JP2970519B2 - Optical circuit and its manufacturing method - 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 circuit and a method of manufacturing the same, and more particularly to an optical circuit used in an optical network system.
In an optical device such as a transmitter or a receiver using an optical waveguide formed on a substrate such as a Si substrate, an optical circuit for converting an optical axis of light emitted from the optical waveguide and an optical coupling with a light receiving element are performed. The present invention relates to an optical circuit and its manufacturing method.

[0002]

2. Description of the Related Art As the capacity of an optical communication system has been increased and a multifunctional advanced system has been demanded, there has been a strong demand for cost reduction of an optical fiber network. Among them, downsizing, high integration, and low cost of optical devices such as optical transmitters and optical receivers are essential.

At present, practically used optical transmitters and receivers use a structure in which a lens is provided between a semiconductor light source and a semiconductor photodetector and an optical fiber to ensure spatial optical connection. ing. A structure that spatially secures optical connection using this lens is called “microoptics”.

In this micro-optics structure, it is difficult to reduce the size because the shape of the lens and the shape of the package of the semiconductor light source and the semiconductor photodetector are limited. Also, in order to efficiently couple light propagating in space to an optical fiber or a photodetector, precise optical axis adjustment is required. The current situation is that it does not drop. Also,
Needless to say, it is completely unsuitable for highly integrating the same function or different functions.

[0005] In recent years, the need for a two-way communication system has increased, and it has been desired to introduce this system to homes. As an optical device that enables two-way communication, an optical transmitter and a receiver are required, but if these were separately configured, the optical transmitting and receiving apparatus would become large,
It hinders the spread of the system. Therefore, an optical device (optical transceiver) integrating two functions is desired. However, it is difficult to realize this in the micro-optics structure for the above-described reason.

For this reason, an optical transceiver integrated using an optical waveguide is desired as a structure aiming at miniaturization and cost reduction.

In order to realize the integration of the optical transceiver,
It is necessary to integrate optical components such as a semiconductor light source, a semiconductor photodetector, and an optical fiber on the same substrate or on the edge of the substrate. The method of integrating optical components on the same substrate is an effective method in that the optical components can be integrated at an arbitrary position on the substrate, so that the degree of freedom in device design is increased.

When the optical waveguide is optically coupled to an optical component such as a semiconductor photodetector by this method, the optical component is inserted into the optical waveguide and the light emitted from the optical waveguide is received horizontally as it is, or Conversely, there are a horizontal input / output method in which light enters the optical waveguide, and a vertical input / output method in which light emitted from the optical waveguide is converted into an optical axis, light is taken out vertically to the substrate, and coupling with an optical component is performed.

FIG. 5 is a side view showing an example of a conventional horizontal input / output system (for example, a document (Yamada: J. Lightwave Tec)).
hnol., 10, 3, p. 383 (1992)). In FIG. 4, 1 is S
The i-substrate, 2 indicates an optical waveguide, and 14 indicates an optical component. The optical waveguide 2 includes a lower clad 3, a core 4, and an upper clad 5. This method is advantageous in reducing the cost because the structure is simple and suitable for miniaturization, but the optical component 14 is limited to a waveguide type optical component. The optical waveguide 2 and the optical component 1
4, especially in the optical waveguide thickness direction, it is difficult to align the optical axis, and there is still a problem in practical use.

On the other hand, a vertical input / output method (for example, a reference (Uchi
da: Jpn.J.Appl.Phys., 31, Pt.1,5B, p.1652 (1992))
For example, various optical components such as a surface-type semiconductor photodetector with easy optical axis alignment can be integrated. In this method, a mirror that reflects light emitted from the optical waveguide is required to convert light into an optical axis.

FIG. 6A is a diagram schematically showing a cross section of a first structure of a conventional optical circuit. The reflection mirror 12 having an inclination angle θ = 45 degrees with respect to the Si substrate 1 is fixed to the substrate 1 by an adhesive or the like after the position of the optical axis is adjusted using a manipulator (not shown) or the like. 8 is provided. The reflected light 8 taken out by the reflecting mirror 12 is coupled to an optical component such as a semiconductor photodetector (not shown).

FIG. 6B is a diagram schematically showing a cross section of the second structure of the conventional optical circuit. The reflection surface 13 is formed by anisotropically etching the Si substrate 1. In this structure, the reflection mirror 12 can be formed on the same substrate as the optical waveguide 2 by a photolithography process, and since the reflection surface 13 is obtained by anisotropically etching the Si substrate 1, Since the angle is uniquely determined, an extremely stable optical circuit is obtained. Furthermore, it has high reliability against temperature fluctuations and vibration / shock, and is excellent in mass productivity because there is no need to adjust the optical axis.

[0013]

However, FIG.
The first structure of the conventional optical circuit shown in FIG. 1A requires a great deal of man-hours to adjust the position of the optical axis, hinders cost reduction, and easily relies on temperature fluctuations and vibration shock. It is difficult to secure the property. Further, since it is necessary to use the reflection mirror 12 as an individual component, there is a problem that this also hinders cost reduction.

On the other hand, in the second structure of the conventional optical circuit shown in FIG. 6B, although the above problem is solved,
Since the reflection surface 13 is formed by anisotropic etching of the Si substrate 1, the inclination angle is uniquely determined, and in this case, the inclination angle θ is 54.7 degrees.

Accordingly, in the second structure, since the angle of the reflected light 8 is also limited, there is a problem that the degree of freedom in designing an optical device is reduced. In particular, in order to mount an optical component such as a semiconductor photodetector on a substrate without adjustment, it is desired that the reflected light 8 be taken out perpendicular to the substrate. Therefore, there is a need for a structure capable of selecting the inclination angle to 45 degrees.

In the two structures of the above-mentioned conventional optical circuit, since the reflecting surface 13 is a flat surface, it is necessary to use a lens when optically coupling the actual optical component and the reflected light 8. . However, mounting via a lens hinders reliability against temperature fluctuations, vibration and impact, and furthermore, cost reduction.

Accordingly, an object of the present invention is to solve the above-mentioned various problems, to take out the light emitted from the optical waveguide to the upper part by a reflection mirror, and to make the mirror itself have a lens effect. To provide an optical circuit that is optically efficiently coupled to an optical component such as a semiconductor photodetector and achieves high efficiency and low cost, and has extremely high reliability against temperature fluctuation and vibration / shock and a method of manufacturing the same. It is in.

[0018]

In order to achieve the above object, an optical circuit according to the present invention is an optical circuit in which an optical waveguide is formed on a Si substrate and the optical axis of the light emitted from the optical waveguide is changed. A reflection mirror that reflects light emitted from the optical waveguide is formed on an inclined surface formed by anisotropically etching the Si substrate, and the reflection mirror has at least a reflow-treated quartz-based film layer. An optical circuit is provided.

Further, the method for manufacturing an optical circuit according to the present invention comprises the steps of:
An optical waveguide is formed on a substrate, and in a method of manufacturing an optical circuit for converting the light emitted from the optical waveguide to an optical axis, (a) forming a reflection mirror that reflects the light emitted from the optical waveguide; Forming an inclined surface by anisotropically etching the Si substrate; and (b) depositing a quartz-based film on at least the Si substrate including the etched surface, and then reflowing the quartz-based film. , Is included.

[0020]

In the optical circuit and the method of manufacturing the same according to the present invention, an inclined surface formed by anisotropic etching of a Si substrate is used as a reflecting mirror for extracting the light emitted from the optical waveguide to the upper part, and a quartz-based material or reflow is used. Utilizing this, the reflection surface is formed into a curved surface shape so that the inclination angle becomes gentler than the inclined surface of the Si substrate.

As a result, the angle of the reflected light can be arbitrarily selected, so that the degree of freedom in designing the optical device is greatly improved. In addition, since the reflection surface itself has a light condensing effect, there is no need to use a lens for optical coupling with an optical component.

Further, according to the present invention, since the reflecting surface can be formed by a photolithography process, the positional accuracy between the optical waveguide and the reflecting surface is extremely high, the mass productivity is excellent, and a reflecting mirror as a solid element on a substrate is provided. Since it is formed, it is possible to realize an optical circuit having extremely high reliability even with respect to temperature fluctuation, vibration and shock.

In the present invention, the material of the optical waveguide is not particularly limited to a quartz-based material as long as the material can withstand the reflow temperature. The optical waveguide and the quartz-based film are formed of the same material by stopping the etching in the middle of forming the quartz-based film so that it is not necessary to deposit them separately.
It is possible to provide a manufacturing method suitable for a batch process and excellent in mass productivity.

[0024]

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

FIG. 1 is a side view schematically showing the structure of an optical circuit according to one embodiment of the present invention. Referring to FIG.
This embodiment includes a Si substrate 1 using a Si member, an optical waveguide 2 using a quartz-based material, and a reflection mirror 12.

The optical waveguide 2 has a layer structure including a lower clad layer 3, a core 4, and an upper clad layer 5. For example, in the case of a single mode optical waveguide, the thickness of the lower cladding 3 and the upper cladding layer 5 is about 10 μm, and the thickness and width of the core 4 are about 6 μm. As a typical quartz-based material, P and B are doped into the upper clad 3 and the lower clad 5, and P, B, Ge and the like are doped into the core 4 by several wt%, respectively.

The height of the reflection mirror 12 may be substantially the same as that of the optical waveguide 2. The distance from the end face 11 of the optical waveguide to the reflection mirror 12 is about 20 μm. The reflection mirror 12 is formed using the inclined surface 6 of the Si substrate 1 by anisotropic etching. In the anisotropic etching of the Si substrate 1, the (1,1,1) plane is exposed, and the inclination angle θ of the inclined surface 6 can be formed with high precision, that is, about 54.7 degrees in the present embodiment. It is also known that the exposed (1,1,1) plane has excellent flatness.

A quartz-based film layer 7 formed on the inclined surface 6 of the Si substrate 1 by reflow so as to have a curved surface and a smaller inclination angle than the inclined surface 6 of the Si substrate 1.
(A thickness of several μm), and further coated with Au, Al, or the like as a reflection member 10 that reflects light emitted from the optical waveguide 2. As the quartz-based film layer 7, for example, a quartz-based material doped with P, Ge, B, or the like is used. In particular, a quartz-based film doped with B is easily reflowed.

In this structure, the angle of inclination of the reflecting surface 13 is determined by the reflow of the quartz-based film layer 7,
For example, if the inclination angle is selected to be 45 degrees, the reflected light 8 can be taken out perpendicular to the substrate. Further, since the reflecting surface 13 is formed in a curved shape, the reflected light 8 is collected by the curvature. Although a quartz-based material has been described as a material of the optical waveguide 2, the material is not particularly limited to a quartz-based material as long as the material can withstand a reflow temperature.

FIG. 2 is a view showing a first method of manufacturing an optical circuit according to an embodiment of the present invention in the order of steps.

First, referring to FIG.
After forming an inclined surface 6 by performing anisotropic etching on
The optical waveguide 2 is formed in the concave portion of the i-substrate 1 (step A).

Next, referring to FIG. 2B, a quartz-based film 9 is deposited on the Si substrate 1 including the inclined surface 6 (step B).
For deposition of the quartz-based film 9, for example, a CVD method, a sputtering method, a flame deposition method, or the like is used.

Next, referring to FIG.
Is formed so as to have a gentler inclination angle than the inclined surface 6 of the Si substrate 1, and the surface is coated with a reflecting member 10 such as Au or Al (Step C). At this time, the inclination angle and the curvature of the reflection surface 13 are controlled by the thickness of the quartz-based film 9, the reflow temperature, and the time. The reflow is usually performed at a temperature of 850 ° C. or more. At this time, even if the surface of the upper clad 5 of the optical path waveguide 2 is reflowed, the influence on the characteristics of the optical waveguide 2 is small.

However, since the optical waveguide end face 11 may lose its perpendicularity due to reflow, the reflection mirror 12
Local heating limited to (see FIG. 1) is desirable. This local heating is performed, for example, by irradiating a laser beam such as CO ₂ or Ar or using a normal heater. When depositing the quartz-based film 9, the quartz-based film 9 is also deposited on the surface of the upper clad 5 and the end face 11 of the optical waveguide 2, but the deposition on the surface of the upper clad 5 affects the characteristics of the optical waveguide 2. Is not
Further, since the end face 11 is perpendicular to the substrate, the quartz-based film 9 is hardly deposited on the end face 11, and there is almost no influence by this.

FIG. 3 is a diagram showing a second method of manufacturing an optical circuit according to the embodiment of the present invention in the order of steps. This manufacturing method is different from the first manufacturing method in that a quartz-based material is used as the material of the optical waveguide 2 and the etching is stopped in the course of forming the optical waveguide end face 11 to leave the quartz-based film 9. (See FIG. 3B). The following steps are the same as in the first manufacturing method.

According to this method, since the optical waveguide 2 and the quartz-based film 9 are formed of the same material, they need not be individually deposited, and a manufacturing method suitable for a batch process and excellent in mass productivity is provided. Can be provided.

Using the optical circuit according to the embodiment of the present invention,
When the angle of the actual reflected light with respect to the Si substrate 1 was measured,
The characteristic as shown in FIG. 4 was obtained with respect to the reflow temperature.
When the reflected light 8 was received by a semiconductor photodetector at a distance of 200 μm from the Si substrate, good results with almost no loss were obtained.

[0038]

As described above, according to the present invention, a reflecting mirror is formed by forming an inclined surface by anisotropically etching a Si substrate and then depositing and reflowing a quartz-based film on the inclined surface. I do. Light emitted from the optical waveguide is extracted upward by a reflecting mirror and optically coupled to an optical component such as a semiconductor photodetector. However, since the inclination angle of the reflecting mirror can be selected according to reflow conditions and the like, freedom in optical device design is provided. The coupling efficiency is high because the reflection surface is curved and has a light collecting effect.

Further, according to the present invention, since the reflection mirror can be collectively formed as an individual element on the same substrate as the optical waveguide, an optical circuit having excellent mass productivity and extremely high reliability against temperature fluctuation, vibration and shock is realized. It has the effect of being able to.

[Brief description of the drawings]

FIG. 1 is a side view showing a structure of an optical circuit according to an embodiment of the present invention.

FIG. 2 is a view showing a process showing a first embodiment of the method of manufacturing an optical circuit according to one embodiment of the present invention.

FIG. 3 is a diagram showing a process showing a second embodiment of the method of manufacturing an optical circuit according to one embodiment of the present invention.

FIG. 4 is a diagram showing a characteristic representing an angle of reflected light with respect to a reflow temperature.

FIG. 5 is a side view showing a horizontal input / output type optical circuit.

FIG. 6 is a side view showing the structure of a conventional optical circuit.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 Si substrate 2 Optical waveguide 3 Lower cladding 4 Core 5 Upper cladding 6 Si substrate inclined surface 7 Reflowed quartz-based film layer 8 Reflected light 9 Quartz-based film layer 10 Reflecting member 11 Optical waveguide end surface 12 Reflecting mirror 13 Reflecting surface 14 Light parts

Claims (3)

(57) [Claims] 1. An optical circuit in which an optical waveguide is formed on a Si substrate, and an optical circuit for converting the light emitted from the optical waveguide to an optical axis, wherein a reflection mirror for reflecting the light emitted from the optical waveguide is different from the Si substrate. An optical circuit formed on an inclined surface formed by isotropic etching, wherein the reflection mirror includes at least a reflow-treated quartz-based film layer. 2. A method for manufacturing an optical circuit in which an optical waveguide is formed on a Si substrate and converts the light emitted from the optical waveguide into an optical axis, wherein: (a) a reflecting mirror that reflects the light emitted from the optical waveguide; Forming an inclined surface by anisotropically etching the Si substrate, and (b) depositing a quartz-based film on the Si substrate including at least the inclined surface, and then forming the quartz-based film. And a step of reflowing the optical circuit. 3. The method according to claim 1, wherein the quartz-based film is formed by the reflow treatment so as to have a predetermined curved surface shape on the inclined surface of the Si substrate and a smaller inclination angle than the inclined surface. 3. The method for manufacturing an optical circuit according to claim 2, wherein: