JP2007171553A - Method of connecting optical fiber, and optical module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of connecting an optical waveguide and an optical fiber, a method that is inexpensive and has low insertion loss as well as low return loss, and also to provide an optical module. <P>SOLUTION: In the method of connecting an optical waveguide and an optical fiber; in an optical circuit in which a single coated optical fiber and two or more optical fibers of a coated optical fiber ribbon are fixed in V grooves 24 formed on a waveguide substrate, the tip end face 26 of the optical fibers is formed obliquely at a specific angle to the optical axis. In the end of the optical waveguide substrate, there are formed the V grooves in numbers equal to or more than those of the optical fibers. At least on the extension of one V groove, an optical waveguide core 25 is formed in the manner that the optical axis of the optical fiber placed in the V groove is nearly aligned with the optical axis of the optical waveguide. At the end of the V groove, a groove is formed that has a face with nearly the same angle as the one formed by the optical fiber and the optical axis, in the direction vertical to the optical axis, wherein the optical fiber is abutted against the optical waveguide and fixed with an adhesive. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for connecting and optically coupling an optical circuit having an optical waveguide and an optical fiber, and an optical module using the method.

  In an optical communication system, the higher the reception sensitivity and the transmission output, the higher the signal transmission reliability and the longer the communication becomes, but there are technical limitations and the cost increases. The value is also defined by the standards taking into account the current technical capabilities. Considering the cost of the system, the lower the reception sensitivity and transmission output, the cheaper, but the connection loss between the optical fiber and the optical device used is as low as possible in order to use equipment with low reception sensitivity and transmission output. Is required.

  Further, each member is required to be as cheap as possible from the viewpoint of cost for constructing the system.

  In addition, it is necessary to suppress the transmitted signal from being reflected in the path and affecting the transmitter as much as possible. Therefore, it is necessary to reduce the return loss of each member.

  Of these, the bonding method between the optical fiber and the optical waveguide is important, and as for this bonding method, a method is known in which the optical connection block and the optical waveguide are actively aligned, fixed with an adhesive, and connected. (For example, refer to Patent Document 1).

  Further, a method is known in which a groove is formed at the end of a V groove formed by anisotropic etching of Si, and an optical fiber is placed in the V groove and coupled to an optical waveguide (see Patent Document 2).

Also known is a method in which the end face of the optical waveguide and the end face of the optical fiber are cut at a predetermined angle with respect to the traveling direction of light, and both are coupled and fixed by the cut face (see Patent Documents 3 and 4).
JP 2000-19346 A Japanese Patent No. 2771167 Japanese Patent Laid-Open No. 4-180004 Japanese Patent Laid-Open No. 1-261604

  As shown in FIG. 4, the fiber array 16 (optical connection block) and the optical waveguide 19 are connected by active alignment as described above, and the end face of the fiber array 16 and the end face of the optical device 18 are inclined. Although it is possible to suppress the return loss, an expensive self-aligning machine is necessary to match the optical axis of the optical fiber 17 and the optical axis of the optical waveguide, and it takes time to connect and increases the cost. Become. Further, in order to reduce the coupling loss, it is necessary to polish both surfaces, which also contributes to an increase in cost.

  For example, as shown in FIG. 5, a groove is formed at the end of the V-groove 20 formed by anisotropic etching of Si in Patent No. 2771167, and an optical fiber 22 is placed in the V-groove 20 to form an optical waveguide 21. The coupling method is more efficient than the above method because the optical fiber 22 and the optical waveguide 21 can be passively coupled, but both the end surface of the optical fiber 22 and the end surface of the optical waveguide 21 are perpendicular to the optical axis. There is a disadvantage that reflection occurs at the joint surface between the optical waveguide 21 and the optical fiber 22 and the return loss does not become sufficiently low.

  In the method disclosed in Japanese Patent Laid-Open No. 4-180004, the optical waveguide end face and the optical fiber end face are cut at a predetermined angle with respect to the light traveling direction, and both are coupled and fixed at the cut face. Since it is very difficult to match the oblique surface of the fiber with the oblique surface of the waveguide end, it takes time to join and the insertion loss is also deteriorated.

  Further, the method of forming a tip lens at the fiber tip described in Japanese Patent Laid-Open No. 1-261604 is difficult to process the tip lens and takes time and cost, and does not satisfy the demand for cost reduction of the system. Also, the method of processing the tip of the fiber and the tip of the V-groove obliquely and joining them together is the same as the method of Japanese Patent Laid-Open No. 4-180004 in that this method of installing an optical fiber in the V-groove matches both the oblique surfaces. Therefore, it takes time to join and the insertion loss is also deteriorated.

  Even in the method using a tape fiber, it is difficult to match the oblique surface at the tip of the optical fiber with the oblique surface at the tip of the V-groove, and it takes time to manufacture and increases the loss.

  The present invention relates to a method for connecting an optical waveguide to an optical fiber, in which an optical fiber having a single-core optical fiber and a two-core or more tape fiber is fixed in a V-groove formed on an optical waveguide substrate. The tip end face of the optical waveguide is formed at a constant angle with respect to the optical axis, and the same number or more V grooves as the optical fiber are formed at the end of the optical waveguide substrate. The optical waveguide core is formed on the extension line of the groove so that the optical axis of the optical fiber placed in the V-groove is substantially in line with the optical axis of the optical waveguide, and the end of the V-groove is perpendicular to the optical axis. This is a method of connecting an optical waveguide and an optical fiber, in which a groove having a surface that forms substantially the same angle as the angle between the optical fiber and the optical axis is formed, and the optical fiber is abutted against the optical waveguide and fixed with an adhesive.

  Adjacent V-grooves are formed with their positions shifted by a certain amount along the optical axis direction, and a dicer groove is formed along the end of the V-groove to form a groove having a predetermined angle with the optical axis. Then, the above-mentioned optical waveguide and optical fiber connection method is characterized in that a core fiber core having the above-mentioned angle is placed in a V-groove.

  Also, the tape fiber from which the end of the tape fiber holder is removed is fixed, and the fiber alignment direction perpendicular to the longitudinal direction of the tape fiber and the V groove alignment direction perpendicular to the longitudinal direction of the V groove are parallel and kept parallel. In this connection method, the optical fiber is placed in a V-groove and the optical fiber is abutted against the optical waveguide and fixed with an adhesive.

  Furthermore, an optical module is characterized in that the method for connecting the optical waveguide and the optical fiber is used.

  According to the present invention, the return loss is suppressed by making the coupling surface between the optical fiber and the optical waveguide slant with respect to the optical axis, and the optical fiber is formed by using a tape fiber composed of two or more optical fibers. It is possible to easily match the inclined end face and the inclined end face of the optical waveguide, and to obtain an optical module and optical fiber connection method and optical module at low cost with low insertion loss and low return loss. it can.

  The present invention relates to a method for connecting an optical waveguide to an optical fiber, in which an optical fiber having a single-core optical fiber and a two-core or more tape fiber is fixed in a V-groove formed on an optical waveguide substrate. The tip end face of the optical waveguide is formed at a constant angle with respect to the optical axis, and the same number or more V grooves as the optical fiber are formed at the end of the optical waveguide substrate. The optical waveguide core is formed on the extension line of the groove so that the optical axis of the optical fiber placed in the V-groove is substantially in line with the optical axis of the optical waveguide, and the end of the V-groove is perpendicular to the optical axis. This is a method of connecting an optical waveguide and an optical fiber, in which a groove having a surface that forms substantially the same angle as the angle between the optical fiber and the optical axis is formed, and the optical fiber is abutted against the optical waveguide and fixed with an adhesive.

  As shown in FIGS. 6 and 7, the oblique surface 26 on the optical waveguide side is installed in the V-groove 24 by forming a groove perpendicular to the longitudinal direction of the V-groove 24 by giving an angle to the blade of the dicer and the substrate. A slope having a unique angle with respect to the optical axis of the plurality of optical fibers 29 of the tape fiber 30 is formed. The slope of the tip of the optical fiber 29 is formed by protruding the optical fiber 29 from the tip of the tape fiber 30 and cutting it at a predetermined angle, and bonding them together.

  As this method, it is formed by holding the tape portion and the fiber portion of the tape fiber 30 on the jig in which the V-groove 24 is formed, and fixing with a metal fitting or wax and polishing at a predetermined angle. It is possible to cut by using a jig that can cut 29 at a predetermined angle, or to cut diagonally with a dicer.

  In the present invention, adjacent V-grooves are formed by shifting the position by a certain amount along the optical axis direction, and by forming a dicer groove along the end of the V-groove, a groove that forms a predetermined angle with the optical axis. After the above is formed, the above-mentioned optical waveguide and optical fiber connection method is characterized in that a core fiber core having the above-mentioned angle is placed in a V-groove.

  In this case, as shown in FIG. 8, the positions of the adjacent V grooves 31 are shifted by a certain amount along the optical axis direction. A dicer groove is formed along the end of the V groove 31. In this embodiment, the waveguide end 33 formed at this time does not have to be a slope. As for the optical fiber, as shown in FIG. 9, the optical fiber 34 is protruded from the tip of the tape fiber 35 and fixed to the stage with wax, and cut with a dicer at a predetermined angle with respect to the longitudinal direction of the tape fiber 35, thereby A slope having a predetermined angle can be formed.

  Hereinafter, an example explains.

  First, a V-grooved waveguide was produced. A thermal oxide film on a 4-inch thermal oxide film (1 μm) silicon substrate is processed into a V-groove pattern by photolithography and wet etching, and then a V-groove is formed by wet etching using silicon anisotropy. did. Next, the portions other than the V-groove portion and the marker portion were covered with a photoresist by photolithography, and 1 μm of Al was deposited on this substrate. Thereafter, the resist was peeled off, and an Al film was left only in the V groove portion and the marker portion. Next, in order to improve the adhesion between the fluorinated polyimide and the silicon substrate, an adhesion improving agent was formed by spin coating and baked.

  Subsequently, an optical waveguide was produced. The resin used for the optical waveguide is fluorinated polyimide. After applying a fluorinated polyamic acid varnish for cladding to the substrate on which the adhesion layer has been formed using a spin coating apparatus, firing is performed using an oven maintained in an inert atmosphere to form a lower cladding layer of 15 μm, and then The core fluorinated polyamic acid varnish was applied by a spin coating apparatus and then baked using an oven kept in an inert atmosphere to form a core layer having a thickness of 7 μm. The core layer used had a refractive index of (1.51), and the core-clad relative refractive index difference was 0.33%.

A photoresist layer was formed on the core layer, and a pattern of a 4-channel linear waveguide having a pitch of 250 μm and a length of 1 cm was exposed by an aligner using a photomask to form a patterned resist layer. Next, the core layer not protected by the resist layer was etched using an RIE apparatus while injecting O ₂ gas. Thereafter, the resist is peeled off and dried, and further, the same kind of fluorinated polyimide resin as that of the lower clad is applied by a spin coating apparatus, and then baked using an oven kept in an inert atmosphere to form an upper clad layer having a thickness of 18 microns. Formed. The core size is 7 × 7 μm.

  Next, the resin layer (lower clad, core, upper clad layer) formed in the V-groove region was removed.

  The resist layer was formed with a spin coating apparatus and pre-baked, and then exposed with an aligner using a photomask to form a patterned resist layer. The resist layer was formed outside the V-groove region. Next, the resin layer in the V-groove region not protected by the resist layer was removed by etching. At this time, etching was performed until at least the surface of the silicon substrate was exposed. Next, the substrate was immersed in a stripping solution containing hydrochloric acid to remove the polyimide in the V-groove.

  A dicer was used for this substrate, and a groove perpendicular to the longitudinal direction of the V-groove was formed at the end of the V-groove so that the waveguide end had a slope with an inclination of 82 degrees with respect to the upper surface of the substrate.

  Regarding the processing of the tape fiber, the tip of the four-core tape fiber was exposed using a heating type stripper, fixed to a jig for 8 degree polishing, and the end was polished 8 times.

  Next, for the joining of the optical fiber and the optical waveguide, a tape fiber holder to which a tape fiber whose tip coating is removed and the tip is cut at a fixed angle is fixed to a six-axis stage, and a waveguide with a V groove is formed. Attached to the sample stage, adjust each axis of the 6-axis stage so that the fiber alignment direction orthogonal to the tape fiber longitudinal direction and the V groove alignment direction orthogonal to the V groove longitudinal direction are parallel, and orthogonal to the tape fiber longitudinal direction The optical fiber is placed in the V-groove in a state where the fiber alignment direction and the V-groove alignment direction orthogonal to the longitudinal direction of the V-groove are held in parallel, and the optical fiber is abutted against the optical waveguide to transmit ultraviolet rays onto the fiber. The lid was placed and fixed with an ultraviolet curing adhesive.

When placing the optical fiber in the V-groove, the tape fiber holder is inclined with respect to the V-groove optical waveguide, the optical fiber is applied to the V-groove, and then the fiber holder is pushed down so that the optical fiber extends over the entire V-groove. Can be contacted.
The combined diagram is shown in FIG. The coupling loss between the two channels was 0.5 dB or less for all four channels, and the return loss was also 50 dB or more for all four channels.

  In the same manner as in Example 1, an optical waveguide was formed on a V-grooved substrate. The mask pattern was formed using an X-shaped optical waveguide photomask. A groove for inserting a filter was formed with a dicer in a branch portion of the formed optical waveguide, a dielectric multilayer filter was inserted, UV adhesive was poured, and UV light was applied to cure. The used filter has characteristics of transmitting light having wavelengths of 1.3 μm and 1.49 μm and reflecting light having a wavelength of 1.55 μm.

  Four V-grooves were formed on both the incident side and the emission side, and two ports of the X-shaped waveguide were disposed at the ends of the two V-grooves, respectively. The formation of the slopes of the optical fiber and the optical waveguide and the connection between them were performed in the same manner as in Example 1.

  The obtained WDM with pigtail is shown in FIG. For each wavelength, the insertion loss was 1.5 dB or less, the isolation of 1.3 μm was 35 dB or more, the isolation of 1.49 μm was 22 dB, the isolation of 1.55 μm was 40 dB or more, and the return loss was 50 dB or less.

In the same manner as in Example 1, a V-grooved optical waveguide substrate was produced. The optical waveguide pattern was formed using a 1 × 8 splitter photomask. Four V-grooves were formed on the incident side, and an optical waveguide on the incident side of the 1 × 8 splitter was disposed at the tip of one of the V-grooves. On the emission side, eight V-grooves corresponding to each of the eight ports were formed. Both the incident-side and emission-side V-grooves were formed so that the line connecting the V-groove ends was 8 degrees with respect to the optical axis. Dicer grooves were formed along the ends of the V grooves.
Regarding the processing of tape fibers, 4-core and 8-core tape fibers are fixed to a dicer stage with wax, the tip is cut so as to form an angle of 8 degrees with the longitudinal direction of the tape fiber, and the tape fiber coating is heated with a stripper. Was removed using an ultrasonic cleaner, and dirt adhered to the optical fiber was removed using an ultrasonic cleaner. The formation of the slopes of the optical fiber and the optical waveguide and the connection between them were performed in the same manner as in Example 1.

  The combined diagram is shown in FIG. The insertion loss of the 1 × 8 splitter was 11 dB or less, and the return loss was 50 dB or more.

  The present invention can be used not only in a communication system in the field of optical communication but also in an application field of optical transmission such as evaluation and measurement.

It is the side view and top view which show Example 1 of this invention. It is a figure which shows Example 2 of this invention. It is a figure which shows Example 3 of this invention. It is a figure which shows schematic structure of the connection method of the conventional optical fiber and an optical device. It is a figure which shows schematic structure of the connection method of the conventional optical fiber and an optical device. It is the top view and side view which show the groove | channel formed in the optical waveguide end. It is a figure which shows a tape fiber and an optical fiber. It is the top view and side view which show the groove | channel formed in the optical waveguide end. It is a figure which shows a tape fiber and an optical fiber.

Explanation of symbols

1 Optical waveguide (core)
2 Optical fiber 3 Tape fiber 4 Lid 5 Holding plate 6 Tape fiber holder 7 Optical fiber 8 Lid 9 4 core tape fiber 10 Dielectric multilayer filter 11 Filter groove 12 Optical fiber 13 Lid 14 4 core tape fiber 15 8 core tape fiber 16 Fiber array 17 Optical fiber 18 Optical device 19 Optical waveguide (core)
20 V-groove 21 Optical waveguide (core)
22 Optical fiber 23 Optical waveguide substrate 24 V groove 25 Optical waveguide (core)
26 Groove slope 29 Optical fiber 30 Tape fiber 31 V groove 32 Optical waveguide (core)
33 Slope of groove 34 Optical fiber 35 Tape fiber

Claims (4)

In a method of connecting an optical waveguide and an optical fiber, an optical circuit in which a single-core optical fiber and an optical fiber of two or more cores are fixed in a V-groove formed on an optical waveguide substrate, and the tip end face of the optical fiber is The optical waveguide substrate is formed at a certain angle obliquely with respect to the optical axis, and the same number or more of V-grooves as the optical fiber are formed at the end of the optical waveguide substrate, on the extension line of at least one V-groove The optical waveguide core is formed so that the optical axis of the optical fiber placed in the V-groove is substantially in line with the optical axis of the optical waveguide, and the optical fiber is perpendicular to the optical axis at the end of the V-groove. A method of connecting the optical waveguide and the optical fiber, in which a groove having a surface that forms substantially the same angle as the angle formed by the optical axis is formed and the optical fiber is abutted against the optical waveguide and fixed with an adhesive. Adjacent V-grooves are formed by shifting the position by a certain amount along the optical axis direction, and after forming a dicer groove along the end of the V-groove, forming a groove having a predetermined angle with the optical axis, 2. The method of connecting an optical waveguide and an optical fiber according to claim 1, wherein the core wire of the tape fiber having the tip having the angle is placed in the V groove. The optical fiber is fixed in a state in which the tape fiber from which the coating at the tip of the tape fiber holder is removed is fixed, the fiber alignment direction perpendicular to the longitudinal direction of the tape fiber is parallel to the V groove alignment direction perpendicular to the longitudinal direction of the V groove, and the parallelism is maintained. The method of connecting an optical waveguide and an optical fiber according to claim 1 or 2, wherein the optical fiber is placed in a V-groove and the optical fiber is abutted against the optical waveguide and fixed with an adhesive. An optical module using the method for connecting an optical waveguide and an optical fiber according to claim 1.

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