Optical device

An optical device 1 has a photodetecting element 6, an optical waveguide layer 4 containing core portions 4a to 4c extending in directions crossing a layer thickness direction and a clad portion 4h covering the core portions 4a to 4c, and an optical waveguide substrate 2 having the end face 4g of the core portion 4c optically coupled to the photodetecting element 6 on the side surface 2a thereof. The optical waveguide substrate 2 has substrates 3 and 5 disposed so that the principal surfaces 3a and 5a face each other. The optical waveguide layer 4 is provided between the substrate 3 and the substrate 5. The photodetecting element 6 is mounted on the mount area 2c on the side surface 2a of the optical waveguide substrate 2. The mount area 2c is set to contain the end face 4g of the core portion 4c, a part of the side surface 3b of the substrate 73 and a part of the side surface 5b of the substrate 5. Accordingly, in the optical device, the optical coupling efficiency between a semiconductor optical element such as a light emission element and a photodetecting element and an optical waveguide can be enhanced.

FIELD OF THE INVENTION

The present invention relates to an optical device having a semiconductor optical element and an optical waveguide.

RELATED BACKGROUND OF THE INVENTION

In an optical communication field, an optical waveguide substrate having an optical waveguide coupled to an optical fiber is used to make signal light incident to an optical transmission medium such as an optical fiber or the like or take out signal light propagating through the optical transmission medium. For example, an optical waveguide coupler described in Japanese Published Unexamined Patent Application No. 10-293219 has an optical waveguide on a quartz type substrate, filters or reflecting mirrors are embedded in plural dicing grooves formed in the optical waveguide, and photodetecting elements or light emitting elements adhesively attached onto the grooves.

However, the optical waveguide coupler disclosed in Japanese Published Unexamined Patent Application No. 10-293219 has the following problem. That is, in the optical waveguide coupler, when light guided along the optical waveguide is detected by the photodetecting element, the light is detected via a quartz type substrate (clad) around the optical waveguide. Or, when light from a light emitting element is made incident into the optical waveguide, it is made incident via the quartz type substrate (clad) around the optical waveguide. Accordingly, light is scattered by the quartz type substrate (clad) around the optical waveguide, and thus the optical coupling efficiency (that is, the light take-out efficiency or incident efficiency) between each of the light emitting element and the photodetecting element and the optical waveguide is lowered.

The present invention has been implemented in view of the foregoing problem, and has an object to provide an optical device that can enhance the optical coupling efficiency between a semiconductor optical element such as the light emitting element or the photodetecting element and the optical waveguide.

SUMMARY OF THE INVENTION

In order to solve the problem, the optical device according to the present invention has a semiconductor optical element, and an optical waveguide substrate having a core portion extending in a direction crossing a layer thickness direction and an optical waveguide layer containing a clad portion covering the core portion, an end face of the core portion that is optically coupled to the semiconductor optical element being provided to the side surface of the optical waveguide substrate, wherein the optical waveguide substrate further has first and second substrates disposed so that the principal surfaces thereof are facing each other, the optical waveguide layer is provided between the first substrate and the second substrate, the semiconductor optical element is disposed on a mount area of the side surface of the optical waveguide substrate, and the mount area contains the end face of the core portion, a part of the side surface of the first substrate and a part of the side surface of the second substrate.

In the above-described device, for example, the mount area in which a semiconductor optical element such as the photodetecting element, the light emitting element or the like is provided to the side surface of the optical waveguide substrate, and the mount area contains the end face of the core portion serving as the optical waveguide and a part of the side surface of each of the first and second substrates. With this construction, a space in which the semiconductor optical element can be mounted can be secured on the side surface of the optical waveguide substrate, and the semiconductor optical element strides over the end face of the core portion, whereby the semiconductor optical element and the end face of the core portion can be optically coupled to each other without a clad portion. Therefore, according to the optical device, the optical coupling efficiency between the semiconductor optical element and the core portion (optical waveguide) can be enhanced.

Furthermore, the mount area may be contained in the bottom surface of a recess portion formed on the side surface of the optical waveguide substrate, whereby an adhesive agent layer, a refractive index matching resin layer or the like can be easily formed in the recess portion formed on the side surface of the optical waveguide substrate.

Furthermore, the optical device may be constructed so that the recess portion of the optical waveguide substrate contains a step portion formed along the edge of the principal surface in each of the first and second substrates. When the first and second substrates are cut out from a wafer, a groove having a rectangular section along a cutting-plane line is formed in advance, whereby such a step portion can be easily formed. Therefore, according to the optical device, the recess portion containing the mount area in the bottom surface thereof can be easily formed on the side surface of the optical waveguide substrate.

Furthermore, the optical device may be constructed so that the optical waveguide substrate has, on the side surface, a first mark indicating the position of the end face in a direction along the edge of the principal surface of each of the first and second substrates. In the optical waveguide layer, there is a case where both the core portion and the clad portion are formed of transparent materials to light. In such a case, even when the end face of the core portion is exposed from the side surface of the optical waveguide layer, it is difficult to visually recognize the end face. However, if it is impossible to grasp the accurate position of the end face of the core portion, some displacement may occur between the relative positions of the end face of the core portion and the semiconductor optical element. When the relative position precision between the end face of the core portion and the semiconductor optical element is low, the optical coupling efficiency between the end face and the semiconductor optical element is suppressed to a small level. On the other hand, according to the above-described optical device, first marks for indicating the positions of the end faces of core portions in the direction along the edge of the principal surface of the first and second substrates is provided to the side surface of the optical waveguide substrate, whereby the positions of the end faces of the core portions in the direction along the edge of the principal surface can be easily and accurately visually recognized, and the semiconductor optical element can be secured with high positional precision. Therefore, according to the optical device, the precision of the relative position between the semiconductor optical element and the end face of the core portion can be enhanced, so that the optical coupling efficiency between the semiconductor optical element and the end face of the core portion can be further enhanced.

Furthermore, the optical device may be constructed so that the first mark includes a groove formed on the principal surface of the first substrate so as to reach the side surface of the optical waveguide substrate. Accordingly, the first mark that can be easily formed and accurately visually recognized can be provided to the side surface of the optical waveguide substrate.

Furthermore, the optical device may be constructed so that the optical waveguide layer has, on the side surface, a second mark indicating the position of the end face in the layer thickness direction. Accordingly, the position of the end face of the core portion in the layer thickness direction can be easily and accurately visually recognized, and the semiconductor optical element can be secured with high positional precision. Therefore, according to the optical device, the precision of the relative position between the semiconductor optical element and the end face of the core portion can be enhanced, so that the optical coupling efficiency between the semiconductor optical element and the end face of the core portion can be further enhanced.

Furthermore, the optical device may be constructed so that the second mark includes a film that contains a material different from that of the clad portion and embedded in the clad portion so as to be exposed from the side surface of the clad portion. Accordingly, the second mark that can be clearly visually recognized can be formed on the side surface of the optical waveguide layer.

Furthermore, the optical device may be constructed so that the optical waveguide substrate has a step between the side surfaces of the first and second substrates in the mount area. When a semiconductor optical element is mounted on such a mount area, the semiconductor optical element is inclined with respect to the optical axis of to-be-detected light emitted from the end face of the core portion by the step between the side surfaces of the first and second substrates. Therefore, according to the optical device, when a photodetecting element is used as the semiconductor optical element, the photodetecting face of the photodetecting element is preferably inclined with respect to the optical axis of the to-be-detected light, thereby suppressing Fresnel reflection in which reflected light of the to-be-detected light from the photodetection face is made incident to the core portion again. Furthermore, a gap occurs between the semiconductor optical element and the end face of the core portion by the step between the side surfaces of the first and second substrates, so that refractive index matching resin can be easily poured into this gap.

Furthermore, the optical device may be constructed so that the optical waveguide substrate further has a wiring pattern electrically connected to the semiconductor optical element on the side surface of each of the first and second substrates in the mount area. Accordingly, electrical connection means of the semiconductor optical element can be secured, and the semiconductor optical element can be directly mounted on the side surface of the optical waveguide substrate.

Furthermore, the optical device may further include a wiring substrate having a wiring pattern electrically connected to the semiconductor optical element between the side surface of the optical waveguide substrate and the semiconductor optical element, and the wiring substrate has a light passing portion at the position corresponding to the end face of the core portion. The light passing portion may be an opening (through hole) formed in the wiring substrate, or a lens embedded in the wiring board. Accordingly, the semiconductor optical element can be preferably mounted on the side surface of the optical waveguide substrate, and also the semiconductor optical element and the end face of the core portion can be preferably optically coupled to each other via the light passing portion provided to the wiring substrate.

Furthermore, the optical device may be constructed so that the optical waveguide substrate further has a metal layer for joining the second substrate and the optical waveguide layer to each other between the second substrate and the optical waveguide layer. When the optical waveguide substrate is manufactured, the optical waveguide substrate having the optical waveguide layer between the first and second substrates can be preferably manufactured by joining the surface of the optical waveguide layer formed on the principal surface of the first substrate to the principal surface of the second substrate. In this case, a metal film is formed on each of both the surface of the optical waveguide layer and the principal surface of the second substrate, and these metal films are bonded by the thermo compression bonding to each other, whereby the optical waveguide layer and the second substrate can be firmly joined to each other. Therefore, according to the optical device, there can be implemented the optical waveguide substrate in which the optical waveguide layer and the second substrate are firmly joined to each other.

Furthermore; an optical device according to the present invention is characterized by including semiconductor optical elements of n (n represents an integer of 2 or more) and an optical waveguide substrate having optical waveguide layers of n layers that contain core portions extending in a direction crossing a layer thickness direction and a clad portion covering the core portions, and laminated in the layer thickness direction, and having on a side surface thereof an end face of the core portion of each optical waveguide layer optically coupled to each of the semiconductor optical elements of n, wherein the optical waveguide substrate further has substrates of (n+1) that are laminated in the layer thickness direction so as to be alternated with the optical waveguide layers of n layers, the semiconductor optical elements of n are respectively mounted on mount areas of n on the side surface of the optical waveguide substrate, and each of the mount area of n contains the end face of the core portion of the corresponding optical waveguide layer of the optical waveguide layers of n layers and a part of the side surface of each of the substrates disposed at both sides of the optical waveguide layer.

In the above-described optical device, n mount areas in which n semiconductor optical elements are mounted are provided on the side surface of the optical waveguide substrate, and also each of the n mount areas contains the end face of the core portion of the corresponding optical waveguide layer out of the optical waveguide layers of n layers and a part of the side surface of each of the substrates disposed at both sides of the optical waveguide layer. With this constriction, a space in which semiconductor optical elements of n can be mounted can be secured on the side surface of the optical waveguide substrate, and also each of the n semiconductor optical elements strides over the end face of the core portion of the corresponding optical waveguide layer, whereby the end face of the core portion of each optical waveguide layer and each semiconductor optical element can be optically coupled to each other without a clad portion. Therefore, according to the optical device, the optical coupling efficiency between the core portion of each optical waveguide layer and each semiconductor optical element can be enhanced. Furthermore, the optical waveguide layers of n layers are laminated in the layer thickness direction, whereby many optical waveguides can be integrated in the optical device and also the optical device can be miniaturized.

Furthermore, an optical device according to the present invention is characterized by including plural semiconductor optical elements, and an optical waveguide substrate having an optical waveguide layer containing core portions extending in directions crossing a layer thickness direction and a clad portion covering the core portions, and having plural end faces of the core portions optically coupled to the plural semiconductor optical elements on the side surfaces thereof, wherein the optical waveguide substrate further has first and second substrates disposed so that the principal surfaces thereof face each other, the optical waveguide layer is provided between the first substrate and the second substrate, the plural semiconductor optical elements are mounted on plural mount areas on the side surface of the optical waveguide substrate, and each of the plural mount areas contains at least one end face of the plural end faces of the core portions, a part of the side surface of the first substrate and a part of the side surface of the second substrate.

In the above-described optical device, the plural mount areas in which the plural semiconductor optical elements are mounted are provided on the side surface of the optical waveguide substrate, and each of the plural mount areas contains at least one end face of the plural end faces of the core portion, a part of the side surface of the first substrate and a part of the side surface of the second substrate. With this construction, the space in which the plural semiconductor optical elements can be mounted can be secured on the side surface of the optical waveguide substrate, and also each of the plural semiconductor optical elements strides over the corresponding end face, whereby each semiconductor optical element and each end face of the core portion can be optically coupled to each other without a clad portion. Therefore, according to the optical device described above, the optical coupling efficiency between each semiconductor optical element and the core portion can be enhanced. Furthermore, the plural semiconductor optical elements are disposed on the side surface of the optical waveguide substrate, whereby many semiconductor optical elements can be integrated in the optical device and also the optical device can be miniaturized.

In each optical device described above, the case that plural (or n) semiconductor optical elements are provided means a case where there are provided a plurality of (or n) semiconductor optical elements each of which has one active region (a photosensitive region, a light emitting region or the like) and a case where there is provided at least one semiconductor optical element array in which plural semiconductor optical elements as described above are integrally formed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of an optical device according to the present invention will be described hereunder in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are represented by the same reference numerals, and overlapping description thereof is omitted.

First Embodiment

FIG. 1andFIG. 2are diagrams showing the construction of an optical device according to the present invention.FIG. 1(a) is a perspective view showing the construction of an optical device according to an embodiment.FIG. 1(b) is a side view showing an optical device1shown inFIG. 1(a) which is viewed in a direction along optical waveguides (core portions)4aand4bprovided to the optical device1.FIG. 2(a) is a side cross-sectional view showing the cross-section along I-I line of the optical device1shown inFIG. 1(a) (that is, the cross-section containing optical waveguides (core portions)4ato4cprovided to the optical device1).FIG. 2(b) is a side view showing the optical device1shown inFIG. 1(a) when it is viewed in a direction along the optical waveguide (core portion)4cprovided to the optical device1. In order to make the understanding easy, a semiconductor optical element (photodetecting element)6provided to the optical device1is omitted from the illustration ofFIG. 2(b).

Referring toFIG. 1andFIG. 2, the optical device1of this embodiment has the optical waveguide substrate2and the photodetecting element6. The optical waveguide substrate2is a so-called buried type optical waveguide substrate, and it has two substrates3and5and an optical waveguide layer4disposed between the substrates3and5. The substrates3and5correspond to the first and second substrates of this embodiment.

The substrates3and5have principal surfaces3aand5arespectively, and the planar shapes thereof (the shapes viewed in directions perpendicular to the principal surfaces3aand5arespectively) are set to rectangular shapes. The substrates3and5are disposed so that the principal surfaces3aand5aface each other. A step portion3cis formed on one side surface3bof the substrate3so as to extend along the edge of the principal surface3aon the side surface3b. Likewise, a step portion5cis formed on one side surface5bof the substrate5so as to extend along the edge of the principal surface5aon the side surface5b. The step portions3cand5cand the side surface4rof the optical waveguide layer4are aligned with one another on the same plane, and have the bottom surface of a recess portion2bon the side surface2aof the optical waveguide substrate2.

Grooves3dto3fare formed on the principal surface3aof the substrate3. The grooves3dto3fserve as first marks indicating the positions of the end faces4eto4gin the directions along the edges of the principal surfaces3aand3a. The end faces4eto4gcorrespond to the end faces of core portions4ato4c(described later) provided in the optical waveguide layer4. That is, the grooves3dto3fare formed so that the longitudinal directions thereof are set to the direction intersecting the edge of the principal face3a, and one ends thereof reach the positions corresponding to the end faces4eto4gon the side surface of the optical waveguide substrate2so as to be visually recognizable from the side of the optical waveguide substrate2. The grooves3dto3fare preferably designed to have a clear V-shaped section at the center positions thereof. However, if the grooves3dto3fare designed excessively deep, unevenness of coating occurs when a clad portion4h(described later) of the optical waveguide layer4is coated, and thus the depth of the grooves3dto3fpreferably ranges from 20 μm to 50 μm, and it is particularly preferably equal to about 30 μm. Furthermore, with respect to the width of the grooves3dto3f, for example, when the grooves3dto3fare formed by anisotropic etching using an alkali solution, it is determined in consideration of the crystal axis direction on the principal surface3aof the substrate3.

The substrates3and5are formed of material such as silicon, polyimide, glass, quartz, glass epoxy, ceramic or the like. In the case where the optical waveguide layer4is formed of a polymer, the optical waveguide layer4is contracted when it is thermally cured, and thus it is preferable that the substrates3and5are also formed of the same kind of material as the optical waveguide layer4in order to make the coefficient of thermal expansion match among them. However, if an Si substrate is used, the Si substrate itself is barely thermally contracted, and thus the alignment precision of the substrate as a whole can be maintained. Furthermore, the “first mark” such as the V grooves or the like can be efficiently formed by wet etching, and the positional precision is excellent. In the case of the Si substrate, it is impossible to perfectly nullify the difference in thermal expansion coefficient. However, as a countermeasure, a layer having an intermediate thermal expansion coefficient between the Si substrate and the optical waveguide layer4may be provided between the Si substrate and the optical waveguide layer4, whereby the difference in stress at the thermal contraction can be reduced. When attention is paid to the optical waveguide characteristic, the substrate is preferably formed of the same kind of material as the optical waveguide layer4in order to match the thermal expansion coefficient. However, when the overall of the device is considered like the alignment precision, formation of the alignment marks (first marks, the grooves3dto3f), etc., the Si substrate is further preferable as the substrates3and5. Furthermore, when the substrates3and5and the optical waveguide layer4are formed of different materials (for example, a silicon substrate or glass substrate is used while the optical waveguide layer4of a polyimide is used), in order to suppress warp of the optical waveguide layer4due to the contraction of the optical waveguide layer4, it is preferable that the thickness of the substrates3and5(particularly the substrate3) is set to a relatively large value (for example, from not less than 300 μm to not more than 1 mm in thickness).

The optical waveguide layer4contains core portions4ato4cfor waveguiding light, and it is provided between the principal surface3aof the substrate3and the principal surface5aof the substrate5. The optical waveguide layer4is designed so that the planar shape thereof is rectangular as in the case of the substrates3and5, and it has a side surface4rcontained in the side surface2aof the optical waveguide substrate2and side surfaces4pand4q(seeFIG. 2(b)) extending along a direction crossing the side surface4r.

Furthermore, the optical waveguide layer4has a clad portion4hand core portions4ato4clarger in refractive index than the clad portion4h. The clad portion4his formed in a layer form on the principal surface3aof the substrate3(that is, between the principal surface3aof the substrate3and the principal surface5aof the substrate5), and the core portions4ato4care covered by the clad portion4h. The core portions4ato4cextend in the direction crossing the thickness direction of the optical waveguide layer4(the direction vertical to the principal surfaces3aand5a), in other words, the direction along the principal surfaces3aand5a. In this embodiment, the core portions4aand4bare formed so that the longitudinal directions thereof are set to the direction crossing the side surfaces4pand4q, and the core portion4cis formed so that the longitudinal direction thereof is set to the direction crossing the side surface4r. One end of the core portion4ais exposed at the side surface4p, and serves as the end face4e. One end of the core portion4bis exposed at the side surface4q, and serves as the end face4f. One end of the core portion4cis exposed at the side surface4r, and serves as the end face4g. The other end of the core portion4aand the other end of the core portion4bare facing each other in the optical waveguide layer4, and the other end of the core portion4cis disposed to face the gap between the other ends of the core portions4aand4b.

Furthermore, the optical waveguide layer4contains a wavelength filter4d. The wavelength filter4dis an optical part for selectively reflecting the wavelength components contained in light in accordance with the wavelength, and it is covered by the clad portion4h. The wavelength filter4dhas a reflecting face for selectively reflecting light in accordance with the wavelength, and it is disposed along the principal surface3abetween the gap between the core portions4aand4bso that light waveguided by the core portion4ais reflected to the core portion4cat the reflecting face (on the contrary, the light waveguided by the core portion4cis reflected to the core portion4aat the reflecting face). For example, the wavelength filter4dhas a base portion and a dielectric multi-layered film provided to the reflecting face side of the base portion. The dielectric multi-layered film is formed by laminating plural dielectric layers having a predetermined thickness and refractive index, and it can selectively reflect light in accordance with the wavelength.

The core portions4ato4cand the clad portion4hof the optical waveguide layer4are formed so as to contain a polymer containing as a main agent at least one kind of organic materials such as a polyimide, silicone, epoxy, acrylate, polymethylmethacrylate (PMMA), etc. Or, in order to achieve the optimal transmission characteristic corresponding to the wavelength of light to be waveguided, the core portions4ato4cand the clad portion4hmay be formed so as to contain a polymer containing as a main agent deuteride (for example, deuterated silicone) achieved by substituting H of C-H groups of these organic materials by deuterium, or fluoride (for example, fluorinated polyimide) achieved by substituting H of C-H groups by fluorine (in the following description, these organic materials or polymer containing as a main agent deuterides thereof, fluorides thereof are merely “a polymer such as a polyimide or the like”). It is preferable that the core portions4ato4cand the clad portion4hcontain a polyimide that has a higher glass transition temperature and excellent heat resistance in these organic materials. When the core portions4ato4cand the clad portion4hcontain a polyimide, the reliability of the optical waveguide layer4can be kept for a long period, and it can endure heat when soldering is carried out. More preferably, the core portions4ato4cand the clad portion4hmay contain fluorinated polyimide in consideration of optical transmission, refractive index characteristic, etc.

Furthermore, when the core portions4ato4cand the clad portion4hare formed of a polymer such as a polyimide or the like, the core portions4ato4cand the clad portion4hare contracted when they are thermally cured, and thus it is preferable that the wavelength filter4dcontains a polymer such as a polyimide or the like as in the case of the core portions4ato4cand the clad portion4h. Furthermore, more preferably, the wavelength filter4d, the core portions4ato4cand the clad portion4hmay contain the same kind of material. For example, when the core portions4ato4cand the clad portion4hare formed of a polymer containing fluorinated polyimide as a main agent, it is preferable that the wavelength filter4dis formed of a polymer containing fluorinated polyimide as a main agent.

Here, the optical waveguide layer4further has films4ito4o. The films4ito4oserve as second marks indicating the positions of the end faces4eto4gof the core portions4ato4cin a layer thickness direction of the optical waveguide layer4. The films4ito4ocontain a material (for example, metal) different from the clad portion4h, it is embedded in the clad portion4hso as to expose from the side surfaces4pto4rof the clad portion4h.

Specifically, the films4iand4jare provided in the vicinity of the end face4eof the core portion4aso as to be arranged in the direction crossing both the layer thickness direction of the optical waveguide layer4and the longitudinal direction of the core portion4aand so that the core portion4ais disposed between the film4iand the film4j. The films4iand4jare formed in the same layer as the core portion4ain the optical waveguide layer4, and one ends thereof are exposed at the side surface4pso as to be visually recognizable from the side surface4pside of the optical waveguide layer4. The films4kand4mare provided in the vicinity of the end face4fof the core portion4bso as to be arranged in the direction crossing both the layer thickness direction of the optical waveguide layer4and the longitudinal direction of the core portion4band so that the core portion4bis disposed between the film4kand the film4m. The films4kand4mare formed in the same layer as the core portion4binside the optical waveguide layer4, and one ends thereof are exposed at the side surface4qso as to be visually recognizable from the side surface4qside of the optical waveguide layer4. Furthermore, the films4nand4oare provided in the vicinity of the end face4gof the core portion4cso as to be arranged in the direction crossing both the layer thickness direction of the optical waveguide layer4and the longitudinal direction of the core portion4cand so that the core portion4cis disposed between the film4nand the film4o. The films4nand4oare formed in the same layer as the core portion4cinside the optical waveguide layer4, and one ends thereof are exposed at the side surface4rso as to be visually recognizable from the side surface4rside of the optical waveguide layer4.

The films4ito4oare positioned in the same layer as the core portions4ato4c, and thus when they are formed so as to be excessively near to the core portions4ato4c, they affect propagation of light in the core portions4ato4c. Accordingly, it is preferable to provide a sufficient interval (for example, 20 μm) between the film4ito4oand the core portion4ato4c.

The interval between the core portion4aand the films4iand4jand the interval between the core portion4band the films4kand4mare preferably set in accordance with the diameter of the optical fiber coupled with the end faces4eand4fof the core portions4aand4b. Here,FIG. 3is a diagram showing the state that the optical fiber is coupled to the end faces4eand4f. InFIG. 3, a circumference10represents the outer edge of the optical fiber. For example, the diameter d of a general single mode optical fiber is equal to 125 μm. Accordingly, when the interval between the core portion4aand the films4iand4j(the interval between the core portion4band the films4kand4m) x is set to a half of the diameter d as an example, that is, 62.5 μm, the outer circumference10of the fiber end and the end portion of the film4ito4mare positionally coincident with each other, so that the alignment of the optical fiber can be preferably performed with high precision. Furthermore, the films4ito4mcan be used to check the alignment precision after the coupling of the optical fiber.

For example, Al, Ti, Cr, WSi or the like may be used as the material of the films4ito4o. When the thickness of the films4ito4ois relatively large, the films4ito4ocan be easily visually recognized on the side surface4pto4r. However, as described later, the films4ito4oare formed by dry etching or the like, and thus when the etching condition is considered, the preferable thickness of the films4ito4oranges from 0.2 μm to 1.5 μm.

The photodetecting element6is a semiconductor optical element of this embodiment. For example, a photodiode is preferably used as the photodetecting element6. The photodetecting element6of this embodiment has a photodetecting area (photodetecting face)6aon the surface thereof. Furthermore, the photodetecting element6is mounted on the mount area2c(seeFIG. 2(b)) of the side surface2aso that the photodetecting area6afaces the side surface2aof the optical waveguide substrate2. In the side surface2aof the optical waveguide substrate2, the mount area2cis set in an area containing the end face4gof the core portion4c, a part of the side surface3bof the substrate3and a part of the side surface5bof the substrate5. Accordingly, the photodetecting element6strides over the end face4gof the core portion4cand it is mounted over the area from the side surface3bof the substrate3to the side surface5bof the substrate5. The photodetecting element6is positioned so that the photodetecting area6aand the end face4gof the core portion4care optically coupled to each other.

The photodetecting element6is fixed to the optical waveguide substrate2by an adhesive agent layer (not shown) provided on the side surface2a. The adhesive agent layer is formed of transparent resin, for example, and it fixes the photodetecting element6and the optical waveguide substrate2to each other, and functions to match the refractive index between the photodetecting area6aand the end face4gby filling the adhesive agent layer in the gap between the photodetecting area6aof the photodetecting element6and the end face4gof the core portion4c. This adhesive agent layer is formed by pouring transparent resin into the recess portion2bof the optical waveguide substrate2and curing it. Accordingly, the mount area2cis preferably contained in the bottom surface of the recess portion2b.

A back-side incident photodiode as an example is preferably used as the photodetecting element6of this embodiment. Furthermore, the semiconductor optical element provided to the optical device1is not limited to the photodetecting element6, a light emitting element (for example, a laser diode, LED or the like) may be used. A optical transmission medium such as an optical fiber or the like or a semiconductor optical element different from the photodetecting element6is coupled to the end face4eof the core portion4aand the end face4fof the core portion4b.

The method of manufacturing the optical waveguide substrate2of the thus constructed optical device1will be described.FIGS. 4 to 12are diagrams sequentially showing the manufacturing process of the optical waveguide substrate2according to this embodiment.

First, a wafer30having a main principal surface30ais prepared as shown inFIG. 4(a).FIG. 4(a) is a plan view showing the appearance of the wafer30, andFIG. 4(b) is a perspective view when a part30bof the wafer30shown inFIG. 4(a) is cut out. Next, as shown inFIG. 4(a) andFIG. 4(b), grooves3dto3fare formed on the principal surface30aof the wafer30. In this case, in the case where an Si substrate is used, if the grooves3dto3fare formed by wet etching as an example, grooves3dto3feach having a V-shaped cross-section as shown in the figure can be formed. Furthermore, if the grooves3dto3fare formed by dry etching, the grooves3dto3feach having a rectangular cross-section can be formed.

Subsequently, as shown inFIG. 5, a lower clad layer40ais formed on the principal surface30aof the wafer30. The lower clad layer40ais a layer constituting a part of the clad portion4hshown inFIG. 1andFIG. 2. At this time, when the lower clad layer40ais formed of a polymer such as a polyimide or the like, the lower clad layer40amay be formed on the principal surface30aby coating (preferably, spin coating). Thereafter, the films4ito4oare formed on the lower clad layer40a. Specifically, a metal film is formed on the lower clad layer40a, and the metal film is etched (preferably, dry-etched) by using a mask having the pattern corresponding to the planar shapes of the films4ito4oto thereby form the films4ito4o.

Subsequently, as shown inFIG. 6, the core portions4ato4care formed on the lower clad layer40a. Specifically, a core layer formed of the material of the core portions4ato4cis coated and formed on the lower clad layer40a, and a mask having the pattern corresponding to the planar shapes of the core portions4ato4c(core pattern) is formed on the core layer. Then, the core layer is etched via the mask to form the core portions4ato4c. At this time, the core portions4ato4care formed of material having a higher refractive index than the lower clad layer40a. Thereafter, as shown inFIG. 7, the wavelength filter4dis mounted on the lower clad layer40a.

Subsequently, as shown inFIG. 8(a) andFIG. 8(b), the same clad material as the lower clad layer40ais coated and formed so as to cover all the lower clad layer40a, the core portion4ato4cand the wavelength filter4d. Thereby, the clad layer40bcontaining the core portions4ato4cand the wavelength filter4dtherein is formed.

Subsequently, as shown inFIG. 9(a) andFIG. 9(b), grooves30ceach having a rectangular section is formed on the principal surface30aof the wafer30. At this time, the grooves30cmay be formed by carrying out dicing (half cutting) of the wafer30until some midpoint of the thickness of the wafer30along at least a part of a cutting-scheduled line in the next step. In the example ofFIG. 9, the grooves30care formed along the surfaces on which the end faces4eto4gof the core portions4ato4cwill be formed. The clad layer40bis cut by the grooves30c, the optical waveguide layer4having the side surfaces4pto4rare formed, and also the end faces4eto4gof the core portions4ato4care formed. Furthermore, the grooves3dto3fformed on the principal surface30aof the wafer30and the films4ito4oformed inside the optical waveguide layer4are exposed at the side surfaces4pto4r.

Subsequently, as shown inFIG. 10(a) andFIG. 10(b), the wafer30is cut in the form of a chip along the cutting lines A1by dicing or the like. At this time, when the grooves30care formed along the cutting lines A1, the wafer30is cut along the center lines of the grooves30c.FIG. 10(b) is a perspective view showing a chip after cutting. As shown inFIG. 10(b), the substrate3having the side surface3band the step portion3cis formed in this cutting step.

Furthermore, as shown inFIG. 11(a) andFIG. 11(b), a wafer50different from the wafer30is prepared, and grooves50ceach having a rectangular section are formed on the principal surface50aof the wafer50. At this time, the grooves50care formed so as to be symmetrical with the grooves30cshown inFIG. 9. The wafer50is cut in the form of a chip along the cutting lines A2by dicing or the like. At this time, when the grooves50care formed along the cutting lines A2, the wafer50is cut along the center lines of the grooves50c.FIG. 11(b) is a perspective view showing the chip after cutting. As shown inFIG. 11(b), the substrate5having the principal surface5a, the side surface5band the step portion5cis formed in the cutting step. The step of forming the substrate5may be carried out before the steps of forming the substrate3and the optical waveguide layer4described above or in parallel with these steps.

Subsequently, as shown inFIG. 12, the chip including the substrate3and the optical waveguide layer4is affixed to the substrate5, thereby completing the optical waveguide substrate2. At this time, the principal surface3aof the substrate3and the principal surface5aof the substrate5are facing each other so that the side surface3band the side surface5bare aligned with each other, and the surface of the optical waveguide layer4on the substrate3and the principal surface5aof the substrate5are affixed to each other. At this time, the optical waveguide layer4and the substrate5may be affixed to each other via an adhesive agent such as resin or the like, whereby the optical waveguide substrate2of this embodiment is completed. When the optical device1of this embodiment is manufactured, the photodetecting element6is mounted on the mount area2cof the optical waveguide substrate2. At this time, the groove3findicating the position of the end face4gof the core portion4cand the films4nand4oare formed on the side surface2aof the optical waveguide substrate2. Therefore, the photodetection area6aof the photodetecting element6(seeFIG. 1andFIG. 2) can be easily positioned on the end face4g.

The recess portion (for example,2b) on the side surface of the optical waveguide substrate2is implemented by forming the grooves30cand50cshown inFIG. 9andFIG. 11. Accordingly, by forming the grooves30cand50calong any cutting lines A1and A2of the cutting lines A1and A2of the wafers30and50, a recess portion can be formed on any side surface of the optical waveguide substrate2.

Furthermore, in the above-described manufacturing method, after the wafers30and50are individually cut, the chip-type substrates3and5are affixed to each other to form the optical waveguide substrate2. In another manufacturing method, after the grooves30cand50care formed on the wafers30and50respectively, the wafers30and50may be affixed to each other before the wafers are cut in the form of a chip, and then the wafers30and50may be collectively cut out, thereby forming the optical waveguide substrate2. In this case, the wafers30and50are affixed to each other so that the grooves30cand50cface each other, so that the grooves30cand50care concealed after the affixing. Accordingly, marks indicating the cutting lines A1and A2are provided to the back surfaces of the wafers30and50before the wafers30and50are affixed to each other, and the wafers30and50are cut out in conformity with these marks after the wafers30and50are affixed to each other. Furthermore, when an adhesive agent such as resin or the like is used to affix the wafers30and50to each other, it is preferable to prevent the adhesive agent from intruding into the grooves30cand50c.

Furthermore, when light is waveguided in a single mode, the thickness of the lower clad layer40a(FIG. 5) preferably ranges from not less than 10 μm to not more than 20 μm. Particularly, when the optical waveguide layer4is formed of fluorinated polyimide, the preferable thickness of the lower clad layer40ais equal to 15 μm, for example. Furthermore, the thickness of the core portions4ato4c(FIG. 6) (the height in the layer thickness direction) preferably ranges from not less than 5 μm to not more than 10 μm. Particularly, when the optical waveguide layer4is formed of fluorinated polyimide, the preferable thickness of the core portions4ato4cis equal to 9 μm, for example. Furthermore, the thickness of the clad layer40b(FIG. 8) preferably ranges from not less than 10 μm to not more than 30 μm from the top surfaces of the core portions4ato4c. Particularly, when the clad layer40bis formed of fluorinated polyimide, the preferable thickness of the clad layer40bis set to 20 μm from the top surfaces of the core portions4ato4c, for example.

Furthermore, when light is waveguided in a multi-mode, the thickness of the lower clad layer40a, the core portions4ato4cand the clad layer40bmay be freely set in a broad range from 10 μm to several hundreds μm, and it is determined in accordance with the application thereof.

Furthermore, the thickness of the wavelength filter4din the direction parallel to the principal surface3apreferably ranges from about 30 μm to about 100 μm when the wavelength filter4dis formed of a polyimide, for example. However, in order to suppress the loss of light passing through the wavelength filter4d, it is better that the thickness of the wavelength filter4dis smaller (for example, 30 cm to 40 μm). Furthermore, it is necessary that the wavelength filter4dis covered by the clad layer40b, and thus it is preferable that the height of the wavelength filter4d(that is, the width of the wavelength filter4din the normal direction of the principal surface3a) ranges from about 30 μm to about 50 μm, for example. Furthermore, the width of the wavelength filter4din the direction parallel to the principal surface3acan be appropriately determined in accordance with the mount stability and the breadth of the mount space of the wavelength filter4d, and for example, the range from about 200 μm to about 400 μm is proper.

The effect of the optical device1according to the above-described embodiment will be described. In the optical device1of this embodiment, the mount area2cfor mounting the photodetecting element6therein is provided to the side surface2aof the optical waveguide substrate2, and also the mount area2ccontains the end face4gof the core portion4cserving as the optical waveguide and parts of the side surfaces3band5bof the substrates3and5. With this construction, the space in which the photodetecting element6can be mounted can be secured on the side surface2aof the optical waveguide substrate2, and the photodetecting element6strides over the end face4gof the core portion4c, whereby the photodetecting element6and the end face4gof the core portion4ccan be optically coupled to each other without a clad portion4c. Therefore, according to the optical device1of this embodiment, light scattering that occurs in an optical waveguide coupler disclosed in Japanese Published Unexamined Patent Application No. 10-293219 and is caused by the clad portion or the like can be avoided, so that the optical coupling efficiency between the photodetecting area6aof the photodetecting element6and the core portion4ccan be enhanced.

In the optical waveguide coupler disclosed in Japanese Published Unexamined Patent Application No. 10-293219, a wavelength filter is embedded in a dicing groove. However, since the dicing groove is linearly formed along one direction, all optical waveguides extending in directions crossing the formation direction of the dicing groove are cut out, so that the optical waveguides bypassing the wavelength filter are cut. On the other hand, in the optical device1of this embodiment, the core portion4cand the photodetecting element6are optically coupled to each other on the side surface4rof the optical waveguide layer4, and thus for example, even when the end face4eand the end face4fare required to be directly optically coupled to each other while bypassing the wavelength filter4d, such a bypassing core portion can be preferably formed in the optical waveguide layer4.

Furthermore, according to this embodiment, the mount area2cis preferably contained in the bottom surface of the recess portion2bformed on the side surface2aof the optical waveguide substrate2. Accordingly, a resin layer for adhesion and matching of the refractive index can be easily formed by pouring resin into the recess portion2b.

Still furthermore, it is preferable that the recess portion2bof the optical waveguide substrate2is constructed to contain the step portions3cand5cformed along the edges of the principal surfaces3aand5aof the substrates3and5as in the case of this embodiment. The step portions3cand5cas described above can be easily formed by forming the grooves30cand50ceach having the rectangular section along the cutting lines A1and A2in advance when the substrates3and5are cut out from the wafers30and50(seeFIGS. 9 to 11). Therefore, according to the optical device1of this embodiment, the recess portion2bcontaining the mount area2cin the bottom surface thereof can be easily formed on the side surface2aof the optical waveguide substrate2.

Still furthermore, it is preferable that the first marks (grooves3dto3f) indicating the positions of the end faces4eto4gof the core portions4ato4cin the directions along the principal surfaces3aand5aof the substrates3and5are formed on the side surface2aof the optical wave guide substrate2as in the case of this embodiment. In the optical waveguide layer4, the core portions4ato4cand the clad portion4hare formed of materials transparent to waveguided light in many cases. In such a case, even when the end faces4eto4gof the core portions4ato4care exposed from the side surfaces4pto4rof the optical waveguide layer4, it is difficult to visually recognize the end faces4eto4g. However, if the accurate positions of the end faces4eto4gcannot be grasped, some displacement might occur between the relative position between the end face4gand the photodetecting element6or the relative position between the end faces4eand4fand the optical transmission medium. When the relative position precision between the end faces4eto4gand the photodetecting element6or the optical transmission medium is low, the optical coupling efficiency between each end face and the photodetecting element6or the optical transmission medium is reduced to a low level.

On the other hand, according to the optical device1of this embodiment, the first marks indicating the positions of the end faces4eto4gin the directions along the principal surfaces3aand5aare formed on the side surfaces (2a, etc.) of the optical waveguide substrate2, whereby the positions of the end faces4eto4gin the directions along the edges of the principal surfaces3aand5acan be easily and accurately visually recognized. Therefore, the photodetecting element6or the optical transmission medium can be secured to the side surfaces (2a, etc.) of the optical waveguide substrate2with high positional precision. Therefore, according to the optical device1of this embodiment, the relative positional precision between the photodetecting element6or the optical transmission medium and the end faces4eto4gcan be enhanced, so that the optical coupling efficiency between the photodetecting element6and the end faces4gcan be further enhanced, and the optical coupling efficiency between the optical transmission medium and the end faces4eand4fcan be enhanced.

Still furthermore, it is preferable that the first marks indicating the positions of the end faces4eto4ghave the grooves3dto3fformed on the principal surface3aof the substrate3so as to reach to the side surfaces of the optical waveguide substrate2as in the case of this embodiment. Thereby, the first marks which can be easily formed and reliably visually recognized can be provided to the side surfaces (2a, etc.) of the optical waveguide substrate2.

Still furthermore, it is preferable that the second marks indicating the positions of the end faces4eto4gin the layer thickness direction are provided on the side surfaces4pto4rof the optical waveguide layer4as in the case of this embodiment. Accordingly, the positions of the end faces4eto4gin the layer thickness direction of the optical waveguide layer4can be easily and accurately visually recognized, and thus the photodetecting element6or the optical transmission medium can be secured to the side surfaces (2a, etc.) of the optical waveguide substrate2with high positional precision. Therefore, according to the optical device1of this embodiment, the precision of the relative position between the photodetecting element6or the optical transmission medium and the end faces4eto4gcan be enhanced, so that the optical coupling efficiency between the photodetecting element6and the end face4gcan be further enhanced, and also the optical coupling efficiency between the optical transmission medium and the end faces4eand4fcan be enhanced.

Still furthermore, it is preferable that the second marks indicating the positions of the end faces4eto4gare the films4ito4othat contain materials different from the clad portion4hand embedded in the clad portion4hso as to be exposed from the side surfaces4pto4rof the clad portion4h. Accordingly, the second marks which can be reliably visually recognized can be formed on the side surfaces4pto4rof the optical waveguide layer4.

Second Embodiment

FIG. 13(a) is a perspective view showing the construction of a second embodiment of the optical device according to the present invention.FIG. 13(b) is a side view of the optical device11shown inFIG. 13(a) when it is viewed along the core portions4aand4bprovided to the optical device11. The difference in construction between the optical device11of this embodiment and the optical device1of the first embodiment resides in the presence or absence of the metal films7aand7b. That is, as shown inFIG. 13(a) andFIG. 13(b), the optical waveguide substrate21provided to the optical device11of this embodiment further has the metal films7aand7bin addition to the construction of the optical waveguide substrate2of the first embodiment. Since the construction other than the metal films7aand7bin the optical device11is similar to the construction of the optical device1of the first embodiment, detailed description thereof is omitted.

The metal films7aand7bare films formed of a metal such as Cr/Au, Ti/Pt/Au, Au/Sn or the like. The metal film7ais formed on the side surface3bof the substrate3(in this embodiment, on the step portion3c). Furthermore, the metal film7bis formed on the side surface5b(on the step portion5c) of the substrate5and between the principal surface5aof the substrate5and the optical waveguide layer4. Among these, the metal film7aand a portion which is a part of the metal film7band formed on the step portion5cof the substrate5constitute a wiring pattern to be electrically connected to the photodetecting element6. Furthermore, the portion located between the principal surface5aof the substrate5of the metal film7band the optical waveguide layer4constitutes a layer (metal layer) for joining the substrate5and the optical waveguide layer4.

That is, the metal film7aextends in the direction along the edge of the principal surface3aon the step portion3cof the substrate3, and a bump electrode6bof the photodetecting element6is joined to the portion of the metal film7awithin the mount area2c. Furthermore, the portion of the metal film7aout of the mount area2cis electrically connected to an external circuit of the optical device11via a bonding wire or the like (not shown). Furthermore, the portion of the metal film7bwhich is provided on the step portion5cof the substrate5extends in the direction along the edge of the principal surface5aon the step portion5c, and the portion thereof within the mount area2cis joined to another bump electrode6bof the photodetecting element6. Furthermore, the portion of the metal film7bout of the mount area2cis electrically connected to an external circuit of the optical device11via a bonding wire or the like (not shown). A surface incident type photodiode is preferably used as the photodetecting element6of this embodiment.

Furthermore, the portion of the metal film7bwhich is located between the principal surface5aof the substrate5and the optical waveguide layer4is formed in the form of a layer between the principal surface5aof the substrate5and the optical waveguide layer4. This portion of the metal film7bis used when the substrate5and the optical waveguide layer4are joined to each other in the manufacturing step of the optical waveguide substrate21, and the metal film (for example, Cr/Au) formed on the optical waveguide layer4and the metal film (for example, Cr/Au) formed on the principal surface5aof the substrate5are bonded by thermo conpression bonding to each other as described later.

A method of manufacturing the optical device11according to this embodiment thus constructed will be described.FIGS. 14 to 16are side cross-sectional views showing the manufacturing process of the optical device11in sequence.

First, as shown inFIG. 14(a), the optical waveguide layer4is formed on the principal surface30aof the wafer30, and the grooves30care formed in the wafer30. The method of forming the optical waveguide layer4and the grooves30cis the same as the first embodiment (FIGS. 4 to 9). Subsequently, as shown inFIG. 14(b), a metal film70of Cr/Au, Ti/Pt/Au, Au/Sn, for example, is formed on the optical waveguide layer4and on the bottom surfaces and side surfaces of the grooves30cof the wafer30by deposition or sputtering. Only portions that are parts of the metal film70formed on the side surfaces of the grooves30cand are formed on the side surfaces4pto4rof the optical waveguide layer4are thinly scraped by dicing half cut (FIG. 14(c)) so that the side surfaces4pto4rof the optical waveguide layer4are exposed from the metal film70. Furthermore, these portions of the metal film70may be removed by etching or the like. Then, as shown inFIG. 14(d), the wafer30is cut along the cutting lines A1(seeFIG. 10), thereby forming the substrate3.

Still furthermore, as shown inFIG. 15(a), the grooves50care formed in the principal surface50aof the wafer50. The method of forming the groove50cis the same as the first embodiment (seeFIG. 11). Subsequently, as shown inFIG. 15(b), a metal film71of Cr/Au is deposited and formed on the main principal surface50aof the wafer50and on the bottom surfaces and side surfaces of the grooves50c. Then, as shown inFIG. 15(c), the wafer50is cut along the cutting lines A2(seeFIG. 11)to form the substrate5.

Subsequently, as shown inFIG. 16(a), the chip including the substrate3and the optical waveguide layer4and the substrate5are affixed to each other to complete the optical waveguide substrate21. At this time, the principal surface3aof the substrate3and the principal surface5aof the substrate5are facing each other, and the metal film70on the optical waveguide layer4and the metal film71on the principal surface5aare press-fitted to each other while heat is applied thereto. At this time, as shown inFIG. 16(b), the metal film70on the optical waveguide layer4and the metal film71on the principal surface5are integrated with each other, and the layered portion of the metal film7bwhich is located between the optical waveguide layer4and the substrate5is formed. Accordingly, the optical waveguide substrate21of this embodiment is formed. Finally, the photodetecting element6is joined via the bump electrodes6bof the photodetecting element6to the metal film70(that is, the metal film7a) formed on the portion contained within the mount area2cout of the step portion3cof the substrate3and the metal film71formed on the portion contained within the mount area2cout of the step portion5cof the substrate5(that is, the portion on the step portion5cout of the metal film7b), whereby the photodetecting element6is mounted on the optical waveguide substrate21. Furthermore, when Au/Sn is used for the metal layer (metal films7aand7b) of this embodiment, a semiconductor optical element can be joined without any bump electrode if there is provided an electrode surface only in the semiconductor optical element. Accordingly, the optical device11of this embodiment is completed as described above.

According to the optical device11of this embodiment, as in the case of the optical device1of the first embodiment, the space in which the photodetecting element6can be mounted can be secured on the side surface of the optical waveguide substrate21, and also the end face of the core portion4cof the optical waveguide layer4and the photodetecting element6can be preferably optically coupled to each other. Accordingly, the optical coupling efficiency between the photodetecting area6aof the photodetecting element6and the core portion4ccan be enhanced.

Furthermore, as in the case of the optical device11of this embodiment, the optical waveguide substrate21may have a wiring pattern such as the metal films7aand7bto be electrically connected to the photodetecting element6on the side surfaces3band5bof the substrates3and5in the mount area2c(in this embodiment, on the step portions3cand5c). Accordingly, the electrical connecting means of the photodetecting element6can be secured on the side surface of the optical waveguide substrate21, and the photodetecting element6can be directly mounted on the side surface of the optical waveguide substrate21. In the optical device11of this embodiment, in order to enhance the optical coupling efficiency in the gap between the core portion4cof the optical waveguide layer4and the photodetecting area6aof the photodetecting element6, a refractive index matching resin layer is preferably formed between the end face of the core portion4cof the optical waveguide layer4and the photodetecting element6.

Furthermore, as in the case of the optical device11of this embodiment, the optical waveguide substrate21may have the metal layer (metal layer7b) for joining the substrate5and the optical waveguide layer4between the substrate5and the optical waveguide layer4. That is, when the optical waveguide substrate21is manufactured, the metal films70and71are formed on the surface of the optical waveguide layer4and the principal surface5aof the substrate5as described above, and the metal films70and71are bonded by thermo compression bonding to each other, whereby the optical waveguide layer4and the substrate5can be firmly joined to each other. Therefore, according to the optical device11of this embodiment, there can be implemented the optical waveguide substrate21in which the optical waveguide layer4and the substrate5are firmly joined to each other.

FIG. 17is a perspective view showing the construction of the optical waveguide substrate22as a first modification of the optical device1according to the first embodiment. The difference in construction between the optical waveguide substrate2of this modification and the optical waveguide substrate2of the first embodiment resides in the presence or absence of the recess portion2b(seeFIG. 1). That is, the optical waveguide substrate22of this modification is designed so that the side surface22athereof is flat. Specifically, the optical waveguide substrate22has substrates31and51, and an optical waveguide layer4provided between the substrate31and the substrate51. The side surface31bof the substrate31and the side surface51bof the substrate51are formed to be flat. The side surfaces31band51bof the substrates31and51are preferably formed by cutting the wafers30and50without forming grooves30cand50cin the manufacturing steps shown inFIGS. 9 to 11.

On the side surface22aof the optical waveguide substrate22of this modification, the mount area2cfor mounting the photodetecting element6thereon is set to an area containing the end face4gof the core portion4c, a part of the side surface31bof the substrate3in the vicinity of the end face4gand a part of the side surface51bof the substrate5in the vicinity of the end face4g.

The optical waveguide substrate provided to the optical device may be designed so that the side surface is flat as in the case of the optical waveguide substrate22of this modification. The optical device has the optical waveguide substrate22as described above, so that the same operation and effect as the optical device1of the first embodiment can be achieved.

FIG. 18(a) is a perspective view showing the construction of an optical waveguide substrate23as a second modification of the optical device1according to the first embodiment.FIG. 18(b) is a side view showing the construction of the optical device12of this modification.FIG. 18(b) is a side view showing the optical device12when it is viewed in a direction along the core portions4aand4bprovided to the optical device12.

The difference in construction between the optical device12of this modification and the optical device1of the first embodiment resides in the shape of the optical waveguide substrate23. That is, the optical waveguide substrate23of this modification has a substrate52in place of the substrate5of the first embodiment. The step portion52cof the substrate52is formed to be shallower than the step portion3cof the substrate3. Thereby, a step occurs between the side surface3bof the substrate3and the side surface52bof the substrate52. This step also occurs between a part of the side surface3bof the substrate3which is contained in the mount area2cand a part of the side surface52bof the substrate52which is contained in the mount area2c. Accordingly, in the optical device12, the photodetecting element6mounted on the side surface23aof the optical waveguide substrate23is inclined as shown inFIG. 18(b).

As described above, according to the optical device12of this modification, the photodetecting element6is inclined with respect to the optical axis of light (to-be-detected light) emitted from the end face4gof the core portion4cby the step between the side surface3bof the substrate3and the side surface52bof the substrate52. Accordingly, when the photodetecting element6is used as the semiconductor optical element as in the case of this modification, the photodetecting area6aof the photodetecting element6can be preferably inclined with respect to the optical axis of the to-be-detected light, thereby Fresnel reflection in the photodetecting area6acan be reduced. The Fresnel reflection means the reflection at the boundary end faces of the incident portion and emission portion of the optical waveguide. By bringing the boundary face with an angle, return light based on reflection can be reduced. In the case of this embodiment, the semiconductor optical element is mounted being inclined, whereby the Fresnel reflection can be reduced, and the angle thereof is preferably equal to about 8°. Since the gap occurs between the photodetecting area6aof the photodetecting element6and the end face4gof the core portion4cby the step between the side surface3band the side surface52b, the refractive index matching resin can be easily poured into the gap and thus the optical coupling efficiency between the photodetecting element6and the core portion4ccan be further enhanced.

FIG. 19is a perspective view showing the construction of an optical device13as a third modification of the optical device1according to the first embodiment. The main difference in construction between the optical device13of this modification and the optical device1of the first embodiment resides in the number of photodetecting elements6. That is, the optical device13of this modification has a plurality of (for example, four) photodetecting elements6. The optical waveguide substrate24of this modification has an optical waveguide layer41in place of the optical waveguide layer4of the first embodiment. The optical waveguide layer41is constructed to contain the core portions4cand the wavelength filters4dwhose numbers correspond to the number of the photodetecting elements6.

Specifically, the optical waveguide substrate24has a substrate32(first substrate) and a substrate5(second substrate) and an optical waveguide layer41provided between the substrate32and the substrate5. The construction of the substrate5is the same as the first embodiment except that the dimension thereof is longer by the amount corresponding to the incremental number of the photodetecting elements6. The optical waveguide layer41contains plural core portions4cand plural wavelength filters4dwhose numbers correspond to the number of the photodetecting elements6, and the end face4gof each of the plural core portions4cis exposed at the side surface4rof the optical waveguide layer41. These end faces4gare arranged on the side surface4rof the optical waveguide layer41in juxtaposition with one another in the direction along the edges of the principal surface3aand5a. The optical waveguide layer41contains the films4nand4oexposed at the side surface4ras marks indicating the position of each end face4gin the layer thickness direction in the vicinity of each end face4g. Furthermore, the optical waveguide layer41has core portions4f. The core portions4fare disposed between plural wavelength filters4d, and the longitudinal directions thereof are set to the direction crossing the side surfaces4pand4q. Plural grooves3ffor indicating the positions of the respective end faces4gare formed on the substrate32in accordance with the positions of the respective end faces4gin the direction along the edge of the principal surface3a.

Plural mount areas2cwhose number corresponds to the number of the photodetecting elements6are set on the side surface of the optical waveguide substrate24. Each of the plural mount areas2cis set to contain each end face4g, a part of the side surface3bof the substrate32(a part of the step portion3cin this modification) and a part of the side surface5bof the substrate5(a part of the step portion5c). Each of the plural photodetecting elements6is disposed in each of the plural mount areas2c.

According to the optical device13of this modification, the space in which the plural photodetecting elements6can be mounted can be secured on the side surface of the optical waveguide substrate24, and each of the photodetecting elements6strides over the corresponding end face4g, so that each photodetecting element6and each end face4gof the core portion4ccan be optically coupled to each other without a clad portion4h. Therefore, according to the optical device13of this modification, as in the case of the optical device1of the first embodiment, the light scattering caused by the clad portion or the like can be avoided, and the optical coupling efficiency between each photodetecting element6and each core portion4ccan be enhanced. Furthermore, the plural photodetecting elements6are disposed on the side surface of the optical waveguide substrate24, so that many photodetecting elements6can be integrated in the optical device13and the optical device13can be miniaturized.

In the optical waveguide coupler disclosed in Japanese Published Unexamined Patent Application No. 10-293219, the grooves for mounting the wavelength filters are formed so as to cut the optical guide into pieces, and thus light is attenuated by the grooves. Accordingly, when light waveguided through the core is branched by plural wavelength filters, the light loss is increased and thus the number of branches (that is, the number of semiconductor optical elements to be mounted) is suppressed to a small value. On the other hand, in the optical de-vice13of this modification, each photodetecting element6and each core portion4care directly optically coupled to each other. Therefore, the light loss is small and the number of branches for light (the number of photodetecting elements6) can be increased. When plural wavelength filters which are different in reflection wavelength are used, the wavelength components whose number corresponds to the number of the semiconductor optical elements can be branched.

Furthermore, in the optical waveguide coupler disclosed in Japanese Published Unexamined Patent Application No. 10-293219, the optical waveguide and the semiconductor optical element are optically coupled to each other via the clad, and thus when plural semiconductor optical elements are provided, light propagates through the clad, and thus there is a risk that cross-talk occurs between adjacent semiconductor optical elements. Furthermore, in order to avoid cross-talk, it is necessary that the plural semiconductor optical elements are disposed keeping a sufficient interval therebetween. On the other hand, in the optical device13of this modification, each photodetecting element6and each core portion4care directly optically coupled to each other, and thus the cross-talk between the adjacent photodetecting elements6can be reduced. Accordingly, plural photodetecting elements6can be arranged every short interval. Therefore, as compared with the optical waveguide coupler disclosed in Japanese Published Unexamined Patent Application No. 10-293219, the plural photodetecting elements6can be integrated with high density, or the optical device can be further miniaturized.

FIG. 20is a perspective view showing the construction of an optical device14as another mode of this modification. The difference in construction between the optical device14and the optical device13shown inFIG. 19resides in that a photodetecting element array61is provided in place of plural photodetecting elements6. That is, the optical device14has the photodetecting element array61including plural integrated photodetecting elements on the side surface of the optical waveguide substrate24. The photodetecting element array61is mounted over plural mount areas2con the side surface of the optical waveguide substrate24, and the plural photodetecting areas6acorrespond to the plural mount areas2c.

The above-described effect of this modification can also be preferably achieved even when the photodetecting element array61having the integrated plural photodetecting elements is used in place of plural photodetecting elements6as in the case of the optical device14.

FIG. 21is a perspective view showing the construction of the optical device15as a fourth modification of the optical device1according to the above-described first embodiment. The main difference in construction between the optical device15of this modification and the optical device1of the first embodiment resides in the shape of the substrates31and51, the number of layers of the substrate31and the optical waveguide layer4and the number of photodetecting elements6. That is, the optical waveguide substrate25of this modification has optical waveguide layers4of n layers (n represents an integer of 2 or more, andFIG. 21shows a case where n is equal to 4 as an example) laminated in the layer thickness direction. Each of the optical waveguide layers4of n layers has the same construction as the optical waveguide layer4of the first embodiment. The optical waveguide substrate25has substrates31of n and the optical waveguide layers4of n layers which are alternately laminated in the layer thickness direction, and one substrate51. Specifically, each of the optical waveguide layers4of n layers is formed on each of the n substrates31, and n layers each of which has a unit of each substrate31and each optical waveguide layer4are laminated in the layer thickness direction and joined to each other. The substrate51is joined to the surface of the optical waveguide layer4located at the most end portion in the layer thickness direction. The substrates31and51of this modification are designed so that the side surfaces31band51bthereof are flat as in the case of the substrates31and51of the first modification.

Mount areas2cof n are set on the side surface25aof the optical waveguide substrate25. Each of the n mount areas2cis set to contain the end face4gof the core portion4cof the corresponding optical waveguide layer4out of the optical waveguide layers4of n layers and parts of side surfaces31bof the substrates31(and the side surfaces51bof the substrates51) disposed at both sides of the optical waveguide layer4. Each of the photodetecting elements6of n is disposed in each of the mount areas2cof n.

According to the optical device15of this modification, the space in which the photodetecting elements6of n can be mounted can be secured on the side surface of the optical waveguide substrate25, and each of the photodetecting elements6of n strides over the end face4gof the core portion4cof the corresponding optical waveguide layer4, whereby the end face4gof the core portion4cof each optical waveguide layer4and each photodetecting element6can be optically coupled to each other without a clad portion4h. Therefore, according to the optical device15of this modification, as in the case of the optical device1of the first embodiment, light scattering caused by the clad portion, etc., can be avoided, and the optical coupling efficiency between the core portion4cof each optical waveguide layer4and each photodetecting element6can be enhanced. Furthermore, the optical waveguide layers4of n layers are laminated in the layer thickness direction, whereby many optical waveguides (core portions4ato4c) are integrated in the optical device15, and also the optical device15can be miniaturized.

FIG. 22is a perspective view showing the construction of a optical waveguide substrate26as a fifth modification of the optical device1according to the first embodiment. The difference in construction between the optical waveguide substrate26of this modification and the optical waveguide substrate2of the first embodiment resides in the presence or absence of the recess portion2b(seeFIG. 1) and the number of layers of the optical waveguide layers4disposed between the two substrates. That is, the optical waveguide substrate26of this modification has two substrates31disposed so that the principal surfaces3athereof are facing each other, and the optical waveguide layers4of two layers are superposed between the two substrates31. In this modification, one substrate31of the two substrates31corresponds to a first substrate of the present invention, and the other substrate31corresponds to a second substrate of the present invention. The construction of the optical waveguide layers4(the core portions4ato4c, the wavelength filter4d, the clad portion4h, and the films4ito4o) are the same as the construction of the optical waveguide layers4of the first embodiment.

The two substrates31have the same construction as the substrate31of the first modification (seeFIG. 17). In this modification, the optical waveguide layers4are formed on the principal surfaces3aof the two substrates31, and the surfaces of the optical waveguide layers4are joined to each other, thereby constructing the optical waveguide substrate26. Furthermore, the mount area2con the side surface26aof the optical waveguide substrate26may collectively contain the end faces4gof the core portions4cof the optical waveguide layers4of 2 layers as shown inFIG. 22. Or, the mount areas2cmay be set individually to the end faces4g.

As in the case of this modification, the optical waveguide substrate may have plural optical waveguide layers4between the two substrates31. Even in the above construction, the same operation and effect as the optical device1of the first embodiment can be achieved.

FIG. 23is a side cross-sectional view showing the construction of an optical device16as a sixth modification of the optical device1according to the first embodiment. The difference in construction between the optical device16of this modification and the optical device1of the first embodiment resides in the presence or absence of a wiring substrate8. That is, the optical device16of this modification has a wiring substrate8having a wiring pattern (for example,9aand9b) electrically connected to the photodetecting element6between the side surface2aof the optical waveguide substrate2and the photodetecting element6. The construction of the optical waveguide substrate2in the optical device16of this modification is the same as the first embodiment.

The wiring substrate8is a plate-shaped member having the principal surface8a. The wiring substrate8is mounted on the side surface2aof the optical waveguide substrate2so that the back surface thereof and the side surface4rof the optical waveguide layer4are facing each other. Furthermore, a light passing portion as an opening (through hole)8bis formed at the position corresponding to the end face4gof the core portion4cin the wiring substrate8, and to-be-detected light L passes through this opening8b, whereby the photodetecting area6aof the photodetecting element6and the end face4gof the core portion4care optically coupled to each other.

Furthermore, metal wiring patterns9aand9bare provided on the principal surface8aof the wiring substrate8. The wiring patterns9aand9bare provided in an area containing the corresponding area above the mount area2cin which the photodetecting element6is mounted in the principal surface8aof the wiring substrate8. The photodetecting element6is joined on the wiring patterns9aand9bvia the bump electrodes6bto thereby mount the photodetecting element6. The wiring patterns9aand9bare electrically connected to an external circuit of the optical device16through wires10and10bor the like.

According to the optical device16of this modification, the photodetecting element6can be preferably mounted on the side surface2aof the optical waveguide substrate2, and also the photodetecting element6and the end face4gof the core portion4ccan be preferably optically coupled to each other via the opening8bprovided to the wiring substrate8. Furthermore, after the photodetecting element6is mounted on the wiring substrate8, the wiring substrate8is secured to the optical waveguide substrate2. Accordingly, particularly when plural photodetecting elements6are used (seeFIG. 19andFIG. 21), the photodetecting elements6can be easily mounted. As the light passing portion provided to the wiring substrate8, not only the opening8bshown in this modification, but also various types for transmitting light (to-be-detected light) therethrough such as a lens, a transparent member or the like embedded in the wiring substrate8, for example, may be applied.

FIGS. 24 to 29are diagrams showing another manufacturing method of the optical waveguide layer4provided to the optical device1of the first embodiment as a seventh modification.

First, the wafer30having the principal surface30ais prepared as shown inFIG. 24. Subsequently, as shown inFIG. 25(a) andFIG. 25(b) showing an enlarged view of a part ofFIG. 25(a), the lower clad layer40ais formed on the principal surface30aof the wafer30. At this time, when the lower clad layer40ais formed of a polymer such as a polyimide or the like, the lower clad layer40amay be coated (preferably, spin-coated) on the main principal surface30a.

Subsequently, as shown inFIG. 26(a) andFIG. 26(b) showing an enlarged view of a part ofFIG. 26(a), the core layer40cis formed on the lower clad layer40a. At this time, the core layer40cis formed of material having a higher refractive index than the lower clad layer40a. Furthermore, when the core layer40cis formed of a polymer such as a polyimide or the like, the core layer40cmay be coated (preferably, spin-coated) on the lower clad layer40aas in the case of the lower clad layer40a.

Subsequently, the core layer40cand the lower clad layer40aare etched by using a mask to form the core portions4ato4cand positioning portions4tand4uas shown inFIG. 27. At this time, the core layer40cand the lower clad layer40aare etched (preferably dry-etched) by using a mask having a planar shape of the core portions4ato4cand the positioning portions4tand4u. Here, the positioning portions4tand4uare portions for defining the position of the reflecting face of the wavelength filter4dmounted in the subsequent step. The positioning portions4tand4uare formed juxtaposed to each other along the longitudinal direction of an area in which the wavelength filter4dshould be mounted. Furthermore, the positioning portions4tand4uhave the recess portion including side surfaces4vand4wfacing each other and a side surface4x, and the recess portions of the positioning portions4tand4uare disposed to face each other. The portions of the positioning portions4tand4uat which the core layer40cis etched are positioned in the same layer as the core portions4ato4c, and also formed of the same material.

When the core portions4ato4cand the positioning portions4tand4uare formed, the core layer40cand the lower clad layer40aare preferably etched by dry etching. Furthermore, in order to secure the height of the positioning portions4tand4u, it is preferable that the etching depth when the core layer40cand the lower clad layer40aare etched is larger than the thickness of the core layer40c. For example, the core layer40cand the lower clad layer40amay be etched until the principal surface30aof the wafer30is exposed.

Subsequently, as shown inFIG. 28, the wavelength filter4dis mounted on the principal surface30aof the wafer30. At this time, the wavelength filter4dis mounted so that the reflecting face of the wavelength filter4dis pressed against the side surface4vof the positioning portions4tand4u. As described above, the positioning portions4tand4uformed by using the same mask as the core portions4ato4care used to position the reflecting face of the wavelength filter4d, whereby the positional precision of the reflecting face of the wavelength filter4dto the core portions4ato4ccan be enhanced. When the clad player40bformed in the next step contains a polymer such as a polyimide or the like, the wavelength filter4dcontaining a polymer such as a polyimide or the like may be likewise mounted. Furthermore, more preferably, the wavelength filter4dcontaining the same kind of material as the clad layer40bmay be mounted.

Subsequently, as shown inFIG. 29, the clad layer40bhaving a lower refractive index than the core portions4ato4cis formed. At this time, the clad layer40bis formed so as to cover all the principal surface30a, the core portions4ato4c, the positioning portions4tand4uand the wavelength filter4d. Accordingly, the clad layer40bcontaining the core portions4ato4cand the wavelength filter4dtherein is formed. When the clad layer40bis formed of a polymer such as a polyimide or the like, the clad layer40bmay be formed by coating (preferably, spin-coating). Thereafter, by carrying out the same steps as shown inFIGS. 9 to 11of the first embodiment, the optical waveguide substrate according to this modification is completed.

As described above, according to one or more embodiments and modifications of the optical device of the present invention, the optical coupling efficiency between the semiconductor optical element and the optical waveguide can be enhanced.

The optical device of the present invention is not limited to each embodiment and each modification, and various other modifications may be made. For example, in the respective embodiments and the respective modifications, the optical part such as the wavelength filter is contained in the optical waveguide layer, however, no optical part may be contained in the optical waveguide layer. Furthermore, various parts (for example, a half mirror) other than the wavelength filter may be used as the optical part.