JPH09325228A - Glass waveguide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glass waveguide suppressing the shape change of a core waveguide at the time of forming a clad glass film by subjecting a porous glass membrane to heat treatment by providing the core waveguide formed on a substrate and a clad glass film covering the waveguide and making the cross sectional shape of the core waveguide a trapezoid. SOLUTION: Core waveguides 11a, 11b having trapezoidal cross-sectional shapes are formed on a quartz substrate 10 and a glass waveguide 13 is formed by covering the core waveguides 11a, 11b and the substrate 10 by a clad glass film 12. In the glass waveguide 13, the difference α-β between the length αof the lower side and the length β of the higher side is preferably made to be 1μm>α-β>0.1μm. Consequently, by making the cross sectional shapes of the core waveguides 11a, 11b trapezoids, since the shape is stable even when approaching core waveguides are softened with each other due to heat at the time of converting a porous glass membrane to transparent glass, the approach of upper parts of the core waveguies 11a, 11b to each other and the deterioration of a multiplexing/demultiplexing characteristic are suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a glass waveguide provided with a core waveguide formed on a substrate and a clad glass film covering the core waveguide.

[0002]

2. Description of the Related Art With the spread of communication systems using light, development of optical components with lower loss and higher reliability has been actively pursued. A glass waveguide is one of such optical components. This is one in which a core waveguide is formed on a substrate and the core waveguide is covered with a clad glass film. In such a glass waveguide, for example, a core waveguide is formed on a quartz glass substrate by photolithography and ion etching, porous glass is formed so as to cover the core waveguide by a flame deposition method, and then the glass waveguide 1300 is formed by an electric furnace. It is obtained by forming transparent glass at a high temperature of ℃ or more to form a clad glass film.

[0003]

By the way, in the above-mentioned conventional example, when forming the porous glass film, in order to keep the transparent vitrification temperature below the temperature at which the quartz glass substrate is deformed, P ₂ O ₅ or B ₂ O is used. A porous glass film of SiO ₂ with ₃ added is used.

FIG. 3 (a) is a plan view of a conventional optical waveguide, and FIG. 3 (b) is a sectional view taken along the line AA of FIG. 3 (a).
FIG. 3C is a sectional view taken along line BB of FIG. This optical waveguide 1 is an optical multiplexer / demultiplexer in which a Mach-Zehnder type optical circuit is formed, and its optical coupling portions (shown by broken lines) 2a and 2b have a structure in which core waveguides 3a and 3b are close to each other within 3 μm. are doing.

However, in such an optical waveguide 1, when the porous glass film is subjected to heat treatment to be made into a transparent glass, bubbles are generated between the core waveguides 3a and 3b, or formed by an ion etching process. The core waveguide 3a,
It was observed that the upper portions of 3b approached each other as shown in FIG. 3 (b) and the multiplexing / demultiplexing characteristics deteriorated.

Therefore, an object of the present invention is to solve the above problems and to provide a glass waveguide having high characteristics in which the shape change of the core waveguide is suppressed when the porous glass film is heat-treated to form the clad glass film. To provide.

[0007]

To achieve the above object, the present invention provides a core waveguide in a glass waveguide including a core waveguide formed on a substrate and a clad glass film covering the core waveguide. The waveguide has a trapezoidal cross section.

In addition to the above structure, the glass waveguide of the present invention is
The difference α-β between the length α of the bottom of the trapezoid and the length β of the top is 1μ
It is preferable that m>α-β> 0.1 μm.

By making the cross-sectional shape of the core waveguide of the glass waveguide trapezoidal, the shape is stable even if the core waveguides that have come close to each other are softened by the heat when the porous glass film is made into transparent glass. Therefore, it is possible to prevent the upper portions of the core waveguides from approaching each other. Therefore, the deterioration of the multiplexing / demultiplexing characteristics can be suppressed more than ever before.

[0010]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1A is a plan view showing an embodiment of the glass waveguide of the present invention, and FIG. 1B is its CC view.
It is a line sectional view.

Core waveguides 11a and 11b having a trapezoidal cross-section are formed on a substrate 10 made of quartz (or a Si substrate having a quartz glass film formed thereon), and the core waveguides 11a and 11b are formed.
b and the substrate 10 are covered with a clad glass film 12 to form a glass waveguide 13. Reference numerals 14a and 14b are optical coupling portions.

The glass waveguide 13 is a core waveguide 11.
Since the cross-sectional shapes of a and 11b are trapezoidal, even if the core waveguides 11a and 11b are softened by the heat when forming the clad glass film 12 by making the porous glass film into transparent glass, the core waveguides do not change. The upper portions of the waveguides 11a and 11b do not come into contact with each other.

[0014]

EXAMPLE A TiO ₂ —SiO ₂ glass was formed on a transparent quartz glass substrate having a diameter of 3 inches and a thickness of 1 mm by 8 μm by an electron beam evaporation method. The relative refractive index difference is 0.3%. A Mach-Zehnder type MUX / DEMUX optical circuit having a core waveguide having a trapezoidal cross-sectional shape as shown in FIG. 1 was formed by photolithography and reactive ion etching.

The length α of the lower bottom of the core waveguides 11a and 11b
Was 8.1 μm, and the length β of the upper bottom was 7.8 μm. A porous glass film is formed on the substrate 10 by the flame deposition method.
μm was formed. Porous glass membrane P ₂ on SiO ₂ base
The one to which O ₅ and B ₂ O ₃ were added was used. Then, heat treatment was performed at 1335 ° C. in an electric furnace to obtain a transparent clad glass film 12 having a thickness of 32 μm.

FIG. 2 is a diagram showing wavelength loss characteristics of the glass waveguide shown in FIG.

As shown in FIG.
3 μm band single mode optical fiber 15, 16, 17
Is a diagram in which a white light source is incident from the optical fiber 15 side, and wavelength loss characteristics at the optical fiber 16 side and the optical fiber 17 side are simultaneously shown. In the figure, the horizontal axis represents wavelength and the vertical axis represents loss.

The glass waveguide 13 has an optical fiber 15
Light having a wavelength of 1.55 μm that enters from the optical fiber 16 and is emitted from the optical fiber 16 passes through light having a wavelength of 1.3 μm that enters from the optical fiber 15 and exits from the optical fiber 17 (broken line). In other words, it can be seen that the demultiplexer separates the light of wavelength 1.3 μm and the light of wavelength 1.55 μm.

Here, in the cross-sectional shape of the core waveguides 11a and 11b, when the length α of the lower base is equal to the length β of the upper base or α-β = -0.2, the center of FIG. Wavelength η, ξ
Moved to the short wavelength side. 15 nm when α-β = 0,
When α−β = −0.2, the wavelength shifts to the shorter wavelength side by about 32 nm. This is due to the core waveguide 1 as shown in FIG.
This is because the upper portions of 1a and 11b are close to each other and the gap interval is narrowed. This state is SEM (Scanning Electron
Microscope, scanning electron microscope) Judgment was also revealed. It was found that this phenomenon occurs when the core waveguide after the etching process is covered with a porous glass film to be transparent vitrified. This has a porous glass density of about 0.2 g / cm.
³ is believed to be due to shrinkage during the glass (2.2 g / cm ³⁾ of at. Therefore, by making the cross-sectional shape of the core waveguide trapezoidal, the strength against deformation is improved.

When α-β> 0.1 μm, the effect as in the embodiment can be obtained. Therefore, the range of 1 μm>α-β> 0.1 μm is desirable. When α-β is 1 μm or more, the core waveguide can be formed by reactive ion etching, but it is difficult to form the core waveguide with a difference of 1 μm or more under the condition that the cross-sectional shape is trapezoidal, and there is no reproducibility. In addition, the core waveguide 1
It is difficult to control the gap between 1a and 11b to 0.1 μm or less, and the center wavelength is set to the core waveguide 11a,
This is because the dependent control due to the deformation of 11b disappears, but the phenomenon that it fluctuates due to the variation of the gap is observed.

In the above, the characteristics of the glass waveguide can be stabilized by making the cross-sectional shape of the core waveguide trapezoidal and setting it in the range of 1 μm>α-β> 0.1 μm.

Although the glass waveguide having two optical coupling portions has been described in this embodiment, the present invention is not limited to this, and the number of optical coupling portions may be one or more than three. Good.

[0023]

In summary, according to the present invention, the following excellent effects are exhibited.

By making the cross-sectional shape of the core waveguide of the glass waveguide trapezoidal, it is possible to realize the provision of a high-performance glass waveguide in which the shape change of the core waveguide when forming the clad glass film is suppressed. it can.

[Brief description of drawings]

1A is a plan view showing an embodiment of a glass waveguide of the present invention, and FIG. 1B is a sectional view taken along line CC of FIG.

FIG. 2 is a diagram showing wavelength loss characteristics of the glass waveguide shown in FIG.

FIG. 3A is a plan view of a conventional optical waveguide,
(B) is a sectional view taken along line AA of (a), and (c) is B of (a).
FIG. 4 is a cross-sectional view taken along line B.

[Explanation of symbols]

 10 substrate 11a, 11b core waveguide 12 clad glass film 13 glass waveguide

Claims (2)

[Claims] 1. A glass waveguide including a core waveguide formed on a substrate and a clad glass film covering the core waveguide, wherein the core waveguide has a trapezoidal cross-sectional shape. Glass waveguide. 2. The trapezoidal lower base length α and upper base length β
The glass waveguide according to claim 1, wherein the difference α-β is 1 μm>α-β> 0.1 μm.