JPH0792399A - Optical waveguide - Google Patents

Abstract

PURPOSE:To provide an optical waveguide structure which can function as an active element by receiving an external factor exclusive of heat at a plane optical waveguide. CONSTITUTION:A buffer layer 2, a core layer 3 and an overclad layer 4 are laminated on an optical waveguide substrate 1 and this core layer 3 is patterned to be a straight shape. The rear surface of this substrate 1 is partly formed as a thin layer along the stretching direction of the core layer 3. The substrate 1 partly formed as the thin layer and the buffer layer 2, core layer 3 and overclad layer 4 existing in the upper part thereof are formed as a rectangular parallelepiped having its one end 1A as a base and is disconnected from the substrate at the other remaining three surfaces. This disconnected rectangular parallelepiped part constitutes 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 having a buffer layer, a core layer and an overclad layer formed on a flat substrate.

[0002]

2. Description of the Related Art Conventionally, as an optical waveguide of this type, for example, there is an optical waveguide disclosed in Japanese Patent Laid-Open No. 3-75606. This publication discloses a ridge-shaped optical waveguide structure formed by sequentially depositing a silica-based buffer layer, a core layer and a clad layer on a silicon substrate.

[0003]

However, in the above-mentioned conventional optical waveguide structure, since the core layer is formed on the flat substrate, the optical waveguide position is fixed in the plane. Therefore, this type of silica-based optical waveguide generally functions as a passive element that confines the incident light in the core layer and propagates 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 an optical waveguide structure capable of giving an external factor other than heat to a planar optical waveguide to cause it to function as an active element. The purpose is to open new ways.

[0006]

To this end, the present invention provides a substrate, a buffer layer formed on the substrate, a core layer formed on the buffer layer, and a core layer formed on the core layer. In an optical waveguide formed with an overclad layer, a part of the substrate and a buffer layer above the substrate,
The core layer and the overclad layer were separated by leaving one end of the core layer, and the separated part was used as a cantilever having this one end as a fulcrum.

The back surface of a part of the substrate was thinned or removed along the extending direction of the core layer.

[0008]

When the cantilever vibrates, the light propagating through the separated core layer portion causes light leakage 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]

FIG. 1 is a diagram showing the structure of an optical waveguide according to an embodiment of the present invention. FIG. 1 (a) is a plan view, FIG. 1 (b) is a sectional view taken along line Ib-Ib, The same figure (c) shows Ic-
It is a fracture | rupture sectional view along the Ic line.

As shown in each of these figures, 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 shape. An optical 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, the core layer 3 and the overclad layer 4 above the substrate 1 are formed in a rectangular parallelepiped shape having one end 1A of the core layer 3 as a bottom surface. The 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. Further, the plane direction of the bottom surface of the rectangular parallelepiped portion in the one end portion 1A is arranged in a direction substantially orthogonal to the extending direction of the linear core layer 3. The linear core layer 3 is
The movable end 1B, which is the inner end face facing the bottom face, is divided.

An optical waveguide having such a cantilever L is manufactured through the steps shown in FIGS. 2 and 3. In addition, this process cross-sectional view is taken along the line II-II in FIG.

First, S having a thickness of about 0.5 to 1.5 mm
An i (silicon) single crystal substrate 1 is prepared (FIG. 2A).
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 a mask 5 having a U-shaped groove pattern for separating the cantilever L from the substrate is formed on the photoresist (FIG. )reference). The "U" -shaped groove pattern has a quadrangular shape with one side cut off, and in this figure, a groove pattern cross section of the side opposite to this one side is shown. Next, the substrate 1 is immersed in a KOH aqueous solution, and wet etching is performed using the groove pattern mask 5 as an etching mask.
Is cut by the depth of (see (d) in the figure). 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. 3E). This cantilever pattern mask 6 has a pattern in which a square portion surrounded by a U-shaped groove is opened. Then again
The substrate 1 is dipped in a 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 rectangular portion of the substrate 1 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. 9 (g)). 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.

The principle of operation of such a planar optical waveguide is shown in FIG.
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. The core layer 3 forming the linear ridge waveguide is divided at the movable end 1B. 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 leakage of the guided light, that is, the optical waveguide loss is caused by the cantilever L.
The intensity of 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 decreases in proportion to the vibration of the above. Further, when the vibration frequency is increased, the deviation of the optical axis between the divided core layers 3 is reduced, the light leakage is reduced, and the optical waveguide loss is reduced. Therefore, the light intensity modulation according to the vibration frequency of the cantilever L is also possible.

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 according to the present embodiment can be used for an active element such as an optical modulator, and can also be applied to a sensor such as an accelerometer.

In the above embodiment, the structure in which the thinned substrate 1 is partially left under the cantilever L has been described, but the structure is not necessarily limited to this structure. For example, the substrate under the cantilever may be left as it is without being thinned, and the cantilever L may be formed by the remaining substrate and the buffer layer 2, the core layer 3 and the overclad layer 4 on the substrate. On the contrary, the entire substrate 1 under the cantilever may be removed, and the cantilever L may be formed only by the buffer layer 2, the core layer 3 and the over cladding layer 4 on the removed substrate portion. In each of these cases, the same effect as that of the above-described embodiment can be obtained.

[0022]

As described above, according to the present invention, when the cantilever vibrates, the light propagating through the separated core layer portion leaks light 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 plan view and a sectional view of an optical waveguide according to an embodiment of the present invention.

FIG. 2 is a sectional view of a first half of manufacturing steps for manufacturing the optical waveguide according to the present embodiment.

FIG. 3 is a cross-sectional view of the latter half of the manufacturing process for manufacturing the optical waveguide of this embodiment.

FIG. 4 is a perspective view showing the operating principle of the optical waveguide according to the present embodiment.

[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 (3)

[Claims] 1. An optical device including a substrate, a buffer layer formed on the substrate, a core layer formed on the buffer layer, and an overclad layer formed on the core layer. In the waveguide, a part of the substrate and the buffer layer, the core layer, and the overclad layer above the substrate are separated by leaving one end relating to the core layer, and the separated part is a piece whose fulcrum is the one end. An optical waveguide characterized by forming a cantilever. 2. The optical waveguide according to claim 1, wherein the back surface of a part of the substrate is thinned or removed along the extending direction of the core layer. 3. The core layer is linearly patterned, the cantilever is formed in a rectangular parallelepiped shape having the one end as a bottom surface, and the surface direction of the bottom surface is substantially parallel to the extending direction of the core layer. 2. The core layers are arranged in orthogonal directions and separated at the remaining surface of the rectangular parallelepiped, and the core layer is divided by a surface facing the bottom surface of the rectangular parallelepiped.
Alternatively, the optical waveguide according to claim 2.