Optical waveguide transmitter-receiver module

A planar-mounted optical waveguide transmitter-receiver module has a plurality of separated silicon substrates and a PLC substrate hybrid-integrated. In this module, electrical crosstalk between the light emitting element side and photo-receiving element side is reduced, and an adhesion area between substrates is decreased. In this module, a first silicon substrate, on which are mounted a light emitting element and photo-receiving element, is positioned opposing a second silicon substrate, in which is formed a V groove, in which an optical fiber is to be inserted and fixed in place with resin or by other means. On joining surfaces of the first silicon substrate and joining surfaces of the second silicon substrate are positioned and fixed in place joining surfaces on the back face of the optical waveguide (PLC) substrate, in which is formed an optical waveguide. By this means, the light emitting element, the photo-receiving element, and the optical fiber inserted into the V groove are optically aligned with and simultaneously optically coupled with the optical waveguide of the PLC substrate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention concerns a planar-mounted optical waveguide transmitter-receiver module, in which silicon or other substrates, separated into a plurality of substrates, and an optical waveguide (planar lightwave circuit) substrate (hereafter “PLC substrate”), are hybrid-integrated.

2. Description of Related Art

Optical terminal devices for use in optical subscriber systems are subjected to such demands as smaller integration sizes, multi-functionality, and reduced prices. Optical modules with optical waveguides as devices effective for satisfying such demands are coming into widespread use. Conventional silicon platform structures, in which optical waveguides and silicon substrates are united, have problems which include complexity of manufacturing processes and limitations on the manufactured quantity per unit wafer. For this reason, various planar-mounted optical waveguide transmitter-receiver modules in which a silicon substrate and a PLC substrate are hybrid-integrated have been proposed. Below, the structure of conventional optical waveguide transmitter-receiver modules is explained, referring toFIGS. 1 through 3.

FIG. 1is a perspective view of an optical waveguide transmitter-receiver module, representing conventional synchronous-transfer mode passive optical networks (hereafter “STM-PON”) and π-PON systems.

This optical waveguide transmitter-receiver module has a silicon substrate1, and an optical waveguide layer2is formed on this silicon substrate1. The optical waveguide layer2is formed by, for example, deposition of quartz glass by sputtering methods and execution of vitrification processing of this deposited layer by means of high-temperature annealing. In this way, the optical waveguide layer2and silicon substrate1are formed as a unit to constitute the silicon platform substrate. A dual-branching optical waveguide3is formed within the optical waveguide layer2for use in bidirectional communication. The optical waveguide3has entry and exit end faces3ato3d. A groove is cut in the branch part3e, and a wavelength-selection filter embedded therein. The device with this filter4removed is a π-PON device.

On the silicon substrate1, a semiconductor laser or other light emitting element5and photodiode or other photo-receiving element6are fixed in place, by soldering or other means, to oppose the end faces3a,3bof the optical waveguide. The module is designed to enable the connection of optical fibers to the end faces3c,3dof the optical waveguide3by means of optical connectors.

For example, in an optical waveguide transmitter-receiver module for use in STM-PON systems, a light emitting element5and photo-receiving element6operate at different times (with different timing). When the light emitting element5operates, light is emitted from this light emitting element5, and this light is incident on the end face3aof the optical waveguide3. Light incident on the end face3ais transmitted within the optical waveguide3, is wavelength-selected by the filter4provided at the branch part3e, and is, for example, emitted from the end face3cand sent to an optical fiber via an optical connector. On the other hand, light sent from an optical fiber is incident on, for example, the end face3cvia an optical connector. The incident light is wavelength-selected by the filter4, and emitted from the end face3b. The emitted light is received by the photo-receiving element6, converted into an electrical signal, and output. Light of different wavelengths sent from an optical fiber, after incidence on the end face3c, is wavelength-selected by the filter4and emitted from the end face3d.

FIG. 2is a perspective view of an optical waveguide transmitter-receiver module compatible with a conventional asynchronous-transfer mode passive optical network (asynchronous transfer mode PON, hereafter “ATM-PON” systems).

This optical waveguide transmitter-receiver module for ATM-PON systems has nearly the same optical component configuration as inFIG. 1, but the shape of the optical waveguide3A formed within the optical waveguide layer2, and the fixed positions of the emissive element5and photo-receiving element6, are different from those of FIG.1. That is, on a silicon platform substrate in which the optical waveguide3A and silicon substrate1are formed integrally, entry/exit end faces3bto3dare formed in the optical waveguide3A. The photo-receiving element6is fixed in place opposing the end face3bon the silicon substrate1, by soldering or other means, and the light emitting element5is fixed in place on the silicon substrate1opposing the end face3d, distant from the other end face, by soldering or other means. The module is designed such that an optical fiber can be connected, by means of an optical connector, to the end face3c.

In this optical waveguide transmitter-receiver module for ATM-PON systems, the light emitting element5and photo-receiving element6operate simultaneously. Consequently, resistance to crosstalk between optical transmission and reception signals is required. For this reason, the light emitting element5and photo-receiving element6are mounted on the silicon substrate as far apart as possible, and by this means, the adverse effects of electrical crosstalk induced by electromagnetic coupling via the silicon substrate between the light emitting element5and photo-receiving element6are reduced.

FIG. 3is a perspective view of a conventional optical waveguide transmitter-receiver module for π-PON systems, with hybrid-integration of silicon substrate and PLC substrate.

This optical waveguide transmitter-receiver module for π-PON systems has a silicon substrate7with flat surface. On the flat surface of this silicon substrate7is formed by etching a V-shaped etched groove (hereafter “V groove”)8, for aligned mounting of an optical fiber. A light emitting element5and photo-receiving element6are fixed in place on the silicon substrate by soldering or other means. A PLC substrate9, manufactured in advance, is fixed in place by resin, soldering or other means on the silicon substrate7, opposing the light emitting element5, photo-receiving element6, and V groove8. The PLC substrate9is formed by layered deposition of an optical circuit, to serve as the optical waveguide3B, on parent-material or matrix substrate, primarily silicon, quartz, or a polyimide. The optical waveguide3B is provided with entry/exit end faces3ato3copposing the light emitting element5, photo-receiving element6, and V groove8.

In this optical waveguide transmitter-receiver module for π-PON systems, an optical fiber is inserted into the V groove8, and is bonded using a resin. For example, light emitted from the light emitting element5is incident on the end face3aof the optical waveguide3B. The incident light passes through the branch part3e, is emitted from the end face3c, and is sent to the optical fiber in the V groove8. On the other hand, light sent from the optical fiber is incident on the end face3cof the optical waveguide3B. The incident light passes through the branch part3e, and is emitted from the end face3b. The emitted light is received by the photo-receiving element6, and is converted into an electrical signal and output.

However, the conventional optical waveguide transmitter-receiver modules ofFIGS. 1to3have the following problems (1) to (3).

(1) Case of the optical waveguide transmitter-receiver module structure of FIG.1andFIG. 2

An optical waveguide transmitter-receiver module such as that of FIG.1andFIG. 2adopts a silicon platform structure, in which the optical waveguide3,3A and silicon substrate1are integrated. That is, numerous optical waveguide transmitter-receiver module areas are provided on a silicon wafer, for example, and wiring patterns and other electrical circuit parts are formed in each of these areas on the silicon substrate1. At the same time, quartz glass or other material is deposited by sputtering methods to form the optical waveguide layer2, and thereafter a light emitting element5and photo-receiving element6are fixed in place on the silicon substrate1by soldering or other means. Consequently the manufacturing process is complex, and moreover each optical waveguide transmitter-receiver module area formed on the wafer must be made slightly larger in order to expedite manufacturing processes. Hence such problems as limits on the quantity manufactured per unit wafer arise.

Moreover, in manufacturing processes for optical waveguide layers2, high-temperature annealing processing must be used to execute vitrification of quartz waveguide crystals. However, if such high-temperature annealing is performed, defects occur in the silicon crystal of the silicon substrate1, so that highly precise formation of the V groove by etching is made difficult, and consequently the realization of a receptacle structure (an optical connector structure having a function for optical fiber attachment and removal) becomes difficult. Further, when connecting an optical fiber array to the end faces3c,3dof the optical waveguide3,3A, optical core-aligned connection in order to match the optical axes is essential; and for this reason, connection tasks have required much care.

(2) Case of optical waveguide transmitter-receiver modules for ATM-PON systems ofFIG. 2

Since a light emitting element5and photo-receiving element6are operated simultaneously, superior cross-talk performance is required for the transmitting and receiving signals. Therefore, the decrease of electric cross-talk between the light emitting element5and the photo-receiving element6mounted on the silicon substrate1must be attained by making the dimensions of the silicon substrate larger for increasing the distance between the positions where the elements5and6are mounted, and, for this reason, the module becomes large.

(3) Case of optical waveguide transmitter-receiver modules for π-PON systems ofFIG. 3

In these optical waveguide transmitter-receiver modules for π-PON systems, the silicon substrate7and PLC substrate9are manufactured separately and independently, so that manufacturing processes can be simplified, and manufacturing quantities per unit wafer can be increased. Further, the V groove8is formed in integral fashion on the silicon substrate7, so that by inserting an optical fiber into this V groove8and bonding with resin, the optical axes of this optical fiber and the end face3cof the optical waveguide3B are aligned; consequently optically non-aligned mounting of the optical fiber is possible. However, even in the case of this optical waveguide transmitter-receiver module for π-PON systems, as with (2) above, when using this model in an ATM-PON system, the dimensions of the silicon substrate7must be made large in order to secure resistance to electrical crosstalk over the silicon substrate7between the light emitting element5and photo-receiving element6. Further, it is structurally difficult to insert the wavelength-selection filter4into the PLC substrate9, and so there is the added problem that versatility of support for STM and ATM is lacking.

SUMMARY OF THE INVENTION

One object of this invention is to provide an optical waveguide transmitter-receiver module which, by reducing electrical crosstalk, can be made smaller and can be mass-produced.

A second object of this invention is to provide an optical waveguide transmitter-receiver module which, by decreasing the bonding area with the substrate, reduces the occurrence of malfunctions.

A third object of this invention is to provide an optical waveguide transmitter-receiver module comprising a mechanism to prevent influx of the adhesive used for improved manufacturing yields.

In order to resolve the above problems, this invention comprises the configurations described below. This invention concerns a planar-mounted optical waveguide transmitter-receiver module hybrid-integrated onto a plurality of separated substrates. This module comprises a first silicon or other substrate, in the flat surface of which a first groove to accommodate protrusions is formed, and in the flat surface of which a first mark for position alignment is formed; a second silicon or other substrate, having the same thickness as this first substrate, in the flat surface of which is formed a second groove to accommodate a protruding part and a third groove to accommodate an optical fiber, and in the flat surface of which a second mark for position alignment is formed; a semiconductor laser or other light emitting element, fixed in place with position aligned with the surface of either the first or the second substrate; a photodiode or other optical photo-receiving element; and a PCL substrate or other third substrate.

In the case of a configuration in which the photo-receiving element is used in modes in which it operates simultaneously with the light emitting element, the photo-receiving element is fixed in place, with its position aligned, on the surface of either the second or the first substrate, whichever is not the substrate on which the light emitting element is fixed in place. Further, when employing a configuration used in modes in which the photo-receiving element and the light emitting element operate at different times, the photo-receiving element is fixed in place, with its position aligned, on the first or the second substrate, either the same substrate on which the light emitting element is fixed, or the other substrate. In the third substrate is formed a protrusion, of the thickness of the optical waveguide, electrodes and other components, in a position to oppose the first and second grooves and with back surface opposing the first and second substrates. In the third substrate are also formed, at positions on side faces thereof and opposing the emitting part of the light emitting element and the receiving part of the photo-receiving element, respectively, an entry end face and exit end face for the optical waveguide. Further, parts of the back surface of this third substrate are fixed or bonded to parts of the surfaces of the first and second substrates, with positions aligned using the first and second marks as references.

By adopting such a configuration, in the case of an optical waveguide transmitter-receiver module for ATM-PON systems in which the light emitting element and photo-receiving element operate simultaneously, the light emitting element and photo-receiving element are fixed in place, by soldering or other means, to different substrates, so that electrical crosstalk via substrate between the light emitting element and photo-receiving element is simply and appropriately reduced.

In the case of an optical waveguide transmitter-receiver module for STM-PON systems or for π-PON systems in which the light emitting element and photo-receiving element operate at different times, the problem of electrical crosstalk does not often occur, and so the light emitting element and photo-receiving element are fixed in place, by soldering or other means, on the same substrate or on different substrates.

By means of a module of this invention, in the case of specifications in which both a light emitting element and a photo-receiving element operate simultaneously, by separating the substrate on which the light emitting element is mounted and the substrate on which the photo-receiving element is mounted, electrical crosstalk between the light emitting element and the photo-receiving element can be simply and appropriately reduced. By this means, the dimensions of substrates on which light emitting element and photo-receiving elements are mounted can be decreased, and the number of units manufactured from a wafer or similar can be increased. Further, in this configuration parts of a first and second substrate are fixed to parts of a third substrate, so that the adhesive areas between substrates can be decreased; consequently, warping of each substrate, strain arising from differences in linear expansion coefficients, stress concentration, and degradation of bonding strength can be reduced.

In a preferred embodiment of this invention, dicing is used to form dicing grooves in the first and second groove sides, opposing the end of the third groove, the emitting part of the light emitting element and receiving part of the photo-receiving element, respectively. By this means, when for example using adhesive to bond the first, second, and third substrates, excess adhesive resin flows into the dicing grooves, and so prevents flow toward the light emitting element and photo-receiving element.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

FIG. 4is a perspective, exploded view of the optical waveguide transmitter-receiver module of a first embodiment of this invention, applicable to a π-PON system.

In this optical waveguide transmitter-receiver module, a strip or rectangle solid-shaped first substrate (for example, a silicon substrate)10, on which are mounted optical elements, a strip or rectangle solid-shaped second substrate (for example, a silicon substrate)20having the same thickness as the silicon substrate10, and for connection of optical fibers; and a strip or rectangle solid-shaped third substrate (for example, a PLC substrate)30, on which is formed an optical waveguide, are separated. These three substrates10,20, and30are hybrid-integrated in a planar-mounted structure.

One of the principal surfaces of the silicon substrate10, which is the upper face (hereafter simply “surface”), is flat, and in this surface, the first groove is formed (for example, an etched groove11is formed by etching). This first groove11is formed with a constant width, from one side face of the first silicon substrate10to the other side face. Further, this first groove11is formed with a constant depth, in the depth direction, from the flat surface of the silicon substrate10. The etched groove11is to accommodate the protruding part33on the back-face side of the PCL substrate30, that is, the face on the side opposing the first and second substrates10,20. The flat areas of the silicon substrate surface in the vicinity of the etched groove11, remaining after the etched groove11is formed, become the joining surfaces14,15for fixing the PLC substrate30. In this configuration example, the joining surfaces14,15are formed on either side of and enclosing the etched groove11. A first dicing groove16, adjoining and linked with the etched groove11, is formed by dicing. A wiring or interconnection pattern is formed in the surface area of the silicon substrate10outside the grooves, adjoining the dicing groove16. Onto this wiring pattern, a semiconductor laser or other light emitting element18, and a photodiode or other photo-receiving element19, are connected by soldering or other means. When an electrical signal is applied to the light emitting element18, light is emitted from the active layer or other emitting part18a. When light from outside is received by the receiving part19aof the photo-receiving element19, this light is converted into an electrical signal and output.

The second substrate positioned opposing the silicon substrate10, namely, the silicon substrate20, has a smooth upper principal surface (hereafter simply “surface”). Second and third grooves are formed (for example, etching is used to form an etched groove21and V groove22) in the flat surface of this second substrate20. This second groove21is, like the first groove, formed in the second substrate20from one side face on the side of the second silicon substrate20opposing the first substrate10. The second groove21, which is an etched groove, is a groove which accommodates the protruding part33on the above-described back-face side of the PCL substrate30. The flat areas of the silicon substrate surface in the vicinity of the etched groove21, remaining after the etched groove21is formed, become the joining surfaces24,25. The joining surfaces24,25are surface areas for fixing in place the PLC substrate30. The third groove22, which is a V groove, is a groove used for aligned mounting of an optical fiber; by inserting an optical fiber into this groove and fixing it in place using resin or other material, the optical fiber is fixed in place with its optical axis aligned. Between the etched groove21and V groove22of the second silicon substrate20, dicing is used to form a second dicing groove26.

The PLC substrate30fixed on top of the silicon substrates10,20has a layered structure in which a substrate of, for example, silicon, quartz, polyimide, or some other parent material, and an optical circuit to serve as the optical waveguide31on the parent-material or matrix substrate, are layered. The optical waveguide31has a dual-branching structure. This optical waveguide31has a structure in which a core for optical transmission is formed at its center, and surrounding this a cladding layer to envelop light is formed. The entry/exit end faces31ato31cof this optical waveguide31are formed on the side surfaces of the PLC substrate30, and the end faces31a,31bare coupled to the end face31cby the branching part31e. The protruding part33of the cladding layer on the periphery of the optical waveguide core is formed protruding on the back-face side of the PLC substrate30. Flat places on the back surface of the PLC substrate in the vicinity of this protruding part33serve as joining surfaces34,35. In this configuration example, these joining surfaces34,35are formed on both sides of the protruding part. The joining surfaces34,35are used for fixing to the joining surfaces14,15,24,25of the first and second silicon substrates10,20. This PLC substrate30is set such that the height from the joining surfaces34,35to the optical waveguide core is the same as the height of the emitting part18aof the light emitting element18, the receiving part19aof the photo-receiving element19, and the optical fiber core.

Such an optical waveguide transmission/receiving module may, for example, be manufactured as follows.

In the wafer state, numerous chips for silicon substrate10, chips for silicon substrate20, and chips for PLC substrate30are each formed, and dicing used to separate each of the chips. The silicon substrate10and silicon substrate20are positioned opposing each other at a prescribed interval. That is, both the substrates10and20are provided in an arrangement with one side of each mutually opposed. On the joining surfaces14,15,24,25of the surfaces of the silicon substrates10,20, the protruding surfaces34,35of the back surface of the PLC substrate30are placed, and these joining surfaces14,15,24,25and joining surfaces34,35are bonded together with resin, solder, or by similar means, to fix the PLC substrate30in place on the silicon substrates10,20. Position adjustment in the X-Y directions is performed by alignment referring to the images of metal or V groove marks formed with high precision on each of the silicon substrates10,20. By this means, the emitting part18aof the light emitting element18and the end face31aof the optical waveguide31are opposed, the receiving part19aof the photo-receiving element19and the end face31bof the optical waveguide31are opposed, the end part of the V groove22and the end face31cof the optical waveguide31are opposed, and the substrates are fixed in place with these optical axes aligned.

An optical fiber is inserted and fixed in place, with resin or by other means, in the V groove22of an optical waveguide transmitter-receiver module manufactured in this way. When the light emitting element18and receiver element19are operated, light emitted from the emitting part18aof the light emitting element18is incident on the end face31aof the optical waveguide31. Light which has been incident passes through the branch part31eof the optical waveguide31, is emitted from the end face31c, and is sent to the optical fiber in the V groove22. On the other hand, light sent from the optical fiber is incident on the end face31cof the optical waveguide31. Light which has been incident passes through the branch part31eof the optical waveguide31, and is emitted from the end face31b. The emitted light is received at the receiving part19aof the photo-receiving element19, is converted into an electrical signal and output. In this way, through simultaneous optical coupling of the optical waveguide31and the light emitting element18, photo-receiving element19and optical fiber, transmitter-receiver module functions can be obtained.

This first embodiment has the following advantageous results (a) and (b).

(a) The silicon substrates10,20and the PLC substrate30are manufactured separately and independently, so that manufacturing processes can be simplified, and the quantities manufactured per unit wafer can be increased. Further, a V groove22is formed in the silicon substrate20; by inserting an optical fiber into this V groove22and fixing it in place with resin or by other means, non-aligned mounting of the optical fiber can be realized.

(b) The silicon substrates10,20and PLC substrate30are fixed in place by means of these small-area joining surfaces14,15,24,25,34,35, so that the bonding area can be reduced. As a result, warping of each of the substrates10,20,30, strain arising from differences in linear expansion coefficients, stress concentration, and degradation of bonding strength can be reduced.

Second Embodiment

FIG. 5is a perspective, exploded view of the optical waveguide transmitter-receiver module of a second embodiment of this invention as an example of application to an STM-PON system. Components which are common with components inFIG. 4, showing the first embodiment, are assigned common symbols.

In the optical waveguide transmitter-receiver module of the second embodiment, in addition to the V groove22, another V groove23is simultaneously formed by etching in the silicon substrate20of FIG.4. In this configuration example, the V grooves22and23are formed in parallel; but this does not limit the scope of this invention. The optical waveguide31A formed in the PLC substrate30has entry/exit end faces31ato31d; a groove is cut, for example by dicing, in the branching part31ejoining the end faces, and a wavelength-selecting filter32is embedded. Otherwise the configuration is similar to that of FIG.4.

In the method of manufacture of this optical waveguide transmitter-receiver module, the chip for the silicon substrate10, the chip for the silicon substrate20, and the chip for the PLC substrate30are manufactured in advance. The joining surfaces34,35of the PLC substrate30are placed on top of the joining surfaces14,15,24,25of the silicon substrates10,20, and these joining surfaces14,15,24,25,34,35are bonded with resin, solder, or by other means.

In such an optical waveguide transmitter-receiver module, optical fibers are inserted into each of the V grooves22,23, and fixed in place with resin or by other means. When the light emitting element18and photo-receiving element19are operated, for example, light emitted from the emitting part18aof the light emitting element18is incident on the end face31aof the optical waveguide31A. The incident light is wavelength-selected by a filter32for wavelength selection, provided at the branch part31eof the optical waveguide31A, and is emitted from, for example, the end face31c. The emitted light is sent to the optical fiber inserted in the V groove22. On the other hand, light sent from the optical fiber in the V groove22is incident on the end face31cof the optical waveguide31A. The incident light is wavelength-selected by the filter32for wavelength selection, and is, for example, emitted from the end face31b. The emitted light is received by the receiving part19aof the photo-receiving element19, is converted into an electrical signal and output. Light of a different wavelength sent from the optical fiber in the V groove22is incident on the end face31cof the optical waveguide31A. The incident light is wavelength-selected by the filter32for wavelength selection, and emitted from the end face31d. The emitted light is sent to the optical fiber inserted into the V groove23.

In this way, a filter32for wavelength selection is inserted into the branch part31eof the optical waveguide31A, and so the module of the second embodiment is capable of bidirectional communications using two-wavelength signals.

In the module of this second embodiment, advantageous results similar to the results (a), (b) of the first embodiment are obtained, and in addition the following result is obtained. Namely, in this module each of the substrates10,20,30is separated, so that insertion of the filter32for wavelength selection into the PLC substrate30is made easy.

Third Embodiment

FIG. 6is a perspective, exploded view of the optical waveguide transmitter-receiver module of a third embodiment of this invention, as an example of application to an ATM-PON system. Components which are common with components in FIG.4andFIG. 5, showing the first and second embodiments, are assigned common symbols.

For example, in the optical waveguide transmitter-receiver module used in an ATM-PON system, the light emitting element18and photo-receiving element19operate simultaneously, and electrical crosstalk occurs via the silicon substrate between these elements, exerting adverse effects. Hence of the two separate first and second silicon substrates10,20, the photo-receiving element19is fixed in place by soldering or other means to the surface of the silicon substrate10, and the light emitting element18is fixed in place by soldering or other means to the surface of the other silicon substrate20.

Simultaneously with formation of the V groove22for optical fiber insertion, an etched groove26is formed in the vicinity of the V groove22on the surface of the second silicon substrate20. This groove26prevents, for example, the influx toward the light emitting element18of bonding resin when fixing the optical fiber in place in the V groove22. An optical waveguide31B is formed in the PLC substrate30which is connected on top of the silicon substrates10,20. The optical waveguide31B has entry/exit end faces31bto31d, and at the branch part31ewhich couples these, a groove is cut by dicing, for example, and a wavelength-selection filter32is embedded.

In the method of manufacture of this optical waveguide transmitter-receiver module, similarly to the first or the second embodiments, the chip for the silicon substrate10, the chip for the silicon substrate20, and the chip for the PLC substrate30are manufactured in advance. The joining surfaces34,35of the PLC substrate30are placed on top of the joining surfaces14,15,24,25of the silicon substrates10,20, and these joining surfaces14,15,24,25,34,35are bonded with resin, solder, or by other means.

In an optical waveguide transmitter-receiver module manufactured in this way, light emitted from, for example, a light emitting element18is incident on the end face31dof the optical waveguide31B. The incident light is wavelength-selected by the filter32for wavelength selection of the optical waveguide31B, and is emitted from the end face31c. The emitted light is sent to the optical fiber inserted in the V groove22. On the other hand, light which is incident from the optical fiber inserted in the V groove22is incident on the end face31cof the optical waveguide31B. The incident light is wavelength-selected by the filter32for wavelength selection, and is emitted from the end face31b. The emitted light is received by the photo-receiving element19, and converted into an electrical signal.

In this way, by inserting a filter32for wavelength selection at the branch part31eof the optical waveguide31B, similarly to the module ofFIG. 5, the module of this third embodiment is capable of bidirectional communication using two-wavelength signals.

In addition to obtaining the advantageous results of the modules of the first and second embodiments, the module of this third embodiment also affords the advantageous results (c) through (e) below.

(c) The silicon substrate20on which the light emitting element18is mounted and the silicon substrate10on which the photo-receiving element is mounted are separated, so that electrical crosstalk via silicon substrate between the light emitting element18and photo-receiving element19can be greatly reduced. Moreover, there is no need to increase the gap between the light emitting element18and photo-receiving element19in order to reduce electrical crosstalk, as in conventional designs, so that the silicon substrates10and20can be reduced in size and placed in proximity. Hence the reduction in silicon substrate dimensions enables increases in quantities manufactured from a wafer.

(d) An optical waveguide transmitter-receiver module like that of this embodiment is, for example, fixed in place to a package or other mounting frame. When fixing the silicon substrates10,20to a package or other mounting frame, resin, solder, or some other means of bonding is used. In particular, if either an insulating sheet is provided between substrates and mounting frame, or insulating resin is used as the adhesive, electrical crosstalk occurring via the mounting frame between the light emitting element18and photo-receiving element19can be further reduced. In order not to detract from the effect of heat dissipation from the silicon substrate20, which is also a heat sink (heat-dissipating member) for the light emitting element18, silver paste or some other highly heat-conducting resin may be used as the adhesive between the mounting frame and the silicon substrate20on which the light emitting element18is mounted.

(e) As an advantageous effect included in the modules of the first through third embodiments, by selecting a combination of the silicon substrates10,20and PLC substrate30which are the principal components, versatility in application to STM-PON systems, π-PON systems, ATM-PON systems, and other systems is greatly enhanced, and a greater number of optical module manufacturing processes can be performed in common.

In the first through third embodiments, an optical waveguide transmitter-receiver module is formed by bonding together three separately fabricated substrates. In the first through third embodiments, by distributing the semiconductor among separate substrates, optical waveguide crosstalk can be reduced.

Fourth Embodiment

FIG. 7is a diagram explaining a method of position alignment of silicon substrates and PLC substrate, showing a fourth embodiment of this invention.

FIG. 7shows position alignment marks within joining x-y surfaces of the first and second silicon substrates10,20and the PLC substrate30, which is the third substrate, used in the manufacture of, for example, the optical waveguide transmitter-receiver module ofFIG. 4, showing the first embodiment of this invention.

For example, first positioning marks41-1,41-2are formed on the joining surfaces14,15of the silicon substrate10; and second positioning marks41-3,41-4are formed on the joining surfaces24,25of the silicon substrate20. Metal, etched grooves, oxide films, or the like are used to form these marks41-1through41-4. On the joining surfaces34,35on the back face of the PLC substrate30also, third positioning marks42-1through42-4are formed, corresponding to the positioning marks41-1through41-4. Metal, quartz, or the like are used to form these third positioning marks42-1through42-4.

For mark image recognition, application of mark edge recognition methods using a white-light epi-illumination image, a red-light transmissive image or a reflected image, or of area-weighted methods is conceivable. Marks41-1through41-4,42-1through42-4in four corners, or in two opposing corners in strip shape, of the substrates10,20,30are formed with high precision, and image recognition is used to perform three-axis adjustment of the angles and optical axes of the joining-surface directions, or of directions parallel to optical axes.

This fourth embodiment has the following advantageous results.

By simultaneously creating marks41-1to41-4and so on on the silicon substrates10,20for positioning the light emitting element18, photo-receiving element19, optical fiber, and PLC substrate30, mounting of each of these optical components with high-precision positioning is possible.

Fifth Embodiment

FIG. 8is a diagram explaining a method of position alignment, showing a fifth embodiment of this invention, which is an example of application of a mark edge recognition method. In thisFIG. 8, the mark41-1on the silicon substrate10, and part of the mark42-1on the PLC substrate30, are shown.

In this positioning method, by adjusting the distances A, B between edges of the marks41-1,42-1, and similarly for the marks41-1,42-1, . . . of all four corners or of two corners, three-axis adjustment similar to that of the fourth embodiment is possible, and an advantageous result similar to that of the fourth embodiment is obtained.

Sixth Embodiment

FIG. 9is a diagram explaining a method of position alignment, showing a sixth embodiment of this invention, which is an example of application of a mark edge recognition method.

InFIG. 9, an example is shown in which etched grooves are used as the marks41-1, . . . on the silicon substrates10,20. In order to absorb the thickness of the mark or marks42-1formed on the PLC substrate30(for example, the thickness of a metal mark, or the swelling of quartz due to a mark), a construction is adopted in which the mark42-1of the PLC substrate30is superposed on the etched groove side of the marks41-1, . . . of the silicon substrates10,20.

This sixth embodiment has the following advantageous result.

The mark42-1on the PLC substrate30is superposed on the V groove mark or marks41-1formed in the silicon substrates10,20, so that the thickness of the mark42-1on the PLC substrate30is absorbed. Consequently the mounting precision of the joining surfaces of the silicon substrates10,20and the PLC substrate30is not degraded, and no positional deviations occur in the heights of the optical axes of each of the optical components.

Seventh Embodiment

FIG. 10is a diagram explaining a method of position alignment in a seventh embodiment of this invention, which is an example of the application of a mark edge recognition method.

InFIG. 10, similarly toFIG. 9, an example is shown of the use of etched grooves, for example V grooves in an L shape, as the marks41-1, . . . on the silicon substrates10,20. An aperture part43-1is formed in the end part of the etched groove of the mark41-1, and an aperture part43-2is also formed in the end part of the dicing groove16. The aperture part43-1is provided as an entrance for influx of adhesive resin applied from the side faces of the silicon substrates10,20. The aperture part43-2is an aperture to exude adhesive resin, and to prevent voids from remaining in the etched groove upon influx of the adhesive resin.

This seventh embodiment has the following advantageous result.

Because the aperture parts43-1,43-2are provided as apertures for influx and exuding of adhesive resin in the V groove mark41-1of the silicon substrates10,20, the functions of a mark for position adjustment and of a means for the smooth influx of adhesive resin can be combined.

In this invention, the positioning marks can be formed on a substrate with high precision. This is because the positioning marks and the optical waveguide formed of glass are divided into separate substrates and formed using separate processes, so that a silicon substrate need not be subjected to heat treatment in order to render glass transparent, so that defects do not occur in the silicon crystal. Further, in this invention it is possible to form positioning marks on substrates without using mask members for application of metal material to the substrate; hence there is no shifting of a mask member position, nor is there dispersion of the metal material caused by a gap between a mask member and the substrate.

In this invention, positioning marks and grooves can be formed in a single process; as a result, positioning marks can be formed on a substrate with high precision, and without shifts in position.

Examples of Variations of Embodiments

This invention is not limited to the above embodiments, and other variations and embodiments are possible. Such variations or embodiments may, for example, include the following (1) and (2).

(1) In the first through third embodiments, examples of application to optical waveguide transmitter-receiver modules used in STM-PON systems, π-PON systems, ATM-PON systems, and other systems were described; but by application to optical multiplexer/demultiplexer arrays employing optical waveguides, and to connection of multi-core waveguides and optical fibers, advantageous results similar to those of the above embodiments can be anticipated.

(2) By combining a plurality of silicon substrates10,20, . . . and PLC substrates30, . . . , optical circuit configurations more complex than those of the above embodiments are possible. This method is not limited to silicon substrates10,20, . . . and PLC substrates30, . . . , but can also be applied to join substrates of the same type, or to join flat substrates using other types of materials.

Specific configurations of these modules are explained usingFIGS. 11 through 17.

The silicon substrate10is the first substrate. A fiber52, cover53, monitor photodiode55, and laser diode56are mounted on the silicon substrate10. A V-shape groove54for mounting of the fiber52, first positioning marks60-1and60-2, and a groove11are formed in the silicon substrate10. The groove11is provided so that the silicon substrate10does not interfere with the optical waveguide provided in the PLC substrate50; by this means, the junction of the silicon substrate10and the PLC substrate50is made smooth.

The silicon substrate20is the second substrate. A photodiode57is mounted on the silicon substrate20. Second positioning marks61-1and61-2, and a groove21, are formed in the silicon substrate20. The groove21is provided in order that the silicon substrate20does not interfere with the optical waveguide provided in the PLC substrate50; by this means, the junction of the silicon substrate20and the PLC substrate50is made smooth.

The PLC substrate50is the third substrate. An optical waveguide is formed in the PLC substrate50and a slight protrusion is formed on the periphery of the optical waveguide. Wavelength-division multiplexing (WDM)59, which separates wavelengths, is mounted on the PLC substrate50. Third positioning marks62-1to62-4are formed on the PLC substrate50. The PLC substrate50is positioned above the silicon substrate10such that the third positioning marks62-1and62-2are aligned with the first positioning marks60-1and60-2, and the two substrates are bonded together; and the PLC substrate50is positioned above the silicon substrate20such that the third positioning marks62-3and62-4are aligned with the second positioning marks61-1and61-2, and the two substrates are bonded together.

A ceramic substrate51, which is a fourth substrate, is bonded to the bottom of the module formed by the silicon substrate10, silicon substrate20, and PLC substrate50, to support these. The ceramic substrate51electrically insulates the silicon substrate10, silicon substrate20, and PLC substrate50from the outside, and provides protection to prevent deformation of the silicon substrate10, silicon substrate20, and PLC substrate50.

In the example shown inFIG. 11, a groove is provided in the top surface of the silicon substrates to prevent interference with the optical waveguide; but other constructions are possible.FIG. 12shows another construction, andFIG. 13shows still another construction.FIG. 12shows that protruding portions63-1and63-2are provided on the silicon substrate10′ and the silicon substrate20′.FIG. 13shows that protruding portions65-1and65-2are provided on the PLC substrate50′.

FIG. 14shows a configuration in which the first substrate and the second substrate are integrated.

A common substrate70is the result of integrating the first substrate and the second substrate. The common substrate70is bonded to the PLC substrate71above, and to the ceramic substrate51below.

FIG. 15shows a configuration in which fibers are mounted on the silicon substrates without mounting an optical element (emission element, receiving element).

On a silicon substrate80, which is the first substrate, no optical elements (emission element, receiving element) are mounted, but fibers83-1and83-2are mounted. On silicon substrate81, which is the second substrate, no optical elements (emission element, receiving element) are mounted, but a fiber84is mounted.

FIG. 16shows a configuration in which the first substrate and second substrate are integrated with fibers mounted, without mounting any optical elements (emission elements, receiving elements).

Fibers92,93-1, and93-2are mounted in common substrate90without mounting any optical elements (emission elements, receiving elements).FIG. 16shows that the number of input members and the number of output members can be modified arbitrarily.

FIG. 17shows a configuration in which a fiber array, obtained by bundling a plurality of fibers, is mounted on a common substrate.

On common substrate100are mounted a fiber array102, obtained by bundling a plurality of fibers103-1to103-4; a fiber array104, obtained by bundling a plurality of fibers105-1and105-2; and a PLC substrate101.FIG. 17shows that the number of input members and the number of output members can be changed to m×n.