JPH10282362A - Optical waveguide substrate, optical module and manufacture of optical waveguide substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form an optical waveguide and an optical element alignment structure at almost the same time, simplify processes and improve a yield by forming a polygonally columnar rod optical waveguide of silicon containing impurities on a silicon substrate. SOLUTION: A trapezoidal and angularly columnar rod optical waveguide 11 of silicon in which impurities are diffused is formed on a silicon substrate 12. The waveguide 11 with impurities diffused has larger refractivity than the silicon substrate 12. On this account, light is prevented from leaking from the waveguide 11 to the silicon substrate 12. If single crystal silicon is used for the silicon substrate 12 to apply epitaxial growth reflecting the crystal orientation of the silicon substrate during layering, the silicon substrate 12 and a silicon layer formed thereon the have the same crystal orientation as a whole. In this way, aeolotropic etching for which the crystal orientation is used is applicable in the next etching process and the optical waveguide 11 is more easily manufactured with precision.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a three-dimensional optical waveguide substrate, an optical module for coupling optical input / output of an optical element to an optical fiber, and a method of manufacturing a three-dimensional optical waveguide substrate.

[0002]

2. Description of the Related Art FIG. 11 shows a conventional three-dimensional optical waveguide substrate. Here, FIG. 11A is a plan view of a conventional three-dimensional optical waveguide, and FIG. 11B is a side view. An optical waveguide 11 is formed on an optical waveguide substrate 100. Here, the optical waveguide 11
Is made of a material having a higher refractive index to light than the material of the optical waveguide substrate 100. As a result, the light is confined in the optical waveguide 11 and the light travels along the waveguide 11. The optical waveguide substrate is formed by diffusing Ti into a LiNbO3 substrate, forming a glass film on a Si substrate by a flame deposition method, spin coating an organic material on the substrate, and the like.

The input / output of light to / from the optical waveguide 11 is performed by the optical waveguide 1
1 and optical elements such as an optical fiber, a light emitting element, and a light receiving element. FIG. 12 shows this example. The optical waveguide 11 and the optical fiber 40 are optically coupled. Optical waveguide 11 formed on optical waveguide substrate 100
The core 41 of the optical fiber 40 is closely opposed to the end of the optical fiber 40. Therefore, the light that has passed through the optical fiber 40 toward the left is emitted from the end of the core 41, enters the optical waveguide 11, and proceeds as it is. Conversely, light passing right through 11 is emitted from the end of the optical waveguide 11,
The light enters the core 41 of the optical fiber 40 and proceeds as it is. For efficient optical coupling between the optical waveguide 11 and the optical fiber 40, alignment between the optical waveguide 11 and the optical fiber 40 is indispensable. For this reason, active alignment for aligning and fixing the optical waveguide 11 and the optical fiber 40 while checking the light conduction state is performed. As a method of not performing active alignment, there is a V-groove fixing method for fixing the optical fiber 40 to a substrate on which a V-groove is formed.

[0004]

However, the conventional optical waveguide substrate 100 has a drawback in performing alignment with an optical element. In active alignment, the alignment process itself is complicated. In the V-groove method, the alignment process itself is relatively simple, but the production of the V-groove must be performed separately from the production of the optical waveguide. In any case, considering the alignment with the optical element, the optical waveguide substrate 100
A complicated process was required to produce the, and the yield was not good.

[0005]

In the optical waveguide substrate according to the present invention, a polygonal rod optical waveguide made of silicon containing impurities is formed on a silicon substrate. Further, as a useful application of the optical waveguide, an optical module for connecting an optical element and an optical fiber has been described. Further, as a method of manufacturing the optical waveguide substrate, a step of forming a silicon epitaxial film containing impurities on a silicon substrate and performing anisotropic etching was described.

[0006]

The optical waveguide according to the present invention can be formed by etching silicon. Therefore, it can be manufactured by a process common to a process of forming an optical element alignment structure such as a V-groove in a silicon substrate. Therefore, the formation of the optical waveguide and the formation of the optical element alignment structure can be performed almost simultaneously, which contributes to simplification of the manufacturing process and improvement of the yield.

[0007]

FIG. 1 shows a first embodiment of the present invention. FIG. 1A is a plan view of an optical waveguide substrate 100 according to the present invention, and FIG. 1B is a side view. A trapezoidal prism-shaped optical waveguide 11 made of silicon in which impurities are diffused is formed on a silicon substrate 12. Here, as a result of diffusing impurities, the optical waveguide 11 has a higher refractive index than the silicon substrate 12. Therefore, light is prevented from leaking from the optical waveguide 11 to the silicon substrate 12, and the optical waveguide 11 functions as a waveguide. The optical waveguide 11
Is higher than that of the surroundings, that is, usually in the air or vacuum, is also a factor that causes the optical waveguide 11 to function as an optical waveguide. A thin film portion 11a is formed on the lower side of the trapezoidal prismatic rod shape. If the thickness of this portion is sufficiently smaller than the thickness dz of the trapezoidal prismatic rod, it can be ignored as an optical waveguide. For example, phosphorus or the like can be used as the impurity, and the refractive index can be controlled by changing the amount of the impurity contained in silicon. Silicon is opaque to light in the visible region, but is transparent to light in the infrared region. Therefore, the optical waveguide 11
Is an optical waveguide in the infrared region, for example, a wavelength of 1.3 μm,
Light of 1.55 μm is guided. And the width dx of the trapezoid,
Height dz, refractive index n ₀ of silicon substrate 12 (= 3.3)
By changing the refractive index n ₁ of the optical waveguide 11 with respect to
The mode of the guided light can be set appropriately. For example, the refractive index _{n 1} of the optical waveguide optical waveguide 11 as 3.4, if the 1μm trapezoidal width dx and height dz respectively, wavelengths 1.
Only 3μ single mode light can be guided. When the width dx and the height dz of the trapezoid are each 35 μm, the optical waveguide 10 suitable for connecting to an optical fiber having a core diameter of 50 μm as a multimode can be formed.

To form this optical waveguide, a silicon layer in which impurities are diffused is formed on a silicon substrate 12. This layer can be formed by various methods such as a liquid phase or gas phase method. For example, a silicon layer containing phosphorus can be formed by applying a CVD method using silane gas containing PH ₃ as an impurity material. By adjusting the mixing ratio of silane and PH _3, it can be controlled content of phosphorus in the silicon. Here, if single crystal silicon is used as the silicon substrate 12 and epitaxial growth reflecting the crystal orientation of the silicon substrate is applied when forming the layer, the silicon substrate 12
And the silicon layer formed thereon have the same crystal orientation as a whole. This makes it possible to perform anisotropic etching utilizing the crystal orientation in the next etching step, and it becomes easier to manufacture the optical waveguide 11 precisely. The anisotropic etching can be performed using, for example, an aqueous solution of KOH. (1,1,1) as silicon substrate 12
Anisotropic etching is performed after epitaxial growth of a silicon layer containing an impurity part using a plane-oriented one.
The angle θ between the base and the side surface of the trapezoid 1 is 54.7 °.
When the orientation of the silicon substrate is the (1,1,0) plane, the angle θ between the bottom and the side of the trapezoid of the optical waveguide 11 is 90 °.
°, and transition from a trapezoid to a rectangle. In this embodiment, since the waveguide structure is formed by forming an impurity silicon layer on the entire silicon substrate and etching as a single waveguide substrate 100, it is extremely easy to fabricate. Further, since anisotropic etching can be used, there is an advantage that a waveguide structure can be formed extremely precisely.

FIG. 2 shows a modification of the first embodiment of the present invention. 2A is a plan view, and FIG. 2B is a side view. FIG. 2 is different from FIG. 1 in that a part of the silicon substrate 12 forms a trapezoidal bottom. At this time, the optical waveguide 11 made of impurity silicon functions as a waveguide, and even if the silicon substrate 12 forms a trapezoidal bottom, it does not function as a waveguide. The waveguide mode of the waveguide is determined by the bottom side dx and the height dz of the waveguide.
This is the same as in FIG. 2 may be formed by making the etching time longer than in the case of FIG. Even if the etching time becomes somewhat longer, the width dx of the trapezoid of the waveguide 11 does not change significantly, and the height dz of the trapezoid does not change. Therefore, there is no significant influence on the waveguide mode. From the above, it can be said that the strictness of the etching control has little effect on the waveguide characteristics of the optical waveguide 11. For this reason, in the optical waveguide 10 of the present invention, it is easy to produce a large number of optical waveguides having uniform properties. For example, when a large number of optical waveguide substrates are formed on one substrate at one time, or when a plurality of substrates are etched at the same time, there is a possibility that the etch rates become uneven. Even in such a case, the optical waveguide 10 according to the present invention has an advantage that a large number of optical waveguide substrates 100 having uniform properties can be simultaneously formed. In particular, if a (1,1,0) plane silicon substrate is used, the angle θ between the base and the side of the trapezoid will be described.
Is 90 °, it is possible to minimize the influence when the etch rates become uneven.

FIG. 3 shows a second embodiment of the present invention. The optical waveguide substrate main body 10 and the optical fiber fixing substrate 20 are integrally formed as an optical waveguide substrate 100, and a vertical groove 30 is formed between the optical waveguide substrate main body 10 and the optical fiber fixing substrate 20. The optical waveguide 11 is formed on the optical waveguide substrate body 10 as in the first embodiment. Then, a V-groove 21 having an end face facing the end face of the optical waveguide 11 is formed in the optical fiber fixing substrate 20. V
The groove 21 can be formed by anisotropic etching using a silicon substrate having a (1,1,0) plane orientation. Here, it should be noted that the formation of the optical waveguide 11 and the formation of the V-groove 21 can be performed in the same steps. That is, when the impurity-containing silicon necessary for forming the optical waveguide 11 is formed by epitaxial growth, the impurity-containing silicon and the silicon substrate thereunder have the same orientation, so that even if the impurity-containing silicon and the silicon substrate are in layers, There is no problem in forming the V groove 21. As a result, the optical waveguide substrate main body 10 and the optical fiber fixing substrate 20 can be formed by forming the impurity-containing silicon on the entire surface of the silicon substrate and performing etching. The vertical groove 30 is 10
And 20 can be formed by dicing. FIG. 4 shows a state in which an optical fiber is installed in the optical waveguide substrate body 10 according to the second embodiment. FIG. 4A is a plan view and FIG. 4B is a side view. The optical fiber 40 is fixed on the V-groove 21 of the optical fiber fixing substrate 20, and its core 41
Is in close proximity to the end face of the optical waveguide 11 and opposes it.
From this, the optical waveguide substrate body 10 and the optical fiber 40
Light can come and go between each other. Although the method of fixing the optical fiber 40 is not shown in the drawing, it can be performed, for example, with an adhesive, or by pressing down from above with another plate-like body or the like. Here, the formation of the vertical groove 30 removes the end face of the optical waveguide 11 which has become the slope wall by the etching. That is, by forming the vertical groove 30, the optical waveguide 11
The end face of the core 41 can be made closer to the end face of the optical waveguide 11 and the efficiency of optical coupling between the optical waveguide 11 and the optical fiber 40 can be improved.

FIG. 5 shows a third embodiment of the present invention. The optical waveguide substrate main body 10 and the optical element fixing substrate 50 are integrally formed as an optical waveguide substrate 100, and a vertical groove 30 is formed between the optical waveguide substrate main body 10 and the optical element fixing substrate 50. A flat groove 51 is formed on the optical element fixing substrate 50 so that the end face thereof faces the end face of the optical waveguide 11. The formation of the flat groove 51 can be performed by anisotropic etching of the silicon substrate as in the second embodiment, and can be formed in almost the same steps as in the step 11. That is, it can be formed by epitaxially growing impurity-containing silicon on a silicon substrate and then performing anisotropic etching. FIG. 5 shows a case where a silicon substrate having an orientation of (1,1,0) plane is used. A substrate having an orientation of (1,1,1) is used, and the optical waveguide 11 and the flat groove 51 are used. May have a trapezoidal cross section. The vertical grooves 30 can be formed by dicing as in the second embodiment. FIG. 6 shows a third embodiment in which light emitting elements are installed. The light emitting element 60 is installed in the flat groove 51 such that the light emitting end of the light emitting section 61 is close to and opposed to the end of the optical waveguide 11. Light emitted from the light emitting end of the light emitting unit 61 enters the optical waveguide 11. Here, the depth of the flat groove 51 is controlled so as to match the height of the end of the light emitting section 61 with the end of the optical waveguide 11. Even if the light emitting unit 61 is installed below the light emitting element 60, the light emitting unit 61
Is from the lower surface of the light emitting element 60 to a distance of several μm to 10 μm. Light emitting element 6
As 0, a semiconductor light emitting element such as an LED or an LD is used. Applying a light receiving element instead of the light emitting element 60 can be easily achieved by those skilled in the art.

An optical module is shown as an application example of the third embodiment of the present invention. FIG. 7 shows a perspective view of the optical module 200 with the casing upper cover 204 opened. FIG.
FIG. 9 is a front view of the optical module 200, and FIG. 9 is a cross-sectional view showing a connected state of the optical module 200 and the optical connector 250. An optical waveguide substrate 100 in which an optical waveguide substrate main body 10 and an optical element fixing substrate 50 are integrally formed in a casing 201.
Is installed. Here, the optical waveguide substrate body 10 has a (1,1,0) plane orientation as a silicon substrate and is formed by anisotropic etching. Therefore, the cross section of the optical waveguide 11 and the flat groove 51 is trapezoidal. I have. However, a structure having a rectangular cross section as shown in FIG. 5 may be used. The casing 201 has a receptacle 202 for connecting to an optical connector, and an external lead terminal 203 for introducing current.
a and 203b are provided. Further, electrodes 52a and 52b are formed on the optical element fixing substrate 50. This formation can be easily performed, for example, by etching or lifting off Al after forming Al by vacuum evaporation. Electrode 5
2a is electrically connected directly to the lower surface of the light emitting element 60, and the electrode 52b is electrically connected to the upper surface of the light emitting element 60 via a bonding wire. Further, the electrode 52a, the electrode 5
2b is a bonding wire for the external lead terminal 203
a and 203b, respectively. An end face of the receptacle 202 is opposed to an end face of the light emitting element 60 opposite to the end face of the optical waveguide 11, and a casing recess 210 and a casing opening 220 are provided in the casing 201 at the end face of the receptacle 202. The ends of the silicon substrate 12 and the optical waveguide 11 and the surface of the casing recess 210 are arranged on the end surface of the receptacle 202 such that they are substantially flush with each other. There is a gap between the optical waveguide 11, the silicon substrate 12 and the casing recess 210.
Sealed at 30. The adhesive 230 has a smaller refractive index than the optical waveguide 11 in consideration of the refractive index with the optical waveguide 11. For this, a commercially available optical adhesive can be used. As a result, when the casing upper lid 204 is sealed, the light emitting element 60 and the like in the casing 201 can be completely shut off from the outside air, and is effectively protected from moisture and the like. Note that a transparent protective film that is thin enough not to hinder optical coupling with an optical fiber described later can be coated on the end face of the optical waveguide 11. This coating serves to protect the end face of the optical waveguide 11. The casing upper lid 204 can be sealed by connecting to the casing 201 with an adhesive,
At this time, replacing the atmosphere in the casing with a nitrogen gas or an inert gas, or evacuating the vacuum is effective in preventing deterioration of the light emitting element 60 and the like in the casing 202 due to moisture, oxygen, and the like in the atmosphere. As shown in FIG. 9, the optical connector 250 to which the optical fiber 40 is connected is inserted into the receptacle 202. Then, the end face of the optical fiber 40 appearing on the end face of the optical connector 250 comes into contact with the optical waveguide 11. as a result,
The light emitted from the light emitting element 60 in the casing 202 and having passed through the optical waveguide 11 enters the optical fiber 40. Although not shown, the light emitting element 60 can be modulated by a power supply connected to the external lead terminal 203.

FIG. 10 shows a conventional optical module in contrast to the optical module according to the present invention. The light emitting element 60 is installed on the optical element fixing substrate 50 on which the electrodes 52 are formed, and the optical element fixing substrate 50 is hermetically installed in the casing 202. A glass window 260 is provided in the casing 202, and the glass window 260 faces the light emitting surface of the light emitting element 60. The optical fiber 40 is detachable from the optical module 200.
00, the optical fiber 40
Abuts. Light emitted from the light emitting element 60 flows into the optical fiber 40 through the glass window 260. In this conventional optical module 200, the distance between the light emitting end of the light emitting element 60 and the end face of the optical fiber 40 is increased by the thickness of the glass window 260. And the glass window 260
Since it is necessary to provide a certain degree of strength, there is a certain limit in reducing the thickness. Therefore, the distance between the light emitting end of the light emitting element 60 and the end face of the optical fiber 40 is inevitably several hundred μm.
Because the light is diffused during this time,
The efficiency of optical coupling between the light emitting element 60 and the optical fiber 40 cannot be said to be high. In particular, when the optical fiber 40 is a single mode fiber, the conventional optical module 200 in which light does not flow into the optical fiber 40 almost completely does not exist. Could not be used practically. That is, conventionally, it has not been compatible with the optical module 200 to be a receptacle type to which an optical fiber can be attached and detached and to seal with good environmental resistance.

On the other hand, in the optical module 200 according to the present invention, since the optical waveguide 11 is interposed between the light emitting element 60 and the optical fiber 40, the light is effectively transferred to the optical fiber 40 without being diffused. I do. That is, the optical module 200 according to the present invention has a feature that the entirety is sealed and a receptacle type is realized.

[0015]

As described above, the optical waveguide substrate according to the present invention has an effect that can be realized by an easy process including the alignment with the optical element. The yield can be improved due to the ease of the process. Further, the optical module using the optical waveguide substrate according to the present invention has an effect of achieving both the characteristics of the sealing and the receptacle type.

[Brief description of the drawings]

FIG. 1 is a plan view and a side view showing an optical waveguide according to a first embodiment of the present invention.

FIG. 2 is a plan view showing a modification of the first embodiment of the present invention;
It is a side view.

FIG. 3 is a perspective view showing an optical waveguide according to a second embodiment of the present invention.

FIG. 4 is a plan view and a side view showing a state where an optical fiber is installed in a second embodiment of the present invention.

FIG. 5 is a perspective view showing an optical waveguide according to a third embodiment of the present invention.

FIG. 6 is a plan view and a side view showing a state where an optical element is installed in a third embodiment of the present invention.

FIG. 7 is a perspective view showing an optical module using an optical waveguide according to a third embodiment of the present invention, with a casing upper cover opened.

FIG. 8 is a side view of an optical module using an optical waveguide according to a third embodiment of the present invention.

FIG. 9 is a cross-sectional view showing a coupling state between an optical module and an optical connector according to a third embodiment of the present invention.

FIG. 10 is a partial cross-sectional view showing a coupling state of an optical connector by cutting a part of a casing of a conventional optical module.

FIG. 11 is a plan view and a side view showing a conventional optical waveguide.

FIG. 12 is a plan view showing a coupling state between a conventional optical waveguide and an optical fiber.

[Explanation of symbols]

 10: Optical waveguide substrate body 11: Optical waveguide 12: Silicon substrate 20: Optical fiber fixing substrate 21: V groove 30: Vertical groove 40: Optical fiber 41: Core 50: Optical element fixing substrate 51: Flat groove 52, 52a, 52b : Electrode 60: Light emitting element 61: Light emitting unit 100: Optical waveguide substrate 200: Optical module 201: Casing 202: Receptacle 203 a, 203 b: External lead terminal 204: Casing upper lid 210: Casing recess 220: Casing opening 230: Adhesive 250 : Optical connector 260: Glass window

Claims (7)

[Claims] 1. An optical waveguide substrate comprising a silicon substrate and a three-dimensional optical waveguide formed on the silicon substrate, wherein the three-dimensional optical waveguide is in the shape of a polygonal column made of silicon containing impurities. Optical waveguide substrate 2. An optical waveguide substrate according to claim 1, wherein the optical fiber fixing substrate is formed integrally with the optical waveguide substrate, and the end surface thereof is opposed to the end surface of the optical waveguide. An optical waveguide substrate, further comprising a V-groove that performs 3. The optical waveguide substrate according to claim 1, wherein the optical device fixed substrate is formed integrally with the optical waveguide substrate, the optical device fixed substrate is formed on the optical device fixed substrate, and the end surface thereof faces the end surface of the optical waveguide. An optical waveguide substrate, further comprising: 4. The optical waveguide substrate according to claim 2, wherein a vertical groove is formed between the optical fiber fixing substrate or the optical element fixing substrate and the optical waveguide substrate main body. Optical waveguide substrate 5. An optical module for connecting an optical element to an optical fiber, comprising: a silicon substrate; a polygonal rod-shaped three-dimensional optical waveguide formed on the silicon substrate and made of silicon containing impurities; A flat groove whose end face is opposed to the end face of the optical waveguide,
An optical module, comprising: an optical element installed on a flat groove of an optical waveguide substrate; an optical waveguide substrate; and a casing covering the optical element and having an opening facing an end face of the optical waveguide. 6. The optical module according to claim 5, further comprising an optical connector receptacle having an end face facing the opening of the casing. 7. A method for manufacturing an optical waveguide substrate according to claim 1, wherein a step of forming a silicon epitaxial film containing impurities on a silicon substrate is performed, wherein the formed silicon film is anisotropically. A method of manufacturing an optical waveguide substrate, comprising: a step of performing reactive etching.