JP2013214115A - Optical coupling device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical coupling device for coupling optical waveguides, such as an optical waveguide and an optical fiber, with each other with high reliability.SOLUTION: The sum of the thicknesses of a first fixture 5 and a first substrate 2 is made smaller than the sum of the thicknesses of a second fixture 10 and a second substrate 6. In a step part generated by the difference of the sum of the thickness between the upper face of the first fixture 5 and the edge of the second fixture 10, a first adhesive reservoir 14 is formed in a state where adhesive projects into the upper face of the first fixture 5. In a step part generated by the difference of the sum of the thickness between the lower face of the first substrate 2 and the edge of the second substrate 6, a second adhesive reservoir 12 is formed in a state where the adhesive projects into the lower face of the first substrate 2. Consequently, the stress in a substrate thickness direction generated in the first adhesive reservoir 14 and the stress in the substrate thickness direction generated in the second adhesive reservoir 12 are canceled with each other.

Description

  The present invention relates to an optical coupling device that couples optical waveguides such as optical waveguides and optical fibers with high reliability.

(Conventional technology)
There are known optical coupling devices for optically coupling an optical waveguide and a quartz optical waveguide formed on a lithium niobate (LiNbO ₃ or LN) substrate, and a quartz optical waveguide and an optical fiber. FIG. 6 is a schematic perspective view of an optical coupling device for optically coupling an optical waveguide formed on a lithium niobate substrate and an optical fiber.

Reference numeral 1 denotes a part of the package housing, which is called a pedestal here. 2 is a first substrate made of LN or the like, 3a, 3b and 3c are optical waveguides formed by diffusing Ti at 1100 ° C. for 12 hours, and 4 is a SiO ₂ buffer layer. 5 is a first Yatoi made of LN, 6 is a second substrate made of a glass block, 7a, 7b and 7c are V grooves, 8a ', 8b' and 8c 'are optical fibers, 8a, 8b and 8c are The cores of the optical fibers 8a ′, 8b ′, and 8c ′, 9a, 9b, and 9c are clads of the optical fibers 8a ′, 8b ′, and 8c ′, and 10 is a second Yatoi made of a glass block or the like. The optical fibers 8a ′, 8b ′ and 8c ′ are fixed to the V grooves 7a, 7b and 7c by an adhesive.

  Note that the first Yatoi 5 is bonded on the surface facing the first substrate 2, and the second Yatoi 10 is bonded on the surface facing the second substrate 6 (in FIG. The illustration of the adhesive is omitted). Reference numeral 11 denotes an adhesive that bonds the first substrate 2 and the second substrate 6, and the first Yatoi 5 and the second Yatoi 10 at their end faces, and usually an optical adhesive is used. . As this optical adhesive, an ultraviolet curable adhesive (UV adhesive) is suitable.

  FIG. 7 shows a cross-sectional view taken along line AA ′ of FIG. As can be seen from FIG. 7, the lower surface 2 ′ of the first substrate 2 and the lower surface 6 ′ of the second substrate 6 are not in the same horizontal plane, and there is a step H between them. Therefore, as shown in FIGS. 6 and 7, an optical adhesive reservoir 12 protruding from between the opposing substrates is formed. That is, the lower surface 2 ′ of the first substrate 2 is higher than the lower surface 6 ′ of the second substrate 6 by the step H.

  In general, the optical waveguides 3a, 3b, and 3c shown in FIGS. 6 and 7 are used as optical waveguides of a high-speed optical modulator. As described in Patent Document 1, in this high-speed optical modulator, if the thickness of the LN substrate 2 is thick, the substrate tends to resonate. That is, a dip occurs in the light modulation characteristics at a high frequency of 15 GHz or higher. This is particularly serious in an ultrahigh frequency band such as 40 GHz. In order to avoid the occurrence of this substrate resonance, it is effective to make the LN substrate thinner. For example, when the glass block 6 has a thickness of about 1 to 2 mm, the LN substrate 2 needs to be much thinner than the glass block 6, about 0.3 mm. These are the same even when the glass block 6 is a quartz optical waveguide.

  Next, FIG. 8 shows a cross-sectional view taken along the line BB ′ of FIG. Due to surface tension, the optical adhesive reservoir 12 tends to accumulate thickly near the center of the second substrate 6 as shown in FIG.

  When the optical coupling device of the prior art is subjected to a heat cycle test at −40 to 80 ° C., the optical adhesive reservoir 12 repeats thermal expansion and thermal contraction, and stress as indicated by the arrow 13 in FIG. 8 is generated. The force pulling the second substrate 6 upward (the direction in which the second Yatoi 10 is present) acts. The direction of the arrow of the stress 13 represents the direction of the stress, and the length represents the magnitude of the stress.

  As can be seen from FIG. 7, the area of the optical adhesive 11 that bonds and fixes the first and second yatoes 5 and 10 and the first and second substrates 2 and 6 (between each yatoi and each Comparing the area of the portion where the substrates face each other) and the area of the optical adhesive reservoir 12 (area contacting the second substrate 6), the former is much wider. This means that the optical adhesive 11 has a larger adhesive force.

  However, in the heat cycle test, the direction of the fixing force of the optical adhesive 11 that bonds the first Yatoi 5 and the second Yatoi 10 and the first substrate 2 and the second substrate 6 ( The optical adhesive reservoir 12 applies a stress 13 due to contraction and expansion in the shear direction (substrate thickness direction) with respect to the normal direction of the opposing surfaces of each yatoi and each substrate. And it is a serious situation that this shear direction (substrate thickness direction).

  That is, even if the optical adhesive 11 exerts a force to firmly bond in the normal direction of the opposing surface, the optical adhesive reservoir 12 generates the stress 13 in the direction perpendicular to the force. Sometimes, the relative positions of the optical fiber cores 8a, 8b, 8c and the optical waveguides 3a, 3b, 3c in the vertical direction (substrate thickness direction) are gradually and gradually shifted. As a result, the insertion loss of light transmitted from the optical fiber cores 8a, 8b, 8c to the optical waveguides 3a, 3b, 3c gradually increases.

  As estimated from the length of the arrow of the stress 13 indicated by the arrow in FIG. 8, the axial misalignment in the vertical direction is greatest in the optical fiber core 8b and the optical waveguide 3b. That is, in the combination of the optical fiber core 8a and the optical waveguide 3a, the core 8b and the optical waveguide 3b, and the core 8c and the optical waveguide 3c, the axial misalignment between the core 8b and the optical waveguide 3b is the largest.

  FIG. 9 shows an increase in insertion loss of light transmitted from the optical fiber core 8b to the optical waveguide 3b during the heat cycle test. As can be seen from FIG. 9, when the number of heat cycles is increased, the light insertion loss is remarkably increased, which causes a serious problem in reliability.

  Note that the contraction and expansion of the optical adhesive reservoir 12 during the heat cycle test generates a stress 13, and as a result, the first substrate 2 and the second substrate 6 are axially displaced vertically at the end surfaces where the first substrate 2 and the second substrate 6 are bonded to each other. Increasing the insertion loss is not a known fact, but is a knowledge obtained for the first time as a result of investigations by the authors.

  Although different from the configurations shown in FIGS. 6 and 7, Patent Document 2 discloses a configuration in which the substrates are joined together using a Yatoi provided on the end portions of the substrates and the upper portions of the substrates.

JP 2007-334124 A JP 2009-175364 A

  As described above, in the optical coupling device in which the end portions of the first substrate and the second substrate, and the end surfaces of the first and second yatoies provided on each substrate are attached with an optical adhesive. In the prior art, particularly in a reliability test such as a heat cycle, the optical adhesive reservoir in which a step is formed between the lower surface of the first substrate and the lower surface of the second substrate contracts or expands. The optical waveguides and optical fiber cores possessed by the first substrate and the second substrate are misaligned in the vertical direction (substrate thickness direction). As a result, there has been a problem that the insertion loss of light between the optical waveguide and the optical fiber core possessed by the first substrate and the second substrate increases with the lapse of the test time. Therefore, there has been an urgent need to develop an optical coupling device having high reliability.

  The present invention has been made in view of such circumstances, and an object thereof is to provide an optical coupling device that is resistant to reliability tests such as a heat cycle.

  In order to solve the above-described problem, the optical coupling device according to claim 1 of the present invention is configured such that the first substrate and the second substrate are opposed to each other at the end of each substrate and at the end of the upper surface of each substrate. In an optical coupling device in which an optical waveguide provided on each substrate is optically coupled with an adhesive provided by the first and second yatoi provided, and the thickness of the first substrate is the second The first Yatoi is formed thinner than the second Yatoi, and the sum of the thickness of the first Yatoi and the first substrate is thereby set to the second Yaito. A step portion formed between the top surface of the first yatoy and the end of the second yatoy due to the difference in the sum of the thicknesses. 1 adhesive reservoir portion is inserted into the upper surface of the first yatoy. And the second adhesive reservoir portion is formed on the step formed between the lower surface of the first substrate and the end of the second substrate by the difference in the sum of the thicknesses. By forming in a state of protruding to the lower surface of the first substrate, the stress in the substrate thickness direction generated in the first adhesive reservoir portion and the thickness direction of the substrate generated in the second adhesive reservoir portion. It is characterized by stress canceling each other out.

  In order to solve the above problem, an optical coupling device according to a second aspect of the present invention is the optical coupling device according to the first aspect, wherein the amount of the adhesive in the first adhesive reservoir and the second The amount of adhesive in the adhesive reservoir portion is substantially equal.

  In order to solve the above-described problem, an optical coupling device according to a third aspect of the present invention is the optical coupling device according to the first or second aspect, wherein the first and second adhesive reservoirs are: It is characterized by comprising an optical adhesive.

  In order to solve the above-described problem, an optical coupling device according to a fourth aspect of the present invention is the optical coupling device according to any one of the first to third aspects, wherein the first substrate and the first optical coupling device are the same. The width / thickness ratio of at least one of the two substrates is greater than 1.

  In the present invention, a step is provided on the upper surfaces of the first and second yatoys, and an adhesive reservoir is formed there, for example, a step between the lower surface of the first substrate and the lower surface of the second substrate. It cancels out the stress caused by thermal contraction and thermal expansion of the optical adhesive reservoir formed at a certain location. Thereby, there exists the outstanding effect that the optical coupling device with a yield strength can be implement | achieved with respect to reliability tests, such as a heat cycle.

The perspective view which shows schematic structure of 1st Embodiment which concerns on the optical coupling device of this invention. FIG. 1 is a schematic cross-sectional view taken along line AA ′ FIG. 2 is a schematic cross-sectional view along BB ′ The figure explaining the effect of a 1st embodiment Schematic sectional view of a second embodiment according to the optical coupling device of the present invention The perspective view which shows schematic structure about the optical coupling device of a prior art Sectional drawing in AA 'of FIG. Sectional drawing in BB 'of FIG. Diagram explaining the problems of the prior art

  Hereinafter, embodiments of the present invention will be described. However, since the same reference numerals as those in the related art shown in FIGS. 6 to 9 correspond to the same functional units, description of functional units having the same reference numerals is omitted here. To do.

(First embodiment)
FIG. 1 shows a schematic perspective view of the present invention. Further, FIG. 2 shows a cross-sectional view taken along line AA ′. In the present embodiment, a step H ′ is provided between the upper surface 5 ′ of the first yatoy 5 and the upper surface 10 ′ of the second yatoy 10, and the adhesive reservoir 14 is formed here.

  Here, for the sake of simplicity, 14 is the same UV adhesive as the optical adhesive 11, but may be a normal adhesive. In the case where a normal adhesive is applied, after bonding both the substrates and the two yatoi with the optical adhesive 11 and the optical adhesive reservoir 12, the upper surface 5 'of the first yatoy 5 is bonded with the adhesive reservoir 14. The side surface of the second yatoy 10 is bonded. Since the adhesive reservoir 14 does not enter the optical path, no problem occurs.

  FIG. 3 is a cross-sectional view taken along the line BB ′ of FIG. Here, 15 is a stress generated when the present embodiment is subjected to a heat cycle test, and acts to lower the second yato 10 downward (substrate direction) with respect to the first yato 5. 13 is also a stress generated when the heat cycle test is performed, and a force for pulling the second substrate 6 upward with respect to the first substrate 2 works (the same as the stress 13 in the prior art shown in FIG. 8). Is).

  As can be seen from FIG. 3, in this embodiment, the stress 15 generated by the adhesive reservoir 14 and the stress 13 generated by the optical adhesive reservoir 12 are opposite in direction and cancel each other.

  FIG. 4 shows an increase in insertion loss of light transmitted from the optical fiber core 8b to the optical waveguide 3b when the first embodiment is subjected to a heat cycle test at −40 to 80 ° C. From this figure, it can be seen that by using this embodiment, the vertical axis displacement is virtually eliminated and an optical coupling system having extremely high reliability can be realized.

  Since the adhesive force of the first adhesive 5 and the second adhesive 10 and the optical adhesive 11 that fixes the first substrate 2 and the second substrate 6 is quite strong, the stress 15 in FIG. It has been confirmed that even if the stress 13 does not completely cancel each other, the effects of the present invention can be sufficiently exerted. Accordingly, in FIG. 2, it is experimentally confirmed that the two steps H and H ′ need not be equal to each other, and the amounts of the optical adhesive reservoir 12 and the adhesive reservoir 14 need not be completely equal. doing.

(Second Embodiment)
FIG. 5 shows a cross-sectional view of a second embodiment of the present invention. In the present embodiment, a third Yatoi 16 made of, for example, an LN substrate or the like is bonded to the lower surface of the first substrate 2 to increase the bonding area with the second substrate 6. An optical adhesive reservoir 12 is formed across the lower surface 16 ′ of the third Yatoi and the end surface of the second substrate 6. Similar to the first embodiment, the adhesive reservoir 14 cancels the stress in the vertical direction (substrate thickness direction) generated by the optical adhesive reservoir 12. Needless to say, the adhesive reservoir 14 may be a normal adhesive as described above.

(Each embodiment)
In the embodiment described in the present specification, the coupling structure of the array type optical waveguide and the array type optical fiber has been described. However, the present invention is also suitable for connection between the array type optical waveguides. Further, although an LN substrate using an LN substrate as the optical waveguide has been described as a so-called LN optical waveguide, it is needless to say that the present invention can also be applied to other optical waveguides such as a quartz optical waveguide.

  The present invention is particularly effective for an optical coupling device using a substrate or yatoi having a square bond cross section. When the aspect ratio (substrate width / substrate thickness) of the width and thickness of the substrate at the bonding end face is larger than 1, the amount of the optical adhesive reservoir on the lower surface of the substrate inevitably increases, so that the optical adhesive reservoir The stress in the vertical direction by the part becomes strong. Therefore, the present invention is extremely effective for an optical coupling device having an aspect ratio larger than 1.

1: Pedestal 2: First substrate (LN substrate)
2 ′: lower surface of first substrate 3a, 3b, 3c: optical waveguide 4: SiO ₂ buffer layer 5: first yatoi 5 ′: upper surface of first yatoi 6: second substrate (glass block)
6 ': lower surface of the second substrate 7a, 7b, 7c: V-grooves 8a, 8b, 8c: cores of optical fibers 8a', 8b ', 8c' 8a ', 8b', 8c ': optical fibers 9a, 9b, 9c: Cladding of optical fibers 8a ', 8b', 8c '10: Second Yatoi 10': Upper surface of second Yatoi 11: Optical adhesive 12: Optical adhesive reservoir 14: Adhesive reservoir 13, 15 : Stress 16: Third yatoy 16 ': Lower surface of third yatoy

Claims (4)

The first substrate and the second substrate are bonded to each other by an adhesive at the end of each opposing substrate and the first and second yatoi provided at the upper end of each substrate. In the optical coupling device in which the optical waveguide provided in is optically coupled,
The thickness of the first substrate is made thinner than the second substrate, and the thickness of the first yatoy is made thinner than the second yatoy. The sum of the thickness of the substrate is smaller than the sum of the thickness of the second Yatoi and the second substrate,
The first adhesive reservoir portion is formed on the step portion formed between the upper surface of the first yatoy and the end of the second yatoy due to the difference in the sum of the thicknesses. The second adhesive reservoir portion is formed in a step portion formed between the lower surface of the first substrate and the end of the second substrate due to the difference in the sum of the thicknesses. By forming the adhesive so as to protrude to the lower surface of the first substrate,
The optical coupling device, wherein the stress in the substrate thickness direction generated in the first adhesive reservoir portion and the stress in the substrate thickness direction generated in the second adhesive reservoir portion cancel each other.   2. The optical coupling device according to claim 1, wherein the amount of the adhesive in the first adhesive reservoir and the amount of the adhesive in the second adhesive reservoir are substantially equal.   The optical coupling device according to claim 1, wherein the first and second adhesive reservoir portions are made of an optical adhesive.   4. The optical coupling device according to claim 1, wherein a ratio of a width to a thickness of at least one of the first substrate and the second substrate is larger than 1. 5.

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