JPH0310207A - Mode shape converter and production thereof - Google Patents

Abstract

PURPOSE:To decrease the coupling loss between an optical device and an optical fiber by forming a waveguide on the same substrate as the substrate for the optical device and decreasing the thickness of the waveguide toward the end part on the optical device side. CONSTITUTION:The waveguide 5 formed on the same substrate 1 as the substrate for the optical device is so formed that the thickness thereof decreases continuously or stepwise toward and optical device forming region. The section of the waveguide 5 of the mode shape converter is, therefore, of a flat shape in the coupling part of the optical device and the mode shape converter and can be made into substantially the same shape as the sectional shape of the waveguide of the optical circuit; therefore, the coupling property of the optical device and the mode shape converter is high. On the other hand, the thickness at the end of the waveguide 5 of the mode shape converter on the side opposite to the optical device is relatively large and the sectional shape thereof is nearly circular and, therefore, the coupling property between the optical fiber and the mode shape converter is high. The coupling loss between the optical device and the optical fiber is lowered in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Fields of Application] The present invention is used in the fields of optical communications and optical information processing, when the present invention is arranged between a substrate-type optical device such as an optical switch or an optical modulator and an optical fiber. The present invention relates to a mode shape converter that optically connects an optical fiber and a method of manufacturing the same, and a mode shape converter that improves coupling with an optical fiber without impairing the performance of a functional device and a method of manufacturing the same.

[Prior Art] In general, the waveguide (optical waveguide) of an optical circuit constituted by a substrate-type optical device is made of Si or LiN. ] A high refractive index material is deposited on a predetermined region of a substrate made of a low refractive index material such as 03 using a method such as a sputtering method or a CVD method.

Furthermore, Ti, A1, etc. have the effect of increasing the refractive index of the substance when it enters the substrate made of the low refractive index substance,
A method is also used in which a waveguide is formed by diffusing and introducing Ti or A1 as an impurity into a predetermined region of the substrate.

However, in either method, the waveguide needs to be smaller in its thickness direction than in its width direction. For example, when attempting to form a waveguide by depositing a high refractive index material on a substrate by sputtering or CVD, the thickness of the waveguide cannot be increased because the deposited layer must be microfabricated. In addition, in a diffusion-type guiding waveguide that diffuses impurities, assuming that the impurity diffusion rate does not depend on the crystal direction of the substrate, the length of the waveguide in the thickness direction is inevitably shorter than that in the width direction. For this reason, substrate-type optical devices.

Outgoing spot shape (mode shape) from the vice waveguide
has a flat shape.

On the other hand, the output spot shape of the optical fiber connected to the waveguide of this substrate type optical device is circular.

For this reason, if the waveguide of a substrate-type optical device and an optical fiber are directly joined by, for example, the butt joint method,
Coupling loss of optical signals occurs due to the difference in mode shape between the two. Therefore, mode shape converters are used to avoid this mode coupling loss.

FIG. 4 is a perspective view showing a conventional mode shape converter.

A conventional mode shape converter is of a fiber type and is composed of a core 11 made of a high refractive index material and a cladding layer 12 made of a low refractive index material covering the circumferential surface of the core 11. One end of the core 11 has a circular shape, and the other end has a rectangular shape that is the same in cross section as the waveguide of the optical circuit.

As shown in FIG. 5, this mode shape converter is used with one end connected to an optical fiber and the other end connected to a waveguide of an optical circuit. Thereby, coupling loss between the optical device and the optical fiber can be reduced.

[Problems to be Solved by the Invention] 5 However, the above-described conventional fiber-type mode shape converter is a separate body from the optical device formed on the substrate, and needs to be manufactured in a separate process. In addition, since it cannot be manufactured on the same substrate as the optical device, in order to couple the optical device and the optical fiber, it is necessary to connect the optical device and the mode shape converter and between the mode shape converter and the optical fiber. It is necessary to align the optical axes, and the process for aligning the optical axes is required twice, making the work extremely complicated.

The present invention has been made in view of such problems, and includes:
A mode shape that can be manufactured on the same substrate and in the same process as the optical device, which simplifies the manufacturing process and requires only one optical axis alignment when coupling the optical device and optical fiber. The object of the present invention is to provide a converter and a method for manufacturing the same.

[Means for Solving the Problems] A mode shape converter according to the first invention of the present application is a mode shape converter for connecting a substrate type optical device and an optical fiber, in which the optical device is formed. It has a waveguide formed on the same substrate as the substrate and whose thickness decreases continuously or stepwise toward the formation region of the optical device, and the end of the waveguide on the optical device side is It is characterized in that it is combined with the optical device.

The method for manufacturing a mode shape converter according to the second invention of the present application includes:
A step of forming a diffusion source layer containing an impurity that increases the refractive index of the diffusion introduction region in a predetermined region on the substrate, and a step of forming the diffusion source layer on the substrate so that the layer thickness increases continuously toward one end of the diffusion source layer. Alternatively, the method may include the steps of forming an upper cladding layer that decreases in steps, and diffusing the impurity from the diffusion source layer into the substrate and the upper cladding layer to form a waveguide.

The method for manufacturing a mode shape converter according to the third invention of the present application includes:
forming a lower cladding layer on the substrate; forming a diffusion source layer containing an impurity that increases the refractive index of the diffusion introduction region in a predetermined region on the lower cladding layer; forming an upper cladding layer whose layer thickness decreases continuously or stepwise toward one end; and diffusing the impurity from the diffusion source layer into the lower cladding layer and the upper cladding layer to form a waveguide. and a step of forming.

[Operation] The mode shape converter according to the present invention is formed on the same substrate as the optical device, and the thickness of the waveguide decreases continuously or stepwise toward the optical device formation region. As a result, at the coupling portion between the optical device and the mode shape converter, the waveguide of the mode shape converter has a flat cross-sectional shape, and can be made substantially the same as the cross-sectional shape of the waveguide of the optical circuit. Therefore, the coupling between the optical device and the mode shape converter is high.

On the other hand, since the end of the waveguide of the mode shape converter opposite the optical device is relatively thick, its cross-sectional shape is circular or nearly circular. Therefore, the coupling between the optical fiber connected to this end and the mode shape converter is also high. Therefore, coupling loss between the optical device and the optical fiber can be reduced.

Furthermore, in the present invention, since the leading waveguide of the mode shape converter is formed on the same substrate as the optical device, alignment is only required between the leading waveguide and the optical fiber, which simplifies the alignment work. can.

On the other hand, in the method of the present invention, a diffusion source layer containing an impurity that has the effect of increasing the refractive index of the diffusion region when diffused into the substrate or the cladding layer is used as the substrate (in the case of claim 2). ) or in a predetermined area on the Kura Soto layer (in the case of claim 3).

Such impurities include metals such as T i+ AI and Ge, and oxides of these metals.

An upper cladding layer is formed on this impurity layer (diffusion source layer), the layer thickness of which decreases continuously or stepwise toward one end of the mode shape converter forming region. Thereafter, the impurity is diffused into the substrate or into the lower cladding layer and the upper cladding layer to form a waveguide.

In this case, the impurities are diffused in the vertical direction to form a waveguide with a predetermined thickness of 9 mm, but near the one end, the layer thickness of the upper cladding layer is thin, so the impurities are diffused in the upper cladding layer. reach the surface.

Therefore, the thickness of the formed waveguide decreases toward the one end, and the cross section at this end becomes flat. Therefore, the coupling property with the waveguide of the substrate type optical device is excellent. Furthermore, the cross section at the other end of the waveguide has a circular or nearly circular shape because the waveguide is thick.

Therefore, the coupling property with the optical fiber is also good.

Note that when a waveguide of an optical device is formed by impurity diffusion, the method of the present invention can be carried out on the same substrate as the optical device in the same process as the manufacturing process of the optical device.

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

FIGS. 1(a) to 1(C) are cross-sectional views showing the method of the first embodiment of the present invention in the order of steps.

First, as shown in FIG. 1(a), a temporary cladding layer 2 made of SiO2 is formed by holding the Si substrate 10 in an oxyhydrogen flame at a temperature of 1100°C for 35 hours, for example.
form. The layer thickness of this temporary cladding layer 2 is, for example, about 4
It is μm. After sputtering Ti on this temporary cladding layer 2, Ti is selectively removed from areas other than the predetermined areas using photolithography to form a band-shaped Ti/iW3 with a width of 6 μm and a thickness of 200 mm, for example. do.

Next, as shown in FIG. 1(b), one end of the substrate is thickened by using a shadow mask sputtering method on the temporary cladding layer 2 and the Ti layer. By continuously changing the layer thickness in the range of 0 to 1 μm, Si
An upper cladding layer 4 made of O2 is formed.

Then, as shown in Figure 1 (C), 7
Ti is diffused from the Ti layer 3 into the temporary cladding layer 2 and the upper cladding layer 4 for a certain period of time to form a waveguide 5.

FIG. 2 is a perspective view showing a mode shape converter actually formed by the above method. The mode shape at one end of the waveguide 5 of the mode shape converter thus formed has a width of 7 μm and a depth of 4 μm, and the mode shape at the other end has a width of 7 μm and a depth of 2.0 μm. It was 5 μm.

Next, a second embodiment method of the present invention will be described.

First, metallic Ti is deposited to a thickness of 600 nm on a LiNbO3 substrate using a sputtering method.

Then, the Ti layer is left only in the band-shaped region by a lift-off method.

Next, a shadow mask sputtering method was used to deposit LiNbO3 on the substrate and the Ti layer in a thickness of 0 to 1 μm.
The upper cladding layer is formed by depositing the layer with a layer thickness that is continuously changed within the range of .

Next, Ti is thermally diffused into the L i N b 03 substrate and the upper cladding layer by holding it in an inert gas at a temperature of 050° C. for 6 hours to form a waveguide. The method of this second embodiment also has the same effects as the first embodiment.

The mode shape of the waveguide of the mode shape converter actually formed by the above method has a width of 9 μm at one end.
7μm deep and 9μm wide at the other end
It had an elliptical shape with a depth of 5.6 μm.

Furthermore, when a directional coupler optical switch (optical circuit) was simultaneously formed on the extension of the waveguide of the mode shape converter as shown in Figure 3 under similar conditions, the switching performance of the optical switch remained unchanged. , coupling loss with optical fiber is 2.0d
B. An improved optical switch was obtained.

[Effects of the Invention] As explained above, the mode shape converter according to the present invention has the following effects:
It is formed on the same substrate as the optical device, and the thickness of the waveguide decreases toward the end on the optical device side.
The cross-sectional shape of the waveguide of the optical circuit at the coupling portion between the mode shape converter and the optical circuit can be made substantially the same as the cross-sectional shape of the waveguide of the mode shape converter. Therefore, the connectivity with optical devices is improved. Furthermore, since the thickness of the waveguide at the other end of the mode shape converter can be increased, the cross-sectional shape of the waveguide at the other end can be circular or nearly circular.

Therefore, the coupling performance with the optical fiber is also improved. Thereby, the coupling loss between the optical device and the optical fiber is small, and the optical fiber and the optical device can be coupled with one axis alignment.

Further, according to the method of the present invention, an upper cladding layer whose thickness decreases continuously or stepwise toward one end thereof is formed on the diffusion source layer, and from the diffusion source layer to the upper cladding layer. Since the waveguide is formed by diffusing impurities, the mode shape converter described above can be easily manufactured in the same process as the functional device of the optical circuit.

[Brief explanation of drawings]

FIGS. 1(a) to (c) are cross-sectional views showing the method according to the first embodiment of the present invention in the order of steps, FIG. 2 is a perspective view showing the completed mode shape converter, and FIG. FIG. 4 is a schematic side view showing a state in which an optical fiber and an optical circuit are coupled by a mode shape converter completed by the method of the second embodiment; FIG. 4 is a perspective view showing a conventional 4-mode shape converter; FIG. 5 is a schematic side view showing a state in which an optical fiber and an optical circuit are coupled by a conventional mode shape converter. 1: Substrate, 2: Temporary cladding layer, 3: Ti layer, 4: Upper cladding layer, 5: Waveguide, 11: Core, 12: Cladding layer

Claims (6)

[Claims] (1) In a mode shape converter that connects a substrate-type optical device and an optical fiber, the mode shape converter is formed on the same substrate on which the optical device is formed, and its thickness increases toward the formation area of the optical device. 1. A mode shape converter comprising a waveguide that decreases continuously or stepwise, and an end of the waveguide on the optical device side is coupled to the optical device. (2) forming in a predetermined region on the substrate a diffusion source layer containing an impurity that increases the refractive index of the diffusion introduction region;
forming an upper cladding layer on the diffusion source layer, the layer thickness of which decreases continuously or stepwise toward one end; and transferring the impurities from the diffusion source layer to the substrate and the upper cladding layer. 1. A method for manufacturing a mode shape converter, comprising the step of: diffusing into a waveguide to form a waveguide. (3) forming a lower cladding layer on the substrate; and forming a diffusion source layer containing an impurity that increases the refractive index of the diffusion introduction region in a predetermined region on the lower cladding layer;
forming an upper cladding layer on the diffusion source layer, the layer thickness of which decreases continuously or stepwise toward one end; and transferring the impurities from the diffusion source layer to the lower cladding layer and the upper cladding layer. 1. A method for manufacturing a mode shape converter, comprising the step of diffusing into a layer to form a waveguide. (4) The method for manufacturing a mode shape converter according to claim 2 or 3, wherein the diffusion source layer is a metal selected from the group consisting of Ti, Al, and Ge or an oxide thereof. (5) The upper cladding layer is made of LiNbO_3, LiTa
Claim 2 characterized in that the transparent dielectric material is selected from the group consisting of O_3, Al_2O_3 and SiO_2.
5. A method for manufacturing a mode shape converter according to any one of items 4 to 4. (6) The method for manufacturing a mode shape converter according to any one of claims 3 to 5, wherein the substrate is made of Si, and the lower cladding layer is formed by thermally oxidizing the substrate. (7) The waveguide is made of Ti in LiNbO_3.
2. The mode shape converter according to claim 1, wherein the mode shape converter is formed by diffusing.