JP2006039078A - Optical module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positioning method to make it possible to perform passive alignment of a single mode optical waveguide and a single mode optic fiber and also an optical module for FTTH which can be mass-produced inexpensively. <P>SOLUTION: This optical module is built by securing a flat optical waveguide 10 having a core and optical fibers 30, 32, 34 in a clad layer on a flat positioning substrate 20. On this flat positioning substrate 20, a rectilinear groove wide and deep as predetermined at a predetermined position and a quadratic groove deeper than the clad of the flat optical waveguide are formed with the hole of a predetermined shape. The optical fibers are supported by the sides and bottom of the rectilinear groove. Further, the area having no core in the clad layer of the optical waveguide is partially removed except the areas to engage with the quadratic groove, and the optical waveguide engages with this groove. Thus, the optical module is built to connect the light propagating in the core of the optical waveguide, and the light propagating in the core of the optical fiber is constituted. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical module used in the field of optical communication, and more particularly to an optical module using a combination of an optical waveguide and an optical fiber.

  Optical functional elements using optical waveguides are widely used in the optical communication field. Usually, an optical fiber is used to couple light to the optical waveguide from the outside. However, in order to obtain efficient optical coupling, it is necessary to align the optical axis of the optical waveguide and the optical fiber, that is, to align the optical fiber. . As a method for performing the alignment, so-called active alignment is generally used in which light is actually introduced from an optical fiber into an optical waveguide to obtain an optimum position. The alignment procedure is basically such that an optical signal is incident on one end face of an optical waveguide element from one optical fiber and the light intensity emitted from the other end face is maximized or exceeds a certain level. Thus, the positions of the optical fiber and the optical waveguide element are adjusted.

  In recent years, with the increase in the amount of information to be processed, it has become necessary to couple a plurality of optical fibers and a plurality of optical waveguides in parallel. In such a case, it is desirable to use an optical fiber array chip in which the intervals between the optical fibers are accurately maintained. As an optical fiber array chip, (1) a substrate provided with a groove having a V-shaped cross section (hereinafter referred to as a V-groove substrate), (2) by precision molding of quartz glass, (3) by precision injection molding of resin (For example, standardized as an MT connector) and the like are all expensive.

  In addition, active alignment basically requires adjustment by coupling light for each element, and aligning such multiple elements at the same time is an extremely complicated assembly process and requires a long time for work. Cost. Also, the alignment device is complicated and expensive.

  In view of this, a passive alignment method has been developed in which alignment is performed only by mechanical reference such as butting and fitting based on the dimensional accuracy of the optical element without using an optical signal. Especially in recent years, so-called fiber-to-the-home (FTTH) optical components that lay optical fibers in ordinary homes are required to be mass-produced and reduced in price, so the importance of passive alignment has increased. (For example, see Patent Document 1 and Non-Patent Document 1).

  7 and 8 show a conventional example of a structure in which the 1 × 2 branch optical waveguide 110 and the optical fibers 30, 32, and 34 are connected by passive alignment. FIG. 7 is a sectional view on the optical path, and FIG. 7A is a sectional view parallel to the flat substrate 122. (B) is also a vertical cross-sectional view, but the portion where the waveguide is bifurcated is a cross-sectional view of the surface along one of the optical paths. FIG. 8 is a cross-sectional view perpendicular to the optical axis at positions AA ′, DD ′, and BB ′ shown in FIG. 7, respectively, (a), (b), and (c). ing.

The three optical fibers 30, 32, and 34 are fixed by forming a V-groove 123 in the flat substrate 122. The clad layer 114 is directly formed on the substrate processed with the V-groove 123, and the core 116 is formed at a certain distance from the substrate surface. The V-groove is formed in advance so as to match this core position. The depth of the V-groove is also set in advance so that the core position of the optical fiber matches the core position of the optical waveguide. Thus, the optical fiber and the optical waveguide can be coupled by pressing the optical fiber against the V-groove with the pressing plate 150 and fixing it with the adhesive 160.
JP 2003-241009 A Masuda, “Polymer Optical Waveguide Design Technology”, Hitachi Chemical Technical Report, Hitachi Chemical Co., Ltd., July 2002, No. 39, p. 37-40

  However, when aligning a single mode optical fiber (SMF) and a single mode optical waveguide, since the core diameter is about several μm, alignment accuracy of 1 μm or less is required. In the example of the conventional passive alignment using a V-groove substrate, the position and depth of the V-groove in the substrate surface direction must be processed with the above-described accuracy. For this reason, although the cost of the alignment itself is reduced, the V-groove substrate itself that requires high-precision machining is expensive, so there is a limit to reducing the cost as a whole.

  The present invention has been made to solve such problems, and provides a positioning method that enables passive alignment of a single mode optical waveguide and a single mode optical fiber, enabling mass production at low cost. An object of the present invention is to provide an optical module for FTTH.

  The optical module of the present invention is obtained by fixing a flat optical waveguide having a core in a clad layer provided on a flat substrate surface and an optical fiber on the flat positioning substrate. A linear recess having a predetermined width and depth and a two-dimensional recess having a predetermined opening and deeper than the thickness of the clad layer of the flat optical waveguide are provided at predetermined positions on the flat positioning substrate. The optical fiber is supported and fixed by the side surface and the bottom surface of the linear recess. Further, the optical waveguide device, in which a part of the portion of the cladding layer where the core is not present, is removed except for the portion that can be fitted into the two-dimensional recess, is fitted and fixed to the two-dimensional recess. The optical module which couple | bonds the light which propagates the core of a flat optical waveguide, and the light which propagates the core of an optical fiber by the above is comprised.

  By using a flat positioning substrate as described above, even single-mode optical fibers and single-mode optical waveguides can be positioned efficiently only by mechanical fitting. It becomes easy. Therefore, a large number of optical modules for FTTH can be provided at low cost.

In the above configuration, if the cladding diameter of the optical fiber is D and the depth of the linear recess is H, the distance from the plane including the surface of the portion where the cladding layer is removed to the center position of the core of the flat optical waveguide is H−. D / 2 is desirable.
By setting the distance in this way, positioning in a direction perpendicular to the substrate surface by mechanical fitting becomes possible. Note that the above distance includes a deviation due to an error in film thickness due to normal film formation, an error in the cladding diameter of the optical fiber, and the like.

  It is desirable that the concave portion provided in the flat positioning substrate is formed by forming a solid layer having a thickness H on the surface of the flat substrate and removing it in a predetermined portion of this layer. According to this method, the thickness H can be obtained with high accuracy.

  Moreover, it is desirable that the linear expansion coefficient of the flat positioning substrate is 150 ppm / ° C. or less. By keeping the linear expansion coefficient low, it is possible to propose a positional shift due to temperature fluctuation.

  Further, the solid layer is preferably a resin material or an organic-inorganic hybrid material. If a photosensitive material is used, high-precision processing by photolithography is possible, and these materials can also be high-precision processing by molding.

According to the present invention, even a single mode optical fiber and a single mode optical waveguide can be efficiently positioned only by mechanical fitting, so that the assembly of the optical module becomes extremely easy. Therefore, a large number of optical modules for FTTH can be provided at low cost.
Since the flat positioning substrate of the present invention can be manufactured by film formation and photolithography or molding, high dimensional accuracy can be realized.

Embodiments of the present invention will be described below in detail with reference to the drawings.
In this embodiment, an optical module in which an optical fiber is connected to each port of a 1 × 2 optical branching waveguide element will be described. FIG. 1A is a perspective view of the optical waveguide element 10. Here, in order to facilitate the following description, xyz axes orthogonal to each other are taken as follows. The z-axis is taken in the direction of the straight portion of the optical waveguide. The y axis is in a direction perpendicular to the surface of the substrate, and the x axis is in a direction parallel to the surface of the substrate. In the optical module described below, the direction is defined with reference to this coordinate axis.

  The optical waveguide device 10 has a structure in which a clad layer 14 is formed on the surface of a flat substrate 12 and a core 16 is embedded. A part of the clad layer is removed so that the substrate is exposed. The clad layer removal portion 18 will be described later. The optical waveguide element pattern has a Y-shaped two-branch structure as shown in the plan view of FIG. However, this pattern is an example and any pattern may be used, and the present invention is not limited to this.

  In the present optical module, the above-described optical waveguide element and the optical fiber connected thereto are all fixed on a flat positioning substrate 20 as shown in FIG. A positioning structure for determining the position of the optical waveguide element serving as a reference is provided at the center of the positioning substrate 20. This positioning structure is provided with a convex portion 28 so that the cladding layer removing portion 18 of the optical waveguide element is fitted. In other words, it can be said to be a recess in which the remaining portion of the cladding layer 14 fits.

  FIG. 3 is an assembly view of the optical module. The optical branching waveguide element 10 is inserted from above the positioning substrate 20 with the optical waveguide surface down. That is, the clad layer removal portion 18 of the optical waveguide element 10 and the convex portion of the positioning substrate 20 are formed in advance so as to be accurately fitted. Here, the side wall of the convex portion 28 includes a surface 28x along the x direction and a surface 28z along the z direction. As a result, the optical waveguide element is accurately positioned in both the x and z directions by fitting.

  Note that the shape is not limited to this as long as the clad layer removing portion of the optical waveguide element and the convex portion of the positioning substrate are formed so as to fit accurately. However, in order to define two directions of x and z, it is necessary to have side walls in two or more directions. It may be a curved surface such as a cylinder and may be a two-dimensional shape.

  The y direction is accurately determined by pressing the surface of the substrate 12 of the optical waveguide against the upper surface of the convex portion 28. That is, since the distance h from the substrate surface to the core center is determined in advance, the center of the core of the optical waveguide is located at a distance h below the upper surface of the convex portion of the positioning substrate.

  As described above, if the accuracy of fitting between the concave-convex pattern on the positioning substrate and the cladding layer removal portion of the optical waveguide is increased, the positioning accuracy in the x and z directions is improved, and the height H of the positioning substrate convex portion and the optical waveguide substrate If the accuracy of the distance h from the core to the core is increased, the positioning accuracy in the y direction is improved.

  On both sides of the positioning substrate 20, convex portions 24, 25, and 26 for positioning the optical fiber in the x and y directions are provided. In the drawing, for convenience of explanation, each of the convex portions 24, 25, 26, and 28 is shown separately. However, it is preferable to form the convex portions 24 and 28, and 26 and 28 integrally. desirable.

  As shown in FIG. 3, the optical fiber is pressed and fixed in the groove between the convex portions. The x direction is positioned by fitting the groove of each convex portion with the optical fiber, and the y direction is positioned by pressing the optical fiber against the flat substrate with a constant force. Assuming that the optical fiber is used in a state where the coating is removed, assuming that the cladding diameter is D, it is necessary to determine the relationship of h, H, and D so that the relationship of h = H−D / 2 is established. Generally, since the eccentricity of the core of the optical fiber is ± 0.5 μm or less, this is almost the positioning accuracy of the optical fiber.

  4A is a cross-sectional view parallel to the substrate along the optical path of the optical module that has been assembled, and FIG. 4B is a cross-sectional view that is also perpendicular to the substrate. However, the section where the waveguide is bifurcated shows a cross section of the surface along one of the optical paths. 5 and 6 are sectional views perpendicular to the optical axis at A-A ', D-D', B-B ', and C-C', respectively.

  The optical fiber 30 is pressed between the convex portions 26, and the optical fibers 32 and 34 are pressed between the convex portions 24 and 25 by the pressing plate 50 and fixed by the adhesive 60. The optical waveguide element 10 is concavo-convexly fitted as described above, and the optical waveguide substrate 12 is pressed against the upper surface of the convex portion 28 of the positioning substrate 20 and fixed. Since a space is formed between the upper surface of the clad layer 14 of the optical waveguide and the exposed surface of the substrate 22 of the positioning substrate 20, the adhesive 62 is filled and bonded and fixed.

  The portion of the convex portion 28 facing the side surface in the x direction is fabricated so as to expose the substrate 22 like the other portions in FIG. 2, but fills this space as shown in FIG. 6B. In this way, a portion 29 in which a part of the material for forming the convex portion is left may be provided. As a result, the upper surface of the clad layer 14 and the portion 29 can be closely adhered and fixed. However, since the positioning of the optical waveguide element in the y direction can be performed by the close contact between the convex portion 28 and the surface of the substrate 12, the portion 29 is not necessarily required.

  Photolithography or a molding method can be selected as a method for processing the concavo-convex structure with high accuracy.

  For example, when photolithography is used, the following steps can be considered. A photosensitive resin such as a photoresist is uniformly applied on the substrate. If this is exposed through a mask on which a pattern of concavo-convex parts is formed, and the exposed part or the non-exposed part is dissolved and removed with a solvent, the concavo-convex part can be easily formed. When the uneven structure is formed of a resin other than the photosensitive resin, the resin may be applied on the substrate. A concavo-convex structure is formed by applying a photoresist to the surface, exposing it through a mask, and subjecting the resin layer to liquid phase or gas phase etching using the patterned resist as a mask. In this case, the pattern accuracy can be ± 0.1 μm or less.

In the case of a molding method, a resin or an organic-inorganic composite material is applied onto a substrate, and a molding die (stamper) that forms an inverted concavo-convex structure while it is not cured is pressed. In this state, a desired concavo-convex structure can be formed by heat-curing the resin or the like and then releasing the mold. Generally, when an organic material or an organic-inorganic hybrid material is used, a spin coater with excellent film thickness controllability is used as the film forming method, but ± 0.5 to 1.0 μm even when two spin coater films are combined. A certain degree of positioning accuracy can be secured.
In addition to this, a method of forming a recess in the flat substrate itself by etching or the like is also possible.

  From the above, the positioning accuracy of the optical fiber and the optical waveguide core in the x direction and the y direction can be controlled to about ± 0.5 to 1.0 μm and about ± 1.0 to 1.5 μm. The coupling loss due to can be reduced to 0.3 dB / plane or less when a waveguide having a core diameter of 8 μm is used. The coupling loss hardly changes if the gap between the optical fiber and the optical waveguide is about 0 to 10 μm. Therefore, it is preferable to push it down from above and completely insert it into the groove while looking through the microscope from the y direction.

  Since alignment of several μm is possible by adjusting the waveguide pressure in the y direction, if active alignment using this structure is performed, the positioning accuracy in the y direction will be significantly improved. Positioning accuracy becomes dominant, and the coupling loss when an 8 μm waveguide is used can be within 0.15 dB / plane. In addition, since the alignment in this case is only one axis, the increase in the process time required for assembly is not so large, and an expensive alignment device is not required, so alignment is performed at a cost that is not so different from passive alignment. Is possible.

  If the linear expansion coefficients of the optical waveguide substrate and the positioning substrate are matched, the position change in the x direction due to the temperature change does not occur. Most of the change in position in the y direction is caused by the difference in linear expansion coefficient between the positioning structure and the optical fiber. Therefore, the temperature dependence loss (TDL) is 0.2 dB or less.

  As described above, the optical waveguide device of the present invention can be applied not only to 1 × 2 branches but also to multi-branched optical waveguides such as 1 × 4 and 1 × 8. Also, it can be widely applied to optical modules in which many optical waveguide optical elements and optical fibers are coupled in the optical communication field, such as optical switches based on waveguide type directional couplers and crossed waveguides, and other functional elements. .

  Furthermore, if only a fixed portion of the optical fiber is taken out and applied to a plurality of optical fibers, an optical fiber array chip can be configured. It is possible to provide an inexpensive optical fiber array chip as compared with the one using the V-groove.

FIG. 1A is a schematic perspective view and FIG. 1B is a schematic plan view showing an example of a flat optical waveguide of the present invention. FIG. 2 is a schematic perspective view showing an example of the flat positioning substrate of the present invention. FIG. 3 is a view for explaining the fixing of the optical fiber and the flat optical waveguide to the flat positioning substrate of the present invention. FIG. 4 is a view showing an example of the optical module of the present invention. FIG. 5 is a diagram showing the incorporation of the optical fiber into the optical module of the present invention. FIG. 6 is a diagram showing the incorporation of a flat optical waveguide into the optical module of the present invention. FIG. 7 is a diagram showing a conventional optical module. FIG. 8 is a diagram showing the incorporation of an optical fiber into a conventional optical module.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Optical waveguide device 12, 22 Flat substrate 14 Clad layer 16 Core 20 Flat positioning substrate 30, 32, 34 Optical fiber 50 Push plate 60, 62 Adhesive

Claims (5)

An optical module in which a flat optical waveguide having a core in a clad layer provided on a flat substrate surface and an optical fiber are fixed on the flat positioning substrate,
A linear recess having a predetermined width and depth and a two-dimensional recess having a predetermined shape and deeper than a clad layer thickness of the flat optical waveguide at a predetermined position on the flat positioning substrate; The optical waveguide element is supported and fixed by the side surface and the bottom surface of the linear recess, and a part of the cladding layer where the core is not present is removed leaving a part that can be fitted to the two-dimensional recess. An optical module characterized in that the light propagating through the core of the flat optical waveguide and the light propagating through the core of the optical fiber are coupled by fitting and fixing to the two-dimensional recess.   The cladding diameter of the optical fiber is D, the depth of the linear recess is H, and the distance from the plane including the surface of the portion from which the cladding layer is removed to the center position of the core of the flat optical waveguide is HD / The optical module according to claim 1, wherein the optical module is 2.   3. The optical module according to claim 2, wherein the recess provided in the flat positioning substrate is formed by forming a solid layer having a thickness of H on the surface of the flat substrate and removing a predetermined portion of the layer.   The optical module according to claim 1, 2, or 3, wherein a linear expansion coefficient of the flat positioning substrate is 150 ppm / ° C or less. The optical module according to any one of claims 1 to 4, wherein the solid layer is a resin material or an organic-inorganic hybrid material.

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