Optical module

There is provided an optical module in which leaked light or the like from a plurality of optical elements on the same substrate is made less likely to affect adjacent optical elements, and a cross-talk noise can be thereby significantly reduced. The optical module includes an internal waveguide in a first trench of a substrate, a mirror section, and optical elements. A plurality of the first trenches of the substrate are formed independently of each other and substantially in parallel with each other, and lengths of adjacent first trenches from the end surface of the substrate are made different from each other. The optical elements are mounted on the surface of the substrate so as to oppose the minor sections formed at the tip portions of the first trenches having the different lengths.

RELATED APPLICATIONS

This application is the U.S. National Phase under 35 U.S.C. §371 of International Application No. PCT/JP2012/003904, filed Jun. 14, 2012, which in turn claims the benefit of Japanese Application No. 2011-137962, filed on Jun. 22, 2011 and Japanese Application No. 2011-194766, filed on Sept. 7, 2011, the disclosures of which Applications are incorporated by reference herein.

TECHNICAL FIELD

The present invention relates to an optical module including an optical element.

BACKGROUND ART

Conventionally, there is known an optical module that includes an internal waveguide, a mirror section for changing an optical path, an optical element, and an external waveguide. The internal waveguide is provided in a trench formed in the surface of a substrate. The mirror section for changing the optical path is formed at the tip portion of the trench. In addition, the optical element is mounted on the surface of the substrate so as to oppose the mirror section. The optical element emits an optical signal to a core section of the internal waveguide via the mirror section, or receives the optical signal from the core section of the internal waveguide via the mirror section. The external waveguide has a core section optically coupled to the core section of the internal waveguide.

In such an optical module, in order to achieve bidirectional transmission or an increase in transmission capacity, it is necessary to use a plurality of the optical modules. As a result, a device including a plurality of the optical module is increased in size. To cope with this, it is desired to implement the optical module that is small in size, low in height, and capable of bidirectional or multi-channel transmission.

In order to implement such an optical module, it is conceived to mount a plurality of the optical elements on the surface of the substrate such that the optical elements are disposed close to each other. In this case, it is necessary to form the internal waveguides and the mirror sections at a small pitch so as to correspond to the interval of the plurality of the optical elements.

Conventionally, like an optical module described in Patent Document 1, there is proposed an optical module in which a plurality of optical transmission paths having different lengths from the end surface of the substrate are formed on the substrate, the optical elements are disposed close to each other at the ends of the individual optical transmission paths, and each of the optical elements is a light-emitting element or a light-receiving element. In this optical module, countermeasures against a cross-talk noise are not taken.

In a case where a plurality of the optical elements are close to each other, and the internal waveguides and the mirror sections are formed so as to reduce the pitch between the internal waveguides and the pitch between the mirror sections, leaked light from the optical element or scattered light from the mirror section or the internal waveguide enters the mirror section and the internal waveguide of the adjacent optical element, and the cross-talk noise is thereby generated. Such a cross-talk noise causes a transmission error. Consequently, it is requested to reduce the cross-talk noise as much as possible.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an optical module small in size and low in height in which leaked light or the like from a plurality of optical elements on the same substrate is made less likely to affect the adjacent optical elements and a cross-talk noise can be thereby reduced significantly.

The present invention is an optical module including a substrate that is formed with a plurality of first trenches in a surface thereof, an internal waveguide that is provided in each of the plurality of first trenches and has a core section, a mirror section for changing an optical path, formed at each of tip portions of the plurality of first trenches, and an optical element that is mounted on the surface of the substrate so as to oppose the mirror section, and emits an optical signal to the core section of the internal waveguide via the mirror section or receives the optical signal from the core section of the internal waveguide via the mirror section, wherein the plurality of first trenches of the substrate are formed independently of each other and substantially in parallel with each other, lengths of the adjacent first trenches from an end surface of the substrate are different from each other, and the optical elements are mounted on the surface of the substrate so as to oppose the mirror sections formed at the tip portions of the first trenches having the different lengths.

A configuration can be adopted in which a plurality of the optical elements include a light-emitting element and a light-receiving element, and the light-emitting element is mounted on the surface of the substrate so as to oppose the mirror section formed at a tip portion of the internal waveguide shorter in length than the internal waveguide optically coupled to the light-receiving element.

A configuration can be adopted in which the optical module further includes an external waveguide that has a core section optically coupled to the core section of the internal waveguide, a second trench extending from the first trench of the internal waveguide is formed in the surface of the substrate, and an optical axis of the internal waveguide and an optical axis of the external waveguide are set so as to match with each other by fitting and fixing the external waveguide in and to the second trench.

A configuration can be adopted in which a partition wall portion is formed between the adjacent second trenches so as not to be separated from a partition wall portion between the adjacent first trenches.

A configuration can be adopted in which the optical module further includes an external waveguide that has a core section optically coupled to the core section of the internal waveguide, and the external waveguide is a multi-channel optical fiber.

A configuration can be adopted in which the optical module further includes the external waveguide that has the core section optically coupled to the core section of the internal waveguide, and the external waveguide is a multi-channel film-like flexible waveguide, i.e., a flexible waveguide film.

A configuration can be adopted in which a convex layer made of a material identical with a material of a cladding section of the internal waveguide is formed on the surface of the substrate between the optical elements.

A configuration can be adopted in which the optical module further includes an external waveguide that has a core section optically coupled to the core section of the internal waveguide, a plurality of second trenches deeper than the plurality of first trenches and each having a substantially V-shaped cross section are formed in the surface of the substrate continuously from the first trenches, and the external waveguide includes an optical fiber that has a fiber cladding section disposed in each of the plurality of second trenches and a fiber core section as the core section of the external waveguide.

A configuration can be adopted in which the optical module further includes an external waveguide that has a core section optically coupled to the core section of the internal waveguide, a plurality of second trenches deeper than the plurality of first trenches are formed in the surface of the substrate continuously from the first trenches, the external waveguide includes an optical fiber that has a fiber cladding section disposed in each of the second trenches and a fiber core section as the core section of the external waveguide, and the second trench includes a bottom surface that is formed to have a predetermined width and inclined surfaces that are connected to both ends of the bottom surface in a width direction and support an outer periphery of the fiber cladding section.

A configuration can be adopted in which the core section of the internal waveguide has an inclined surface that gradually reduces a width of the core section from the mirror section toward a connection end portion with the fiber core section of the optical fiber in a case where the optical element is a light-emitting element.

A configuration can be adopted in which the core section of the internal waveguide has an inclined surface that gradually reduces a width of the core section from a connection end portion with the fiber core section of the optical fiber toward the mirror section in a case where the optical element is a light-receiving element.

A configuration can be adopted in which the width of the core section of the internal waveguide is smaller than a width of an upper end of the first trench.

A configuration can be adopted in which the first trench has a substantially trapezoidal cross section, and a bottom surface of the first trench is wider than the core section of the internal waveguide.

A configuration can be adopted in which a third trench deeper than the second trench is formed in the surface of the substrate continuously from the second trench, and the third trench is bonded to a sheathing section of the optical fiber.

A configuration can be adopted in which the substrate is disposed on another substrate larger in size than the substrate, and a sheathing section of the optical fiber is fixed to the other substrate.

A configuration can be adopted in which the substrate is disposed on another substrate larger in size than the substrate, a sheathing body is fixed to an outer periphery of a sheathing section of the optical fiber, and the sheathing body is fixed to the other substrate.

According to the present invention, the lengths of the adjacent first trenches are different from each other, and the optical elements are mounted on the surface of the substrate so as to oppose the mirror sections formed at the tip portions of the first trenches having the above lengths. Accordingly, it is possible to secure a large distance between the adjacent optical elements disposed at different positions in a length direction, e.g., the unaligned adjacent optical elements.

Consequently, leaked light from the optical element or reflected scattered light from the mirror section or the internal waveguide becomes less likely to enter the mirror section or the internal waveguide of the adjacent optical element, and hence a cross-talk noise becomes less likely to occur. In addition, the internal waveguides are provided in the plurality of the first trenches formed independently of each other and substantially in parallel with each other, and hence the internal waveguides don't interfere with each other due to the partition wall portion between the adjacent first trenches.

Thus, a plurality of the optical elements are mounted on the substrate so as to be close to each other in a width direction, and the internal waveguides and the mirror sections are formed at a small pitch so as to correspond to an interval of the optical elements. With this, it becomes possible to implement small in size, low in height, and bidirectional or multi-channel transmission. In addition, it is possible to significantly reduce the cross-talk noise by securing the large distance between the adjacent optical elements and preventing the interference between the adjacent internal waveguides.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinbelow, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

Each ofFIGS. 1 to 5shows a single channel optical module in which one internal waveguide16is formed in one first trench1aof each of first substrates1and3. The outline of the single channel optical module will be described first with reference toFIGS. 1 to 5and, thereafter, a detailed description will be given of a multi-channel optical module according to a first embodiment of the present invention that includes the structure of the single channel optical module with reference toFIGS. 6 to 9.

FIG. 1is a schematic side view of the single channel optical module.FIGS. 2A to 2Care views showing the first substrate1of the optical module on a light-emitting side ofFIG. 1,FIG. 2Ais a side cross-sectional view of the first substrate1,FIG. 2Bis a I-I line cross-sectional view ofFIG. 2A, andFIG. 2Cis an II-II line cross-sectional view ofFIG. 2A.FIGS. 3A and 3Bare views showing the first substrate1,FIG. 3Ais a perspective view of the first substrate1, andFIG. 3Bis a perspective view of the first substrate1formed with the internal waveguide16.FIGS. 4A and 4Bare views showing the first substrate1,FIG. 4Ais a perspective view of the first substrate1on which a light-emitting element12ais mounted, andFIG. 4Bis a perspective view of the first substrate1into which an optical fiber2is inserted.FIG. 5Ais a perspective view of the first substrate1to which a holding block24is fixed, andFIG. 5Bis a perspective view of the optical fiber2.

InFIG. 1, the optical module includes the first substrate (mount substrate)1on a light-emitting side, the first (mount) substrate3on a light-receiving side, and the optical fiber2that optically couples the first substrates1and3. Note that, in the following description, a vertical direction (a direction of an arrow Y) inFIG. 1is referred to as a vertical direction (height direction), a direction orthogonal to paper withFIG. 1is referred to as a lateral direction (width direction), the left side inFIG. 1is referred to as the front, and the right side inFIG. 1is referred to as the rear.

Each of the first substrates1and3requires heat radiation properties and stiffness in order to avoid an influence by heat during mounting and an influence by a stress resulting from a usage environment. In addition, in the case of optical transmission, optical coupling efficiency of a predetermined ratio or more is required from the light-emitting element12ato a light-receiving element12b, and hence it is necessary to mount the light-emitting element12aand the light-receiving element12bwith high accuracy and suppress the position fluctuation thereof during use as much as possible. Accordingly, as each of the first substrates1and3, a silicon (Si) substrate is used in this single channel optical module.

In particular, when each of the first substrates1and3is the silicon substrate, it becomes possible to perform high-accuracy etching trench processing in the surface by utilizing the crystal orientation of silicon. For example, by utilizing this trench, it is possible to form a high-accuracy mirror section15described later and the high-accuracy internal waveguide16. In addition, the etched surface of the silicon substrate is excellent in planarity.

The first substrates1and3are disposed on the surfaces (upper surfaces) of second substrates (interposer substrates)6larger in size than the first substrates1and3. To the back surface (lower surface) of each second substrate6, a connector7for electrical connection to other circuit devices is attached.

On the surface (upper surface) of the first substrate1, the light-emitting element12afor converting an electric signal to an optical signal is flip-chip mounted using a bump12c(seeFIG. 2) with its light-emitting surface faced downward. In addition, on the surface of the second substrate6, an IC substrate (signal processing section)4afor transmitting the electric signal to the light-emitting element12ais mounted.

In this single channel optical module, a vertical cavity surface emitting laser (VCSEL) as a semiconductor laser is used as the light-emitting element12a. An LED or the like may also be used as the light-emitting element12a.

The IC substrate4ais a driver IC that drives the VCSEL, and is disposed in the vicinity of the light-emitting element12a. The light-emitting element12aand the IC substrate4aare connected to a metal circuit (a patterning circuit by copper or gold sputtering) and a gold wire formed on the surface of the first substrate1.

As shown inFIG. 3A, a first trench (waveguide formation trench)1ain a substantially trapezoidal shape and a second trench1bin a substantially V shape that is deeper than the first trench1aare continuously formed in the surface of the first substrate1in a front and rear direction.

At the tip portion of the first trench1a, a mirror section15for changing an optical path that bends the optical path by 90 degrees is formed at a position immediately below the light-emitting element12a.

As shown inFIG. 3B, in the first trench1aof the first substrate1, there is provided the internal waveguide16that is optically coupled to the light-emitting element12aof the first substrate1. The internal waveguide16extends from the mirror section15in the direction of the second trench1b, and the end surface of the internal waveguide16is flush with a rear end portion1dof the first trench1aor slightly recessed toward the mirror section15.

The internal waveguide16is constituted by a core section17having a substantially square cross section that has a high refractive index of light propagation, and a cladding section18having a refractive index lower than that of the core section17. As shown inFIG. 2C, both right and left surfaces of the core section17are covered with the cladding section18. The upper surface of the core section17is also thinly covered with the cladding section18though not shown in the drawing.

As shown inFIG. 4A, at a predetermined position on the surface of the first substrate1on which the internal waveguide16is provided, the light-emitting element12ais mounted. As shown inFIG. 2A, a space between the light-emitting element12aand the core section17is filled with an adhesive optically transparent resin (under-fill material)13.

Herein, a description will be given of a production method of the optical module on the light-emitting side. Note that, since it is possible to produce the optical module on the light-emitting side and the optical module on the light-receiving side separately and the production methods thereof are the same, only the production method of the optical module on the light-emitting side will be described.

A plurality of the mount substrates1are formed at the same time by using a silicon wafer (silicon substrate), the silicon wafer is finally cut, and the mount substrates1shown inFIG. 3are individually separated from the silicon wafer. As the silicon wafer, for etching performed at the subsequent step, the silicon wafer of which the crystal orientation is selected is prepared.

Next, in the silicon wafer, the first trench (waveguide formation trench)1aand a surface inclined by 45° for forming the mirror section15are formed. They are formed by anisotropic etching that uses a difference in the etching rate of a silicon crystal. The 45°-inclined surface is formed by adjusting the shape of an etching mask and etchant concentration and composition. In addition to the anisotropic etching, the formation method of the first trench1aincludes a formation method of dry etching such as reactive ion etching or the like.

When the first trench1ais formed at the same time as the 45°-inclined surface, the shape of the cross section of the first trench1abecomes substantially trapezoidal, and the width of the first trench1ais increased. No problem arises if the first trench1adoes not contact a bonding pad for the light-emitting element12aformed in the next step, and hence the first trench la may have the increased width as described above.

Although the second trench1bcan be formed by the anisotropic etching, the second trench1bmay be formed concurrently with the formation of the first trench1a, or may be formed separately from the first trench1a.

A wiring pattern (not shown) for mounting the light-emitting element12ais formed on the silicon wafer. The wiring is performed by depositing gold on the silicon wafer and patterning the gold. At this point, the gold is also deposited on the 45°-inclined surface and the mirror section15is thereby formed. Note that, although depending on a wavelength to be used, it is also possible to use the 45°-inclined surface as the mirror section15without depositing the gold, but reflectance and optical coupling efficiency are increased by depositing the gold on the 45°-inclined surface in a case where, e.g., a light source of near infrared rays is used. Note that, as the wiring material other than gold, there are cases where a multilayer structure of titanium, nickel, gold, and aluminum, or chromium, nickel, and gold is formed on the mount substrate from the viewpoint of easiness and connection reliability in soldering process in the subsequent step. Examples of the thickness when the multilayer structure is formed include 0.5 μm, 1 μm, and 0.2 μm.

Next, as shown inFIGS. 3A and 3B, the internal waveguide16is formed in the first trench1a. First, a core material is applied onto the first substrate1, and the core material is made even on the first substrate1so as to be flat by using a flat mold. Thereafter, only the core portion is irradiated with ultraviolet rays using a mask, the core section is thereby cured, and an unnecessary portion other than the core section is developed and removed. Subsequently, a cladding material having the refractive index lower than that of the core material is applied to the first trench1aformed with the core section, and is made even on the first substrate1similarly to the core material. With the cladding material being flat, the cladding material is blocked using the mask such that the portion of the first trench1ais irradiated with ultra violet rays, and the cladding material is thereby cured. The mask is adjusted such that only a region covering the outer peripheral portion of the core section is cured, and is designed such that the cladding material does not cover a circuit in a portion where the light-emitting element12ais amounted.

Subsequently, as shown inFIGS. 4A and 4B, the light-emitting element12ais mounted on the silicon wafer. A bump is formed at the light-emitting element12aby stud bump bonding, the silicon wafer and the light-emitting element12aare heated to 200° C., and ultrasonic bonding thereof is performed.

Note that, although not shown in the drawing, after the light-emitting element12ais mounted, the space between the light-emitting element12aand the first substrate1is filled with the under-fill material, and the bonding strength between the light-emitting element12aand the first substrate1is reinforced. The under-fill material also has the effect of eliminating an air layer between the optical element and the internal waveguide and enhancing the optical coupling efficiency. In addition, in order to improve an environmental resistance, the entire substrate may also be sealed with an elastic sealing material.

Then, as shown inFIG. 1, the first substrate1on which the light-emitting element12ais mounted is mounted on the surface (upper surface) of the second substrate6, the IC substrate4ais also mounted thereon, and the connector7is attached to the lower surface of the second substrate6.

As described above, in the first embodiment, the light-emitting element12ais mounted on the upper surface of the first substrate1mounted on the upper surface of the second substrate6, the IC substrate4ais mounted on the upper surface of the second substrate6, and the connector7is mounted on the lower surface thereof.

With this, it becomes easy to inspect the IC substrate4aof the first substrate6and the light-emitting element12aof the first substrate1individually before the first substrate1is mounted on the upper surface of the second substrate6.

In addition, even when one of the light-emitting element12aand the IC substrate4ais faulty, only one of the second substrate6and the first substrate1becomes faulty, and hence the loss of the entire substrate can be avoided.

Further, the light-emitting element12ais mounted on the first substrate1instead of the second substrate6on which the IC substrate4ais mounted, and the mirror section15and the internal waveguide16are formed on the first substrate1. With this, a thermal influence from the IC substrate4ais made less likely to be exerted on the light-emitting element12a, and light emission characteristics are stabilized.

Returning toFIG. 1, the first substrate3on the light-receiving side will be described. The basic configuration of the first substrate3on the light-receiving side is similar to that of the first substrate1on the light-emitting side. However, the first substrate3on the light-receiving side is different from the first substrate1on the light-emitting side in that the light-receiving element12bthat converts the optical signal to the electric signal is flip-chip mounted on the surface (upper surface) of the first substrate3on the light-receiving side using the bump with the light-receiving surface faced downward. In addition, the second substrate6on the light-receiving side is different from the second substrate6on the light-emitting side in that an IC substrate (signal processing section)4bthat receives the electric signal from the light-receiving element12bis mounted on the surface of the second substrate6on the light-receiving side. As the light-receiving element12b, a PD (Photo Diode) is used, and the IC substrate4bis an element such as a TIA (Trans-Impedance Amplifier) that performs the conversion of current and voltage or the like.

The first substrate1on the light-emitting side, the first substrate3on the light-receiving side, and the IC substrates4aand4bare shielded by shield cases8attached to the surfaces of the second substrates6. The optical fiber2is extended through holes8aof the shield cases8.

Next, the configuration of the optical fiber (external waveguide)2will be described. As shown inFIGS. 1 and 5, the optical fiber2includes a fiber core section21that can optically couple the core section17of the internal waveguide16of the first substrate1on the light-emitting side and the core section17of the internal waveguide16of the first substrate3on the light-receiving side. The optical fiber2is a cord type optical fiber constituted by a fiber cladding section22that surrounds the outer periphery of the fiber core section21and a sheathing section23with which the outer periphery of the fiber cladding section22is sheathed. The fiber core section21, the fiber cladding section22, and the sheathing section23are concentrically disposed, and the optical fiber2constituted by these has a circular cross section.

With this structure, the optical fiber2functions as the external waveguide that transmits light outside the first substrate1.

As shown inFIG. 1, the optical fiber2is extended through the through holes8aof the shield cases8. The sheathing section23is peeled at a position just before the second trench1bof the first substrate1, and the fiber cladding section22is exposed.

As shown inFIGS. 2A,2C and4B, the fiber cladding section22of the optical fiber2is disposed in the second trench1bof the first substrate1. The fiber cladding section22is positioned by a rising inclined portion10d(seeFIG. 2A) at the boundary portion with the first trench1a. At this point, the optical coupling is established in a positioning state where the optical axis of the core section17of the internal waveguide16of the first substrate1and the optical axis of the fiber core section21of the optical fiber2match with each other.

A gap between the end surface of the core section17of the internal waveguide16of the first substrate1and the end surface of the fiber core section21of the optical fiber2is in a range of 0 to 200 μm. Although the preferably range depends on the size of each of the core sections17and21, the gap is preferably 0 to 60 μm in general.

At the position on the surface of the first substrate1, as shown inFIGS. 2A and 5, a holding block24is disposed on the upper portion of the fiber cladding section22of the optical fiber2. A space between the holding block24and the second trench1bis filled with an adhesive14.

Thus, the portion on the tip side of the fiber cladding section22of the optical fiber2is held down onto the second trench1bby the holding block24. The portion on the tip side is bonded and fixed to the first substrate1together with the holding block24with the adhesive14.

In the optical module configured in the manner described above, the internal waveguide16constituted by the core section17and the cladding section18is provided in the first trench1aof the first substrate1. The fiber core section21of the optical fiber2disposed in the second trench1bof the first substrate1is optically connected to the core section17of the internal waveguide16. In the first substrate1on the light-emitting side having the light-emitting element12aas the optical element, the optical signal is emitted to the core section17of the internal waveguide16via the mirror section15and, in the first substrate3on the light-receiving side having the light-receiving element12bas the optical element, the optical signal from the core section17of the internal waveguide16is received via the mirror section15.

Thus, since the internal waveguide16is interposed between the tip of the fiber core section21of the optical fiber2and the mirror section15, a luminous flux emitted from the light-emitting element12adoes not spread, and the luminous flux emitted from the fiber core section21of the optical fiber2does not spread. Consequently, the propagation loss of the optical signal between the tip of the fiber core section21of the optical fiber2and the mirror section15is almost eliminated, and hence the optical coupling efficiency is improved.

In addition, similarly to the optical module of a second embodiment described later, when the bottom surface of the first trench1ais made wider than the core section17of the internal waveguide16, as shown inFIG. 15, when the core section17of the internal waveguide16is subjected to patterning (photo-cured) during the formation of the core section17, unnecessary reflection on the bottom surface is prevented. Consequently, in this case, it is possible to obtain a high-accuracy core shape.

Next, a description will be given of the multi-channel optical module according to the first embodiment of the present invention with reference toFIGS. 6 and 7.

FIG. 6Ais a plan view of the first substrate1, andFIG. 6Bis an enlarged plan view of first trenches1a-1and1a-2and internal waveguides16-1and16-2of the first substrate1. Note that, inFIG. 6B, in order to clarify the range of the cladding section18, the cladding section18is hatched.FIG. 7Ais a III-III line enlarged cross-sectional view ofFIG. 6A, andFIG. 7Bis a IV-IV line enlarged cross-sectional view ofFIG. 6A.

The multi-channel optical module according to the first embodiment of the present invention shown inFIGS. 6 and 7includes two single channel optical modules shown inFIGS. 1 to 5. Specifically, the multi-channel optical module is as follows.

On the surface of the first substrate1, a plurality of (two in the example shown in each ofFIGS. 6 and 7) the substantially trapezoidal first trenches1a-1and1a-2are formed independently of each other (i.e., in a state where they are separated or spaced from each other), i.e., a plurality of the adjacent first trenches1a-1and1a-2are formed substantially in parallel with each other in a state where they are separated from each other by a partition wall portion1e.

The adjacent first trenches1a-1and1a-2have lengths L1and L2from the end surface of the first substrate1(the rear end portion1dof the first trench1ain the example shown in each ofFIGS. 6 and 7) which are different from each other. Similarly to the foregoing, the internal waveguides16-1and16-2are provided in the first trenches1a-1and1a-2, respectively.

The optical elements (the light-emitting element12aand the light-receiving element12b) are mounted on the surface of the first substrate1so as to oppose the mirror sections15formed at the tip portions of the first trenches1a-1and1a-2having different lengths. In the first embodiment, the mirror section disposed at the end portion of the long internal waveguide16-1having the length L1opposes the light-receiving element12b, and the mirror section15disposed at the end portion of the short internal waveguide16-2having the length L2shorter than the length L1opposes the light-emitting element12a. Note that only the light-emitting elements12aor only the light-receiving elements12bcan be disposed to oppose the mirror sections15formed at the tip portions of the internal waveguides16-1and16-2. In addition, the number of formed first trenches1a-1and1a-2is not limited to two, and three or more trenches may also be formed. In this case, it is sufficient for three adjacent first trenches to have different lengths, and the lengths of the first and third first trenches may be equal to each other. In a case where four or more first trenches are formed, similarly, the first trenches that are not adjacent to each other may have the same length.

Two second trenches1b-1and1b-2are formed in the surface of the first substrate1. Herein, each of the second trenches may be substantially trapezoidal or V-shaped as long as the second trench does not come in contact with the bottom surface of the optical fiber. The adjacent second trenches1b-1and1b-2are separated from each other by a partition wall portion1f. The partition wall portion1fis separated from the partition wall portion1ebetween the first trenches1a-1and1a-2in an inclined portion1hof the bottom surfaces of the second trenches1b-1and1b-2and the bottom surfaces of the first trenches1a-1and1a-2.

As shown inFIG. 6A, the optical fiber (external waveguide)2has two parallel fiber core sections21(multi-channel) which can be optically coupled to the core sections17of the internal waveguides16-1and16-2, and the outer periphery of each fiber core section21is surrounded by the fiber cladding section22. Note that, instead of the optical fiber2, it is also possible to use a multi-channel film-like flexible waveguide, i.e., a flexible waveguide film (external waveguide).

By fitting and fixing the fiber cladding sections22in and to the second trenches1b-1and1b-2, the optical axes of the core sections17of the internal waveguides16-1and16-2and the optical axes of the fiber core sections21of the optical fiber2are set so as to match with each other.

In the configuration of the optical module described above, the lengths L1and L2of the adjacent first trenches1a-1and1a-2of the first substrate1are different from each other. In addition, the optical elements (the light-emitting element12aand the light-receiving element12b) are mounted on the surface of the first substrate1so as to oppose the mirror sections15at the tip portions of the first trenches1a-1and1a-2having the different lengths L1and L2. With this, it is possible to secure a large distance (space) S between the adjacent optical elements (the light-emitting element12aand the light-receiving element12b) disposed at different positions in a length direction (seeFIG. 6A).

Consequently, leaked light from the optical element, particularly from the light-emitting element12a, or reflected scattered light from the mirror section15or the internal waveguide16-2becomes less likely to enter the adjacent optical element, particularly the mirror section15of the light-receiving element12band the internal waveguide16-1. With this, even when the optical paths are formed at a small pitch, a cross-talk noise becomes less likely to occur.

In addition, since the internal waveguides16-1and16-2are provided in the plurality of (two in the present embodiment) the first trenches1a-1and1a-2formed independently of each other and substantially in parallel with each other, the internal waveguides16-1and16-2don't interfere with each other due to the partition wall portion1ebetween the adjacent first trenches1a-1and1a-2.

Thus, the plurality of the optical elements (the light-emitting element12aand the light-receiving element12b) are mounted on the first substrate1so as to be close to each other in the width direction of the first substrate1, the internal waveguides16-1and16-2are formed at the small pitch so as to correspond to the interval of the optical elements (the light-emitting element12aand the light-receiving element12b), and the mirror sections15at the end portions of the internal waveguides16-1and16-2are formed at the small pitch. With this, it becomes possible to implement small in size, low in height, and bidirectional or multi-channel transmission.

Further, the adjacent optical elements (the light-emitting element12aand the light-receiving element12b) are separated by the large distance S, and the interference between the adjacent internal waveguides16-1and16-2is prevented by the partition wall portion1e, whereby it becomes possible to significantly reduce the cross-talk noise.

In addition, as shown inFIG. 6A, in the case where both of the light-emitting element12aand the light-receiving element12bare included as the optical elements, the light-emitting element12ais mounted on the surface of the first substrate1so as to oppose the mirror section15of the internal waveguide16-2having the length L2shorter than the long internal waveguide16-1having the length L1to which the light-receiving element12bis optically coupled.

Thus, the light-emitting element12ais disposed closer to the end surface of the first substrate1(the rear end portion1dof the first trench1ain the present embodiment) than the light-receiving element12b. With this, the reflected scattered light of the mirror section15on the side of the light-emitting element12abecomes less likely to affect the side of the light-receiving element12bdue to the orientation of the mirror section15on the side of the light-emitting element12a. Consequently, even when both of the light-emitting element12aand the light-receiving element12bare mounted on the first substrate1, it becomes possible to significantly reduce the cross-talk noise.

Further, the second trenches1b-1and1b-2extending from the first trenches1a-1and1a-2of the internal waveguides16-1and16-2are formed in the surface of the first substrate1. The fiber cladding sections22of the optical fiber2are fitted in and fixed to the second trenches1b-1and1b-2, whereby the optical axes of the core sections17of the internal waveguides16-1and16-2and the optical axes of the fiber core sections21of the optical fiber2match with each other. Consequently, by forming the first trenches1a-1and1a-2and the second trenches1b-1and1b-2in which the fiber cladding sections22of the optical fiber2are fitted in the first substrate1, it becomes easy to optically couple the internal waveguides16-1and16-2and the optical fiber2. As a result, it becomes possible to produce the high-accuracy optical module at low cost.

Further, in a case where the external waveguide is the multi-channel optical fiber2, by matching the pitch of the internal waveguides16-1and16-2with the pitch of the commercial optical fiber2, it becomes easy to perform optical assembly and it becomes possible to produce the optical module at low cost.

Moreover, in a case where the external waveguide is the multi-channel flexible waveguide film, by matching the pitch of the internal waveguides16-1and16-2with the pitch of the commercial flexible waveguide film, it becomes easy to perform the optical assembly and it becomes possible to produce the optical module at low cost.

Note that, as a modification of the first embodiment of the present invention, as shown inFIG. 8, a partition wall portion1gbetween the adjacent second trenches1b-1and1b-2is formed so as not to be separated from the partition wall portion1ebetween the adjacent first trenches1a-1and1a-2. The second trenches1b-1and1b-2are formed independently of each other, and the partition wall portion1gis thereby formed between the adjacent second trenches1b-1and1b-2. According to the configuration, the leaked light does not interfere with the adjacent waveguides at an optical coupling portion of the internal waveguides16-1and16-2and the optical fiber2, and hence it becomes possible to further reduce the cross-talk noise.

In addition, each ofFIGS. 9A and 9Bshows another modification of the first embodiment of the present invention.FIG. 9Ais a plan view of the substrate1of the modification, whileFIG. 9Bis a V-V line enlarged cross-sectional view ofFIG. 9A. A convex layer26containing the same material as that of the cladding section18of the internal waveguide16is formed on the surface of the first substrate1between the light-emitting element12aand the light-receiving element12b.

In the configuration, by forming the convex layer26containing the same material as that of the cladding section18on the surface of the first substrate1between the light-emitting element12aand the light-receiving element12b, it is possible to trap the leaked light between the light-emitting element12aand the light-receiving element12b. Consequently, it is possible to further reduce the cross-talk noise. In addition, it is also possible to use the convex layer26as a stopper for preventing the under-fill material as the optically transparent resin13filled in the space between the light-emitting element12aand the light-receiving element12band the surface of the first substrate1from flowing out. Although the material of the convex layer26is not limited to the material of the cladding section18, when the material thereof is the same as the material of the cladding section18, it is possible to form the convex layer26in the step of forming the cladding section18concurrently.

Additionally, when an absorber that absorbs light is used as the material of the convex layer26instead of the material of the cladding section18, the leaked light between the light-emitting element12aand the light-receiving element12bcan be absorbed, and hence it becomes possible to further reduce the cross-talk noise. Herein, an example of the absorber includes a colored resin, e.g., an opaque acrylic resin or an epoxy resin.

As described above, the optical module according to the first embodiment includes the substrate formed with the plurality of the first trenches in the surface, the internal waveguides that are provided in the plurality of the first trenches and have the core sections, the mirror sections for changing the optical path that are formed at the tip portions of the plurality of the first trenches, and the optical elements that are mounted on the surface of the substrate so as to oppose the mirror sections and that emits the optical signal to the core section of the internal waveguide via the mirror section or receives the optical signal from the core section of the internal waveguide via the mirror section, the plurality of the first trenches of the substrate are formed independently of each other and substantially in parallel with each other, and the lengths of the adjacent first trenches from the end surface of the substrate are different from each other. The optical elements are mounted on the surface of the substrate so as to oppose the mirror sections formed at the tip portions of the first trenches having different lengths.

According to the configuration, the lengths of the adjacent first trenches are made different from each other and the optical elements are mounted on the surface of the substrate so as to oppose the mirror sections at the tip portions of the first trenches having different lengths, whereby it is possible to secure the large distance between the adjacent optical elements disposed at different positions in the length direction, e.g., the unaligned adjacent optical elements.

Consequently, since the leaked light from the optical element or the reflected scattered light from the mirror section or the internal waveguide becomes less likely to enter the mirror section or the internal waveguide of the adjacent optical element, even when the optical paths are formed at the small pitch, the cross-talk noise becomes less likely to occur. In addition, since the internal waveguides are provided in the plurality of the first trenches formed independently of each other and substantially in parallel with each other, the internal waveguides don't interfere with each other due to the partition wall portion between the adjacent first trenches.

Thus, the plurality of the optical elements are mounted on the substrate so as to be close to each other in the width direction of the substrate, and the internal waveguides and the mirror sections are formed such that the pitch of the internal waveguides and the pitch of the mirror sections are reduced so as to correspond to the interval of the optical elements, whereby it becomes possible to implement the small in size, low in height, and bidirectional or multi-channel transmission. Further, by securing the large distance between the adjacent optical elements and preventing the interference between the adjacent internal waveguides, it becomes possible to significantly reduce the cross-talk noise.

A configuration can be adopted in which the plurality of the optical elements include both of the light-emitting element and the light-receiving element, and the light-emitting element is mounted on the surface of the substrate so as to oppose the mirror section formed at the tip portion of the internal waveguide shorter in length than the internal waveguide optically coupled to the light-receiving element.

According to the configuration, by disposing the light-emitting element closer to the end surface of the substrate than the light-receiving element, the reflected scattered light of the mirror section on the side of the light-emitting element becomes less likely to affect the side of the light-receiving element due to the orientation of the mirror section on the side of the light-emitting element. Consequently, even when both of the light-emitting element and the light-receiving element are mounted on the substrate, it becomes possible to significantly reduce the cross-talk noise.

A configuration can be adopted in which the optical module includes the external waveguide having the core section optically coupled to the core section of the internal waveguide, the second trench extending from the first trench of the internal waveguide is formed in the surface of the substrate, and the optical axis of the internal waveguide and the optical axis of the external waveguide are set so as to match with each other by fitting and fixing the external waveguide in and to the second trench.

According to the configuration, by forming the first trench and the second trench in which the external waveguide is fitted in the substrate, it becomes easy to optically couple the internal waveguide and the external waveguide, and it becomes possible to produce the high-accuracy optical module at low cost.

A configuration can be adopted in which the partition wall portion is formed between the adjacent second trenches so as not to be separated from the partition wall portion between the adjacent first trenches.

According to the configuration, since the leaked light does not interfere with the adjacent waveguides at the optical coupling portions of the internal waveguides and the external waveguides, it becomes possible to further reduce the cross-talk noise.

A configuration can be adopted in which the optical module includes the external waveguide having the core section optically coupled to the core section of the internal waveguide, and the external waveguide is the multi-channel optical fiber.

According to the configuration, by matching the pitch of the internal waveguide with the pitch of the commercial optical fiber, it becomes easy to perform the optical assembly and it becomes possible to produce the optical module at low cost.

A configuration can be adopted in which the optical module includes the external waveguide having the core section optically coupled to the core section of the internal waveguide, and the external waveguide is the multi-channel flexible waveguide film.

According to the configuration, by matching the pitch of the internal waveguide with the pitch of the commercial flexible waveguide film, it becomes easy to perform the optical assembly, and it becomes possible to produce the optical module at low cost.

A configuration can be adopted in which the convex layer containing the same material as that of the cladding section of the internal waveguide is formed on the surface of the substrate between the optical elements.

According to the configuration, since it is possible to trap the leaked light between the optical elements by forming the convex layer containing the same material as that of the cladding section that has a high refractive index on the surface of the substrate between the optical elements, it becomes possible to further reduce the cross-talk noise. In addition, it is also possible to use the convex layer as the stopper for preventing the under-fill material filled in the space between the optical elements and the substrate from flowing out.

A configuration can be adopted in which the convex layer is the absorber that absorbs light.

According to the configuration, since it is possible to absorb the leaked light between the optical elements by forming the absorber on the surface of the substrate between the optical elements, it becomes possible to further reduce the cross-talk noise.

A configuration can be adopted in which the plurality of the second trenches each having the substantially V-shaped cross section that are deeper than the plurality of the first trenches are formed in the surface of the substrate continuously from the first trenches, and the external waveguide includes the optical fiber having the fiber cladding sections disposed in the second trenches and the fiber core sections as the core sections of the external waveguide.

According to the configuration, the plurality of the second trenches each having the substantially V-shaped cross section that are deeper than the plurality of the first trenches are formed in the surface of the substrate continuously from the first trenches, and the fiber core section of the optical fiber disposed in the second trench of the substrate is optically coupled to the core section of the internal waveguide. In a case where the optical element is the light-emitting element, the optical signal is emitted to the core section of the internal waveguide via the mirror section and, in a case where the optical element is the light-receiving element, the optical signal from the core section of the internal waveguide is received via the mirror section. Thus, since the internal waveguide is interposed between the tip of the fiber core section of the optical fiber and the mirror section, the luminous flux emitted from the light-emitting element does not spread, and the luminous flux emitted from the fiber core section of the optical fiber does not spread. Consequently, since the propagation loss of the optical signal between the tip of the fiber core section of the optical fiber and the mirror section is almost eliminated, the optical coupling efficiency is improved.

In the first embodiment, although the example in which the second trench having the V-shaped cross section in which the optical fiber2functioning as the external waveguide is fitted is formed is described, the present invention is not limited thereto and, as in a second embodiment shown below, a structure may also be adopted in which the second trench having a trapezoidal cross section, i.e., the second trench in a shape having a bottom surface having a predetermined width and two inclined surfaces on both ends of the bottom surface is provided.

Herein, in order to describe, in detail, the structure of the optical module of each channel included in the multi-channel optical module (seeFIGS. 23A and 23B) according to the second embodiment of the present invention, first, a description will be given by using the single channel optical module inFIGS. 10 to 22as an example of a simplified structure.

Note that the configuration of the single channel optical module shown inFIGS. 10 to 14as the second embodiment is different from the configuration of the optical module having the second trench1bhaving the V-shaped cross section shown inFIGS. 1 to 5as the first embodiment in having the second trench1bhaving the trapezoidal cross section, and is otherwise the same as the optical module as the first embodiment so that the description of portions which are the same as those of the optical module as the first embodiment will be omitted.

As shown inFIGS. 10 to 14, in the optical module according to the second embodiment, the first trench (waveguide formation trench)1ahaving a substantially trapezoidal cross section and the second trench1bin a substantially trapezoidal shape that is deeper than the first trench1aare formed in the surface (upper surface) of the first substrate1continuously in the front and rear direction, as shown inFIG. 12A.

As shown inFIG. 11BandFIGS. 12A and 12B, the second trench1bincludes a bottom surface10fformed to have a predetermined width and two inclined surfaces10ethat come in contact with the outer periphery of the fiber cladding section22of the optical fiber2described later to support the optical fiber2. The inclined surfaces10eare connected to both ends of the bottom surface10fin the width direction and are extended from the both ends to the surface (i.e., the upper surface) of the first substrate1obliquely upward such that the distance between the inclined surfaces10eis gradually increased as it goes upward. The outer periphery of the fiber cladding section22of the optical fiber2comes in contact with the inclined surfaces10e, and it is thereby possible to perform centering of the fiber cladding section22.

In addition, the bottom surface10fis formed so as not to be in contacted with the outer periphery of the fiber cladding section22when the inclined surfaces10eand the outer periphery of the fiber cladding section22of the optical fiber2come in contact with each other.

Similarly to the optical module of the first embodiment, in the optical module of the second embodiment as well, the internal waveguide16constituted by the core section17and the cladding section18is provided in the first trench1aof the first substrate1. In addition, the fiber core section21of the optical fiber2disposed in the second trench1bof the first substrate1is optically connected to the core section17of the internal waveguide16. In the first substrate1on the light-emitting side having the light-emitting element12aas the optical element, the optical signal is emitted to the core section17of the internal waveguide16via the mirror section15, while in the first substrate3on the light-receiving side having the light-receiving element12bas the optical element, the optical signal from the core section17of the internal waveguide16is received via the mirror section15.

Thus, since the internal waveguide16is interposed between the tip of the fiber core section21of the optical fiber2and the mirror section15, the luminous flux emitted from the light-emitting element12adoes not spread, and the luminous flux emitted from the fiber core section21of the optical fiber2does not spread. Consequently, since the propagation loss of the optical signal between the tip of the fiber core section21of the optical fiber2and the mirror section15is almost eliminated, the optical coupling efficiency is improved.

In addition, as shown inFIG. 15, in a case where the bottom surface of the first trench1ais formed to have the width wider than that of the core section17of the internal waveguide16, when the core section17of the internal waveguide16is subjected to patterning (photo-cured) during the formation of the core section17, the unnecessary reflection on the bottom surface is prevented. Consequently, in this case, in is possible to obtain the high-accuracy core shape.

In the internal waveguide16of the second embodiment shown inFIGS. 10 to 15, the first trench1aas the waveguide formation trench of the first substrate1has the substantially trapezoidal cross section, the core section17has a substantially square cross section, and both left and right surfaces of the core sections17are covered with the cladding section18.

However, the internal waveguide16is not limited to the waveguide of this type. For example, like the internal waveguide16shown inFIGS. 16A and 16B, the first trench1aof the first substrate1may be formed to be shallower than the second trench1band have the substantially V-shaped cross section, the core section17may be formed to have a substantially pentagonal cross section matching the first trench1a, and both of the left and right surfaces of the core section17may be covered with the cladding section18. For example, the core section17may be appropriately formed to have the substantially pentagonal cross section so as to have an upper surface, a pair of parallel side surfaces, and a V-shaped lower surface.

In addition, like the internal waveguide16shown inFIG. 17, in a case where a silicon oxide film40for insulation is formed not only on the surface of the first substrate1but also on the surface in the first trench1a, the silicon oxide film40functions as the cladding section18having the refractive index lower than that of the core section17. Consequently, by filling the entire space in the first trench1aformed with the silicon oxide film40functioning as the cladding section18with a core resin, the core section17having a substantially inverted triangular cross section may also be formed.

In the internal waveguide16shown inFIG. 17, the core section17occupies the entire space in the first trench1a, and hence the luminous flux from the light-emitting element12aspreads in the core section17in the width direction, and a part of the luminous flux may not reach the fiber core section21of the optical fiber2.

To cope with this, as shown inFIG. 16B, by setting a width W1of the core section17to substantially the same width as a width W2of the fiber core section21, almost all of the luminous flux can reach the fiber core section21of the optical fiber2and, as a result, the optical coupling efficiency is improved. Note that it is not always necessary to set the width W1of the core section17to substantially the same width as the width W2of the fiber core section21, and it is only necessary for the width W1of the core section17to be smaller than a width W3of the upper end of the first trench1a. The same applies to the core section17having the substantially square cross section, as shown inFIG. 11C.

In the first substrate1on the light-emitting side having the light-emitting element12aas the optical element, as shown inFIGS. 19A and 19B, the core section17of the internal waveguide16can be formed into the shape of an inclined surface such that the width W of the core section17(the distance between both side surfaces17a) is gradually reduced straightly from the mirror section15toward the connection end portion with the fiber core section21of the optical fiber2. In addition, each of the both side surfaces17acan be formed into the shape of an inclined surface constituted by a plurality of planes having inclination angles that are different stepwise as shown inFIG. 19C, or can be formed into the shape of an inclined surface constituted by a curved plane as shown inFIG. 19D.

On the other hand, in the first substrate3on the light-receiving side having the light-receiving element12bas the optical element, as shown inFIGS. 20A and 20B, the core section17of the internal waveguide16can be formed in the shape of an inclined surface such that the width W of the core section17(the distance between both side surfaces17a) is gradually reduced straightly from the connection end portion with the fiber core section21of the optical fiber2toward the mirror section15. In addition, each of both side surfaces17acan be formed into the shape of an inclined surface constituted by a plurality of planes having inclination angles that are different stepwise as shown inFIG. 20C, or can be formed into the shape of an inclined surface constituted by a curved plane as shown inFIG. 20D.

With this, when the optical element is the light-emitting element12a, by tapering the core section17of the internal waveguide16(i.e., a shape of which the width is gradually reduced as it goes forward), the luminous flux emitted from the light-emitting element12ais caused to converge. In addition, when the optical element is the light-receiving element12b, by inversely tapering the core section17of the internal waveguide16(i.e., a shape of which the width is gradually reduced as it goes rearward), the luminous flux emitted from the fiber core section21of the optical fiber2is caused to converge. Consequently, in either case, the optical coupling efficiency is further improved.

As shown inFIGS. 18A and 18B, a third trench1chaving a substantially trapezoidal cross section that is deeper than the second trench1bis formed continuously from the second trench1bin the surface (upper surface) of the first substrate1. It is possible to dispose the sheathing section23of the optical fiber2in the third trench1c.

Specifically, the third trench1cof the second embodiment includes a bottom surface10hformed to have a predetermined width and two inclined surfaces10gthat come in contact with the outer periphery of the sheathing section23of the optical fiber2to support the optical fiber2. The inclined surfaces10gof the third trench are connected to both ends of the bottom surface10hof the third trench1cin the width direction and extended from the both ends to the surface of the first substrate1obliquely upward such that the distance between the inclined surfaces10gis gradually increased as it goes upward. In addition, the bottom surface10hand the inclined surfaces10gof the third trench1care formed so as not to come in contact with the outer periphery of the sheathing section23of the optical fiber2.

With this, it is possible to dispose the cladding section22of the optical fiber2in the second trench1bof the first substrate1, and also dispose the sheathing section23of the optical fiber2in the third trench1cof the first substrate1. Consequently, it is possible to prevent the stress from the optical fiber2from being concentrated on the boundary portion with the sheathing section23of the fiber cladding section22.

Similarly to the fiber cladding section22, when the sheathing section23is boded and fixed to the third trench1cwith the adhesive, the fixing strength of the optical fiber2is improved. In addition, even when a bending force or a tensile force acts on the optical fiber2from the outside of the module, the optical coupling portion with the internal waveguide16is not affected, and hence the optical coupling efficiency is not reduced.

Further, in a case where the sheathing section23is not bonded and fixed to the third trench1c, as shown inFIG. 21, with an adhesive20thickly applied (i.e., applied so as to protrude upward) onto the surface of the second substrate6, it is possible to fix the sheathing section23of the optical fiber2to the second substrate6.

With such a configuration, since it is possible to dispose and fix the sheathing section23of the optical fiber2on the second substrate6, the fixing strength of the optical fiber2is improved. In addition, even when the bending force or the tensile force acts on the optical fiber2from the outside of the module, the optical coupling portion with the internal waveguide16is not affected, and hence the optical coupling efficiency is not reduced. Further, when the structure in which the sheathing section23of the optical fiber2is disposed and fixed in the third trench1cof the first substrate1is used in combination, the fixing strength is further improved.

As shown inFIG. 22, in a case where a tubular sheathing body25is fitted over the sheathing section23of the optical fiber2, it is possible to fix the sheathing section23of the optical fiber2and the sheathing body25to the second substrate6with the adhesive20. Note that the sheathing body25is not limited to the one fitted over the sheathing section23as long as the sheathing body covers the outer periphery of the sheathing section23.

In addition, the sheathing body25may be bonded to the portion of the third trench1cof the first substrate1(not shown).

The sheathing section23is a layer having a thickness of about 5 to 100 μm that is formed of, e.g., a UV-setting resin, while the sheathing body25is formed of, e.g., PCV, nylon, or thermoplastic polyester elastomer (e.g., Hytrel (registered trademark)). The outer diameter of the sheathing body25is, e.g., about 900 microns in the case of a single-core optical fiber.

With such a configuration, it is possible to dispose the sheathing body25on the second substrate6, and fix the sheathing body25to the second substrate6together with the sheathing section23of the optical fiber2. With this, the fixing strength of the optical fiber2is improved. In addition, even when the bending force or the tensile force acts on the optical fiber2from the outside of the module, the optical coupling portion with the internal waveguide16is not affected, and hence the optical coupling efficiency is not reduced. Further, when the structure in which the sheathing section23of the optical fiber2is disposed in and fixed to the third trench1cof the first substrate1is used in combination, the fixing strength is further improved. Additionally, with the thickness of the sheathing body25, it is possible to prevent a flection caused by the weight of the optical fiber2with, and an external force becomes less likely to be applied to the bonding portion between the optical fiber2and the substrate1. With this, the stress is less likely to occur in the optical coupling portion between the optical fiber2and the internal waveguide16, and hence the optical coupling efficiency becomes less likely to be reduced. Note that, even when only the sheathing body25is fixed to the second substrate6with the adhesive20, the same operation and effect can be achieved.

In the optical module according to the second embodiment, in a case where the inclination angle of the mirror section15is 45 degrees, the optical coupling efficiency becomes excellent.

In addition, in a case where the first substrate1is made of silicon (Si), the first trench la and the second trench1bcan be formed by anisotropic etching of silicon. According to this, it is possible to perform trench processing that utilizes the crystal orientation of silicon, and it is possible to form the high-accuracy mirror shape in the first trench1aand reduce a displacement of the position of the optical fiber2in the second trench1b.

Further, as the material of the internal waveguide16, it is possible to use a photosensitive resin. According to this, as compared with an inorganic internal waveguide that is formed by repeating ion doping or a deposition method, the internal waveguide16made of the photosensitive resin is inexpensive and can be easily formed.

Furthermore, it is possible to form the silicon oxide film on the surface of the first substrate1including the internal portion of the first trench1ato thereby increase the refractive index of the core section17of the internal waveguide16to be larger than that of the silicon oxide film. According to this, by filling the first trench1awith the material of the core section17of the internal waveguide16, it is possible to easily form the internal waveguide16.

In the multi-channel optical module according to the second embodiment of the present invention shown inFIGS. 23A and 23B, a plurality of the first trenches1aand a plurality of the second trenches1bare formed, the plurality of the first trenches1aare disposed in parallel with each other, and the plurality of the second trenches1bare also disposed in parallel with each other.

Specifically, in the optical module shown inFIGS. 23A and 23B, on the surface of the first substrate1, as shown inFIG. 23A, a plurality of the first trenches (waveguide formation trenches)1aeach having a substantially trapezoidal cross section are disposed in parallel with each other in a state where the first trenches1aare separated from each other with the material of the first substrate1. Similarly to the first embodiment, the lengths of the plurality of the first trenches1aare set such that the lengths of the adjacent first trenches1aare different from each other.

Further, in the surface of the first substrate1, a plurality of the second trenches1beach having the substantially trapezoidal cross section that are deeper than the first trenches1aare formed continuously from the end portions of the individual first trenches1ain the front and rear direction.

As shown inFIG. 23A, at the tip portion of each first trench1a, the mirror section15for changing the optical path is formed. As shown inFIG. 23B, the internal waveguide16that is optically coupled to the light-emitting element12acorresponding to the first trench1ais provided in each first trench1a.

The internal waveguide16is constituted by the core section17having a substantially square cross section and a high refractive index of light propagation, and the cladding section18having a refractive index lower than that of the core section17. As shown inFIG. 23B, both left and right surfaces (both side surfaces) of the core section17are covered with the cladding section18. In addition, the upper surface of the core section17is thinly covered with the cladding section18.

Each of the second trenches1bshown inFIGS. 23A and 23Bincludes the bottom surface10fformed to have a predetermined width and the two inclined surfaces10ethat come in contact with the outer periphery of the fiber cladding section22of the optical fiber2to support the outer periphery thereof. The inclined surfaces10eare connected to both ends of the bottom surface10fin the width direction and are extended from the both ends to the surface (upper surface) of the first substrate1obliquely upward such that the distance between the inclined surfaces10eis gradually increased as it goes upward. The outer periphery of the fiber cladding section22of the optical fiber2comes in contact with the inclined surfaces10e, and it is thereby possible to perform centering of the fiber cladding section22.

In addition, the bottom surface10fis formed so as not to be in contact with the outer periphery of the fiber cladding section22when the inclined surfaces10eand the outer periphery of the fiber cladding section22of the optical fiber2come in contact with each other.

In the configuration shown inFIGS. 23A and 23B, since the plurality of the first trenches la are disposed in the state where the first trenches1aare separated from each other with the material of the first substrate1, it is possible to prevent the optical signal passing through each first trench1afrom being leaked (cross talk) to the adjacent first trench1a.

In addition, as shown inFIG. 23B, an interval P between the core sections17of the adjacent internal waveguides16is not particularly limited in the present invention, and the interval P can be set arbitrarily. For example, the interval P between the core sections17may be set to about 250 μm in consideration of the disposition of the optical fiber of a conventionally known optical fiber array at an interval of 250 μm.

The size of the second trench1bis not particularly limited in the present invention. The size of the second trench1bmay be set to a size corresponding to the optical fiber having the outer diameter of the cladding section22of about 125 μm in consideration of the outer diameter of the most widely used small-diameter optical fiber of 125 μm. Note that, in order to prevent the cross talk, the second trench1bis preferably separated from the adjacent second trench1bas shown inFIG. 23.

Further, as another modification of the second embodiment of the present invention, in the optical module shown inFIG. 24, in the structure in which a plurality of the first trenches1aare disposed, an oxide film layer34is formed on the entire surface of the substrate1(i.e., the entire surface of the first trenches1aand the entire surface of the partition wall portion1f). The partition wall portion1ffunctioning as a shielding section is a portion protruding upward between the first trenches1aon the substrate1. The partition wall portion1fshields the first trench1asuch that a scattered component a of the reflected light of the mirror section15between the first trenches1ais not leaked.

The oxide film layer34is capable of reflecting the optical signal such that the optical signal is not leaked to the outside of the first trench1a, and is also capable of preventing the leakage of the scattered component a of the reflected light of the mirror section15. According to the configuration, the oxide film layer34serves as the reflection layer that reflects the optical signal, and hence it is possible to prevent the leakage (cross talk) of the optical signal more effectively. Strictly speaking, the optical signal including infrared rays and the like has a property that the optical signal passes through the substrate1made of silicon or the like while being attenuated. However, as described above, by reflecting the optical signal using the oxide film layer34, it is possible to improve the cross talk prevention effect.

Note that, inFIG. 24, although the gap between an optical element11having the light-emitting section12aand the substrate1is largely illustrated for easy visual recognition of the optical path, the gap is actually extremely small, and large cross talk does not occur. The same applies toFIGS. 25 and 26.

Further, as still another modification of the second embodiment of the present invention, in the optical module shown inFIG. 25, in the structure in which the oxide film layer34is formed on the surface of the substrate1as shown inFIG. 24, the oxide film layer34on the surface of the upwardly protruding partition wall portion1fis partially removed, and a removal portion32is thereby formed. According to the configuration, in a case where leaked light d that is multiply reflected between the optical element11having the light-emitting section12aand cladding section18occurs, the leaked light d can be absorbed into the first substrate1from the removal portion32of the oxide film layer34.

Furthermore, as yet another modification of the second embodiment of the present invention, in the optical module shown inFIG. 26, on the surface of the upwardly protruding partition wall portion1fof the first substrate1, a light absorber35is disposed along the partition wall portion1f. As the light absorber35, for example, opaque acrylic or epoxy resin is used. According to the configuration, in the case where the leaked light d that is multiply reflected between the optical element11having the light-emitting section12aand the cladding section18occurs, it is possible to cause the light absorber35to absorb the leaked light d to stop the leakage of light.

In the optical element11shown in each ofFIGS. 24 to 26, although the light-emitting elements12aare separated from each other, the light-emitting element12aand the light-receiving element12bmay be mounted in combination.

In the second embodiment, although the bottom surface of the second trench of the first substrate is formed into the flat shape, the present invention is not limited to this mode, and the shape of the bottom surface can be appropriately changed. For example, as shown inFIG. 27A, a bottom surface100fof a second trench100bof a first substrate100may be formed into a curved shape, and inclined surfaces100emay be formed to be extended from both ends of the bottom surface100fin the curved shape in the width direction obliquely upward.

In the second embodiment, although the bottom surface and the inclined surfaces of the second trench of the first substrate are directly connected to each other, the present invention is not limited to this mode, and the mode can be appropriately changed. For example, as shown inFIG. 27B, inclined surfaces200eand a bottom surface200fmay also be indirectly connected to each other via connection sections200i.

Specifically, a second trench200bof a first substrate200includes the connection sections200ithat are vertically extended from both ends of the bottom surface200fin the width direction, and the inclined surfaces200eare formed to be extended obliquely upward from the connection sections200i. Note that, similarly to the second trench, the third trench may also have the bottom surface in the curved shape and the bottom surface and the inclined surfaces may also be indirectly connected to each other via the connection sections, and the mode can be appropriately changed.

In the second embodiment, although the connector7is attached to the back surface (lower surface) of the second substrate6, the present invention is not limited to this mode and, e.g., as shown inFIG. 28A, a connector107can be disposed on the surface (upper surface) of the second substrate6, and the mode can be appropriately changed.

In addition, instead of the connector7, an electric terminal207may also be provided on the surface of the second substrate6. Further, another connector207athat is detachably fitted over the end portion of the second substrate6is provided with an electric terminal207bthat is connected to the electric terminal207, and the other connector207ais fitted over the second substrate6. With such a configuration, the electric terminal207may be connected to the electric terminal207bof the other connector207a.

Thus, the optical module according to the second embodiment of the present invention includes the substrate in which the plurality of the first trenches and the plurality of the second trenches that are deeper than the first trenches are continuously formed in the surface, the internal waveguide provided in each first trench of the substrate, the mirror section for changing the optical path provided at the tip portion of the first trench, the optical element that are mounted on the surface of the substrate so as to oppose the mirror sections and that emits the optical signal to the core section of the internal waveguide via the mirror section or receives the optical signal from the core section of the internal waveguide via the mirror section, and the optical fiber as the external waveguide having the fiber core section that is optically connected to the cladding section provided in the second trench and the core section of the internal waveguide, the second trench includes the bottom surface formed to have the predetermined width and the inclined surfaces that are connected to both ends of the bottom surface in the width direction to support the outer periphery of the fiber cladding section.

According to the configuration, the internal waveguide having the core section is provided in the first trench of the substrate, and the fiber core section of the optical fiber disposed in the second trench of the substrate is optically coupled to the core section of the internal waveguide. The optical signal is emitted to the core section of the internal waveguide via the mirror section in the case where the optical element is the light-emitting element, and the optical signal from the core section of the internal waveguide is received via the mirror section in the case where the optical element is the light-receiving element.

Thus, since the internal waveguide is interposed between the tip of the fiber core section of the optical fiber and the mirror section, the luminous flux emitted from the light-emitting element does not spread, and the luminous flux emitted from the fiber core section of the optical fiber does not spread. Consequently, since the propagation loss of the optical signal between the tip of the fiber core section of the optical fiber and the mirror section is almost eliminated in any direction, the optical coupling efficiency is improved.

For example, in the flip chip mounting in which the light-emitting surface of the optical element is on the substrate side, it is desirable to dispose the optical fiber close to the position immediately below the optical element. However, there are cases where it is difficult to dispose the optical fiber close to the position immediately below the optical element depending on the size of the outer diameter of the fiber. In addition, when the depth of the trench in the substrate is increased, the distance between the optical fiber and the optical element is increased. Even in these cases, since the internal waveguide is interposed therebetween as described above, it becomes possible to almost eliminate the propagation loss of the optical signal between the tip of the fiber core section of the optical fiber and the mirror section, and it is possible to improve the optical coupling efficiency.

Further, since the second trench has the bottom surface, unlike the trench having the V-shaped cross section, it is not necessary to increase the depth of the trench to increase the lengths of the inclined surfaces. Accordingly, in a case where the second trench is formed by etching, the second trench can be formed easily and in a short period of time as compared with the trench having the V-shaped cross section.

A configuration can be adopted in which, in the case where the optical element is the light-emitting element, the core section of the internal waveguide has the inclined surfaces that gradually reduce the width of the core section from the mirror section toward the connection end portion with the fiber core section of the optical fiber.

According to the configuration, when the optical element is the light-emitting element, by tapering the core section of the internal waveguide, the luminous flux emitted from the light-emitting element is caused to converge. Consequently, the optical coupling efficiency is further improved.

A configuration can be adopted in which, in the case where the optical element is the light-receiving element, the core section of the internal waveguide has the inclined surfaces that gradually reduce the width of the core section from the connection end portion with the fiber core section of the optical fiber toward the mirror section.

According to the configuration, when the optical element is the light-receiving element, by inversely tapering the core section of the internal waveguide, the luminous flux emitted from the fiber core section of the optical fiber is caused to converge. Consequently, the optical coupling efficiency is further improved.

A configuration can be adopted in which the width of the core section of the internal waveguide is smaller than the width of the upper end of the first trench.

In a case where the width of the core section of the internal waveguide is equal to the width of the upper end of the first trench, the luminous flux from the optical element spreads in the width direction in the core section, and a part of the luminous flux may not reach the fiber core section of the optical fiber. To cope with this, by making the width of the core section smaller than the width of the upper end of the first trench, preferably making the width of the core section substantially equal to the width of the fiber core section, it is possible to cause almost all of the luminous flux to reach the fiber core section of the optical fiber, and hence the optical coupling efficiency is improved.

A configuration can be adopted in which the first trench has the substantially trapezoidal cross section and the bottom surface of the first trench is wider than the core section of the internal waveguide.

According to the configuration, when the core section of the internal waveguide is subjected to patterning (photo-cured) during the formation of the core section, since the unnecessary reflection on the bottom surface is prevented, it is possible to obtain the high-accuracy core shape.

A configuration can be adopted in which the third trench deeper than the second trench is formed in the surface of the substrate continuously from the second trench, and the third trench is fixed to the sheathing section of the optical fiber.

According to the configuration, since the sheathing section of the optical fiber can be disposed in the third trench of the first substrate, it is possible to prevent the stress from the optical fiber from being concentrated on the boundary portion with the sheathing section of the fiber cladding section.

In addition, since the third trench includes the bottom surface, unlike the trench having the V-shaped cross section, it is not necessary to increase the depth of the trench to increase the lengths of the inclined surfaces and, in a case where the third trench is formed by, e.g., etching, the third trench can be formed easily and in a short period of time as compared with the trench having the V-shaped cross section.

A configuration can be adopted in which the substrate is disposed on another substrate larger in size than the substrate, and a sheathing section of the optical fiber is fixed to the other substrate.

According to the configuration, since the sheathing section of the optical fiber can be disposed on and fixed to the other substrate, the fixing strength of the optical fiber is improved. In addition, even when the bending force or the tensile force acts on the optical fiber from the outside of the module, the optical coupling portion with the internal waveguide is not affected, and hence the optical coupling efficiency is not reduced.

A configuration can be adopted in which the substrate is disposed on another substrate larger in size than the substrate, a sheathing body is fixed to an outer periphery of a sheathing section of the optical fiber, and the sheathing body is fixed to the other substrate.

According to the configuration, since the sheathing body can be disposed on and fixed to the other substrate, the fixing strength of the optical fiber is improved. In addition, even when the bending force or the tensile force acts on the optical fiber from the outside of the module, the optical coupling portion with the internal waveguide is not affected, and hence the optical coupling efficiency is not reduced. Additionally, with the thickness of the sheathing body, it is possible to prevent the flection caused by the weight of the optical fiber to thereby prevent the external force from being applied to the bonding portion of the optical fiber. With this, the stress is less likely to occur in the optical coupling portion with the internal waveguide, and hence the optical coupling efficiency becomes less likely to be reduced.

A configuration can be adopted in which the plurality of the first trenches are disposed on the substrate so as to be separated from each other.

According to the configuration, since the plurality of the first trenches1aare disposed so as to be separated from each other, it is possible to prevent a phenomenon in which the optical signal passing through each first trench1ais leaked and the optical signal passing through the adjacent first trench1ais affected, i.e., what is called the cross talk. In addition, with this, the optical coupling efficiency in each first trench1ais enhanced.

Industrial Applicability

The present invention is useful for the optical module including the optical element.

EXPLANATION OF REFERENCE NUMERALS