JP2009223184A - Optical waveguide structure and method of manufacturing the same, and optical module - Google Patents

Abstract

The reliability of a small-sized optical waveguide structure having an optical waveguide (curved waveguide) on a curved surface is improved.
An optical waveguide structure includes a clad structure having a groove formed on a curved surface, a waveguide core formed in the groove, and a clad film covering the waveguide core. The stress relaxation layer 6 formed on the surface of the clad film 5 is provided.
[Selection] Figure 1

Description

  The present invention relates to a method for manufacturing an optical waveguide structure used for optical communication, for example, and more particularly to an optical waveguide structure suitable for coupling an optical element such as a laser diode and a transmission medium such as an optical fiber. The present invention relates to an optical module.

In recent years, development of multi-channel optical transceivers (for example, wavelength division multi-channel optical transceivers) including surface optical elements such as surface-emitting lasers and photodiodes (photo detectors) has been underway.
For example, when using a surface optical element such as a surface emitting laser or a photodiode in an optical module such as a multi-channel optical transceiver, the light incident surface or light exit surface of the surface optical element is parallel to the mounting substrate. Then, light is incident or emitted perpendicularly to the mounting substrate.

On the other hand, it is necessary to reduce the size and thickness of such an optical module.
In order to reduce the size and thickness, it is desirable to arrange the optical fiber (optical fiber array) in parallel with the mounting substrate. In this case, the end face of the optical fiber and the light incident surface or light emitting surface of the surface optical element are in a substantially right-angle positional relationship.
For this reason, an optical fiber and a planar optical element are bent by approximately 90 degrees in the path (optical path) of light incident or emitted perpendicular to the light incident surface or the light emitting surface of the planar optical element mounted on the substrate. Need to be optically connected.

Therefore, for example, an optical waveguide structure having an optical waveguide (curved waveguide) on a substantially right-angled curved surface is used in a planar optical element in order to sharply bend the light path in a narrow space in an apparatus such as an optical transceiver. On the other hand, there is a technique in which incident or outgoing light is guided along a curved surface and coupled to an optical fiber array.
In such an optical waveguide structure, a liquid core material is dropped on a curved surface, a film is pasted thereon, and the liquid core material is thinned by pressing with a constant pressure using a soft material such as silicon rubber. Produced by stretching and curing by UV irradiation.
JP 2005-115346 A JP 2007-264033 A

  By the way, in the above optical waveguide structure, the film affixed on the curved surface constitutes a clad portion of the optical waveguide structure as a final product. For this reason, the film has (1) a refractive index slightly lower (for example, 1%) than the liquid core material used as the waveguide core, (2) it is transparent to light of the wavelength used, (3) It is required to be easily bent to a predetermined curvature and to have sufficient bending strength.

However, the films that satisfy such requirements are extremely limited. In particular, there is a limit to reducing the bend radius for overall miniaturization.
For example, when a film having a thickness of 50 μm is formed of a polyolefin-based resin and bent so that the radius of curvature is, for example, about 1 mm, a large compressive stress / tensile stress equivalent to the breaking stress is applied to the inner periphery / outer periphery, and crack There is a concern that this will occur. In particular, once a crack occurs, it grows with time, and in some cases reaches the core portion, resulting in an increase in loss.

  Therefore, it is desired to improve the reliability of a small optical waveguide structure having an optical waveguide (curved waveguide) on a curved surface.

For this reason, the optical waveguide structure was formed on the surface of the clad film having the groove formed on the curved surface, the waveguide core formed in the groove, the clad film covering the waveguide core, and the clad film. It is a requirement to provide a stress relaxation layer.
An optical module is required to include the optical waveguide structure described above.
The optical waveguide structure manufacturing method is required to fill a groove of a clad structure having a groove on a curved surface with a core material, cover the groove with a clad film, and form a stress relaxation layer on the surface of the clad film. To do.

  Therefore, according to the optical waveguide structure, the manufacturing method thereof, and the optical module, there is an advantage that the reliability of the small-sized optical waveguide structure having the optical waveguide (curved waveguide) on the curved surface can be improved.

Hereinafter, an optical waveguide structure, a manufacturing method thereof, and an optical module according to the present embodiment will be described with reference to FIG.
First, the present optical waveguide structure is a curved optical waveguide component (for example, a polymer optical waveguide) formed so that light propagates in a curved waveguide core, and as shown in FIG. A clad structure (lower clad) 1 having a plurality of grooves 3 formed in each of the above, a waveguide core 4 formed in each groove 3, a clad film (upper clad) 5 covering the plurality of waveguide cores 4, and And a stress relaxation layer (cover resin layer) 6 formed on the surface of the clad film 5.

  Here, the clad structure 1 is a curved structure having a groove (waveguide groove; narrow groove) 3 extending from one end to the other end of the curved surface 2 on the curved surface 2 of the surface of the structure as shown in FIG. It is. Here, the cladding structure 1 is a transparent structure formed of a transparent member made of a transparent cladding material, and has a refractive index n1. For example, a molded product (resin molded product) using an olefin polymer (for example, polyolefin).

  As shown in FIGS. 1 and 2, the waveguide core 4 is formed by embedding the groove 3 formed in the curved surface layer portion of the cladding structure 1 with a transparent core material. For this reason, the waveguide core 4 is formed in a curved shape along the curved surface 2 of the cladding structure 1 and has a columnar shape. The waveguide core 4 has a refractive index n2 larger than the refractive index n1 of the cladding structure 1 (n2> n1).

As will be described later, in the present embodiment, the waveguide core 4 is formed by applying a liquid core material (liquid adhesive) and curing it, so that the refractive index after curing is n2 ( A transparent solid having a refractive index of n2).
As shown in FIGS. 1 and 2, the clad film 5 is laminated so as to cover the waveguide core 4 formed in the groove 3 on the curved surface 2 of the clad structure 1. The clad film 5 has a refractive index n3 smaller than the refractive index n2 of the waveguide core 4 (n3 <n2).

  By the way, if the clad film 5 is formed so as to have a refractive index slightly lower than that of the waveguide core 4, transparent to the light propagating in the waveguide core 4 and having a constant refractive index, the cladding film 5 has ductility and flexibility. It tends to be insufficient, and cracks are likely to occur. Further, once a crack occurs, the crack gradually grows due to stress concentration, and when it reaches the waveguide core 4, it leads to light loss.

For this reason, in this embodiment, as shown in FIG. 1 and FIG. 2, a stress relaxation layer 6 for relaxing stress generated in the clad film 5 is provided.
By providing the stress relaxation layer 6, it is difficult for cracks to occur in the clad film 5, and even if cracks occur in the manufacturing process, the cracks are difficult to grow thereafter. Thereby, it is possible to prevent the loss from increasing due to cracks over time.

  Here, as will be described later, the stress relaxation layer 6 is a resin layer formed by applying a transparent liquid resin material (liquid adhesive) to the surface of the clad film 5 and curing it. Thus, by using a resin material that is transparent to the light propagating in the waveguide core 4, the light propagating in the waveguide core 4 can be prevented from being affected. If the stress relaxation layer 6 does not affect the light propagating in the waveguide core 4 so much, it need not be formed of a transparent material.

  When cracks are generated on the surface of the clad film 5 before forming the stress relaxation layer 6, the cracks generated on the surface of the clad film 5 are embedded in the resin layer as the stress relaxation layer 6. It is formed. Here, a liquid resin material is applied so as to enter a wedge-shaped crack and solidified integrally. In this case, the resin layer as the stress relaxation layer 6 may be formed to a thickness that can fill a crack generated on the surface of the clad film 5 (for example, a thickness equivalent to that of the clad film 5). As a result, the resin layer 6 functioning as an adhesive is tightly fixed and cracks are less likely to grow.

In this way, the crack grows with time by solidifying the surface with the resin layer 6 functioning as an adhesive in the initial stage before the crack grows, and sometimes reaches the core part, resulting in loss. Can be prevented in advance.
The resin layer as the stress relaxation layer 6 may be formed so as to cover only the cracked portion of the surface of the clad film 5; however, in consideration of the possibility of the crack occurring after that, the crack is generated. Regardless of whether or not it is formed, it is preferably formed on the entire surface of the clad film 5. Thereby, it becomes difficult to generate | occur | produce a crack and generation | occurrence | production of a crack can be prevented beforehand.

  By the way, when light is incident on the waveguide core from the outside, a certain amount of error is unavoidable in the alignment, and a part thereof leaks out around the waveguide core as shown in FIG. Among these, the light leaked to the clad film side is reflected by this surface (that is, the interface with air) because the surface of the clad film is smooth, and returns while spreading toward the waveguide core. Since a plurality of waveguide cores are formed adjacent to each other on the curved surface of the cladding structure, some of them enter the adjacent waveguide cores, and crosstalk (crosstalk noise) occurs. End up.

Therefore, in the present embodiment, the refractive index n4 of the stress relaxation layer 6 is set larger than the refractive index n3 of the cladding film 5 (n4> n3).
For example, the stress relaxation layer 6 may be formed of the same material as the waveguide core 4. In this case, the refractive index n4 of the stress relaxation layer 6 is the same as the refractive index n2 of the waveguide core 4 (n2− = n4). Thereby, there is an advantage that it is not necessary to prepare a separate material in order to form the stress relaxation layer 6.

  As will be described later, in this embodiment, since the resin layer as the stress relaxation layer 6 is formed by applying a liquid resin material and curing it, a material whose refractive index after curing is n4 is used. . Further, the stress relaxation layer 6 may be any layer having a refractive index larger than that of the clad film 5. For example, the stress relaxation layer 6 may be formed of a material different from that of the waveguide core 4 or may have a refractive index different from that of the waveguide core 4. You may have.

For this reason, as shown in FIG. 2, even if the leakage light from the waveguide core 4 is reflected by the surface of the stress relaxation layer 6 (that is, the interface with air), it is confined in the stress relaxation layer 6 and terminated. Will be propagated. Moreover, since the surface of the resin layer as the stress relaxation layer 6 is not as smooth as a film, it is scattered and radiated to the outside.
As a result, it is possible to prevent leakage light from one waveguide core 4 from returning to another adjacent waveguide core 4 and causing crosstalk. As a result, increase in loss due to cracks can be prevented, crosstalk between adjacent channels can be reduced, crosstalk performance can be improved, and reliability can be increased.

Further, the stress relaxation layer 6 may have the same refractive index as that of the clad film 5 as long as it is not necessary to consider improvement of the crosstalk performance. Also in this case, an increase in loss due to cracks can be prevented and reliability can be improved.
Next, a method for manufacturing the optical waveguide structure according to the present embodiment will be described with reference to FIGS.

The manufacturing method of this optical waveguide structure includes each process as shown in FIGS.
First, as shown in FIG. 4A, a curved structure (clad structure) having a groove (waveguide groove; narrow groove) 3 extending from one end to the other end of the curved surface 2 on the curved surface 2 of the structure surface. Transparent structure) 1 is produced by molding using, for example, an olefin polymer (polyolefin; a transparent member made of a transparent clad material). That is, the curved surface structure (mold base material: mold optical waveguide) 1 in which the groove 3 is previously formed on the curved surface 2 is produced.

Next, as shown in FIG. 4B, a dispenser (quantitative dispenser; liquid core material dropping device) is placed on the curved surface 2 including the groove 3 on one end side or the other end side of the groove 3 of the curved structure 1. A predetermined amount of liquid core material (waveguide core liquid; transparent polymer liquid; transparent liquid; transparent adhesive) 4 is dropped.
Next, as shown in FIG. 4C, the clad film (for example, olefin film) 5 is gradually pressed and covered from the side where the liquid core material 4 is dropped toward the opposite side (that is, the clad). While laminating the film 5), the groove 3 is filled with the liquid core material 4.

Next, as shown in FIG. 4D, the liquid core material is irradiated with, for example, ultraviolet rays while being covered with the clad film 5 (that is, with the clad film 5 pressed against the curved surface 2). (For example, UV epoxy resin; ultraviolet curable resin material; photocurable resin material) 4 is cured (here, semi-cured; temporarily cured).
In this embodiment, since the liquid core material 4 is kept in a semi-cured state at this stage, the cover resin liquid is then used in the step of curing the cover resin liquid for forming the stress relaxation layer (cover resin layer) 6. At the same time as 6 is cured, the liquid core material 4 is completely or substantially completely cured. In the present specification, hereinafter, such complete or almost complete curing is referred to as “main curing”.

Here, the liquid core material 4 is cured (semi-cured in this case) by irradiating, for example, ultraviolet rays from the back surface side of the transparent curved structure 1 through the curved structure 1. When a transparent film is used as the clad film 5, the liquid core material 4 may be cured (here, semi-cured) by irradiating, for example, ultraviolet rays through the clad film 5 from the surface side.
Here, the liquid core material 4 is semi-cured at this stage, but the present invention is not limited to this, and it may be fully cured at this stage.

  After the liquid core material 4 is cured (semi-cured here) in this way, as shown in FIG. 4E, the cover resin liquid (liquid resin material; transparent liquid) is coated so that the surface of the clad film 5 is covered. A thermosetting resin material) 6 is applied (overcoated). For example, the cover resin liquid 6 may be one having a refractive index n4 after curing larger than the refractive index n3 of the clad film 5 (n4> n3). For example, the same transparent polymer liquid as the liquid core material 4 can be used.

Thereafter, as shown in FIG. 4F, for example, heat is applied to cure the cover resin liquid 6. In the present embodiment, the liquid core material 4 is fully cured simultaneously with this. Thereby, the cover resin layer (stress relaxation layer) 6 is formed so as to cover the surface of the clad film 5, and the waveguide core 4 is formed.
In this manner, an optical waveguide structure 8 including a plurality of channel-shaped optical waveguides (curved waveguides; optical paths) 7 on the curved surface 2 is manufactured. The optical waveguide structure 8 is a polymer optical waveguide whose main material is a polymer, and is also referred to as an optical waveguide member.

Therefore, according to the optical waveguide structure and the manufacturing method thereof according to the present embodiment, the reliability of the small-sized optical waveguide structure 8 having the optical waveguide (curved waveguide) 7 on the curved surface having a small curvature radius can be improved. There is an advantage. There is also an advantage that the crosstalk performance of the optical waveguide structure 8 can be improved.
The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

  Further, in the above-described embodiment, as the liquid core material 4, for example, an ultraviolet curable resin material such as a UV epoxy resin material is used and cured by irradiating with ultraviolet rays, but is not limited thereto. For example, a photocurable resin material may be used as the liquid core material and cured by irradiation with light. Further, a thermosetting resin material may be used as the liquid core material and cured by applying heat.

Further, in the above-described embodiment, a thermosetting resin material is used as the liquid resin material for forming the stress relaxation layer 6 and is cured by applying heat. However, the present invention is not limited to this. A photocurable resin material such as a curable resin material may be used and cured by irradiation with light.
The optical waveguide structure 8 manufactured in this way includes, for example, a function (optical transmitter) that converts an input electric signal into an optical signal and transmits the optical signal via an arrayed optical fiber, and an optical fiber. It is used for a multi-channel optical transceiver (optical module) having a function (optical receiver) for converting an optical signal input through an array into an electrical signal and receiving the electrical signal.

  In this case, as shown in FIG. 5, for example, the multi-channel optical transceiver includes a printed circuit board (circuit board) 30, a surface light receiving element array 31 composed of a plurality of surface light receiving elements having an incident surface on the surface, and a surface. The light emitting device includes a surface light emitting element array 32 including a plurality of surface light emitting elements having an emission surface, a driver IC 35, a receiver IC 36, and an optical waveguide structure 8 including a plurality of curved waveguides 7. An optical transceiver with 4 channels on the transmission side and 4 channels on the reception side is taken as an example.

Here, the surface light receiving element is a photodiode (PD; Photo detector), and the surface light receiving element array 31 is a PD array chip. The surface light emitting element is a surface emitting laser (VCSEL (Vertical-Cavity Surface-Emitting Laser)), and the surface light emitting element array 32 is a VCSEL array chip.
The optical waveguide structure 8 is mounted on the printed circuit board 30 through one end face thereof, and a surface light receiving element array 31 and a surface light emitting element array 32 are provided on the one end face via, for example, a lens. An optical fiber array 33 composed of a plurality of optical fibers is optically connected to the other end face orthogonal to the one end face. Here, the optical fiber array 33 is a ribbon fiber. Here, an optical fiber array 33 with an optical connector 34 is used.

The printed circuit board 30 is electrically connected to an external device via a device-side electrical connector, and an electrical signal is input or output (electrical I / O).
Here, as an optical module including the optical waveguide structure 8 described above, an optical transceiver including an optical transmitter and an optical receiver is described as an example. However, the present invention is not limited to this. For example, The optical transmitter including the above-described optical waveguide structure 8 or the optical receiver including the above-described optical waveguide structure 8 can also be configured.

Hereinafter, it demonstrates still in detail according to an Example. However, the present invention is not limited to the following examples.
In this example, a sample of an optical waveguide structure (polymer optical waveguide) having an optical waveguide on a curved surface is produced by the manufacturing method (process flow) described in the above embodiment, and cracks generated on the surface are conventionally treated. It compared with the sample produced by the manufacturing method.

  In this example, the transparent curved surface structure 1 was produced and used by injection molding (mold molding). In other words, a curved surface (¼ arc) having a curvature radius of 2.0 mm is a convex surface, and eight grooves (waveguide grooves) having a shape of 0.05 mm in length × 0.05 mm in width along the curved surface 2 constituting the convex surface. ) A molded body having 3 formed in parallel was used as the curved surface structure 1. Polyolefin was used as the material. The refractive index at a wavelength of 850 nm was 1.5.

For the core liquid (polymer liquid) 4 for filling, an ultraviolet curable epoxy resin having a refractive index after curing of 1.6 was used.
A film (transparent film; olefin film) made of polyolefin and having a thickness of 0.05 mm was used for the clad film 5 covering the upper part of the groove (waveguide groove) 3 filled with the core liquid 4.

An epoxy resin having a refractive index after curing of 1.5 was used for the cover resin liquid 6 applied to the surface of the clad film 5 after the core liquid 4 was cured.
Using these, a sample of the optical waveguide structure 8 was produced as follows.
First, for example, 0.1 cc of the core liquid 4 was dropped into the groove portion on the curved surface 2 of the transparent curved surface structure 1 by a quantitative dispenser.

Next, the core liquid 4 was completely filled in the groove 3 while pressing the clad film 5 against the surface, and at the same time, the core liquid 4 other than the groove 3 was removed.
In this state, the core liquid 4 was irradiated with ultraviolet rays and semi-cured. Although the core liquid 4 is semi-cured here, it may be cured at this stage.
Subsequently, the cover resin liquid 6 was applied onto the surface of the clad film 5 with a dispenser, and the cover resin liquid 6 was coated by thinly spreading using a spin coater. The thickness of the cover resin liquid 6 is not necessarily uniform, but is desirably as thin as possible in order to reduce the stress from the stress relaxation layer 6 formed by curing the cover resin liquid 6.

And this was put into oven and heated at 120 degreeC over 60 minutes, the cover resin liquid 6 was hardened, and the core liquid 4 was fully hardened. Thereby, the cover resin layer (stress relaxation layer) 6 and the waveguide core 4 are formed.
On the other hand, a sample produced by a conventional manufacturing method was also prepared as a comparative example. That is, after semi-curing the core liquid, without applying the cover resin liquid (that is, without forming the stress relaxation layer), the core liquid is put into an oven as it is and heated at 120 ° C. for 60 minutes to remove the core liquid. A sample prepared by full curing was prepared.

The surface of the sample thus obtained was observed, and the presence or absence of cracks in the clad 6 on the top of the core 4 was evaluated.
In the sample prepared by the conventional manufacturing method, cracks were observed in 14 out of 20 samples, whereas in the sample manufactured by this manufacturing method, the occurrence of cracks was not confirmed, and 0 out of 20 samples. there were.

Next, light having a wavelength of 850 nm is incident on one of the eight waveguide cores 4 through a multimode fiber having a diameter of 50 μm, and is emitted from the other waveguide core 4 at the opposite end. The intensity of light (the intensity of light leaking to the adjacent channel) was measured.
As a result, in the sample manufactured by the conventional manufacturing method, the amount of light emitted from the other waveguide core 4 (the amount of light emitted from the leaked light) was in the range of −20 to −25 dB of the amount of incident light. In the sample produced by the above, the range is −30 to −35 dB, and it was confirmed that noise (crosstalk noise) can be reduced.

Hereinafter, additional notes will be disclosed regarding the above-described embodiment.
(Appendix 1)
A clad structure having a groove formed on a curved surface;
A waveguide core formed in the groove;
A clad film covering the waveguide core;
An optical waveguide structure comprising: a stress relaxation layer formed on a surface of the clad film.

(Appendix 2)
The optical waveguide structure according to appendix 1, wherein the stress relaxation layer is a resin layer applied to a surface of the clad film.
(Appendix 3)
The optical waveguide structure according to appendix 1 or 2, wherein the stress relaxation layer has a higher refractive index than the clad film.

(Appendix 4)
4. The optical waveguide structure according to any one of appendices 1 to 3, wherein the stress relaxation layer is formed so that a crack generated on a surface of the clad film is embedded.
(Appendix 5)
The optical waveguide structure according to any one of appendices 1 to 4, wherein the stress relaxation layer is made of the same material as the waveguide core.

(Appendix 6)
An optical module comprising the optical waveguide structure according to any one of appendices 1 to 5.
(Appendix 7)
Filling the groove of the clad structure having a groove on the curved surface with a core material, covering the groove with a clad film,
A method for producing an optical waveguide structure, comprising forming a stress relaxation layer on a surface of the clad film.

(Appendix 8)
8. The method of manufacturing an optical waveguide structure according to appendix 7, wherein a liquid resin material is applied to the surface of the clad film and cured to form the stress relaxation layer.
(Appendix 9)
Filling the groove with a liquid core material and covering the groove with a clad film,
The method for manufacturing an optical waveguide structure according to appendix 7 or 8, wherein the liquid core material is cured in a state of being covered with the clad film.

(Appendix 10)
Filling the groove with a liquid core material and covering the groove with a clad film,
Temporarily curing the liquid core material in a state covered with the clad film,
Applying a liquid resin material to the surface of the clad film,
8. The method for manufacturing an optical waveguide structure according to appendix 7, wherein the liquid resin material is cured to form the stress relaxation layer and the liquid core material is fully cured.

It is a typical perspective view which shows the structure of the optical waveguide structure concerning one Embodiment of this invention. It is typical sectional drawing which shows the structure of the optical waveguide structure concerning one Embodiment of this invention. It is typical sectional drawing for demonstrating the subject of the optical waveguide structure concerning one Embodiment of this invention. (A)-(G) is a figure for demonstrating the manufacturing method of the optical waveguide structure concerning one Embodiment of this invention. It is a typical perspective view for demonstrating the multichannel optical transceiver (optical module) using the optical waveguide structure concerning one Embodiment of this invention.

Explanation of symbols

1 Curved structure (clad structure)
2 Curved surface (convex surface)
3 grooves (grooves for waveguides)
4 Liquid core material (waveguide core)
5 Clad film 6 Stress relaxation layer (cover resin liquid)
7 Optical waveguide (curved waveguide)
8 Optical waveguide structure (polymer optical waveguide)
30 Printed circuit board (circuit board)
31 Surface light receiving element array (PD array chip)
32 Planar light emitting device array (VCSEL array chip)
33 Optical fiber array (ribbon fiber)
34 Optical connector 35 Driver IC
36 Receiver IC

Claims (5)

A clad structure having a groove formed on a curved surface;
A waveguide core formed in the groove;
A clad film covering the waveguide core;
An optical waveguide structure comprising: a stress relaxation layer formed on a surface of the clad film.   The optical waveguide structure according to claim 1, wherein the stress relaxation layer has a higher refractive index than the clad film.   3. The optical waveguide structure according to claim 1, wherein the stress relaxation layer is formed so that a crack generated on a surface of the clad film is embedded.   An optical module comprising the optical waveguide structure according to claim 1. Filling the groove of the clad structure having a groove on the curved surface with a core material, covering the groove with a clad film,
A method for producing an optical waveguide structure, comprising forming a stress relaxation layer on a surface of the clad film.

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