JPH0926515A - Optical waveguide circuit and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a more multifunctional optical waveguide circuit and a process for producing the circuit by providing a structure to allow the packaging of a surface type PD in the arbitrary position in an optical circuit without affecting other circuits. SOLUTION: This optical waveguide circuit consists of a core 12 and a clad 13 formed on a substrate 11. The circuit has an optical waveguide 14 consisting of the clad 13 which encloses the core 12 and has the refractive index lower than the refractive index of the core 12, a waveguide end 15 which is a perpendicular first end face intersecting nearly orthogonally to the optical axis direction of the core 12 of the optical waveguide 14 and a counter clad end face 16 which is a second end face facing the waveguide end 15. The circuit consists of a groove 18 of a rectangular section deeper than the core 12, a reflection material supporting layer 19 which is disposed at the counter clad end face 16 of the groove 18 facing the waveguide end 15 and has an angle of nearly 45 deg. to the optical axis direction at the height of the center of the core 12 and a reflection layer 20 which is disposed on the surface of the reflection material supporting layer 19.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide circuit used in the fields of optical communication and optical information processing, and a method for manufacturing the optical waveguide circuit, and more particularly to a mounting structure of a planar photodiode on the optical waveguide circuit. .

[0002]

2. Description of the Related Art FIG. 5 schematically shows a conventional mounting structure of a surface photodiode in an optical waveguide circuit. As shown in the figure,
An oblique groove 4 inclined at 45 degrees for reflecting light is provided at a desired portion of an optical waveguide circuit including a core 2 and a clad 3 formed on a substrate 1. Then, the guided light is totally reflected by the oblique groove 4 and emitted upward so as to be orthogonal to the waveguide circuit surface, and a surface photodiode (hereinafter referred to as "PD") 5 is directed to this portion with the light receiving surface facing downward. It is installed and receiving light.

[0003]

By the way, in the structure shown in FIG. 5, the method of forming the oblique groove 4 is a problem. That is, at present, the oblique groove 4 can be formed most accurately by a machining method. For example, the rotary round blade is inclined at 45 degrees to slide and cut the sample. At that time, the groove 4 is formed over the entire surface of the waveguide circuit.

Therefore, for example, when there is another waveguide near the portion where the PD 5 is to be installed,
Since this waveguide is also cut, the installation site of the PD 5 is naturally limited.

As described above, in the conventional optical waveguide circuit, the portion where the oblique groove for reflection does not cross other waveguide circuits,
That is, there is a problem that the surface-type PD can be mounted only at the end of the circuit.

In view of the above-mentioned problems, the present invention provides a surface type P without affecting other circuits at an arbitrary position in an optical circuit.
It is an object of the present invention to provide a structure in which D can be mounted, and to realize a more multifunctional optical waveguide circuit and a manufacturing method thereof.

[0007]

The structure of an optical waveguide circuit according to the present invention for achieving the above object is an optical waveguide circuit comprising a core and a clad formed on a substrate, and the core is surrounded by the core. The optical waveguide includes a clad having a lower refractive index, a vertical first end surface substantially orthogonal to the optical axis direction of the core of the optical waveguide, and a second end surface facing the first end surface. A groove having a rectangular cross section deeper than the core, and a second end surface of the groove facing the first end surface,
It is characterized in that it comprises a reflecting material support layer forming an angle of about 45 ° with respect to the optical axis direction at the height of the center of the core, and a reflecting material provided on the surface of the reflecting material support layer.

In the above-mentioned optical waveguide circuit, the waveguide having the second end face opposed to the first end face is composed of an independent island clad surrounded by a groove deeper than the core, and the island clad. Form a liquid reservoir on the upper surface of
It is characterized in that an opening communicating with the liquid reservoir and the groove is provided at a position not facing the first end face.

In the above optical waveguide circuit, the length of the clad in the optical axis direction of the groove provided in the clad surrounding the core of the optical waveguide, the depth of the clad in the direction orthogonal to the optical axis direction, the thickness of the core, and The relationship of numerical aperture is as follows (1), (2)
It is characterized by satisfying the relation of expressions.

[0010]

L <(A / θm) (1) D> 2Lθm + B (2) where L is the length of the groove in the optical axis direction,
A is the thickness of the upper cladding of the waveguide, θm is the numerical aperture of the optical waveguide, D is the depth of the recess from the cladding surface, and B is the thickness of the core.

In the above optical waveguide circuit, the bottom surface of the groove reaches the substrate.

The method of manufacturing an optical waveguide circuit according to the present invention is
In a method of manufacturing an optical waveguide circuit composed of a clad and a core formed on a flat substrate, a vertical first first portion substantially orthogonal to the optical axis direction of the core of the optical waveguide is provided at a desired portion in the circuit surface. A step of forming a groove having a deep rectangular cross section, which has an end face and a second end face facing the first end face, and which is deeper from the clad surface to the core; and then, a liquid at a corner portion of the second end face. The method is characterized by comprising a step of filling a curable substance and then curing the liquid curable substance to form a slope, and thereafter, forming an optical waveguide by attaching a reflection increasing film on the slope. .

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The contents of the embodiments for carrying out the present invention will be described below with reference to the drawings.

(First Embodiment) First, the first embodiment of the present invention
An embodiment will be described. FIG. 1 is a schematic sectional view according to the first configuration of the present invention. As shown in FIG. 1, the structure of the waveguide circuit 10 of the present invention is an optical waveguide circuit including a core 12 and a clad 13 formed on a substrate 11.
An optical waveguide 14 that surrounds the core 12 and includes a clad 12 having a lower refractive index than the core 12, and a waveguide end 15 that is a vertical first end face that is substantially orthogonal to the optical axis direction of the core 12 of the optical waveguide 14. A groove 18 having a rectangular cross section deeper than the core 12 and having an opposed cladding end surface 16 which is a second end surface opposed to the waveguide end 15 and an opposed cladding opposed to the waveguide end 15 of the groove. Provided on the end face 16,
The height of the center of the core 12 is about 45 with respect to the optical axis direction.
It is characterized by comprising a reflective material support layer 19 forming an angle of ° C and a reflective layer 20 provided on the surface of the reflective material support layer.

That is, as shown in FIG. 1, in the present invention, the waveguide circuit component at a predetermined portion to which the planar PD 21 is to be mounted is removed by an etching method so as to be perpendicular to the optical axis direction. A groove 18 having a rectangular cross section having a waveguide end 15 that is a first end face and an opposing cladding end face 16 that is a second end face that opposes the waveguide end 15 is formed. Next, the cladding wall surface 1 facing the waveguide end 15 of the groove 18
6, the corner portion formed by the bottom surface of the groove 18 and the end surface 16 of the opposite cladding is filled with a liquid substance and then cured, so that the surface tension of the liquid substance causes the surface height of the core 12 at the height of the center of the core 12 in the optical axis direction. A reflective material support layer 19 having an angle of about 45 ° with respect to the reflective material support layer 19 is formed, and then a highly reflective substance is adhered onto the cured slope of the reflective material support layer 19 to adhere the reflective layer 20 to form an optical waveguide circuit. It is composed. As a result, the guided light emitted from the waveguide end 15 is extracted through the reflection layer 20 in the vertical direction orthogonal to the waveguide circuit surface, and the guided light is guided to the planar PD 21.

Now, the present embodiment will be described in more detail.
As shown in FIG. 1, the upper clad 13a is formed on the substrate 11.
An optical waveguide circuit is formed from a clad 13 composed of a lower clad 13b and a lower clad 13b, and a core 12 surrounded by the clad 13. The waveguide material is removed by etching at a desired portion in the middle of the optical waveguide circuit. Groove 18
Is formed. One wall surface of the groove 18 is formed on the waveguide 14
Of the waveguide end 15, and a filling material is adhered to the corner portion of the cladding end surface 16 facing the waveguide end 15 along the corner portion. The filler is applied in a liquid state and then cured. As a result, the filling material is filled along the corner portion formed by the clad end surface 16 and the bottom surface of the groove 18, and the surface shape is about 45 ° C. in the optical axis direction at the center height of the core 12 due to the surface tension. The surface is a smooth slope on which the reflecting material support layer 19 having an angle of is formed. On this slope, a highly reflective substance such as gold is attached by a vapor deposition method or the like to form the reflective material 20. The outgoing guided light that has entered such a slope is reflected by the slope and is emitted perpendicularly to the waveguide circuit.

Since the slope shape is concave, the spread of the emitted light is larger than that of the conventional example. However, if the light receiving surface of the PD 21 provided on the upper surface of the optical waveguide circuit is brought close to the surface of the waveguide. The emitted guided light is all incident on the light receiving surface. Further, the degree of depression of the slope is also linear if the wetting property of the filling material 24 is selected so as to be better for the cladding end face 16 than for the bottom face of the groove 18, as shown in a later example. It is possible to get as close as possible to.

Here, in the present invention, as a filler for forming the above-mentioned reflecting material support layer 19, for example, a resin such as epoxy or polyimide, or a low melting point sealing glass (melting point 400 to 500 ° C.) as a material which can withstand higher temperatures. However, the present invention is not limited to this as long as the same action is exhibited.

Next, the relationship between the waveguide parameter and the size of the rectangular groove will be described with reference to FIG. As shown in FIG. 2, in order for all the light emitted from the waveguide end 15 to be reflected upward, the following two conditions may be satisfied.

Assuming that the numerical aperture of the optical waveguide 14 is θm, the length of the groove 18 in the optical axis direction is L, and the thickness of the upper cladding 13a of the waveguide 14 is A, the outgoing guided light on the opposing cladding wall surface 16 is directed upward. Is Lθm. Further, since the thickness of the upper clad 13a must be larger than this in order to reflect all the upward spread, the length L of the groove in the optical axis direction is

[0021]

## EQU00003 ## The condition L <(A / .theta.m) (1) is defined. Further, considering the downward spread of the emitted guided light, the depth D from the surface of the upper clad 13a to the lower clad 13b of the groove 18 is set such that the thickness of the core 12 is B.

[0022]

## EQU00004 ## It is necessary to set D> 2L.theta.m + B (2).

(Second Embodiment) Next, an embodiment of the second invention will be described. 3 and 4 are the second of the present invention.
3 is a schematic cross-sectional view related to the configuration of FIG. In the figure, reference numeral 12 is a core, 21 is a planar PD, 15 is a waveguide end, 16 is a wall surface of an opposing cladding, 19 is a reflecting material support layer, 20 is a reflective layer, 21 is a planar PD, and 22 is an island cladding. , 23 is a reservoir, 24 is a filler, 25 is an adhesive dispenser, 26 is a PD electrode, and 27 is a PD fixing pad.

In the above-described embodiment, as shown in FIG. 1, the wall surface including the waveguide end 15 of the waveguide layer 14 including the core 12 and the clad 13 and the opposite clad wall surface 16 for forming the oblique reflection portion. Are included in the same plane topologically, when the filler is dropped on the corner portion near the facing clad wall surface 16, the filler also wraps around to the facing waveguide end face 15 side and reaches the waveguide end 15. Is afraid.

A structure for preventing this is shown in FIG. 3 and FIG.
Shown in That is, in the configurations shown in these drawings, in order to facilitate the filling of the filler 24 which is a liquid substance, the wall surface including the facing cladding wall surface 16 is topologically not coincident with the wall surface including the waveguide end 15, The wall surface including the opposed clad wall surface 16 constitutes an island clad 22, and the island clad 22 is provided with a liquid reservoir 23 for filling a liquid substance. The filling material 24 may be added to the liquid reservoir 11 provided in the island-shaped clad 23 so that the volume of the liquid reservoir 23 is dropped. If you do this,
The filling material 24 does not wrap around the waveguide end 15,
It is prevented that the waveguide end 15 is reached.

Here, in the above embodiment, the shape of the groove and the like may be set to the conditions shown in "Equation 3" and "Equation 4" as described above.

Further, in the structure shown in FIGS. 1 and 3 and 4, in order to prevent the dripping of the filler, etching is performed so as to reach the substrate 11 on the lower surface of the lower cladding layer 13b when forming the groove. You can do it like this. This is due to the difference in wetting property between the clad and the substrate with respect to the filler, so that the substrate (silicon substrate) remains only at the corners.
The filling material is filled only in the corner portion of the facing clad wall surface 16 and then cured to form the reflecting material support layer 19.

[0028]

Next, an example of application to the following optical waveguide circuit will be described as a preferred embodiment of the present invention, but the present invention is not limited to this.

(1) First, similar to the one shown in FIG.
A Si substrate is used as the substrate 11, and a silica-based optical waveguide circuit made of glass containing SiO ₂ as a main component is applied to the waveguide by a flame direct deposition method and a dry etching method. Was produced. Here, the relative refractive index difference between the core 12 and the clad 13 is 0.
75%, thickness of lower clad 13b is 15 μm, core 1
2 is a 6 μm square, and the thickness of the upper clad 13a is 15 μm. (2) A predetermined portion on the surface of this waveguide circuit is dug by dry etching until it reaches the Si substrate.
A groove having a concave sectional shape as shown in (a) was formed.
The waveguide end 15 of the waveguide 14 and the facing cladding wall surface 16
In the meantime, the distance L and the etching depth D are the same as those in the above-mentioned
And inequality (1) and inequality (2) described in "Equation 4"
So that L = 80 μm and D = 36.5 μ
m. As described above, the facing clad wall surface 7 forms one wall surface of the island-shaped clad 22, and has an area of 1 square mm.
A liquid sump 23 was provided. (3) Next, as the filler 24, here, Epotek 3
After selecting 53ND (trade name: manufactured by Rikei Co., Ltd.) and thoroughly defoaming it, 30 μcc of the adhesive was dropped on the liquid reservoir 23 using the dispenser 25 as shown in FIG. 3B. Then, the filler 24 was cured at 100 ° C.
Now, in the case of the present embodiment, the bottom surface of the formed groove is S
i, the wall surface is made of oxide glass. The filler (Epotek 353ND: trade name) 24 used above has poor wettability with respect to Si, and the contact angle of the liquid filler 24 is 30.
It ’s big. On the other hand, the oxide glass has good wettability and the contact angle is as small as about 5 degrees. Therefore, the filler 2
Although No. 4 easily wets the wall surface 16 of the opposite cladding, it was difficult to spread to the bottom surface of the groove, and a slope having an inclination angle of 40 to 50 degrees could be obtained with good reproducibility. The filling material 24 was hardened in a nitrogen atmosphere in order to prevent the oxidation of Si. This is due to the fact that S
This is because when i is oxidized, the filling material 24 spreads to the bottom surface of the groove. (4) Further, in order to prepare for heating in the PD mounting step to be performed later, the filler 24 was degassed by heating at 300 degrees. (5) Next, as shown in FIG.
Gold was evaporated to a thickness of i 1000 angstroms and gold to a thickness of 2000 angstroms to form the highly reflective substance 20, the PD electrode 26 and the PD fixing pad 27. The lift-off method was used for patterning. (6) Finally, as shown in FIG. 4D, a 80 μm light-receiving InGaAsPD (0.
3 mm square) 22 was heated and cooled at 200 degrees and fixed.

The coupling efficiency of the PD 22 thus mounted with the optical waveguide was evaluated at a wavelength of 1.3 μm. As a result, the coupling efficiency was as high as 95% of that when the light receiving surface was directly parallel to the end of the waveguide.

[0031]

As described above, according to the present invention, P is placed at an arbitrary position in the optical waveguide circuit without affecting other waveguides.
It becomes possible to implement D. For example, since the PD can be installed inside the optical circulation circuit or the light reflection circuit, the dead space in the optical circuit can be reduced and the function of the optical waveguide circuit itself can be increased.

Further, since the periphery of the PD mounting portion is surrounded by a flat upper clad having no step, capping sealing is also possible. The present invention provides a multifunctional optical device,
It is a great contribution to lower prices.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of the first configuration of the present invention.

FIG. 2 is an explanatory diagram of a condition of a recess size.

FIG. 3 is a perspective view of the second configuration of the present invention.

FIG. 4 is a perspective view of the second configuration of the present invention.

FIG. 5 is a schematic view of a conventional mounting structure of a planar photodiode on an optical waveguide circuit.

[Explanation of symbols]

 11 Substrate 12 Core 13 Cladding 14 Oblique Groove 15 Planar PD 16 Waveguide Edge 17 Opposing Cladding Wall Surface 18 Filling Material 19 High Reflective Material 22 Island Cladding 23 Liquid Reservoir 24 Filling Material 25 Adhesive Dispenser 26 PD Electrode 27 for PD Fixing pad

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yoshinori Nakasuka 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Inside Nippon Telegraph and Telephone Corporation (72) Toshikazu Hashimoto 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo No. Japan Telegraph and Telephone Corporation

Claims (5)

[Claims] 1. An optical waveguide circuit comprising a core and a clad formed on a substrate, the optical waveguide comprising a clad surrounding the core and having a refractive index lower than that of the core, and an optical axis of the core of the optical waveguide. Vertical first, almost orthogonal to the direction
A groove having a rectangular cross section deeper than the core and having a second end surface opposed to the first end surface, and a second end surface facing the first end surface, and a second end surface facing the first end surface of the groove, The height of the center of the core is about 45 with respect to the optical axis direction.
An optical waveguide circuit comprising a reflecting material support layer forming an angle of ° and a reflecting material provided on the surface of the reflecting material support layer. 2. The optical waveguide circuit according to claim 1, wherein the waveguide having a second end face opposite to the first end face is an island-shaped clad surrounded by a groove deeper than the core. At the same time, a liquid reservoir is formed on the upper surface of the island-shaped clad, and an opening communicating the liquid reservoir with the groove is provided at a position not facing the first end face. Wave circuit. 3. The optical waveguide circuit according to claim 1 or 2, wherein the length of the clad in the optical axis direction of the groove provided in the clad surrounding the core of the optical waveguide, and the clad in the direction orthogonal to the optical axis direction. The optical waveguide circuit characterized in that the relationship among the depth, the core thickness, and the numerical aperture satisfies the following expressions (1) and (2). ## EQU1 ## L <(A / θm) (1) D> 2Lθm + B (2) where L is the length of the groove in the optical axis direction,
A is the thickness of the upper cladding of the waveguide, θm is the numerical aperture of the optical waveguide, D is the depth of the recess from the cladding surface, and B is the thickness of the core. 4. The optical waveguide circuit according to claim 1, wherein the bottom surface of the groove reaches the substrate. 5. A method of manufacturing an optical waveguide circuit comprising a clad and a core formed on a flat substrate, wherein a desired portion in the circuit plane is substantially orthogonal to the optical axis direction of the core of the optical waveguide. Forming a groove having a deeper rectangular cross section from the cladding surface to the core, the groove having a vertical first end face and a second end face facing the first end face, and then the second end face A step of filling a liquid curable substance into the corners of the substrate and then curing the liquid curable substance to form an inclined surface, and thereafter forming an optical waveguide by attaching a reflection increasing film on the inclined surface. A method for manufacturing an optical waveguide circuit, comprising: