JP2007072307A - Optical module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical module in which the deterioration of optical coupling efficiency due to the displacement of positions of an optical element and an optical waveguide substrate which are separately mounted on a wiring substrate is suppressed. <P>SOLUTION: The optical module 1A is provided with the optical element 2, the optical waveguide substrate 3 having a core 31 and a clad 32 and the wiring substrate 4 on which the optical element 2 and the optical waveguide substrate 3 are mounted. In the optical module 1A, positioning parts 35 and 45 for mounting the optical waveguide substrate 3 on the wiring substrate 4 are provided are provided on the optical waveguide substrate 3 and the wiring substrate 4, and at least the end part 31a of the core 31 on the side of the optical element is tapered with which the width increases as approaching to the optical element 2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical module.

  Conventionally, there has been known an optical module including an optical element, an optical waveguide substrate having a core and a clad, and optically coupled to the optical element, and a wiring substrate on which the optical element and the optical waveguide substrate are mounted. ing.

For example, in Patent Document 1, a lower surface of an optical waveguide substrate is bonded to a wiring substrate, a recess is formed on the upper surface of the optical waveguide substrate, and an optical element is bonded to the recess of the optical waveguide substrate. An optical module in which an optical element is mounted on a wiring substrate via an optical waveguide substrate is described. This Patent Document 1 also describes an optical module in which the end of the core on the optical element side is tapered.
JP 7-35933 A

  In the optical module, since the optical element is bonded to the optical waveguide substrate, the optical element and the optical waveguide substrate are directly aligned to increase the optical coupling efficiency between the optical element and the optical waveguide substrate. Although it can be kept high, an optical waveguide substrate is always required at the position where the optical element is disposed, and thus the optical waveguide substrate cannot be freely designed.

  Therefore, in order to improve the degree of freedom in designing the optical waveguide substrate, there is a demand for mounting the optical element and the optical waveguide substrate separately on the wiring substrate. However, in this case, the optical element and the optical waveguide substrate may be misaligned, which may reduce the optical coupling efficiency.

  In view of such circumstances, an object of the present invention is to provide an optical module capable of suppressing a decrease in optical coupling efficiency due to a positional shift when an optical element and an optical waveguide substrate are separately mounted on a wiring substrate. And

  In order to solve the above problems, an optical module of the present invention includes an optical element, an optical waveguide substrate having a core and a clad, and optically coupled to the optical element, and the optical element and the optical waveguide substrate are mounted. An optical module including a wiring board, wherein a positioning portion for mounting the optical waveguide board on the wiring board is provided on the optical waveguide board and the wiring board, and at least the light of the core of the optical waveguide board is provided. The end portion on the element side is tapered so that the width dimension in the direction parallel to the wiring board increases as the optical element is approached.

  In order to reduce the fluctuation of the optical coupling efficiency due to the mounting position shift also in the optical waveguide substrate having the mirror portion, the optical waveguide substrate has a mirror portion, and the core is connected to the mirror portion. It is preferable that the shape of the core is a trapezoidal shape with the optical element side being wide.

  In order to improve the optical coupling efficiency between the optical element and the optical waveguide substrate, an extended core extending from the mirror portion to the vicinity of the optical element is provided, and the extended core is viewed from the extending direction of the core. It is preferable to form a taper that increases the width on the optical element side.

  In order to reduce the mounting cost and improve the optical coupling efficiency, the light emitted from the optical element is condensed between the optical element and the core in a direction perpendicular to the wiring board and guided into the core. It is preferable to provide a condensing part.

  According to the present invention, the optical waveguide substrate and the wiring substrate are provided with the positioning portion when the optical waveguide substrate is mounted on the wiring substrate. Therefore, even if the optical element and the optical waveguide substrate are separately mounted on the wiring substrate, There is no significant displacement between the optical waveguide substrate and the optical element. Therefore, it is possible to improve the degree of freedom in designing the optical waveguide substrate while suppressing a decrease in optical coupling efficiency due to the displacement. Moreover, since at least the end of the core on the optical element side is tapered such that the width dimension increases as it approaches the optical element, even if the optical element and the optical waveguide substrate are misaligned, Since most of the light emitted from the optical element is guided into the core, fluctuations in the optical coupling efficiency due to misalignment are reduced.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

  As shown in FIGS. 1A, 1B, and 2, an optical module 1A according to the first embodiment of the present invention includes an optical element 2 and an optical waveguide substrate 3 that is optically coupled to the optical element 2. And a printed wiring board 4 on which the optical element 2 and the optical waveguide substrate 3 are mounted.

  On the upper surface of the printed wiring board 4, electrical wiring 41 is formed with a predetermined wiring pattern, and a pair of bonding pads are connected so as to be electrically connected to the electrical wiring 41 at a position where the optical element 2 is mounted. 46 is formed. The optical element 2 is bonded onto the bonding pad 46 by solder bumps 5.

  The optical element 2 is a photodiode, for example, and has a rectangular parallelepiped shape in plan view. The lower surface of the optical element 2 is electrically connected to the electrical wiring 41 via the solder bump 5 and the bonding pad 46. Further, the optical element 2 has a light emitting portion on the end face, and as indicated by an arrow c in FIG. 1A, a direction parallel to the printed wiring board 4, that is, a direction along the upper surface of the printed wiring board 4. Light is emitted in the right direction (in FIG. 1A).

  The optical waveguide substrate 3 has a rectangular parallelepiped shape extending in the light emitting direction of the optical element 2 in the plan view (left and right direction in FIG. 1A), and the left end face faces the optical element 2 with a slight distance therebetween. It is mounted on the upper surface of the printed wiring board 4 as described above. The optical waveguide substrate 3 includes a core 31 that guides light emitted from the optical element 2 and a clad 32 that surrounds the core 31 in a direction orthogonal to the direction in which the core 31 extends. . The refractive index of the core 31 is 1.53, for example, and the refractive index of the clad 32 is 1.51, for example.

  The optical waveguide board 3 and the printed wiring board 4 are provided with positioning portions when the optical waveguide board 3 is mounted on the printed wiring board 4. Specifically, as the positioning portion, a pair of bonding pads 45 arranged in a direction orthogonal to the light emitting direction of the optical element 2 are provided on the upper surface of the printed wiring board 4, while the lower surface of the optical waveguide substrate 3 is provided. A pair of bonding pads 35 corresponding to the bonding pads 45 are provided. The optical waveguide substrate 3 is made of a transparent material, and the bonding pads 35 are visible from the upper surface.

  When mounting the optical waveguide substrate 3, the optical waveguide substrate 3 is turned upside down from the state shown in FIG. 2, and the optical waveguide substrate 3 and the printed wiring board 4 are aligned so that the bonding pad 35 and the bonding pad 45 are matched. The bonding pads 35 and 45 are joined to each other by the solder bump 6. The alignment is performed by adjusting the position of the optical waveguide substrate 3 by a machine while performing image processing using a CCD camera or the like. Further, after bonding with the solder bumps 6, an optical adhesive is applied to the upper surface of the printed wiring board 4 so as to border the optical waveguide board 3, and the optical waveguide board 3 and the printed wiring board 4 are firmly bonded. .

  The end 31a on the optical element side of the core 31 has a tapered shape in which the width dimension in the direction parallel to the printed wiring board 4 (vertical direction in FIG. 1A) increases as the optical element 2 is approached. .

  In optical communication used for LAN communication or the like, a multi-mode optical signal that is easy to optically connect is often used, judging from high speed and transmission distance. In this case, the cross-sectional shape of the core 31 is generally in the range of 30 to 100 μm □, and is determined by the size of the light emitting part of the light emitting element and the size of the light receiving part of the light receiving element. In the present embodiment, the height dimension of the core 31 and the width dimension of the part other than the tapered part are set to about 100 μm, the length of the tapered part is set to about 5 mm, and the maximum width dimension is set to about 200 μm. .

  In the optical module 1A of the present embodiment, since the optical waveguide substrate 3 and the printed wiring board 4 are provided with bonding pads 35 and 45 that are positioning portions when the optical waveguide substrate 3 is mounted on the printed wiring board 4, the optical element Even if 2 and the optical waveguide substrate 3 are separately mounted on the printed wiring board 4, the optical waveguide substrate 3 and the optical element 2 are not greatly displaced. Therefore, the degree of freedom in designing the optical waveguide substrate 3 can be improved while suppressing a decrease in the optical coupling efficiency due to the positional deviation.

  Here, in this embodiment, the end 31a on the optical element side of the core 31 is tapered, but when the core 31 is linear over the entire length, the curve a in FIG. As shown, when the optical element 2 and the optical waveguide substrate 3 are misaligned, in other words, when the optical axis center of the light emitting portion of the optical element 2 and the optical axis center of the core 31 are misaligned, optical coupling is performed. If the efficiency is extremely reduced and a positional shift larger than the width of the core 31 occurs, the optical coupling efficiency becomes almost zero. Since the mounting position of the optical element 2 and the mounting position of the optical waveguide substrate 3 are determined by the height of the solder bumps 5 and 6 in the direction perpendicular to the printed wiring board 4, the amount of positional deviation in that direction is small. The amount of positional deviation in the direction parallel to the wiring board 4 is large unless the bonding pads 35 and 45 are completely matched.

  Therefore, as in the present embodiment, the end 31a on the optical element side of the core 31 is tapered so that the width dimension increases as it approaches the optical element. 3 is misaligned, most of the light emitted from the optical element 2 is guided into the core 31 by the taper portion. Therefore, as shown by the curve b in FIG. Efficiency fluctuations are reduced. Furthermore, since the tapered portion can guide even the diffused light indicated by the arrow d in FIG. 1A into the core 31, even when the optical element 2 and the optical waveguide substrate 3 are separated from each other, A decrease in optical coupling efficiency due to diffused light can be suppressed.

  In the embodiment, the end 31a on the optical element side of the core 31 is tapered. However, the core 31 may be tapered over the entire length, and at least the end 31a on the optical element side is at least. It only needs to be tapered.

  In addition to the bonding pads 35 and 45, various positioning units can be used as the positioning unit. For example, like the optical module 1 </ b> A ′ of the modified example shown in FIGS. 4A and 4B, the positioning portion can be configured in a fitting shape.

  That is, the printed circuit board 4 having the submount substrate 7 mounted on the upper surface thereof is used as a wiring board. A concave portion 71 having a rectangular shape in a plan view to be fitted, and a groove portion 72 extending in the left-right direction from the right end surface of the submount substrate 7 to the vicinity of the center, and fitted to the lower portion of the optical waveguide substrate 3, are provided. The positioning portion may be configured by 72 and the end surface in the width direction of the optical waveguide substrate 3.

  The submount substrate 7 is a three-dimensional circuit (MID; Molded Interconnect Device) formed by resin molding. Since MID is a circuit in which a circuit is three-dimensionally formed on an injection molding resin, a three-dimensional shape can be formed with high accuracy.

  In addition, the shape of the groove part 72 and the optical waveguide board | substrate 3 can be selected suitably, for example, as shown in FIG. 5, you may make the groove part 72 and the optical waveguide board | substrate 3 into substantially T shape by planar view. If it does in this way, it will become possible to position also in the light emission direction of optical element 2.

  In the said embodiment, the light emitting element is employ | adopted as the optical element 2, and the end part 31a by the side of the optical element of the core 31 shows the form which becomes the taper shape from which a width dimension becomes large as it approaches the optical element 2. However, when a light receiving element is employed as the optical element 2, conversely to the above embodiment, the end 31a on the optical element side of the core 31 is tapered so that the width dimension decreases as the optical element 2 approaches the optical element 2. You can do it.

  Next, an optical module 1B according to a second embodiment of the present invention will be described with reference to FIGS. 6 (a) and 6 (b).

  In the optical module 1B, a VCSEL (Vertical Cavity Surface Emitting Laser) that emits light in a direction perpendicular to the printed wiring board 4 from the upper surface (upward in FIG. 6B) is employed as the optical element 2. This VCSEL has, for example, an outer diameter of 0.27 × 0.22 mm, a height of 0.185 mm, a light emitting area of 15 μmφ, and an oscillation wavelength of 850 nm. The bonding pad 21 of the optical element 2 is electrically connected to the electric wiring 41 on the printed wiring board 4 by wire bonding 42.

  The optical waveguide substrate 3 has a rectangular shape in plan view, and the lower surface 3 b is bonded to the upper surface of the printed wiring board 4 while covering a part of the upper surface of the optical element 2. Positioning portions such as the bonding pads 35 and 45 shown in the first embodiment are provided on the upper surface of the printed wiring board 4 and the lower surface 3b of the optical waveguide substrate 3, although not shown.

  In addition, the optical waveguide substrate 3 has a mirror portion 3 a directly above the light emitting portion of the optical element 2, and the core 31 reaches the mirror portion 3 a from the end surface opposite to the mirror portion 3 a of the optical waveguide substrate 3. Extends in a direction parallel to the printed wiring board 4 (left and right in FIG. 6B). Further, the optical waveguide substrate 3 is provided with an extended core 31 ′ extending in the light emitting direction of the optical element 2 from the position where the core 31 reaches in the mirror portion 3 a to the vicinity of the optical element 2. The light emitted right above the light emitting part of the optical element 2 propagates through the extending core 31 ′ to the mirror part 3 a, and is reflected by the mirror part 3 a in the direction of 90 degrees, Is propagated in the direction of the other end of the core 31 in the extending direction (the right end in FIG. 6B).

  The mirror portion 3a is configured by cutting a portion located immediately above the light emitting portion of the optical element 2 in the optical waveguide substrate 3 at 45 degrees. The cut surface is coated with a metal film or a dielectric film, Reflectivity is improved.

  The end 31a on the optical element side of the core 31 has a tapered shape in which the width dimension in the direction parallel to the printed wiring board 4 (vertical direction in FIG. 6A) increases as the optical element 2 is approached. . Since the end portion 31a of the core 31 is connected to the mirror portion 3a without returning to a linear shape, the shape of the core 31 in the mirror portion 3a is as shown in FIGS. 7 (a) and 7 (b). It has a trapezoidal shape with the optical element side wide.

  As shown in FIG. 7C, the extending core 31 ′ has a tapered shape that increases the width dimension on the optical element side when viewed from the extending direction of the core 31.

  Thus, by forming the shape of the core 31 in the mirror part 3a into a trapezoidal shape with the optical element side wide, even in the optical waveguide substrate 3 having the mirror part 3a, at least the end 31a on the optical element side of the core 31. Thus, the variation in optical coupling efficiency due to mounting position shift can be reduced.

  Even if the extended core 31 ′ is omitted and the portion where the extended core 31 ′ is present is filled with the clad 32, the light emitted from the optical element 2 passes through the clad 32 and then passes through the mirror portion 3 a. The light is reflected and propagates in the core 31, but in this case, the light spreads when passing through the clad 32 under the core 31, and the optical coupling efficiency is lowered. On the other hand, since the extended core 31 ′ is provided as in the present embodiment, the light does not spread in the lower clad 32, so that the optical coupling efficiency between the optical element 2 and the optical waveguide substrate 3 is improved. . Furthermore, since the extending core 31 'is tapered so that the optical element side becomes wider, it is possible to cope with even larger positional deviations.

  Next, an optical module 1C according to a third embodiment of the present invention will be described with reference to FIGS. In this optical module 1 </ b> C, a cylindrical lens 8 is disposed between the optical element 2 and the optical waveguide substrate 3. In the optical module 1C, the core 31 is tapered not only at the end portion 31a but also over the entire length, and although not shown, the upper surface of the printed wiring board 4 and the optical waveguide are omitted as in the first embodiment. Positioning portions such as bonding pads 35 and 45 are provided on the lower surface of the waveguide substrate 3.

  The cylindrical lens 8 extends in a direction (vertical direction in FIG. 8A) orthogonal to the light emitting direction of the optical element 2, and is convex toward the optical element side and the optical waveguide substrate side in a side view. Then, as shown in FIG. 8B, the light emitted from the optical element 2 is condensed in a direction perpendicular to the printed wiring board 4 (vertical direction in FIG. 8B) by the cylindrical lens 8 to be the core. 31 is led.

  When light is collected using a lens composed of a three-dimensional free-form surface, the alignment accuracy between the lens center and the optical element 2 becomes severe, and the mounting cost increases, but the direction perpendicular to the printed wiring board 4 By using the cylindrical lens 8 that collects light at the position, it is only necessary to provide alignment accuracy only in that direction, and the mounting cost can be reduced. And by condensing in this way, optical coupling efficiency can be improved.

  This effect is not limited to the arrangement of the cylindrical lens 8 between the optical element 2 and the optical waveguide substrate 3, and the light emitted from the optical element 2 is printed between the optical element 2 and the core 31. It can be obtained by providing a condensing part that condenses light in a direction perpendicular to the substrate 4 and guides it into the core 31.

  For example, like the optical module 1C ′ of the modification shown in FIGS. 9A and 9B, the clad 32 is formed in a shape that covers the end face 31b on the optical element side of the core 31, and the end face 32a on the optical element side. May be a convex surface that is convex toward the optical element in a side view. Alternatively, a portion on the optical element side from the end surface 31b of the core 31 which is a portion having a convex surface is formed as a separate member, and this separate member is formed on the optical device side of the optical waveguide substrate 3 shown in FIGS. You may join to an end surface.

  Even in this case, the light emitted from the optical element 2 on the convex surface can be condensed and guided into the core 31.

It is a figure which shows the optical module which concerns on 1st Embodiment of this invention, (a) is a top view, (b) is a side view. It is a disassembled perspective view of the optical module of 1st Embodiment. It is a graph showing the relationship between positional offset amount and optical coupling efficiency. It is a figure which shows the optical module of the modification of 1st Embodiment, (a) is a disassembled perspective view, (b) is a side view. It is a disassembled perspective view of the optical module of the modification of 1st Embodiment. It is a figure which shows the optical module which concerns on 2nd Embodiment of this invention, (a) is a top view, (b) is a side view. It is the figure which expanded the principal part of the optical module of 2nd Embodiment, (a) is a top view, (b) is a side view, (c) is the sectional view on the AA line of (b). It is a figure which shows the optical module which concerns on 3rd Embodiment of this invention, (a) is a top view, (b) is a side view. (A) is a side view of the optical module of the modification of 3rd Embodiment, (b) is a perspective view of a waveguide board | substrate.

Explanation of symbols

1A, 1A ′, 1A ″, 1B, 1C, 1C ′ Optical module 2 Optical element 3 Optical waveguide substrate 3a Mirror part 31 Core 31a End part 31 ′ Extension core 32 Clad 32a Convex surface (condensing part)
35 Bonding pad (positioning part)
4 Wiring board 45 Bonding pad (positioning part)
48 Indentation part 5,6 Solder bump 7 Submount substrate 72 Groove part (positioning part)
8 Cylindrical lens (condenser)

Claims (4)

An optical module comprising: an optical element; an optical waveguide substrate having a core and a clad, and optically coupled to the optical element; and a wiring substrate on which the optical element and the optical waveguide substrate are mounted,
The optical waveguide substrate and the wiring substrate are provided with a positioning portion for mounting the optical waveguide substrate on the wiring substrate, and at least the end of the core of the optical waveguide substrate on the optical element side is brought closer to the optical element. An optical module having a tapered shape in which a width dimension in a direction parallel to the wiring board is increased.   The optical waveguide substrate has a mirror part, the core is connected to the mirror part, and the shape of the core in the mirror part is a trapezoidal shape with the optical element side wide. The optical module as described in.   An extending core extending from the mirror portion to the vicinity of the optical element is provided, and the extending core is tapered so that the width dimension on the optical element side is increased when viewed from the extending direction of the core. The optical module according to claim 2. 2. A condensing unit that condenses light emitted from the optical element in a direction perpendicular to the wiring substrate and guides the light into the core between the optical element and the core. 4. The optical module according to any one of 3 above.

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