JPH1184157A - Manufacturing method of optical waveguide - Google Patents

Abstract

(57) [Problem] To provide a method of manufacturing an optical waveguide capable of improving the adhesion of an upper clad layer to a core and a lower clad layer without adversely affecting the core and the lower clad layer. Provide a deposition material. SOLUTION: A lower cladding layer 3 is formed on a substrate 4 by using a plasma deposition method (Step 1). Lower cladding layer 3
After the core layer 1 'is formed thereon, unnecessary portions of the core layer 1' are removed to form the core 1 (step 2). The upper cladding layer 2 is formed by an ionization deposition method using a deposition material containing silicon dioxide as a main component and a mixture of phosphorus pentoxide and boron oxide (step 3). The content of phosphorus pentoxide and boron oxide in the deposition material is made equal. Thereafter, heat treatment is performed for a predetermined time. By using a deposition material containing a substance having a lower melting point than silicon dioxide, the upper cladding layer 2 is heated at a temperature lower than the melting point of pure silicon dioxide in a heat treatment after forming a film by ionization deposition. By melting, the adhesion of the upper cladding layer 2 to the lower cladding layer 3 and the surface of the core 1 can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for manufacturing a silica-based optical waveguide used for optical communication and optical computing, and more particularly to an optical waveguide formed by forming a cladding covering a core of an optical waveguide by an ionization vapor deposition method. And a method for producing the same.

[0002]

2. Description of the Related Art FIGS. 2A and 2B are cross-sectional views showing the optical waveguide structure of a quartz optical waveguide coupler. In the optical waveguide shown in FIG. 2A, a lower cladding layer 3 is formed on a substrate 4,
After a core layer 1 'is formed thereon, an excess portion of the core layer 1' is removed by etching to form a core 1 having a rectangular cross section, and an upper cladding layer 2 is formed so as to embed the core 1. Do it. The optical waveguide shown in FIG.
The core 1 is provided directly on the substrate 5 by using a synthetic quartz substrate 5 having a low refractive index and omitting the lower clad 3. The core 1 is made of silicon dioxide (SiO ₂ ) to which a dopant for controlling the refractive index (such as TiO ₂ ) is added, and the upper clad layer 2 and the lower clad layer 3 are made of pure silicon dioxide. The upper cladding layer 2 and the lower cladding layer 3 are formed by ionization vapor deposition, which is a kind of vacuum vapor deposition. In the ionization deposition method, the vaporized deposition material is ionized and deposited in a gas plasma, or the ionized gas molecules are accelerated by an electric field to collide with a target, thereby depositing the deposition material hit from the target surface. By doing so, a film is formed. Then, after the film is formed by the ionization vapor deposition method, heat treatment is performed to increase the degree of adhesion of the upper clad layer 2 to the surface to be vapor-deposited.

[0003]

However, conventionally, since pure silicon dioxide having a high melting point was used as the material for depositing the upper cladding layer 2, the upper cladding layer was not heat-treated after the film was formed by ionization deposition. Layer 2 cannot be melted sufficiently. This is because heating to about 1500 ° C., which is the melting point of silicon dioxide, causes problems such as melting and deformation of the core 1. As a result, the adhesion of the upper clad layer 2 to the surface to be deposited is deteriorated,
As shown in FIG. 3, the embedding of the core 1 may be incomplete. If there is such a defective portion, propagation light leaks from the surface of the core 1 at that portion, and transmission loss increases significantly. Therefore, an object of the present invention is to provide a method for manufacturing an optical waveguide that can increase the adhesion of an upper clad layer to a core and a lower clad layer without adversely affecting the core and the lower clad layer.

[0004]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a method of embedding a core on a substrate surface or a lower cladding layer formed on the substrate surface after projecting the core. A method of manufacturing an optical waveguide comprising forming an upper clad layer by ionization vapor deposition, comprising: a vapor deposition material obtained by mixing silicon dioxide and phosphorus pentoxide and boron oxide in an amount smaller than the number of moles of the silicon dioxide. After the upper cladding layer is formed by ionization vapor deposition using, heat treatment is performed at a temperature equal to or higher than the melting point of boron oxide and lower than the melting point of silicon dioxide. As shown in Table 1 below, since both phosphorus pentoxide and boron oxide have lower melting points than silicon dioxide, a deposited film formed by an ionization deposition method using a deposition material containing these substances is pure. Melts at a temperature lower than the melting point of pure silicon dioxide. Therefore, after the upper clad layer is formed by ionization vapor deposition, the core and the lower clad layer are melted by performing a heat treatment at a temperature equal to or higher than the melting point of boron oxide and lower than the melting point of silicon dioxide. Since only the upper cladding layer can be melted without causing any adverse effects on the core, the lower cladding layer, and the like, the adhesion of the upper cladding layer to them can be increased.

[0005]

[Table 1]

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the embodiments shown in the accompanying drawings. FIG. 1 is an explanatory view of a process when an optical waveguide having the structure shown in FIG. 2A is manufactured by using the method of the present invention. First, the lower cladding layer 3 is formed on the substrate 4 by using a plasma deposition method (Step 1). Pure silicon dioxide is used as the deposition material for the lower cladding layer 3 as in the prior art. Next, after the core layer 1 'is formed on the lower cladding layer 3, unnecessary portions of the core layer 1' are removed by photolithography and reactive ion etching to form the core 1 (step 2). As a material of the core layer 1, a material obtained by adding, for example, TiO ₂ as a refractive index controlling dopant to silicon dioxide (SiO ₂ ) is used.
Thereafter, the deposition material of the present invention, namely, silicon dioxide (S
iO ₂ ) as a main component and phosphorus pentoxide (P ₂ O ₅ )
The upper cladding layer 2 is formed by an ionization deposition method using a deposition material obtained by mixing the oxide and boron oxide (B ₂ O ₃ ) (Step 3). The content of phosphorus pentoxide and boron oxide in the deposition material is made equal. The above steps are performed in a decompression chamber (not shown). Thereafter, the substrate 4 on which the lower clad layer 3, the core 1, and the upper clad layer 2 are formed is transferred into an electric furnace (not shown), and heat-treated for a predetermined time mainly from above. The heat treatment temperature at this time is boron oxide (B ₂ O ₃ ).
From the melting point temperature of 460 ° C. of silicon dioxide (SiO 2)
₂ ) between 1500 ° C. which is the melting point temperature. After the heat treatment, the entire substrate 4 is naturally cooled to complete the optical waveguide. As described above, the upper cladding layer 2 is formed by an ionization deposition method using a deposition material containing silicon dioxide as a main component and phosphorus pentoxide and boron oxide, which are substances having lower melting points. Melts the upper cladding layer 2 at a temperature lower than the melting point of pure silicon dioxide to form the upper cladding layer 2 with respect to the surface of the lower cladding layer 3 and the core 1. Can be improved in adhesion.

[0007]

As described above, according to the method of manufacturing an optical waveguide according to the present invention, after a core is protruded from the surface of a substrate or the surface of a lower cladding layer formed on the surface of the substrate, the core is removed. In a method of manufacturing an optical waveguide formed by forming an upper clad layer by ionization vapor deposition method as embedded,
After the upper cladding layer is formed by ionization vapor deposition, heat treatment is performed at a temperature higher than the melting point temperature of boron oxide and lower than the melting point temperature of silicon dioxide, so that the core and the lower cladding layer are melted. Since only the upper clad layer can be melted without causing the core and the lower clad layer to have an adverse effect, the adhesion of the upper clad layer to the core and the lower clad layer can be increased.

[Brief description of the drawings]

FIG. 1 is a process explanatory view showing an example of a method for manufacturing an optical waveguide according to the present invention.

FIGS. 2A and 2B are cross-sectional views showing a basic structure of a silica-based optical waveguide.

FIG. 3 is an explanatory diagram showing a film formation state when a quartz-based film is formed by ionization vapor deposition on a stepped surface using a conventional vapor deposition material.

[Explanation of symbols]

1 core, 1 'core layer, 2 upper cladding layer, 3 lower cladding layer, 4 substrates

Claims (1)

[Claims] An optical waveguide formed by projecting a core on the surface of a substrate or a lower cladding layer formed on the surface of a substrate and then forming an upper cladding layer by ionization vapor deposition so as to embed the core. In the manufacturing method, the upper clad layer was formed by ionization deposition using a deposition material obtained by mixing silicon dioxide and phosphorus pentoxide and boron oxide in an amount smaller than the number of moles of the silicon dioxide. Thereafter, a heat treatment is performed at a temperature equal to or higher than the melting point of boron oxide and lower than the melting point of silicon dioxide.