JPS61267010A - Optical waveguide circuit and its manufacture - Google Patents

Abstract

PURPOSE:To align the axis of an optical waveguide circuit with the axis of an optical fiber without decreasing the thickness of the clad of the optical fiber by removing part of the substrate of the optical waveguide and forming a guide groove. CONSTITUTION:A material which can be etched anisotropically so as to form a V-shaped or rectangular guide groove later is selected for the substrate and sapphire, Si, etc., are usable. A buffer layer 4, a light guide layer, and a cover layer 6 are laminated on the substrate 3 successively. The light guide layer 5 is made of a material having a larger refractive index than the buffer layer 4 and cover layer 6 so as to confine light in the light guide layer 5. Then, the cover layer 6, light guide layer 5, and buffer layer 4 are removed except the pattern of a channel waveguide and the pattern of a guide for fiber insertion to expose the surface of the substrate 3. Further, the exposed substrate 3 is etched to form the V-shaped or rectangular guide groove 9 for optical fiber insertion.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical waveguide circuit optically coupled to an optical fiber and a method for manufacturing the same.

BACKGROUND OF THE INVENTION Recent developments in optical communication systems using optical fibers have been remarkable. In order to configure this optical communication system, in addition to light emitting and light receiving elements, optical modulators, optical switches,
Optical components such as an optical branching/coupling device, a light combining/demultiplexing device, and an optical filter are required, and optical coupling between these optical components and optical fibers is also required.

In early optical communication systems, the above-mentioned optical components were used as lenses,
It was composed of a combination of mirrors, prisms, etc. Although it is relatively easy to couple such optical components with optical fibers, optical devices constructed from conventional optical components such as lenses, mirrors, and prisms are large and expensive, and are difficult to use for optical communication. It has become difficult to provide the mechanical stability and reliability required for the device.

Therefore, an optical waveguide circuit, which is a new optical system in which an optical waveguide is formed on a substrate, was devised. In this optical waveguide circuit, an optical waveguide made of a material with low optical loss and a high refractive index is provided on a substrate by a diffusion method, a deposition method, or the like, and light is propagated within the optical waveguide. Various types of optical elements are then fabricated on the substrate, such as configuring lenses or prisms by changing the thickness of a part of the optical waveguide, or configuring an optical modulator by providing electrodes and applying electrolysis to the optical waveguide. It can be configured as follows.

Furthermore, in the optical waveguide circuit, a so-called optical integrated circuit in which a plurality of optical elements are integrated in a hybrid or monolithic manner becomes possible. For this reason, expectations have arisen for optical circuits to be smaller, lower in cost, higher in performance, and higher in reliability, and research and development of optical waveguide circuits is progressing in various fields.

Problems to be Solved by the Invention In order to introduce light into the optical waveguide of this optical waveguide circuit, it is necessary to couple the optical waveguide to an external optical transmission line. Optical fibers are most commonly used as external optical transmission lines, and optical coupling between the two is usually achieved by abutting the polished end face of the optical fiber against the end face of an optical waveguide.

However, the size of the optical waveguide and the core diameter of the optical fiber are generally very small, for example,
When using single mode light of μm, it is necessary to make the thickness about 10 μm or less. Therefore, the alignment between the end faces of the optical waveguide and the optical fiber must be performed with extremely high precision. If alignment is not performed well and axis misalignment occurs, the degree of coupling will decrease and a large coupling loss will occur.

By using optical waveguide circuits in this way, optical devices can be made smaller, but on the other hand, operators must perform extremely high-precision positioning that requires a great deal of effort to couple with optical fibers.

Therefore, in order to relatively easily perform high-precision alignment, a method was devised to form a guide groove for coupling the optical fiber and optical waveguide, as shown in Figure 3. It was announced at ``Nα311'' in 2017. That is, a channel waveguide 7 consisting of a buffer layer 4, an optical waveguide layer 5, and a cover layer 6 is formed on a substrate 3, and at the same time two guides 8 having an interval equal to the outer diameter of the optical fiber 1 to be optically coupled are formed in the channel guide. It is formed at a symmetrical position with respect to the center line of the wave path 7. By inserting the optical fiber 1 into the guide groove formed by the guide 8, the axes of the channel waveguide 7 and the optical fiber 1 are aligned.

However, the buffer layer 4 formed between the substrate 3 and the optical waveguide layer 5 is intended to relatively increase the refractive index of the optical waveguide 5 and enhance the light confinement effect within the optical waveguide layer 5. Generally, a film thickness of about 10 μm is sufficient. Further, if the refractive index of the optical waveguide layer 5 is sufficiently larger than the refractive index of the substrate 1, the buffer layer 4 is unnecessary. On the other hand, the cladding of the optical fiber 1 generally has a thickness of several tens of micrometers or more in order to maintain the strength of the optical fiber.

As described above, since the thickness of the buffer layer 4 is smaller than the thickness of the cladding of the optical fiber 1, when the optical fiber 1 is inserted into the guide groove, the height of the core 2 in the optical fiber 1 and the height of the optical waveguide layer 5 are The height won't match. If the heights of the two do not match, most of the light transmitted inside the core 2 will not enter the optical waveguide layer 5 and will be lost. Therefore, in order to match the height of the core 2 and the optical waveguide layer 5, conventionally, a part of the cladding of the optical fiber 1 that contacts the substrate 3 is removed, and the thickness of the cladding of this part is set to the thickness of the buffer layer 4. The optical fiber 1 was inserted into the guide groove after being thinned to a certain degree. In this way, optical fiber 1 and channel waveguide 7 can be optically coupled with less loss.

However, it takes a lot of effort to thin the cladding of minute optical fibers, and optical fibers with thinner claddings have lower strength and are more likely to bend or break, reducing work efficiency when inserting optical fibers. There's a problem.

Thus, an object of the present invention is to provide an optical waveguide circuit that can be easily and accurately optically coupled to an optical fiber without thinning the cladding of the optical fiber.

A further object of the present invention is to provide a manufacturing method that can easily and reliably manufacture the optical waveguide circuit as described above.

Means for Solving the Problems As a result of various studies on optical waveguides that are optically coupled to optical fibers, the inventor found that if a part of the substrate of the optical waveguide circuit is removed to form a guide groove, the cladding of the optical fiber can be removed. We have discovered that it is possible to align the axes of an optical waveguide circuit and an optical fiber without making them thinner.

That is, an optical waveguide circuit of the present invention includes a substrate and an optical waveguide formed on the substrate and optically coupled to an external optical fiber, in which the substrate is connected to an outer peripheral surface of one end of the optical fiber. The optical waveguide is characterized by having a guide groove that aligns the axes of the optical fiber and the optical waveguide by abutting the optical fiber and the optical waveguide.

The optical waveguide circuit according to the present invention described above is provided by forming at least two layers of an optically transparent material having a composition different from that of the substrate on a substrate having a flat surface, and forming the optically transparent material layer in a predetermined pattern. Remove the etching according to the
forming an optical waveguide and forming guides on both sides of one end of the optical waveguide; then surrounding one end of the optical waveguide and the guide with an etching material that does not remove the optically transparent material but removes the substrate; It can be manufactured by etching the exposed surface of the substrate.

In a preferred embodiment of the present invention, the substrate is made of Si, and the optical waveguide includes a first layer formed on the substrate and having a refractive index greater than the refractive index of the substrate, and a first layer formed on the first layer. a second layer having a refractive index smaller than that of the first layer;
a first layer formed on a substrate; a second layer formed on the first layer and having a refractive index greater than the refractive index of the first layer; and a third layer formed thereon and having a refractive index smaller than the refractive index of the second layer.

Preferably, the guide groove provided on the substrate is a square groove or a square groove.

By configuring the optical waveguide circuit as described above, the optical waveguide formed on the substrate and the inside of the optical fiber can be easily connected by simply inserting the optical fiber into the guide groove of the substrate formed in advance to a predetermined size. can be aligned with the core of

Moreover, according to the manufacturing method according to the present invention described above, it is possible to reliably and easily manufacture a groove that allows the axes of the optical waveguide and the core within the optical fiber to be aligned.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a partial perspective view of an optical waveguide circuit according to an embodiment of the present invention. This embodiment includes a substrate 3 provided with a ■-shaped guide groove 9, a buffer layer 4 formed on the substrate 3, an optical waveguide layer 5, and a cover layer 6 for protecting the optical waveguide layer 5.
and two guides 8 which are also formed on the substrate 3 and have an interval equal to the outer diameter of the optical fiber l. The refractive index of the optically transparent material constituting the optical waveguide layer 5 is made larger than the refractive index of the materials constituting the buffer layer 4 and the cover layer 6. That is, in the conventional example shown in FIG. 3, the board 3 is provided with a ■-shaped guide groove 9.

Next, the method for manufacturing the optical waveguide circuit as described above is shown in Figure 2 (1).
) to (4) will be explained with reference to process diagrams.

First, as the substrate 3 shown in FIG. 2 (1),
In order to form the letter-shaped or rectangular guide grooves, a material that can be anisotropically etched is selected, and sapphire, Si, etc. can be used. Among these, Sl is the most effective material because it is easily available and the processing method has been established.

Next, as shown in FIG. 2 (2), a buffer layer 4 is placed on this substrate 3.
, an optical waveguide layer 5 and a cover layer 6 are sequentially laminated. At this time, in order to confine light within the optical waveguide layer 5, the optical waveguide layer 5 is made of a material having a higher refractive index than the buffer layer 4 and the cover layer 6, as described above. However, if the refractive index of the optical waveguide layer 5 is sufficiently larger than the refractive index of the substrate 3,
Even if the buffer layer 4 is omitted, the effect of confining light within the optical waveguide layer 5 can be obtained. Therefore, it is sufficient to laminate only the optical waveguide layer 5 and the cover layer 6 on the substrate 3.

Note that the buffer layer 4, the optical waveguide layer 5, and the cover layer 6 are
When forming an iO2-based crystal, the CVD method or plasma CVD method is mainly used as a lamination method, and Ta
A sputtering method is mainly used when forming with crystals such as 21s.

In addition, in order to make the refractive index of the buffer layer 4 and the cover layer 6 smaller than that of the optical waveguide layer 5, when the buffer layer 4, the optical waveguide layer 5, and the cover layer 6 are formed of SiO, system crystal, the buffer layer 4 and the cover layer 6 may be made of a material doped with a refractive index decreasing dopant such as fluorine or boron, or the optical waveguide layer 5 may be made of a material doped with a refractive index increasing dopant such as Ge.

Alternatively, by combining both of them, the optical waveguide layer 5 doped with a refractive index increasing dopant may be formed on the buffer layer 4 doped with a refractive index decreasing dopant.

Next, as shown in No. 2E9(3), the cover layer 6, optical waveguide layer 5, and buffer layer 4 of other parts are removed, leaving the channel waveguide pattern and the guide pattern for optical fiber insertion. , exposing the surface of the substrate 3. Wet l' etching and dry etching can be used as a removal method, but when forming fine patterns, anisotropic etching with little change in pattern dimensions is required, and RIE using CF4 etc. as an etching gas is recommended. It becomes effective.

Furthermore, by etching the substrate 3 whose surface was exposed in the above step, a square or square guide groove 9 for inserting the optical fiber is formed as shown in FIG. 2(4). However, in this step, it is necessary to use a method of etching only the substrate 3 without etching the cover layer 6, optical waveguide layer 5, and buffer layer 4. When Si is used as the substrate 3, KOH is used.

HF + HN O3 + CH3COOH, N2H4
Wet etching using +CH3CHOHC83 etc. as a crystal plane anisotropic etching material, or CC1,, CCl
2F2, CClF3, C2F6+CI2, CB, F
Anisotropic etching can be performed using plasma etching using etching gas such as No. 3 etching gas.

Furthermore, when sapphire is used as the substrate 3, Hs
Wet etching or the like using PO4 as an etching liquid can be used.

The shape of the guide groove 9 is determined by the material of the substrate 3, the plane index of the crystal plane constituting the surface of the substrate 3, and the etching method. For example, when etching the Si substrate 3 with alkali, the (100) plane is If the substrate surface is taken as the substrate surface, it will be formed in a figure 7 shape, and if the (110) plane is taken as the substrate surface, it will be formed in a rectangular shape.

Next, a specific example will be explained.

First, a buffer layer 4 of 5 iOz doped with fluorine is deposited to a thickness of 10 μm on a Si substrate 3 with the (100) plane as the upper surface.
1 An optical waveguide layer 5 of pure silica with a thickness of 50 μm and a cover layer 6 of 5 in 2 doped with fluorine with a thickness of 10 μm were sequentially laminated by plasma CVD.

Next, a chrome mask with a pattern of the channel waveguide 7 and two guides 8 is formed by a lift-off method, and the CF
, as an etching gas, and etched the cover layer 6, optical waveguide layer 5, and buffer layer 4 until the surface of the substrate 3 was exposed.

At this time, the width of the channel waveguide 7 was 50 μm, and the interval between the two guides 8 was 125 μm.

Furthermore, after removing the chrome mask, 2
The surface of the substrate 3 between the two guides 8 was wet-etched in a figure 7 shape, and the etching was completed when the substrate 3 was etched by 27.5 μm in the depth direction.

When the optical fiber 1 having an outer diameter of 125 μm and a core 2 of 50 μm was brought into contact with the guide groove 9 of the optical waveguide circuit of this example manufactured in this way for optical coupling, the coupling was achieved with a loss of approximately 1 dB. Therefore, it can be seen that the optical coupling is very efficient and efficient.

As described above in detail, according to the present invention, optical coupling between an optical waveguide circuit and an optical fiber can be easily and extremely efficiently performed. Moreover, since there is no need to thin the cladding of the optical fiber for coupling, labor is saved and work efficiency is improved.

Furthermore, since the strength of the optical fiber does not decrease, the stability and reliability of a device or system using the optical waveguide circuit of the present invention is improved.

Further, according to the method for manufacturing an optical waveguide circuit of the present invention described above,
The grooves of the optical waveguide circuit according to the present invention described above can be easily and reliably made. Therefore, by using the manufacturing method of the present invention, the optical waveguide circuit according to the present invention can be manufactured in large quantities at low cost.

[Brief explanation of drawings]

FIG. 1 is a partial perspective view of an optical waveguide circuit according to an embodiment of the present invention, and FIGS. 2 (1) to (4) show an optical waveguide circuit of the present invention for manufacturing an optical waveguide circuit according to the present invention. A process diagram of one embodiment of the manufacturing method, and FIG. 3 is a partial perspective view of a conventional example. (Main reference numbers) 1. Optical fiber, 2. Core, 3. Substrate, 4. Buffer layer, 5. Optical waveguide layer, 6. Cover layer, 7. Channel waveguide, 8.・Guide, 9...Guide groove

Claims (10)

[Claims] (1) In an optical waveguide circuit having a substrate and an optical waveguide formed on the substrate and optically coupled to an external optical fiber, the substrate is configured to connect the optical fiber by contacting the outer peripheral surface of one end of the optical fiber. An optical waveguide circuit comprising a guide groove for aligning the axes of a fiber and the optical waveguide. (2) The optical waveguide circuit according to claim 1, wherein the substrate is made of Si. (3) The optical waveguide includes a first layer formed on the substrate and having a refractive index larger than the refractive index of the substrate, and a first layer formed on the first layer and having a refractive index smaller than the refractive index of the first layer. 3. The optical waveguide circuit according to claim 1 or 2, characterized in that the optical waveguide circuit comprises a second layer having a radial index of 1. (4) The optical waveguide includes a first layer formed on the substrate, a second layer formed on the first layer and having a refractive index larger than the refractive index of the first layer, and a second layer formed on the first layer and having a refractive index larger than the refractive index of the first layer. a third layer formed on the two layers and having a refractive index smaller than the refractive index of the second layer;
The optical waveguide circuit according to claim 1 or 2, characterized in that it consists of a layer. (5) The optical waveguide circuit according to any one of claims 1 to 4, wherein the guide groove is a V-groove. (6) The optical waveguide circuit according to any one of claims 1 to 4, wherein the guide groove is a rectangular groove. (7) forming at least two layers of an optically transparent material having a different composition from that of the substrate on a substrate having a flat surface, etching and removing the optically transparent material layer according to a predetermined pattern;
forming an optical waveguide and forming guides on both sides of one end of the optical waveguide; then surrounding one end of the optical waveguide and the guide with an etching material that does not remove the optically transparent material but removes the substrate; 1. A method of manufacturing an optical waveguide circuit, comprising etching the exposed surface of a substrate. (8) The method of manufacturing an optical waveguide circuit according to claim 7, wherein the etching of the exposed surface of the substrate surrounded by one end of the optical waveguide and the guide is anisotropic etching. (9) The substrate is a single crystal of Si, the flat surface thereof is a (100) plane, and a V-groove is formed by the etching. A method for manufacturing an optical waveguide circuit. (10) The substrate is a single crystal of Si, the flat surface thereof is a (110) plane, and a rectangular groove is formed by the etching. A method for manufacturing an optical waveguide circuit.