Optoelectronic integrated circuit board and communications device using the same

In the optical connection between multi-layered optical waveguides and photoelectric converting elements or optical waveguide array connectors formed on a substrate, the optical coupling efficiency is to be prevented from degrading due to deviation of the optical axis positions between optical elements and the optical waveguide layers that is caused by a radiation due to a beam expansion or by a deviation of positioning layers in producing the optical waveguides. There are stacked, on a substrate, optical waveguide layers, each of which comprises a clad layer and a core having a higher refractive index than the clad layer, and optical elements formed on the uppermost optical waveguide layer. The optical elements are positioned such that they correspond to the optical path conversion mirrors of the cores of the underlaying optical waveguide layer. The light transmission/reception between the optical elements and the optical path conversion mirrors of the cores of the underlaying optical waveguide layer is performed via the cores of overlying optical waveguide layer.

TECHNICAL FIELD

The present invention relates to an optical wiring structure and an optical coupling system of an optoelectronic integrated circuit capable of processing high-capacity optical signals transmitted and received between substrates in a communication device and a communication device using the circuit.

BACKGROUND ART

Currently, in the field of information processing and telecommunications, an improvement of communication traffics communicating high-capacity data using the optical technology is rapidly progressing, and there have been developed optical fiber networks such as a backbone, Metro, and Access for long distances of a few kilometers and more. It would be effective in the future to use optical wirings for processing a large volume of data without delay for signal transmission between communication devices (over the distance from several meters to several hundreds meters), and even for communications over an extremely short distance (in the range from several centimeters to several tens meters) within a device.

When an optical wiring is used for communication within a device such as, for instance, a router/switch device, high-frequency signals transmitted from external networks such as Ethernet via an optical-fiber is input to a Line card. Multiple sheets of line cards are used for each backplane. The signals input to each of the line cards are concentrated on switch cards via the backplane, processed by an LSI (large scale integration) included in the switch card, and are output to each line card via the backplane. Conventionally, the signals of 300 Gigabits per second have been concentrated on the switch card via the backplane. To transmit the signals through the conventional electrical wiring, segmentation of the signals into about one to three Gigabits per second for each wiring is required, because of a propagation loss, and thus, 100 and more wirings are required.

Furthermore, the high-frequency lines need a waveform shaping circuit and require countermeasures against such problems as reflection and crosstalk between the wirings. Because there is the tendency for growth in system capacity, it is anticipated that the problems including increase of the number of wirings and crosstalk between wirings will become more serious in a device using the conventional electric wirings for processing a large volume of information at a processing speed of T bit/s or more. As a solution for the problems, it is effective to replace the conventional signal transmission lines between the line cards, the backplane, and the switch card with the optical technology. With the optical technology, the high-frequency signals of 10 Gigabits and more can be propagated with a reduced loss, and a less number of wirings are required with the necessity for countermeasures against the high-frequency signals eliminated, and therefore the optical technology is very promising.

To realize the high-capacity optical interconnection circuit as described above, it is necessary to develop an easy-to-manufacture integrated circuit board which allows for high density integration of optical wirings and optical coupling with a low loss. For the high density integration of wirings, it is effective to laminate a number of optical wiring layers such as optical waveguide arrays two-dimensionally arranged in the thickness direction of the substrate and optically connect the optical wiring layers to a surface light-emitting (or receiving) type photonic device array, because integration of wiring at a higher density is possible with a smaller mounting area in this configuration.

An example of the implementation as described above in which multiple optical wiring layers and photonic device arrays can be optically connected to each other with a low loss is disclosed in Patent Document 1. As illustrated in FIG. 1 of Patent Document 1, the example includes an arrayed optical waveguide unit for optically coupling each of the multiple wiring layers to the photonic device array, so that the light from the optical wiring layer is transferred via a core of the optical waveguide for optical coupling and thus a reduction in efficiency of the optical coupling caused by a beam spread is avoided.

Furthermore, Patent Document 2 describes another example which suppresses a reduction in efficiency of the optical coupling caused by a beam spread. As illustrated in FIG. 1 of Patent Document 2, in the example, a light beam going out from a light-emitting device is collimated by mounting a micro-lens in each of the multi-layer optical waveguide and the light-emitting elemental device, and furthermore the light beam is collected by the micro-lens and is introduced into the core of the optical waveguide. In this example, a radiation loss caused by the beam spread from the optical device is suppressed to avoid reduction in the efficiency in the optical coupling.

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

In the beam conversion device disclosed in Patent Document 1, however, the arrayed optical waveguide unit for optical coupling must be prepared independently from the main body unit. Furthermore, in response to the number of laminated arrayed optical waveguide units, optical waveguide units each having a different length are required for optical coupling, and therefore the number of required parts and the number of manufacturing steps disadvantageously increase. Furthermore, when preparing each arrayed optical wavelength unit, positioning is difficult, and an optical loss may becomes larger due to positional displacement of a light axis of an optical device from that of each optical waveguide. The influence becomes more remarkable when the number of laminated optical waveguide units increases, and therefore there is a limit in increasing the number of optical waveguide units laminated.

The approach disclosed in Patent Document 2 also increases the number of components and the processes for manufacturing, because a distance between a light-emitting optical device array and a core of the optical waveguide differs depending on the number of the laminated optical waveguide units in the laminated structure, and thus each layer requires a lens having a different focal length, namely a different non-spherical surface form, which also increases the number of components and processes for manufacturing. Also, the positioning between the layers is difficult, and the optical loss may increase because of positional displacement of an light axis between the optical device and each waveguide layer.

Therefore, an object of the present invention is to provide an optoelectronic integrated circuit board and a device using the board which, for optical connection between a multi-layer optical waveguide prepared on the board and a photonic device or an optical waveguide array connector, reduces eradiation caused by the beam spread, reduces lowering of optical coupling performance caused by positional displacement of a light axis between an optical device and each waveguide layer due to positional displacement between the layers when preparing the multilayered optical waveguide unit, enables high density integration of optical wiring, reduces a number of components and manufacturing processes, and furthermore enables cost reduction.

Means for Solving the Problems

To solve the problems described above, in the present invention, a mirror which changes a light path by an angle of 90 degrees is provided in each core having a high refraction index at an appropriate position corresponding to an optical device for transfer of a light beam in each layer of the multilayered optical waveguide unit. More specifically, the light path of an outgoing light from a light-emitting optical device arranged on a top surface of the multilayered optical waveguide unit is changed by 90 degrees by a mirror arranged in the core of the optical waveguide, and then the light beam propagates through the core. The propagated light, after the light path is changed by 90 degrees by a mirror arranged at another position in the core of the optical waveguide, propagates toward a top surface of the multilayered optical waveguide unit, and is received by an optical device arranged on the top surface of the multilayered optical waveguide unit arranged at the position, such as a surface illuminating photo detector. In the present invention, spread of a light beam is suppressed by having a light beam propagating to a second and the subsequent optical waveguide layers from the uppermost layer in the multilayered optical waveguide unit and passing through a core provided in the upper layer to prevent lowering of the optical coupling efficiency. In this configuration, a core provided in the propagation path of the light beams from the second or other optical waveguide is separated from other core areas, so that the effect of suppressing spread of a light beam is further improved. In addition, by designing the separated and isolated isolation core so that a light beam passing through the core is focused, the beam spread suppression effect can further be enhanced.

EFFECTS OF THE INVENTION

The present invention enables highly accurate positioning of an optical device arranged on the top surface of the multilayered optical waveguide unit by positioning of a mirror arranged in the core having a high refractive index provided in an optical waveguide. Furthermore, light propagated to the second and subsequent optical waveguide layers is from an upper optical waveguide via a core having a high refractive index provided in the upper optical waveguide layer, so that spread of the light beam is suppressed with lowering of the optical coupling efficiency prevented, and furthermore a light path of a light beam propagating through the core is changed and guided to an optical device provided on a top surface of the board, so that a required space can be ensured between the optical devices, which allows for high density integration of optical wirings and prevention of cross talk between the wirings. Furthermore, the present invention advantageously provides an optoelectronic integrated circuit board which allows for reduction of required components and manufacturing processes and also enables cost reduction.

BEST MODE FOR CARRYING OUT THE INVENTION

First Embodiment

FIG. 1is a perspective view illustrating an optoelectronic integrated circuit board100according to a first embodiment of the present invention. A board11is prepared with glass epoxy, ceramics, and the like. A configuration of the board11is two-layered and includes a first optical waveguide layer14having a plurality of cores13aeach having a high refraction index and embedded by a cladding layer, and a second optical waveguide layer15formed on the first optical waveguide layer having a plurality of cores13beach having a high refractive index and embedded by a cladding layer, the first and second optical waveguide layers arranged on the substrate11. The core13aand the core13bare positioned at the same position in the vertical direction. Mirrors16and18, and mirrors17and19are arranged in the cores13aand13bwhich are respectively included in the optical waveguide layers14and15. As illustrated in the figure, reflection surfaces of the mirrors16and18included in the core13aof the optical waveguide layer14are inverted to each other. Thus, a light path of a light beam introduced via the top surface of the board100into the mirror16is changed by 90 degrees and the light beam propagates through the core13aand goes to the mirror18. A light path of the light introduced into the mirror18is changed by 90 degrees and the light beam propagates toward the top surface of the board100. The same optical mechanism is provided also in the mirrors17and19arranged in the cores13bincluded in the optical waveguide layer15. On the top surface of the board100, at the positions corresponding to the mirrors16and18of the core13a, optical device arrays20and22including the same number of light-emitting optical devices26and photo detectors28as the number of the cores13aare arranged. The same number of optical device arrays20and22are provided also at the positions corresponding to the mirrors17and19on the top surface of the board100. Patterns for electrical wiring required by each device array are arranged on the top surface of the board100(although not illustrated). The patterns are formed by the lithography technology like in the case of the cores13aand13b, and by adjusting the positions to the cores13aand13b. The patterns are then electrically connected to the light-emitting electrical device26and the light-receiving electrical device28provided at the prespecified positions.

An example of a size of the main portion of the optoelectronic integrated circuit board100illustrated inFIG. 1is described below. On the cross sections of the cores13aand the core13btaken along the direction vertical to the longitudinal direction thereof, the surface area is 50 μm by 50 μm, a space between the cores13ain the optical waveguide layer14and a space between the cores13bin the optical waveguide layer15(a distance between centers of the cores) are 250 μm respectively, and the vertical thickness of the cladding layers in the optical waveguide layers14and15is 25 μm. A space between the cores in the vertical direction is 100 μm. The space between the cores13ain the optical waveguide layer14and a space between the cores13bin the optical waveguide layer15(a distance between centers of the cores) are set at the value of 250 μm for compliance to a current fiber pitch of the MT connectors and the like.

The cores13aand13bof the optical waveguide layer14and the optical waveguide layer15are prepared, as described below, by means of the lithography which enables an appropriate and relative positioning for implementing the core13bimmediately above the core13a. Thus, a light beams output from the light-emitting device26of the optical device array20is propagated to the mirror16of the core13avia the core13b. Likewise, the light beam reflected by the mirror18is propagated to the photo detectors28of the optical device array22via the core13b. As a result, for transfer of a light beam between the mirror16and the mirror18arranged in the core13apositioned away from the optical devices20and22on the top surface of the board100and having a high refraction index, the beam spread is reduced and lowering of performance of an optical coupling caused by a radiation loss is avoided, because the light beam is propagated via the core13bwhich is more reflective compared to the cladding layer around the core. The optical devices26and28are surface light-emitting laser diode or a surface illuminating photo detector which are appropriate for surface implementation using the flip-chip. What is described above is also applicable to the optical devices27and29.

For positioning of mirrors in the cores13a,13bwith optical devices arranged on a top surface of the circuit board100, in the first embodiment, the optical devices can be positioned at prespecified positions on the wiring pattern in the state where the optical devices are placed on the wiring pattern formed on the top surface of the circuit board100, so that the optical devices are arranged at the accurate positions.

FIG. 2AtoFIG. 2Gare views each illustrating an example of a processing sequence for configuring the optoelectronic integrated circuit board according to the first embodiment of the present invention illustrated inFIG. 1.

FIG. 2Ais a view illustrating a state in which a cladding layer25is prepared on the board11and a layer made of a material for the first core13ahaving a high refraction index is formed by prepared by means of coating or adhering the material. The material for the cladding layer25as well as for the layer13may be a resin such as polymer or silica. It is to be noted that thickness of the cladding layer25is 30 μm and that of the layer13is 50 μm in response to the size described above.

FIG. 2Bis a view illustrating a state of the circuit board in a preparation process, in which a pattern is formed for the core13aon the layer13on the top surface of the cladding layer25by means of the photolithography, etching or the like, and then mirrors16and18for changing a light path are formed at required positions by means of cutting, etching, or the like. Surfaces of the mirrors16and18are coated with a metal such as gold (Au) through evaporation, plating, and the like for enabling efficient reflection of the light.

FIG. 2Cis a view illustrating a state of the circuit board in a preparation process, in which the material12for the cladding layer made of the same material as that for the cladding layer25is mounted on the core13aon which the pattern is formed. Thickness of the material12for the cladding layer is 80 μm. The whole circuit board is heated for softening the cladding layer25and the material12for the cladding layer, and then pressed with a push plate having a flat surface from the upper side, so that the material12for the cladding layer fills the spaces among the cores13aand is integrated with the layer25placed on the substrate11so that an optical waveguide layer14in which the core13aembedded by the cladding layer25is formed.

FIG. 2Cis a view illustrating a state of the circuit board in a preparation process, in which the first optical waveguide layer14with the core13aembedded by the cladding layer25is formed. In the view, only the mirrors16,18are shown in the core13aon the front surface for simplicity of the figure.

FIG. 2Eis a diagram illustrating a state of the circuit board in a preparation process, in which, on the cladding layer25of the optical waveguide layer14illustrated inFIG. 2D, by laminating a layer13made of a material for a second core13bby means of the same process as described inFIG. 2AandFIG. 2B, a pattern is formed on the core13bby means of the photolithography, etching or the like, and then mirrors17and19for changing a light path are formed at required positions. A distance between the mirrors16and18in the core13aand a distance between the mirrors17and19in the core13bare each preferably 250 μm in the longitudinal direction. This space is required for compliance to the current standard fiber pitch of the MT connectors. The reflection surfaces of the mirrors17and19for changing a light path are coated with a metal such as gold (Au) by means of vapor deposition, plating, and the like so that the light beam is reflected more efficiently.

FIG. 2Fis a view illustrating a state of the circuit board in a preparation process, in which a second optical waveguide layer15with the second core13bembedded with the cladding layer25is formed by means of the same process as that described in relation toFIG. 2CandFIG. 2D. With the operations described above, the circuit board100having a two-layered core layer is formed, and in the circuit board100, the first core13ais formed in the first optical wave layer14and the second core13bis formed in the second optical waveguide layer15. With the processes described in relation toFIG. 2AtoFIG. 2F, according to the processes described inFIG. 2AtoFIG. 2F, a circuit board is provided, and a cross-sectional area of the core is 50 μm×50 μm, a space (a distance between centers of) between the first cores13ain the first optical waveguide layer14and a space (a distance between centers of) between the second cores13bin the second optical waveguide layer14are 250 μm respectively, and thickness of the cladding layers in the first and second optical waveguide layers14and14are 25 μm respectively. Therefore, the circuit board100, in which thickness of each optical waveguide layer in the vertical direction is 100 μm, is formed.

FIG. 2Gis a view illustrating a final process for preparing the optoelectronic integrated circuit board100illustrated inFIG. 1. On the top surface of the cladding layer25, electrical wiring patterns required by each of the device arrays20,21,22, and23are formed by the lithography as is the case with the core13aand the core13b, and by adjusting the positions to the core13aand the core13b. At a pre-defined position on the wiring pattern, a solder bump31and each of the optical devices are arranged, and then the optical devices20,21,22, and23are electrically connected to the light-emitting optical device26and the photo detector28. With this operation, the optoelectronic integrated circuit board100illustrated inFIG. 1is completed.

FIG. 3is a perspective view illustrating an example in which an optical connector35is arranged instead of the optical device arrays22and23on the top surface of the optoelectronic integrated circuit board100. The reference numeral36denotes an optical fiber provided at the position where the illuminating devices28and29are originally arranged. In the first embodiment of the present invention, the space between the mirrors18and19in the longitudinal direction is 250 μm, and the space between the cores13aand13bis 250 μm, and thus spaces between the optical fibers36in a direction between the cores and in the longitudinal direction of the core are also 250 μm, so that the standard MT connector can be applied. When the optical connector35is arranged on the top surface of the cladding layer25, based on the process in which, similarly to the core13aand the core13b, the electrical wiring pattern is formed on the top surface of the cladding layer25through the lithography technology, the positioning of the optical connector35is indicated while adjusting the positioning to the core13aand the core13b. Therefore, the optical connector35can be arranged without positional displacement. In the process, the top surface of the cladding layer25and a face of the optical connector35touching the layer25may be fixed by a concavity and convexity engagement. The fixation enables a simple and highly accurate adjustment of positioning of the optical connector35and the mirrors in the Optical waveguide layers.

Second Embodiment

FIG. 4is a perspective view illustrating an optoelectronic integrated circuit board200according to a second embodiment of the present invention. In the optoelectronic integrated circuit board200, different from the optoelectronic integrated circuit board100, the mirrors16,18of the core13alocated at a position further from a top surface of the optoelectronic integrated circuit board200and the core13bthrough which light passes when transmitted and received to and from an optical device on the top surface of the optoelectronic integrated circuit board200are separated and isolated from each other in each light path. Because of the configuration, propagated light in the vertical direction is more tightly blocked in the separated and isolated isolation cores13b1,13b2, which enables realization of highly efficient optical coupling performance. Also in this embodiment, a path of light propagated through the cores13a,13bis represented by a broken line like inFIG. 1.

As clearly understood by comparingFIG. 4withFIG. 1, in the optoelectronic integrated circuit board200, the mirrors16,18of the lower core13aand the cores13b1,13b2which light passes through when transmitted and received to and from an optical device on a top surface of the optoelectronic integrated circuit board200are separated and isolated in each light path. Because of this configuration, to prevent propagation of light through the core13bbetween the mirror17and the mirror18from being impeded, the mirror17of the core13bis positioned in the inner side from the mirror16of the core13a. In relation to the position of the mirror17, also the optical device arrays20,21are positioned with the contrary positional relation. Furthermore, the outer sides of the mirrors17and19in the core13bare cut off, and separated and isolated isolation cores13b1and13b2embedded by a cladding layer are formed. The processing for forming the configuration described above can be performed by means of the patterning employed for patterning of the core13adescribed in related toFIG. 2BandFIG. 2E. The separated and isolated isolation cores13b1and13b2are naturally located at positions aligned with the light path between the mirrors16,18in the core13aand an optical device located on a top surface of the optoelectronic integrated circuit board200.

Because a peripheral surface of a light path to and from an optical device located on a top surface of the optoelectronic integrated circuit board200is embedded by a cladding layer made of a material having a lower refraction index as compared to that of optical waveguide layer, the isolated isolation cores13b1,13b2can block propagated light in the vertical direction in the core area more tightly as compared to a case in which light passes through the optical waveguide layer13b, which enables realization of highly efficient optical coupling performance. Furthermore, the rectangular core structure can be realized only by changing a layout of the patterning for the core13aand the patterning for the core13bdescribed in relation toFIG. 2BandFIG. 2E, and therefore it is not necessary to add any additional parts nor additional process.

In the embodiment shown inFIG. 4, the isolated isolation cores13b1,13b2have a rectangular form and are isolated respectively, butFIG. 5(A)shows an example of a tapered and isolated core formed by cutting off a tip portion of a square pyramid or a cone. Other components are the same as those in the example shown inFIG. 4. For the purpose of simplification, only the board11, the cores13a,13b, and isolated isolation cores13b1,13b2are shown with hatching in the cross-sectional view shown inFIG. 5(A).FIG. 5(B)andFIG. 5(C)are enlarged perspective views each illustrating the isolated isolation core13b1. The isolated isolation core13b2is arranged with the inverted positional relation with the isolation core13b1. As described above, because the isolated isolation cores13b1and13b2have an isolated and petrous structure, the cores13b1and13b2can reflect and send out light coming in from an end face on a side face of the tapered and isolated core from an end face in the contrary side in the focused state. Because of the feature, light propagating through the isolated isolation cores13b1and13b2is blocked in more tightly as compared to an insolated rectangular form, and even when the light leaks outs from the isolated isolation cores13b1,13bw, the light is refracted with extension of the light beam suppressed, which enables realization of highly efficient optical coupling performance. In addition, because a diameter of a light beam going out from the core can be focused more as compared to that when coming into the core, the light beam can be introduced onto a surface of the mirror section17more efficiently, which substantially reduce the light coupling loss due to displacement between centers of light axes of the core41and the mirror17. A structure of the core41can be formed by the techniques such as cutting or etching often used for preparing a light path conversion mirror, but the laser beam irradiation system is most effective, because a form inclining at a desired angle can be formed at a desired position by the laser beam irradiation system.

FIGS. 6(A),6(B), and6(C) are conceptual views each schematically illustrating the effect obtained by arranging the isolated isolation cores13b1,13b2as tapered isolated cores. In the figures, only the optical device array20, the isolated isolation core13b1, and the mirror16are shown. InFIG. 6(A), central positions of the components are aligned as represented by a dashed line, while, inFIG. 6(B), only the array20is displaced by Δ.FIG. 6(C)is a view illustrating an angle θ between a side face and an axis when the isolated isolation cores13b1,13b2are tapered and isolated ones.

InFIG. 6(A), the line extending from the optical device20toward the isolated isolation core13b1represents an outer edge of a light beam going out from a light emitting optical device in the optical device array20. When this light beam hits a side face of the isolated isolation core13b1, the light beam is refracted and goes toward an inner surface of the isolated isolation core13b1, goes out from an end face of the isolated isolation core13b1, is reflected on the mirror16, and goes though the core. Namely, a diameter of a light beam can be made smaller than that when incoming by the isolated isolation core13b1, and thus extension of the light beam can be suppressed. InFIG. 6(B), a light axis of the optical device array20is displaced by Δ from light axes of the isolated isolation core13b1and the mirror16, so that a portion of the light emitted from the light-emitting optical device is not introduced to the isolated isolation core13b1. Therefore, the light coupling loss increases. As shown inFIG. 6(C), a side face and an axis of each of the isolated isolation core13b1, and the isolated isolation core13b2forms an angle θ. When the angle θ is in the range from 5 to 10° C., an excellent result is provided. When this angle θ is made larger, the focusing effect becomes more remarkable, and the angle may be around 30 degrees. In this case, the light emitted from the light-emitting optical device is refracted on the side face, and the light axis is bent, so that all of the emitted light is not lost.

Third Embodiment

FIG. 7is a cross-sectional view illustrating a optoelectronic integrated circuit board300according to a third embodiment of the present invention. In the example shown inFIG. 7, a two-layered optical waveguide comprising a first optical waveguide14and a second optical waveguide15is laminated on a substrate11like in the first and second embodiments described above, and then a third optical waveguide40is laminated on the two-layered optical waveguide by the same technique as described in relation toFIG. 2E, andFIG. 2F. In the third optical waveguide layer40, a core13c, mirrors41and42, a tapered isolated cores13c1,13c2,13c3and13c4each separated from the core13care formed. These components can be formed by the same technique as that employed for preparing the tapered and isolated cores13b1and13bsseparated from the core13in the second optical waveguide. The mirror16in the optical waveguide layer40, the separated and isolated tapered core13b1of the optical waveguide layer15, and the separated and isolated tapered core13bcof the optical waveguide layer40are aligned on the same light axis. Also the mirror18in the optical waveguide layer14, the separated and isolated tapered core13b2in the optical waveguide layer15, and the separated and isolated tapered core13c4in the optical waveguide40are aligned on the sane light axis. Furthermore also the mirror17in the optical waveguide layer15, the separated and isolated tapered core13c1in the optical waveguide layer40, the mirror19in the optical waveguide layer15, and the separated and isolated tapered core13c3in the optical waveguide40are also aligned on the same light axis. An optical device array comprising light-emitting optical devices aligned on each light axis is provided on a top surface of the optoelectronic integrated circuit board300, and an optical connector35comprising optical fibers36arranged two-dimensionally is provided on each light axis.

In the third embodiment, the core13ain the optical waveguide layer14propagates an optical signal propagated through the two optical waveguide layers15and40. However, the light from the optical device is propagated through the separated and isolated tapered cores13c2,13b1, so that the optical signal can be transmitted and received with low loss. Therefore, density of an optoelectronic integrated circuit board can be made higher.

Fourth Embodiment

FIG. 4is a cross-sectional view illustrating an optoelectronic integrated circuit board400according to a fourth embodiment of the present invention. In the fourth embodiment, the board is configured with the so-called multilayered printed board. A board11awith electric wirings51,52provided at a central portion of the surface and a board11bwith electric wirings53,54provided at a central portion of the surface are laminated at a central portion of the surface of the board400. The electric wirings51,52are connected with the electric wirings53,54through electric wirings55,56provided in through holes, respectively, if required. The optical waveguide layers14,15each having the configuration according to the second embodiment described in relation toFIG. 5are formed on a top surface of the board11b. The optical waveguide layers according to the embodiment described above are formed on this board. In the fourth embodiment, the cores13a,13b, the mirrors16to19, and the separated and isolated tapered cores13b1,13b2are formed in the left halves of the optical waveguide layers14,15respectively, and the corresponding cores13d,13e, the mirrors43to46, and the separated and isolated tapered cores13e1,13e2are formed in the right halves of the layers14,15respectively.

The optical connector35is provided at a left edge portion of a top surface of the optical waveguide layer15, and fibers36of a fiber array38are provided at positions opposite to the separated and isolated tapered core13b1and the mirror17. On the other hand, the optical device array23having photo detectors opposite to the separated and isolated tapered core13b2and the mirror18are provided at position closer to a central portion of the top surface of the optical waveguide layer15. An integrated circuit (LSI)50is provided at a center of the top surface of the optical waveguide layer15. An optical device array having photo detectors is provided in the contrary side from the optical device array23on the top surface of the optical waveguide layer15. The optical device arrays23, the integrated circuit (LSI)50, and the optical device array21are electrically connected to the electric wiring pattern provided on the top surface of the optical waveguide layer15, and also are connected via electric wirings57,58through a through-hole formed by making use of an area with the cores13a,13b,13d, and13eof the optical waveguide layers14,15not provided therein to the electric wirings53,54. A light-emitting surface of the light-emitting optical device provided in the optical device array23faces the separated and isolated tapered core13e1and the mirror45.

On the other hand, a optical waveguide array connector500is provided at a right end portion of the top surface of the optical waveguide layer15. The optical waveguide array connector500has a optical waveguide layer including a core13fand a core13g. The core13fhas a mirror47provided at one end portion thereof, while the core13ghas a mirror49and a separated and isolated papered core13g1. A mirror46provided at another end portion of the core13eof the board400and the separated and isolated tapered core13e2face the separated and isolated core13g1of the core13gof the optical waveguide array connector500and the mirror49respectively. An external surface of the optical waveguide layer of the optical waveguide array connector500is covered with and protected by a cover layer501. In the portion where light is exchanged with cores of the optoelectronic integrated circuit board400, the cover layer501is opened so that light can pass through the portion.

With the configuration according to the forth embodiment, an optical signal introduced from the fiber36into the optoelectronic integrated circuit board400is converted to an electric signal via the cores13a,13bby the photo detectors of the optical device array23, and is introduced into the integrated circuit (LSI)50, where the electric signal is subjected to necessary signal processing. The electric signal having been subjected to the signal processing in the integrated circuit (LSI)50is converted to an optical signal by a light-emitting optical device of the optical device array21, transferred via the cores13d,13eand also via the cores13gand13fin the board500to another optoelectronic integrated circuit board. AS described above, when a signal is transmitted to or received from an optical device on a circuit board. transfer of an optical signal is performed at least twice between an optical device and a code on the circuit board, but the signal transfer is performed via a separated and isolated tapered cores, so that optical coupling can be realized with a low loss not negatively affecting the transfer performance.

(Example of a Quantitative Assessment of the Effect Provided by the Present Invention)

FIG. 9is a view illustrating a result of computing a loss in optical coupling between an optical device provided on a optoelectronic integrated circuit board and a core of a optical waveguide layer transmitting or receiving an optical signal to and from the optical device by means of the light beam tracking method. In the case shown inFIG. 9, the optical device is a light-emitting optical device with the beam spreading angle of 23 degrees, the optical waveguide layer has a core/clad specific refraction index of 1%, the core has a cross section of 50 μm×50 μm as described above, and a thickness of the clad embedding the core is 25 μm. Therefore, a space between core centers in each optical waveguide layer is 100 μm, and a distance between an upper edge of the uppermost optical waveguide layer and a light-emitting surface of the optical device provided on the board is 50 μm.

FIG. 9is a graph plotted with a distance between an optical device and a core along the horizontal axis and with an optical coupling loss along the vertical axis. In the figure, the dotted line with open circles thereon represents an optical coupling loss between an optical device and a core of the lowermost optical waveguide layer when a propagated light between the optical device and the core passes only a cladding layer; a solid line with triangles thereon represents the optical coupling loss when the propagated light between the optical device and the core passes a core in the upper layer; a solid line with filled squares represents the coupling loss when the propagated light between the optical device and the core passes a separated and isolated isolation core in the upper layer; and a line with filled circles thereon represent the coupling loss when the propagated light between the optical device and the core passes through the separated and isolated tapered core in the upper layer. Therefore, the expression of “single-layered” as used herein means that there is only one optical waveguide layer, while the expression of “two-layered” means that there are two optical waveguide layers. A form of the separated and isolated isolation core is rectangular or as shown inFIG. 5(B). Therefore, the expression of “four-layered” as used herein means the optical coupling loss when the fourth optical waveguide layer receives an optical signal from the optical device through three optical waveguide layers. As understood from the figure, when the optical waveguide layer is a single-layered one or a two-layered one, a distance between a core in the optical waveguide layer and an optical device is relatively small, for instance, 150 μm, and therefore there is substantially no loss due to spread of a light beam, and the effect provided by the present invention is not remarkable.

However, as the number of constituent layers in a optical waveguide layer increases, the distance to the optical device becomes larger, and when the propagated light represented by the broken line passes only a cladding layer, the loss due to the beam spread described above becomes larger. In contrast, when propagated light to the lower optical waveguide layer is passed through a core in the upper layer like in the structure according to the present invention which is represented by the solid line in the figure, even if the optical waveguide layer includes 5 constituent layers, the loss is not more than −1.6 dB (about 30%) in all of the embodiments. In contrast, when the propagated light is passed through only the cladding layer, the loss is not less than −6 dB (about 80%). The comparative data above indicates that the present invention is effective in suppression of beam spread and the effect provided by the present invention is visible.

In the example shown inFIG. 1, light propagating through the core13band light transmitted from the optical device26to the core13acrosses each other, but the traveling directions are different by about 90 degrees, so that there is no possibility of performance deterioration due to interference between the two light beams. In addition, althoughFIG. 9illustrates the characteristics of light transfer among a light-emitting optical device, a photo detector, and a core, the same result can be obtained also by using an optical connector between the light-emitting optical device and the photo detector.

FIG. 10is a view plotted by using the same parameters as those inFIG. 9, and illustrates a result of computing for a relation between a tolerance for a positional displacement of a light axis (Δ inFIG. 6(B)) and a core to optical device distance when a separated and isolated isolation core is moved in a direction parallel to the board (in a direction parallel to the paper surface). The same result can be obtained also for a tolerance for a positional displacement of the light axis when the core is moved in the vertical direction (in a direction vertical to the paper surface), but illustration is omitted herein because the graphical expression becomes extremely complicated. A taper angle of the separated and isolated isolation core shown inFIG. 6(C)is 7 degrees. The tolerance for positional displacement is defined with a travel to a point where the loss is −2 dB for the maximum optical coupling efficiency. In the figure, the tolerance for positional displacement in movement of a core in a direction vertical to a board surface is shown. Furthermore, when propagated light passes through a cladding layer, a tolerance for positional displacement of a mirror is shown in place of a tolerance for positional displacement of a separated and isolated isolation core.

FIG. 10shows the maximum tolerance for positional displacement of a separated and isolated isolation core in a case where light propagates between a core of the lowermost optical waveguide layer and an optical device. More specifically, the dotted line with open circles thereon represent the maximum tolerance when light propagating between the optical device and the core passes through only a cladding layer; the line with triangles thereon represent the maximum tolerance when the light propagating between the optical device and the core passes through a core in the upper optical waveguide layer; the line with filled squares thereon represent the maximum tolerance when the light propagating between the optical device and the core passes through a separated and isolated isolation core in the upper optical waveguide layer; and the line with filled circles thereon represent the maximum tolerance when the light propagating between the optical device and the core passes through a separated and isolated tapered core in the upper optical waveguide layer. When there is only one optical waveguide layer (single-layered), the light does not pass through a separated and isolated isolation core, and therefore a case of a single-layered structure is not shown inFIG. 9, and the figure illustrates data when there are two or more optical waveguide layers. Therefore, for instance, in the “four-layered” structure, the maximum tolerance for positional displacement means a tolerance for positional displacement of a separated and isolated isolation core when an optical signal from an optical device is received via three optical waveguide layers by the fourth optical waveguide layer. As understood from the figure, with the separated and isolated tapered core, the visible effect is provided irrespective of the number of optical waveguide layers. The maximum tolerance when light passes through a separated and isolated isolation core and a core in the upper layer is not substantially different from that when the light passes through a cladding layer in the case of two- or three-layered structure, but when there are four or more optical waveguide layers, the tolerance for positional displacement of a light axis of not less than 10 μm can be obtained, for instance, in a case of the four-layered structure, which indicates that the effect provided by the present invention is large.

From the result shown inFIG. 10, it is understood that, in a case where the propagated light represented by the dotted line passes through only a cladding layer, the more optical waveguide layers are laminated, the distance from the optical device becomes larger and the loss due to spread of a light beams becomes larger, and also that, when three or more layers are laminated, a tolerance for positional displacement of a light axis cannot be ensured among an optical device, a core, and a mirror. In contrast, in the structure represented by the broken line and described in the first embodiment, even when three layers are laminated, the tolerance for the positional displacement can be improved to not less than 20 μm by suppressing the optical coupling loss due to spread of a light beam and furthermore by providing a taper angle represented by the solid line to reduce a surface area of the core in the propagating direction of a light beam passing therethrough, because of the effect of narrowing a light beam diameter.

The optical coupling with any other optical device in the optoelectronic integrated circuit board according to the present invention is defined in the sense that a light beam is introduced once from a surface of the board and is reflected by a mirror to change the light path, and then is introduced into a core, or that a path of a light beam transferred through a core is changed by a mirror toward a surface of the board. Furthermore, a space between optical devices arranged on a surface of the board, for instance, between fibers can be set to a standard value for an MT connector, and therefore, even if a distance between cores in a direction in which optical waveguide layers are laminated is shortened, the cross talk never occurs, and therefore a distance between a core and an optical device arranged on a top surface of the optoelectronic integrated circuit board can be made smaller as shown inFIGS. 9andFIG. 10.

Fifth Embodiment

FIG. 11is a view illustrating an outline of a fifth embodiment in which the optoelectronic integrated circuit board according to the present invention is applied, and is a perspective view illustrating an optical transmission device having a configuration in which the optoelectronic integrated circuit board400according to the fourth embodiment shown inFIG. 8is applied. InFIG. 11, reference numeral60denotes an electric integrated circuit board, which is based on the optoelectronic integrated circuit board400described in relation toFIG. 8. Components61,62represented by broken lines are embedded optical waveguide layers, which correspond to the optical waveguide layers14,15including cores corresponding to the cores13a,13b,13d, and13e. Components63,64, and65correspond to the optical device arrays23,21, and the integrated circuit (LSI)50respectively. Components66and67,68correspond to the optical connector35and the fiber array38respectively. Reference numerals69,70, and71each denote an electronic circuit. A reference numeral is not assigned to the electronic circuit in front of the integrated circuit (LSI)50for simplification. Reference numerals72,73generically denote electric wirings, which are used for connection with electronic circuits in other electric integrated circuit board60as well as for connection with electronic circuits on a switch card80described below. Reference numeral74denotes an optical connector compatible with the optoelectronic integrated circuit board500shown inFIG. 8, and in the case shown inFIG. 11, the optical connector receives light beams from cores in the optical waveguide layers14,15and transfers the light beams through optical fibers. The electric integrated circuit board60not only receives and processes an optical signal, but also is required to again transmit the processed optical signal. Another set of optical waveguide layers61,62corresponding to the optical waveguide layers14,15described in relation toFIG. 8and optical device arrays63,64is required for the transmission function, but description thereof is omitted herefrom.

Reference numeral80demotes a switch card. The switch card comprises an optical connector74, an optical waveguide layer62, an optical device array64, electric wirings72,73, and an electronic circuit with no reference numeral assigned thereto.

Reference numeral90denotes a backplane, which mechanically supports the electric integrated circuit board60and comprises a fiber75for transferring an optical signal from the optical connector74, and wiring (not shown) for connection between the wirings72,73in the electric integrated circuit board.

Optical signals introduced from optical fibers in the fiber arrays67,68are processed in the electric integrated circuit board60, and then are collected via the backplane90in the switch card80, where the signals are subjected to necessary processing, and are again transmitted via the optical fiber in the fiber arrays67,78via the electric integrated circuit board60.

INDUSTRIAL APPLICABILITY

The present invention provides an optoelectronic integrated circuit board enabling improvement for higher density of optical wirings, reduction of required parts and steps for manufacturing the same, and cost reduction, and also provides an optical communication device using the same.

DESCRIPTION OF SYMBOLS