resin adhesive layer 24 that adheres and fixes the portion between the connection end faces of the PLC 22 and the fiber block 23 where light input and output between the optical fiber 21 and the PLC 22 does not pass, and a glass layer 25 that adheres and fixes the portion between the connection end faces of the PLC 22 and the fiber block 23 where light input and output between the optical fiber 21 and the PLC 22 passes. The glass layer 25 of this optical module 20 is produced, for example, by a liquid-phase synthesis method. One simple method of the liquid-phase synthesis method is to use polysilazane as a glass precursor. Polysilazanes are polymer materials based on the fundamental unit [( _R1 )( _R2 )Si-N( _R3 )] ( _R1 , _R2 , _R3 = hydrogen, alkyl group, vinyl group), and they react with water to form _SiO2 glass, thus possessing resistance to high-energy light.

However, depending on the type of polysilazane, it may not wet the fiber or fiber block material well and may repel it, making it difficult to reliably perform the operation of dropping polysilazane into a gap several micrometers wide, as shown in Patent Document 2, and filling the optical axis. Furthermore, even if filling was possible, as shown in Patent Document 3 (Japanese Patent Application Publication No. 2013-001721), the curing shrinkage rate of polysilazane is large, causing air gaps and voids to occur after curing, making it difficult to form an _SiO2 glass layer in the optical axis. In addition, even if the amount of polysilazane dropped is increased to adequately fill the area, the polysilazane penetrates areas other than the optical axis, causing stress due to curing shrinkage, which leads to the problem of the optical axis shifting after curing.

Furthermore, to lower the conversion temperature to _SiO2 glass, polysilazanes often contain dopants such as Pb compounds, which are dehydrogenation and oxidation catalysts, and amine-based catalysts, which promote reactions with water. However, these catalysts often absorb high-energy visible light and need to be sufficiently volatilized after curing. Volatilizing the catalyst in the polysilazane between the fiber block (including the optical axis portion) and the PLC takes time. This is because the polysilazane in the optical axis portion (fiber portion) that needs to be volatilized is located near the center of the polysilazane-filled region between the fiber block and the PLC, making it difficult to volatilize. Here, even if a catalyst to promote the reaction is added, polysilazane cannot be cured in the short time possible, unlike UV-curing resin adhesives, so it goes without saying that it is difficult to use polysilazane as a substitute for UV-curing resin adhesives.

As described above, with conventional optical connection technologies, when high-energy light such as visible light is propagated, the UV-curing resin adhesive used in the optical connection deteriorates, dust collection occurs if there are gaps in the optical connection, and even if attempts are made to fill the gaps with glass, it is practically difficult as mentioned above. Therefore, conventional optical module optical connection technologies have the problem of not being able to achieve stable and long-term reliable optical connections.

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

Japanese Patent Publication No. 2014-048628 Japanese Patent Publication No. 2018-194802 Japanese Patent Publication No. 2013-001721

To achieve this objective, an optical module in one embodiment of the present disclosure comprises one or more optical fibers, a planar optical wave circuit optically connected to one or more optical fibers, a fiber block into which one or more optical fibers are inserted and fixed, a glass layer for bonding and fixing the optical fibers and the planar optical wave circuit, and an adhesive layer for bonding and fixing the fiber block and the planar optical wave circuit, wherein the glass layer is provided only between the end face of the optical fiber and the planar optical wave circuit, the fiber block has an opening on its upper surface configured to expose the connection between the optical fiber and the planar optical wave circuit, and the adhesive layer is provided only between the end face of the fiber block and the planar optical wave circuit and not in the opening .

Furthermore, one embodiment of the present disclosure is 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 optical wave circuit, and is characterized by including the steps of: inserting an optical fiber into a fiber block; applying a glass precursor material to the end face of an optical fiber; adjusting the position of the optical fiber and the planar optical wave circuit using a fine adjustment device and bringing the glass precursor material applied to the end face of an optical fiber into contact with the planar optical wave circuit; partially curing the glass precursor material and temporarily bonding and fixing the optical fiber and the planar optical wave circuit; bonding and fixing the fiber block to the end face of the planar optical wave circuit and simultaneously bonding and fixing the fiber block and the optical fiber; and fully curing the glass precursor material between the optical fiber and the planar optical wave circuit.

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

The embodiments of this disclosure will be described in detail below with reference to the drawings.

(Examples)
Figure 3 is a cross-sectional view of an optical module 100 according to a first embodiment of the present disclosure. Figure 3 shows an optical module 100 comprising an optical fiber 101, a PLC 102 optically connected to the optical fiber 101, a fiber block 103 for inserting and fixing the optical fiber, a glass layer 104 for bonding and fixing the optical fiber 101 and the PLC 102, and an adhesive layer 105 for bonding and fixing the fiber block and the PLC. For simplification, Figure 3 shows a configuration where the optical fiber is connected only to the input side of the PLC.

As shown in Figure 4, the fiber block 103 consists of a V-groove plate 106 with a V-groove 108 for arranging optical fibers, an upper plate 107, and an adhesive layer 109 for fixing them together. 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 portion on the opposite side of the opening 110 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 used without worrying about the front-to-back direction when connecting them. The PLC 102 has an embedded waveguide structure in which a core 112 layer is embedded with a cladding 113 layer on a Si substrate 111.

As shown in Figure 3, in the embodiment of this disclosure, the glass layer 104 is provided only between the optical fiber end face and the PLC, and the glass layer 104 is produced by a liquid-phase synthesis method. As a liquid-phase synthesis method, for example, a sol-gel method can be used, in which liquid raw materials polymerize to form a gel, which is then cured by leaving it at room temperature or firing to produce glass; a polysilazane method, which is a type of sol-gel method in which polysilazane is cured by leaving it at room temperature or firing to produce glass; or a liquid-phase precipitation method can be used, in which liquid raw materials are hydrolyzed to cure and produce glass. In this embodiment, polysilazane is used as the precursor material for the glass layer. In addition to inorganic polymer materials with _SiH2NH as the basic unit, such as polysilazane, for example, materials mainly composed of silicon alcoside (Si( _OC2H5 ) _{4 )} or hydrogen silica fluoride ( _{H2SiF6 )} can be used. The adhesive layer 105 can be formed using adhesives with short curing times, such as UV-curing resin adhesives, thermosetting adhesives, and two-component adhesives.

The manufacturing method for each embodiment of this disclosure will be described below.

(PLC fabrication)
A 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 a high refractive index due to ge doping are deposited sequentially on a Si substrate. The core layer is formed into an optical waveguide pattern using general exposure and etching techniques. After that, an overcladding layer made of quartz glass with a thickness of 20 μm is stacked 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 blocks)
A fiber block can be manufactured, for example, by the following procedure: A glass plate measuring 1.0 mm thick and 5.0 mm x 5.0 mm is machined to form a V-groove for fixing fibers with a diameter of φ125 μm, thereby creating a V-groove plate. Next, a glass plate measuring 0.5 mm thick and 5.0 mm x 4.9 mm is prepared and fixed to the center of the previously manufactured V-groove plate with adhesive. At this time, if an oxygen-inhibiting adhesive is used, even if the adhesive flows into the V-groove, it will not harden, and the adhesive that has flowed into the V-groove can be removed by washing with ethanol after hardening.

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

The optical fiber is first inserted into the fiber block (201). Then, 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). Alternatively, the glass precursor material may be applied 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 optical fiber may be fixed to the fine-adjustment device (202).

The application of a glass precursor material (polysilazane) to the end face of the tip of an optical fiber can be carried out, for example, by the procedure shown in Figure 6. Figure 6 shows an example of a method for applying a glass precursor material to the end face of an optical fiber. A glass precursor material 302, specifically 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 some extent. Here, the guideline is that the dropped polysilazane 302 on 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 previously fixed to the fine-adjustment device, is brought into contact with the polysilazane 302 on the glass plate 301, thereby applying polysilazane to the end face of the optical fiber 303. In Figure 6, a single optical fiber 303 is shown inserted into the fiber block 304 as an example. However, even when multiple optical fibers are inserted into the fiber block, the glass precursor material can be applied to the end faces of the optical fibers in the same manner at once.

Returning to Figure 5, polysilazane, a glass precursor material, is applied to the end face of the tip of the optical fiber (203). Then, the position of the PLC and the optical fiber is adjusted using a fine-adjustment device to bring the glass precursor material applied to the end face of the optical fiber into contact with the PLC (204). Specifically, the position of the PLC and the optical fiber is adjusted on the fine-adjustment device to align the optical axis, bringing the distance between the PLC and the optical fiber to about 1 μm, and bringing the polysilazane applied to the end face of the optical fiber into contact with the PLC.

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

Subsequently, 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, UV-curing resin adhesive is applied to the fiber block, the fiber block with the optical fiber already inserted is moved to the connection point with the PLC, the fiber block is brought into contact with the PLC, and cured by irradiation with UV light. At this time, the UV-curing resin adhesive spreads into the V-groove of the fiber block by capillary action, so that the PLC and the fiber block are fixed together, and the optical fiber and the fiber block are fixed together.

After removing the bonded and fixed PLC, optical fiber, and fiber block from the fine-tuning device, the glass precursor material was cured using an electric furnace (207). Here, polysilazane was cured by heating at 150°C for 48 hours. Even if a glass layer is not formed on the optical axis due to curing shrinkage of the polysilazane, in each embodiment of this disclosure, the connection portion between the optical fiber and the PLC is largely exposed by the opening provided in the fiber block. Therefore, a glass layer can be formed by dripping polysilazane through the opening in the fiber block and heating it again.
As described above, optical modules according to each embodiment of the present disclosure can be manufactured.

As described above, in the manufacturing method of this disclosure, first, a glass precursor material is applied only to the end face of the optical fiber, and the optical fiber end face and the PLC are brought into contact and partially cured to temporarily bond and fix them. Then, the fiber block and the PLC and the fiber block and the optical fiber are simultaneously bonded and fixed with a UV-curing resin adhesive, and finally, 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 face of the optical fiber and the PLC. Therefore, in all optical modules of this embodiment, the connection portion between the optical fiber and the PLC is formed with a glass layer, resulting in an optical module that is resistant to high-energy visible light.

Furthermore, the coating area of the glass precursor in each embodiment of the optical module of this disclosure is limited to the end face of the optical fiber. As a result, for example, in the case of a standard optical fiber, the coating area of the glass drive body can be limited to a minute area of about φ125 μm, thereby suppressing optical axis misalignment due to stress caused by hardening shrinkage.

In addition, while the glass precursor material is partially heated externally during pre-curing and heated in an electric furnace during full curing, the fiber blocks in each embodiment of this disclosure are provided with openings that expose the connection between the optical fiber and the PLC, allowing for effective heating. Furthermore, because the connection between the optical fiber and the PLC is exposed by the openings, 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 cured by heating at both the semi-curing and full-curing stages. However, either one or both of these curing stages may be performed by leaving the glass precursor material at room temperature.

Furthermore, when using the method of coating the optical fiber end with glass precursor material as shown in Figure 6, the glass precursor material coated onto the optical fiber is used in a state where the catalyst has been partially volatilized, which further reduces the generation of air gaps and voids due to hardening shrinkage.

(Second example)
In the first embodiment of this disclosure, a fiber block consisting of a V-groove plate and a top plate was used, but as shown in Figures 7 and 8, a capillary can also be used as the fiber block.

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 comprising an optical fiber 401, a PLC 402 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 adheres and fixes the optical fiber 401 and the PLC 402, and an adhesive layer 405 that adheres and fixes the fiber block and the PLC. In Figure 7, for simplification, the configuration when the optical fiber is connected only to the input side of the PLC is shown.

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

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

(Third embodiment)
Next, with reference to Figure 9, an optical module according to a third embodiment of this disclosure will be described.

Figure 9 shows an optical module 500 comprising 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. In Figure 9, for simplification, the configuration is shown when the optical fiber is connected only to the input side of the PLC. Also, similar to the first embodiment, the fiber block 503 is composed of a V-groove plate 506 with a V-groove formed therein for arranging the optical fiber, an upper plate 507, and an adhesive layer for fixing them. The fiber block is provided with a 50 μm long opening 510 so that the connection portion between the optical fiber and the PLC is exposed. The fiber insertion portion on the opposite side of the opening 510 has the same structure. In this embodiment as well, as shown in Figure 9, the glass layer 504 is provided only between the end face of the optical fiber and the PLC. In this embodiment, an adhesive reinforcing plate 515 is provided for bonding 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 described above can also be manufactured by the method for manufacturing the optical module according to the first embodiment described above.

In the method for manufacturing an optical module according to the embodiments of the present disclosure described above, the optical fiber is temporarily connected to the PLC by the glass precursor material by semi-curing the glass precursor material, and then the fiber block and the PLC, and the fiber block and the optical fiber are simultaneously fixed with a UV-curing resin adhesive, and then the glass precursor material is fully cured by heat treatment. Of these, the fixing with the UV-curing resin adhesive and the full curing are performed after the optical axis adjustment using a fine-adjustment device is completed, so it does not require optical axis adjustment using a fine-adjustment device and can be performed for multiple optical fibers at once, so the mass production capacity is not significantly reduced.
Therefore, the manufacturing method of the optical module disclosed herein enables the stable production of optical connections that are resistant to high-energy light, taking advantage of the benefits of the glass precursor material. Accordingly, this disclosure will greatly contribute to expanding the applications of PLCs.

For simplicity, the optical modules in the embodiments described above are illustrated with a configuration in which one optical fiber is connected to the input terminal of a PLC. However, the invention is not limited to this configuration, and an optical fiber can also be connected to the output terminal of the PLC. Furthermore, multiple V-grooves or insertion holes can be formed in a fiber block for inserting and fixing multiple optical fibers, and multiple optical waveguides can be formed in the PLC, with multiple optical fibers connected to its input and output terminals. Moreover, multiple fiber blocks can be used to connect multiple optical fibers to the input and output terminals of a PLC.

This disclosure provides an optical module resistant to high-energy visible light and a method for manufacturing the optical module.

Claims (8)

One or more optical fibers,
A planar light wave circuit optically connected to the one or more optical fibers,
A fiber block in which one or more optical fibers are inserted and fixed,
A glass layer that adheres and fixes the optical fiber and the plane light wave circuit,
An adhesive layer for bonding and fixing the fiber block and the plane light wave circuit,
An optical module equipped with,
The glass layer is provided only between the end face of the optical fiber and the plane light wave circuit.
The fiber block has an opening on its upper surface configured to expose the connection between the optical fiber and the plane light wave circuit , and the adhesive layer is provided only between the end face of the fiber block and the plane light wave circuit, and not in the opening .
An optical module characterized by the following features. The optical module according to claim 1, characterized in that the fiber block comprises a V-groove plate having V-grooves for arranging the optical fibers, an upper plate, and an adhesive layer for fixing 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 portion opposite to the opening. The optical module according to any one of claims 1 to 3, characterized in that the opening of the fiber block extends 50 μm or more in the longitudinal direction of the fiber block from the end of the fiber block. A method for manufacturing an optical module in which one or more optical fibers inserted into and fixed in a fiber block are optically connected to a planar optical wave circuit,
The steps include inserting the optical fiber into the fiber block,
The steps include: applying a glass precursor material to the end face of the optical fiber;
A step of adjusting the position of the optical fiber and the plane light wave circuit using a fine adjustment device, and bringing the glass precursor material coated on the end face of the optical fiber into contact with the plane light wave circuit,
The process involves partially curing the glass precursor material and temporarily bonding and fixing the optical fiber and the plane light wave circuit,
The process involves bonding and fixing the fiber block to the end face of the planar optical circuit, and simultaneously bonding and fixing the fiber block to the optical fiber.
A step of curing the glass precursor material between the optical fiber and the plane light wave circuit,
A method for manufacturing an optical module, characterized by including the following: The step of applying the glass precursor material to the end face of the optical fiber is
A step of dropping the glass precursor material onto a glass plate,
A step of preheating the glass plate on which the glass precursor material has been dropped,
The steps include: attaching the glass plate to the fine-adjustment device, and using the fine-adjustment device to bring the optical fiber into contact with the glass precursor material coated on the glass plate;
A method for manufacturing an optical module according to claim 6, characterized by including the following: The method for manufacturing an optical module according to claim 6, characterized in that the semi-curing and/or full curing of the glass precursor material is performed by leaving the glass precursor material at room temperature or by heating the glass precursor material.