JPH0792340A - 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 core layer 3 and an overclad layer 4 is formed on a silicon substrate 1. The optical waveguide is then etched from the overclad layer 4 side to form a cutting-off groove reaching the substrate 1 by using a U-shaped groove pattern mask 5. The substrate 1 is etched from the rear surface side of the substrate by using a mask 6 opened in the part enclosing this groove pattern. The substrate 1 existing under the core layer 3 is formed as a thin layer reaching the disconnecting groove by this etching 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. Using the linear groove pattern surrounding the core layer leaving the upper end as a mask, the second step of etching the optical waveguide from the over cladding layer side to form a separation groove reaching the substrate, and surrounding the groove pattern Etching the substrate from the back side of the substrate using a mask with an open face, separating the substrate under the core layer and thinning or removing it until it reaches the groove to form a cantilever with one end as a fulcrum. And a third step of forming the optical waveguide.

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 third 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 surface of the overclad layer 4, and a mask 5 having a U-shaped groove pattern for separating the cantilever from the substrate is formed on the photoresist. (Refer to the same figure (c)). The "U" -shaped groove pattern has a quadrangular shape with one side cut off, and the one missing side is arranged orthogonal to the extending direction of the linearly patterned core layer 3. The one end lacking one side is located above the core layer 3, and the other three sides surround the core layer 3 from the substrate surface side 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, reactive ion etching (RIE) is performed using the groove pattern mask 5 as an etching mask. C ₂ F ₆ gas is used as an etchant for this RIE. This etching is performed until the “U” -shaped groove pattern hits the substrate 1, and the waveguide formed of the SiO ₂ cladding layer 4 / SiO ₂ —GeO ₂ core layer 3 / SiO ₂ buffer layer 2 is “U” shaped. It is carved along the groove pattern. Subsequently, RIE is performed using the same groove pattern mask 5 as an etching mask and CCl ₂ F ₂ gas as an etchant. By this etching, the Si single crystal substrate 1 is cut to a depth of 5 μm, and a “U” -shaped separation groove reaching the substrate 1 is formed (FIG. 2D).
reference).

Next, the groove pattern mask 5 on the front surface of the substrate is removed, and a cantilever pattern mask 6 is newly formed on the back surface of the substrate (see FIG. 8E). The cantilever pattern mask 6 has a pattern in which a rectangular surface portion surrounded by a U-shaped groove is opened on the back surface of the substrate. Next, the substrate is dipped in a KOH aqueous solution, and wet etching is performed using this cantilever pattern mask 6 as an etching mask (see FIG. 6F). This etching is performed until the thickness of the substrate 1 below the core layer 3 reaches the "U" -shaped separation groove.
By this etching, the rectangular portion of the substrate 1 surrounded by the U-shaped groove is thinned. Then, by removing the cantilever pattern mask 6 on the back surface of the substrate, a cantilever L having a rectangular parallelepiped shape with one end 1A as the bottom surface is formed.
Is formed. In addition, the movable end 1B of the cantilever L
Is etched on the side opposite to the one side lacking the U-shaped groove pattern, 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, if a large stress is applied to the waveguide and a large polarization occurs 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 on the core layer along the extending direction of the core layer. A second step of forming a separation groove reaching the substrate by etching the optical waveguide from the overcladding layer side using a linear groove pattern surrounding the layer as a mask, and a mask in which a surface portion surrounding the groove pattern is opened. Etching the substrate from the back surface side of the substrate by using to thin or remove the substrate under the core layer until it reaches the separation groove to form a cantilever with the one end as a fulcrum. A method of manufacturing an optical waveguide, comprising: a third step. 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 cut 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 cut side in the third step. 1. The method for manufacturing an optical waveguide according to 1.