JPWO2007111327A1 - OPTICAL TRANSMISSION BOARD, MANUFACTURING METHOD THEREOF, AND OPTICAL TRANSMISSION DEVICE - Google Patents

Abstract

In an opto-electric hybrid circuit board, the coupling efficiency between an optical element and an optical waveguide through a through-hole penetrating the board is increased, thereby enabling accurate and highly efficient optical signal transmission. It has a substrate 2 provided with a through hole 2c as an optical path of signal light between two main surfaces 2a and 2b, and an optical transmission body 1 provided between both end openings 2d1 and 2d2 of the through hole. A high refractive index portion including at least one high refractive index portion 1a1, 1a2 having a first refractive index and at least one low refractive index portion 1b having a second refractive index smaller than the first refractive index; And the low refractive index portion are formed in the vicinity of at least one opening, and the low refractive index portion side is made concave in the optical axis direction of the signal light, thereby condensing the signal light.

Description

  The present invention relates to an optical transmission circuit having a through hole in which an optical transmission body for optically connecting the front surface and the back surface of a substrate is formed in a substrate for an opto-electric hybrid circuit constituting an electrical signal wiring and an optical signal wiring in an electronic device. The present invention relates to a substrate, a manufacturing method thereof, and an optical transmission device.

In order to increase the amount of processing in information processing and improve the processing speed, the operating speed of the semiconductor device and the number of signal input / output terminals tend to increase in the future. At the same time, the number of signal wirings on the circuit board on which the semiconductor device is mounted has increased remarkably, and the wiring density tends to increase.
Along with this, signal attenuation in the electrical wiring formed on the circuit board and crosstalk between adjacent wirings remarkably increase, which is a serious problem. In particular, in a large-scale semiconductor integrated circuit typified by a microprocessor, it is a big problem to stably input and output signals at a GHz level with low power consumption.

In order to solve this problem, an optical transmission technique in which an electrical signal input to and output from a semiconductor device is converted into an optical signal and the optical signal is transmitted through an optical wiring such as an optical waveguide formed on a circuit board is being studied. .
In optical transmission technology using optical wiring, not only optical waveguides formed on the front and back surfaces of circuit boards, but also signal signal transmission paths using through holes provided between the front and back surfaces of circuit boards are proposed. Has been. Such a transmission path is formed, for example, by filling a hole penetrating the circuit board perpendicular to the optical waveguide with a transparent resin. By using the through-hole as the optical path of the signal light, an optical transmission board capable of three-dimensional transmission of optical signals can be configured as in the conventional electric wiring board. Since the optical transmission board is usually in a form in which electric wiring is also mixed, it is more generally referred to as an opto-electric hybrid circuit board.

FIG. 7 is a schematic diagram showing a representative example of a conventional opto-electric hybrid circuit board having a through hole for an optical path (for example, disclosed in Patent Document 1). FIG. 7A is an overall cross-sectional view of the optical transmission board, and FIG. 7B is an enlarged cross-sectional view of the optical path through hole.
As shown in FIG. 7A, surface light emitting / receiving elements 103a and 103b are mounted on one surface of the substrate 102, and an optical waveguide 104 is formed on the other surface of the substrate. On the two end faces of the optical waveguide 104, 45 degree micromirrors 105a and 105b are formed. The surface light emitting / receiving elements 103a and 103b and the optical waveguide 104 are optically coupled by optical path through holes 101a and 101b penetrating the substrate 102, respectively.

As shown in FIG. 7B, the optical path through-holes 101a and 101b have a clad portion 111 made of a conductor layer formed on the inner wall thereof by plating, and a core portion made of transparent resin or air filled in the internal space. 112.
In the example of FIG. 7, the signal light incident on the optical path through hole is totally reflected and propagated at the interface between the clad portion 111 and the core portion 112, whereby the surface light emitting / receiving elements 103 a and 103 b and the optical waveguide 104 are transmitted. It has been proposed that each be optically connected.

Next, FIG. 8 is a schematic sectional view showing another representative example of a conventional opto-electric hybrid circuit board having a through hole for an optical path (for example, disclosed in Patent Document 2).
As shown in FIG. 8, a planar light emitting element 203A is mounted on a substrate 202A, and an optical path through hole 201A is formed in a direction opposite to the light emitting point. Below the optical path through-hole 201A, another substrate 202B is disposed at a predetermined interval (electrically connected via the solder connection portion 205C). An optical waveguide 204B is formed on the surface of another substrate 202B. Further, the end surface of the optical waveguide 204B is located immediately below the lower end opening of the optical path through hole 201A and is an optical path conversion mirror 205B. A similar optical path configuration has been proposed for a light receiving element that receives signal light.

Further, in the example of FIG. 8, a micro lens 206A is disposed at the end of the gap 208A between the opening of the optical path through hole 201A and the surface light emitting element 203A. The micro lens 206A has a function of condensing the signal light and can reduce a transmission loss of the signal light. It has been proposed that the microlens 206A is formed by bonding and fixing an optical lens or by dropping a resin for an optical lens and curing it to a hemisphere by surface tension.
JP 2000-81524 A JP 2002-329891 A

  However, in the conventional example of FIG. 7 disclosed in Patent Document 1, the coupling efficiency of optical coupling between the optical path through holes 101a and 101b and the surface light emitting / receiving elements 103a and 103b is not sufficient as described below. In the conventional example of FIG. 7, when the diameter of the core portion 112 of the optical path through hole 101a is equal to or larger than the diameter of the light receiving surface of the surface light emitting and receiving element 103a, the optical path through hole 101a passes through the optical path through hole 101a. Since the signal light that reaches the surface light emitting / receiving element 103a while being diffused is naturally larger than the diameter of the light receiving surface, the amount of light that is lost without being received increases.

When the surface-emitting light-emitting / receiving element 103b is a light-emitting element, for example, a general surface-emitting laser (VCSEL), the half-value full angle of 20 to 30 degrees larger than the total reflection 10 degrees shown in the embodiment of Patent Document 1 is used. The light is emitted toward the optical path through hole 101b through the air layer with a spread. And when the core part of the through-hole 101b for optical paths is comprised with transparent resin, it propagates by the angle slightly reduced only by the difference of the relative refractive index with air, and when the core part is air, it remains at that angle Propagate while totally reflecting the core.
After that, when reaching the lower cladding of the optical waveguide 104, it diffuses again and reaches the core of the 45 degree micromirror 105b. Since the 45 degree micro mirror 105b totally reflects while maintaining the angle, most of the reflected light is emitted to the upper and lower cladding layers.
Therefore, the conventional example of FIG. 7 is a configuration in which the effect is exhibited by a combination in which the diameter of the core portion of the through hole for the optical path is smaller than the diameter of the light receiving surface of the surface light emitting and receiving element. Attenuation increases. Therefore, there is a problem that the limitation on the combination or the size of the through hole for the optical path and the surface light emitting / receiving element becomes large.

Next, the conventional example shown in FIG. 8 disclosed in Patent Document 2 has a problem in optical coupling between the optical path through hole 201A and the optical waveguide 204B.
First, in the conventional example shown in FIG. 8, the emitted light from the lower end opening of the optical path through-hole 201A made of a resin composition diffuses in the propagation direction, and the beam diameter increases as the propagation distance increases. This is difficult to avoid in terms of material since the refractive index of the resin composition is usually about 1.4 to 1.6 and higher than the refractive index 1 of air. In the configuration in which the diffused light is incident on the optical waveguide 204B with a predetermined interval as shown in FIG. 8, only a part of the light is transmitted unless the cross-sectional size of the optical waveguide is considerably increased with respect to the spread beam diameter. Does not enter the waveguide. If the cross-sectional size of the optical waveguide is increased, the propagation mode increases. However, since the mode dispersion increases, the transmission band of the optical waveguide is limited.

  Further, in Patent Document 2, by forming the micro lens 206A, it is possible to condense emitted light from the lower end opening of the optical path through hole 201A toward the optical waveguide 204B as compared to the case without the micro lens 206A. It has been proposed that higher coupling efficiency can be expected. However, for this purpose, it is necessary to align the through hole 201A for the optical path and the optical waveguide 204B with sufficiently high accuracy. In general, a circuit board has a size of several tens of millimeters to several centimeters, and is at most an order of magnitude larger than a light emitting element or a light receiving element that is several mm square at most. . For this reason, it becomes difficult to accurately position and join the circuit boards and hold them. For example, when the optical waveguide 204B is a multimode optical waveguide having a cross section of 30 to 100 μm square, the positioning and joining accuracy between the emitted light and the optical waveguide is required to be on the order of μm. It is extremely difficult to position and bond circuit boards having a size of several tens of millimeters to several centimeters with high accuracy. Therefore, even when the light is condensed by the micro lens 206A, the structure in which the emitted light is incident on the optical waveguide on another substrate cannot realize high-efficiency optical coupling.

  In addition, as shown in FIG. 8, the microlens 206A of Patent Document 2 includes an optical signal transmission optical path 210A formed by an optical path through hole 201A filled with a resin composition and an air gap 208A (gap 208A). The outer periphery of the microlens 206A is joined to the edge of the solder resist layer 209A (paragraph 0071 of Patent Document 2). Thus, when providing in the edge part of the space | gap 208A, an optical lens must be attached with an adhesive agent (patent document 2 paragraph 0139). However, it is very difficult to ensure the positioning accuracy so that the optical axis of the optical lens matches the optical axis of the optical signal transmission optical path 210A.

  Further, in Patent Document 2, the micro lens 206A may be inside the optical signal transmission optical path 210A formed by the optical path through hole 201A filled with the resin composition and the gap 208A. However, the inside of the optical signal transmission optical path 210A in Patent Document 2 is an end portion of the resin composition filled in the optical path through-hole 201A (Patent Document 2, paragraph 0073). In any embodiment, this resin composition is completely filled between the openings at both ends. Therefore, although not shown in Patent Document 2, the micro lens 206A provided at the end of the resin composition protrudes outward from the opening surface of the optical path through hole 201A, that is, the surface of the substrate 202A. This is clear from the disclosed manufacturing method. According to the manufacturing method, the lens resin is dropped into the opening of the optical path through-hole 201A filled with the resin composition, and is cured into a hemisphere by surface tension (Patent Document 2, Paragraph 0140). . Therefore, when dropping the lens resin, it is very difficult to ensure positioning accuracy so that the optical axis of the microlens coincides with the optical axis of the optical path for optical signal transmission.

  As described above, Patent Document 2 discloses that a microlens having a condensing function is provided in order to reduce optical transmission loss, but the installation location is the end of an optical path for transmitting an optical signal. Regardless of whether it is inside or not, a technique for providing the optical axis of the microlens and the optical axis of the signal light so as to coincide with each other with accuracy is not presented, and this is not sufficient as a practically usable technique.

  As described above, in the optical path through hole proposed in the prior art, in the optical coupling between the light emitting element and the light receiving element that penetrates the substrate and the optical waveguide, the spread of the outgoing light beam after penetrating the substrate The problem of causing optical transmission loss due to the above, the problem of high accuracy positioning with an optical waveguide on another substrate even if light is collected using a lens, and the high accuracy positioning of the lens itself are also difficult The problem is not fully resolved. As a result, a high amount of combined light cannot be obtained, and accurate and highly efficient optical signal transmission cannot be realized.

  In the present invention, by solving the above-described problem, the optical waveguide formed on one main surface of the substrate and the light-emitting element or the light-receiving element mounted at a position penetrating the substrate are opposed to each other or the substrate faces each other. An object of the present invention is to improve the optical coupling efficiency in the coupling between the optical waveguides respectively provided on the two main surfaces. It is another object of the present invention to provide a substrate manufacturing method with improved optical coupling efficiency and an optical transmission device in which a light emitting element and / or a light receiving element are mounted on the substrate.

The present invention provides the following configurations to achieve the above object.
(1) An optical transmission board according to the present invention is a board in which a through hole is provided as an optical path of signal light between two main surfaces, and an optical transmission body provided between both ends of the through hole. At least one high refractive index portion having a refractive index of and at least one low refractive index portion having a second refractive index smaller than the first refractive index, and the high refractive index portion and the low refractive index portion. A light transmitting body for condensing the signal light by forming a joint surface with the refractive index portion in the vicinity of at least one opening and making the low refractive index portion concave in the optical axis direction of the signal light. Have.

(2) In addition to the above, the optical transmission substrate is formed by disposing the high refractive index portions at both ends of the low refractive index portion, thereby forming the joint surfaces in the vicinity of the both end openings, respectively. .

(3) In addition to the above, the optical transmission board is formed by disposing the low refractive index portions at both ends of the high refractive index portions, respectively, and forming the joint surfaces in the vicinity of the openings at both ends. .
(4) In addition to the above, when the optical transmission board has the vicinity of the opening of the through-hole forming the joint surface and the propagation direction of the signal light is changed by the joint surface, the condensing point is the through-hole. It is a position which becomes the outside.

(5) In addition to the above, the optical transmission board has a coefficient of thermal expansion within the range of 80 to 120% of the coefficient of thermal expansion of the board.

(6) In addition to the above, the optical transmission board further includes an optical waveguide provided on the main surface including at least the opening on the signal light emission side and optically coupled to the optical transmission body. is there.

(7) A multilayer optical transmission board according to the present invention is obtained by laminating a plurality of the above optical transmission boards.

(8) An optical transmission device according to the present invention is an optical semiconductor device provided on any one of the main surfaces of at least one of the optical transmission substrate and the optical transmission substrate and optically coupled to the optical transmission body. It has.

(9) In the method of manufacturing an optical transmission board according to the present invention, the low refractive index having the second refractive index is obtained by filling a transparent resin in a molten state in a through hole of the board and forming a recess by curing shrinkage. A step of providing a refractive index portion, and filling the through-hole in a molten state with a transparent resin so as to be in contact with the concave portion of the low refractive index portion, and curing the high refractive index having the first refractive index. A step of providing a portion.

(10) A composite optical transmission board according to the present invention includes a first board that is the optical transmission board according to any one of claims 1 to 5, and a second board that is arranged in parallel with the first board. And an optical waveguide provided on a main surface of the second substrate facing the first substrate and optically coupled to the optical transmission body on the first substrate.

  The optical transmission board of the present invention has an optical transmission body in which at least one high refractive index portion and at least one low refractive index portion are formed in a through-hole penetrating the substrate. In this optical transmission body, a joint surface of a high refractive index portion and a low refractive index portion is formed in the vicinity of at least one opening of the through hole, and this joint surface is on the low refractive index portion side in the optical axis direction of the signal light. It is a refractive index interface which becomes a concave shape. This refractive index interface plays the same role as the lens surface. That is, the signal light propagating through the optical transmission body receives a condensing action so as to approach the optical axis at this refractive index interface. Therefore, the signal light incident on the optical transmission body from the opening in the vicinity of the joint surface is propagated through the optical transmission body with its spreading angle reduced. Further, the signal light emitted from the optical transmission body at the opening in the vicinity of the joint surface is emitted from the optical transmission body with its spreading angle reduced.

As a result, when a light-emitting element or light-receiving element is mounted on one main surface of the substrate, and an optical path conversion mirror whose end is processed at 45 degrees is provided on the other main surface, the light receiving element is received in addition to the thickness of the substrate. At the same time as securing a necessary distance between the light emitting element and the substrate surface, it becomes possible to condense the signal light in the optical axis direction in the optical coupling between the light emitting / receiving element and the optical path conversion mirror.
That is, in the configurations of Patent Documents 1 and 2 described above, a large amount of loss occurs in optical coupling with the light emitting / receiving element or the optical waveguide because the signal light diffuses, but according to the present invention, in the same optical coupling. A sufficiently high efficiency can be easily realized.
For example, the amount of light entering and propagating into the optical waveguide formed on the substrate and the amount of light entering the light receiving element after propagating through the optical waveguide on the substrate naturally increase. This facilitates signal light processing and enables highly efficient optical signal transmission.
Eventually, the operation of the opto-electric hybrid circuit including the optical circuit is stabilized, and a long life can be realized by reducing excess energy consumption.

In addition, since the optical transmission body of the optical transmission board of the present invention is provided between the openings at both ends of the board, the refractive index interface is always located inside the through hole. Therefore, it is easy to make the optical axis of the refractive index interface as the lens surface coincide with the axial direction of the through hole. This is because there is no displacement in the direction parallel to the substrate.
On the other hand, in Patent Document 2 described above, since the lens is provided outside the both end openings of the optical path through hole filled with the resin composition, it is extremely difficult to match the axial direction of the optical path through hole with the optical axis of the lens. Have difficulty. In Patent Document 2, it is assumed that the lens is formed by adhesion or dripping hardening of a resin material. However, such a forming method tends to cause a positional shift in a direction parallel to the substrate.

Furthermore, since the optical transmission board of the present invention has bonding surfaces near both ends of the optical transmission body, signal light is collected both immediately after entering the optical transmission body and immediately before exiting from the optical transmission body. Due to the light action, the coupling loss can be further reduced.
Furthermore, the optical transmission board of the present invention maintains the integrity of the optical transmission body and the substrate against temperature fluctuations by substantially matching the thermal expansion coefficient of the optical transmission body and the thermal expansion coefficient of the substrate. Can do.

  Furthermore, in the optical transmission board of the present invention, when the optical waveguide is provided on the main surface including the opening on the signal light emission side, the optical waveguide is provided on another substrate as described in Patent Document 2 described above. Compared to the case, the positioning accuracy in the optical coupling with the signal light incident side can be easily ensured. In particular, since the optical waveguide is processed using a photomask process capable of forming a pattern with high accuracy on the order of μm, it can be formed with sufficiently high positional accuracy with respect to the through hole for the optical path.

Furthermore, the multilayer optical transmission board of the present invention can improve the optical transmission efficiency between the two principal surfaces even if it is a thick multilayer board by laminating a plurality of optical transmission boards of the present invention. An opto-electrical wiring mixed circuit board to be applied to the application can be configured.
Furthermore, the optical transmission device of the present invention has an optical element mounted on the optical transmission substrate of the present invention, so that the light emitted from the light emitting element and / or the light incident on the light receiving element passes through the optical transmission body. The light transmission efficiency can be increased by reducing the divergence angle.

  Furthermore, in the method for manufacturing an optical transmission substrate of the present invention, a transparent resin having a low refractive index is filled in a through-hole in a molten state, and a concave portion is formed by curing shrinkage to provide a low refractive index portion. Since the recess is naturally formed by the surface tension between the transparent resin and the inner wall of the through hole, the center of the recess can be positioned on the axis of the through hole without performing an artificial process. Further, a transparent resin having a high refractive index is filled in the through-hole in a molten state so as to be in contact with the concave portion of the low refractive index portion, and cured to provide a high refractive index portion. According to this manufacturing method, the axial direction of the through hole and the optical axis direction of the optical transmission body naturally coincide with each other. Accordingly, unlike the case where the lens is formed by dripping and curing the resin on the outside of the optical path through-hole as disclosed in the above-mentioned Patent Document 2, it is not necessary to position the lens in a direction parallel to the substrate.

  Furthermore, the composite optical transmission board of the present invention uses the optical transmission board provided with the above optical transmission body as the first board, and arranges the second board in parallel with the first board, and one of the second boards. An optical waveguide is provided on the main surface. In the composite optical transmission board of the present invention, an optical waveguide is provided on the second substrate as in Patent Document 2, but in Patent Document 2, the optical axis of the lens and the axis of the through hole coincide with each other in the first substrate. However, in the present invention, the optical axis of the refractive index interface that is the lens surface and the axis of the through hole can be easily matched in the first substrate. Therefore, the optical transmission efficiency can be improved even in the composite optical transmission substrate including two substrates, and an opto-electric wiring mixed circuit substrate applied to various applications can be configured.

Hereinafter, embodiments of an optical transmission board according to the present invention will be described with reference to the drawings.
FIG. 1 is a partial sectional view showing a schematic configuration of a first embodiment of an optical transmission board according to the present invention. In FIG. 1, the thick line schematically shows the signal light 7 and the broken line schematically shows the optical axis A.
In FIG. 1, a through hole 2 c is provided between two main surfaces 2 a and 2 b of a substrate 2 (here, meaning a substrate base material portion) perpendicular to these main surfaces. The through hole 2c serves as an optical path for signal light that couples the two main surfaces by forming the optical transmission body 1 in the internal space. The axial direction of the through hole 2 c is the direction of the optical axis A of the optical transmission body 1. Both end openings 2d1 and 2d2 of the through-hole 2c are located on the respective main surfaces, and the optical transmission body 1 is formed by filling a predetermined resin between these both end openings.

  The optical transmission body 1 includes high refractive index portions 1a1 and 1a2 having a first refractive index n1, and a low refractive index portion 1b having a second refractive index n2 smaller than the first refractive index n1. Typically, the high refractive index portion and the low refractive index portion are each made of a transparent resin having an appropriate refractive index. The comparison of the refractive indexes of the high refractive index portion and the low refractive index portion can be performed, for example, by refractive index distribution measurement by a refractive near field (RNF) method. Specifically, in the case of FIG. 1, the optical transmission body 1 is cut so as to include the central axis of the cylindrical optical transmission body 1, and the optical transmission body 1 is further divided into high refractive index portions 1a1, 1a2 and low refractive index. The refractive index distribution can be measured by cutting into the rate part 1b and measuring them using, for example, OWA-9500 manufactured by Optoscience. In the example of FIG. 1, a low refractive index portion 1b is disposed in the middle along the axial direction of the through hole 2c, and two high refractive index portions 1a1, 1a2 are disposed at both ends thereof. The ends of the high refractive index portions 1a1 and 1a2 form flat surfaces located at both end openings 2d1 and 2d2 of the through hole 2c, respectively.

The joint surface 1c1 between the high refractive index portion 1a1 and the low refractive index portion 1b and the joint surface 1c2 between the high refractive index portion 1a2 and the low refractive index portion 1b inside the optical transmission body 1 are respectively open at both end openings 2d1 and 2d2. The curved surface is formed in the vicinity and has a concave shape on the low refractive index portion 1b side in the direction of the optical axis A of the signal light. In other words, the high refractive index portions 1a1, 1a2 are convex curved surfaces. Here, the curved surface means a surface that is at least partially curved. Further, the low refractive index portion 1b side being concave means that when the optical transmission body is cut so as to include the central axis of the columnar optical transmission body 1, the high refractive index portion 1a1 and the low refractive index portion in the cross section thereof. The boundary line with 1b as a whole (for example, when observed at a scale such that the width of the optical transmission body 1 is within the field of view of a scanning electron microscope or an optical microscope), the boundary line has a low refractive index. It means that it is protruding to the club side.
The cemented surfaces 1c1 and 1c2 are refractive index interfaces and have the same function as the lens surface. Since these joint surfaces 1c1, 1c2 are always located inside the through hole 2c, it is easy to make the optical axis A of the lens surface coincide with the axial direction of the through hole 2c. On the other hand, in the above-mentioned Patent Document 2, positioning is difficult because lenses are provided outside both end openings of the optical path through hole filled with the resin composition.

  Each layer of the electrode 8 and the solder resist 9 is formed on one main surface 2a of the substrate 2 (this surface is referred to as “surface” for convenience of description).

  By providing a light emitting element or light receiving element 3 (hereinafter referred to as “optical element”) on the surface of the substrate 2, the optical transmission substrate functions as an optical transmission device. The optical element 3 is arranged at a predetermined interval immediately above the opening 2d1 of the through hole 2c, and the light emitting point or the light receiving point is located on the optical axis A of the optical transmission body 1. The terminals of the optical element 3 are bonded to the electrode 8 by a conductive bonding material 5 such as a stud bump, a solder ball, or a conductive resin, and mounted on the substrate 2. Thereby, the photoelectric conversion operation of the optical element 3 becomes possible.

  A gap 6 exists between the optical element 3 and the high refractive index portion 1a1. The gap 6 is air in the example of FIG. 1, but may be filled with an appropriate transparent resin. When the gap 6 is air, the refractive index is naturally smaller than that of the high refractive index portion 1a1, but when the gap 6 is filled with a transparent resin, the refractive index is preferably sufficiently smaller than that of the high refractive index portion 1a1.

  Furthermore, an optical waveguide 4 is provided on the other main surface 2b of the substrate 2 (for convenience of explanation, this surface is referred to as a “back surface”). The optical waveguide 4 is composed of a layered lower clad 4b, a core 4a having a rectangular cross section, and a layered upper clad 4c in order from the substrate 2 side, and its end face is approximately 45 degrees with respect to the axial direction of the optical waveguide 4. The processed optical path conversion mirror 4d is formed. The optical path conversion mirror 4d is located immediately below the opening 2d2 of the through hole 2c, and is arranged so that the core 4a is located on the optical axis A of the optical transmission body 1.

Optical transmission in the optical transmission board or optical transmission apparatus of FIG. 1 configured as described above is performed as follows.
When the optical element 3 is a light emitting element (for example, a surface emitting laser (VCSEL)), the signal light 7 emitted from the light emitting point spreads radially in the gap 6 and is highly refracted by the optical transmission body 1 at the opening 2d1 of the through hole 2c. It enters the rate part 1a1. At that time, the signal light 7 is refracted so as to approach the optical axis A according to the relative refractive index difference between the air or resin existing in the gap 6 and the high refractive index portion 1a1, and the spread angle is narrowed.
Next, the signal light 7 passes through the joint surface 1c1 between the high refractive index portion 1a1 and the low refractive index portion 1b and enters the low refractive index portion 1b. The joint surface 1c1 has a substantially circular cross section, that is, a three-dimensional curved surface. Therefore, the light incident on the low refractive index portion 1b side from the high refractive index portion 1a1 side is refracted so as to be closer to the optical axis A according to the curved surface shape of the joint surface 1c1 and the relative refractive index difference, and the divergence angle. Narrows.
As described above, the effect of narrowing the divergence angle of the signal light can be obtained even when the light is incident on the high refractive index portion inside the light transmitting body 1 from the outside of the light transmitting body 1 and further enters the low refractive index portion. Therefore, this case is also referred to as “condensing”.

The signal light 7 that has propagated through the low refractive index portion 1b is incident on another high refractive index portion 1a2, but as in the first case, the optical axis A depends on the curved surface shape of the joint surface 1c2 and the relative refractive index difference. Are collected.
The signal light 7 enters the lower clad 4b of the optical waveguide 4 from the high refractive index portion 1a2 at the opening 2d2 of the through hole 2c. Also at this time, the light is further condensed with respect to the optical axis A according to the relative refractive index difference with the lower clad 4b of the optical waveguide, passes through the lower clad 4b, and enters the core 4a. Thereafter, the signal light 7 is reflected by the optical path conversion mirror 4d, and the optical path is converted by approximately 90 degrees, and propagates in the axial direction of the core 4a of the optical waveguide 4.

  As described above, the signal light 7 emitted from the light emitting element mounted on the surface of the substrate 2 propagates while condensing in the optical transmission body 1 formed between the openings at both ends of the substrate 2, and finally the substrate 2. It reaches the optical waveguide 4 formed on the back surface of the light, and further propagates after the optical path conversion. The light condensing action at the joint surfaces 1c1, 1c2 and the both end openings 2d1, 2d2 inside the optical transmission body 1 corrects the spread of the outgoing light from the light emitting element 3 and the spread of the outgoing light from the optical transmission body 1, thereby reducing transmission loss. Is reduced.

  Here, the position of “the vicinity of the opening at both ends” of the through-hole 2c in which the joint surfaces 1c1 and 1c2 are respectively provided is changed in the propagation direction of the signal light by the joint surfaces 1c1 and 1c2, and the condensing point thereof is the through-hole 2c. A position that is on the outside.

  In addition, although not shown in figure, as another embodiment, it is good also as an optical transmission body which provided only any one among the high refractive index parts 1a1 and 1a2 of the form of FIG. The end of the optical transmission body on the side where the high refractive index portion is not provided is a low refractive index portion up to the through hole opening surface. Therefore, there is only one joint surface between the high refractive index portion and the low refractive index portion. In this case, the above-described light condensing action can be obtained at the through hole opening surface on the side where the high refractive index portion is provided and one joint surface.

2A to 2E are partial cross-sectional views showing an example of the method of manufacturing the optical transmission board of the present invention shown in FIG. 1 in the order of steps.
As shown in FIG. 2A, an electrode layer 8 and a solder resist layer 9 are formed on the surface 2a of the substrate 2 by a known photolithography process or etching process according to the circuit and the mounting structure. Note that an electrode layer and a solder resist layer may also be formed on the back surface 2b in places other than the optical waveguide provided in a later step. The substrate 2 is not limited to a printed wiring board, and may be a ceramic wiring board using alumina or the like as an insulating layer inside the board, or a board in which electric wiring is formed on silicon, glass, or the like. A general-purpose glass epoxy wiring board may be used. Note that a multilayer substrate in which electrical wiring layers and insulating layers are alternately stacked may be used as the substrate 2, and the electrical wiring layer may be formed inside the substrate 2.
Furthermore, a through hole 2c that penetrates the substrate 2 is provided at a position facing a light emitting point or a light receiving point of an optical element that is installed in a later step. A drill or a laser is used for processing the through hole 2c. The diameter is usually 100 to 200 μm.

Next, as shown in FIG. 2 (b), the surface 2a of the substrate 2 is disposed vertically upward, and the low refractive index transparent resin 1b ′ having the second refractive index n2 is inserted into the through hole 2c using a syringe or the like. Dripping into. In order to completely fill the inside of the through-hole 2c with the low refractive index transparent resin 1b ′, it is desirable to drop it until it rises outside the opening 2d1 on the surface side.
As the low refractive index transparent resin 1b ′, polysilane (refractive index of about 1.6), acrylic (refractive index of about 1.5), epoxy (refractive index of about 1.5) (provided as materials for optical waveguides) ( In any case, a resin material having a wavelength of 850 nm can be used, and a relatively low refractive index material used for the cladding is preferable. The viscosity at the time of dropping these transparent resin materials is preferably 1000 to 2000 (mP · s). If it is the viscosity of this range, it does not flow out of the through-hole 2c, or does not permeate into the through-hole 2c, but penetrates into the through-hole 2c without a gap and reaches the opening 2d2 on the back surface side. And the end surface which exists on the same plane as the back surface 2b of the board | substrate 2 is formed with low refractive index transparent resin 1b '.

  Subsequently, as shown in FIG. 2 (c), the low refractive index transparent resin raised on the surface 2a by pressing the end of the thin plate-shaped tool against the surface 2a of the substrate 2 and moving it parallel to the substrate surface. Remove 1b '. By this operation, an end surface which is on the same plane as the surface 2a of the substrate 2 is formed of the low refractive index transparent resin 1b '. Then, the whole board | substrate 2 is heated from the state of FIG.2 (c), and low refractive index transparent resin is hardened.

  After curing, as shown in FIG. 2 (d), the low refractive index transparent resin 1b 'becomes a curved surface 1c1', 1c2 'having concave concave ends due to shrinkage during heat curing. Since these concave shapes are determined by the surface tension of the low refractive index transparent resin 1b 'with respect to the inner wall of the through hole 2c, normally the center point of the concave shape is naturally determined on the axis of the through hole 2c. The curvature of the concave shape can be adjusted by the viscosity of the low refractive index transparent resin 1b '. Thus, the low refractive index portion 1b is formed.

Subsequently, as shown in FIG. 2E, a high refractive index transparent resin is dropped on the concave curved surfaces 1c1 ′ and 1c2 ′ formed in FIG. As the high refractive index transparent resin, polysilane (refractive index of about 1.6), acrylic (refractive index of about 1.5), epoxy (refractive index of about 1.5), which are provided as materials for optical waveguides (all A resin material having a wavelength of 850 nm can be used, and a relatively high refractive index material used for the core is preferable. The viscosity at the time of dropping is preferably about the same as that of the above-mentioned low refractive index transparent resin. When dropped, a bulge is formed as in FIG. 2 (b), and then flattened with a thin plate-like tool as in FIG. 2 (c).
Thereafter, the entire substrate 2 is heated to cure the high refractive index transparent resin. A concave curved surface is formed again by shrinkage during curing, but a flat end surface can be finally formed by repeating this process several times. The two end surfaces of the finally obtained high refractive index transparent resin are on the same plane as the front surface 2a and the back surface 2b of the substrate 2, respectively. Thus, the high refractive index portions 1a1 and 1a2 and the joint surfaces 1c1 and 1c2 are formed.
As another example, the end surface of the high refractive index transparent resin may be raised from the front surface 2 a and the back surface 2 b of the substrate 2. In that case, since the high refractive index transparent resin becomes a lens, the light condensing effect becomes higher.

  The optical transmission body in the through hole 2c is completed through the steps up to FIG. In order to maintain the integrity of the optical transmission body and the substrate, the thermal expansion coefficient of the optical transmission body is preferably in the range of 80 to 120% of the thermal expansion coefficient of the substrate. As the low refractive index transparent resin and the high refractive index transparent resin, materials satisfying such a thermal expansion coefficient are selected. For example, when the optical transmission body is formed of a photocurable epoxy resin, the substrate is an epoxy substrate (for example, a glass epoxy substrate).

Finally, the optical waveguide 4 is formed on the back surface 2b of the substrate 2 as shown in FIG. The order of forming the optical waveguide 4 is as shown in the following steps f1 to f4, which is a known technique.
Step f1: A clad material is applied by spin coating or the like and heated and cured to form the lower clad layer 4b.
Step f2: After applying the core material in the same manner, only the pattern that becomes the core is cured by UV exposure through a photomask, and development with an organic solvent is performed to remove the non-exposed portion. The core layer 4a is formed. The cross-sectional shape of the core layer 4a is a rectangle of 50 to 100 μm square.
Step f3: The clad material is again applied in the same manner and cured by heating to form upper and side clad layers 4c.
Step f4: Finally, an end portion of the optical waveguide 4 is cut off using a dicing blade whose end face has an angle of 90 degrees, and an optical path conversion mirror having an optical path conversion function having an angle of 45 degrees with respect to the optical axis A 4d is formed.

FIG. 3 is a partial sectional view showing a schematic configuration of the second embodiment of the optical transmission board according to the present invention.
In the embodiment shown in FIG. 3, as in the embodiment shown in FIG. 1, a through hole 2c is formed in the substrate 2, electrodes 8 and solder resist 9 are provided on the front surface 2a, and an optical waveguide is provided on the back surface 2b. 4 is provided. The optical element 3 is installed at a position facing the opening 2d1 of the through hole 2c on the surface 2a, thereby functioning as an optical transmission device.

  3 differs from the embodiment of FIG. 1 in the structure of the optical transmission body 10 formed in the through hole 2c. The optical transmission body 10 includes a high refractive index portion 10a having a first refractive index n1 and low refractive index portions 10b1 and 10b2 having a second refractive index n2 smaller than the first refractive index n1. The high refractive index portion and the low refractive index portion are each made of a transparent resin having an appropriate refractive index. In the example of FIG. 3, the high refractive index portion 10a is disposed in the middle along the axial direction of the through hole 2c, and two low refractive index portions 10b1 and 10b2 are disposed at both ends thereof. The end portions of the low refractive index portions 10b1 and 10b2 form flat surfaces respectively positioned at both end openings 2d1 and 2d2 of the through hole 2c.

The joint surface 10c1 between the low refractive index portion 10b1 and the high refractive index portion 10a and the joint surface 10c2 between the low refractive index portion 10b2 and the high refractive index portion 10a inside the optical transmission body 10 are respectively open at both end openings 2d1 and 2d2. It is formed in the vicinity, and in the direction of the optical axis A of the signal light, it is formed in a curved surface having a concave shape on the low refractive index portions 10b1, 10b2 side. In other words, the high refractive index portion 10a side is a convex curved surface.
The joint surfaces 10c1 and 10c2 are refractive index interfaces and have the same action as the lens surface in the same manner as in the embodiment of FIG. Also in the embodiment of FIG. 3, these joint surfaces 10c1 and 10c2 are always located inside the through hole 2c, so that it is easy to make the optical axis A of the lens surface coincide with the axial direction of the through hole 2c.

  The manufacturing method of the optical transmission body 10 of the form of FIG. 3 is as follows, for example. First, a high refractive index transparent resin that has been pre-cured into a biconvex cylindrical shape is prepared in advance, inserted into the through-hole 2c in the substrate 2, and again heated and cured to form the high refractive index portion 10a. . Alternatively, after a suitable amount of high refractive index transparent resin is dropped and infiltrated into the through-hole 2c, a high refractive index portion 10a is formed by pressing a mold against both end faces and curing it. After forming the high refractive index portion 10a, the low refractive index portions 10b1, 10b2 are obtained by dropping and curing a low refractive index transparent resin in the same manner as in the step of FIG. Form.

  Another manufacturing method of the optical transmission body 10 in the form of FIG. 3 is as follows. First, one minute ball made of a high refractive index resin having a first refractive index n1 and having a diameter that can be fitted and slid into the through hole 2c is inserted into the through hole 2c, and then the same refraction is performed. An appropriate amount of a high refractive index transparent resin having a refractive index n1 is dropped and infiltrated, and another fine ball made of high refractive index resin is inserted. Thereafter, the high refractive index portion 10a is formed by heat curing. After forming the high refractive index portion 10a, the low refractive index portions 10b1, 10b2 are obtained by dropping and curing a low refractive index transparent resin in the same manner as in the step of FIG. Form.

Optical transmission in the optical transmission board or optical transmission apparatus of FIG. 3 configured as described above is performed as follows. In the figure, the thick line schematically shows the signal light 7 and the broken line schematically shows the optical axis A.
When the optical element 3 is a light emitting element (for example, a surface emitting laser (VCSEL)), the signal light 7 emitted from the light emitting point spreads radially in the gap 6 while being low refraction of the optical transmission body 1 at the opening 2d1 of the through hole 2c. It enters the rate part 10b1. At that time, the signal light 7 is refracted so as to approach the optical axis A according to the relative refractive index difference between the air or resin existing in the gap 6 and the low refractive index portion 10b1, and the spread angle is narrowed. When the gap 6 is filled with resin, a material having a refractive index smaller than that of the low refractive index portion 10b1 is used.

Next, the light passes through the joint surface 10c1 between the low refractive index portion 10b1 and the high refractive index portion 10a and enters the high refractive index portion 10a. The joint surface 10c1 has a substantially arc shape in cross section, that is, a three-dimensional curved surface. Therefore, the light incident on the high refractive index portion 10a side from the low refractive index portion 10b1 side is refracted so as to be closer to the optical axis A according to the curved surface shape of the joint surface 10c1 and the relative refractive index difference, and the divergence angle. Narrows.
As described above, the effect of narrowing the divergence angle of the signal light is also obtained when the light is incident on the low refractive index portion inside the light transmitting body 10 from the outside of the light transmitting body 10 and further enters the high refractive index portion. Therefore, this case is also referred to as “condensing”.

The signal light 7 that has propagated through the high refractive index portion 10a is incident on another low refractive index portion 10b2, but as in the first case, the optical axis A depends on the curved surface shape of the joint surface 10c2 and the relative refractive index difference. Are collected.
Then, the light enters the lower clad 4b of the optical waveguide 4 from the low refractive index portion 10b2 through the opening 2d2 of the through hole 2c. Also at this time, the light is further condensed with respect to the optical axis A according to the relative refractive index difference with the lower clad 4b of the optical waveguide, passes through the lower clad 4b, and enters the core 4a. After that, the light path is reflected by the optical path conversion mirror 4d and the optical path is converted by approximately 90 degrees, and propagates in the axial direction of the core 4a of the optical waveguide 4.

  Here, the position of the vicinity of the opening at both ends of the through hole 2c in which the joint surfaces 10c1 and 10c2 are provided, respectively, is such that the propagation direction of the signal light is changed by the joint surfaces 10c1 and 10c2, and the condensing point thereof is the through hole 2c. A position that is on the outside.

  Although not shown, as another embodiment, an optical transmission body provided with only one of the low refractive index portions 10b1 and 10b2 in the form of FIG. 3 may be used. The side where the low refractive index portion is not provided is the high refractive index portion up to the through hole opening surface. Therefore, there is only one joint surface between the high refractive index portion and the low refractive index portion. In this case, the above-described light condensing action can be obtained at the through hole opening surface on the side where the low refractive index portion is provided and one joint surface.

FIG. 4 is a partial cross-sectional view showing a schematic configuration of a modified embodiment of the optical transmission board shown in FIG.
The structure of the optical transmission body 1 formed in the through hole 2c of the substrate 2 is the same as that of the optical transmission substrate of FIG. 1, and high refractive index portions 1a1 and 1a2 are provided at both ends with the low refractive index portion 1b interposed therebetween. ing. 1 is that optical waveguides 4 and 40 are formed on two main surfaces 2a and 2b of the substrate 2, respectively. The optical path conversion mirror 4d2 at the end of the optical waveguide 4 is disposed at a position facing the opening 2d2, and the optical path conversion mirror 4d1 at the end of the optical waveguide 40 is disposed at a position facing the opening 2d1.

Optical transmission in the optical transmission board configured as shown in FIG. 4 is performed as follows. In the figure, the thick line schematically shows the signal light 7 and the broken line schematically shows the optical axis A.
The signal light propagating through the optical waveguide 40 is subjected to an optical path conversion of 90 degrees by the optical path conversion mirror 4d1 provided on the end face. Thereafter, the signal light propagates while spreading and enters the high refractive index portion 1a1 of the optical transmission body 1 through the opening 2d1. Thereafter, the light is condensed at the refractive index interface between the high refractive index portion 1a1 and the low refractive index portion 1b and at the refractive index interface between the low refractive index portion 1b and the high refractive index portion 1a2, as in the embodiment of FIG. The light enters the lower clad 4b of the optical waveguide 4 through the opening 2d2, and propagates through the core 4a after optical path conversion by the optical path conversion mirror 4d2 provided at the end.

FIG. 5 is a partial cross-sectional view showing a schematic configuration of an optical transmission apparatus to which a modification of the optical transmission board shown in FIG. 1 is applied.
The structure of the optical transmission body 1 formed in the through hole 2c of the substrate 2 is the same as that of the optical transmission substrate of FIG. 1, and high refractive index portions 1a1 and 1a2 are provided at both ends with the low refractive index portion 1b interposed therebetween. ing. 1 is that optical elements 3 and 30, electrodes 8 and 80, and solder resists 9 and 90 are respectively installed on two main surfaces 2 a and 2 b of the substrate 2. The optical element 3 is disposed immediately above the opening 2d1 as in the embodiment of FIG. The optical element 30 is disposed immediately below the opening 2d2, and the light emitting point or the light receiving point is disposed on the optical axis A of the optical transmission body 1. The terminal of the optical element 30 is bonded to the electrode 80 by a conductive bonding material 50 such as a stud bump, a solder ball, or a conductive resin. As a result, the photoelectric conversion operation of the optical element 30 becomes possible.

Optical transmission in the optical transmission board or the optical transmission apparatus configured as shown in FIG. 5 is performed as follows. In the figure, the thick line schematically shows the signal light 7 and the broken line schematically shows the optical axis A.
When the optical element 3 is a light emitting element (for example, a surface emitting laser (VCSEL)), the signal light 7 emitted from the light emitting point spreads radially in the gap 6 and is highly refracted by the optical transmission body 1 at the opening 2d1 of the through hole 2c. It enters the rate part 1a1. At that time, the signal light 7 is collected with respect to the optical axis A according to the relative refractive index difference between the air or resin existing in the gap 6 and the high refractive index portion 1a1.
Next, the light passes through the joint surface 1c1 between the high refractive index portion 1a1 and the low refractive index portion 1b and enters the low refractive index portion 1b. The joint surface 1c1 has a substantially circular cross section, that is, a three-dimensional curved surface. Therefore, the light incident on the low refractive index portion 1b side from the high refractive index portion 1a1 side is further condensed with respect to the optical axis according to the curved surface shape of the joint surface 1c1 and the relative refractive index difference.

The signal light 7 that has propagated through the low refractive index portion 1b is incident on another high refractive index portion 1a2, but in the same manner as in the first case, the signal light 7 is incident on the optical axis according to the curved surface shape of the joint surface 1c2 and the relative refractive index difference. Condensed.
Then, the light enters the gap 60 from the high refractive index portion 1a2 at the opening 2d2 of the through hole 2c. At this time, the light is further condensed with respect to the optical axis in accordance with the relative refractive index difference with respect to the gap 60 and is incident on the light receiving point of the optical element 30 which is a light receiving element.

  Although not shown, as another embodiment of the optical transmission board according to the present invention, a multilayer optical transmission board may be configured by laminating a plurality of optical transmission boards shown in the above embodiments. However, the optical waveguide is generally provided on the main surface of the substrate facing the outside. By arranging the optical axes of the optical transmission bodies provided on the substrates of the respective layers in the multilayer optical transmission substrate so as to coincide with each other, transmission can be performed with a reduced loss even with a thick multilayer substrate.

  FIG. 6 is a partial cross-sectional view showing a schematic configuration of an example of a composite optical transmission board to which the optical transmission board shown in FIG. 1 is applied. The composite optical transmission board of the present invention is composed of two or more optical transmission boards arranged at a predetermined interval from each other. Note that in a composite optical transmission substrate composed of three or more optical transmission substrates, at least two adjacent optical transmission substrates among those substrates take the form shown in FIG.

  Referring to FIG. 6, the first substrate 2 is substantially the same as the optical transmission substrate of FIG. 1, the structure of the optical transmission body 1 in the through hole 2c is the same as that of FIG. 1, and the low refractive index portion 1b. The high refractive index portions 1a1 and 1a2 are provided at both ends with respect to each other. On one main surface 2a of the first substrate 2, an optical element 3, an electrode 8, and a solder resist 9 are arranged. The optical element 3 is disposed immediately above the opening of the through hole 2c.

  On the other hand, an optical waveguide is not provided on the other main surface 2b of the first substrate 2 unlike the embodiment of FIG. Instead, the second substrate 20 is arranged in parallel with the first substrate 2 at a predetermined interval, and one main surface 20 a of the second substrate is the main surface of the first substrate 2. 2b. In one embodiment, the first board is a daughter board, the second board is a mother board, and the electrical wirings on both boards are electrically connected via, for example, an appropriate solder connection portion (not shown). . In another example, the first board may be a mother board and the second board may be a daughter board.

  An optical waveguide 4 and an optical path conversion mirror 4d are provided on the main surface 20a of the second substrate. The optical waveguide 4 is composed of a layered lower cladding 4b, a core 4a having a rectangular cross section, and a layered upper cladding 4c in order from the substrate 20 side, and the axial direction of the optical waveguide 4 is opposed to the end face of the optical waveguide 4. An optical path conversion mirror 4d processed at approximately 45 degrees is disposed. The optical path conversion mirror 4d is disposed so as to be located immediately below the opening of the through hole 2c and on the optical axis A of the optical transmission body 1.

Optical transmission in the composite optical transmission board or optical transmission apparatus configured as shown in FIG. 6 is performed as follows. In the figure, the thick line schematically shows the signal light 7 and the broken line schematically shows the optical axis A. When the optical element 3 is a light emitting element (for example, a surface emitting laser (VCSEL)), the signal light 7 emitted from the light emitting point spreads radially in the gap 6 and is high in the refractive index of the optical transmission body 1 at the opening of the through hole 2c. Incident on the part 1a1. At that time, the signal light 7 is collected with respect to the optical axis A according to the relative refractive index difference between the air or resin existing in the gap 6 and the high refractive index portion 1a1.
Next, the light passes through the joint surface 1c1 between the high refractive index portion 1a1 and the low refractive index portion 1b and enters the low refractive index portion 1b. The joint surface 1c1 has a substantially circular cross section, that is, a three-dimensional curved surface. Therefore, the light incident on the low refractive index portion 1b side from the high refractive index portion 1a1 side is further condensed with respect to the optical axis according to the curved surface shape of the joint surface 1c1 and the relative refractive index difference.

The signal light 7 that has propagated through the low refractive index portion 1b is incident on another high refractive index portion 1a2, but in the same manner as in the first case, the signal light 7 is incident on the optical axis according to the curved surface shape of the joint surface 1c2 and the relative refractive index difference. Condensed.
And it injects into the gap | interval 60 from the high refractive index part 1a2 in opening of the through-hole 2c. Also at this time, the light is further condensed with respect to the optical axis according to the relative refractive index difference with the gap 60, reflected by the optical path conversion mirror 4d, and the optical path is converted by about 90 degrees, and in the axial direction of the core 4a of the optical waveguide 4 Propagate.

A method for manufacturing the composite optical transmission substrate of FIG. 6 is as follows, for example.
In the first step, the optical waveguide 4 is produced on one main surface 20a of the second substrate 20 (for example, a mother board). In the second step, the optical transmission body 1 is produced on the first substrate 2 (for example, a daughter board). In addition, since the 1st process and the 2nd process can be performed independently, they are random. In the third step, the optical element 3 is mounted on the first substrate 2. Finally, in the fourth step, the first substrate is mounted on the second substrate.

  In the embodiment shown in FIG. 6, the same optical transmission body 1 as shown in FIG. 1 is formed on the first substrate 2. However, as another embodiment, the optical transmission body shown in FIG. 10 may be formed. Further, instead of mounting the optical element 3 on the main surface 1a of the first substrate 2, an optical waveguide 40 may be formed as in the embodiment shown in FIG.

It is sectional drawing which shows 1st Embodiment of the optical transmission board | substrate by this invention. It is sectional drawing which shows each process of the manufacturing method of the optical transmission board | substrate by this invention. It is sectional drawing which shows 2nd Embodiment of the optical transmission board | substrate by this invention. It is sectional drawing which shows the example of application of 1st Embodiment of the optical transmission board | substrate by this invention. It is sectional drawing which shows another example of application of 1st Embodiment of the optical transmission board | substrate by this invention. It is sectional drawing which shows embodiment of the composite optical transmission board | substrate by this invention. It is a figure which shows the example of the conventional optical transmission board | substrate, (a) is sectional drawing, (b) is sectional drawing of the through-hole for optical paths. It is sectional drawing which shows the example of the conventional optical transmission board | substrate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 10 Optical transmission body 1a, 10a High refractive index part 1b, 10b Low refractive index part 1c1, 1c2, 10c1, 10c2 Joint surface 2 Board | substrate (1st board | substrate)
2a Surface (one main surface)
2b Back surface (the other main surface)
2c Through hole 2d1, 2d2 Opening of through hole 3, 30 Semiconductor optical element (light emitting element or light receiving element)
4 Optical waveguide 4a Core (layer)
4b Lower clad (layer)
4c Upper clad (layer)
4d Optical path conversion mirror 5, 50 Conductive bonding material 6, 60 Gap (air or transparent resin)
7 Signal light 8, 80 Electrode (layer)
9, 90 Solder resist (layer)
20 Second substrate 20a Surface (one main surface)
20b Back surface (the other main surface)
A Optical axis

Claims (10)

A substrate provided with a through hole as an optical path of signal light between two main surfaces;
An optical transmission body provided between the openings at both ends of the through-hole, wherein at least one high refractive index portion having a first refractive index and at least a second refractive index smaller than the first refractive index. A low refractive index portion, wherein a joint surface between the high refractive index portion and the low refractive index portion is formed in the vicinity of at least one opening, and the low refractive index portion in the optical axis direction of the signal light An optical transmission board comprising: an optical transmission body for condensing the signal light by making the side concave.   2. The optical transmission board according to claim 1, wherein the bonding surface is formed in the vicinity of each of the openings at both ends by disposing the high refractive index portions at both ends of the low refractive index portion.   2. The optical transmission board according to claim 1, wherein the bonding surfaces are formed in the vicinity of the openings at both ends by disposing the low refractive index portions at both ends of the high refractive index portion, respectively.   2. The vicinity of the opening of the through hole forming the joint surface is a position where the condensing point is outside the through hole when the propagation direction of the signal light is changed by the joint surface. The optical transmission board according to any one of?   The optical transmission substrate according to any one of claims 1 to 4, wherein a thermal expansion coefficient of the optical transmission body is in a range of 80 to 120% of a thermal expansion coefficient of the substrate.   The optical transmission board according to any one of claims 1 to 5, further comprising an optical waveguide provided on the main surface including at least an opening on the output side of the signal light and optically coupled to the optical transmission body.   A multilayer optical transmission board in which a plurality of the optical transmission boards according to claim 1 are laminated. The optical transmission board according to any one of claims 1 to 6,
An optical transmission apparatus comprising: an optical semiconductor device provided on at least one main surface of the optical transmission substrate and optically coupled to the optical transmission body. A method for manufacturing the optical transmission board according to claim 2, comprising:
Filling the through-hole with a transparent resin in a molten state, forming a recess by curing shrinkage thereof, and providing the low refractive index portion having the second refractive index;
Providing the high refractive index portion having the first refractive index by filling the through hole with a transparent resin in a molten state so as to be in contact with the concave portion of the low refractive index portion, and curing the transparent resin. Manufacturing method of optical transmission board. A first substrate which is the optical transmission substrate according to any one of claims 1 to 5;
A second substrate disposed in parallel with the first substrate;
A composite optical transmission board having an optical waveguide provided on a main surface of the second board facing the first board and optically coupled to the optical transmission body on the first board.

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