JP3147327B2 - Optical waveguide circuit and manufacturing method thereof - Google Patents

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 field of optical communication and optical information processing and a method of manufacturing the optical waveguide circuit, and more particularly to a mounting structure of a surface-type photodiode on an optical waveguide circuit. .

[0002]

2. Description of the Related Art FIG. 5 schematically shows a structure for mounting a surface-type photodiode on a conventional optical waveguide circuit. As shown in the figure,
At a desired portion of the optical waveguide circuit composed of the core 2 and the clad 3 formed on the substrate 1, an oblique groove 4 inclined at 45 degrees for light reflection is provided. The guided light is totally reflected by the diagonal groove 4 and emitted upward perpendicular 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. Installed and receiving light.

[0003]

However, in the structure shown in FIG. 5, the method of forming the above-mentioned oblique groove 4 is problematic. That is, at present, the diagonal groove 4 is formed by machining with the most accurate method. For example, the rotary round blade is inclined at 45 degrees to slide and cut the sample. At this 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,
This waveguide is also cut, and the installation site of the PD 5 is naturally limited.

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

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a planar type P at an arbitrary position in an optical circuit without affecting other circuits.
It is an object of the present invention to provide a structure on which D can be mounted and realize a multifunctional optical waveguide circuit and a method for manufacturing the same.

[0007]

According to the present invention, there is provided an optical waveguide circuit comprising a core and a clad formed on a substrate, wherein the optical waveguide circuit surrounds the core, and An optical waveguide made of a clad having a lower refractive index, a first end face perpendicular to the optical axis direction of the core of the optical waveguide, and a second end face facing the first end face; A groove having a rectangular cross section deeper than the core, and a second end face of the groove facing the first end face;
In the optical waveguide circuit consisting of a reflective material supporting layer forms an angle of about 45 °, a reflection member provided on the surface of the reflective material supporting layer with respect to the optical axis direction at the height of the center of the core, the first
A waveguide having a second end face facing the first end face;
Independent island clad surrounded by trenches deeper than a
And a reservoir is formed on the upper surface of the island-shaped cladding.
And the opening communicating the reservoir with the groove is
1 characterized in that it is provided at a location that does not face the end face.
And

[0008]

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

[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 of the groove reaches the substrate.

Further, the method for manufacturing an optical waveguide circuit according to the present invention comprises:
An optical waveguide consisting of a core and a clad is formed on a flat substrate.
And a step of forming, at a desired portion of the optical waveguide , a first end face perpendicular to the optical axis direction of the core and a second end face facing the first end face. Along with the step of forming a groove having a deeper rectangular cross section from the cladding surface to the core , and then filling the corner portion of the second end face with a liquid curable substance, and then curing the liquid curable substance. The method is characterized by comprising a step of forming a slope, and thereafter, a step of attaching a reflection enhancing film on the slope.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) First, the first embodiment of the present invention will be described.
An embodiment will be described. FIG. 1 is a schematic sectional view according to a first configuration of the present invention. As shown in FIG. 1, the configuration 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 comprising the clad 12 surrounding the core 12 and having a lower refractive index than the core 12; and a waveguide end 15 which is a first end face perpendicular to the optical axis direction of the core 12 of the optical waveguide 14 and perpendicular thereto. A groove 18 having a rectangular cross-section deeper than the core 12 and a facing clad facing the waveguide end 15 of the groove. Provided on the end face 16,
The height of the center of the core 12 is approximately 45 with respect to the optical axis direction.
It is characterized by comprising a reflective material support layer 19 at 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, a waveguide circuit component at a predetermined portion to which the surface type PD 21 is to be mounted is removed by an etching method, and the vertical direction is substantially perpendicular to the optical axis direction. A groove 18 having a rectangular cross section having a waveguide end 15 that is a first end surface and a facing clad end surface 16 that is a second end surface facing the waveguide end 15 is formed. Next, the cladding wall surface 1 facing the waveguide end 15 of the groove 18
In step 6, a liquid material is filled into a corner formed by the bottom surface of the groove 18 and the opposing cladding end surface 16 and then hardened, so that the surface tension of the liquid material causes the height of the center of the core 12 to rise in the optical axis direction. Is formed at an angle of approximately 45 ° C. with respect to the light guide circuit. Then, a highly reflective substance is deposited on the hardened slope of the reflector support layer 19, and the reflective layer 20 is deposited. It is constituted. Thus, the guided light emitted from the waveguide end 15 is extracted through the reflective layer 20 in the vertical direction perpendicular to the waveguide circuit surface, thereby guiding the guided light to the surface type PD 21.

Here, this embodiment will be described in more detail.
As shown in FIG. 1, an upper clad 13a
An optical waveguide circuit is formed from a clad 13 composed of a clad 13 and a lower clad 13b, and a core 12 surrounded by the clad 13. A waveguide material is removed by etching only at a desired portion in the middle, and a rectangular cross section is formed. Groove 18
Is formed. One wall surface of the groove 18 is
The filler material is attached to the corner portion of the clad end surface 16 facing the waveguide end 15 along the corner portion. The filler is applied in a liquid state and then hardens. As a result, the filler is buried along the corner formed by the cladding end face 16 and the bottom face of the groove 18, and its surface shape is approximately 45 ° C. with respect to the optical axis direction at the height of the center of the core 12 by surface tension. A smooth slope having the reflective material support layer 19 formed at an angle of. The reflective material 20 is formed on the slope by, for example, depositing a highly reflective material of gold or the like by an evaporation method or the like. The outgoing guided light incident on such a slope is reflected by the slope and emitted perpendicular to the waveguide circuit.

Since the shape of the inclined surface 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, , Outgoing guided light all enter the light receiving surface. In addition, the degree of the concave shape of the slope may be linear as long as the filling property of the filler 24 is selected so as to be better with respect to the cladding end face 16 than with respect to the bottom face of the groove 18 as shown in the later embodiment. As close as possible.

In the present invention, the filler forming the reflective material support layer 19 in the present invention is, for example, a resin such as epoxy or polyimide, or a low-melting sealing glass (melting point of 400 to 500 ° C.) as a material that 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, the following two conditions only need to be satisfied in order for all the light emitted from the waveguide end 15 to be reflected upward.

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 13 a of the waveguide 14 is A, the upward guided light on the opposed clad wall surface 16 is located above. Is Lθm. Also, in order to reflect all of the upward spread, the thickness of the upper cladding 13a must be larger than this, so that the length of the groove in the optical axis direction L is:

[0021]

The condition of L <(A / θm) (1) is defined. Also, considering the downward spread of the output guided light, the depth D from the surface of the upper cladding 13a of the groove 18 to the lower cladding 13b is represented by the thickness B of the core 12.

[0022]

D = 2Lθm + B (2)

(Second Embodiment) Next, an embodiment of the second invention will be described. 3 and 4 show the second embodiment of the present invention.
FIG. 3 is a schematic sectional view according to the configuration of FIG. In the figure, reference numeral 12 denotes a core, 21 denotes a planar PD, 15 denotes a waveguide end, 16 denotes a facing clad wall surface, 19 denotes a reflective material support layer, 20 denotes a reflective layer, 21 denotes a planar PD, and 22 denotes an island clad. , 23 are 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 opposing clad wall surface 16 for forming the oblique reflection portion are formed. When the filler is topologically contained on the same surface, when the filler is dropped on the corner portion near the opposing clad wall surface 16, the filler also wraps around the opposing waveguide end surface 15 and reaches the waveguide end 15. Is worried.

FIGS. 3 and 4 show a configuration for preventing this.
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 opposing clad wall surface 16 is not topologically matched with the wall surface including the waveguide end 15, The wall surface including the opposing clad wall surface 16 constitutes an island-shaped clad 22, and the island-shaped clad 22 is provided with a reservoir 23 for filling a liquid substance. It is sufficient that the filler 24 drops the volume of the liquid reservoir 23 to the liquid reservoir 11 provided in the island-shaped cladding 23. If you do this,
The filling material 24 is prevented from wrapping around the waveguide end 15,
It is possible to prevent reaching to the waveguide end 15.

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.

1 and FIGS. 3 and 4, in order to prevent the filler from dripping or the like, when forming the groove, the etching is performed so as to reach the substrate 11 under the lower cladding layer 13b. What should I do? This is because of the difference in the wetting property between the clad and the substrate with respect to the filler, the substrate (silicon substrate) remains only at the corners,
The above-mentioned filler is filled only in the corners of the opposing clad wall surface 16 and then cured to form the reflector support layer 19.

[0028]

Next, an example in which the present invention is applied 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, as shown in FIG.
A waveguide 14 comprising a clad 13 layer surrounding a core 12 by a flame direct deposition method and a dry etching method using a Si substrate as a substrate 11 and a quartz optical waveguide circuit composed of glass containing SiO ₂ as a main component. Was prepared. Here, the relative refractive index difference between the core 12 and the clad 13 is 0.1.
75%, thickness of lower cladding 13b is 15 μm, core 1
2 is a 6 μm square, and the thickness of the upper cladding 13 a is 15 μm. (2) A predetermined portion in the plane of the waveguide circuit is dug by dry etching until it reaches the Si substrate.
A groove having a concave cross-section was formed as shown in FIG.
Waveguide end 15 of waveguide 14 and opposing cladding wall surface 16
In the meantime, the distance L and the etching depth D are equal to the above “Equation 3”.
And inequality (1) and inequality (2) described in "Equation 4"
L = 80 μm and D = 36.5 μ so that
m. As described above, the opposing clad wall surface 7 forms one wall surface of the island-shaped clad 22 and has an area of 1 square mm.
Was provided. (3) Next, Epotech 3 is used as the filler 24 here.
53ND (trade name: manufactured by Rikei Co., Ltd.) was selected, and after sufficient degassing, 30 μcc of the adhesive was dropped into the reservoir 23 using the dispenser 25 as shown in FIG. Thereafter, the filler 24 was cured at 100 ° C.
Now, in the case of this embodiment, the bottom surface of the formed groove is S
i, the wall surface is an oxide glass. The filler (Epotech 353ND: trade name) 24 used above has poor wettability with respect to Si, and the contact angle of the liquid filler 24 is 30.
Degree and 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
No. 4 easily wets the opposing cladding wall surface 16, but hardly spreads to the groove bottom surface, and a slope with a tilt angle of 40 to 50 degrees could be obtained with good reproducibility. The curing of the filler 24 was performed in a nitrogen atmosphere to prevent oxidation of Si. This is because during the curing process of the filler 24, S
This is because when i is oxidized, the filler 24 spreads to the groove bottom surface. (4) Further, in order to prepare for heating in a later PD mounting step, the filler 24 was degassed by heating to 300 degrees. (5) Next, as shown in FIG.
Gold was deposited to a thickness of 1000 angstroms and gold to a thickness of 2000 angstroms to form a highly reflective material 20, a PD electrode 26 and a PD fixing pad 27. The lift-off method was used for patterning. (6) Finally, as shown in FIG. 4D, a light receiving system 80 μm InGaAsPD (0.
(3 mm square) 22 was fixed by heating and cooling at 200 degrees.

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

[0031]

As described above, according to the present invention, the P waveguide can be placed at an arbitrary position in the optical waveguide circuit without affecting other waveguides.
D can be implemented. For example, since the PD can be installed inside the optical 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 increases.

Further, since the periphery of the PD mounting portion is surrounded by a flat upper cladding having no step, capping sealing is also possible.
This is a major contributor to lower prices.

[Brief description of the drawings]

FIG. 1 is a sectional view of a 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 a second configuration of the present invention.

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

FIG. 5 is a schematic diagram of a conventional structure for mounting a surface photodiode on an optical waveguide circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Substrate 12 Core 13 Cladding 14 Diagonal groove 15 Surface type PD 16 Waveguide end 17 Opposed cladding wall surface 18 Filler 19 Highly reflective object 22 Island-like cladding 23 Liquid reservoir 24 Filler 25 Adhesive dispenser 26 PD electrode 27 PD fixing pad

──────────────────────────────────────────────────続 き Continued on the front page (72) Yoshinori Nakasuga, Inventor 1-6-1, Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Toshikazu Hashimoto 1-6-1, Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) References JP-A-5-264870 (JP, A) JP-A-63-191111 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 6/12-6/14 G02B 6/26-6/27 G02B 6/30-6/35 G02B 6/42-6/43

Claims (4)

(57) [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 lower refractive index than the core, and an optical axis of the core of the optical waveguide. The first perpendicular to the direction
A groove having a rectangular cross section deeper than the core, and a second end face of the groove facing the first end face, the end face having a second end face facing the first end face, The height of the center of the core is approximately 45 with respect to the optical axis direction.
In a light guide circuit comprising a reflector support layer forming an angle of .degree. And a reflector provided on the surface of the reflector support layer , a waveguide having a second end face facing the first end face
Are isolated islands surrounded by grooves deeper than the core.
And a reservoir on the upper surface of the island-shaped cladding.
Forming an opening for communicating the reservoir with the groove.
Is provided at a location that does not face the first end surface.
An optical waveguide circuit characterized by the following. 2. A light waveguide circuit according to claim 1 Symbol mounting, the grooves provided in the cladding surrounding the core of the optical waveguide in the optical axis direction of the clad of the length, in the direction perpendicular to the optical axis direction of the clad An optical waveguide circuit, wherein the relationship among the depth, the thickness of the core, and the numerical aperture satisfies the relationship of the following expressions (1) and (2). 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. 3. A light waveguide circuit according to claim 1 or 2, wherein the optical waveguide circuit characterized in that the bottom of the groove reaches the substrate. 4. A core and a clad formed on a flat substrate.
Forming an optical waveguide having a first end face perpendicular to the optical axis direction of the core and a second end face facing the first end face at a desired portion of the optical waveguide . together, the upper from the clad surface
Forming a groove having a deeper rectangular cross section deeper to the core , and then filling a corner of the second end surface with a liquid curable substance, and then curing the liquid curable substance to form a slope. And thereafter, attaching a reflection-enhancing film on the inclined surface.