JPH1138252A - Optical circuit and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lessen the influence of the reflected light of UV rays at the time of forming a diffraction grating, etc., by utilizing photoirradiation refractive index modulation, by forming an absorption layer to UV light between a plane substrate and an optical waveguide. SOLUTION: A Ge-added quartz glass layer 14 is formed between the optical waveguide consisting of a core 11, an upper clad 12 and a lower clad 13 and an Si substrate 10. The upper and lower clad layers 12 and 13 have the refractive index lower than the refractive index of the core 11. The core 11 is irradiated with UV light 16 through a phase mask 17, to generate the refractive index modulation in the core 11. Usually, the UV light 16 past the optical waveguide is reflected by the substrate surface and is again cast as return light 18 to the core 11. Since the return light 18 is different from an ideal intensity distribution, the contrast of the refractive index modulation by the photoirradiation degrades. The Ge-added quartz glass layer 14 which is the absorption layer to the UV light 16 is, thereupon, disposed between the optical waveguide and the Si substrate 10, by which the return light 18 may be decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical circuit and a method of manufacturing the same, and more particularly, to a method of arranging an optical waveguide on a flat substrate and using the phase mask method or the two-beam interference method on the optical waveguide to change the photoinduced refractive index. The present invention relates to an optical circuit that suppresses the reflection of ultraviolet light from the substrate of an optical circuit when forming a diffraction grating or the like using the above method.

[0002]

2. Description of the Related Art A quartz optical waveguide doped with a substance such as Ge shows a permanent change in refractive index when irradiated with ultraviolet rays. Therefore, only by irradiating light into the optical waveguide, a diffraction grating or the like can be easily formed in the optical waveguide.
Practical applications are being promoted in various fields such as filters and wavelength dispersion elements.

As a method of forming a diffraction grating in an optical waveguide by light irradiation, there are mainly a phase mask method and a two-beam interference method. The former is a method of irradiating an optical waveguide with light through a phase mask, which is described in detail in Japanese Patent Application Laid-Open No. H7-140311. This method is a method of transferring a pattern written on a phase mask to an optical waveguide, and has a drawback that when different diffraction gratings are formed, each mask must be prepared and the mask is expensive. However, it is advantageous in that the optical system is simple and the light source does not require much spatial coherence, and is particularly excellent in mass productivity.

On the other hand, the latter interference method is a method of forming a diffraction grating by dividing one beam into a beam splitter and interfering two beams into an optical waveguide at a desired angle. This is reported in detail in Japanese Unexamined Patent Publication No. 8-338920.

FIG. 9 is a diagram for explaining a method of writing a diffraction grating in a conventional optical circuit using the former phase mask method. Reference numeral 10 denotes a substrate, 11 denotes a core, and 12 and 13 denote upper and lower clads, respectively.

In this example, when a diffraction grating is formed on the core 11 by utilizing the photo-induced refractive index change, the phase mask 1
The diffraction grating is formed by irradiating ultraviolet light 16 through 7 and causing a modulation of the refractive index depending on the intensity distribution of the ultraviolet light 16. However, when Si (silicon) is used as the substrate 10 of the optical circuit, since the reflectance of Si to ultraviolet light is as large as 50 to 60%, ultraviolet light not absorbed in the waveguide is reflected on the Si substrate. And return light 1
The core 11 is irradiated again as 8.

Since the intensity distribution of the return light 18 is different from the ideal intensity distribution, only a refractive index modulation characteristic 27 having a lower contrast than an ideal refractive index modulation characteristic 26 is obtained as shown in FIG. And the deterioration of the characteristics of the diffraction grating occurs. By using quartz as the substrate 10, the return light 18 can be suppressed. However, a laser diode (LD) or a photodiode (P
In integrating various elements such as D), the merit of using a Si substrate is great. For this reason, it is important to reduce the influence of reflected light in order to write a highly efficient diffraction grating on a Si substrate.

[0008]

A problem with the conventional optical circuit is that when a highly reflective substance such as Si is used as a substrate, the ultraviolet light to be irradiated has a large reflection from the substrate, and the refractive index modulation degree is low. That is, it is difficult to form a high diffraction grating.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical circuit and a method of manufacturing the same in which the influence of ultraviolet reflected light is reduced when forming a diffraction grating or the like using light irradiation refractive index modulation.

[0010]

According to the present invention, a core portion made of quartz glass that propagates light and a clad portion having a low refractive index around the core portion are provided on a flat substrate. An optical circuit having an optical waveguide comprising: an optical circuit characterized by forming an absorption layer for ultraviolet light between the planar substrate and the optical waveguide.

According to the present invention, there is further provided an optical waveguide comprising a core portion made of quartz glass for transmitting light and a cladding portion having a low refractive index around the core portion on a flat substrate. An optical circuit characterized in that a scattering layer for ultraviolet light is formed between the planar substrate and the optical waveguide.

Further, the absorption layer is made of quartz glass to which GeO2 is added, and the absorption layer is made of one kind of material of ΤiN, TiO2, and Si3 N4. I do.

Further, according to the present invention, an optical waveguide is formed after an absorption layer made of quartz glass doped with GeO2 and P205 is formed on a flat substrate by a normal pressure chemical vapor deposition method. Thus, a method of manufacturing an optical circuit can be obtained.

Further, according to the present invention, there is provided a method for manufacturing an optical circuit, comprising forming a light guide after forming a scattering layer on a flat substrate by roughly polishing the surface of the flat substrate. Can be

In the optical circuit of the present invention, an absorption layer or a scattering layer for infrared light is formed between the optical waveguide including the core and the clad and the plane substrate. This makes it possible to suppress the reflected light from the substrate when forming the diffraction grating by light irradiation, and to form the diffraction grating with little deterioration in the degree of modulation of the refractive index.

[0016]

Next, an embodiment of an optical circuit according to the present invention will be described in detail with reference to the drawings.

FIGS. 1A and 1B show an embodiment of the present invention, wherein FIG. 1A is a longitudinal sectional view and FIG. 1B is a transverse sectional view. still,
9 are denoted by the same reference numerals. Referring to FIG. 1, an optical circuit according to the present invention comprises a core 11, an upper clad 1
2. Optical waveguide comprising lower clad 13 and Si substrate 10
In between, a Ge-added quartz glass layer 14 is formed. The upper and lower claddings 12 and 13 have a lower refractive index than the core 11.

The Ge-doped quartz glass layer 14 is formed by adding 8 mol% of GeO 2 to quartz glass. FIG. 2 shows G
The graph shows the characteristics of the absorption coefficient of the e-doped quartz glass layer 14 with respect to the wavelength. The wavelength 1 of the Ge-added quartz glass layer 14
The absorption coefficient at 93 nm is about 800 cm ^-1 .

FIG. 3 is a diagram for explaining a method of forming a diffraction grating by irradiating ultraviolet light.
6 is irradiated through the phase mask 17 to cause the core 11 to have a refractive index modulation. Normally, the ultraviolet light 16 that has passed through the optical waveguide is reflected on the surface of the substrate, and is again applied to the core 11 as return light 18. Since the return light 18 is different from the ideal intensity distribution, the contrast of the refractive index modulation due to light irradiation decreases.

In the conventional optical circuit, since the reflectance of Si is high, about 60% of the light transmitted through the core 11 or the claddings 12 and 13 is again irradiated on the core 11 as return light 18. In contrast, in the optical circuit of the present invention, the optical waveguide and S
G, which is an absorption layer for ultraviolet light 16 between
By providing the e-added quartz glass layer 14, the return light 1
8 can be reduced.

Assuming that 100% of the ultraviolet light is incident on the Ge-doped quartz glass layer 14, the Ge-doped quartz glass layer 1
When the film thickness of No. 4 is 5 μm, the return light is reduced to about 27% and 10 μm.
In the case of m, it can be suppressed to about 12%. The Ge-added quartz glass layer 14 can be formed by using a normal pressure chemical vapor deposition method utilizing a reaction between an organic material and ozone.

FIG. 4 shows the effective refractive index variation 19 in the conventional optical circuit when the diffraction grating is formed, the effective refractive index variation 18 and the maximum refractive index variation 21 in the optical circuit of the present invention. The case where the thickness of the absorbing layer 14 is 10 μm is shown. As shown in the figure, the refractive index modulation of about 50% of the maximum refractive index change amount cannot be obtained conventionally, but can be improved to about 80% in the present invention.

In this embodiment, Ge is used as the absorbing layer.
Although the case of quartz glass to which O2 is added has been described, the same effect can be obtained by using ΤiN, TiO2, and Si3 N4 as the absorption layer. Ti as an absorption layer
When N, TiO2, or Si3 N4 is used, the return light 18 can be suppressed to 20% or less.

FIG. 5 is a view showing another embodiment of the present invention, in which a TiO2 layer 22 is formed on an Si substrate 10 as an absorption layer.
And a Ge-added quartz glass layer 14 having a thickness of 5 μm. In this embodiment, the return light 18 can be suppressed to 10% or less by using two types of absorption layers.

FIG. 6 is a diagram showing another embodiment of the present invention. Referring to the figure, in the optical circuit of the present embodiment, a scattering layer 23 is formed between the Si substrate 10 and the optical waveguide. The scattering layer 23 can be formed by polishing the surface of the Si substrate.

FIG. 7 is a view showing the reflectances (24 and 25) before and after rough polishing of the Si substrate surface. The surface was polished to a surface roughness of about 0.5 μm. As is clear from the figure, by providing the scattering layer on the Si substrate, the return light at the wavelength of 193 nm can be suppressed from 60% to 15%.

FIG. 8 is a diagram showing another embodiment of the present invention. Referring to the figure, in the optical circuit of the present embodiment, the scattering layer 23 and the 5 μm thick G are disposed between the Si substrate 10 and the optical waveguide.
An e-added quartz glass layer 14 is formed. In this optical circuit, return light at a wavelength of 193 nm is reduced from about 10% to 1%.
It can be suppressed to 5%.

[0028]

As described above, according to the present invention,
When forming a diffraction grating or the like by utilizing light irradiation refractive index modulation, it is possible to provide an optical circuit in which the influence of light reflected from a substrate of ultraviolet light is reduced. This enables writing of a diffraction grating having a high refractive index modulation degree.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is a diagram showing an absorption coefficient of an absorption layer of the optical circuit of FIG.

FIG. 3 is a diagram for explaining the operation of the optical circuit of FIG. 1;

FIG. 4 is a diagram for explaining an effect of the optical circuit of FIG. 1;

FIG. 5 is a sectional view of another embodiment of the present invention.

FIG. 6 is a sectional view of still another embodiment of the present invention.

FIG. 7 is a diagram showing a reflectance of a scattering layer of the optical circuit of FIG. 6;

FIG. 8 is a sectional view of another embodiment of the present invention.

FIG. 9 is a diagram showing a conventional optical circuit.

FIG. 10 is a diagram for explaining a problem of a conventional optical circuit.

[Explanation of symbols]

 Reference Signs List 10 Si substrate 11 Core 12 Upper clad 13 Lower clad 14 Ge-doped quartz glass layer 16 Ultraviolet light 17 Phase mask 18 Return light 22 TiO2 layer 23 Scattering layer

Claims (6)

[Claims] 1. An optical circuit having an optical waveguide on a planar substrate, the optical waveguide comprising a core portion made of silica-based glass that transmits light and a clad portion having a low refractive index around the core portion. An optical circuit, wherein an absorption layer for ultraviolet light is formed between the planar substrate and the optical waveguide. 2. An optical circuit having an optical waveguide comprising a core portion made of silica-based glass for transmitting light and a clad portion having a low refractive index around the core portion on a flat substrate, An optical circuit, wherein a scattering layer for ultraviolet light is formed between the planar substrate and the optical waveguide. 3. The optical circuit according to claim 1, wherein said absorption layer is made of quartz glass doped with GeO2. 4. The method according to claim 1, wherein the absorption layer is made of ΤiN, TiO2, Si.
2. The optical circuit according to claim 1, wherein the optical circuit is made of one kind of material among 3N4. 5. An optical circuit manufacturing method, wherein an optical waveguide is formed after an absorption layer made of quartz glass to which GeO2 and P205 are added is formed on a flat substrate by a normal pressure chemical vapor deposition method. Method. 6. The rough polishing of the surface of a flat substrate,
A method for manufacturing an optical circuit, comprising forming an optical waveguide after forming a scattering layer on a flat substrate.