JPH11183761A - Optical connection structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide optical connection structure capable of preventing the generation of light attenuation due to reflected light on the end face of an optical waveguide and the generation of an adverse effect due to the adhesion of dust to a mirror surface and allowed to be easily and accurately produced as compared with conventional optical connection structure. SOLUTION: The optical connection structure is obtained by optically connecting an optical waveguide 12 consisting of a clad part 12b formed on the upper surface of a substrate and a core part 12a to a photoelectric conversion element 13 packaged on the substrate 11 through a mirror surface 14 formed on the upper surface of the substrate 11, inclining the end face 12c of the waveguide 12 and the mirror surface 14 from the upper surface of the substrate 11 respectively at 32 to 162 deg. and 30 to 60 deg. and a gap between the end face 12c of the waveguide 12 and the mirror surface 14 is filled with resin 15 having approximately the same refractive index as that of the core part 12a of the waveguide 12. Since the adhesion of dust to the mirror surface 14 can be suppressed and the generation of light scattering or the like on the end face 12c of the waveguide 12 can also be prevented, optical signals can be efficiently inputted/outputted between the waveguide 12 and the element 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical connection structure for transmitting an optical signal between a light receiving / light emitting element and an optical waveguide in an optical signal-to-electrical signal conversion module substrate used in an optical communication system or a computer / switch. More specifically, the present invention relates to an optical connection structure for easily and accurately connecting incoming and outgoing light between a photoelectric conversion element and an optical waveguide via a mirror surface formed on a substrate.

[0002]

2. Description of the Related Art In an optical signal transmission system such as an optical communication system or a computer / exchanger, a signal processing of a transmitted optical signal is performed by an electronic device, and therefore, a photoelectric conversion for converting an optical signal into an electric signal. Equipment is needed,
In the boundary region between such an optical signal and an electric signal, a light transmission path such as an optical fiber or an optical waveguide, a light emitting element such as a laser diode, a photoelectric conversion element such as a light receiving element such as a photodiode, and the photoelectric conversion element. In addition, LSIs for controlling electronic elements and processing of electric signals, electric circuits for driving electronic components, and the like are mixed.

[0003] Above all, in order to realize a high-speed and wide-band communication system, there is an increasing interest in a device or an optical module using optical surface mounting or optical wiring as an optical interconnection between chips in an optical communication system. As one of the elemental technologies, there is a demand for a technology for efficiently optically connecting an optical waveguide and a photoelectric conversion element such as a light-emitting element such as a laser diode or a light-receiving element such as a photodiode.

In response to such a requirement, as shown in a cross-sectional view of FIG. 3, for example, a light receiving surface 3a on the lower surface of a surface light receiving type photodiode as a photoelectric conversion element 3 surface-mounted on the substrate 1, In order to make the light propagating through the core portion 2a of the optical waveguide 2 formed on the upper surface of the optical waveguide 2 incident thereon, a 45 ° angle was cut out on the upper surface of the substrate 1 as a reflection surface facing the end of the optical waveguide 2. A technique has been proposed in which a mirror surface 4 is formed and the light path is converted upward by the mirror surface 4.

According to this technique, the photoelectric conversion element 3
Emitting surface 3a on the lower surface of surface emitting laser diode
In the case where the light emitted from the optical waveguide 2 is made incident on the core portion 2a of the optical waveguide 2, the emitted light is converted into an optical path by the mirror surface 4 in a direction parallel to the upper surface of the substrate 1, and Will be incident on the end face of.

[0006]

However, in the conventional optical connection structure in which the optical path is changed via the mirror surface 4, the space between the end surface of the optical waveguide 2 and the mirror surface 4 is usually an air layer, When the conversion element 3 is surface-mounted, dust or the like may adhere to the mirror surface 4. In such a case, the light that has propagated through the optical waveguide 2 is scattered by the dust and the like, and the propagated light can be accurately reflected. There has been a problem that the optical path cannot be changed, and the propagation loss increases due to scattering.

Furthermore, in the conventional optical connection structure, the end face of the optical waveguide 2 is cut out in the direction of propagation of the propagation light, that is, perpendicular to the upper surface of the substrate 1, and the core 2a of the optical waveguide 2 is formed. Is significantly different from the refractive index of the air layer, reflection of the propagating light at the end face of the optical waveguide 2 occurs, which causes a problem of attenuating an optical signal.

[0008] Such an optical connection structure is, for example, 2
When the two optical waveguides 2 and the photoelectric conversion element 3 are connected, the two optical waveguides 2 are arranged such that their light transmission directions are 90 degrees and their end faces are adjacent to each other. In this case, two mirror surfaces 4 adjacent to each other at 90 degrees are formed.

However, in the above-described conventional optical connection structure, the mirror surface 4 is anisotropically etched on the end of the optical waveguide 2 by using an ECR device, for example, to form the substrate 1.
After being cut out perpendicular to the upper surface of the substrate, the mirror surface 4 is similarly processed by using the ECR device so that the inclination of the mirror surface 4 becomes 45 degrees, or the optical waveguide 2 is formed on the upper surface of the substrate 2 and the end portion thereof is formed. Is anisotropically etched using an ECR apparatus, and cut out perpendicularly to the upper surface of the substrate 1. The mirror surface 4 forms a mirror support on a different substrate, and has a 45 ° inclination using a dicing saw or a diamond saw. It is formed by mounting the mirror surface support base and the mirror surface 4 using an adhesive according to a positioning guide formed on the upper surface of the substrate 1 so as to face the end surface of the optical waveguide 2. One processing is required for each of the optical waveguides 2 in one direction, and as described above, the mirror surface 4 is formed facing the optical waveguides 2 having different directions arranged at 90 degrees to each other. Is the processing There was also very problem that the time and effort it takes to.

The present invention has been devised in view of the above-mentioned problems of the prior art, and has as its object the purpose of attenuating light due to the reflected light of light at the end face of an optical waveguide and of removing dust to the mirror surface. The optical waveguide formed on the upper surface of the substrate and the photoelectric conversion element mounted on the substrate can be efficiently optically connected to each other through a mirror surface, preventing the adverse effects of adhesion, and is easier than the conventional optical connection structure. An object of the present invention is to provide an optical connection structure that can be manufactured accurately and accurately.

[0011]

An optical connection structure according to the present invention comprises:
An optical waveguide formed on an upper surface of a substrate, comprising a clad portion and a core portion in the clad portion, and a photoelectric conversion element mounted on the substrate and having a light receiving portion or a light emitting portion on a lower surface, An optical connection structure formed on an upper surface of the optical waveguide, and optically connected to a light receiving portion or a light emitting portion of the photoelectric conversion element through a mirror surface below the light receiving portion or the light emitting portion of the photoelectric conversion element. The end surface of the waveguide and the mirror surface are inclined at 32 to 162 degrees and 30 to 60 degrees with respect to the upper surface of the substrate, respectively, and between the end surface of the optical waveguide and the mirror surface are substantially the same as the core portion of the optical waveguide. It is characterized by being filled with a resin having a refractive index.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an optical connection structure according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a sectional view showing an example of an embodiment of the optical connection structure of the present invention. In FIG. 1, reference numeral 11 denotes a substrate, 12 denotes an optical waveguide formed on an upper surface of the substrate 11 and includes a clad portion 12b and a core portion 12a in the clad portion 12b, and 13 denotes a light-receiving portion mounted on the substrate 11 and a lower surface. Alternatively, it is a photoelectric conversion element having a light receiving / emitting surface 13a as a light emitting unit. Reference numeral 14 denotes a mirror surface formed on the upper surface of the substrate 11, which faces the end face 12c of the optical waveguide 12 and faces the light receiving / emitting surface 13a of the photoelectric conversion element 3 below the end face. A resin having a refractive index substantially the same as that of the core portion 12a of the optical waveguide 12, which is filled between the optical waveguide 12 and the mirror surface 14.

As the substrate 11, a silicon substrate with a V-groove for mounting an optical fiber or a multilayer ceramic circuit substrate, an organic system using an insulating layer of polyimide resin, fluorine resin, olefin resin, epoxy resin or the like and a wiring conductor of copper or the like. A ceramic electric circuit board made of alumina, mullite, aluminum nitride, glass ceramics, or the like in which thin-film multilayer circuits are stacked, a multilayer organic circuit board, or the like can be used.

When a quartz substrate or a silicon substrate is used as the substrate 11, the surface roughness of the upper surface of the substrate 11 is Ra =
Since it is very flat at 0.1 μm or less, it is advantageous in that when the optical waveguide 12 made of quartz is formed on the substrate 11 by the flame deposition method, good propagation characteristics are exhibited. Further, the silicon substrate has a KOH
In the connection between the optical waveguide 12 and the optical fiber used for the connection with the outside, the optical fiber must be mounted in the V-groove because a V-groove having an angle of about 57 degrees can be easily formed on the upper surface thereof by etching with This is advantageous in that the optical waveguide 12 and the optical fiber can be connected on the substrate 11 with high accuracy.

When a multilayer ceramic substrate made of alumina, mullite, aluminum nitride, glass ceramic, or the like is used as the substrate 11, electric wiring can be provided inside the substrate 11, so that a quartz substrate or a silicon substrate can be used. Since the electric wiring formed on the upper surface of the substrate can be routed inside the substrate 11, it is advantageous in that the size of the substrate 11 can be reduced.

Furthermore, aluminum nitride has a thermal conductivity of about 17
Since it is as large as about 0 W / K, heat generated from the photoelectric conversion element 13 mounted on the substrate 11 can be efficiently released to the lower surface of the substrate 11 through the wiring provided in the substrate 11, whereby Because the temperature of the photoelectric conversion element 13 is stable,
It is also advantageous in that a stable operation can be obtained.

When glass ceramics is used as the substrate 11, a multilayer wiring board can be formed, and the electric wiring in the inner layer can be made of silver or copper.
When the substrate is made of alumina, mullite, aluminum nitride, etc., the electric resistance is less than half of that of the refractory metal such as tungsten or molybdenum, which is the wiring material. It is also advantageous in that an electric signal or power can be supplied to the photoelectric conversion element 13 without attenuation, and a stable operation can be obtained.

If a multi-layer ceramic circuit board is used as the substrate 11, a conventionally well-known technique is used.
For example, an appropriate solvent is mixed with a ceramic raw material powder such as alumina or silica to produce a ceramic green sheet that becomes an insulating layer formed into a sheet, and a high melting point metal such as tungsten or molybdenum is contained on the ceramic green sheet. The conductive paste to be the wiring conductors to be printed is screen-printed in a predetermined pattern and sequentially laminated, and then the ceramic green sheets and the conductive paste are simultaneously fired simultaneously to produce a multilayer ceramic circuit board. Further, a metal pad for mounting and fixing the photoelectric conversion element 13 is formed on a mounting portion for mounting the photoelectric conversion element 13, and the photoelectric conversion element 13 is mounted and fixed at a predetermined position by a connection terminal 16 such as a solder bump. At the same time, the electrical connection between the wiring conductor and the photoelectric conversion element 13 is performed.

The optical waveguide 12 formed on the upper surface of the substrate 11 comprises a cladding portion 12b and a core portion 12a in the cladding portion 12b, and an end surface 12c on the side optically connected to the photoelectric conversion element 13 is formed on the substrate.
11 is formed so as to form an inclined surface having an angle θ ₁ of 32 to 162 degrees with respect to the upper surface of the optical disk 11. Optically connected to a conversion element and the like.

The reason why the end surface 12c of the optical waveguide 12 is inclined with respect to the upper surface of the substrate 11 at an angle θ ₁ of 32 to 162 degrees is as follows.

First, in the case where the angle θ ₁ is an acute angle with respect to the upper surface of the substrate 11, the horizontal distance between the core portion 12a of the end surface 12c of the optical waveguide 12 and the mirror surface 14 indicated by L in FIG. 1 will be described later. This end face needs to be 40 μm or less.
The angle θ ₂ of the mirror surface 14 facing the surface 12a is set to a minimum of 30 degrees as described later, and when the lower end of the end surface 12a and the lower end of the mirror surface 14 are in contact with each other on the upper surface of the substrate 11, the center of the core portion 12a extends from the upper surface of the substrate 11 Assuming that the height up to h = 12 μm, θ ₁ ≧ 32 (degrees) from h (1 / tan θ ₁ + 1 / tan θ ₂ ) ≦ 40 (μm). On the other hand, when the angle θ ₁ is an obtuse angle with respect to the upper surface of the substrate 11, the horizontal distance L is similarly set to 40 μm or less,
As the largest 60 degrees as described below the angle theta ₂ of the mirror surface 14 opposed to the end surface 12a, the upper end of the upper surface and the mirror surface 14 of the optical waveguide 12 is anisotropically etched between the two at the same height Assuming that 10 μm is secured as a gap required for performing the above operation and that the height from the center of the core portion 12a to the upper end of the mirror surface 14 is h ′ = 12 μm, h ′ ｛1 / tan (180−θ ₁ ) + ( 1 / tan
θ ₂ )｝ ≦ 40−10 (μm), θ ₁ ≦ 162 (degrees). Therefore, the angle theta ₁ of the inclined surface with respect to the upper surface of the substrate 11 of the end face 12c of the optical waveguide 12 is required to be in the range of 32 degrees to 162 degrees.

As the optical waveguide 12, a general embedded optical waveguide formed on the upper surface of the substrate 11 can be used.
For example, an SiO ₂ film is used for the clad part, and a Si
A silica-based material using O ₂ —GeO ₂ , a siloxane polymer in the clad portion and the core portion, polyimide / benzocyclobutene / PMMA / SiO ₂ —TiO
Those using ₂ etc. can be used.

In particular, when the optical waveguide 12 made of a siloxane polymer is used, the optical waveguide 12 serving also as a planarizing material of the base is used.
As the material for the lower cladding part 12b, the shrinkage ratio of the film thickness before and after curing is extremely small at about 99%,
Even if there are steps or grooves on the substrate that have a thickness of about 100 μm, only a step of about 1 μm will occur after the formation of the lower clad portion 12b, and if the loss in forming the optical waveguide 12 is almost a problem, And optical transmission with sufficiently low loss becomes possible. At the same time, scattering due to the undulating shape of the upper surface of the substrate 11 becomes extremely small, and the generation of scattered light that causes the generation of crosstalk noise can be suppressed. In addition, since the siloxane polymer serves as both the underlying planarization layer and the clad portion 12b below the optical waveguide 12, the siloxane polymer is excellent in ease of manufacture and economical.

The formation of the optical waveguide 12 made of such a siloxane polymer may be performed, for example, as follows. First, a siloxane polymer solution is applied on the upper surface of the substrate 11 by a spin coating method, and heat treatment is performed at 100 ° C./30 minutes + 270 ° C./60 minutes to obtain a 9 μm-thick siloxane polymer film (refractive index: 1.4440, λ = 1.3 μm). Is formed. Next, tetra-n-butoxytitanium /
A siloxane polymer mixed solution is applied by spin coating, roll coating, spray coating, etc.
A heat treatment is performed for + 270 ° C./60 minutes to form a core portion 12a made of a 6 μm-thick siloxane polymer film (refractive index: 1.4482, λ = 1.3 μm). Subsequently, an Al film serving as a mask for performing RIE processing is formed by a sputtering method, and a resist pattern having a line width of 7 μm serving as a pattern of the core portion 12a is formed by a photolithography method, and H ₃ PO ₄ / CH ₃ COOH is formed. The resist pattern is transferred to the Al film by etching the Al film with a mixed solution of / HNO ₃ . Next, after removing the resist pattern, the core portion 12a is etched by RIE using fluorine gas, and then the Al film is removed to form the clad portion 12b.

As described above, a buried optical waveguide 12 made of a siloxane polymer having a core portion 12a having a height of 6 μm, a width of 7 μm, a refractive index of 1.4482, and a cladding portion 12b having a refractive index of 1.4440 can be obtained. .

The core 12a and the clad 12b of the optical waveguide 12 can be made of the following various materials as described above. Material having a refractive index film formation method polyimide from 1.53 to 1.60 a spin coating method, a roll coating method or the like benzocyclobutene 1.53 to 1.58 Ditto PMMA from 1.53 to 1.56 Ditto SiO ₂ -TiO ₂ 1.44~2.00 sputtering, CVD method, or the like SiO ₂ -GeO ₂ 1.44 ~ 2.00 Same as above. Among these materials, the refractive index of the core
What is necessary is just to select and use each so that it may become larger than the refractive index of 12b. The core 12 made of these materials
Photolithography and RIE may be used for the processing of a in the same manner as in the above example. For example, after forming a siloxane polymer film as the lower cladding portion 12b as described above, a SiO 2 film having a refractive index of 1.45 and a thickness of 8 μm is formed. _2- TiO ₂
A film is formed by a sputtering method.
The processing of a may be performed in the same manner.

In order to make the end face 12c of the optical waveguide 12 a slope having an angle θ ₁ of 32 to 162 ° with respect to the upper surface of the substrate 11, for example, anisotropic etching using an ECR device or a fluorine gas atmosphere (Reactive ion etching) or the like.

For example, if the optical waveguide 12 made of the siloxane polymer film is used as the optical waveguide 12,
First, R is added to the end of the optical waveguide 12 formed as described above.
An aluminum film serving as a mask at the time of IE is formed by a sputtering method or the like, and a pattern of an inclined surface forming the end face 12c is patterned by using a photolithography technique. RIE is performed in a fluorine-based gas atmosphere using the patterned aluminum film as a mask.
Processed into slope having an angle theta ₁ with respect to the upper surface of the substrate 11 of 162 ° end face 12c from 32 degrees. The angle θ ₁ with respect to the upper surface of the substrate 11 can be set arbitrarily by optimizing the RIE conditions.

The mirror surface 14 formed on the upper surface of the substrate 11 faces the end face 12c of the optical waveguide 12 and the light receiving / emitting surface 13a of the photoelectric conversion element 13 under the mirror surface 14 as described above. angle theta ₂ is formed to be 30 to 60 degrees of slope relative to the top surface. Such a mirror surface 14
Using a part of the upper surface of the substrate 11, or as shown in FIG.
Using a mirror support 17 stacked in the same manner as in b, a slope having an angle θ ₂ of 30 to 60 degrees with respect to the upper surface of the substrate 11 is formed, and a metal film such as aluminum, titanium, copper, or silver is formed on the slope. Is formed by a known vapor deposition method, a sputtering method, or the like.

For example, if the mirror support 17 is the same as the clad portion 12b made of a siloxane polymer film described above, first, the mirror support having substantially the same height as the optical waveguide 12 is formed in the same manner as described above. Form a platform 17, then
An aluminum film serving as a mask at the time of RIE is formed by a sputtering method, and a pattern having an inclined surface forming the mirror surface 14 is patterned by using a photolithography technique. Using the patterned aluminum film as a mask, the angle θ with respect to the upper surface of the substrate 11 of 30 ° to 60 ° to become the mirror surface 14 by RIE in a fluorine-based gas atmosphere.
Machine the slope with ₂ . The angle θ ₂ with respect to the upper surface of the substrate 11 can be arbitrarily set by optimizing the RIE conditions. Next, in order to apply a metal film to a portion of the slope that becomes a mirror surface 14 for converting an optical path, only that portion is exposed by forming a mask by a photolithography technique. Then, a metal film such as aluminum is deposited by an evaporation method, a sputtering method, or the like.

The angle θ ₂ with respect to the upper surface of the substrate 11 is the refraction angle θ ₃ when the light reflected by the mirror surface 14 exits from the resin 15 filled between the optical waveguide 12 and the mirror surface 14 to the air layer. Is set to be 45 degrees or less with respect to a direction perpendicular to the upper surface of the substrate 11. Therefore, the mirror surface 14 does not necessarily have to be flat over the entire surface, and the angle θ ₂ with respect to the upper surface of the substrate 11 is 30 in the region facing the core portion 12a.
It is sufficient that within the range of 60 degrees, may be a curved surface such as an angle theta ₂ with respect to the upper surface of the substrate 11 is varied continuously.

The reason for setting the angle θ ₂ with respect to the upper surface of the substrate 11 is that when the refraction angle θ ₃ when light exits into the air layer becomes 45 degrees or more, the mirror surface 14 and the surface light emitting / receiving surface 13 a of the photoelectric conversion element 13 become This is because the optical coupling becomes difficult.

That is, light parallel to the upper surface of the substrate 11 is incident on the mirror surface 14 from the core portion 12a of the optical waveguide 12 and totally reflected by the mirror surface 14 to fill the space between the end surface 12c of the optical waveguide 12 and the mirror surface 14. Through a resin 15 having a refractive index of n ₁ from the surface parallel to the upper surface of the substrate 11 to an air layer having a refractive index of n ₂ = 1.0.
Considering the case where the direction perpendicular to the top surface 11 and exits at a refractive angle theta _3, the angle of refraction for light incident on the lower surface of the light emitting and receiving surface 13a of the photoelectric conversion element 13 mounted above the mirror 14 theta ₃ is required to be within the range of -45 degrees to + 45 degrees.

First, in order for the refraction angle θ _{3 to} be +45 degrees, n
₁ = When 1.445, from _{n 1 sin (90-2θ 2) =} n 2 sinθ 3 sin (90-2θ 2) = (n 1 / n 2) sinθ 3 = (1 / 1.445) sin45, 90-2θ 2 ≒ 30 θ ₂ ≒ 30 (degrees). On the other hand, in order for the refraction angle θ _{3 to} be −45 degrees, similarly, n ₁ sin (2θ ₂ −90) = n ₂ sin θ ₃ sin (2θ ₂ −90) = (n ₁ / n ₂ ) sin θ ₃ = (1 /1.445) sin (−45), so that 2θ ₂ −90 ≒ 30 θ ₂ ≒ 60 (degrees). Therefore, the angle θ ₂ of the inclined surface of the mirror surface 14 with respect to the upper surface of the substrate 11 needs to be in the range of 30 degrees to 60 degrees.

When the light emitted from the photoelectric conversion element 13 is desired to be efficiently incident on the optical waveguide 12, the angle θ _{2 of the} mirror surface 14 is set to approximately 45 degrees, and the light emitted from the photoelectric conversion element 13 is emitted. This is preferable because the optical path of the light is converted by 90 degrees on the mirror surface and becomes parallel to the light transmission direction of the optical waveguide 12 and easily enters the core 12a.

Here, usually, the end face 12c and the mirror surface 14 of the optical waveguide 12 are simultaneously formed as a slope by the same manufacturing process, and after the slope is formed, an air gap is formed between the two as in the conventional optical connection structure. (Voids) are present.

Therefore, in the present invention, this optical waveguide
An air layer (gap) between the end surface 12c of the optical waveguide 12 and the mirror surface 14 is filled with a resin 15 having substantially the same refractive index as the core 12a of the optical waveguide 12. By filling the space between the end surface 12c of the optical waveguide 12 and the mirror surface 14 with the resin 15 having substantially the same refractive index as the core portion 12a, dust can be left on the mirror surface 14 when the photoelectric conversion element 13 is surface-mounted. At the same time as preventing the adhesion, the optical signal can be coupled to the photoelectric conversion element 13 without losing the optical signal in the filling portion filled with the resin 15.

In such a filling portion of the resin 15, light propagating through the optical waveguide 12 causes Fresnel reflection at the end face 12 c of the optical waveguide 12. Generally, the core portion 12a of the optical waveguide 12
The greater the difference between the refractive index of the optical waveguide 12 and the refractive index of the resin 15 filled between the end face 12c of the optical waveguide 12 and the mirror surface 14, the greater the Fresnel reflectivity. Therefore, it is optimal that the refractive index of the core portion 12a is the same as the refractive index of the resin 15, but if the Fresnel reflectivity is 1% or less, the propagation loss of light propagating through the optical waveguide 12 is increased. Since it can be ignored, the refractive index difference Δn between the refractive index of the core portion 12a of the optical waveguide 12 and the resin 15 filled between the end face 12c and the mirror surface 14 of the optical waveguide 12 is between 4.0% and + 5.6%.
It is desirable that the refractive indices are substantially the same within the range. Examples of such a resin include a siloxane polymer, a fluororesin, an epoxy resin, and a polyimide resin, which are the same as those of the core portion 12a.

As described above, the end surface 12 c of the optical waveguide 12 and the mirror surface 14
The space between the photoelectric conversion element and the
It is possible to prevent dust from adhering to the mirror surface 14 when the surface 13 is mounted. Also, a core portion forming the optical waveguide 12
The end face of the optical waveguide 12 is made of resin 15 having substantially the same refractive index as 12a.
In order to fill the space between 12c and mirror surface 14, core 12a and resin
Since the difference in the refractive index from the optical waveguide 15 is smaller than the difference in the refractive index between the core 12a and the air layer, it is possible to suppress the reflection of light on the end face 12c of the optical waveguide 12, which is a problem in the conventional optical connection structure. For example, the reflectance can be reduced to 1% or less.

Since the refractive indices of the core portion 12a and the resin 15 are substantially the same and the difference between the refractive indices of the two is small enough to be almost negligible, the angle of the end face 12c of the optical waveguide 12 is set at the upper surface of the substrate 11. Even when the angle is 90 degrees, the reflection of the propagating light on the end face 12c can be suppressed to an almost negligible level.

The horizontal distance (the distance in the direction parallel to the upper surface of the substrate 11) between the end surface 12c (center portion) of the optical waveguide 12 and the mirror surface 14, which is indicated by L in FIG. Light dispersed and spread from the end surface 12a of the optical waveguide 12 efficiently hits the mirror surface 14, and light reflected by the mirror surface 14 efficiently enters the light receiving / emitting surface 13a of the photoelectric conversion element 13 mounted on the upper surface.
However, considering the processing limit of the mirror surface 14 and the end face 12c of the optical waveguide 12, the end face 12c of the optical waveguide 12 (center portion)
The shortest distance between the mirror surface 14 and the horizontal distance L is about 22 μm.

On the other hand, when the light propagating in the optical waveguide 12 is approximated by a Gaussian beam, the beam diameter ω of the light emerging from the end face 12a of the optical waveguide 12 is ω ₀ in the optical waveguide 12 and λ _{0 in} the incident wavelength. , When the horizontal distance is L, the equation ω = λL / 2ω
_{From 0} , it is calculated to have a spread of about ± 5 degrees. In order for the dispersed and spread light to hit the mirror surface 14 and the light reflected by the mirror surface 14 to be incident on the light emitting / receiving section 13a of the photoelectric conversion element 13 mounted on the substrate 11, the end face 12 of the optical waveguide 12 is required.
It is desirable that the horizontal distance L between c (center) and the mirror surface 14 be about 40 μm or less. On the other hand, when the horizontal distance L is 40
If the value is larger than μm, the spread light will escape to the air layer on the substrate 11 without reaching the mirror surface 14, or will be incident on the substrate 11 side and diffusely reflected, resulting in a large loss. . Therefore, it is desirable that the horizontal distance L between the end surface 12c (center portion) of the optical waveguide 12 and the mirror surface 14 be in the range of about 22 to 40 μm.

As the photoelectric conversion element 13 mounted on the substrate 11 and located above the mirror surface 14 and having a light receiving / emitting surface 13a on the lower surface, for example, there is a photodiode or the like. The distance between the light receiving / emitting surface 13a of the photoelectric conversion element 13 and the mirror surface 14 is such that light emitted from the end surface 12c of the optical waveguide 12 and dispersed and spread into the resin 15 hits the mirror surface 14 and is reflected by the mirror surface 14. It is necessary to design a structure to be incident on the light receiving / emitting surface 13a of the photoelectric conversion element 13 mounted thereon, but the light reflected by the mirror surface 14 has a spread when it exits from the resin 15 to the air layer.
The extent of this spread depends on the magnitude of the difference in the refractive index between the resin 15 and the air layer.
In consideration of the above-mentioned ranges of the respective parameters, the upper surface of the mirror surface 14 indicated by D in FIG. 1 (the upper surface of the resin 15 positioned above the mirror surface 14) must be considered. Surface) to the light receiving / emitting surface of photoelectric conversion element 13
It is desirable that the distance to 13a is set within a range of about 0 to 20 μm.

Next, in the optical connection structure of the present invention, the two optical waveguides 12 are disposed such that their light transmission directions are at 90 degrees and their end faces 12c are adjacent to each other.
FIG. 2 is a plan view showing an example in which two mirror surfaces 14 adjacent to each other at 90 degrees are formed so as to face c. FIG. 2 shows a state before the resin 15 is filled and the photoelectric conversion element is removed, and the same portions as those in FIG. 1 are denoted by the same reference numerals.

According to the example shown in FIG. 2, the filling portion filled with the resin 15 is formed such that the angle θ _{1 of the} two optical waveguides 12 arranged so that the light transmission direction of each other is 90 degrees is an acute angle. The end faces 12c form slopes, respectively, and the two optical waveguides
The mirror surfaces 14 facing each other are arranged adjacent to each other so as to be at 90 degrees to each other, and are formed as square holes having a tapered surface so as to form a slope.

Such a square hole is, for example, an optical waveguide
12 and the mirror surface support 17 of the mirror surface 14
Formed of a material that forms a 12b, when setting the angle θ ranges are also from 30 to 60 degrees _first end surface 12c of the light guide 12 and an end surface 12c and the specular 14 of the optical waveguide 12 with respect to the upper surface of the substrate 11 By performing simultaneous processing by the above-described RIE or the like so as to form an inclined surface having an angle of 30 to 60 degrees, it is possible to form easily and accurately.

By processing a rectangular hole having a tapered surface as shown in FIG. 2, the processing of the end surface 12c and the mirror surface 14 of the optical waveguide 12 in two directions can be performed at one time. The number of steps in manufacturing a circuit board for mounting a conversion element can be reduced.

Further, a mirror surface support for the optical waveguide 12 and the mirror surface 14
When the same material is used for the light guide 17 and the mirror 17 at the same time, the alignment between the end face 12c of the optical waveguide 12 and the mirror surface 14 can be easily performed without worrying about shifting in the height direction or right and left.

After a predetermined square hole is formed and a mirror surface 14 is formed by applying a metal film, a square is formed with a resin 15 having substantially the same refractive index as the core portion 12a, for example, a siloxane polymer doped with TiO _2. A circuit board for an optical module is obtained by filling the holes and forming electrode pads and the like for surface-mounting the photoelectric conversion element 13 as necessary by forming and patterning a metal film such as aluminum. be able to.

In the above example, the angle θ ₁ of the end face 12 c of the optical waveguide 12 is set in the range of 32 to 162 degrees,
If it is different from ₂ , the end face 12c of the optical waveguide 12
It goes without saying that the mirror surface 14 and the mirror surface 14 may be processed and formed under different conditions and steps.

The present invention is not limited to the above-described embodiment, and various modifications and improvements can be made without departing from the scope of the present invention. For example,
In FIG. 2, the two optical waveguides are connected with each other in a light transmission direction.
Although the optical connection structures are shown to be 90 degrees, they may be set at an arbitrary angle to form a slope corresponding to the optical waveguide and a mirror surface facing the optical waveguide.

[0052]

According to the present invention, the end face and the mirror surface of the optical waveguide formed facing the upper surface of the substrate are inclined at 32 to 162 degrees and 30 to 60 degrees with respect to the upper surface of the substrate, respectively. Dust adheres and propagates on the mirror surface when the photoelectric conversion element is surface-mounted above the mirror surface because resin between the end face of the waveguide and the mirror surface is filled with a resin having the same refractive index as the core of the optical waveguide. While preventing light from being scattered by dust and causing attenuation of light due to reflected light, the light propagating between the end surface of the optical waveguide and the mirror surface is reduced in scattering as compared with the case where the light propagates through the air layer. Optically good connection with the conversion element can be achieved. Further, it is possible to suppress the reflection of the light propagating in the optical waveguide or the light incident on the optical waveguide on the end face of the optical waveguide, and to efficiently input and output the light to and from the photoelectric conversion element.

Further, by simultaneously processing the end face and the mirror surface of the optical waveguide, it is possible to simultaneously process the end face and the mirror surface of the optical waveguide in two directions, for example, and to easily and accurately align them. And the number of steps in manufacturing a circuit board for an optical module or the like can be reduced.

As described above, according to the present invention, it is possible to prevent the scattering of light on the end face of the optical waveguide and the adverse effect due to the adhesion of dust to the mirror surface, and the optical waveguide formed on the upper surface of the substrate and the photoelectric device mounted on the substrate. It is possible to provide an optical connection structure that can efficiently optically connect the conversion element via a mirror surface and that can be manufactured more easily and more accurately than a conventional optical connection structure.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of an embodiment of an optical connection structure of the present invention.

FIG. 2 is a plan view showing another example of the embodiment of the optical connection structure of the present invention.

FIG. 3 is a cross-sectional view showing an example of a conventional optical connection structure.

[Explanation of symbols]

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End face 13: Photoelectric conversion element 13a: Light receiving / emitting surface 14: Mirror surface 15: Resin

Claims (1)

[Claims] 1. A photoelectric conversion element having an optical waveguide formed on an upper surface of a substrate and comprising a cladding portion and a core portion in the cladding portion, and a light receiving portion or a light emitting portion on a lower surface mounted on the substrate. And an optical connection structure formed on the upper surface of the substrate and optically connected to a light receiving portion or a light emitting portion of the photoelectric conversion element via a mirror surface facing the light receiving portion or the light emitting portion below the optical waveguide. The end surface and the mirror surface of the optical waveguide are inclined at 32 to 162 degrees and 30 to 60 degrees with respect to the upper surface of the substrate, respectively, and the optical waveguide is disposed between the end surface of the optical waveguide and the mirror surface. An optical connection structure characterized by being filled with a resin having substantially the same refractive index as the core portion.