JPH0792341A - Production of optical waveguide - Google Patents

Abstract

PURPOSE:To provide a process for production of optical waveguide which can function as an active element by receiving an external factor exclusive of heat at a plane optical waveguide. CONSTITUTION:The optical waveguide consisting of a buffer layer 2, a straight core layer 3 and an overclad layer 4 is formed on a silicon substrate 1. A groove pattern of a specified depth is formed on the rear surface of the substrate 1 by using a U-shaped groove pattern mask 5. The rear surface of the substrate 1 is then etched until the groove pattern reaches the buffer layer 2 by using a mask 6 opened in the part enclosing the groove pattern. The buffer layer 2, the core layer 3 and the overclad layer 4 are etched until the groove pattern penetrates the surface of the substrate 1 by using the substrate 1 partly formed as the thin layer as a mask to form a cantilever L having its one end 1A as a fulcrum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide manufacturing method for manufacturing an optical waveguide by forming a buffer layer, a core layer and an overclad layer on a flat substrate.

[0002]

2. Description of the Related Art Conventionally, as a method of manufacturing an optical waveguide of this type, there is, for example, a manufacturing method disclosed in Japanese Patent Laid-Open No. 3-75606. This publication discloses a method of manufacturing an optical waveguide in which a silica-based buffer layer and a core layer are deposited on a silicon substrate, the core layer is patterned into a ridge shape, and then the core layer patterned with a clad layer is embedded. .

[0003]

However, in the above-mentioned conventional method for manufacturing an optical waveguide, since the core layer is formed on the flat substrate and the core layer is filled with the cladding layer, the position of the optical waveguide is fixed in the plane. It was Therefore, the silica-based optical waveguide obtained by this type of manufacturing method generally functions as a passive element for confining incident light in the core layer and propagating the incident light to a predetermined position.

Further, an active element such as a switching element or an interferometer may be realized by changing the refractive index by applying heat to this type of silica type planar optical waveguide. However, the planar optical waveguide rarely functions as an active element due to an external factor other than heat, and the use of the planar optical waveguide is limited.

The present invention has been made in view of the above problems, and provides a method of manufacturing an optical waveguide capable of functioning as an active element by giving an external factor other than heat to the planar optical waveguide. The purpose is to open new ways in the waveguide.

[0006]

To this end, the present invention provides a first step of forming an optical waveguide comprising a buffer layer, a core layer and an overclad layer on a substrate, and a core layer extending in the direction of extension of the core layer. A second step of forming a linear groove pattern surrounding the core layer with a certain depth on the back surface of the substrate leaving one end below, and a groove pattern is formed by using a mask whose surface portion surrounding the groove pattern is open. The third step of etching the back surface of the substrate until the buffer layer is reached, and thinning the back surface of the substrate surrounded by the groove pattern, and using this partially thinned substrate as a mask A fourth step of etching the optical waveguide until it penetrates the surface and forming a cantilever with the one end as a fulcrum is provided, and the optical waveguide is manufactured.

Further, in the first step, the core layer is linearly patterned, and in the second step, the groove pattern is formed into a "U" shape in which one side of the quadrangle is cut off, and the one side is cut off. The core layer is arranged substantially orthogonal to the extending direction of the core layer, and in the fourth step, the core layer is divided along one side of the groove pattern facing the one side where the chip is missing.

[0008]

According to this manufacturing method, an optical waveguide having a new function which has never been obtained is manufactured. That is, when the manufactured cantilever of the optical waveguide vibrates, the light propagating through the core layer portion that is cut through by the groove pattern is leaked according to the vibration.

When stress is applied to the optical waveguide at the fulcrum of the cantilever, the polarization state of the guided light propagating through the optical waveguide changes according to the applied stress.

[0010]

1 and 2 are process sectional views showing a method of manufacturing an optical waveguide according to an embodiment of the present invention.

First, S having a thickness of about 0.5 to 1.5 mm
An i (silicon) single crystal substrate 1 is prepared (FIG. 1A).
reference). The plane orientation of the main surface of the substrate 1 is (110). Then, by flame hydrolysis deposition (FHD), soot made of SiO ₂ is deposited on the Si single crystal substrate 1, the soot made of SiO ₂ doped with GeO ₂ are deposited subsequently. Then, the substrate is heat-treated to turn each soot into a transparent glass, and the buffer layers 2 and 8 having a thickness of 25 μm are formed.
The core layer 3 having a thickness of μm is formed. This core layer 3 is
It is patterned into a linear ridge waveguide shape by using a photolithography technique. Next, SiO ₂ is again deposited on the patterned core layer 3 by the FHD method, and heat-treated to form vitrified glass. As a result, the over-cladding layer 4 having a thickness of 25 μm is formed so as to cover the core layer 3 (see FIG. 7B).

Next, a photoresist is applied to the back surface of the substrate 1, and the cantilever is applied to the photoresist.
A mask 5 having a U-shaped linear groove pattern for separating the substrate from the substrate is formed (see FIG. 7C).
The U-shaped groove pattern has a quadrangular shape with one side cut off, and the one side cut off is arranged substantially orthogonal to the extending direction of the linearly patterned core layer 3. The one end lacking one side is located below the core layer 3, and the other three sides surround the core layer 3 from the back side of the substrate along the extending direction of the core layer 3. In the figure,
The groove pattern cross section of the side opposite to the one side which is lacked is shown. Next, the substrate 1 is dipped in a KOH aqueous solution, and wet etching is performed using the groove pattern mask 5 as an etching mask, and the Si single crystal substrate 1 is ground to a depth of 10 μm (see FIG. 3D). By this wet etching, a U-shaped separation groove is shallowly formed on the back surface of the substrate.

Next, the groove pattern mask 5 on the back surface of the substrate is removed, and a cantilever pattern mask 6 is newly formed on the back surface of the substrate (see FIG. 2E). The cantilever pattern mask 6 has a pattern in which a square surface portion surrounded by a U-shaped groove is opened. next,
The substrate 1 is again immersed in the KOH aqueous solution, and wet etching is performed using the cantilever pattern mask 6 as an etching mask (see FIG. 6F). This etching is performed until the “U” -shaped separation groove hits the buffer layer 2. By this etching, the back surface of the substrate in the rectangular portion surrounded by the U-shaped groove is thinned.

Next, the cantilever pattern mask 6 on the back surface of the substrate is removed, and reactive ion etching (RIE) is performed using the exposed Si substrate 1 as an etching mask (see FIG. 4G). C ₂ F ₆ gas is used as an etchant for this RIE. This etching is SiO
₂ clad layer 4 / SiO ₂ —GeO ₂ core layer 3 / SiO
_This is performed until the waveguide including the ₂ buffer layer 2 penetrates through the separation groove. By this RIE, one end 1A
A rectangular parallelepiped cantilever L having a bottom surface is formed.
Further, the movable end 1B of the cantilever L is etched on the side opposite to the one side where the U-shaped groove pattern is lacking, and the linear core layer 3 is divided by the side of this groove pattern.

3A and 3B show an optical waveguide structure manufactured by the method for manufacturing an optical waveguide according to this embodiment. FIG. 3A is a plan view and FIG. 3B is a fracture along the line Ib-Ib. A cross-sectional view, the same figure (c) is a fracture | rupture sectional view along the Ic-Ic line. The manufacturing process sectional views shown in FIGS. 1 and 2 correspond to the sectional view taken along the line II-II of FIG.

As shown in FIG. 3, a buffer layer 2, a core layer 3 and an overclad layer 4 are laminated on an optical waveguide substrate 1. The core layer 3 is linearly patterned to form a ridge-shaped optical waveguide. A waveguide is formed. A part of the back surface of the substrate 1 below the core layer 3 is thinned along the extending direction of the linear core layer 3. The partially thinned substrate 1 and the buffer layer 2, core layer 3 and overclad layer 4 on the substrate 1 are the core layer 3
It is formed in a rectangular parallelepiped shape having the one end 1A according to the above as a bottom surface. This rectangular parallelepiped portion is separated from the substrate on the other three remaining surfaces, and the separated rectangular parallelepiped portion constitutes a cantilever L having one end 1A as a fulcrum.

The operating principle of the thus manufactured flat optical waveguide is shown in the perspective view of FIG.

The movable end 1B of the cantilever L is separated as shown in the drawing, and when the substrate 1 is vibrated, the movable end 1B vibrates in the direction of the arrow with the one end 1A as a fulcrum. Further, the core layer 3 forming the linear ridge waveguide is divided by the movable end 1B of the cantilever L. Therefore, by vibrating the cantilever L while allowing light to pass through the ridge-shaped waveguide, the split light propagating from the one core layer 3 to the other core layer 3 leaks according to the vibration. The leak of the guided light, that is, the optical waveguide loss is proportional to the vibration of the cantilever L, and the guided light propagating from the one core layer 3 vibrating together with the cantilever L to the other core layer 3 fixed to the substrate 1. The intensity decreases as the amplitude of the vibration increases. Moreover, when the vibration frequency becomes high, the deviation of the optical axis between the divided core layers 3 decreases,
Light leakage is reduced and optical waveguide loss is reduced. Therefore,
It is also possible to modulate the light intensity according to the vibration frequency of the cantilever L.

Further, by vibrating the cantilever L while allowing light to pass through the ridge-shaped waveguide or by applying pressure to the movable end 1B, the one end portion 1A serving as a fulcrum of the cantilever L.
Stress is applied to the optical waveguide of. When stress is applied to the optical waveguide, the polarization state of the guided light B propagating through the optical waveguide changes according to the applied stress. Therefore, if a polarizer (polarizer) 7 is placed at the exit end as shown in the figure, the light polarized according to the applied stress passes through the polarizer 7 to modulate the light intensity according to the degree of polarization. Will be received. For example, when a large stress is applied to the waveguide and a large polarization is generated in the guided light, the vertical component of the light decreases,
The intensity of light passing through the polarizer 7 becomes small.

That is, by vibrating the cantilever L while passing light through the waveguide, or by applying stress to the cantilever L, the vibration intensity and the vibration frequency,
It is possible to perform optical modulation according to external factors such as applied stress. Therefore, the planar optical waveguide manufactured according to this example can be used for an active element such as an optical modulator,
It can also be applied to sensors such as accelerometers.

In the above embodiment, the case where the thinned substrate 1 is partially left under the cantilever L is described, but the thinned substrate portion is not necessarily left under the cantilever L. There is no. That is, the substrate 1 under the cantilever may be entirely removed, and the cantilever L may be formed only by the buffer layer 2, the core layer 3 and the overclad layer 4 on the removed substrate portion. Also in this case, the same effect as that of the above-described embodiment is obtained.

[0022]

As described above, according to the present invention, an optical waveguide having a new function which has not been heretofore produced can be manufactured. That is, when the manufactured cantilever of the optical waveguide vibrates, the light propagating in the separated core layer portion causes light leakage according to the vibration. Therefore, the intensity of the guided light propagating through the optical waveguide changes according to the amplitude and frequency of the vibration of the cantilever.
When stress is applied to the optical waveguide of the cantilever fulcrum, the polarization state of the guided light propagating through the optical waveguide changes according to the applied stress. Therefore, by combining a polarizer with this optical waveguide, the light intensity of the guided light can be modulated. Therefore, it becomes possible to apply optical modulation to the guided light by adding an external factor other than heat to the planar optical waveguide, and it is possible to find a new application for the planar optical waveguide.

[Brief description of drawings]

FIG. 1 is a process sectional view showing a first half of a method for manufacturing an optical waveguide according to an embodiment of the present invention.

FIG. 2 is a process sectional view showing the latter half of the method for manufacturing an optical waveguide of the present embodiment.

3A and 3B are a plan view and a sectional view of an optical waveguide obtained by the manufacturing method according to the present embodiment.

FIG. 4 is a perspective view showing the operating principle of the optical waveguide obtained in this example.

[Explanation of symbols]

1 ... Si single crystal substrate, 2 ... buffer layer, 3 ... core layer, 4
... over cladding layer, 5 ... groove pattern mask, 6 ... cantilever pattern mask, 7 ... Polarizer (polarizer), L ... cantilever, 1A ... one end surface of cantilever L, 1B ... movable end.

Claims (2)

[Claims] 1. A first step of forming an optical waveguide comprising a buffer layer, a core layer and an overclad layer on a substrate, and the core leaving one end below the core layer along the extending direction of the core layer. A second step of forming a linear groove pattern surrounding the layer on the back surface of the substrate to a constant depth, and using a mask having an open surface portion surrounding the groove pattern until the groove pattern reaches the buffer layer. A third step of etching the back surface of the substrate to thin the back surface of the substrate surrounded by the groove pattern, and using the partially thinned substrate as a mask And a fourth step of forming a cantilever having the one end as a fulcrum until the end of the cantilever is penetrated. 2. In the first step, the core layer is linearly patterned, and in the second step, the groove pattern has a "U" shape in which one side of a quadrangle is cut off. The chipped side is arranged substantially orthogonal to the extending direction of the core layer, and the core layer is divided by one side of the groove pattern facing the chipped side in the fourth step. 1. The method for manufacturing an optical waveguide according to 1.